TL neuro

September 9, 2015

MDPV conditions a place preference in rats; but what about this CTA?

Filed under: Animal Models, Behavior, Cathinones, MDPV — mtaffe @ 10:44 am

A new paper presents what appear to be conflicting results about the rewarding properties of MDPV (“bathsalts”) in rats:

King HE, Wakeford A, Taylor W, Wetzell B, Rice KC, Riley AL. Sex differences in 3,4-methylenedioxypyrovalerone (MDPV)-induced taste avoidance and place preferences. Pharmacol Biochem Behav. 2015 Jul 26;137:16-22 [ PubMed ][ Publisher Link ]

King15-MDPV-CPPKing and colleagues have conducted a conditioning experiment in male and female Sprague-Dawley rats. In outline, place conditioning involves a two-compartment apparatus in which the two sides can be distinguished by tactile, visual and/or odor cues. Typically, a baseline session will be conducted in which the rat is allowed to roam around the entire apparatus (in this experiment for 15 min). The baseline amount of time spent on each side is then recorded. During the conditioning training, animals are injected with a drug (in this study 0.0, 1.8 or 3.2 mg/kg of MDPV, intraperitoneally) and confined in their non-preferred side of the apparatus for 30 min. On alternate days, all animals are injected with saline and confined to their initially-preferred side of the apparatus for 30 min. The key 15 min test, depicted in this graph, comes after 4 repetitions of each training session; the data are represented by the proportion of time spent on the drug-paired side. As you can see, the group of animals that received only saline injections on all eight days changed from the slightly less-preferring baseline test (~39% on the drug-paired side) to no-preference (~50% time spent on each side). In contrast, the groups that got active MDPV doses during active drug conditioning sessions increased the time spent on the drug-paired side (* depicts a significant difference from the 0 dose group on the post-conditioning test). These data are collapsed across the rat sex and the paper indicates that no sex differences were confirmed in the statistical analysis.

This is interpreted as a rewarding effect of MDPV at these doses.

So far so good.

There is a slightly less-intuitive finding in this paper as well.

King15-MDPV-CTAThe authors also conducted a taste-aversion study in the same animals. In a classic Conditioned Tasted Aversion study, rats are allowed to consume some food or fluid that they find palatable, such as saccharin-sweetened water. If the rats are given some treatment that makes them feel bad (such as an injection of lithium chloride) after consuming the highly-palatable food/fluid, they tend to avoid it on a subsequent re-test. In this King study, the investigators allowed the rats to consume saccharin solutions for 20 min just prior to receiving their MDPV injections for the above-described place preference assay. Pretty efficient design!

What you can see from this graph is that the male and female rats that only received saline injections after drinking saccharin (M0 and F0 groups) gradually consumed more saccharin prior to each of the three remaining active-drug conditioning sessions. In contrast, the groups that received MDPV consumed less saccharin solution. The stats symbols are a little complicated on this one so from the paper: [Panel A (males): *M0 significantly greater than M1.8 and M3.2; ^M0 significantly greater than all drug-treated groups; %M1.0 and M1.8 significantly greater than M3.2; #M3.2 significant decrease from Trial 1; αM3.2 significant decrease from Trial 2. Panel B (females); *F0 significantly greater than F1.8 and F3.2; ^F0 and F1.0 significantly greater than F3.2; #F1.0 significant increase from Trial 1.].

Wait, huh? This implies that the animals are expressing feeling bad because of MDPV (hence the Taste Aversion) and feeling good because of MDPV (the Place Preference).

At the same time and from the exact same doses, thanks to this efficient experimental design.

The answer to this conundrum lies in an older paper by Linda Parker.

Parker LA. Rewarding drugs produce taste avoidance, but not taste aversion. Neurosci Biobehav Rev. 1995 Spring;19(1):143-57. [ PubMed ]

Parker95-CTA-AversiveTasteReactionThis paper contrasted changes in sucrose preference induced by lithium chloride versus a number of abused drugs that are are reinforcing in self-administration and place preference assays such as amphetamine, cocaine, nicotine, morphine, etc. There were low/medium dose and high doses tested, I’m including only the high-dose graph here for simplicity but the takeaway message isn’t changed. As you can tell from this high-dose graph, all test drugs except morphine produced a significant reduction in sucrose drinking compared with the injection of saline (CTA). The key part of this study was that the rats were video taped for behavioral scoring by a reviewer blinded to drug treatment condition. Importantly, the rats were scored for Aversive Taste Reactions (ARs) to the drinking spouts / fluid taste. This included gaping, chin rubbing, paw pushing and letting fluid drip from the spout without consuming it. Lithium Chloride and nicotine were the only drugs that resulted in drug-injected rats expressing more ARs to the sucrose on the test day compared with the saline-injected rats. This implies, as the author underlined in discussion comments, that the mechanisms by which saccharin preference is reduced differs. Sometimes when a CTA is produced in a rat, it really is a reflection of the conditioning process making the rat find the saccharin taste unpleasant. Other times, the conditioning process doesn’t make the taste unpleasant, but rats certainly find it less pleasurable, reinforcing or rewarding.

In slightly different language, we might interpret this as meaning that the experience of the type of pleasurable experience caused by drugs of abuse can diminish the value of other stimuli or experiences that rats would otherwise find to be pleasurable.

This interpretation dovetails nicely with our prior paper in which rats were permitted to both self-administer MDPV intravenously and to run on an activity wheel [see blog post]. What we found was that as the rats initiate the consistent self-administration of MDPV, they decrease the amount of wheel activity that they engage in. That study was consistent with an earlier one we published showing that self-administration of methamphetamine also gradually decreases the amount rats will use the activity wheel [ see blog post ].

We interpret this phenomenon to reflect the drug stimulus devaluing the degree to to which a rat finds wheel activity rewarding.

As such, this gives us an animal model to further explore concepts that may explain why some individuals who use drugs regularly become addicted whereas some other individuals can cease drug use. The comparative value of other sources of reinforcement (social, family, vocational, recreational, etc) versus the drug experience may be a critical determinant of who will spiral into a compulsive drug use problem.

Additional reading: Hunt and Amit, 1987.

July 29, 2015

Modeling the preference for peers that you get high with

Filed under: Animal Models, Behavior, Cocaine, Neuroscience — mtaffe @ 1:02 pm

A new paper from Mark Smith and colleagues addresses whether drug exposure can differentially condition a preference for certain peers in a rat model.

Smith MA, Strickland JC, Bills SE, Lacy RT. The effects of a shared history of drug exposure on social choice. Behav Pharmacol. 2015 Apr 28. [Epub ahead of print]

The study focused on “choice” rat groups, one of which (N=16) was to receive cocaine injections and one of which (N=16) was to receive saline injections. The choice rats were then destined to have social interactions with a social peer rat that had received cocaine or a social rat that had received saline.

Smith15-RatPrefThe social choice apparatus is depicted in this figure from the paper. The choice rat is permitted to roam about the apparatus and choose proximity to one of two partner rats. A pre-conditioning test established the amount of time a given choice rat spent in proximity to each of the saline- or cocaine-treated partner rats.

The choice rats then underwent a total of 10 conditioning sessions in normal home cages. For these sessions, the choice rats would receive their cocaine or saline injections and then interact with a single partner rat for 30 min. On five of those sessions the partner rat was as cocaine treated animal and on the other five the partner was saline treated.

The critical post-conditioning preference test was then conducted.

A change in preference was expressed as the amount of time spent on the side of the apparatus containing each partner rat divided by the time spent with that partner during the pre-conditioning test. Two analyses were conducted, one just scoring time in each half of the apparatus and a second analysis scoring time spent in ~the front half of each side, i.e., in closer proximity to the partner. This made no difference in the results, including the fact that there was no change in the amount of time spent in this “neutral” or non-social zone after conditioning.

The takeaway message was that there was a significant increase in the amount of time spent with the similarly-treated partner when all choice rats were considered. However when the group analysis was conducted, only the cocaine-treated choice rats exhibited increased preference for the cocaine-treated partner. Saline-treated choice rats had no partner preference.

The takeaway message is that cocaine-treated rats prefer to hang out with other cocaine-treated rats. It wasn’t a general social-conditioning effect, since there was no differential effect on time spent in the non-social part of the apparatus.

There is one major caveat. The size of the effect was about an 8% increase in the time cocaine-treated choice rats spent with the cocaine-treated partner during the choice test. This amounted to about 49 seconds.

This is a limited initial finding but it obviously has promise for investigating social factors that enhance or diminish drug preferences, drug reward and the power of drug-related cues to shape behavior.

July 2, 2015

CPDD 2015: Sex as a biological variable and pitfalls for behavioral studies

Filed under: Animal Models, CPDD, SABV — mtaffe @ 10:18 am

Cora Lee Wetherington presented on the new NIH initiative on sex as a biological variable (SABV) at the Animals-in-Research forum at the recent CPDD meeting held at the Arizona Biltmore.

Dr. Wetherington has long headed up NIDA’s operations on Sex/Gender differences in substance abuse research and is therefore a key voice on how the NIH will be responding to this new SABV initiative.

Her main point was to outline the elements of the new approach to sex-differences, starting with the Clayton and Collins editorial and leading up to the NOT-OD-15-102 Consideration of Sex as a Biological Variable in NIH-funded Research. This NOT warns NIH applicants that applications submitted after Jan 25, 2015 will need to take new steps in considering SABV.

In the Q&A after Dr. Wetherington’s presentation, Mike Bardo (lab website) asked a deceptively simple question. He wanted to know if people ran their male and female rats in different operant boxes. The point being that male rats might smell something related to the presence of a female in the box just prior to his session, or vice versa. This might have an effect that differed in some way from the presence of a same-sex rat. Bardo indicated that many labs try to have a set of operant boxes that are dedicated to each sex, perhaps even in separate experimental rooms, but intimated that this may become impractical in the new order of SABV after Jan 25, 2015.

Simple question, right? Well, this plays right into the determination of how practical it will be to tell behavioral pharmacology people to start running studies with both sex of rats. The immediate response to the SABV initiative is to say “This will double our experiment size!”. And this comment is rapidly followed by “Wait, by the time we consider female rat cycle, we are not just doubling the experment but possibly increasing our number of groups by 4-fold or more.”.

And indeed several prior questions directed at Dr. Wetherington touched on such issues.

The Bardo question, however, is an even more practical one of experimental throughput. Any given lab is going to be more inflexible in experimental equipment than in the sex of rats it chooses to run from month to month or year to year. Operant boxes are expensive and experimental space to house them is very dear. One cannot just outfit a parallel series of rooms to run the opposite sex. This is going to require compromises. It is going to involve more unknown variability introduced into the design. And it is going to be expensive merely to estimate this variability so as to come up working rules of thumb to address the problem raised by Mike Bardo.

I jumped up to try to emphasize the following points although I am not sure that Wetherington understood what I was driving at.

There are several options available to a lab like mine, if it wants to start running both male and female groups. First, we could do it entirely sequentially. Only females for a 3-4 month interval, then males, etc. This is less than ideal because if we are comparing the sexes, we would like to hold other variables constant. Cohorts run at the approximately the same time has a better chance of doing this. Second, we could run them in different rooms but this has a limit. We only have so many operant box testing rooms and this is typically far too few to accomplish all that we would like to accomplish in a perfect way. (For example, we simply cannot run all of our rats starting at the same exact time of day, relative to their light cycle. Totally impractical.) We have a lot of different projects going on at one time and lining them all up so that males are in one room and females another would slow overall progress. Third, we could keep some boxes within a room for males and some for females. This isn’t much better than separate rooms for operational flexibility purposes and it adds the additional factor of subjects being able to smell (and possible hear the ultrasonic vocalizations of) adjacent animals (the boxes are vented to/from room air). Fourth, we could run the sexes in sequence throughout the day with an extra dose of box cleaning and bedding changing in between the sexes. It adds some work, but preserves a great deal of flexibility.

But really, and getting back to Bardo’s question, we want to know if it matters if we run male and female rats in the same boxes. If it doesn’t, then all of my objections are moot.

So I was trying to point out to Wetherington how much effort it would take for just one of our experimental models to determine if there even were effects of mixed-sex operations on the rats’ behavior that needed to be accommodated. This is at least six months or a year of experiments, running to the tune of tens of thousands of precious direct costs from our NIH grants, to even begin to estimate the kind of variability that would be introduced by running male and female rats in a study within the same limited number of operant boxes. This is methodological work. Not work that can be easily risked by just launching off into the “real” study that is intended to be done.

How tolerant will grant review panels be of proposals that do not address these matters? How tolerant will they be of proposals that do address these matters seriously but plan to burn the first year on such methodological minutia?

How many reviwers will insist on “perfect” design (no females and males run in the same boxes or even housed in the same vivarium room!) regardless of whether it is necessary?

This is just one tiny, tiny, minute methodological question in a restricted subfield of investigation. How many similar questions apply to all of the research funded by the NIH that is poised to come under the SABV dictum seven months from now?

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