TL neuro

July 19, 2019

Cannabidiol by vapor inhalation in rats

Filed under: Cannabidiol, Cannabis, E-cigarettes, Tobacco/Nicotine, Vapor Inhalation — mtaffe @ 2:37 pm

Cannabidiol is increasingly popular, occurring in a dizzying array of products in a highly unregulated retail market. This includes creams, oils, lotions, capsules and e-cigarette liquids, among many other items. A simple search for CBD on google will give you a taste of what I mean, if this is new to you. Just about every single senior person I talk to, it seems, is using CBD or knows another person who is using CBD  for various ailments.

The following has just been accepted for publication:

Javadi-Paydar, M.,  Creehan, K.M., Kerr, T.M.  and Taffe, M.A. Vapor inhalation of cannabidiol (CBD) in rats.  Pharmacol Biochem Behav, 2019 Jul 20:172741. doi: 10.1016/j.pbb.2019.172741. [ Publisher Site ][ PubMed ]

Figure 1: This figure has been adapted from Taffe et al. 2015. Click to enlarge.

We have been interested in studying the effects of CBD ever since reading a paper [Morgan et al., 2010] that appeared to show that the presence of CBD in cannabis protected users against the memory impairing effects of acute THC intoxication, subsequent to smoking their preferred cannabis. This led to our interest in the potentially interactive effects of CBD and THC and, in particular, tests of the hypothesis that CBD would reduce the effects of THC. Our initial papers on this were Wright et al 2013 and Taffe et al 2015. Of primary relevance for the discussion of our new work, the latter paper showed that CBD did not alter the body temperature (see Figure 1 C, D; blue bars) or activity of rats when injected at doses of 30 or 60 mg/kg, i.p.. Our new work confirms our prior finding that this may be due to the route of administration since, when male or female Wistar rats experience CBD by vapor inhalation, their body temperature does go down, albeit not as severely as when exposed to THC [Javadi-Paydar et al, 2018].

This finding required some follow-up, extraordinary claims requiring extraordinary evidence and all that. Although in the Taffe et al 2015 paper, CBD did appear to increase the magnitude of the hypothermia associated with THC when each were injected, i.p., (red trace and summary bars in Figure 1) there are data suggesting that this may be due to metobolic interference whereby CBD merely prolongs the activity of THC. Another thing that was slightly strange was the fact we observed that CBD reduces temperature of Wistar rats. We used Sprague-Dawley rats for the Taffe et al 2015 paper because initial pilot experiments suggested that perhaps Wistar (male) rats were less sensitive to the body temperature lowering effects of THC [a follow up to that is available in a pre-print]. Yet Javadi-Paydar et al (2018) found effects of vaporized CBD in male and female Wistar rats. Perhaps this is due to the difference between CB1 receptor mediated effects and serotonin 1a (5-HT1a) receptor mediated effects. There is growing evidence that CBD works in part by activating 5-HT1a receptors, and activation of this receptor (e.g., by injecting the agonist 8-OH-DPAT) drops the body temperature of rats precipitously. As an example we had published a figure on this as a positive control in the Wright et al 2012 paper focused on the activity of the cathinone mephedrone [blog post summary]. To further complicate matters, the response of male Wistar rats to 8-OH-DPAT in that paper seemed to be slightly greater than the response of male Sprague-Dawley rats.

Figure 2: Plasma CBD in male and female Wistar rats after vapor inhalation (top panels) or injection (bottom panels).Click to enlarge.

An earlier version of this manuscript was posted as a pre-print on June 04, 2019, and updated with a version almost identical to the final submitted manuscript on Jul 18, 2019.

The first critical thing in this new paper was to get a point of reference for the doses the animals were getting through vaporized CBD versus i.p. injection. This figure shows the plasma levels experienced at the end of vapor sessions are within the range of plasma levels observed 35 minutes after an injection. This was in male and female Wistar rats, making it a follow-up to the thermoregulatory data in the Javadi-Paydar et al (2018) paper. One of the major ways that we control dose with our inhalation model is to alter the concentration of the drug in the e-liquid vehicle (we use propylene glycol; PG), while holding other parameter fixed. So for CBD we have used concentrations of 100 and 400 mg per mL of the PG. Now admittedly we have only published the effects of 30 mg/kg CBD when injected, at the lower end of the dose range. But based on some pilot work I doubt that we’ll find out that lower dose of CBD are causing hypothermia when injected- but it could still be about dose. Our time-point here for injection was designed for comparison with the inhalation model but levels were likely much higher at 5 minutes after injection whereas they were increasing essentially linearly across the inhalation interval. Nevertheless, we are clearly not getting much, much higher plasma loads of CBD via inhalation, at least not in the blood.

The next step for this paper was to replicate the body temperature effect, which we did in a group of male Wistar rats.

Figure 3: Temperature responses to vapor inhalation of CBD and nicotine in male Sprague-Dawley rats. Open and grey symbols depict statistical differences summarized in the manuscript. Adapted from Javadi-Paydar et al 2019. Click to enlarge.

We then went on to evaluate the effect of CBD inhalation on body temperature in male Sprague-Dawley rats and found a similar (perhaps slightly increased relative to the Wistar male rats) degree of hypothermia under identical vaping conditions.

Figure 3 shows that CBD concentration-dependent reductions in body temperature are found in male Sprague-Dawley rats (blue data series), thereby replicating and extending to an additional rat strain. The next experiment showed that the effect of CBD (at the 100 mg/mL concentration) is attenuated when animals are pre-treated with the 5-HT1a antagonist WAY 100,635. This shows that the 5-HT1a receptor is very likely involved in the hypothermic response to vaporized CBD, further adding to the growing evidence that CBD acts at this receptor.

You may have noticed that the top two panels of Figure 3 include a nicotine inhalation condition and a CBD + nicotine inhalation condition. There are a couple of reasons for this. Most generally, CBD has been shown to attenuate relapse to alcohol and cocaine self-administration in rats and may reduce the salience of cigarette-associated cues in humans. Reviews of the potential of CBD as an anti-drug abuse treatment can be found here and here. The second rationale is that human substance users often use more than one drug at a time. THC and CBD co-occur in cannabis. People frequently use cannabis along with tobacco and/or alcohol. Our work in Javadi-Paydar et al 2019 examined potential interactive effects of THC with nicotine thus it was an obvious followup to see if CBD interacted with nicotine. As you can see in Figure 3, the effect of nicotine alone on body temperature is not obvious in this group (although it did enhance locomotor activity). Nicotine did, however, increase the effect of CBD when the two were co-administered. Interestingly CBD also suppressed the locomotor activating effects of vaporized nicotine inhalation in this study. So the combined effect appears to be independent, not interactive- i.e., an opposition when the two independent drug effects are in the opposite direction (locomotor activity) and add together when the two independent drug effects are in the same direction (see Javadi-Paydar et al 2019 for more on this interactive drug logic and on the hypothermia caused by nicotine inhalation).

CBD is often described as non-psychoactive constituent of cannabis because it does not appear to have the same dramatic subjective properties as delta-9-tetrahydrocannabinol. Also because there are a lot of studies where it does not appear to do much to a rodent when administered by itself. There are exceptions, but I think a fair take away is that often enough it has been found inactive. This may very well be due to investigating CBD in assays that are tuned to detect THC-like effects that are presumably mediated by the CB1 or CB2 receptors. Our thermoregulatory assay, fortunately, is sensitive to both CB1 and 5-HT1a agonists. It may also be the case that the route of administration is a fundamental contributor to observing or not observing effects of CBD in a rat. There are several pharmacokinetic possibilities that may explain this. Our plasma data are fairly limited in a temporal sense and we don’t know from plasma levels what the kinetics look like in the brain. It could be that there is a much different blood/brain ratio associated with the two routes of administration. It may be that the speed of initial brain entry of a threshold amount of drug varies as well. Additional work will be necessary to full determine how the route of administration alters the effects of CBD in rats and how this might translate to the human condition.



November 23, 2014

Cannabidiol fails to attenuate THC-induced hypothermia

Filed under: Cannabidiol, Cannabis — mtaffe @ 11:24 am

The following has been accepted for publication:

M A Taffe, K M Creehan, S A Vandewater Cannabidiol fails to reverse hypothermia or locomotor suppression induced by ∆9-tetrahydrocannabinol in Sprague-Dawley rats. (2015) British Journal of Pharmacology, in press. [Publisher Site; PubMed]

Cannabidiol (CBD) is a constituent of some strains of recreational cannabis plant material but the content of CBD-enriched strains is highly variable in the market (Morgan et al., 2010; Burgdorf et al., 2011). Cannabidiol has traditionally been viewed as an inactive constituent of cannabis, for example it produces minimal disruption of behavioral tasks in humans, monkeys or rodents (Belgrave et al., 1979; Lichtman et al., 1995; Winsauer et al., 1999). There has been a lot of recent interest in CBD for anti-seizure properties (see this blog post for example)

Morgan and colleagues have shown (blog writeup) that smoking cannabidiol-enriched marijuana does not cause the deficits of immediate and delayed prose recall that were caused by CBD-poor cannabis (Morgan et al., 2010) and users habitually exposed to CBD-containing cannabis may have relatively preserved recognition memory versus CBD-poor cannabis users (Morgan et al., 2011). The limits of human field studies (varying CBD/THC dose, no control of individuals who select CBD-rich vs. CBD-poor cannabis) and human lab studies (limited dosing ranges of CBD vs THC) motivate animal studies to investigate how CBD modulates the effects of THC.

Unfortunately, the available evidence on interactive effects of CBD and THC in rodent models present a more complicated picture. While CBD can reverse a conditioned place aversion produced by 10 mg/kg THC in rats (Vann et al., 2008), it may be the case that CBD potentiates the anxiogenic and locomotor suppressant effects of THC in rats treated chronically (Klein et al., 2011). In addition CBD / THC interactions may depend on the pre-treatment offset, as briefly reviewed (Zuardi et al., 2012). When CBD is administered 30 min (or up to 24 hrs) prior to THC in rats or mice, a potentiation can be observed whereas co-administration results in blockade or amelioration of THC effects. The picture may be complicated even further by a suggestion that CBD/THC ratios on the order of 8 are necessary for antagonistic properties and only 1.8 for potentiation of THC-related effects in rodents (Zuardi et al., 1984).

Our study was designed to determine if CBD attenuates, potentiates or extends the duration of hypothermia and hypomotility produced by acute THC in rats, using radiotelemetric monitoring.

The investigation found no evidence that cannabidiol can ameliorate the thermoregulatory or hypolocomotor effects of THC when administered either simultaneously (as in Figure 1, below) or prior to THC. Increasing the ratio of CBD:THC from 1:1 to 3:1 had no differential effect. Thus we find no protective effect of CBD against these particular endpoints in the rat. This contrasts with our recent finding that CBD can be protective against memory-impairing effects of THC in the monkey (PubMed, blogpost).

Taffe2015CBD-THCFig1Figure 1: Mean (N=5; ±SEM) telemetered body temperature (left panels) and activity rate (right panels) after treatment with 30 mg/kg THC with 30 mg/kg cannabidiol or the vehicle, i.p., administered simultaneously. A Vehicle-only control condition (Veh) is also depicted. Upper panels display the data as collected (5 min intervals) and the lower panels depict the hourly averages used for analysis. A significant difference from Veh (only) is indicated by * and from both other conditions by #. Significant differences from the first hour (within treatment condition) are indicated by §.

July 9, 2014

Medical marijuana, skepticism and the content of that marijuana

Filed under: Cannabidiol, Cannabis — mtaffe @ 1:08 pm

Physician Peter Lipson has posted an opinion on Forbes that expresses his skepticism about the benefits of medical marijuana.

Why I’m Skeptical About Marijuana’s Medical Benefits

In this article he criticizes a CNN bit by Sanjay Gupta on medical marijuana called “Weed2: Meet Vivian“.

From Lipson:

It followed the sad case of a young girl with a horrible seizure disorder and her parents’ struggle to get her help. According to Sanjay Gupta, they finally found some help with cannabis, and the piece documents their struggle to get their daughter the medicine that they believe is helping her.

He then goes on to make an assertion that I think is really flawed:

It makes for a great story, but it gives us no help in deciding if marijuana has any legitimate medical uses. A thorough search of the medical literature finds no good studies that support the use of cannabis or any of its constituents in seizure disorders.

I think there are certainly good studies that support the use of cannabis constituents and, pertinent to the “Vivian” story a compound called cannabidiol*.

The CNN story, and much other popular media coverage of the antiepileptic effects of cannabidiol is doing a serious, perhaps intentional, disservice by referring to “marijuana” only.

There is a published case report on “Vivian” (she’s “Charlotte” in the Case) by Maa and Figi. This specifies that the strain of cannabis being used to generate the crude extract that they are dosing with contains “a high concentration cannabidiol/Δ(9)-tetrahydrocannabinol (CBD:THC)“. I didn’t find a content analysis in the Case Report but an article in the Huffington Post contains aclaim from the grower/breeder developing what is now called the “Charlotte’s Web” strain of cannabis: “This particular plant has 0.5 percent THC and 17 percent CBD — or cannabidiol“. I’ll assume that is a valid statement, although of course we have no independent verification at this time.

We can see from Morgan et al 2010 [see Figure, left, and my blogpost] and from Burgdorf et al 2011 that 0.5% THC is really low for recreational grade cannabis. The North American Industrial Hemp Council, Inc claimsIndustrial hemp has a THC content of between 0.05 and 1%. Marijuana has a THC content of 3% to 20%“. A white paper from El Sohly, who grows the marijuana supplied by NIDA for research purposes attests to about a 1.6-1.8% THC content in the “low potency” research marijuana.

These analyses also verify that 17% cannabidiol is really high for a recreational marijuana strain. CBD appears to come in around 0.5% of the vast majority of street marijuana with a range of about 2-6% in the low proportion of high CBD strains identified in Morgan et al 2010.

In short, this “marijuana” which so bothers Dr. Lipson is not really “marijuana” in terms of what people tend to assume. Most particularly, it is not “marijuana” in the sense that we infer harms associated with substantial THC content. It would be better for understanding if media reports were very clear on this because cannabidiol (CBD) has never been found to be psychoactive in the sense of producing a high or any sort of dependence profile. In fact, it seems to counter* some of the effects of THC.

This brings us to whether any marijuana constituents have evidence for utility in seizure disorders.

Here are a few papers I pulled up on PubMed which attest to the fact that CBD can block seizure in rodent models.

Hill et al 2013 : Cannabidivarin-rich cannabis extracts are anticonvulsant in mouse and rat via a CB1 receptor-independent mechanism.

Jones et al 2012: Cannabidiol exerts anti-convulsant effects in animal models of temporal lobe and partial seizures

Jones et al 2010: Cannabidiol displays antiepileptiform and antiseizure properties in vitro and in vivo.

Martin et al, 1987: Structure-anticonvulsant activity relationships of cannabidiol analogs. [I had to go pull this NIDA Research Monograph off the departmental bookshelf, but it indeed reports that CBD is anticonvulsant]

Finally, there is a parent survey of people like the parents of Vivian/Charlotte. Porter and Jacobson (2013) surveyed a Facebook group dedicated to parents using cannabis (allegedly CBD enriched, but this was in no way verified). Of the nineteen surveys suitable for inclusion 10 reported greater than 80% reduction in seizure frequency and 6 reported 25-60% reduction.

The paper also references a mixed bag of prior clinical trials in adult populations. The authors cite Mechoulam and Carlini (1978) and Cunha et al. (1980) as reporting some beneficial effect of CBD. Ames and Cridland (1986) found no effect.

Not overwhelming evidence, certainly. The translation from animal models to humans may be overconfident at this point. And perhaps we may find that there are other cannabinoids in “Charlotte’s Web” strains (even the remaining THC) that may be driving any anticonvulsant effect.

But there is definitely some evidence. In my view it is sufficient evidence not to dismiss the notion that CBD might have use as an anticonvulsant medication.

*In full disclosure, I have a grant which is funding research in the lab to determine the degree to which cannabidiol can oppose the effects of Δ9Tetrahydrocannabinol.

Maa E, Figi P. The case for medical marijuana in epilepsy. Epilepsia. 2014 Jun;55(6):783-6. doi: 10.1111/epi.12610. Epub 2014 May 22.

March 28, 2013

Cannabidiol attenuates memory deficits that are caused by Δ9-tetrahydrocannabinol

Filed under: Cannabidiol, Cannabis, CANTAB, vsPAL — mtaffe @ 1:30 pm

A prior post discussed an apparently protective effect of cannabidiol (CBD) against memory deficits in humans caused by smoking cannabis. The key feature of the design was that Morgan and colleagues examined the Δ9-tetrahydrocannabinol (THC) and CBD content of their subjects’ (self-provided cannabis). The authors then grouped subjects into those who had relatively high-CBD cannabis and relatively poor-CBD cannabis; THC content was roughly equivalent. The authors reported that delayed recall was impaired acutely by cannabis smoking…but only if the cannabis was low in CBD. The relatively higher CBD content cannabis did not impair the memory performance of those individuals who smoked it.

The major concern with the study is that the humans subjects self-selected themselves into the treatment groups. Higher-CBD cannabis is relatively rare in recreational markets. It is possible that cannabis users who have access to (or intentionally choose) this restricted sub-population of the available cannabis are different, in one or more ways, than those users who do not have access or prefer other types of cannabis. Since they obtained their own cannabis we cannot know if there were other factors, socio-economic, regional, use-profile, peer groups, etc that were associated with choosing one type of cannabis over another. We similarly cannot know if they differed in memory ability and indeed there was a nonsignificant trend for better baseline memory in the CBD-enriched cannabis subjects.

We therefore conducted a controlled animal study in which the effects of CBD on a memory-impairing dose of THC could be assessed in the same subjects. This paper has recently been accepted for publication published.

Wright, M.J., Jr., Vandewater, S.A. and Taffe, M.A. Cannabidiol attenuates deficits of visuo-spatial associative memory induced by Δ9-tetrahydrocannabinol, Brit J Pharmacol, 2013 Dec;170(7):1365-73 [ PubMed ][ Publisher Link ]

PALFig-3stimGreyIn this task the animal first sees a given pattern in a single spatial location on the screen (“sample” phase of the trial). After touching it, there is a brief screen blank and then the pattern is presented in two or more positions (“choice” phase). Touching the pattern in the same location is a correct response. The difficulty of each trial is increased by presenting 2, 3 or 4 stimulus-location associations first and then querying all of them- in this case a successful trial completion requires touching the correct location for each stimulus that was presented. We’ve previously shown that THC degrades performance of this task in a manner that depends on both the trial difficulty (how many pattern-location associations have to be remembered) as well as the THC dose. This is interpreted as a relatively selective effect- in contrast a spatial memory task which does not depend on associating any pattern with the spatial location is impaired in a difficulty-independent manner.

CBD-THC-vsPALIn this figure we show the effect of multiple treatment conditions on the performance of the most difficult trials in which 4 stimulus-location associations have to be completed correctly. In this case, the animals are permitted up to 6 attempts to get each trial right. The data show that both 0.2 and 0.5 mg/kg doses of THC reduce the proportion of correctly completed trials. This effect is ameliorated if the THC is injected simultaneously with 0.5 mg/kg CBD. Since it was the same subjects, tested repeatedly, the effects of pre-existing differences in memory function can be ruled out.


These studies were supported in part by P20 DA024194.

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