CB(1) receptor mediation of cannabinoid behavioral effects in male and female rats

Effects of cannabidiol, with and without ∆9-tetrahydrocannabinol, on anxiety-like behavior following alcohol withdrawal in mice

Introduction

Alcohol use disorder (AUD) is commonly associated with anxiety disorders and enhanced stress-sensitivity; symptoms that can worsen during withdrawal to perpetuate continued alcohol use. Alcohol increases neuroimmune activity in the brain. Our recent evidence indicates that alcohol directly modulates neuroimmune function in the central amygdala (CeA), a key brain region regulating anxiety and alcohol intake, to alter neurotransmitter signaling. We hypothesized that cannabinoids, such as cannabidiol (CBD) and ∆9-tetrahydrocannabinol (THC), which are thought to reduce neuroinflammation and anxiety, may have potential utility to alleviate alcohol withdrawal-induced stress-sensitivity and anxiety-like behaviors via modulation of CeA neuroimmune function.

Methods

We tested the effects of CBD and CBD:THC (3:1 ratio) on anxiety-like behaviors and neuroimmune function in the CeA of mice undergoing acute (4-h) and short-term (24-h) withdrawal from chronic intermittent alcohol vapor exposure (CIE). We further examined the impact of CBD and CBD:THC on alcohol withdrawal behaviors in the presence of an additional stressor.

Results

We found that CBD and 3:1 CBD:THC increased anxiety-like behaviors at 4-h withdrawal. At 24-h withdrawal, CBD alone reduced anxiety-like behaviors while CBD:THC had mixed effects, showing increased center time indicating reduced anxiety-like behaviors, but increased immobility time that may indicate increased anxiety-like behaviors. These mixed effects may be due to altered metabolism of CBD and THC during alcohol withdrawal. Immunohistochemical analysis showed decreased S100β and Iba1 cell counts in the CeA at 4-h withdrawal, but not at 24-h withdrawal, with CBD and CBD:THC reversing alcohol withdrawal effects..

Discussion

These results suggest that the use of cannabinoids during alcohol withdrawal may lead to exacerbated anxiety depending on timing of use, which may be related to neuroimmune cell function in the CeA.

Correlations of the CNR1 Gene with Personality Traits in Women with Alcohol Use Disorder

Alcohol use disorder (AUD) is a significant issue affecting women, with severe consequences for society, the economy, and most importantly, health. Both personality and alcohol use disorders are phenotypically very complex, and elucidating their shared heritability is a challenge for medical genetics. Therefore, our study investigated the correlations between the microsatellite polymorphism (AAT)n of the Cannabinoid Receptor 1 (CNR1) gene and personality traits in women with AUD. The study group included 187 female subjects. Of these, 93 were diagnosed with alcohol use disorder, and 94 were controls. Repeat length polymorphism of microsatellite regions (AAT)n in the CNR1 gene was identified with PCR. All participants were assessed with the Mini-International Neuropsychiatric Interview and completed the NEO Five-Factor and State-Trait Anxiety Inventories. In the group of AUD subjects, significantly fewer (AAT)n repeats were present when compared with controls (p = 0.0380). While comparing the alcohol use disorder subjects (AUD) and the controls, we observed significantly higher scores on the STAI trait (p < 0.00001) and state scales (p = 0.0001) and on the NEO Five-Factor Inventory Neuroticism (p < 0.00001) and Openness (p = 0.0237; insignificant after Bonferroni correction) scales. Significantly lower results were obtained on the NEO-FFI Extraversion (p = 0.00003), Agreeability (p < 0.00001) and Conscientiousness (p < 0.00001) scales by the AUD subjects when compared to controls. There was no statistically significant Pearson's linear correlation between the number of (AAT)n repeats in the CNR1 gene and the STAI and NEO Five-Factor Inventory scores in the group of AUD subjects. In contrast, Pearson's linear correlation analysis in controls showed a positive correlation between the number of the (AAT)n repeats and the STAI state scale (r = 0.184; p = 0.011; insignificant after Bonferroni correction) and a negative correlation with the NEO-FFI Openness scale (r = -0.241; p = 0.001). Interestingly, our study provided data on two separate complex issues, i.e., (1) the association of (AAT)n CNR1 repeats with the AUD in females; (2) the correlation of (AAT)n CNR1 repeats with anxiety as a state and Openness in non-alcohol dependent subjects. In conclusion, our study provided a plethora of valuable data for improving our understanding of alcohol use disorder and anxiety.

The impact of pregnancy and associated hormones on the pharmacokinetics of Δ9-tetrahydrocannabinol

INTRODUCTION

(-)-Δ9-tetrahydrocannabinol (THC) is the main psychoactive component of cannabis. Cannabis is the most widely used drug of abuse by pregnant individuals, but its maternal-fetal safety is still unclear. The changes in THC disposition during pregnancy may affect THC safety and pharmacology.

AREAS COVERED

This review summarizes the current literature on THC metabolism and pharmacokinetics in humans. It provides an analysis of how hormonal changes during pregnancy may alter the expression of cannabinoid metabolizing enzymes and THC and its metabolite pharmacokinetics. THC is predominately (>70%) cleared by hepatic metabolism to its psychoactive active metabolite, 11-OH-THC by cytochrome P450 (CYP) 2C9 and to other metabolites (<30%) by CYP3A4. Other physiological processes that change during pregnancy and may alter cannabinoid disposition are also reviewed.

EXPERT OPINION

THC and its metabolites disposition likely change during pregnancy. Hepatic CYP2C9 and CYP3A4 are induced in pregnant individuals and in vitro by pregnancy hormones. This induction of CYP2C9 and CYP3A4 is predicted to lead to altered THC and 11-OH-THC disposition and pharmacodynamic effects. More in vitro studies of THC metabolism and induction of the enzymes metabolizing cannabinoids are necessary to improve the prediction of THC pharmacokinetics in pregnant individuals.

Electroacupuncture attenuates inflammatory pain via peripheral cannabinoid receptor type 1 signaling pathway in mice

Pain is strongly associated with neuro-immune activation. Thus, the emerging role of the endocannabinoid system in neuro-inflammation is important. Acupuncture has been used for over 2500 years and is widely accepted for the management of pain. Our study aimed to investigate the effects of electroacupuncture on the regulation of cannabinoid receptor type 1 within the peripheral nervous system. Inflammatory pain was induced by injecting Complete Freund's adjuvant to induce mechanical and thermal hyperalgesia. Electroacupuncture significantly attenuated the mechanical and thermal sensitivities, and AM251, a cannabinoid receptor type 1 antagonist, eliminated these effects. Dual immunofluorescence staining demonstrated that electroacupuncture elevated expression of cannabinoid receptor type 1, co-localized with Nav 1.8. Furthermore, electroacupuncture significantly reduced levels of Nav 1.8 and COX-2 by western blot analysis, but not vice versa as AM251 treatment. Our data indicate that electroacupuncture mediates antinociceptive effects through peripheral endocannabinoid system signaling pathway and provide evidence that electroacupuncture is beneficial for pain treatment.

Behavioral Studies of p62 KO Animals with Implications of a Modulated Function of the Endocannabinoid System

Elementary emotional states and memory can be regulated by the homeostasis of the endocannabinoid system (ECS). Links between the ECS and the autophagy receptor p62 have been found at the molecular level and in animal studies. This project aimed to validate the anxiety and memory phenotype of p62 knockout (KO) animals and whether the ECS plays a role in this. We examined the behavior of p62 KO animals and analyzed whether endocannabinoid levels are altered in the responsible brain areas. We discovered in age-dependent obese p62-KO mice decreased anandamide levels in the amygdala, a brain structure important for emotional responses. Against our expectation, p62 KO animals did not exhibit an anxiety phenotype, but showed slightly increased exploratory behavior as evidenced in novel object and further tests. In addition, KO animals exhibited decreased freezing responses in the fear conditioning. Administration of the phytocannabinoid delta9-tetrahydrocannabinol (THC) resulted in lesser effects on locomotion but in comparable hypothermic effects in p62 KO compared with WT littermates. Our results do not confirm previously published results, as our mouse line does not exhibit a drastic behavioral phenotype. Moreover, we identified further indications of a connection to the ECS and hence offer new perspectives for future investigations.

Receptor mechanisms underlying the CNS effects of cannabinoids: CB1 receptor and beyond

Cannabis legalization continues to progress in many US states and other countries. Δ9-tetrahydrocannabinol (Δ9-THC) is the major psychoactive constituent in cannabis underlying both its abuse potential and the majority of therapeutic applications. However, the neural mechanisms underlying cannabis action are not fully understood. In this chapter, we first review recent progress in cannabinoid receptor research, and then examine the acute CNS effects of Δ9-THC or other cannabinoids (WIN55212-2) with a focus on their receptor mechanisms. In experimental animals, Δ9-THC or WIN55212-2 produces classical pharmacological effects (analgesia, catalepsy, hypothermia, hypolocomotion), biphasic changes in affect (reward vs. aversion, anxiety vs. anxiety relief), and cognitive deficits (spatial learning and memory, short-term memory). Accumulating evidence indicates that activation of CB1Rs underlies the majority of Δ9-THC or WIN55121-2's pharmacological and behavioral effects. Unexpectedly, glutamatergic CB1Rs preferentially underlie cannabis action relative to GABAergic CB1Rs. Functional roles for CB1Rs expressed on astrocytes and mitochondria have also been uncovered. In addition, Δ9-THC or WIN55212-2 is an agonist at CB2R, GPR55 and PPARγ receptors and recent studies implicate these receptors in a number of their CNS effects. Other receptors (such as serotonin, opioid, and adenosine receptors) also modulate Δ9-THC's actions and their contributions are detailed. This chapter describes the neural mechanisms underlying cannabis action, which may lead to new discoveries in cannabis-based medication development for the treatment of cannabis use disorder and other human diseases.

Cannabinoids: Revealing their complexity and role in central networks of fear and anxiety

The first aim of the present review is to provide an in-depth description of the cannabinoids and their known effects at various neuronal receptors. It reveals that cannabinoids are highly diverse, and recent work has highlighted that their effects on the central nervous system (CNS) are surprisingly more complex than previously recognized. Cannabinoid-sensitive receptors are widely distributed throughout the CNS where they act as primary modulators of neurotransmission. Secondly, we examine the role of cannabinoid receptors at key brain sites in the control of fear and anxiety. While our understanding of how cannabinoids specifically modulate these networks is mired by their complex interactions and diversity, a plausible framework(s) for their effects is proposed. Finally, we highlight some important knowledge gaps in our understanding of the mechanism(s) responsible for their effects on fear and anxiety in animal models and their use as therapeutic targets in humans. This is particularly important for our understanding of the phytocannabinoids used as novel clinical interventions.

Cannabis sativa and/or melatonin do not alter brain lipid but alter oxidative mechanisms in female rats

Background

Lipid profile and redox status play a role in brain (dys)functions. Cannabinoid and melatonergic systems operate in the brain and contribute to brain (patho)physiology, but their roles in the modulation of brain lipid and redox status are not well-known. We studied the effect of ethanol extract of Cannabis sativa (CS) and/or melatonin (M) on the lipid profile and anti-oxidant system of the rat brain.

Methods

We randomly divided twenty-four (24) female Wistar rats into 4 groups (n = 6 rats each). Group 1 (control) received distilled water mixed with DMSO. Groups II–IV received CS (2 mg/kg), M (4 mg/kg), and co-administration of CS and M (CS + M) respectively via oral gavage between 8:00 am and 10:00 am once daily for 14 days. Animals underwent 12-h fasting after the last day of treatment and sacrificed under ketamine anesthesia (20 mg/kg; i.m). The brain tissues were excised and homogenized for assay of the concentrations of the total cholesterol (TC), triacylglycerol (TG), high-density lipoprotein cholesterol (HDL-C), nitric oxide (NO), malondialdehyde (MDA), and the activities of glucose-6-phosphate dehydrogenase (G6PD), glutathione reductase (GR), glutathione peroxidase (GPx), catalase (CAT), superoxide dismutase (SOD), and acetylcholinesterase (AChE). One-way analysis of variance (ANOVA) was used to compare means across groups, followed by the least significant difference (LSD) post-hoc test.

Results

CS and/or M did not affect the lipid profile parameters. However, CS increased the G6PD (from 15.58 ± 1.09 to 21.02 ± 1.45 U/L; p = 0.047), GPx (from 10.47 ± 0.86 to 17.71 ± 1.04 U/L; p = 0.019), and SOD (from 0.81 ± 0.02 to 0.90 ± 0.01 μM; p = 0.007), but decreased NO (from 9.40 ± 0.51 to 6.75 ± 0.21 μM; p = 0.010) and had no effect on MDA (p = 0.905), CAT (p = 0.831), GR (p = 0.639), and AChE (p = 0.571) in comparison with the control group. M augmented the increase in G6PD (from 21.02 ± 1.45 U/L to 27.18 ± 1.81 U/L; p = 0.032) and decrease in NO (from 6.75 ± 0.21 to 4.86 ± 0.13 μM; p = 0.034) but abolished the increase in GPx (from 17.71 ± 1.04 to 8.59 ± 2.06 U/L; p = 0.006) and SOD (from 0.90 ± 0.01 to 0.70 ± 0.00 μM; p = 0.000) elicited by CS in the rat brain in comparison with the CS group.

Conclusions

CS and M do not alter brain lipid profile. Our data support the contention that CS elicits an anti-oxidative effect on the brain tissue and that CS + M elicits a pro-oxidant effect in rat brain.

Supplementary Information

The online version contains supplementary material available at 10.1186/s42238-021-00095-9.

Cannabidiol has therapeutic potential for myofascial pain in female and male parkinsonian rats

The musculoskeletal orofacial pain is a complex symptom of Parkinson's disease (PD) resulting in stomatognathic system dysfunctions aggravated by the disease rigidity and postural instability. We tested the effect of cannabidiol (CBD), a non-psychotomimetic constituent of Cannabis sativa, in PD-related myofascial pain. Wistar adult female and male rats orofacial allodynic and hyperalgesic responses were tested by Von Frey and formalin tests, before and 21 days past 6-OHDA lesion. Algesic response was tested after masseter muscle injection of CBD (10, 50, 100 μg in 10 μL) or vehicle. Males compared to females in all estrous cycles' phases presented reduced orofacial allodynia and hyperalgesia. According to the estrous cycle's phases, females presented distinct orofacial nociceptive responses, being the estrus phase well-chosen for nociceptive analysis after 6-OHDA lesion (phase with fewer hormone alterations and adequate length). Dopaminergic neuron lesion decreased mechanical and inflammatory nociceptive thresholds in females and males in a higher proportion in females. CBD local treatment reduced the increased orofacial allodynia and hyperalgesia, in males and females. The female rats were more sensitive to CBD effect considering allodynia, responding to the lowest dose. Although females and males respond to the effect of three doses of CBD in the formalin test, males showed a superior reduction in the hyperalgesic response. These results indicate that hemiparkinsonian female in the estrus phase and male answer differently to the different doses of CBD therapy and nociceptive tests. CBD therapy is effective for parkinsonism-induced orofacial nociception.

The Impact of Cannabidiol on the Induction of Isoflurane Anesthesia and Recovery in Wistar Rats

Background: Beside others, neuroinhibitory and sedative effects of CBD were documented. Aim and Methods: The aim of the study was to assess the dose-related effects of CBD premedication on the course of isoflurane anesthesia. Wistar rats were pretreated with different doses of CBD 1 h before isoflurane anesthesia. In the pretreatment, animals were given CBD at doses of 100, 20, 10, or 2 mg kg^-1. Before the fifth (control) anesthesia, the animals were given only mid-chain triglyceride oil, which served as a solvent in the CBD formulation. The induction time was determined, and on awakening, the time to appearance of the flexion reflex and the recovery from anesthesia were determined. Results: Statistical analysis showed a significantly shorter induction time if animals were pretreated with 20 mg kg^-1 CBD. In addition, pretreatment with 100 mg kg^-1 CBD resulted in a prolonged induction time, while on awakening, delayed appearance of reflexes and prolonged recovery from anesthesia compared to pretreatment with 20 mg kg^-1 CBD were observed. Conclusions: The results indicate that the influence of CBD on the course of isoflurane anesthesia depends on the dose and can reduce the induction time. Although this study was performed in laboratory rats, in clinical practice, these data should be considered when CBD-treated patients undergo isoflurane anesthesia.

An Investigation of Neurochemical Changes in Chronic Cannabis Users

With the legalization of recreational cannabis (CB) the characterization of how it may impact brain chemistry is essential. Magnetic resonance spectroscopy (MRS) was used to examine neurometabolite concentrations in the dorsal anterior cingulate (dACC) in chronic CB users (N = 26; 10 females) and controls (N = 24; 10 females). The concentrations of glutamate (Glu), total creatine (tCr), choline (Cho), total N-acetylaspartate (tNAA), and myo-inositol (mI) were estimated using LCModel. The ANCOVAs failed to show significant differences between controls and CB users. Regression analyses were then performed on the CB group to model each neurometabolite to determine its relationship to monthly CB use, sex, the interaction between CB use and sex. tCr was found to be predicted by both monthly CB use and sex. While the regression model was not significant the relationship between monthly CB use and Glu appears to be modulated by sex with the effect of monthly use (dose) being stronger in males. tNAA failed to show an effect of CB use but did reveal an effect of sex with females showing larger tNAA levels. Although the results presented are preliminary due to the small sample size they do guide future research. The results presented provide direction for further studies as they suggest that dose may significantly influence the observance of CB effects and that those effects may be modulated by sex. Studies with significantly larger sample sizes designed specifically to examine individuals with varying usage as well as sex effects are necessary.

FABP1 controls hepatic transport and biotransformation of Δ9-THC

The increasing use of medical marijuana highlights the importance of developing a better understanding of cannabinoid metabolism. Phytocannabinoids, including ∆⁹-tetrahydrocannabinol (THC), are metabolized and inactivated by cytochrome P450 enzymes primarily within the liver. The lipophilic nature of cannabinoids necessitates mechanism(s) to facilitate their intracellular transport to metabolic enzymes. Here, we test the central hypothesis that liver-type fatty acid binding protein (FABP1) mediates phytocannabinoid transport and subsequent inactivation. Using X-ray crystallography, molecular modeling, and in vitro binding approaches we demonstrate that FABP1 accommodates one molecule of THC within its ligand binding pocket. Consistent with its role as a THC carrier, biotransformation of THC was reduced in primary hepatocytes obtained from FABP1-knockout (FABP1-KO) mice. Compared to their wild-type littermates, administration of THC to male and female FABP1-KO mice potentiated the physiological and behavioral effects of THC. The stark pharmacodynamic differences were confirmed upon pharmacokinetic analyses which revealed that FABP1-KO mice exhibit reduced rates of THC biotransformation. Collectively, these data position FABP1 as a hepatic THC transport protein and a critical mediator of cannabinoid inactivation. Since commonly used medications bind to FABP1 with comparable affinities to THC, our results further suggest that FABP1 could serve a previously unrecognized site of drug-drug interactions.

Broad and Region-Specific Impacts of the Synthetic Cannabinoid CP 55,940 in Adolescent and Adult Female Mouse Brains

Relative to Δ⁹-tetrahydrocannabinol (THC), the synthetic cannabinoid CP 55,940 (CP) is significantly more potent and efficacious at cannabinoid receptors, the primary targets for endogenous cannabinoids (eCBs). eCBs belong to a large, interconnected lipidome of bioactive signaling molecules with a myriad of effects in optimal and pathological function. Recreational use of highly potent and efficacious synthetic cannabinoids is common amongst adolescents, potentially impacting brain development. Knowledge of the molecular outcomes of synthetic cannabinoid use will be important to develop more targeted therapies for synthetic cannabinoid intoxication and to prevent long-term disruption to the CNS. Here, we test the hypothesis that CP has age and region-dependent effects on the brain lipidome. Adolescent [post-natal day (PND) 35 and PND 50] and young adult female mice were given either an acute dose of CP or vehicle and brains were collected 2 h later. Eight brain regions were dissected and levels of ∼80 lipids were screened from each region using HPLC/MS/MS. CP had widespread effects on the brain lipidome in all age groups. Interestingly, more changes were observed in the PND 35 mice and more were reductions in a lipid’s concentration, including region-dependent lowering of eCB levels. CP levels were highest in the cortex at PND 35, the hippocampus at PND 50, and in the cerebellum in the adult. These data provide novel insights into how high-potency, synthetic cannabinoids drive different, age-dependent, cellular signaling effects in the brain.

Effects of Estrogens on Central Nervous System Neurotransmission: Implications for Sex Differences in Mental Disorders

Nearly one of every five US individuals aged 12 years old or older lives with certain types of mental disorders. Men are more likely to use various types of substances, while women tend to be more susceptible to mood disorders, addiction, and eating disorders, all of which are risks associated with suicidal attempts. Fundamental sex differences exist in multiple aspects of the functions and activities of neurotransmitter-mediated neural circuits in the central nervous system (CNS). Dysregulation of these neural circuits leads to various types of mental disorders. The potential mechanisms of sex differences in the CNS neural circuitry regulating mood, reward, and motivation are only beginning to be understood, although they have been largely attributed to the effects of sex hormones on CNS neurotransmission pathways. Understanding this topic is important for developing prevention and treatment of mental disorders that should be tailored differently for men and women. Studies using animal models have provided important insights into pathogenesis, mechanisms, and new therapeutic approaches of human diseases, but some concerns remain to be addressed. The purpose of this chapter is to integrate human and animal studies involving the effects of the sex hormones, estrogens, on CNS neurotransmission, reward processing, and associated mental disorders. We provide an overview of existing evidence for the physiological, behavioral, cellular, and molecular actions of estrogens in the context of controlling neurotransmission in the CNS circuits regulating mood, reward, and motivation and discuss related pathology that leads to mental disorders.

Sex-Dependent Effects of Cannabis and Cannabinoids: A Translational Perspective

Recent policy changes have led to significant increases in the use of cannabis for both medical and recreational purposes. Although men are more likely to endorse past month cannabis use and are more frequently diagnosed with Cannabis Use Disorder relative to women, a growing proportion of medical cannabis users are reported to be women. The increased popularity of cannabis for medical purposes and the narrowing gap in prevalence of use between men and women raises questions regarding sex-dependent effects related to therapeutic efficacy and negative health effects of cannabis and cannabinoids. The objective of this review is to provide a translational perspective on the sex-dependent effects of cannabis and cannabinoids by synthesizing findings from preclinical and clinical studies focused on sex comparisons of their therapeutic potential and abuse liability, two specific areas that are of significant public health relevance. Hormonal and pharmacological mechanisms that may underlie sex differences in the effects of cannabis and cannabinoids are highlighted.

Evaluation of first generation synthetic cannabinoids on binding at non-cannabinoid receptors and in a battery of in vivo assays in mice

Anecdotal reports suggest that abused synthetic cannabinoids produce cannabis-like "highs," but some of their effects may also differ from traditional cannabinoids such as Δ(9)-tetrahydrocannabinol (THC). This study examined the binding affinities of first-generation indole-derived synthetic cannabinoids at cannabinoid and noncannabinoid receptors and their effects in a functional observational battery (FOB) and drug discrimination in mice. All seven compounds, except JWH-391, had favorable affinity (≤159 nM) for both cannabinoid receptors. In contrast, binding at noncannabinoid receptors was absent or weak. In the FOB, THC and the six active compounds disrupted behaviors in CNS activation and muscle tone/equilibrium domains. Unlike THC, however, synthetic cannabinoids impaired behavior across a wider dose and domain range, producing autonomic effects and signs of CNS excitability and sensorimotor reactivity. In addition, mice acquired JWH-018 discrimination, and THC and JWH-073 produced full substitution whereas the 5-HT2B antagonist mianserin did not substitute in mice trained to discriminate JWH-018 or THC. Urinary metabolite analysis showed that the compounds were extensively metabolized, with metabolites that could contribute to their in vivo effects. Together, these results show that, while first-generation synthetic cannabinoids shared some effects that were similar to those of THC, they also possessed effects that differed from traditional cannabinoids. The high nanomolar (or absent) affinities of these compounds at receptors for most major neurotransmitters suggests that these divergent effects may be related to the greater potencies and/or efficacies at CB1 receptors; however, action(s) at noncannabinoid receptors yet to be assessed or via different signaling pathways cannot be ruled out.

Developmental effects of cannabinoids on zebrafish larvae

Cannabinoids are natural or synthetic compounds related chemically to (-)-(6aR,10aR)-6,6,9-trimethyl-3-pentyl-6a,7,8,10a-tetrahydro-6H-benzo[c]chromen-1-ol (Δ(9)-THC), the principle psychotropic constituent of the hemp plant, Cannabis sativa L. Here we examine the effects of the cannabinoids Δ(9)-THC, (R)-(+)-[2,3-dihydro-5-methyl-3-(4-morpholinylmethyl)pyrrolo [1,2,3-de]-1,4-benzoxazin-6-yl]-1-napthalenylmethanone and 2-[(1R,2R,5R)-5-hydroxy-2-(3-hydroxypropyl) cyclohexyl]-5-(2-methyloctan-2-yl)phenol, and the cannabinoid antagonist (AM 251). Exposures were either acute (1-12-h exposure at 108 hours of postfertilization [hpf]) or chronic (96-h exposure starting at 24 hpf). Geometric range finding was used to determine the experimental concentrations. The concentration of the chemical that kills 50% of the test animals in a given time (LC50) was determined based on cumulative mortality at 5 days of postfertilization. At day 5, behavioral analysis (visual motor response test) was carried out in which movement of individual larvae was analysed using automated video-tracking. With acute exposure, embryos showed a biphasic response to the dark challenge with all three cannabinoids tested. This response consisted of stimulation of the locomotor activity at low concentrations, suppression at high doses. With chronic exposure, embryos habituated to the effects of all three cannabinoids when assayed with the dark challenge phase. Further, the excitation was ameliorated when the antagonist AM 251 was coadministered with the cannabinoid. When AM 251 was administered on its own (chronically or acutely), the locomotor activity was suppressed at high concentrations. We examined the embryos for a range of malformations after chronic exposure to cannabinoid. Only Δ(9)-THC was associated with a significant increase in malformations at 5d (yolk sac and pericardial edema, bent tail/body axis). We conclude that cannabinoids have behavioral effects in zebrafish that are comparable to some of those reported in the literature for mammals. In particular, the acute exposure response resembles behavioral effects reported for adult rodents. Our data are consistent with these behavioral effects being mediated, at least in part, by the CB1 receptor.

Pharmacological characterization of the peripheral FAAH inhibitor URB937 in female rodents: interaction with the Abcg2 transporter in the blood-placenta barrier

BACKGROUND AND PURPOSE

URB937 is a peripherally restricted inhibitor of the anandamide-deactivating enzyme fatty-acid amide hydrolase (FAAH). Despite its limited access to the CNS, URB937 produces marked antinociceptive effects in rodents. URB937 is actively extruded from the CNS by the ATP-binding cassette (ABC) membrane transporter, Abcg2. Tissue Abcg2 levels are markedly different between males and females, and this transporter is known to limit the access of xenobiotics to the fetoplacental unit in gestating female rodents. In the present study, we investigated the tissue distribution and antinociceptive properties of URB937 in female mice and rats.

EXPERIMENTAL APPROACH

We studied the systemic disposition of URB937 in female mice and the antinociceptive effects of this compound in models of visceral (acetic acid-induced writhing) and inflammatory nociception (carrageenan-induced hyperalgesia) in female mice and rats. Furthermore, we evaluated the interaction of URB937 with the blood-placenta barrier in gestating mice and rats.

KEY RESULTS

Abcg2 restricted the access of URB937 to the CNS of female mice and rats. Nevertheless, URB937 produced a high degree of antinociception in female mice and rats in models of visceral and inflammatory pain. Moreover, the compound displayed a restricted access to placental and fetal tissues in pregnant mice and rats.

CONCLUSIONS AND IMPLICATIONS

Peripheral FAAH blockade with URB937 reduces nociception in female mice and rats, as previously shown for males of the same species. In female mice and rats, Abcg2 limits the access of URB937, not only to the CNS, but also to the fetoplacental unit. LINKED ARTICLES This article is part of a themed section on Cannabinoids. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2012.167.issue-8.

Effects of gonadal hormones on the peripheral cannabinoid receptor 1 (CB1R) system under a myositis condition in rats

In this study, we assessed the effects of peripherally administered cannabinoids in an orofacial myositis model, and the role of sex hormones in cannabinoid receptor (CBR) expression in trigeminal ganglia (TG). Peripherally administered arachidonylcyclopropylamide (ACPA), a specific CB1R agonist, significantly attenuated complete Freund's adjuvant (CFA)-induced mechanical hypersensitivity in the masseter muscle in male rats. The ACPA effect was blocked by a local administration of AM251, a specific CB1R antagonist, but not by AM630, a specific CB2R antagonist. In female rats, a 30-fold higher dose of ACPA was required to produce a moderate reduction in mechanical hypersensitivity. CFA injected in masseter muscle significantly upregulated CB1R mRNA expression in TG in male, but not in female, rats. There was a close correlation between the CB1R mRNA levels in TG and the antihyperalgesic effect of ACPA. Interleukin (IL)-1β and IL-6, which are elevated in the muscle tissue following CFA treatment, induced a significant upregulation of CB1R mRNA expression in TG from male rats. The upregulation of CB1R was prevented in TG cultures from orchidectomized male rats, which was restored by the application of testosterone. The cytokines did not alter the CB1R mRNA level in TG from intact as well as ovariectomized female rats. Neither estradiol supplement nor estrogen receptor blockade had any effects on CB1R expression. These data indicate that testosterone, but not estradiol, is required for the regulation of CB1Rs in TG under inflammatory conditions, which provide explanations for the sex differences in the antihyperalgesic effects of peripherally administered cannabinoids.

Sex differences in cannabinoid 1 vs. cannabinoid 2 receptor-selective antagonism of antinociception produced by delta9-tetrahydrocannabinol and CP55,940 in the rat

The purpose of this study was to determine whether sex differences in cannabinoid (CB)-induced antinociception and motoric effects can be attributed to differential activation of CB(1) or CB(2) receptors. Rats were injected intraperitoneally with vehicle, rimonabant [5-(4-chlorophenyl)-1-(2,4-dichlorophenyl)-4-methyl-N-1-piperidinyl-1H-pyrazole-3-carboxamide (SR141716A), a putative CB(1) receptor-selective antagonist; 0.1-10 mg/kg] or 5-(4-chloro-3-methylphenyl)-1-[(4-methylphenyl)methyl]-N-[(1S,2S,4R)-1,3,3-trimethylbicyclo[2.2.1]hept-2-yl]-1H-pyrazole-3-carboxamide (SR144528) (a putative CB(2) receptor-selective antagonist; 1.0-10 mg/kg). Thirty minutes later, Δ(9)-tetrahydrocannabinol (THC; 1.25-40 mg/kg) or 5-(1,1-dimethylheptyl)-2-[5-hydroxy-2-(3-hydroxypropyl)cyclohexyl]phenol (CP55,940) (0.05-1.6 mg/kg) was injected. Paw pressure and tail withdrawal antinociception, locomotor activity, and catalepsy were measured. Rimonabant dose-dependently antagonized THC and CP55,940 in each test, but was up to 10 times more potent in female than male rats on the nociceptive tests; estimates of rimonabant affinity (apparent pK(B)) for the CB(1) receptor were approximately 0.5 to 1 mol/kg higher in female than male rats. SR144528 partially antagonized THC-induced tail withdrawal antinociception and locomotor activity in females, but this antagonism was not dose-dependent or consistent; no SR144528 antagonism was observed in either sex tested with CP55,940. Neither the time course of rimonabant antagonism nor the plasma levels of rimonabant differed between the sexes. Rimonabant and SR144528 did not antagonize morphine-induced antinociception, and naloxone did not antagonize THC-induced antinociception in either sex. These results suggest that THC produces acute antinociceptive and motoric effects via activation of CB(1), and perhaps under some conditions, CB(2) receptors, in female rats, whereas THC acts primarily at CB(1) receptors in male rats. Higher apparent pK(B) for rimonabant in female rats suggests that cannabinoid drugs bind with greater affinity to CB(1) receptors in female than male rats, probably contributing to greater antinociceptive effects observed in female compared with male rats.

Attenuation of food intake in chicks by an inverse agonist of cannabinoid receptor 1 administered by either injection or ingestion in hydrocolloid carriers

The cannabinoid receptor (CB(1)) was studied primarily in mammals where it was found to comprise a link between reward processes and addictive behavior such as food consumption. The purpose of this study was twofold: first to characterize the effect of the chicken CB(1) receptor inverse agonist AM251 on food intake, and second, to establish a stress-free approach for application of AM251 to birds using hydrocolloid carriers, which can be mixed with food. A single administration of AM251 by intravenous injection (at 0.85 or 5 mg kg(-1)BW) or by ingestion of hydrocolloid carriers entrapping AM251 at a concentration of 5 mg kg(-1)BW led to a transient attenuation of food intake. The consequent reduced cumulative food intake and BW were observed in the treated chicks for at least 7h post-administration, with no gender differences. Circulating levels of AM251, assessed by LC-MS following 48 h of continuous feeding with hydrocolloid carriers containing 50mg AM 251 kg(-1) BW day(-1), were physiologically significant at 186 ± 73 pmol ml(-1). It is concluded that unlike some other factors, which act differently in birds compared to mammals such as ghrelin, CB(1) inverse agonists attenuate food intake in chicks similar to its effect in mammals. In addition, the new approach for administration of AM251 to birds in hydrocolloid carriers could provide a simple and stress-free tool for prolonged studies of this control mechanism in birds.

How important are sex differences in cannabinoid action?

In humans as in animals, males and females are dissimilar in their genetic and hormonally driven behaviour; they process information differently, perceive experience and emotions in different ways, display diverse attitudes, language and social skills, and show sex-related differences in the brain anatomy and organization. Drug addiction is a widespread relapsing illness that affects both men and women. Sex-dependent differences have been frequently observed in the biological and behavioural effects of substances of abuse, including cannabis. Beside sex differences observed in the cannabinoid-induced effects related to cannabis abuse and dependence, cannabinoids have been shown to exert sex-dependent effects also in other physiological and behavioural aspects, such as food intake and energy balance (more evident in males), or anxiety and depression (more evident in females). Research has just begun to identify factors which could provide a neurobiological basis for gender-based differences in cannabinoid effects, among which, gonadal hormones seem to play a crucial role. Yet, cannabinoid pharmacodynamic and pharmacokinetic may also be important, as sex differences in cannabinoid effects might be due, at least in part, to differences in muscle mass and fat tissue distribution between males and females. Here, we will review both clinical and laboratory-based research evidence revealing important sex-related differences in cannabinoid effects, and put forward some suggestions for future studies to fill the gap in our knowledge of gender-specific bias in cannabinoid pharmacology.

Antinociception and sedation following intracerebroventricular administration of Δ⁹-tetrahydrocannabinol in female vs. male rats

Systemically administered cannabinoids produce greater antinociceptive and sedative effects in female compared to male rats. Sex differences in the brain endocannabinoid system have also been reported. The aim of this study was to determine whether sex differences in antinociceptive and motoric effects of a cannabinoid can be attributed to supraspinal mechanisms. Vehicle or Δ⁹-tetrahydrocannabinol (THC, 100 μg) was administered i.c.v., and behavioral effects were compared between gonadally intact male and female rats, and among females in different estrous stages (early proestrus, late proestrus, estrus and diestrus). Antinociception on the tail withdrawal and paw pressure tests after i.c.v. THC was slightly but not significantly greater in females (pooled across estrous stages) compared to males. THC suppressed locomotor activity similarly in all groups, with the exception that only males showed hyperlocomotion at 4 h post-injection. When females in the four estrous stages were compared, females in late proestrus showed significantly greater THC-induced antinociception than females in estrus (and males). These results suggest that supraspinal mechanisms may contribute to greater systemic THC effects in females compared to males, and to estrous stage-dependent differences in THC effects among females.

Cannabinoid-hormone interactions in the regulation of motivational processes

There is a bi-directionality in hormone-cannabinoid interactions: cannabinoids affect prominent endocrine axes (such as the hypothalamic-pituitary-gonadal), and gonadal hormones modulate cannabinoid effects. This review will summarize recent research on these interactions, with a specific focus upon their implications for motivated behavior. Sexual behavior will serve as a "case study." I will explore the hypothesis that ovarian hormones, in particular estradiol, may serve to release estrous behavior from endocannabinoid inhibition. Hormonal regulation of the endogenous cannabinoid system also affects processes that underlie drug abuse. This review will briefly discuss sex differences in behavioral responses to cannabinoids and explore potential mechanisms by which gonadal hormones alter cannabinoid reward. An examination of this research informs our perspective on how hormones and endocannabinoids may affect drug-seeking behavior as a whole and the development of addiction.

Selecting paradigms from cognitive neuroscience for translation into use in clinical trials: proceedings of the third CNTRICS meeting

This overview describes the goals and objectives of the third conference conducted as part of the Cognitive Neuroscience Treatment Research to Improve Cognition in Schizophrenia (CNTRICS) initiative. This third conference was focused on selecting specific paradigms from cognitive neuroscience that measured the constructs identified in the first CNTRICS meeting, with the goal of facilitating the translation of these paradigms into use in clinical trials contexts. To identify such paradigms, we had an open nomination process in which the field was asked to nominate potentially relevant paradigms and to provide information on several domains relevant to selecting the most promising tasks for each construct (eg, construct validity, neural bases, psychometrics, availability of animal models). Our goal was to identify 1-2 promising tasks for each of the 11 constructs identified at the first CNTRICS meeting. In this overview article, we describe the on-line survey used to generate nominations for promising tasks, the criteria that were used to select the tasks, the rationale behind the criteria, and the ways in which breakout groups worked together to identify the most promising tasks from among those nominated. This article serves as an introduction to the set of 6 articles included in this special issue that provide information about the specific tasks discussed and selected for the constructs from each of 6 broad domains (working memory, executive control, attention, long-term memory, perception, and social cognition).

Gene expression of opioid and dopamine systems in mouse striatum: effects of CB1 receptors, age and sex

RATIONALE

Endocannabinoid, opioid, and dopamine systems interact to exhibit cannabinoid receptor neuromodulation of opioid peptides and D(4) dopamine receptor gene expression in CB(1)-cannabinoid-deficient mouse striatum.

OBJECTIVE

Using CB(1)-transgenic mice, we examine primary age-sex influences and interactions on opioid and dopamine system members' gene expression in striatum.

MATERIALS AND METHODS

Real-time quantitative polymerase chain reaction was used to analyze gene expression of opioid peptides [preproenkephalin (PPENK); preprodynorphin (PPDYN)], opioid receptors [delta-opioid receptor (delta-OR); mu-opioid receptor (micro-OR)] and dopamine receptor subtypes (D(1) through D(5)) in male/female CB(1)(+/+)/CB(1)(-/-) mice striata at two adult ages [young (60-90 days); old (140-300 days)].

RESULTS

(1) Increased PPENK and PPDYN, owing to genotype [CB(1)(+/+) vs. CB(1)(-/-)], depended on sex. When genotype-independent, they depended on sex (PPENK) or age (PPDYN). (2) delta-OR was age-dependent (higher in old). (3) micro-OR, owing to genotype, was age-dependent [higher in old CB(1)(-/-) males]. When genotype-independent, it depended on sex (higher in females). (4) Female D(1) was genotype-independent and age-dependent, while male D(1) was higher in old over young CB(1)(+/+) mice. (5) D(5), owing to genotype, was sex-dependent [higher in young female CB(1)(-/-) mice]. (6) D(2), genotype-independent, was higher in old over young male mice. (7) Young female D(3) was higher in CB(1)(-/-) over CB(1)(+/+) mice. Male D(3) was age-dependent (higher in old mice). (8) D(4), owing to genotype, was sex-dependent [higher in CB(1)(-/-) over CB(1)(+/+) females]. Genotype-independent D(4) was sex-dependent in young mice (higher in females) and age-dependent in males (higher in old).

CONCLUSIONS

Greater striatal expression is genotype-dependent in females (opioid-peptides, D(3), D(4), D(5)) and genotype-independent in both females (PPENK, mu-OR, D(4)) and old males (PPDYN, delta-OR, D(2), D(3), D(4)).

Delta(9)-tetrahydrocannabinol prolongs the immobility time in the mouse forced swim test: involvement of cannabinoid CB(1) receptor and serotonergic system

In the present study, we investigated the effect of Delta(9)-tetrahydrocannabinol (THC), the principal psychoactive component of marijuana, on immobility time during the forced swim test. THC (2 and 6 mg/kg, i.p.) significantly prolonged the immobility time. In addition, THC at the same doses did not significantly affect locomotor activity in the open-field test. The selective cannabinoid CB(1) receptor antagonist rimonabant (3 mg/kg, i.p.) significantly reduced the enhancement of immobility by THC (6 mg/kg). Similarly, the selective serotonin (5-HT) reuptake inhibitor (SSRI) citalopram (10 mg/kg, i.p.) and 5-HT(1A/7) receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT, 0.3 mg/kg, i.p.) significantly reduced this THC-induced effect. Moreover, the selective 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohexane carboxamide dihydrochloride (WAY100635, 1 mg/kg, i.p.) and the postsynaptic 5-HT(1A) receptor antagonist MM-77 (0.1 mg/kg, i.p.) reversed this reduction effect of 8-OH-DPAT (0.3 mg/kg). In contrast, the selective 5-HT(7) receptor antagonist (R)-3-[2-[2-(4-methylpiperidin-1-yl)ethyl]pyrrolidine-1-sulfonyl]phenol hydrochloride (SB269970) had no effect on this reduction effect of 8-OH-DPAT. WAY100635 (1 mg/kg) also reversed the reduction effect of citalopram (10 mg/kg). These findings suggest that the 5-HT(1A) receptors are involved in THC-induced enhancement of immobility.

Delta 9-tetrahydrocannabinol-induced catalepsy-like immobilization is mediated by decreased 5-HT neurotransmission in the nucleus accumbens due to the action of glutamate-containing neurons

Delta(9)-tetrahydrocannabinol (THC) has been reported to induce catalepsy-like immobilization, but the mechanism underlying this effect remains unclear. In the present study, in order to fully understand the neural circuits involved, we determined the brain sites involved in the immobilization effect in rats. THC dose-dependently induced catalepsy-like immobilization. THC-induced catalepsy-like immobilization is mechanistically different from that induced by haloperidol (HPD), because unlike HPD-induced catalepsy, animals with THC-induced catalepsy became normal again following sound and air-puff stimuli. THC-induced catalepsy was reversed by SR141716, a selective cannabinoid CB(1) receptor antagonist. Moreover, THC-induced catalepsy was abolished by lesions in the nucleus accumbens (NAc) and central amygdala (ACE) regions. On the other hand, HPD-induced catalepsy was suppressed by lesions in the caudate putamen (CP), substantia nigra (SN), globus pallidus (GP), ACE and lateral hypothalamus (LH) regions. Bilateral microinjection of THC into the NAc region induced catalepsy-like immobilization. This THC-induced catalepsy was inhibited by serotonergic drugs such as 5-hydroxy-L-tryptophan (5-HTP), a 5-HT precursor, and 5-methoxy-N,N-dimethyltryptamine (5-MeODMT), a 5-HT receptor agonist, as well as by anti-glutamatergic drugs such as MK-801 and amantadine, an N-methyl-d-aspartate (NMDA) receptor antagonist. THC significantly decreased 5-HT and glutamate release in the NAc, as shown by in vivo microdialysis. SR141716 reversed and MK-801 inhibited this decrease in 5-HT and glutamate release. These findings suggest that the THC-induced catalepsy is mechanistically different from HPD-induced catalepsy and that the catalepsy-like immobilization induced by THC is mediated by decreased 5-HT neurotransmission in the nucleus accumbens due to the action of glutamate-containing neurons.

Single and multiple doses of rimonabant antagonize acute effects of smoked cannabis in male cannabis users

RATIONALE

A single 90-mg dose of the cannabinoid CB1 receptor antagonist rimonabant attenuates effects of smoked cannabis in humans.

OBJECTIVES

The objective of this study is to evaluate whether repeated daily 40-mg doses of rimonabant can attenuate effects of smoked cannabis to the same extent as a single higher (90 mg) dose.

MATERIALS AND METHODS

Forty-two male volunteers received one of three oral drug regimens in a randomized, double blind, parallel group design: (1) 40 mg rimonabant daily for 15 days, (2) placebo for 14 days, then 90 mg rimonabant on day 15, or (3) placebo for 15 days. All participants smoked an active or placebo cannabis cigarette 2 h after medication on days 8 and 15. Subjective effects were measured with visual analog scales and the marijuana-scale of the Addiction Research Center Inventory.

RESULTS

Cannabis-induced tachycardia was significantly lower for the 40-mg group on day 8 and for the 40 and 90 mg rimonabant groups on day 15 as compared to placebo. The 40-mg dose significantly decreased peak subjective effects on day 8. Neither the 90-mg nor 40-mg doses significantly decreased peak subjective effects on day 15. Rimonabant treatment did not significantly affect Delta(9)-tetrahydrocannabinnol pharmacokinetics.

CONCLUSIONS

Repeated lower daily rimonabant doses (40 mg) attenuated the acute physiological effects of smoked cannabis to a similar degree as a single 90-mg dose; repeated 40-mg doses attenuated subjective effects after 8 but not 15 days.

Opioid antagonism of cannabinoid effects: differences between marijuana smokers and nonmarijuana smokers

In non-human animals, opioid antagonists block the reinforcing and discriminative-stimulus effects of Delta(9)-tetrahydrocannabinol (THC), while in human marijuana smokers, naltrexone (50 mg) enhances the reinforcing and subjective effects of THC. The objective of this study was to test a lower, more opioid-selective dose of naltrexone (12 mg) in combination with THC. The influence of marijuana-use history and sex was also investigated. Naltrexone (0, 12 mg) was administered 30 min before oral THC (0-40 mg) or methadone (0-10 mg) capsules, and subjective effects, task performance, pupillary diameter, and cardiovascular parameters were assessed in marijuana smoking (Study 1; n=22) and in nonmarijuana smoking (Study 2; n=21) men and women. The results show that in marijuana smokers, low-dose naltrexone blunted the intoxicating effects of a low THC dose (20 mg), while increasing ratings of anxiety at a higher THC dose (40 mg). In nonmarijuana smokers, low-dose naltrexone shifted THC's effects in the opposite direction, enhancing the intoxicating effects of a low THC dose (2.5 mg) and decreasing anxiety ratings following a high dose of THC (10 mg). There were no sex differences in these interactions, although among nonmarijuana smokers, men were more sensitive to the effects of THC alone than women. To conclude, a low, opioid-selective dose of naltrexone blunted THC intoxication in marijuana smokers, while in nonmarijuana smokers, naltrexone enhanced THC intoxication. These data demonstrate that the interaction between opioid antagonists and cannabinoid agonists varies as a function of marijuana use history.

Effects of the cannabinoid antagonist SR141716 (rimonabant) and d-amphetamine on palatable food and food pellet intake in non-human primates

The purpose of this study was to determine if a cannabinoid CB(1) receptor antagonist would selectively decrease consumption of highly palatable food in non-human primates. The CB(1) receptor antagonist SR141716 (rimonabant; 0.12-1.0 mg/kg, i.m.) and the stimulant anorectic drug d-amphetamine (0.12-1.0 mg/kg, i.m.) were administered to non-food deprived baboons for the purpose of measuring the effect of each drug on consumption of the normal diet, and a large single meal of a high-carbohydrate candy. Four male and four female baboons had access to food 24 h each day, but they had to complete a two phase operant procedure in order to eat. Responding on one lever during a 30-min appetitive phase was required before animals could start a consumption phase, where responding on another lever led to food delivery, i.e., a meal. Three days a week baboons received a jelly sugar-coated candy (Skittles) during the first meal and then pellets were available in subsequent meals. All baboons ate as many individual candies in one meal as they did pellets throughout the entire day. Acute d-amphetamine and, to a lesser extent, SR141716 decreased both candy intake in a single meal and pellet intake in a single meal and over 24 h. d-Amphetamine, but not SR141716, increased latency to the candy meal and the first pellet meal indicating that the two drugs differentially altered feeding topography. Although males ate more food pellets than females, few other sex differences were observed. Thus, although effective in decreasing food intake, there was no evidence of a specific effect of CB(1) receptor antagonism on consumption of a large meal or a palatable food.

Involvement of 5-hydroxytryptamine1A receptors in Delta9-tetrahydrocannabinol-induced catalepsy-like immobilization in mice

The present study investigated the involvement of 5-hydroxytryptamine(1A) (5-HT(1A)) receptors in Delta(9)-tetrahydrocannabinol (THC)-induced catalepsy-like immobilization in mice. THC (10 mg/kg, i.p.) induced catalepsy-like immobilization but had no effect on motor coordination in the rota-rod test. The selective cannabinoid CB(1) receptor antagonist rimonabant (3 mg/kg, i.p.) completely antagonized THC-induced catalepsy-like immobilization. The 5-HT(1A)/5-HT(7) receptor agonist 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT; 0.3 and 1 mg/kg, i.p.) and 5-HT(1A) receptor partial agonist buspirone (0.06 and 0.1 mg/kg, i.p.) inhibited this THC-induced catalepsy-like immobilization. Moreover, the selective 5-HT(1A) receptor antagonist N-[2-[4-(2-methoxyphenyl)-1-piperazinyl]ethyl]-N-(2-pyridinyl) cyclohezane carboxamide dihydrochloride (WAY100635; 0.3 or 1 mg/kg, i.p.) reversed the inhibition of THC-induced catalepsy-like immobilization by 8-OH-DPAT (1 mg/kg) or buspirone (0.06 mg/kg). In contrast, the selective 5-HT(7) receptor antagonist (R)-3-[2-[2-(4-methylpiperidin-1-yl)ethyl]pyrrolidine-1-sulfonyl]phenol hydrochloride (SB269970) had no effect on this inhibitory effect of 8-OH-DPAT. On the other hand, WAY100635 (0.3 and 1 mg/kg, i.p.) enhanced the catalepsy-like immobilization induced by THC (6 mg/kg, i.p.). These findings suggest that the 5-HT(1A) receptors are involved in THC-induced catalepsy-like immobilization.

Antipsychotics improve Delta9-tetrahydrocannabinol-induced impairment of the prepulse inhibition of the startle reflex in mice

Recently, cannabinoid receptor agonists have been reported to impair prepulse inhibition (PPI) of the startle reflex. In the current study, we examined the effect of Delta9-tetrahydrocannabinol (THC), the principal psychoactive component of cannabis, on the PPI, and found that THC (10 mg/kg, i.p.) impaired the PPI concomitant with a decrease in the startle response. Antipsychotics such as haloperidol (0.3 mg/kg, i.p.) and risperidone (0.1 mg/kg, i.p.), which are potent dopamine D2 receptor antagonists, and SR141716 (10 mg/kg, i.p.), a CB1 cannabinoid receptor antagonist, reversed these THC-induced PPI deficits. Moreover, THC (10 mg/kg) increased dopamine (DA) release in the nucleus accumbens but not medial prefrontal cortex over a 50-100-min period (time of PPI test) after treatment, and SR141716 (10 mg/kg) reversed this increase in DA release induced by THC. These results suggest that dopaminergic hyperfunction in the nucleus accumbens may be involved in THC-induced PPI deficits.

Sex differences in behavioral effects of cannabinoids

This review summarizes the existing literature on sex differences in the effects of cannabinoid drugs on behavior, primarily in the adult rodent. These preclinical studies, taken together with preliminary reports of sex differences in cannabinoid effects in humans, suggest that sex of subject may be an important modulating factor in a variety of cannabinoid effects. When sex differences are found, females are usually more sensitive than males to cannabinoids. Both pharmacokinetic and pharmacodynamic variables may contribute to sex differences in behavioral effects of cannabinoids. Given the significant therapeutic potential of cannabinoid agonists and antagonists--as well as their widespread recreational use--it will be important to determine the reliability and functional significance of, as well as mechanisms underlying sex differences in cannabinoid effects.

Cannabinoid function in learning, memory and plasticity

Marijuana and its psychoactive constituents induce a multitude of effects on brain function. These include deficits in memory formation, but care needs to be exercised since many human studies are flawed by multiple drug abuse, small sample sizes, sample selection and sensitivity of psychological tests for subtle differences. The most robust finding with respect to memory is a deficit in working and short-term memory. This requires intact hippocampus and prefrontal cortex, two brain regions richly expressing CB1 receptors. Animal studies, which enable a more controlled drug regime and more constant behavioural testing, have confirmed human results and suggest, with respect to hippocampus, that exogenous cannabinoid treatment selectively affects encoding processes. This may be different in other brain areas, for instance the amygdala, where a predominant involvement in memory consolidation and forgetting has been firmly established. While cannabinoid receptor agonists impair memory formation, antagonists reverse these deficits or act as memory enhancers. These results are in good agreement with data obtained from electrophysiological recordings, which reveal reduction in neural plasticity following cannabinoid treatment, and increased plasticity following antagonist exposure. The mixed receptor properties of the pharmacological tool, however, make it difficult to define the exact role of any CB1 receptor population in memory processes with any certainty. This makes it all the more important that behavioural studies use selective administration of drugs to specific brain areas, rather than global administration to whole animals. The emerging role of the endogenous cannabinoid system in the hippocampus may be to facilitate the induction of long-term potentiation/the encoding of information. Administration of exogenous selective CB1 agonists may therefore disrupt hippocampus-dependent learning and memory by 'increasing the noise', rather than 'decreasing the signal' at potentiated inputs.