Δ9-Tetrahydrocannabinol attenuates MDMA-induced hyperthermia in rhesus monkeys

Functional consequences of short-term exposure to opioids versus cannabinoids in nonhuman primates

Opioids provide pain relief but are associated with several adverse effects. Researchers are exploring cannabis-based medicine as an alternative. However, little is known about the tendency for physical dependence on cannabinoids in comparison with that on opioids in primates. The aim of this study was to compare the potency of heroin and delta-9-tetrahydrocannabinol (THC) in eliciting analgesic effects and the development of physical dependence between opioids and cannabinoids in both male and female rhesus monkeys. Systemic administration of either heroin (0.03-0.18 mg/kg) or THC (0.3-1.8 mg/kg) in a dose-dependent manner produced antinociceptive effects against an acute thermal nociceptive stimulus. The μ-opioid receptor antagonist naltrexone (0.01 mg/kg) and the cannabinoid receptor antagonist SR141716A (0.3 mg/kg) produced the same degree of rightward shift in the dose-response curves for heroin- and THC-induced antinociception, respectively. Monkeys implanted with telemetry devices were subjected to short-term repeated administrations (two injections per day for 1-3 days) of either heroin (0.18 mg/kg), morphine (1.8 mg/kg), THC (1.8 mg/kg), or CP 55,940 (0.032 mg/kg). Administration of naltrexone (0.01 mg/kg) increased respiration, heart rate, and blood pressure in heroin- or morphine-treated monkeys. In contrast, administration of SR141716A (0.3 mg/kg) did not cause a significant change in these physiological parameters in THC- or CP 55,940-treated monkeys. Additionally, morphine, but not CP 55,940, enhanced the monkeys' hypersensitivity to the algogen capsaicin. Collectively, these results demonstrate that in nonhuman primates, both opioids and cannabinoids exert comparable antinociception; however, physical dependence on opioids, but not cannabinoids, at their antinociceptive doses, occurs following short-term exposures.

Translational models of cannabinoid vapor exposure in laboratory animals

Cannabis is one of the most frequently used psychoactive substances in the world. The most common route of administration for cannabis and cannabinoid constituents such as Δ-9-tetrahydrocannabinol (THC) and cannabidiol (CBD) is via smoking or vapor inhalation. Preclinical vapor models have been developed, although the vaporization devices and delivery methods vary widely across laboratories. This review examines the emerging field of preclinical vapor models with a focus on cannabinoid exposure in order to (1) summarize vapor exposure parameters and other methodological details across studies; (2) discuss the pharmacological and behavioral effects produced by exposure to vaporized cannabinoids; and (3) compare behavioral effects of cannabinoid vapor administration with those of other routes of administration. This review will serve as a guide for past and current vapor delivery methods in animals, synergize findings across studies, and propose future directions for this area of research.

A Model of Combined Exposure to Nicotine and Tetrahydrocannabinol via Electronic Cigarettes in Pregnant Rats

Nicotine and cannabis are two of the most commonly consumed licit and illicit drugs during pregnancy, often consumed together via e-cigarettes. Vaping is assumed to be a safer alternative than traditional routes of consumption, yet the potential consequences of prenatal e-cigarette exposure are largely unknown, particularly when these two drugs are co-consumed. In a novel co-exposure model, pregnant Sprague-Dawley rats received nicotine (36 mg/mL), tetrahydrocannabinol (THC) (100 mg/mL), the combination, or the vehicle via e-cigarettes daily from gestational days 5–20, mimicking the first and second human trimesters. Maternal blood samples were collected throughout pregnancy to measure drug and metabolite levels, and core body temperatures before and after exposure were also measured. Pregnant dams exposed to combined nicotine and THC had lower plasma nicotine and cotinine levels than those exposed to nicotine alone; similarly, the combined exposure group also had lower plasma THC and THC metabolite (THC-OH and THC-COOH) levels than those exposed to THC alone. Prenatal nicotine exposure gradually decreased initial core body temperatures each day, with chronic exposure, whereas exposure to THC decreased temperatures during the individual sessions. Despite these physiological effects, no changes were observed in food or water intake, weight gain, or basic litter outcomes. The use of this model can help elucidate the effects of co-exposure to THC and nicotine via e-cigarettes on both users and their offspring. Understanding the effects of co-use during pregnancy is critical for improving education for pregnant mothers about prenatal e-cigarette use and has important implications for public policy.

Wonder or evil?: Multifaceted health hazards and health benefits of Cannabis sativa and its phytochemicals

Cannabis sativa, widely known as 'Marijuana' poses a dilemma for being a blend of both good and bad medicinal effects. The historical use of Cannabis for both medicinal and recreational purposes suggests it to be a friendly plant. However, whether the misuse of Cannabis and the cannabinoids derived from it can hamper normal body physiology is a focus of ongoing research. On the one hand, there is enough evidence to suggest that misuse of marijuana can cause deleterious effects on various organs like the lungs, immune system, cardiovascular system, etc. and also influence fertility and cause teratogenic effects. However, on the other hand, marijuana has been found to offer a magical cure for anorexia, chronic pain, muscle spasticity, nausea, and disturbed sleep. Indeed, most recently, the United Nations has given its verdict in favour of Cannabis declaring it as a non-dangerous narcotic. This review provides insights into the various health effects of Cannabis and its specialized metabolites and indicates how wise steps can be taken to promote good use and prevent misuse of the metabolites derived from this plant.

Vapor exposure to Δ9-tetrahydrocannabinol (THC) slows locomotion of the Maine lobster (Homarus americanus)

RATIONALE

Despite a long history of use in synaptic physiology, the lobster has been a neglected model for behavioral pharmacology. A restaurateur proposed that exposing lobster to cannabis smoke reduces anxiety and pain during the cooking process. It is unknown if lobster gill respiration in air would result in significant Δ⁹-tetrahydrocannabinol (THC) uptake and whether this would have any detectable behavioral effects.

OBJECTIVE

The primary goal was to determine tissue THC levels in the lobster after exposure to THC vapor. Secondary goals were to determine if THC vapor altered locomotor behavior or nociception.

METHODS

Tissue samples were collected (including muscle, brain and hemolymph) from Homarus americanus (N = 3 per group) following 30 or 60 min of exposure to vapor generated by an e-cigarette device using THC (100 mg/mL in a propylene glycol vehicle). Separate experiments assessed locomotor behavior and hot water nociceptive responses following THC vapor exposure.

RESULTS

THC vapor produced duration-related THC levels in all tissues examined. Locomotor activity was decreased (distance, speed, time-mobile) by 30 min inhalation of THC. Lobsters exhibit a temperature-dependent withdrawal response to immersion of tail, antennae or claws in warm water; this is novel evidence of thermal nociception for this species. THC exposure for 60 min had only marginal effect on nociception under the conditions assessed.

CONCLUSIONS

Vapor exposure of lobsters, using an e-cigarette based model, produces dose-dependent THC levels in all tissues and reduces locomotor activity. Hot water nociception was temperature dependent, but only minimal anti-nociceptive effect of THC exposure was confirmed.

Explication of CB1 receptor contributions to the hypothermic effects of Δ9-tetrahydrocannabinol (THC) when delivered by vapor inhalation or parenteral injection in rats

The use of Δ⁹-tetrahydrocannabinol (THC) by inhalation using e-cigarette technology grows increasingly popular for medical and recreational purposes. This has led to development of e-cigarette based techniques to study the delivery of THC by inhalation in laboratory rodents. Inhaled THC reliably produces hypothermic and antinociceptive effects in rats, similar to effects of parenteral injection of THC. This study was conducted to determine the extent to which the hypothermic response depends on interactions with the CB₁ receptor, using pharmacological antagonist (SR141716, AM-251) approaches. Groups of rats were implanted with radiotelemetry devices capable of reporting activity and body temperature, which were assessed after THC inhalation or injection. SR141716 (4 mg/kg, i.p.) blocked or attenuated antinociceptive effects of acute THC inhalation in male and female rats. SR141716 was unable to block the initial hypothermia caused by THC inhalation, but temperature was restored to normal more quickly. Alterations in antagonist pre-treatment time, dose and the use of a rat strain with less sensitivity to THC-induced hypothermia did not change this pattern. Pre-treatment with SR141716 (4 mg/kg, i.p.) blocked hypothermia induced by i.v. THC and reversed hypothermia when administered 45 or 90 min after THC (i.p.). SR141716 and AM-251 (4 mg/kg, i.p.) sped recovery from, but did not block, hypothermia caused by vapor THC in female rats made tolerant by prior repeated THC vapor inhalation. The CB₂ antagonist AM-630, had no effect. These results suggest that hypothermia consequent to THC inhalation is induced by other mechanisms in addition to CB₁ receptor activation.

Clinical and Preclinical Evidence for Functional Interactions of Cannabidiol and Δ9-Tetrahydrocannabinol

The plant Cannabis sativa, commonly called cannabis or marijuana, has been used for its psychotropic and mind-altering side effects for millennia. There has been growing attention in recent years on its potential therapeutic efficacy as municipalities and legislative bodies in the United States, Canada, and other countries grapple with enacting policy to facilitate the use of cannabis or its constituents for medical purposes. There are >550 chemical compounds and >100 phytocannabinoids isolated from cannabis, including Δ⁹-tetrahydrocannabinol (THC) and cannabidiol (CBD). THC is thought to produce the main psychoactive effects of cannabis, while CBD does not appear to have similar effects. Studies conflict as to whether CBD attenuates or exacerbates the behavioral and cognitive effects of THC. This includes effects of CBD on THC-induced anxiety, psychosis, and cognitive deficits. In this article, we review the available evidence on the pharmacology and behavioral interactions of THC and CBD from preclinical and human studies, particularly with reference to anxiety and psychosis-like symptoms. Both THC and CBD, as well as other cannabinoid molecules, are currently being evaluated for medicinal purposes, separately and in combination. Future cannabis-related policy decisions should include consideration of scientific findings, including the individual and interactive effects of CBD and THC.

High ambient temperature facilitates the acquisition of 3,4-methylenedioxymethamphetamine (MDMA) self-administration

RATIONALE

MDMA alters body temperature in rats with a direction that depends on the ambient temperature (T_A). The thermoregulatory effects of MDMA and T_A may affect intravenous self-administration (IVSA) of MDMA but limited prior reports conflict.

OBJECTIVE

To determine how body temperature responses under high and low T_A influence MDMA IVSA.

METHODS

Male Sprague-Dawley rats were trained to IVSA MDMA (1.0mg/kg/infusion; 2-h sessions; FR5 schedule of reinforcement) under T_A 20°C or 30°C. Radiotelemetry transmitters recorded body temperature and activity during IVSA.

RESULTS

MDMA intake increased under both T_A during acquisition, but to a greater extent in the 30°C group. The magnitude of hypothermia was initially equivalent between groups but diminished over training in the 30°C group. Within-session activity was initially lower in the 30°C group, but by the end of acquisition and maintenance, activity was similar for both groups. When T_A conditions were swapped, the hot-trained group increased MDMA IVSA under 20°C T_A and a modest decrease in drug intake was observed in the cold-trained group under 30°C T_A. Subsequent non-contingent MDMA (1.0-5.0mg/kg, i.v.) found that rats with higher MDMA IVSA rates showed blunted hypothermia compared with rats with lower IVSA levels; however, within-session activity did not differ by group. High T_A increased intracranial self-stimulation thresholds in a different group of rats and MDMA reduced thresholds below baseline at low, but not high, T_A.

CONCLUSIONS

High T_A appears to enhance acquisition of MDMA IVSA through an aversive effect and not via thermoregulatory motivation.

MDMA, Methylone, and MDPV: Drug-Induced Brain Hyperthermia and Its Modulation by Activity State and Environment

Psychomotor stimulants are frequently used by humans to intensify the subjective experience of different types of social interactions. Since psychomotor stimulants enhance metabolism and increase body temperatures, their use under conditions of physiological activation and in warm humid environments could result in pathological hyperthermia, a life-threatening symptom of acute drug intoxication. Here, we will describe the brain hyperthermic effects of MDMA, MDPV, and methylone, three structurally related recreational drugs commonly used by young adults during raves and other forms of social gatherings. After a short introduction on brain temperature and basic mechanisms underlying its physiological fluctuations, we will consider how MDMA, MDPV, and methylone affect brain and body temperatures in awake freely moving rats. Here, we will discuss the role of drug-induced heat production in the brain due to metabolic brain activation and diminished heat dissipation due to peripheral vasoconstriction as two primary contributors to the hyperthermic effects of these drugs. Then, we will consider how the hyperthermic effects of these drugs are modulated under conditions that model human drug use (social interaction and warm ambient temperature). Since social interaction results in brain and body heat production, coupled with skin vasoconstriction that impairs heat loss to the external environment, these physiological changes interact with drug-induced changes in heat production and loss, resulting in distinct changes in the hyperthermic effects of each tested drug. Finally, we present our recent data, in which we compared the efficacy of different pharmacological strategies for reversing MDMA-induced hyperthermia in both the brain and body. Specifically, we demonstrate increased efficacy of the centrally acting atypical neuroleptic compound clozapine over the peripherally acting vasodilator drug, carvedilol. These data could be important for understanding the potential dangers of MDMA in humans and the development of pharmacological tools to alleviate drug-induced hyperthermia - potentially saving the lives of highly intoxicated individuals.

Inhaled delivery of Δ(9)-tetrahydrocannabinol (THC) to rats by e-cigarette vapor technology

Most human Δ(9)-tetrahydrocannabinol (THC) use is via inhalation, and yet few animal studies of inhalation exposure are available. Popularization of non-combusted methods for the inhalation of psychoactive drugs (Volcano(®), e-cigarettes) further stimulates a need for rodent models of this route of administration. This study was designed to develop and validate a rodent chamber suitable for controlled exposure to vaporized THC in a propylene glycol vehicle, using an e-cigarette delivery system adapted to standard size, sealed rat housing chambers. The in vivo efficacy of inhaled THC was validated using radiotelemetry to assess body temperature and locomotor responses, a tail-flick assay for nociception and plasma analysis to verify exposure levels. Hypothermic responses to inhaled THC in male rats depended on the duration of exposure and the concentration of THC in the vehicle. The temperature nadir was reached after ∼40 min of exposure, was of comparable magnitude (∼3 °Celsius) to that produced by 20 mg/kg THC, i.p. and resolved within 3 h (compared with a 6 h time course following i.p. THC). Female rats were more sensitive to hypothermic effects of 30 min of lower-dose THC inhalation. Male rat tail-flick latency was increased by THC vapor inhalation; this effect was blocked by SR141716 pretreatment. The plasma THC concentration after 30 min of inhalation was similar to that produced by 10 mg/kg THC i.p. This approach is flexible, robust and effective for use in laboratory rats and will be of increasing utility as users continue to adopt "vaping" for the administration of cannabis.

Clinically Relevant Pharmacological Strategies That Reverse MDMA-Induced Brain Hyperthermia Potentiated by Social Interaction

MDMA-induced hyperthermia is highly variable, unpredictable, and greatly potentiated by the social and environmental conditions of recreational drug use. Current strategies to treat pathological MDMA-induced hyperthermia in humans are palliative and marginally effective, and there are no specific pharmacological treatments to counteract this potentially life-threatening condition. Here, we tested the efficacy of mixed adrenoceptor blockers carvedilol and labetalol, and the atypical antipsychotic clozapine, in reversing MDMA-induced brain and body hyperthermia. We injected rats with a moderate non-toxic dose of MDMA (9 mg/kg) during social interaction, and we administered potential treatment drugs after the development of robust hyperthermia (>2.5 °C), thus mimicking the clinical situation of acute MDMA intoxication. Brain temperature was our primary focus, but we also simultaneously recorded temperatures from the deep temporal muscle and skin, allowing us to determine the basic physiological mechanisms of the treatment drug action. Carvedilol was modestly effective in attenuating MDMA-induced hyperthermia by moderately inhibiting skin vasoconstriction, and labetalol was ineffective. In contrast, clozapine induced a marked and immediate reversal of MDMA-induced hyperthermia via inhibition of brain metabolic activation and blockade of skin vasoconstriction. Our findings suggest that clozapine, and related centrally acting drugs, might be highly effective for reversing MDMA-induced brain and body hyperthermia in emergency clinical situations, with possible life-saving results.

In vivo potency and efficacy of the novel cathinone α-pyrrolidinopentiophenone and 3,4-methylenedioxypyrovalerone: self-administration and locomotor stimulation in male rats

RATIONALE

Numerous substituted cathinone drugs have appeared in recreational use. This variety is often a response to legal actions; the scheduling of 3,4-methylenedioxypyrovalerone (MDPV; "bath salts") in the USA was followed by the appearance of the closely related drug α-pyrrolidinopentiophenone (alpha-PVP; "flakka").

OBJECTIVES

This study aimed to directly compare the efficacy and potency of alpha-PVP with that of MDPV.

METHODS

Groups of male Wistar rats were trained in the intravenous self-administration (IVSA) alpha-PVP or MDPV under a fixed-ratio 1 schedule of reinforcement. An additional group was examined for locomotor and body temperature responses to noncontingent administration of MDVP or alpha-PVP (1.0, 5.6, and 10.0 mg/kg, i.p.).

RESULTS

Acquisition of alpha-PVP (0.1 mg/kg/infusion) IVSA resulted in low, yet consistent drug intake and excellent discrimination for the drug-paired lever. Dose substitution (0.05-0.25 mg/kg/infusion) under a fixed-ratio 1 schedule confirmed potency was similar to MDPV in prior studies. In direct comparison to MDPV (0.05 mg/kg/infusion), rats trained on alpha-PVP (0.05 mg/kg/infusion) responded for more infusions but demonstrated similar drug-lever discrimination by the end of acquisition. However, the dose-response (0.018-0.56 mg/kg/infusion) functions of these drugs under a progressive-ratio schedule of reinforcement reflected identical efficacy and potency. Peak locomotor responses to MDPV or alpha-PVP were observed after the 1.0 mg/kg, i.p. dose and lasted ∼2 h. Modest body temperature decreases were of similar magnitude (∼0.75 °C) for each compound.

CONCLUSIONS

The potency and efficacy of MDPV and alpha-PVP were very similar across multiple assays, predicting that the abuse liability of alpha-PVP will be significant and similar to that of MDPV.

Cannabidiol fails to reverse hypothermia or locomotor suppression induced by Δ(9) -tetrahydrocannabinol in Sprague-Dawley rats

BACKGROUND AND PURPOSE

Growing evidence shows cannabidiol (CBD) modulates some of the effects of Δ(9) -tetrahydrocannabinol (THC). CBD is a constituent of some strains of recreational cannabis but its content is highly variable. High CBD strains may have less memory-impairing effects than low-CBD strains and CBD can reverse behavioural effects of THC in monkeys. CBD/THC interactions in rodents are more complicated as CBD can attenuate or exacerbate the effects of THC. This study was undertaken to determine if CBD could reverse hypothermia or hypolocomotor effects caused by THC in rats.

EXPERIMENTAL APPROACHES

Male Sprague-Dawley rats were prepared with radiotelemetry devices and then given doses of THC (10-30 mg·kg(-1) , i.p.) with or without CBD. Experiments determined the effect of simultaneous or 30 min pretreatment with CBD in a 1:1 ratio with THC, as well as the effect of CBD in a 3:1 ratio. Additional experiments determined the effects of pretreatment with the cannabinoid CB1 receptor antagonist SR141716 (rimonabant).

KEY RESULTS

CBD did not attentuate THC-induced hypothermia or hypolocomotion but instead exaggerated these effects in some conditions. The antagonist SR141716 blocked hypolocomotor effects of THC for the first hour after injection and the hypothermia for 6 h; thus validating the pharmacological model.

CONCLUSIONS AND IMPLICATIONS

There is no evidence from this study that elevated CBD content in cannabis could provide protection from the physiological effects of THC, in rats.

Cannabidiol attenuates deficits of visuospatial associative memory induced by Δ(9) tetrahydrocannabinol

BACKGROUND AND PURPOSE

Recent human studies suggest that recreational cannabis strains that are relatively high in cannabidiol (CBD) content produce less cognitive impairment than do strains with negligible CBD and similar Δ(9) tetrahydrocannabinol (THC) content. Self-selection in such studies means it is impossible to rule out additional variables which may determine both cannabis strain selection and basal cognitive performance level. Controlled laboratory studies can better determine a direct relationship.

EXPERIMENTAL APPROACH

In this study, adult male rhesus monkeys were assessed on visuospatial Paired Associates Learning and Self-Ordered Spatial Search memory tasks, as well as additional tests of motivation and manual dexterity. Subjects were challenged with THC (0.2, 0.5 mg·kg(-1) , i.m.) in randomized order and evaluated in the presence or absence of 0.5 mg·kg(-1) CBD.

KEY RESULTS

CBD attenuated the effects of THC on paired associates learning and a bimanual motor task without affecting the detrimental effects of THC on a Self-Ordered Spatial Search task of working memory. CBD did not significantly reverse THC-induced impairment of a progressive ratio or a rotating turntable task.

CONCLUSIONS AND IMPLICATIONS

This study provides direct evidence that CBD can oppose the cognitive-impairing effects of THC and that it does so in a task-selective manner when administered simultaneously in a 1:1 ratio with THC. The addition of CBD to THC-containing therapeutic products may therefore help to ameliorate unwanted cognitive side-effects.

LINKED ARTICLE

This article is commented on by Mechoulam and Parker, pp 1363-1364 of this issue. To view this commentary visit http://dx.doi.org/10.1111/bph.12400.

Blood levels do not predict behavioral or physiological effects of Δ⁹-tetrahydrocannabinol in rhesus monkeys with different patterns of exposure

BACKGROUND

Recent changes in the legality of cannabis have prompted evaluation of whether blood levels of Δ(9)-tetrahydrocannabinol (THC) or its metabolites could be used to substantiate impairment, particularly related to behavioral tasks such as driving. However, because marked tolerance develops to behavioral effects of THC, the applicability of a particular threshold of blood THC as an index of impairment in people with different patterns of use remains unclear. Studies relevant to this issue are difficult to accomplish in humans, as prior drug exposure is difficult to control.

METHODS

Here, effects of THC to decrease rectal temperature and operant response rate compared to levels of THC and its metabolites were studied in blood in two groups of monkeys: one received intermittent treatment with THC (0.1 mg/kg i.v. every 3-4 days) and another received chronic THC (1 mg/kg/12 h s.c.) for several years.

RESULTS

In monkeys with intermittent THC exposure, a single dose of THC (3.2 mg/kg s.c.) decreased rectal temperature and response rate. The same dose did not affect response rate or rectal temperature in chronically exposed monkeys, indicative of greater tolerance. In both groups, blood levels of THC peaked 20-60 min post-injection and had a similar half-life of elimination, indicating no tolerance to the pharmacokinetics of THC. Notably, in both groups, the behavioral effects of THC were not apparent when blood levels were maximal (20-min post-administration).

CONCLUSION

These data indicate that thresholds for blood levels of THC do not provide a consistent index of behavioral impairment across individuals with different patterns of THC exposure.

Sex-dependent psychoneuroendocrine effects of THC and MDMA in an animal model of adolescent drug consumption

Ecstasy is a drug that is usually consumed by young people at the weekends and frequently, in combination with cannabis. In the present study we have investigated the long-term effects of administering increasing doses of delta-9-tetrahydrocannabinol [THC; 2.5, 5, 10 mg/kg; i.p.] from postnatal day (pnd) 28 to 45, alone and/or in conjunction with 3,4-methylenedioxymethamphetamine [MDMA; two daily doses of 10 mg/kg every 5 days; s.c.] from pnd 30 to 45, in both male and female Wistar rats. When tested one day after the end of the pharmacological treatment (pnd 46), MDMA administration induced a reduction in directed exploration in the holeboard test and an increase in open-arm exploration in an elevated plus maze. In the long-term, cognitive functions in the novel object test were seen to be disrupted by THC administration to female but not male rats. In the prepulse inhibition test, MDMA-treated animals showed a decrease in prepulse inhibition at the most intense prepulse studied (80 dB), whereas in combination with THC it induced a similar decrease at 75 dB. THC decreased hippocampal Arc expression in both sexes, while in the frontal cortex this reduction was only evident in females. MDMA induced a reduction in ERK1/2 immunoreactivity in the frontal cortex of male but not female animals, and THC decreased prepro-orexin mRNA levels in the hypothalamus of males, although this effect was prevented when the animals also received MDMA. The results presented indicate that adolescent exposure to THC and/or MDMA induces long-term, sex-dependent psychophysiological alterations and they reveal functional interactions between the two drugs.

Δ(9)Tetrahydrocannabinol impairs reversal learning but not extra-dimensional shifts in rhesus macaques

Expansion of medical marijuana use in the US and the recently successful decriminalization of recreational marijuana in two States elevates interest in the specific cognitive effects of Δ(9)tetrahydrocannabinol (Δ(9)THC), the major psychoactive constituent of marijuana. Controlled laboratory studies in nonhuman primates provide mixed evidence for specific effects of Δ(9)THC in learning and memory tasks, with a suggestion that frontal-mediated tasks may be the most sensitive. In this study, adult male rhesus monkeys were trained on tasks which assess reversal learning, extradimensional attentional shift learning and spatial delayed-response. Subjects were challenged with 0.1-0.5mg/kg Δ(9)THC, i.m., in randomized order and evaluated on the behavioral measures. Peak plasma levels of Δ(9)THC were observed 30min after 0.2mg/kg (69±29ng/ml) and 60min after 0.5mg/kg (121±23ng/ml) was administered and behavioral effects on a bimanual motor task persisted for up to 2h after injection. An increase in errors-to-criterion (ETC) associated with reversal learning was further increased by Δ(9)THC in a dose-dependent manner. The increase in ETC associated with extradimensional shifts was not affected by Δ(9)THC. Spatial delayed-response performance was impaired by Δ(9)THC in a retention-interval-dependent manner. Overall the pattern of results suggests a more profound effect of Δ(9)THC on tasks mediated by orbitofrontal (reversal learning) versus dorsolateral (extradimensional shifts) prefrontal mechanisms.

Δ⁹Tetrahydrocannabinol impairs visuo-spatial associative learning and spatial working memory in rhesus macaques

Cannabis remains the most commonly abused illicit drug and is rapidly expanding in quasi-licit use in some jurisdictions under medical marijuana laws. Effects of the psychoactive constituent Δ⁹tetrahydrocannabinol (Δ⁹THC) on cognitive function remain of pressing concern. Prior studies in monkeys have not shown consistent evidence of memory-specific effects of Δ⁹THC on recognition tasks, and it remains unclear to what extent Δ⁹THC causes sedative versus specific cognitive effects. In this study, adult male rhesus monkeys were trained on tasks which assess spatial working memory, visuo-spatial associative memory and learning as well as motivation for food reward. Subjects were subsequently challenged with 0.1-0.3 mg/kg Δ⁹THC, i.m., in randomized order and evaluated on the behavioral measures. The performance of both vsPAL and SOSS tasks was impaired by Δ⁹THC in a dose and task-difficulty dependent manner. It is concluded that Δ⁹THC disrupts cognition in a way that is consistent with a direct effect on memory. There was evidence for interference with spatial working memory, visuo-spatial associative memory and incremental learning in the latter task. These results and the lack of specific effect of Δ⁹THC in prior visual recognition studies imply a sensitivity of spatial memory processing and/or working memory to endocannabinoid perturbation.