TL neuro

January 2, 2017

Current Topics in Behavioral Neurosciences on Novel Psychoactive Substances

Filed under: 4-MMC/Mephedrone, Cannabimimetics, Cathinones, IVSA, MDPV, Methylone — mtaffe @ 2:08 pm

There is a new Current Topics in Behavioral Neuroscience book on New and Emerging Psychoactive Substances that has been organized by Michael H. Baumann, Ph.D., of the Intramural Research Program of the National Institute on Drub Abuse. This editorial effort resulted in 18 chapters on various topics of interest which are now available online.

Chapter 1: Madras, B. The Growing Problem of New Psychoactive Substances (NPS) [link]

Chapter 2: Glennon, R.A. and Dukat, M. Structure-Activity Relationships of Synthetic Cathinones [link]

Chapter 3: Simmler, L.D. and Liechti, M.E. Interactions of Cathinone NPS with Human Transporters and Receptors in Transfected Cells [link]

Chapter 4: Solis, E. Electrophysiological Actions of Synthetic Cathinones on Monoamine Transporters [link]

Chapter 5: Baumann, M.H., Bukhari, M.O., Lehner, K.R., Anizan, S., Rice, K.C., Concheiro, M. and Huestis, M.A. Neuropharmacology of 3,4-Methylenedioxypyrovalerone (MDPV), its Metabolites, and Related Analogs [link]

Chapter 6: Negus, S.S. and Banks, M.L. Decoding the Structure of Abuse Potential for New Psychoactive Substances: Structure-Activity Relationships for Abuse-Related Effects of 4-Substituted Methcathinone Analogs [link]

Chapter 7: Watterson, L.R. and Olive, M.F. Reinforcing Effects of Cathinone NPS in the Intravenous Drug Self-Administration Paradigm [link]

Chapter 8: Aarde, S.M. and Taffe, M.A. Predicting the Abuse Liability of Entactogen-Class, New and Emerging Psychoactive Substances via Preclinical Models of Drug Self-administration.[link]

Chapter 9: King, H.E. and Riley, A.L. The Affective Properties of Synthetic Cathinones: Role of Reward and Aversion in Their Abuse [link]

Chapter 10: Kiyatkin, E.A. and Ren, S.E. MDMA, Methylone, and MDPV: Drug-induced Brain Hyperthermia and its Modulation by Activity State and Environment [link]

Chapter 11: Angoa-Pérez, M., Anneken, J.H., Kuhn, D.M. Neurotoxicology of Synthetic Cathinone Analogs [link]

Chapter 12: Wiley, J.L, Marusich, J.A. and Thomas, B.F. Combination Chemistry: Structure–Activity Relationships of Novel Psychoactive Cannabinoids [link]

Chapter 13: Tai, S. and Fantegrossi, W.E. Pharmacological and Toxicological Effects of Synthetic Cannabinoids and Their Metabolites [link]

Chapter 14: Järbe, T.U.C. and Raghav, J.G. Tripping with Synthetic Cannabinoids (‘Spice’): Anecdotal and Experimental Observations in Animals and Man [link]

Chapter 15:Halberstadt, A.L. Pharmacology and Toxicology of N-Benzylphenethylamine (“NBOMe”) Hallucinogens [link]

Chapter 16: Papaseit, E., Molto, J., Muga, R., Torrens, M., de la Torre, R. and Farre, M. Clinical Pharmacology of the Synthetic
Cathinone Mephedrone [link]

Chapter 17: Mayer, F.P., Luf, A., Nagy, C., Holy, M., Schmid, R., Freissmuth, M., Sitte, H.H. Application of a Combined Approach to Identify New Psychoactive Street Drugs and Decipher Their Mechanisms at Monoamine Transporters [link]

Chapter 18: Schifano, F., Orsolini, L., Papanti, D., Corkery, J. NPS: Medical Consequences Associated with Their Intake [link]

 

December 3, 2016

New Chapter on Entactogen Self-Administration

Filed under: 4-MMC/Mephedrone, alpha-PVP, Cathinones, MDPV, Methylone — mtaffe @ 2:48 pm

We have recently published a short review on the self-administration of entactogen psychostimulants.

Aarde, S.M. and Taffe, M.A. Predicting the Abuse Liability of Entactogen-Class, New and Emerging Psychoactive Substances via Preclinical Models of Drug Self-administration. Curr Top Behav Neurosci. 2016 Dec 2. [Epub ahead of print] [PubMed][Publisher Site]

This is part of a Current Topics in Behavioral Neuroscience book on New and Emerging Psychoactive Substances organized by Mike Baumann of the NIDA IRP who has been publishing a lot of work on synthetic cathinones lately. Eventually the Chapters will be collected into a book and assigned unique pagination.

For now you can look chronologically in the pre-publication OnlineFirst list.

The first chapter of the series that was published was:
Schifano et al “NPS: Medical Consequences Associated with Their Intake” [link]

The cannabinoids are covered:
Wiley, Marusich and Thomas Combination Chemistry: Structure–Activity Relationships of Novel Psychoactive Cannabinoids [link]

All told there will be around a dozen chapters, I think most of them are on the pre-print list already. Happy reading!

September 20, 2016

Just. Keep. Swimming.

Filed under: 4-MMC/Mephedrone, Cathinones, MDPV, NIH — mtaffe @ 1:07 pm

In the prior post I tried to give some flavor of the sort of grant submission effort that it has taken for me to keep my lab afloat to this point in time. That description gave an overview of my rough success rates which hovers somewhere in the high teens, not too far away from the aggregate NIH success rate over a similar interval of time.

As I point out to trainees now and again, there is no reason for any of us to think we are somehow special in securing grant funding. The NIH system of extramural funding has been under high stress in the past 10-15 years and there are far more deserving proposals being submitted than can be funded.

In this post, I want to outline the course of a particular research program of mine.

In early 2010 I became aware of a new recreational drug called mephedrone, (aka meow-meow or plant-food) which was very popular in the UK. It was not legally controlled and it seemed to emerge in a bit of a MDMA drought in that country. I soon found that 4-methylmethcathinone was the drug of interest, that the core molecule of cathinone was very similar to amphetamine and that it appeared to be only one of several substituted cathinones which were circulating. I did a bit of searching on PubMed and rapidly concluded that very little science had been published with any of the cathinones after a brief interest in methcathinone and cathinone in the 80s. From what little pharmacological evidence was available, combined with human subjective trip reports I could find online, it was pretty clear that we were facing a reboot of the substituted amphetamine era of the 1980s.

Mephedrone had first come to media attention around 2008 with an overdose in Sweden and had gradually grown in popularity through 2009 and into 2010. The UK government was alerted, trying to complete legal controls and had to rely on very imprecise reviews of the available knowledge.

I found this professionally embarrassing that so little was known. We spent so much effort on methamphetamine and MDMA and here, one to two years into a novel drug phenomenon we knew nothing. Nobody was presenting data at the scientific meetings I was attending, either.

I was also very interested scientifically precisely because of my interest in that prior episode of substituted amphetamine popularity and in the clear “winner”, i.e., MDMA or Ecstasy. This highly popular new drug, mephedrone, was being used by MDMA type populations in the MDMA type environment with many of them explicitly saying they were looking for a MDMA substitute. This drew my attention. There was also a very clear under-current that this mephedrone stuff was like a poor echo of MDMA but watch out for the compulsive use risk. Users were suggesting that this compound was perhaps more like a traditional psychostimulant than MDMA is.

This realization came as I was working on a final revision of an R01 proposal I was submitting on the topic of the abuse liability of MDMA, why it differs from a traditional psychostimulant like methamphetamine and how various situational or experiential factors may make MDMA more compulsively abused. The A1 had received a 21 %ile with pretty minor criticisms so of course there was no way I was going to start dragging in new drugs for the A2 (which I submitted in April of 2010).

Instead I started plotting an assault on specific funding for these novel cathinone drugs. I contacted my Program Officer who, having driven some funding opportunities for MDMA back in the day, was of course interested. But this was 2010. And there was about zero enthusiasm down in the NIDA trenches for anything that wasn’t already on NIDA Director Volkow’s current priority list. In emails and eventually in person at CPDD that year, I bounced around from one NIDA person to another and came up with a similar story. Nobody was enthusiastic about generating any special interest. “Get a fundable score and we’ll talk” was the size of it. There was even a hilarious (not really) standoff between DEA who were demanding data from NIDA (for their intent to Schedule some of these drugs) and the latter’s demand that DEA pay for it and sure, they’d see what they could do.

I got friendly with some DEA scientists to find out what was being seen in the US since law enforcement detection usually runs far ahead of any epidemiology in the peer reviewed literature. From this I deduced that mephedrone was actually pretty rare in the US but that MDPV was going to be a thing.

As we all know, Preliminary Data was going to be required to get a grant funded. But that requires….the drugs!

NIDA drug supply wouldn’t provide any of these new drugs. The usual commercial suppliers didn’t have them either.

Luckily, I was working with a couple of investigators in the department of Chemistry. One of them, Tobin Dickerson, took a look at what I needed and said “Looks pretty simple, how’s next Thursday?”. Boom! We were in business.

Our first grant proposal on this topic was submitted in October of 2010 and focused on mephedrone/4-MMC. It included self-administration data, thermoregulation and activity data, metabolism and PK data from Karen Houseknecht at UNE, microdialysis data on dopamine and serotonin responses generated with Larry Parsons’ lab and receptor/transporter screening from Bryan Roth’s Psychoactive Drug Screening Program at UNC. We proposed self-administration investigations, physiological endpoints and PK. In recognition that there were going to be many other substituted cathinone derivatives of interest we proposed a bit of structure-activity manipulation to start looking at whether specific chemical alterations conferred enhanced/decreased risk for adverse outcomes. In retrospect, putting all this together in the early days of this drug trend was probably one of the best things I’ve ever done in terms of a scientific program.

It was triaged. The app went to MNPS study section instead of BRLE (which we had requested) or even NMB, probably because of all the PK and the structure/activity content. Even though the focus was really on the novelty and the abuse liability/risks. We got 4-6s on the Innovation and 5s on the approach. But really, reading on and between the lines of the critiques it was all about “Problem? What problem?“. This could have occurred at any study section.

One has to be a bit sanguine about the inherent conservatism of the NIH grant process. It was absolutely true that there was not as yet overwhelming evidence of broad use of substituted cathinones, no evidence of large numbers of addicted people in serious life crisis and no evidence of weird/unique dangers akin to the serotonergic neurotoxicity that attends high-dose repeated MDMA exposure to drive enthusiasm.

But still. We weren’t the only ones who could see the importance of this. And as I started to present our data at meetings, I would run into colleagues who were also interested in studying these drugs. And their efforts at grant funding were to sound very familiar over the coming years.

The A1 for this initial proposal was submitted July of 2011 and likewise triaged by MNPS. There was still a lot of kvetching about “Problem? What problem?” but also some typical grant stuff. “Too descriptive”. “What’s the hypothesis”. Etc. This is always a problem for how I look at science, of course, but in this case it was kind of annoying since very little was known about any of these drugs yet, and we did have a clear hypothesis under investigation. [Related papers: Huang et al, 2012; Wright, Angrish et al, 2012; Miller et al, 2013; Aarde, Angrish et al, 2013]

I next incorporated cathinone studies on a competing continuation application for a prior MDMA-focused project that admittedly had issues with its chance of being renewed, even before I added cathinones. The first one went in July 2011 and was triaged by BRLE. The A1 went in March 2012 and got a 42 %ile. As far as the inclusion of substituted cathiones goes, it was mixed. Some reviewers saw this as a positive but some also made comments to the effect of “Problem? What problem?” and “Why don’t you have clearer hypotheses?”. Seeing a pattern? [Related paper: Wright, Vandewater et al, 2012]

I had been doing some work on methamphetamine vaccines with the Janda lab, where my collaborator on the cathinones had done his doctoral studies. As a newish PI, he’d been trying to get away from that area of work (successfully) but here I was dragging him back into work on drug abuse. So it seemed natural for us to put in a vaccine proposal in October, 2012. This time we were focused on MDPV because it was becoming clear in our ongoing studies that this was much more like a traditional psychostimulant with a high potential for addiction in humans. Triaged. With reviewers throwing 6s and a 7 and an 8! Ouch. Well, it certainly wasn’t my strongest proposal but, more to the point, there wasn’t much complaint about the drug choice. Maybe because the rest of it drew so much fire, I couldn’t say. [Related paper: Aarde, Huang et al, 2013]

[Updated: I forgot about this one] I tried a slightly different strategy at this point, submitting a new proposal in October 2012 that wasn’t focused on the cathinones, per se. Instead, this was a proposal about another topic in substance abuse research (one which had background, we’d been working a little bit on it, had a pub, etc, etc) where we just used MDPV self-administration as the drug model. Our most recent Preliminary Data were from this so why not, right? The PMDA study section triaged it- one reviewer threw a 9 for approach and a 7 for significance but the other three reviewers were throwing 3s and 4s mostly. Leaving aside the hater reviewer who went off hilariously on ad hominem attacks and thoroughly unjustified complaints (going by my rather considerable collection of grant reviews testifying to my minimal competence level), the remaining three reviewers ranged from slightly skeptical (insufficient justification for selecting MDPV as the model) to out and out objecting (“…should be examined using a drug that has well characterized patterns of self-administration in the laboratory“). Needless to say when I put the revision in it did not include a cathinone as the model. [Related papers: Aarde, Huang et al, 2015; Aarde, Miller et al, 2015]

In Feb 2013 we submitted a new approach to the cathinones, now with the take on Hypothesis B, as opposed to the Hypothesis A that underlay most of our arguments up to this point. Triaged by NMB. Things were improving slightly, however. A little bit of kvetching over methodology but for the most part no complaining about the relevance of studying these emerging drugs. A fascinating new all-reviewers complaint was included about our structure-activity studies somehow informing clandestine chemists how to make better (or worse from another point of view) drugs. [Related paper: Aarde, Creehan et al, 2015]

Of course by this point we had started publishing papers on cathinone-related topics. Our first ones must have appeared online in early 2012 with print versions issued in fall of 2012. I think we had 6 papers published by the end of 2013. I’ve added citations to the above to indicate the approximate stage of Preliminary Data that were available and relevant at each grant submission- obviously the papers appeared later in most cases.

I’m not entirely sure I remember why but we submitted a different take to the question in November 2013. This one backed off of Hypothesis B and struck out on a tack that tried to address what was now a diverse set of substituted cathinones on the open market. This was promptly triaged by BRLE. One reviewer was convinced that we’d never publish many papers. Most of the rest was the usual ticky tack stuff about “why didn’t you do it this way?” and questions that really can only be resolved by getting in there and doing the work. In a word, empirical. By this point, reviewers were viewing the attention to these novel drugs as a strength, no more comments about demonstrating the scope of the real world problem.

In February of 2014, NIDA posted a new funding opportunity announcement on synthetic drugs, the R01 version was PAR-14-106. Actually, it was initially posted as a PA, withdrawn and reposted as a PAR “to allow a Special Emphasis Panel to provide peer review of the applications”. Why? Who knows. But as soon as the original PA was posted I sent an email to the Program Officer in charge that included my summary statements to that point in time and an observation that throwing these apps into regular study sections was unlikely to produce fundable scores. If you are keeping track, nearly everything I had submitted was triaged, except the A1 for my competing continuation (which you might view as a sympathy scoring/discussion).

Up to that point in time, if you search RePORTER for funded grant projects on “mdpv, methylone, mephedrone or cathinone” for fiscal years 2010-2014 you would first find 2 pre-doc fellowships and one post-doc fellowship. Next you would notice that one R01 was funded in FY2012 via a conflict special emphasis panel for a study section chair, one R01 was funded in FY2014 on human epidemiology through a regular standing study section and one R21 was funded through BRLE for FY2012. In addition, five NIDA intramural labs started mentioning these key words and are located by this search.

The point here is that clearly my colleagues who were also submitting grants on cathinone-related topics were having a similar lack of success. We talk at meetings so, trust me, there were several quite accomplished PIs who were applying during this interval of time as well.

We submitted a new version of the Hypothesis B proposal in June 2014 for this new PAR. It got a 25%ile so we resubmitted it in March 2015 again to the PAR. It got a 24%ile. No movement. The resume of discussion for the first version complained about minor technical issues, interdependence of Aims (this is grantsmithing stuff) and “sloppy constructed, lacking clarity and consistency”. This latter bit was interesting since one of the prior reviews of this Hypothesis B lauded it for clarity and fantastic grantsmithing. It happens. Oh, and by now we were trying to get out ahead of the looming SABV initiative and mentioned including female and male rats. Got killed for “design concerns”. The resume of discussion for the second one was a classic case of “we don’t have any real complaints but there are one or more grants better than yours in the list so we have to find something”. Very frustrating. Oh, and we were offered the opportunity to propose a R56 Bridge on the last version of this (yay!) to focus on the sex-differences and improve our hypotheses…..but it wasn’t selected for funding. Another half-submission in late 2015.

In between these submission we put in an R21 on vapor inhalation of cathinones in Jun of 2015 to be reviewed by the SEP. It received a 39 impact score with concerns mostly focused on the novel inhalation model. So no real issues with the cathinone topic itself, after all it was a synthetic drugs SEP! [Related paper: Nguyen, Aarde et al, 2016]

By this time, the MDMA-related grant I mentioned at the top was due for a competing continuation application, which went in November 2015. You may be wondering by now how we were able to sustain the effort to generate new preliminary data and such for all of these applications and, ultimately, papers. Well, our MDMA grant was funded pretty soon after we got really interested in the cathinones. There was a lot of dovetailing of the topic domains, as I mentioned, the mephedrone compound was originally reported as being sort of MDMA-like, but with enhanced abuse liability. Methylone eventually emerged as the direct cathinone cousin of MDMA. So it actually made a lot of sense to draw these together for the competing continuation. It got a 27%ile from BRLE and the reviewers were totally on board with the inclusion of new cathinone experiments as well as the harmony of what we’ve been doing over the past 4 years with the original MDMA proposal (which was originally designed before these designer cathinones appeared in user groups). This put us up to something like 4 straight applications discussed after our initial run of 6 7 triages interrupted only by one kiss-your-sister score of a -06A1 application. Progress! [Related papers: Creehan et al, 2015; Vandewater et al, 2015; Nguyen, Grant et al, 2016]

The stalling of the Hypothesis B proposal at an unfundable 24-25/%ile was frustrating, but what can you do? The ideas seemed to have legs and the complaints were not substantial. We put it back in as new application in October 2015, for the SEP once more. It got an 18%ile. Definitely outside the likely payline for the year*. So I revised and resubmitted it in August 2016. Sixth time (honestly I’m losing track at this point) is the charm for Hypothesis B?

So here we are in September of 2016. We’ve been working on this topic for over 5 years and submitting grants for almost 5 years. We’ve had thirteen papers and I’ve submitted thirteen fourteen grant applications (my collaborator has put in a few more during this interval as well).

NIDA eventually created a FOA for synthetic drugs (not just cathinones, includes cannabinoids and opioids as well). The degree to which this was influenced by our advocacy and publications, I don’t know but it had to have helped. Certainly our early triaged summary statement results were key to getting a SEP convened for this purpose. They’ve funded, by my count, two R15s, one R21 and one R03 via regular study sections and one R21 via SEP for a more general funding opportunity announcement. The PAR on synthetic drugs resulted in the funding of an R21 and four R01s on synthetic cathinones since being issued, that is 6 possible funding rounds to this date*.

We recently received word that the aforementioned October 2015 submission of the Hypothesis B proposal will be funded.

Time to REALLY get to work!

 

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Addendum: We never work alone on these projects and it has been a large team effort. Deepshikha Angrish synthesized compounds in the Dickerson lab in the early days. Deborah Barlow in the Houseknecht lab was essential for the PK work. Matt Buczynski jumped right on a key early neuropharmacology experiment in the Parsons laboratory. Jerry Wright, Shawn Aarde (in particular), Michelle Miller and Jacques Nguyen are postdocs that did heavy lifting on this topic in my group. My laboratory’s incredible technicians Sophia Vandewater, Kevin Creehan and former technician PK Huang (now a graduate student elsewhere) likewise did great work.

 

*There is an interesting vignette in here about the effectiveness of convening SEPs for PARs. My three scores for Hypothesis B in this SEP (which doesn’t have standing members but is convened per-round) ranged from 31-36. At one point the PO seemed to let slip that my 31 was the top score in that round for the SEP. Going from the PO’s general demeanor in discussing how the FOA was going, and the rather thin list of funded grants (not many cannabinoid or opioid ones emerged either), I conclude that reviewers are not issuing clearly-fundable scores in every round. And not many fundable scores all together over 6 rounds. This is somewhat puzzling**.

 

**In FY2014 alone, NIDA funded 37 new R01s that included cocaine as a keyword and 13 with heroin. Eighteen competing continuation R01s with either heroin or cocaine referenced. Of course there would be far more that were in the middle of non-competing intervals of funding.

June 3, 2016

Inhalation delivery of psychostimulants to rats using e-vape technology

Filed under: 4-MMC/Mephedrone, Cathinones, E-cigarettes, MDPV, Methamphetamine — mtaffe @ 4:03 pm

Although inhaled exposure of drugs is a prevalent route of administration for human substance abusers, animal models of inhaled exposure to psychomotor stimulants (cocaine, methamphetamine, synthetic cathinones, etc) are not commonly available. Inhaled use of methamphetamine is more common than other routes of administration in habitual and dependent users (Das-Douglas et al. 2008; Heinzerling et al. 2010; Wood et al. 2008) and the SAMHSA/TEDS treatment admission database for 2012 shows 4.7% of treatment seekers in the USA were admitted for smoked cocaine vs 2.2% for other routes of cocaine administration. There is limited evidence that people are using e-cigarettes for inhalation of methamphetamine (Evans 2014; Rass et al. 2015), “bath salts” (Johnson and Johnson 2014; Rass et al. 2015) and “flakka” (presumptively α-pyrrolidinopentiophenone; alpha-PVP) as reported (Anderson 2015).

We have therefore developed a method for the delivery of psychostimulant drugs to rats and evaluated the impact of methamphetamine (MA), 3,4-methylenedioxypyrovalerone (MDPV; “bath salts”) and 4-methylmethcathinone (4-MMC; mephedrone). The following paper describing our initial studies has been recently accepted for publication in Neuropsychopharmacology:

Locomotor stimulant and rewarding effects of inhaling methamphetamine, MDPV and mephedrone via electronic cigarette-type technology. Jacques D. Nguyen1, Shawn M. Aarde1, Maury Cole2, Sophia A. Vandewater1, Yanabel Grant1 and Michael A. Taffe1
1Committee on the Neurobiology of Addictive Disorders; The Scripps Research Institute; La Jolla, CA, USA
2La Jolla Alcohol Research, Inc, La Jolla, CA, USA

Schematic of the inhalation chamber

Schematic of the inhalation chamber

Our exposure model for this study involved a standard sized rat housing chamber with a sealed lid- these are commercially available for a variety of purposes. The chamber was plumbed for regulated airflow and incorporated the ability to deliver and exhaust the vapor from an e-cigarette type device. The overall approach for delivery to rodents is under patent to La Jolla Alcohol Research, Inc which has been instrumental in developing the equipment for our studies. This collaboration has resulted in a number of studies so far, this one is the second one to be published. The first paper described the effects of THC inhalation (blogpost). The company has also recently been awarded an SBIR Phase II Grant (R44 DA041967) to further develop and enhance commercialization of the device.

Control of the dose administered to the rat in this system is a key initial topic of investigation. We determined in this paper whether the dose can be altered with the manipulation of a number of variables. The concentration off the drug may be altered in the propylene glycol (PG) vehicle (aka “e-juice”)- our standard condition for this study was 100 mg/mL but effects from 12.5-200 mg/mL were also explored for different drugs. For the most part this study found concentration-dependent effects only across drugs (4-MMC was much less potent than MA or MDPV) when the puffing and inhalation duration was held constant. The puffing regimen and duration of inhalation exposure can be altered as well. In most of our studies we delivered 10-s vapor puffs with 2-s intervals between them every 5 minutes for durations of 10-40 min (approximately 0.125 ml was used in a 40 min exposure session). Varying the total duration from 10 to 30 min resulted in dose dependent effects of inhaling MA (12.5 mg/mL) or MA (12.5 mg/mL).

Vape decreases ICSS thresholds

A decrease in ICSS threshold was produced by inhalation exposure to 4MMC (200 mg/mL), MA (100 mg/mL) and MDPV (100 mg/mL). Similar effects were produced by i.p. administration of 4MMC (1.0mg/kg), MA (0.5 mg/kg) or MDPV (0.5 mg/kg). Significant differences from the respective Vehicle condition are indicated by *.

We present data on the intracranial self-stimulation reward paradigm in this paper. This is a model in which electrodes are implanted into the medial forebrain bundle of the rat and it is trained to respond for small deliveries of electrical current which has a rewarding or reinforcing effect. The procedure used for this study ramps the stimulation up and down during a session until the threshold necessary for the individual to experience a reinforcing effect is determined. Once the animals are trained to generate stable thresholds, they can be tested by administering drugs before the session. If a drug has a rewarding or reinforcing effect, it tends to lower the threshold below the baseline level. Here we show that all three drugs decrease reward thresholds in male rats. The reduction in the reward threshold was of a similar magnitude when drug was administered by injection or by vapor inhalation. This is a key indication that this procedure can generate reinforcing or rewarding levels of drug in the rats.

Activity rates after inhalation of  3,4-methylenedioxypyrovalerone (MDPV; 25,50,100mg/mL) or 4-methylmethcathinone (4MMC/mephedrone; 100, 200mg/mL).

Mean (N=13; + SEM) activity rates after inhalation of 3,4-methylenedioxypyrovalerone (MDPV; 25,50,100mg/mL) or 4-methylmethcathinone (4MMC/mephedrone; 100, 200mg/mL). Gray shaded symbols indicate a significant difference from PG vehicle at the corresponding time point. Base = pre-inhalation baseline.

Locomotor activity was measured after vapor inhalation using a radiotelemetry system that generates activity rates as counts per minute. In this figure we show the activity before and after inhalation of the PG vehicle and then three concentrations of MDPV and two concentrations of 4-methylmethcathinone (4-MMC, mephedrone) for 40 min. Locomotor activity was increased for 2-3 h after the initation of vapor for all three MDPV concentrations and for the 200 mg/mL concentration of 4-MMC. Similar effects were observed for MA and we went on to show that the dopamine D1-like receptor antagonist SCH23390 (10 ug/kg, i.p., prior to inhalation) blocked locomotor increases caused by inhalation of each drug. This is as would be expected, similar to the effect of SCH23390 on locomotor stimulant effects of these drugs when injected in rodents.

Wheel Activity after MDPV or MA

Mean (N=7; ± SEM) wheel activity of male rats after inhalation of methamphetamine (100 mg/mL in PG), MDPV (100 mg/mL in PG) or the PG alone for 40 minutes. Gray shaded symbols indicate a significant difference from PG. A significant difference from the 30 min time point within an inhalation condition is indicated with *, and a difference from MA with #, for corresponding time points.

Another study in the paper investigated effects of vapor inhalation of the MA and MDPV on wheel activity. Under vehicle treatment, rats run more on the wheel in the first 30 minutes and then run significantly less for the subsequent 90 min of a 2 h session. When allowed to use the wheel after vapor exposure to MA or MDPV, activity is initially suppressed and then rebounds as the session continues. Presumably, the initial suppression of wheel activity is related to the increase in chamber locomotor activity found in the radiotelemetry study- if the rats were running around the cage they might be unlikely to enter the wheels. In the study depicted, MDPV caused significantly more activity than vehicle inhalation 60-90 min after finishing the vapor inhalation. MA in this experiment did not increase activity compared with vehicle, however activity was significantly higher in the last thirty minutes than the first 30 min after MA inhalation. Additional data found no significant effects of 40 min of inhalation of either MDPV or MA at a 25 mg/mL concentration and a third study found elevations of wheel activity 90-120 min after a 20 min inhalation of MA (100 mg/mL). In total, the wheel activity data confirm dose-dependent effects on a second measure of locomotion.

Overall, this study is the first to demonstrate behavioral effects of e-cigarette type inhalation delivery of psychostimulants to rats. This further validates our model and encourages additional study of the risks of e-cigarette delivery of psychoactive substances in laboratory animal models.
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J. D. Nguyen, S. M. Aarde, M. Cole, S. A. Vandewater, Y. Grant and M. A. Taffe. Locomotor stimulant and rewarding effects of inhaling methamphetamine, MDPV and mephedrone via electronic cigarette-type technology, 2016, accepted article preview 9 June 2016; doi: 10.1038/npp.2016.88 [ PublisherSite ][ PubMed ]

Funding and Disclosures for this paper: This work was funded by support from the United States Public Health Service National Institutes of Health (R01 DA024105, R01 DA024705, R01 DA035281 and R44 DA041967) which had no direct input on the design, conduct, analysis or publication of the findings. Subsets of these data were first presented at the Experimental Biology meeting in 2015 and the Annual Meeting of the Society for Neuroscience 2015. Development of the apparatus was supported by La Jolla Alcohol Research, Inc and MC is inventor on a patent for this device. SAV consults for La Jolla Alcohol Research, Inc.

March 2, 2016

Escalation of mephedrone IVSA under long-access conditions

Filed under: 4-MMC/Mephedrone, Cathinones, Methylone — mtaffe @ 10:41 am

StructureFig-MDMA-Methylone-MephedroneWe continue to be interested in assessing the relative abuse liability of new synthetic cathinone stimulants that pop up in recreational users. The most established entities such as mephedrone (4-methylmethcathinone; 4-MMC) and methylone (3,4-methylenedioxymethcathinone) are of particular interest to our research because they share some pharmacological properties with MDMA (Ecstasy), constituting a class of stimulants sometimes called entactogens. As you can see from the structures at the left, methylone is the direct cathinone cousin of MDMA– the ketone group on the beta carbon is the element that differentiates a cathinone from an amphetamine.

The 2013 and 2014 NFLIS showed that methylone may be more common than MDMA in the US and mephedrone continues to be popular in the UK. Our recent papers (Vandewater et al, 2015 and Creehan et al, 2015) compared the intravenous self-administration (IVSA) of methylone, mephedrone and MDMA within relatively short (2 h) daily training sessions in male and female rats, respectively. We found that rats will IVSA greater amounts of mephedrone compared with MDMA with methylone falling in between the other two. One prior study had found that rats will IVSA methylone at very high rates, more like a traditional stimulant than like MDMA, thus we were curious to further examine potential differences.

It has been shown that relatively long (6 h) daily sessions of access to cocaine (Ahmed and Koob, 1998; Larson et al., 2007) or methamphetamine (Kitamura et al., 2006; Schwendt et al., 2009) IVSA results in both higher daily drug intake and a progressive increase across sessions (termed “escalation”) relative to animals trained only in 1-2 h sessions. This has been conceptualize as a better rat model of the state of human stimulant addiction, as opposed to the interpretation of mere drug liking. In contrast, a prior study found no difference in total session intake of the entactogen class stimulant MDMA between long (6 h) and short (2 h) access groups over the first 11 sessions (Schenk et al., 2003). This seemed a little unusual to us and we showed in Vandewater et al (2015) that when run in the dark cycle (the rats’ active period of the day), male rat IVSA of MDMA
Fig1-LgA-ShA-MethyloneMMC-Revunder 6 h daily access conditions is higher than under 2 h access conditions. So we conducted a new study to determine how the rat IVSA of the two entactogen (MDMA-like) cathinones would fare under 6 h access conditions. The following has been recently accepted for publication:

Nguyen, J.D., Grant, Y., Creehan, K.M., Vandewater, S.A. and Taffe, M.A. Escalation of intravenous self-administration of methylone and mephedrone under extended access conditions., Addict Biol, 2016, in press. [ Publisher Site ][ PubMed ]

This study was conducted in male rats, trained to intravenously self-administer methylone or mephedrone in Short Access (ShA; 2 h) or Long Access (LgA; 6 h) sessions. The training dose was 0.5 mg/kg per infusion for each drug. The mean (SEM) number of infusions obtained by the four different groups is depicted in the first figure from the paper, reproduced here. There are two takeaway messages. First, the total daily intake is higher for the LgA groups for both drugs. Secondly the mephedrone LgA group obtained more infusions than did the methylone LgA group. [Significant differences from the first three sessions within group are indicated by shaded symbols. Significant differences between Access groups within a drug are indicated by * and differences between drugs, within Access condition, by †.] This further confirms, as did our MDMA LgA study, that there is nothing weird about entactogen IVSA under LgA vs ShA conditions- rats take more drug in 6 h than in 2 h. It also emphasizes that rats will take more mephedrone than methylone.

First 2 h intake of LgA groups

First 2 h intake of LgA groups Significant differences from the first three sessions within group are indicated by shaded symbols. Significant differences from MDMA are indicated by * and from methylone by †.

In some senses that is a trivial observation and one of the key measures of rats having achieved a state more similar to the addicted human is whether the LgA animals gradually take more drug in the time interval commensurate with the ShA animals- in our case the initial two hours of their 6 h session. This graph depicts the first 2 h infusions for the mephedrone (4-MMC) and methylone trained animals from this new study as well as the similar data for the MDMA 6 h animals from* Vandewater et al (2015). As you can see in this graph, the three drugs are clearly distinguished from each other on this key measure of “escalated” drug seeking behavior. First 2 h intake of MDMA is relatively stable across this training interval, first 2 h methylone intake increases across sessions and first 2 h mephedrone intake increases even more. The conclusion we reach from this is that both methylone and mephedrone have enhanced abuse liability compared with MDMA and they are more likely to lead to patterns of relatively uncontrolled or compulsive drug use in humans.

We also took this new study one step farther by asking how hard the four groups would work for a given magnitude of drug infusion. We do this by using a Progressive Ratio procedure. In the normal training the animals have a Fixed Ratio (as it is called) of lever presses to infusions. In this study, it was FR1 meaning they had only to make one press on the drug-associated lever to get an infusion of drug. In the PR procedure, the number of responses required for each successive drug infusion is progressively increased throughout the session (e.g., 1, 2, 4, 8, 16….). Eventually the rats will stop obtaining drug infusions. The last ratio they completed for a drug infusion is called the “breakpoint”, indicating how many lever presses they made for that final infusion. We also varied the available drug dose per infusion in a random order across session. Thus, we obtain an estimate of how hard each group will work for a given dose of drug. In order to directly compare liability for stimulant drug seeking across the groups we used the same two test drugs, methamphetamine (MA) and mephedrone/4-MMC.

The top panels contrast breakpoints during methamphetamine (MA) substitution in A) ShA and B) LgA groups. The bottom panels contrast breakpoints reached during mephedrone (4-MMC) dose substitution in C) ShA and D) LgA groups. Significant differences from vehicle control within-group are indicated by *, from the 0.125 dose by # and from all other dose conditions by %. Significant differences from all other groups, within a dose condition, are indicated by †.

The top panels contrast breakpoints during methamphetamine (MA) substitution in A) ShA and B) LgA groups. The bottom panels contrast breakpoints reached during mephedrone (4-MMC) dose substitution in C) ShA and D) LgA groups. Significant differences from vehicle control within-group are indicated by *, from the 0.125 dose by # and from all other dose conditions by %. Significant differences from all other groups, within a dose condition, are indicated by †.

This direct comparison study found that the rats trained to IVSA mephedrone under LgA conditions worked harder for either their training drug mephedrone or MA than did any other the other groups. There was no similar LgA/ShA difference for methylone-trained rats. This further emphasizes the substantial abuse liability of mephedrone/4-MMC. This drug appears to be quite similar to classical stimulants like methamphetamine and cocaine in this respect.

It continues, therefore, to be a mystery why a drug which releases serotonin in the nucleus accumbens to a greater degree than it releases dopamine would be such an effective reinforcer in the rat IVSA assay. There is considerable evidence, beyond just the fact that rats are pretty reluctant to IVSA MDMA compared with methamphetamine, that increasing serotonergic over dopaminergic effects of drugs is going to decrease the effectiveness as a reinforcer. And therefore decrease the liability for repeated use patterns. One of the scientific benefits of looking into the rewarding properties of some of these new cathinone stimulants is precisely this. It can suggest places where the existing dogma, based on the amphetamines in large part, may need some reconsideration.

__
*We originally submitted this paper including a comparison with the prior MDMA group, cited and referenced so that there was no confusion as to where the data came from. First, a reviewer mentioned that this may be inappropriate. Second, the handling Editor noted that this was against journal policy. After a bit of back and forth with the Editor over the reasons for making this comparison we had to cave and remove the direct (i.e. including statistical comparisons) contrast with those prior data.

August 19, 2015

Mephedrone is also more reinforcing than MDMA or Methylone in male rats

Filed under: 4-MMC/Mephedrone, Cathinones, MDMA, Methylone — mtaffe @ 2:30 pm

StructureFig-MDMA-Methylone-MephedroneMethylone has now surpassed MDMA in Forensic Laboratory samples in the US. Mephedrone is less popular in the US but maintains a high degree of popularity in the UK. We recently published a paper [Creehan et al, 2015; PubMed; blogpost] showing that the drug mephedrone was a more effective reinforcer than either MDMA or methylone in female rats.

Our followup study which compared the self-administration of these three drugs in male rats has been accepted for publication.

Vandewater, S.A., Creehan, K.M. and Taffe, M.A. Intravenous self-administration of entactogen-class stimulants in male rats. Neuropharmacology, 2015, 99:538-545. [ PubMed ][ Publisher Site ]

We are interested in the reinforcing potential of mephedrone and methylone due in large part to their neuropharmacological similarity to MDMA. Specifically, these three drugs have a relatively greater enhancement of serotonin in the nucleus accumbens of the rat brain compared with the enhancement of dopamine. The latter effect is associated with pleasurable/rewarding effects of traditional stimulant drugs like methamphetamine whereas the preferential serotonin release/accumulation is associated with reduced reward potential. In short, rats have shown much less intravenous self-administration of MDMA versus methamphetamine.

Fig1-XY-3drg-Acq The fact that Mephedrone and Methylone share the MDMA-like neurochemical profile groups them all together as atypical or entactogen-class stimulant drugs and predicts less compulsive use compared with traditional stimulants like methamphetamine. Yet several self-administration studies with mephedrone have already shown a greater abuse potential compared with MDMA. The one available study with methylone (Watterson et al, 2012; blogpost) prior to our work implied the same. Our study in female rats was the first to directly compare these three drugs and we confirmed that mephedrone is a much more effective reinforcer, thus predicting higher liability for compulsive use. MDMA and methylone, however, appeared to be quite similar.

Our new study in the male rats used essentially the same procedures as the study in females and had the same conclusion. In this figure we show mean (±SEM) daily infusions of drug (upper panel) and the proportion of responses on the drug-associated lever versus the inactive lever (lower panel) obtained for groups of male rats trained to self-administer MDMA (N=17), Methylone (N=14) or Mephedrone (N=15) in 2 hour sessions. [Significant differences from the first session within group are indicated by *, differences between mephedrone and both other groups by #, differences from methylone by ‡ and differences from MDMA by †.] The MDMA and mephedrone groups differed from each other and the methylone-trained group was intermediate.

The results from the female animals in the previous study differed slightly in that the methylone and MDMA intakes were nearly identical and were both significantly different from the mephedrone self-administration.

MDMA-Methylone-AcqWe did some follow up comparisons between males and females for the new paper and those ended up in the Supplemental Materials file. The only significant sex-difference was for the MDMA-trained groups where there was a significant main effect of rat sex confirmed in the analysis. The methylone intakes appeared to be nearly identical between males and females, as is depicted and the mephedrone intakes did not differ either (not shown).We did some further sub-groups analysis and found that this difference in MDMA self-administration was mostly in the less-preferring half of the male group.

At this point we have a direct confirmation of the enhanced liability of mephedrone for compulsive use over that of MDMA. This is a clear rejection of the suggestion based on intra-cranial self-stimulation reward data that it has reduced liability- clearly something is off about the way the results were interpreted by Bonano et al (2014). Methylone appears to be much more similar to MDMA although it might be a slightly more effective reinforcer in male rats. Nevertheless we still cannot reconcile our results with methylone self-administration with the apparently robust self-administration reported by Watterson et al (2012). As there are only now three published studies of the self-administration of methylone, we must await further studies to better understand the reasons for these different outcomes.

July 16, 2015

UPROXX theTRUTH: About Bath Salts

Filed under: 4-MMC/Mephedrone, alpha-PVP, Cathinones, MDPV, Methylone, Public Health — mtaffe @ 11:36 am

The UPROXX folks were kind enough to invite me to make a clip on the synthetic cathinones for their new ‘theTRUTH’ series.

This was a novel experience for me and it was very difficult. If you look closely at this video and the ones linked below, you will notice how many cuts there are. The production team basically wants you to spit out very short and pithy statements which they can edit together into a whole. So it was conducted in a sort of interview style with a producer asking me questions and me responding as briefly as possible. Often times the same point had to be made several times to get it right. I even had to record a series of hand gestures and transitional phrases in case they needed to bridge points!

After that it was in their hands to stitch it together and tell a story. Obviously, one of the things I was trying to do was to not say anything that could be edited into a context that misrepresented anything too badly. On the whole, I think the UPROXX production team did a good job, given the material (me) they had to work with.

Others in this theTRUTH series include pieces on Toxoplasma gondii and large earthquakes.

January 9, 2015

Mephedrone is more reinforcing than methylone or MDMA in female rats

Filed under: 4-MMC/Mephedrone, Cathinones, IVSA, MDMA, Methylone — mtaffe @ 9:27 am

A paper from the laboratory on the self-administration of MDMA-like cathinone drugs has been recently accepted for publication published online.

Creehan, K.M., Vandewater, S.A. and Taffe, M.A. Intravenous self-administration of mephedrone, methylone and MDMA in female rats. Neuropharmacology, 2015, 92:90-97. DOI: 10.1016/j.neuropharm.2015.01.003 [Publisher Link, PubMed]

 

This paper is the result of our “Open Experiment in Open Experimenting” which is chronicled on the linked page.
StructureFig-MDMA-Methylone-MephedroneBackground 1: Cathinones, aka “bathsalts”
There are a number of synthetic cathinone stimulants that are in reasonably substantial and continued use in the US, as well as elsewhere worldwide. Cathinone, the core molecule differs from amphetamine in the addition of a ketone in the beta position. In the figure, 3,4-methylenedioxymethamphetamine (MDMA or “Ecstasy”) can be contrasted with its cathinone cousing Methylone, which might otherwise be called 3,4-methylenedioxymethcathinone. If you see Methylone referred to as “bk-MDMA”, as it sometimes is with users, you will now be able to recognize what “beta-keto-MDMA” means. Mephedrone more or less led the emergence of substituted cathinones with one death noted in Sweden in 2008 and a major increase in prevalence in the UK throughout 2009 and 2010. To my view there has never been a major place in the recreational pharmacopeia for 4-methylmethamphetamine, the amphetamine cousin of mephedrone.

Background 2: Empathogenic or MDMA-like neuropharmacology
We have described in prior posts how mephedrone exhibits an MDMA-like trait of preferentially increasing serotonin versus dopamine overflow in the nucleus accumbens of rats; this is different from the dopamine-dominant response to methamphetamine or amphetamine. This pattern has been proposed to be intimately related to the fact that MDMA is only an uncertain reinforcer in rodent IVSA compared with the more typical amphetamines. Mephedrone is much more readily self-administered than MDMA and a single prior report seemed to indict that methylone likewise is an effective reinforcer in IVSA.

Background 3: Female animals
The NIH has recently issue a policy position which reinforces the critical importance of conducting sex-difference comparisons across biomedical domains (Clayton and Collins 2014). It has been shown that female rats will self-administer more cocaine (Roth and Carroll 2004b; Smith et al. 2011) and more methamphetamine (Reichel et al. 2012; Roth and Carroll 2004a) than males; these sex differences can be more pronounced under long-access escalation and/or Progressive Ratio procedures. Little is known about any possible sex differences in the self-administration of atypical stimulants like MDMA or the recently emerging MDMA-like designer cathinones. In short, we couldn’t find a single report of IVSA of any of these compounds in female rats (although Oakly et al, 2014 fails to specify the sex). Thus, the present study was conducted in female rats to expand understanding of the comparative reinforcing properties of these compounds.

 
Results
Creehan15-Fig2-infusionsThis figure from the paper (click to enlarge) illustrates the number of infusions of drug obtained by three groups of female Wistar rats during the acquisition phase of intravenous self-administration (IVSA). Each group was trained on a different drug. The take-away messages is in the upper panel. At equal training doses the rats trained on mephedrone (4-methylmethcathinone, 4-MMC) take more infusions across the training interval. [Significant difference from the first session within group by *, Between mephedrone and both other groups by #, versus methylone by ‡ and versus MDMA by †.].
The bottom two panels of the figure split the groups into the upper and lower halves based on average drug intake during the acquisition interval. The point of doing so is that the Schenk lab studies (here, here) have shown that ~40-50 percent of (male, normal or wild-type) rats will fail to meet their acquisition criteria for MDMA IVSA. This is unusual for stimulant IVSA- something like 80-100% would be more typical for cocaine. Instead of creating arbitrary “acquisition” criteria, we chose to report subgroup analyses (the paper also contains drug-associated lever discrimination ratio information). Mephedrone was still preferred by the lower-preference animals and we illuminated a small advantage for methylone IVSA in the more-preferring Upper Half compared with the MDMA trained animals.

Conclusions
This direct comparison paper verifies a picture which has been emerging with the nascent IVSA literature on mephedrone- i.e., that it is clearly more effective as a reinforcer compared with MDMA. This points back to the neuropharmacological effects outlined above (enhanced serotonin response in nucleus accumbens of rats) and raises new questions about the relevance of such properties in predicting abuse liability. Together, these behavioral findings oppose a claim advanced by Bonano and colleagues (2014) on the basis of intracranial self-stimulation reward data that mephedrone has decreased abuse liability relative to methylone and MDMA.

There is only the single other paper on methylone IVSA and our results do not concur with the findings of Watterson et al (2012). Obviously there are methodological differences so additional experiments will be needed to gain better clarity on the propensity of methylone to support IVSA compared with MDMA and mephedrone. There was a hint in our data that for the more-preferring animals methylone might be slightly superior to MDMA as a reinforcer. So it isn’t impossible that some methodological issues might uncover a larger methylone/MDMA difference.

 

Relevant Literature
Aarde SM, Huang PK, Creehan KM, Dickerson TJ, Taffe MA. The novel recreational drug 3,4-methylenedioxypyrovalerone (MDPV) is a potent psychomotor stimulant: self-administration and locomotor activity in rats. Neuropharmacology. 2013 Aug;71:130-40. doi: 10.1016/j.neuropharm.2013.04.003. Epub 2013 Apr 15. [PMC (free) Link]

Aarde SM, Angrish D, Barlow DJ, Wright MJ Jr, Vandewater SA, Creehan KM, Houseknecht KL, Dickerson TJ, Taffe MA. Mephedrone (4-methylmethcathinone) supports intravenous self-administration in Sprague-Dawley and Wistar rats. Addict Biol. 2013 Sep;18(5):786-99. doi: 10.1111/adb.12038. Epub 2013 Jan 30.[PMC (free) Link]

Clayton JA, Collins FS (2014) Policy: NIH to balance sex in cell and animal studies. Nature 509: 282-3

Hadlock GC, Webb KM, McFadden LM, Chu PW, Ellis JD, Allen SC, Andrenyak DM, Vieira-Brock PL, German CL, Conrad KM, Hoonakker AJ, Gibb JW, Wilkins DG, Hanson GR, & Fleckenstein AE (2011). 4-Methylmethcathinone (mephedrone): neuropharmacological effects of a designer stimulant of abuse. The Journal of pharmacology and experimental therapeutics, 339 (2), 530-6 PMID: 21810934

Motbey CP1, Clemens KJ, Apetz N, Winstock AR, Ramsey J, Li KM, Wyatt N, Callaghan PD, Bowen MT, Cornish JL, McGregor IS.High levels of intravenous mephedrone (4-methylmethcathinone) self-administration in rats: neural consequences and comparison with methamphetamine.J Psychopharmacol. 2013 Sep;27(9):823-36. doi: 10.1177/0269881113490325. Epub 2013 Jun 5.

Roth ME, Carroll ME (2004a) Sex differences in the acquisition of IV methamphetamine self-administration and subsequent maintenance under a progressive ratio schedule in rats. Psychopharmacology 172: 443-449

Roth ME, Carroll ME (2004b) Sex differences in the escalation of intravenous cocaine intake following long- or short-access to cocaine self-administration. Pharmacol Biochem Behav 78: 199-207

Watterson LR, Hood L, Sewalia K, Tomek SE, Yahn S, Johnson CT, Wegner S, Blough BE, Marusich JA, Olive MF (2012) The Reinforcing and Rewarding Effects of Methylone, a Synthetic Cathinone Commonly Found in “Bath Salts”. J Addict Res Ther S9:002: 1-8

September 17, 2013

Bathsalts involved in 22,904 Emergency Department Visits in the US in 2011

Filed under: 4-MMC/Mephedrone, Cathinones, MDMA, Methylone — mtaffe @ 12:09 pm

Newly released data from the Drug Abuse Warning Network under SAMHSA, detail Emergency Department visits that involved bathsalts in 2011 [PDF].

Samhsa-ER-bathsaltsSep2013Unfortunately I can’t find any definition of the terms so I don’t know if any specific drugs had to be confirmed in body tissues or not. Nor do I know what they lumped under this catchall street-name for their data collecting and analysis. At the very least we have to presume there is some diversity here in terms of the actual drug being used. Mephedrone, methylone and MDPV have to be the suspects based on apparent presence in the US but since medical emergency is presumably rare, it may be that these visits disproportionally represent some other drug. Presumably in the cathinone class…but perhaps not.

One thing that would be of interest, but not something that appears in this dataset, would be a review of symptoms. The presence of “bath salts” with other drug combinations can be interpreted several ways. For example, it could suggest that bathsalts are more of a problem in the presence of other drugs…but symptom discrimination could help. Lethal or near-lethal alcohol and stimulant profiles look very different so if you have an alcohol+bathsalts case that looks like stimulant overdose, the presumption has to be that the alcohol had little to do with it.

In other recent news, three “molly” related deaths over the recent months have been confirmed as involving methylone, MDMA and methylone with MDMA, respectively.

July 15, 2013

Mephedrone and MDPV share discriminative stimulus effects with Cocaine and Methamphetamine

Filed under: 4-MMC/Mephedrone, Cathinones, MDPV, Methylone — mtaffe @ 12:50 pm

A new paper by Gatch [Dept Website] and colleagues describes the locomotor stimulant and discriminative stimulus effects of several cathinone derivatives in mice and rats respectively.

Gatch MB, Taylor CM, Forster MJ. Locomotor stimulant and discriminative stimulus effects of ‘bath salt’ cathinones. Behav Pharmacol. 2013 Jul 8. [Epub ahead of print][PubMed, DOI]

The paper examines the locomotor stimulant effects of MDPV, mephedrone, methylone (bk-MDMA), flephedrone, naphyrone and butylone in mice. Additional comparisons are made with methamphetamine and cocaine. All of the compounds, except cocaine, tested illustrated a typical inverted-U dose-response function in which low doses are ineffective, moderate doses cause a peak in locomotor activity and at the highest dose activity is either no different than the vehicle condition or actually suppressed. Although we didn’t observe any high-dose suppression of activity with mephedrone in our rat studies, this is probably because we didn’t extend to a high enough dose. This is probably the reason Gatch and colleagues only reported increased locomotor activity with cocaine. Of greatest interest to the authors was the finding that the highest doses of MDPV and naphyrone caused locomotor stimulation in the mice that lasted for 6-8 hrs, slightly longer than did the effect of the highest dose of methamphetamine tested.

Of perhaps greater interest are the drug-discrimination data. In this assay, the rat is trained to respond on one of two levers (typically) for food pellet rewards. The key feature is that the animal is injected prior to the session with either a training drug or the inactive vehicle (saline, typically). Then, for that session only responses on one of the levers is rewarded with a food pellet. So the animals are trained to response on one lever when they feel the training drug and the other lever when they feel saline. Once they are trained above 80% correct responding in each condition then the experimenter can start substituting other drugs in place of the training drug. If the rats respond more than 80% on the drug-associated lever at some dose of the new test compound then it is said to substitute for the training drug. In essence to report whether it “feels like” the original drug.

Gatch13-Fig4Although I won’t go into it here, the history of such work is extensive and at least across classes of drugs, the rats will generally fail to report an opiate drug (like heroin, say) to be like cocaine. The results are reasonably selective to drug-class. In Figure 4 of the paper, reproduced here, it is shown that at least one dose of MDPV, methylone, mephedrone (4MMC), Naphyrone, Flephedrone and butylone will lead to 80% or more responding on the lever that had been paired with the training dose of cocaine. You can also see that if the training dose of cocaine is lowered, animals are decreasingly likely to respond on the drug-paired lever.

Gatch13-Fig5In the next figure the same drugs are examined in a group of animals trained to discriminate methamphetamine from saline. Again, all of the cathinones fully substituted for the training drug. You will note that there is some variation in the precise dose at which the methamphetamine-trained animals reported drug-like effects versus the dose for the cocaine-trained animals. The authors then went on to run correlations of the ED50 values (the calculated dose at which 50% drug-appropriate responding would occur based on these curves) with pharmacological properties reported by Eshleman et al, (2013). Gatch and colleagues reported that the potency (ED50) of these compounds in the cocaine-trained animals correlated only with their potency to activate serotonin 1A receptors and in the methamphetamine-trained animals with the cathinone’s potency to release norepinephrine via the vesicular monoamine transporter 2 (VMAT-2). This latter is an intracellular target of the prototypical amphetamines and relates to their neurotransmitter “releasing” (as opposed to merely re-uptake blocking) effect. Curiously, the potency of these drugs to substitute for cocaine was not correlated with the potency to substitute for methamphetamine.

It is worth reminding at this point that these correlative findings (all other properties did not correlate with the differences in potency) do not necessarily identify the major neuropharmacological action of these drugs that make them feel like cocaine and methamphetamine, respectively. These findings identify the reasons for what are subtle differences in the potency of the test drugs. Thus the effect at the serotonin 1A receptor subtype and the VMAT-2 for norepinephrine release must be viewed as modulatory effects. The authors suggest that once a certain threshold for changed monoamine levels is reached, the discrimination assay is insensitive. They overlook, however, the consideration that a multi-factor model might need to be considered. That is, potency might be driven by the precise combination of effects on dopamine, serotonin and norepinephrine transporters as further modified by such considerations as the speed of drug passage into the brain across the blood-brain barrier, speed of metabolism of the drug, any active metabolites, etc.

One of the interesting thing about this paper is perhaps that it highlight the limitations of the drug-discrimination paradigm for making close distinctions within a given drug class such as the psychomotor stimulants. The pharmacological studies being published in recent months are showing pretty clearly that some of the cathinones (MDPV, butylone, naphyrone) are limited to monoamine uptake inhibition like cocaine whereas the others also exhibit the amphetamine-typical monoamine releasing capability. Likewise, the studies show a diversity of potencies at the dopamine, serotonin and noradrenergic transporters and in causing dopamine versus serotonin overflow in nucleus accumbens.

We’ve now shown potency and efficacy differences in drug self-administration for MDPV and mephedrone versus methamphetamine. Likewise, rat activity on a running wheel classifies MDPV and methamphetamine as prototypical stimulants with similar potency compared with mephedrone and MDMA.

Considered as a whole, the behavioral studies should be interpreted with caution in that each comparison with a better known stimulant drug, or each comparison across the cathionone class, depends on the model or measure. Clearly, some behavioral assays will report two different drugs as very similar in effect whereas another might illustrate differences, particularly in potency or the maximum extent of the effect.

Nevertheless, it is also very clear that at least some members of the novel designer cathinone family of recreational drugs have very potent and effective stimulant-like actions.

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