Pharmacokinetic factors in sex differences in Δ9-tetrahydrocannabinol-induced behavioral effects in rats

Sex differences in the acute effects of smoked cannabis: evidence from a human laboratory study of young adults

RATIONALE

Animal studies have found robust sex differences in the pharmacokinetics and pharmacodynamics of Δ⁹-tetrahydrocannabinol (THC). However, the human evidence remains equivocal, despite findings that women may experience more severe consequences of cannabis use than men.

OBJECTIVES

The objective of this secondary analysis was to examine sex differences in THC pharmacokinetics and in acute subjective, physiological, and cognitive effects of smoked cannabis in a sample of regular cannabis users (use 1-4 days per week) aged 19-25 years.

METHODS

Ninety-one healthy young adults were randomized to receive active (12.5% THC; 17 females, 43 males) or placebo (< 0.1% THC; 9 females, 21 males) cannabis using a 2:1 allocation ratio. Blood samples to quantify concentrations of THC, 11-OH-THC, and 11-Nor-carboxy-THC (THC-COOH), as well as measures of subjective drug effects, vital signs, and cognition were collected over a period of 6 h following ad libitum smoking of a 750-mg cannabis cigarette.

RESULTS

Females smoked less of the cannabis cigarette than males (p = 0.008) and had a lower peak concentration of THC and THC-COOH than males (p ≤ 0.01). Blood THC concentrations remained lower in females even when adjusting for differences in estimated dose of THC inhaled. There was very little evidence of sex differences in visual analog scale (VAS) ratings of subjective drug effects, mood, heart rate, blood pressure, or cognitive effects of cannabis.

CONCLUSIONS

Females experienced the same acute effects of smoked cannabis as males at a lower observed dose, highlighting the need for more research on sex differences in the pharmacology of THC, especially when administered by routes in which titrating to the desired effect is more difficult (e.g., cannabis edibles).

Escalating low-dose Δ9 -tetrahydrocannabinol exposure during adolescence induces differential behavioral and neurochemical effects in male and female adult rats

Cannabinoid administration during adolescence affects various physiological processes, such as motor and affective response, cognitive-related functions and modulates neurotransmitter activity. Literature remains scant concerning the parallel examination of the effects of adolescent escalating low-dose Δ⁹ -tetrahydrocannabinol (Δ⁹ -THC) on the behavioral and plasticity profile of adult rats in both sexes. Herein, we investigated the long-term behavioral, neurochemical and neurobiological effects of adolescent escalating low Δ⁹ -THC doses in adult male and female rats. In adult males, adolescent low-dose Δ⁹ -THC exposure led to increased spontaneous locomotor activity, impaired behavioral motor habituation and defective short-term spatial memory, paralleled with decreased BDNF protein levels in the prefrontal cortex. In this brain area, serotonergic activity was increased, as depicted by the increased serotonin turnover rate, while the opposite effect was observed in the hippocampus, a region where SERT levels were enhanced by Δ⁹ -THC, compared with vehicle. In adult females, adolescent Δ⁹ -THC treatment led to decreased spontaneous vertical activity and impaired short-term spatial memory, accompanied by increased BDNF protein levels in the prefrontal cortex. Present findings emphasize the key role of adolescent escalating low Δ⁹ -THC exposure in the long-term regulation of motor response, spatial-related cognitive functions and neuroplasticity indices in adulthood. In this framework, these changes could, at a translational level, contribute to clinical issues suggesting the development of psychopathology in a sex-differentiated manner following Δ⁹ -THC exposure during adolescence.

Cannabidiol and the Remainder of the Plant Extract Modulate the Effects of Δ9-Tetrahydrocannabinol on Fear Memory Reconsolidation

Background: Δ9-Tetrahydrocannabinol (THC, a CB1 receptor agonist) and Cannabidiol (CBD, a non-competitive antagonist of endogenous CB1 and CB2 ligands) are two primary components of Cannabis species, and may modulate fear learning in mammals. The CB1 receptor is widely distributed throughout the cortex and some limbic regions typically associated with fear learning. Humans with posttraumatic disorder (PTSD) have widespread upregulation of CB1 receptor density and reduced availability of endogenous cannabinoid anandamide, suggesting a role for the endocannabinoid system in PTSD. Pharmacological blockade of memory reconsolidation following recall of a conditioned response modulates the expression of learned fear and may represent a viable target for the development of new treatments for PTSD. In this study, we focused on assessing the impact of the key compounds of the marijuana plant both singly and, more importantly, in concert on attenuation of learned fear. Specifically, we assessed the impact of THC, CBD, and/or the remaining plant materials (post-extraction; background material), on reconsolidation of learned fear.

Method: Male Sprague-Dawley rats received six 1.0 mA continuous foot shocks (contextual training). Twenty-four hours later, rats were re-exposed to the context. Immediately following memory retrieval (recall) rats received oral administration of low dose THC, high dose THC, CBD, CBD + low THC, CBD + high THC [as isolated phytochemicals and, in separate experiments, in combination with plant background material (BM)]. Rodents were tested for freezing response context re-exposure at 24 h and 7 days following training.

Results: CBD alone, but not THC alone, significantly attenuated fear memory reconsolidation when administered immediately after recall. The effect persisted for at least 7 days. A combination of CBD and THC also attenuated the fear response. Plant BM also significantly attenuated reconsolidation of learned fear both on its own and in combination with THC and CBD. Finally, THC attenuated reconsolidation of learned fear only when co-administered with CBD or plant BM.

Conclusion: CBD may provide a novel treatment strategy for targeting fear-memories. Furthermore, plant BM also significantly attenuated the fear response. However, whereas THC alone had no significant effects, its effects were modulated by the addition of other compounds. Future research should investigate some of the other components present in the plant BM (such as terpenes) for their effects alone, or in combination with isolated pure cannabinoids, on fear learning.

Fast and Sensitive Quantification of Δ9-Tetrahydrocannabinol and Its Main Oxidative Metabolites by Liquid Chromatography/Tandem Mass Spectrometry

Introduction: Few animal studies have evaluated the pharmacological effects of Δ9-tetrahydrocannabinol (THC) in relation to its pharmacokinetic properties. Understanding this relationship is essential, however, if comparisons are to be drawn across conditions-such as sex, age, and route of administration-which are associated with variations in the absorption, metabolism, and distribution of THC. As a first step toward addressing this gap, in this report, we describe a rapid, sensitive, and accurate method for the quantification of THC and its main oxidative metabolites, and apply it to representative rodent tissues. Materials and Methods: The sample workup procedure consisted of two steps: bulk protein precipitation with cold acetonitrile (ACN) followed by phospholipid removal by elution through Captiva-Enhanced Matrix Removal cartridges. The liquid chromatography/tandem mass spectrometry (LC/MS-MS) protocol utilized a commercially available C18 reversed-phase column and a simple methanol/water gradient system. The new method was validated following Food and Drug Administration (FDA) guidelines, and was applied to the quantification of THC and its main oxidative metabolites-11-hydroxy-Δ9-tetrahydrocannabinol (11-OH-THC) and 11-nor-9-carboxy-Δ9-tetrahydrocannabinol (11-COOH-THC)-in plasma and brain of mice treated with a single intraperitoneal dose of THC (10 mg/kg). Results: ACN precipitation and column elution effectively depleted matrix constituents-most notably choline-containing phospholipids-which are known to interfere with THC analysis, with average recovery values of >85% for plasma and >80% for brain. The LC conditions yielded baseline separation of all analytes in a total run time of 7 min (including re-equilibration). The 10-point calibration curves showed excellent linearity (R 2>0.99) over a wide range of concentrations (1-1000 pmol/100 μL). Lowest limit of quantification was 2 pmol/100 μL for all analytes, and lowest limits of detection were 0.5 pmol/100 μL for THC and 11-OH-THC, and 1 pmol/100 μL for 11-COOH-THC. Intraday and interday accuracy and precision values were within the FDA-recommended range (±15% of nominal concentration). An application of the method to adult male mice is presented. Conclusions: We present a fast and sensitive method for the analysis of THC, which should facilitate studies aimed at linking the pharmacokinetics and pharmacodynamics of this compound in animal models.

Combined ∆9-tetrahydrocannabinol and moderate alcohol administration: effects on ingestive behaviors in adolescent male rats

RATIONALE

Whereas co-use of alcohol and marijuana is prevalent in adolescents, the effects of such drug co-exposure on ingestive and cognitive behaviors remain largely unexplored. We hypothesized that co-exposure to alcohol and ∆⁹-tetrahydrocannabinol (THC), the main psychoactive constitute of marijuana, alters feeding behavior and cognition differently from either drug alone.

METHODS

Male rats received daily THC (3-20 mg/kg/day) or oil vehicle through subcutaneous injection or consumption of a cookie with access to saccharin or saccharin-sweetened alcohol during adolescence (P30-45). Barnes maze and sucrose preference tests were applied to assess spatial memory and behavioral flexibility and abstinence-related anhedonia, respectively.

RESULTS

Subcutaneous THC did not affect alcohol intake but dose-dependently increased acute (3 h) chow intake and reduced weight gain. Moderate alcohol consumption reduced the acute hyperphagic effect of subcutaneous THC. By contrast, oral THC at a dose > 5 mg/kg robustly reduced alcohol intake without affecting 3-h chow intake. At this dose, some rats stopped consuming the THC-laced cookies. Furthermore, oral THC reduced weight gain, and co-exposure to alcohol alleviated this effect. Chronic subcutaneous, but not oral, THC reduced sucrose intake during abstinence. Neither treatment impaired cognitive behaviors in the Barnes maze.

CONCLUSION

Moderate alcohol and THC consumption can interact to elicit unique outcomes on ingestive behaviors and energy balance. Importantly, this study established a novel model of voluntary alcohol and THC consumption for studying mechanisms underlying the consequences of adolescent onset co-use of the two drugs.

Sex, THC, and hormones: Effects on density and sensitivity of CB1 cannabinoid receptors in rats

BACKGROUND

The recent NIH mandate to consider sex as a biological variable in preclinical research has focused attention on delineation of sex differences in behavior. To investigate mechanisms underlying sex differences in Δ⁹-tetrahydrocannabinol (THC) effects, we examined the effects of sex and gonadal hormones on CB₁ receptors in cerebellum, hippocampus, prefrontal cortex, and striatum.

METHODS

Adult Sprague-Dawley rats underwent gonadectomy (GDX) or sham-GDX. Half of the GDX females and males received estradiol or testosterone replacement (GDX+H), respectively. All rats were injected with vehicle or 30 mg/kg THC twice daily for 1 week before brain collection. CP55,940-stimulated [³⁵S]GTPγS and [³H]SR141716A saturation binding assays were performed.

RESULTS

With exception of enhanced receptor activation in the hippocampi of female rats compared to males, vehicle-treated rats exhibited minimal sex differences in CB₁ receptor densities or G-protein coupling. Repeated treatment with THC resulted in pronounced CB₁ receptor desensitization and downregulation in both sexes in all brain regions with a greater magnitude of change in females.

CONCLUSIONS

These results suggest that sex differences in the density and G-protein coupling of brain CB₁ receptors may play a limited role in sex differences in acute THC effects not mediated by the hippocampus. In contrast, sex differences after repeated THC were common, with females (intact, GDX, and GDX+H) showing greater downregulation or desensitization in all four brain regions compared to the respective male groups. This result is consistent with a finding that women tend to progress to tolerance and dependence quicker than men after initiation of cannabis use.

Enhancing effects of acute exposure to cannabis smoke on working memory performance

Numerous preclinical studies show that acute cannabinoid administration impairs cognitive performance. Almost all of this research has employed cannabinoid injections, however, whereas smoking is the preferred route of cannabis administration in humans. The goal of these experiments was to systematically determine how acute exposure to cannabis smoke affects working memory performance in a rat model. Adult male (n = 15) and female (n = 16) Long-Evans rats were trained in a food-motivated delayed response working memory task. Prior to test sessions, rats were exposed to smoke generated by burning different numbers of cannabis or placebo cigarettes, using a within-subjects design. Exposure to cannabis smoke had no effect on male rats' performance, but surprisingly, enhanced working memory accuracy in females, which tended to perform less accurately than males under baseline conditions. In addition, cannabis smoke enhanced working memory accuracy in a subgroup of male rats that performed comparably to the worst-performing females. Exposure to placebo smoke had no effect on performance, suggesting that the cannabinoid content of cannabis smoke was critical for its effects on working memory. Follow-up experiments showed that acute administration of either Δ9-tetrahydrocannabinol (0.0, 0.3, 1.0, 3.0 mg/kg) or the cannabinoid receptor type 1 antagonist rimonabant (0.0, 0.2, 0.6, 2.0 mg/kg) impaired working memory performance. These results indicate that differences in the route, timing, or dose of cannabinoid administration can yield distinct cognitive outcomes, and highlight the need for further investigation of this topic.

Cannabidiol modulation of antinociceptive tolerance to Δ9-tetrahydrocannabinol

RATIONALE

Humans typically self-administer cannabidiol (CBD) and delta-9-tetrahydrocannabinol (THC) together repeatedly (as in cannabis, cannabis extract, or Sativex®) to relieve pain. It has been suggested that one benefit of the drug combination may be decreased tolerance development.

OBJECTIVE

The present study compared the development of tolerance to the antinociceptive effects of THC given alone versus combined with CBD, in rats.

METHODS

THC dose-effect curves on tail withdrawal and paw pressure tests were obtained before and after twice-daily treatment with vehicle or CBD (10 mg/kg), plus vehicle or THC (3.6 mg/kg females; 9.3 mg/kg males) for 4 days.

RESULTS

On the first day, THC was more potent in females than males on both nociceptive tests. From pre- to post-chronic (day 1 to day 6), THC potency on the tail withdrawal test decreased more in females than males, and rats that had been treated with CBD + THC repeatedly showed greater rightward/downward shifts of the THC dose-effect curve than rats that had been treated with THC alone. Analysis of blood samples taken after day 6 testing showed that serum THC levels were higher in CBD + THC-treated females than in vehicle + THC-treated females, and THC's active metabolite 11-OH-THC and its inactive metabolite THC-COOH were lower in CBD + THC-treated rats than in vehicle + THC-treated rats of both sexes. CBD also increased serum levels of the active metabolite cannabinol in both sexes.

CONCLUSION

The decrease in THC's antinociceptive effects after repeated CBD exposure may be due to CBD-induced inhibition of THC metabolism, and/or antagonism of THC effects that emerges with repeated CBD treatment.

Effects of Δ9-THC and cannabidiol vapor inhalation in male and female rats

RATIONALE

Previous studies report sex differences in some, but not all, responses to cannabinoids in rats. The majority of studies use parenteral injection; however, most human use is via smoke inhalation and, increasingly, vapor inhalation.

OBJECTIVES

To compare thermoregulatory and locomotor responses to inhaled ∆⁹-tetrahydrocannabinol (THC), cannabidiol (CBD), and their combination using an e-cigarette-based model in male and female rats METHODS: Male and female Wistar rats were implanted with radiotelemetry devices for the assessment of body temperature and locomotor activity. Animals were then exposed to THC or CBD vapor using a propylene glycol (PG) vehicle. THC dose was adjusted via the concentration in the vehicle (12.5-200 mg/mL) and the CBD (100, 400 mg/mL) dose was also adjusted by varying the inhalation duration (10-40 min). Anti-nociception was evaluated using a tail-withdrawal assay following vapor inhalation. Plasma samples obtained following inhalation in different groups of rats were compared for THC content.

RESULTS

THC inhalation reduced body temperature and increased tail-withdrawal latency in both sexes equivalently and in a concentration-dependent manner. Female temperature, activity, and tail-withdrawal responses to THC did not differ between estrus and diestrus. CBD inhalation alone induced modest hypothermia and suppressed locomotor activity in both males and females. Co-administration of THC with CBD, in a 1:4 ratio, significantly decreased temperature and activity in an approximately additive manner and to similar extent in each sex. Plasma THC varied with the concentration in the PG vehicle but did not differ across rat sex.

CONCLUSION

In summary, the inhalation of THC or CBD, alone and in combination, produces approximately equivalent effects in male and female rats. This confirms the efficacy of the e-cigarette-based method of THC delivery in female rats.

Sex-specific effects of CB1 receptor antagonism and stress in adolescence on anxiety, corticosterone concentrations, and contextual fear in adulthood in rats

There is a paucity of research regarding the role of endogenous cannabinoid signalling in adolescence on brain and behaviour development. We previously demonstrated effects of repeated CB1 receptor antagonism in adolescence on socioemotional behaviours and neural protein expression 24-48 h after the last drug administration in female rats, with no effect in males. Here we investigate whether greater effects would be manifested after a lengthier delay. In Experiment 1, male and female rats were administered either 1 mg / kg of the CB1 receptor-selective antagonist AM251, vehicle (VEH), or did not receive injections (NoINJ) daily on postnatal days (PND) 30-44 either alone (no adolescent confinement stress; noACS), or in tandem with 1 h ACS. On PND 70, adolescent AM251 exposure reduced anxiety in an elevated plus maze in males, irrespective of ACS, with no effects in females. On PND 73, there were no group differences in either sex in plasma corticosterone concentrations before or after 30 min of restraint stress, although injection stress resulted in higher baseline concentrations in males. Brains were collected on PND 74, with negligible effects of either AM251 or ACS on protein markers of synaptic plasticity and of the endocannabinoid system in the hippocampus and medial prefrontal cortex. In Experiment 2, rats from both sexes were treated with vehicle or AM251 on PND 30-44 and were tested for contextual fear conditioning and extinction in adulthood. AM251 females had greater fear recall than VEH females 24 h after conditioning, with no group differences in within- or between-session fear extinction. There were no group differences in long-term extinction memory, although AM251 females froze more during a reconditioning trial compared with VEH females. There were no group differences on any of the fear conditioning measures in males. Together, these findings indicate a modest, sex-specific role of CB1 receptor signalling in adolescence on anxiety-like behaviour in males and conditioned fear behaviour in females.

The interaction of gender and cannabis in early phase psychosis

Cannabis is the third most common recreational drug used world-wide after tobacco and alcohol. Globally, cannabis legalization is becoming more common. In light of its known link to psychosis development, it is imperative that we are well-informed regarding the impact of cannabis on the course of psychosis, in both males and females. However, the majority of the work to date on the role of cannabis in psychosis outcomes has not had a gender focus, important when considering patient specific treatments. This review examines what is currently known, from gender focused studies, about the interaction of gender, cannabis use and psychotic 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.

Effects of CB1 receptor antagonism and stress exposures in adolescence on socioemotional behaviours, neuroendocrine stress responses, and expression of relevant proteins in the hippocampus and prefrontal cortex in rats

Little is known about the consequences of altered endocannabinoid signalling in adolescence. We hypothesized that CB1 receptor antagonism (AM251, 1 mg/kg) and stress exposures (1 h confinement stress) in adolescence (daily, postnatal days 30-44) would interact to increase neuroendocrine stress responses and anxiety when investigated a minimum of 24 h after drug and stress treatments; these treatment effects were independent of each other. Changes in homecage behaviour and in weight gain confirmed that both males and females were sensitive to the treatments. Nevertheless, in males, repeated AM251 administration was without effect on any of the measures investigated in days post-treatment. Males had reduced corticosterone release to the repeated stress and had increased GAD67 expression in the ventral hippocampus under baseline conditions. In females, AM251 also reduced weight gain and increased stereotypic behaviours in the homecage; these same females showed increased sociality, reduced CB1 receptor expression in the dorsal hippocampus, and increased GAD67 expression in the prefrontal cortex. Further, females exposed to repeated stress had enhanced recovery to baseline corticosterone concentrations after stress. The inclusion of a non-injected comparison group also revealed stress of injection effects in both sexes that otherwise would have been masked. Together, the findings demonstrate effects of CB1 receptor antagonism and stress that were more evident in females than males, suggesting that females may be more vulnerable to the consequences of disrupted endocannabinoid signalling during adolescence.

Mechanisms Underlying Sex Differences in Cannabis Use

Purpose of the Review

Cannabis is the most commonly used illicit substance worldwide. In recent decades, highly concentrated products have flooded the market, and prevalence rates have increased. Gender differences exist in cannabis use, as men have higher prevalence of both cannabis use and cannabis use disorder (CUD), while women progress more rapidly from first use to CUD. This paper reviews findings from preclinical and human studies examining the sex-specific neurobiological underpinnings of cannabis use and CUD, and associations with psychiatric symptoms.

Recent Findings

Sex differences exist in the endocannabinoid system, in cannabis exposure effects on brain structure and function, and in the co-occurrence of cannabis use with symptoms of anxiety, depression and schizophrenia. In female cannabis users, anxiety symptoms correlate with larger amygdala volume and social anxiety disorder symptoms correlate with CUD symptoms. Female cannabis users are reported to be especially vulnerable to earlier onset of schizophrenia, and mixed trends emerge in the correlation of depressive symptoms with cannabis exposure in females and males.

Summary

As prevalence of cannabis use may continue to increase given the shifting policy landscape regarding marijuana laws, understanding the neurobiological mechanisms of cannabis exposure in females and males is key. Examining these mechanisms may help inform future research on sex-specific pharmacological and behavioral interventions for women and men with high-risk cannabis use, comorbid psychiatric disease, and CUD.

Effects of oral Δ9-tetrahydrocannabinol on the cerebral processing of olfactory input in healthy non-addicted subjects

BACKGROUND

Considering the increasing acknowledgment of the human sense of smell as a significant component of the quality of life, olfactory drug effects gain potential clinical importance. A recent observation in a human experimental context indicated that Δ⁹-tetrahydrocannabinol (THC) impaired the subject's performance in olfactory tests. To further analyze the role of THC in human olfaction, the present report addresses its effects on the central processing of olfactory stimuli.

METHODS

Employing a placebo-controlled randomized crossover design, an oral dose of 20 mg THC was administered in 15 healthy volunteers. The central processing of olfactory input, consisting of short pulses of gaseous vanillin or hydrogen sulfide, and for comparison, of non-odorous but painful carbon dioxide, were investigated before and after administration of THC or placebo in a pharmacological functional magnet resonance imaging study.

RESULTS

Following THC administration, the vanillin stimuli lost their pleasantness and became hedonically inert. This observation had its functional correlate in reduced stimulus-associated brain activations located in the left amygdala, the hippocampus and superior temporal pole (peak MNI coordinates x = - 27, y = - 1, z = - 26 mm p = 0.039). Differences in amygdala activations were significantly correlated with the corresponding differences in vanillin pleasantness (p = 0.025). By contrast, no effects were observed on the perception of processing of H₂S stimuli.

CONCLUSIONS

The results support that THC induced a modulation of the central processing of olfactory input. The THC-induced reduction in the pleasantness of a pleasurable odor was accompanied by reduced activations in the limbic system. Results agree with previous observation of negative effects of cannabinoids on the human sense of smell and strengthen the evidence that THC-based medications will be among drugs with olfactory side effects.

Single and combined effects of Δ9 -tetrahydrocannabinol and cannabidiol in a mouse model of chemotherapy-induced neuropathic pain

BACKGROUND AND PURPOSE

The non-psychoactive phytocannabinoid cannabidiol (CBD) can affect the pharmacological effects of Δ⁹ -tetrahydrocannabinol (THC). We tested the possible synergy between CBD and THC in decreasing mechanical sensitivity in a mouse model of paclitaxel-induced neuropathic pain. We also tested the effects of CBD on oxaliplatin- and vincristine-induced mechanical sensitivity.

EXPERIMENTAL APPROACH

Paclitaxel-treated mice (8.0 mg·kg^-1 i.p., days 1, 3, 5 and 7) were pretreated with CBD (0.625-20.0 mg·kg^-1 i.p.), THC (0.625-20.0 mg·kg^-1 i.p.) or CBD + THC (0.04 + 0.04-20.0 + 20.0 mg·kg^-1 i.p.), and mechanical sensitivity was assessed on days 9, 14 and 21. Oxaliplatin-treated (6.0 mg·kg^-1 i.p., day 1) or vincristine-treated mice (0.1 mg·kg^-1 i.p. days 1-7) were pretreated with CBD (1.25-10.0 mg·kg^-1 i.p.), THC (10.0 mg·kg^-1 i.p.) or THC + CBD (0.16 mg·kg^-1 THC + 0.16 mg·kg^-1 CBD i.p.).

KEY RESULTS

Both CBD and THC alone attenuated mechanical allodynia in mice treated with paclitaxel. Very low ineffective doses of CBD and THC were synergistic when given in combination. CBD also attenuated oxaliplatin- but not vincristine-induced mechanical sensitivity, while THC significantly attenuated vincristine- but not oxaliplatin-induced mechanical sensitivity. The low dose combination significantly attenuated oxaliplatin- but not vincristine-induced mechanical sensitivity.

CONCLUSIONS AND IMPLICATIONS

CBD may be potent and effective at preventing the development of chemotherapy-induced peripheral neuropathy, and its clinical use may be enhanced by co-administration of low doses of THC. These treatment strategies would increase the therapeutic window of cannabis-based pharmacotherapies.

Cannabidiol-Δ9-tetrahydrocannabinol interactions on acute pain and locomotor activity

BACKGROUND

Previous studies suggest that cannabidiol (CBD) may potentiate or antagonize Δ⁹-tetrahydrocannabinol's (THC) effects. The current study examined sex differences in CBD modulation of THC-induced antinociception, hypolocomotion, and metabolism.

METHODS

In Experiment 1, CBD (0, 10 or 30mg/kg) was administered 15min before THC (0, 1.8, 3.2, 5.6 or 10mg/kg), and rats were tested for antinociception and locomotion 15-360min post-THC injection. In Experiments 2 and 3, CBD (30mg/kg) was administered 13h or 15min before THC (1.8mg/kg); rats were tested for antinociception and locomotion 30-480min post-THC injection (Experiment 2), or serum samples were taken 30-360min post-THC injection to examine CBD modulation of THC metabolism (Experiment 3).

RESULTS

In Experiment 1, CBD alone produced no antinociceptive effects, while enhancing THC-induced paw pressure but not tail withdrawal antinociception 4-6h post-THC injection. CBD alone increased locomotor activity at 6h post-injection, but enhanced THC-induced hypolocomotion 4-6h post-THC injection, at lower THC doses. There were no sex differences in CBD-THC interactions. In Experiments 2 and 3, CBD did not significantly enhance THC's effects when CBD was administered 13h or 15min before THC; however, CBD inhibited THC metabolism, and this effect was greater in females than males.

CONCLUSIONS

These results suggest that CBD may enhance THC's antinociceptive and hypolocomotive effects, primarily prolonging THC's duration of action; however, these effects were small and inconsistent across experiments. CBD inhibition of THC metabolism as well other mechanisms likely contribute to CBD-THC interactions on behavior.

Association between cannabis use and methadone maintenance treatment outcomes: an investigation into sex differences

Background

Cannabis will soon become legalized in Canada, and it is currently unclear how this will impact public health. Methadone maintenance treatment (MMT) is the most common pharmacological treatment for opioid use disorder (OUD), and despite its documented effectiveness, a large number of patients respond poorly and experience relapse to illicit opioids. Some studies implicate cannabis use as a risk factor for poor MMT response. Although it is well established that substance-use behaviors differ by sex, few of these studies have considered sex as a potential moderator. The current study aims to investigate sex differences in the association between cannabis use and illicit opioid use in a cohort of MMT patients.

Methods

This multicentre study recruited participants on MMT for OUD from Canadian Addiction Treatment Centre sites in Ontario, Canada. Sex differences in the association between any cannabis use and illicit opioid use were investigated using multivariable logistic regression. A secondary analysis was conducted to investigate the association with heaviness of cannabis use.

Results

The study included 414 men and 363 women with OUD receiving MMT. Cannabis use was significantly associated with illicit opioid use in women only (OR = 1.82, 95% CI 1.18, 2.82, p = 0.007). Heaviness of cannabis use was not associated with illicit opioid use in men or women.

Conclusions

This is the largest study to date examining the association between cannabis use and illicit opioid use. Cannabis use may be a sex-specific predictor of poor response to MMT, such that women are more likely to use illicit opioids if they also use cannabis during treatment. Women may show improved treatment outcomes if cannabis use is addressed during MMT.

Comparison of the discriminative stimulus and response rate effects of Δ9-tetrahydrocannabinol and synthetic cannabinoids in female and male rats

BACKGROUND

Women report greater sensitivity to the subjective effects of Δ⁹-tetrahydrocannabinol (THC). Similarly, female rodents tend to be more sensitive to some pharmacological effects of THC and synthetic cannabinoids. This study examined sex differences in discriminative stimulus and response rate effects of THC and synthetic cannabinoids in rats.

METHODS

A cumulative dosing THC discrimination procedure was utilized to evaluate sex differences in the discriminative stimulus effects of THC and three synthetic cannabinoids: CP47,497, WIN55,212-2, and JWH-018. Sex differences in the effects of these four compounds and a degradant of A-834735 on response rates also were assessed in a food-reinforced discrete dosing procedure.

RESULTS

Females required a lower training dose than males for acquisition of the discrimination. Further, THC was more potent at producing rimonabant-reversible discriminative stimulus and response rate effects in females. While synthetic cannabinoids were more potent in producing THC-like effects than was THC in female rats, greater discrepancies were observed in male rats. Similar sensitivity to the response rate-decreasing effects induced by most, but not all (A-834735 degradant), synthetic cannabinoids was seen in both sexes.

CONCLUSIONS

This study represents one of the first direct comparisons of sex differences in THC discrimination. Females were more sensitive to THC's effects, which may be related, in part, to sex differences in THC metabolism. Synthetic cannabinoids were more potent than THC in both sexes, but were considerably more so in male than in female rats. Future research should emphasize further characterization of sex differences in cannabinoid pharmacology.

Gonadal hormone modulation of ∆9-tetrahydrocannabinol-induced antinociception and metabolism in female versus male rats

The gonadal hormones testosterone (T) in adult males and estradiol (E2) in adult females have been reported to modulate behavioral effects of ∆⁹-tetrahydrocannabinol (THC). This study determined whether activational effects of T and E2 are sex-specific, and whether hormones modulate production of the active metabolite 11-hydroxy-THC (11-OH-THC) and the inactive metabolite 11-nor-9-carboxy-THC (THC-COOH). Adult male and female rats were gonadectomized (GDX) and treated with nothing (0), T (10-mm Silastic capsule/100g body weight), or E2 (1-mm Silastic capsule/rat). Three weeks later, saline or the cytochrome P450 inhibitor proadifen (25mg/kg; to block THC metabolism and boost THC's effects) was injected i.p.; 1h later, vehicle or THC (3mg/kg females, 5mg/kg males) was injected i.p., and rats were tested for antinociceptive and motoric effects 15-240min post-injection. T did not consistently alter THC-induced antinociception in males, but decreased it in females (tail withdrawal test). Conversely, T decreased THC-induced catalepsy in males, but had no effect in females. E2 did not alter THC-induced antinociception in females, but enhanced it in males. The discrepant effects of T and E2 on males' and females' behavioral responses to THC suggests that sexual differentiation of THC sensitivity is not simply due to activational effects of hormones, but also occurs via organizational hormone or sex chromosome effects. Analysis of serum showed that proadifen increased THC levels, E2 increased 11-OH-THC in GDX males, and T decreased 11-OH-THC (and to a lesser extent, THC) in GDX females. Thus, hormone modulation of THC's behavioral effects is caused in part by hormone modulation of THC oxidation to its active metabolite. However, the fact that hormone modulation of metabolism did not alter THC sensitivity similarly on all behavioral measures within each sex suggests that other mechanisms also play a role in gonadal hormone modulation of THC sensitivity in adult rats.

Sex differences in cannabinoid-regulated biology: A focus on energy homeostasis

Considerable strides have been made over the past 20 years in our understanding of the ligands, receptor subtypes, signal transduction mechanisms and biological actions comprising the endocannabinoid system. From the ever-expanding number of studies that have been conducted during this time, it has become increasingly clear that sex differences are the cornerstone of cannabinoid-regulated biology. Available evidence has demonstrated that these sex differences endure in the absence of gonadal steroids, and are modulated by the acute, activational effects of these hormones. This review focuses on select aspects of sexually differentiated, cannabinoid-regulated biology, with a particular emphasis on the control of energy balance. It is anticipated that it will lend impactful insight into the pervasive and diverse disparities in how males and females respond to cannabinoids--from the organismal level down to the molecular level. Additionally, it will furnish a newfound appreciation for the need to recalibrate our thinking in terms of how cannabinoids are used as therapeutic adjuvants for a broad range of clinical disorders and associated comorbidities, including body wasting and obesity.

Effects of CB1 receptor agonism and antagonism on behavioral fear and physiological stress responses in adult intact, ovariectomized, and estradiol-replaced female rats

There is growing interest in the development of cannabis-based therapies for the treatment of fear and anxiety disorders. There are a few studies, but none in females, of the effects of the highly selective cannabinoid receptor type 1 (CB1) agonist, arachidonyl 2'-chlorethylamide (ACEA), on behavioral fear. In experiment 1 involving gonadally-intact females, ACEA (either 0.1 or 0.01 mg/kg) was without effect in the elevated plus maze (EPM), and the lower dose decreased anxiety in the open field test (OFT). AM251 increased anxiety in the EPM and decreased locomotor activity in the OFT. Twenty-four hours after fear conditioning, neither ACEA nor AM251 affected generalized fear or conditioned fear recall. AM251 and 0.1 mg/kg ACEA impaired, and 0.01 mg/kg ACEA enhanced, within-session fear extinction. AM251 increased plasma corticosterone concentrations after the fear extinction session, whereas ACEA was without effect. Based on evidence that estradiol may moderate the effects of CB1 receptor signaling in females, experiment 2 involved ovariectomized (OVX) rats provided with 10-μg 17β-Estradiol and compared with OVX rats without hormone replacement (oil vehicle). Irrespective of hormone treatment, AM251 increased anxiety in the EPM, whereas ACEA (0.01 mg/kg) was without effect. Neither hormone nor drug altered anxiety in the OFT, but estradiol increased and AM251 decreased distance traveled. After fear conditioning, AM251 decreased generalized fear. Neither hormone nor drug had any effect on recall or extinction of conditioned fear, however, ACEA and AM251 increased fear-induced plasma corticosterone concentrations. Further, when results with intact rats were compared with those from OVX rats, gonadal status did not moderate the effects of either AM251 or ACEA, although OVX displayed greater anxiety and fear than did intact rats. Thus, the effects of CB1 receptor antagonism and agonism in adult female rats do not depend on ovarian estradiol.

The impact of gonadal hormones on cannabinoid dependence

Cannabis is the most widely used illicit substance in the United States. Women report greater positive subjective effects of cannabis, and greater cannabis withdrawal compared to men. Female rodents are more sensitive than males to some acute effects of Δ⁹-tetrahydrocannabinol (THC), and females also develop greater tolerance to THC in some assays. The purpose of this study was to determine whether gonadal hormones modulate THC dependence in rats. Adult rats were gonadectomized (GDX) or sham-GDX, and hormone was replaced in half of the GDX rats of each sex (testosterone in males; estradiol and/or progesterone in females). THC (30 mg/kg) or vehicle was administered twice daily for 6.5 days, followed on the seventh day by vehicle or rimonabant challenge and assessment for withdrawal-related behaviors. Sham-GDX females developed greater tolerance than males to THC-induced hypothermia, and GDX females given progesterone showed greater tolerance to THC-induced locomotor suppression. Rimonabant precipitated withdrawal, as evidenced by increased somatic signs (forepaw tremors, licking) and increased startle amplitude. Testosterone in GDX males decreased withdrawal-induced licking. Estradiol and progesterone in GDX females increased withdrawal-induced chewing, and progesterone increased withdrawal-induced sniffing. These results suggest that estradiol and progesterone may promote the development of dependence, whereas testosterone may protect against dependence. While the present study indicates that testosterone and estradiol produce opposite effects on THC-induced behavior, estradiol appears to play a broader role than testosterone in modulating THC's behavioral effects.

Hormonal status and age differentially affect tolerance to the disruptive effects of delta-9-tetrahydrocannabinol (Δ(9)-THC) on learning in female rats

The effects of hormone status and age on the development of tolerance to Δ(9)-THC were assessed in sham-operated (intact) or ovariectomized (OVX) female rats that received either intraperitoneal saline or 5.6 mg/kg of Δ(9)-THC daily from postnatal day (PD) 75-180 (early adulthood onward) or PD 35-140 (adolescence onward). During this time, the four groups for each age (i.e., intact/saline, intact/THC, OVX/saline, and OVX/THC) were trained in a learning and performance procedure and dose-effect curves were established for Δ(9)-THC (0.56-56 mg/kg) and the cannabinoid type-1 receptor (CB1R) antagonist rimonabant (0.32-10 mg/kg). Despite the persistence of small rate-decreasing and error-increasing effects in intact and OVX females from both ages during chronic Δ(9)-THC, all of the Δ(9)-THC groups developed tolerance. However, the magnitude of tolerance, as well as the effect of hormone status, varied with the age at which chronic Δ(9)-THC was initiated. There was no evidence of dependence in any of the groups. Hippocampal protein expression of CB1R, AHA1 (a co-chaperone of CB1R) and HSP90β (a molecular chaperone modulated by AHA-1) was affected more by OVX than chronic Δ(9)-THC; striatal protein expression was not consistently affected by either manipulation. Hippocampal brain-derived neurotrophic factor expression varied with age, hormone status, and chronic treatment. Thus, hormonal status differentially affects the development of tolerance to the disruptive effects of delta-9-tetrahydrocannabinol (Δ(9)-THC) on learning and performance behavior in adolescent, but not adult, female rats. These factors and their interactions also differentially affect cannabinoid signaling proteins in the hippocampus and striatum, and ultimately, neural plasticity.

Comparative effects of pulmonary and parenteral Δ⁹-tetrahydrocannabinol exposure on extinction of opiate-induced conditioned aversion in rats

RATIONALE

Evidence suggesting that the endogenous cannabinoid (eCB) system can be manipulated to facilitate or impair extinction of learned behaviours has important consequences for opiate withdrawal and abstinence. We demonstrated that the fatty acid amide hydrolase (FAAH) inhibitor URB597, which increases eCB levels, facilitates extinction of a naloxone-precipitated morphine withdrawal-induced conditioned place aversion (CPA).

OBJECTIVES

The potential of the exogenous CB1 ligand, Δ(9)-tetrahydrocannabinol (Δ(9)-THC), to facilitate extinction of this CPA was tested. Effects of both pulmonary and parenteral Δ(9)-THC exposure were evaluated using comparable doses previously determined.

METHODS

Rats trained to associate a naloxone-precipitated morphine withdrawal with a floor cue were administered Δ(9)-THC-pulmonary (1, 5, 10 mg vapour inhalation) or parenteral (0.5, 1.0, 1.5 mg/kg intraperitoneal injection)-prior to each of 20 to 28 extinction/testing trials.

RESULTS

Vapourized Δ(9)-THC facilitated extinction of the CPA in a dose- and time-dependent manner: 5 and 10 mg facilitated extinction compared to vehicle and 1 mg Δ(9)-THC. Injected Δ(9)-THC significantly impaired extinction only for the 1.0-mg/kg dose: it prolonged the CPA fourfold longer than the vehicle and 0.5- and 1.5-mg/kg doses.

CONCLUSIONS

These data suggest that both dose and route of Δ(9)-THC administration have important consequences for its pharmacokinetic and behavioural effects; specifically, pulmonary exposure at higher doses facilitates, whereas pulmonary and parenteral exposure at lower doses impairs, rates of extinction learning for CPA. Pulmonary-administered Δ(9)-THC may prove beneficial for potentiation of extinction learning for aversive memories, such as those supporting drug-craving/seeking in opiate withdrawal syndrome, and other causes of conditioned aversions, such as illness and stress.

Gonadal hormones do not alter the development of antinociceptive tolerance to delta-9-tetrahydrocannabinol in adult rats

The purpose of this study was to determine whether sex differences in the development of antinociceptive tolerance to delta-9-tetrahydrocannabinol (THC) are due to activational effects of gonadal hormones. Rats were sham-gonadectomized (sham-GDX) or gonadectomized (GDX). GDX females received no hormone replacement (GDX+0), estradiol (GDX+E2), progesterone (GDX+P4), or both (GDX+E2/P4). GDX male rats received no hormone (GDX+0) or testosterone (GDX+T). Two weeks later, antinociceptive potency of THC was determined (pre-chronic test) on the warm water tail withdrawal and paw pressure assays. Vehicle or a sex-specific THC dose (females, 5.7mg/kg, males, 9.9mg/kg) was administered twice-daily for 9days, then the THC dose-effect curves were re-determined (post-chronic test). On the pre-chronic test (both assays), THC was more potent in sham-GDX females than males, and gonadectomy did not alter this sex difference. In GDX females, P4 significantly decreased THC's antinociceptive potency, whereas E2 had no effect. In GDX males, T did not alter THC's antinociceptive potency. After chronic THC treatment, THC's antinociceptive potency was decreased more in sham-GDX females than males, on the tail withdrawal test; this sex difference in tolerance was not altered in GDX or hormone-treated groups. These results suggest that greater antinociceptive tolerance in females, which occurred despite females receiving 40% less THC than males, is not due to activational effects of gonadal hormones.

Sex differences in antinociceptive tolerance to delta-9-tetrahydrocannabinol in the rat

BACKGROUND

Sex differences in cannabinoid effects have been reported in rodents, with adult females typically being more sensitive than adult males. The present study compared the development of antinociceptive tolerance to delta-9-tetrahydrocannabinol (THC) in adult, gonadally intact female vs. male rats.

METHODS

Cumulative dose-effect curves were obtained for THC (1.0-18 mg/kg i.p.) on warm water tail withdrawal and paw pressure tests. Vehicle or the sex-specific ED80 dose for THC was administered twice daily for 9 days; THC dose-effect curves were then re-determined.

RESULTS

On the pre-chronic test day, THC was significantly more potent in females than males in producing antinociception on the tail withdrawal and paw pressure tests. After 9 days of twice-daily THC treatment (5.4 mg/kg/injection in females and 7.6 mg/kg/injection in males), THC potency on both tests decreased more in females than males. On the tail withdrawal test, chronic THC produced 4.2- vs. 2.8-fold increases in ED50 values in females vs. males, respectively. On the paw pressure test, chronic THC produced 4.4- vs. 2.9-fold increases in ED50 values in females vs. males, respectively. Chronic THC treatment did not significantly disrupt estrous cycling in females.

CONCLUSIONS

These results demonstrate that--even when sex differences in acute THC potency are controlled--females develop more antinociceptive tolerance to THC than males. Given the importance of drug tolerance in the development of drug dependence, these results suggest that females may be more vulnerable than males to developing dependence after chronic cannabinoid exposure.

A vapourized Δ(9)-tetrahydrocannabinol (Δ(9)-THC) delivery system part I: development and validation of a pulmonary cannabinoid route of exposure for experimental pharmacology studies in rodents

INTRODUCTION

Most studies evaluating the effects of Δ(9)-tetrahydrocannabinol (Δ(9)-THC) in animal models administer it via a parenteral route (e.g., intraperitoneal (IP) or intravenous injection (IV)), however, the common route of administration for human users is pulmonary (e.g., smoking or vapourizing marijuana). A vapourized Δ(9)-THC delivery system for rodents was developed and used to compare the effects of pulmonary and parenteral Δ(9)-THC administration on blood cannabinoid levels and behaviour.

METHODS

Sprague-Dawley rats were exposed to pulmonary Δ(9)-THC (1, 5, and 10mg of inhaled vapour) delivered via a Volcano® vapourizing device (Storz and Bickel, Germany) or to parenteral Δ(9)-THC (0.25, 0.5, 1.0, and 1.5mg/kg injected IP). Quantification of Δ(9)-THC and its psychoactive metabolite, 11-hydroxy-Δ(9)-THC (11-OH-Δ(9)-THC), in blood was determined by liquid chromatography/mass spectrometry (LC/MS). In order to verify the potential for the vapourization procedure to produce a robust conditioned place preference (CPP) or conditioned place avoidance CPA, classical conditioning procedures were systematically varied by altering the exposure time (10 or 20min) and number of exposed rats (1 or 2) while maintaining the same vapourization dose (10mg).

RESULTS

Blood collected at 20min intervals showed similar dose-dependent and time-dependent changes in Δ(9)-THC and 11-OH-Δ(9)-THC for both pulmonary and parenteral administration of Δ(9)-THC. However, vapourized Δ(9)-THC induced CPP under certain conditions whereas IP-administered Δ(9)-THC induced CPA.

DISCUSSION

These results support and extend the limited evidence (e.g., in humans, Naef et al., 2004; in rodents, Niyuhire et al., 2007) that Δ(9)-THC produces qualitatively different effects on behaviour depending upon the route of administration.

Sex differences in Δ(9)-tetrahydrocannabinol metabolism and in vivo pharmacology following acute and repeated dosing in adolescent rats

Mechanisms that may underlie age and sex differences in the pharmacological effects of cannabinoids are relatively unexplored. The purpose of the present study was to determine whether sex differences in metabolism of Δ(9)-tetrahydrocannabinol (THC), similar to those observed previously in adult rats, also occurred in adolescent rats and might contribute to age and sex differences in its in vivo pharmacology. Male and female adolescent rats were exposed to THC acutely or repeatedly for 10 days. Subsequently, some of the rats were sacrificed and blood and brain levels of THC and one of its metabolites, 11-hydroxy-Δ(9)-THC (11-OH-THC), were measured. Other rats were evaluated in a battery of in vivo tests that are sensitive to cannabinoids. Concentrations of 11-OH-THC in the brains of female adult and adolescent rats exceeded those observed in male conspecifics, particularly after repeated THC administration. In contrast, brain levels of THC did not differ between the sexes. In vivo, acute THC produced dose-related hypothermia, catalepsy and suppression of locomotion in adolescent rats of both sexes, with tolerance developing after repeated administration. With a minor exception, sex differences in THC's effects in the in vivo assays were not apparent. Together with previous findings, the present results suggest that sex differences in pharmacokinetics cannot fully explain the patterns of sex differences (and lack of sex differences) in cannabinoid effects across behaviors. Hormonal and/or pharmacodynamic factors are also likely to play a role.

Linkage analysis followed by association show NRG1 associated with cannabis dependence in African Americans

BACKGROUND

A genetic contribution to cannabis dependence (CaD) has been established but susceptibility genes for CaD remain largely unknown.

METHODS

We employed a multistage design to identify genetic variants underlying CaD. We first performed a genome-wide linkage scan for CaD in 384 African American (AA) and 354 European American families ascertained for genetic studies of cocaine and opioid dependence. We then conducted association analysis under the linkage peak, first using data from a genome-wide association study from the Study of Addiction: Genetics and Environment, followed by replication studies of prioritized single nucleotide polymorphisms (SNPs) in independent samples.

RESULTS

We identified the strongest linkage evidence with CaD (logarithm of odds = 2.9) on chromosome 8p21.1 in AAs. In the association analysis of the Study of Addiction: Genetics and Environment sample under the linkage peak, we identified one SNP (rs17664708) associated with CaD in both AAs (odds ratio [OR] = 2.93, p = .0022) and European Americans (OR = 1.38, p = .02). This SNP, located at NRG1, a susceptibility gene for schizophrenia, was prioritized for further study. We replicated the association of rs17664708 with CaD in an independent AAs sample (OR = 2.81, p = .0068). The joint analysis of the two AA samples demonstrated highly significant association between rs17664708 and CaD with adjustment for either global (p = .00044) or local ancestry (p = .00075).

CONCLUSIONS

Our study shows that NRG1 is probably a susceptibility gene for CaD, based on convergent evidence of linkage and replicated associations in two independent AA samples.

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.

Receptor subtypes and signal transduction mechanisms contributing to the estrogenic attenuation of cannabinoid-induced changes in energy homeostasis

We examined the receptor subtypes and signal transduction mechanisms contributing to the estrogenic modulation of cannabinoid-induced changes in energy balance. Food intake and, in some cases, O2 consumption, CO2 production and the respiratory exchange ratio were evaluated in ovariectomized female guinea pigs treated s.c. with the cannabinoid receptor agonist WIN 55,212-2 or its cremephor/ethanol/0.9% saline vehicle, and either with estradiol benzoate (EB), the estrogen receptor (ER) α agonist PPT, the ERβ agonist DPN, the Gq-coupled membrane ER agonist STX, the GPR30 agonist G-1 or their respective vehicles. Patch-clamp recordings were performed in hypothalamic slices. EB, STX, PPT and G-1 decreased daily food intake. Of these, EB, STX and PPT blocked the WIN 55,212-2-induced increase in food intake within 1-4 h. The estrogenic diminution of cannabinoid-induced hyperphagia correlated with a rapid (within 15 min) attenuation of cannabinoid-mediated decreases in glutamatergic synaptic input onto arcuate neurons, which was completely blocked by inhibition of protein kinase C (PKC) and attenuated by inhibition of protein kinase A (PKA). STX, but not PPT, mimicked this rapid estrogenic effect. However, PPT abolished the cannabinoid-induced inhibition of glutamatergic neurotransmission in cells from animals treated 24 h prior. The estrogenic antagonism of this presynaptic inhibition was observed in anorexigenic proopiomelanocortin neurons. These data reveal that estrogens negatively modulate cannabinoid-induced changes in energy balance via Gq-coupled membrane ER- and ERα-mediated mechanisms involving activation of PKC and PKA. As such, they further our understanding of the pathways through which estrogens act to temper cannabinoid sensitivity in regulating energy homeostasis in females.

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.

Sex differences in cannabinoid receptor-1 (CB1) pharmacology in mice selectively bred for high voluntary wheel-running behavior

The endocannabinoid system (ECS) is involved in regulation of various physiological functions, including locomotion, antinociception, emotional states, and motivated behaviors. The ECS has been implicated in regulation of voluntary wheel running in mice via actions at the cannabinoid receptor-1 (CB1). Previously, we showed that four replicate lines of mice bred for high levels of voluntary wheel running (high-runner or HR lines) sex-specifically (females only) decreased running in response to antagonism of the CB1 receptor, as compared with four unselected Control lines. Here, we administered a CB1 receptor agonist, WIN 55,212-2 (WIN). We predicted that if CB1 activation is involved in the regulation of voluntary wheel running, then HR mice would show a greater response to CB1 agonism. Following our previous protocols, mice from generation 53 were acclimated to running wheels for 24 days, then received, in random order, either an intra-peritoneal injection of vehicle or a low (0.5 mg/kg), medium (1 mg/kg) or high dosage (3 mg/kg) of WIN. Each mouse received an injection and then experienced two nights without injections, for a total period of 12 days. Response to WIN was quantified as wheel revolutions, time spent running, and average running speed in the 10-120 min immediately following injection. Injection decreased wheel revolutions in all mice, but male HR mice decreased their running to a greater degree relative to Controls in response to the high dose of WIN over the entire period analyzed, whereas HR females showed a differential response relative to Controls only in the latter 70-120 min post-injection. These results, in conjunction with our previous study, show that (a) aspects of endocannabinoid signaling have diverged in four lines of mice bred for high levels of voluntary exercise and (b) male and female HR mice differ from one another in CB1 signaling as it relates to wheel running.

Sexually dimorphic effects of cannabinoid compounds on emotion and cognition

This review addresses the issue of sex differences in the response to cannabinoid compounds focusing mainly on behaviors belonging to the cognitive and emotional sphere. Sexual dimorphism exists in the different components of the endocannabinoid system. Males seem to have higher CB1 receptor binding sites than females, but females seem to possess more efficient CB1 receptors. Differences between sexes have been also observed in the metabolic processing of THC, the main psychoactive ingredient of marijuana. The consistent dimorphism in the endocannabinoid system and THC metabolism may justify at least in part the different sensitivity observed between male and female animals in different behavioral paradigms concerning emotion and cognition after treatment with cannabinoid compounds. On the basis of these observations, we would like to emphasize the need of including females in basic research and to analyze results for sex differences in epidemiological studies.

Regional enhancement of cannabinoid CB&#8321; receptor desensitization in female adolescent rats following repeated Delta-tetrahydrocannabinol exposure

BACKGROUND AND PURPOSE

Disruption of the substantial re-organization of the brain during adolescence may be induced by persistent abuse of marijuana. The aim of this study was to determine whether adolescent and adult rats exhibit differential adaptation of brain cannabinoid (CB(1)) receptors after repeated exposure to Delta(9)-tetrahydrocannabinol (THC).

EXPERIMENTAL APPROACH

Rats of both ages and sexes were dosed with 10 mg kg(-1) THC or vehicle twice daily for 9.5 days. Subsequently, CB(1) receptor function and density were assessed.

KEY RESULTS

In all brain regions, THC treatment produced desensitization and down-regulation of CB(1) receptors. While the magnitude of down-regulation did not differ across groups, greater desensitization was evident in the brains of THC-treated female adolescent rats for most regions. Adolescent females showed greater desensitization than adult females in the prefrontal cortex, hippocampus, periaqueductal gray (PAG) and ventral midbrain. In contrast, adolescent males exhibited less desensitization in the prefrontal cortex, hippocampus and PAG, an effect opposite to that seen in females. With the exception of the PAG, sex differences were seen only in adolescents, with greater desensitization in the prefrontal cortex, striatum, hippocampus, PAG, and ventral midbrain of females.

CONCLUSIONS AND IMPLICATIONS

These results suggest that the brains of adolescent females may be particularly vulnerable to disruption of CB(1) receptor signalling by marijuana abuse. Alternatively, increased desensitization may reflect protective adaptation. Given the extensive re-organization of the brain during adolescence, this disruption has potential long-term consequences for maturation of the endocannabinoid system.

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.

Exposure to a high-fat diet decreases sensitivity to Δ9-tetrahydrocannabinol-induced motor effects in female rats

Arachidonic acid, a fatty acid component of neuronal cell membranes, forms the backbone of endogenous ligands of the endocannabinoid system. The lipid nature of this system may make it particularly susceptible to changes in fat content of the diet, which may, in turn, affect endocannabinoid tone and subsequent changes in receptor expression or activity. The latter would also be expected to affect responses to exogenous cannabinoids. The purpose of the present study was to determine the effects of a high-fat diet on sensitivity to the pharmacological effects of Δ(9)-tetrahydrocannabinol (Δ(9)-THC). Male and female Long-Evans rats were fed either a diet of standard rodent chow or chow enhanced with corn oil. Subsequently, they were repeatedly assessed for Δ(9)-THC-induced hypomobility, catalepsy and hypothermia. Female rats that received the high-fat diet beginning in adolescence or in adulthood became significantly less sensitive to the effects of Δ(9)-THC on motor behavior, but not its hypothermic effects, with faster development of decreased sensitivity in female rats that began the high-fat diet as adults. In contrast, diet-induced differences either did not occur, or were less pronounced, in male rats of both ages. After acute injection, brain and blood levels of Δ(9)-THC and its two primary metabolites were similar regardless of diet. Combined with the fact that diet differentially affected only some of the measures, these results suggest that pharmacokinetic differences cannot fully account for the effects of the high-fat diet on response to Δ(9)-THC. Further, these results suggest that dietary fat content may represent an important consideration in predicting the effects of marijuana in females.

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.

A follow-up study: acute behavioural effects of Delta(9)-THC in female heterozygous neuregulin 1 transmembrane domain mutant mice

RATIONALE

Heavy cannabis use is linked with an increased risk for schizophrenia. We showed previously that male heterozygous neuregulin 1 transmembrane domain (Nrg1 HET) mice are more sensitive to some effects of the psychotropic cannabis constituent Delta(9)-tetrahydrocannabinol (THC). We report data from a follow-up study in female Nrg1 HET mice, investigating THC effects on behaviours with some relevance to schizophrenia.

METHODS

Mice were injected with THC (0, 5 or 10 mg/kg i.p.) 30 min before a test battery: open field, elevated plus maze, novel object recognition (set 1) or light-dark, social interaction (SI) and prepulse inhibition (PPI 1: variable interstimulus interval (ISI); set 2). Another set (set 3) was injected with the same doses of THC before a fixed interstimulus interval PPI test (PPI 2).

RESULTS

Female Nrg1 HETs displayed the hallmark increased locomotor activity at 5 months and anxiolytic-like behaviour in the open field at 3 and 5 months. THC decreased locomotor activity in both genotypes. THC selectively reduced some SI behaviours in WT mice. Baseline PPI was enhanced in mutants under a variable ISI, while THC had no effect on PPI using either protocol.

CONCLUSIONS

This study reports novel findings on the baseline PPI profile and resistance to THC-induced social withdrawal in female Nrg1 HET mice. This is the first description of THC effects in females of this mouse model and suggests that the transmembrane domain Nrg1 mutation does not appear to have a severe impact on the behavioural sensitivity to THC in female mice.

Sexually dimorphic alterations in locomotion and reversal learning after adolescent tetrahydrocannabinol exposure in the rat

Research suggests that use and abuse of marijuana can be especially harmful if it occurs during adolescence, a period of vast developmental changes throughout the brain. We examined the effects of 2mg/kg (9)-tetrahydrocannabinol (THC) administered daily via intra-peritoneal injections during juvenile/early adolescence (postnatal day 22-40) or late adolescence (postnatal day 41-60) on locomotor activity, development of tolerance, and acquisition/retention of spatial avoidance in adulthood. THC caused locomotor depression in both male and female animals dosed during early adolescence but only in female animals dosed during late adolescence. Evidence of reverse tolerance to THC was seen in early adolescent animals only. In the active place avoidance test (APA), male and female animals administered THC during early adolescence made more errors on the reversal trial requiring flexibility in learning, but in animals dosed during late adolescence there were no significant sex or treatment differences. The results of the locomotor activity study indicate that females may be more sensitive to the effects of THC than males, while results of both locomotor activity and APA studies suggest that early adolescents appear to be more vulnerable to these effects than late adolescents/young adults.

Examining the roles of cannabinoids in pain and other therapeutic indications: a review

IMPORTANCE OF THE FIELD

In recent times, our knowledge of cannabinoids and the endocannabinoid system has greatly advanced. With expanding knowledge, synthetic cannabinoids - including nabilone, dronabinol and a combination of synthetic Delta9-THC and cannabidiol - have been developed and tested for benefit in a variety of therapeutic indications.

AREAS COVERED IN THIS REVIEW

The aim of this article is to provide a summative review of the vast amount of clinical trial data now available on these agents.

WHAT THE READER WILL GAIN

To locate clinical trials for review, a literature search was performed using PubMed between the dates of 25 May and 30 June 2009. Search parameters were set to isolate only human randomized controlled trials (RCTs) published between 1990 and 2009. Keywords consistently used for each search include: cannabinoids, marijuana, THC, nabilone and dronabinol. Preferential selection was given to the best-designed trials, focusing on placebo-controlled, double-blind RCTs with the largest patient populations, if available.

TAKE HOME MESSAGE

As efficacy and tolerability of these agents remain questionable, it is important that cannabinoids not be considered 'first-line' therapies for conditions for which there are more supported and better-tolerated agents. Instead, these agents could be considered in a situation of treatment failure with standard therapies or as adjunctive agents where appropriate.

Sex differences in the cannabinoid regulation of energy homeostasis

This review highlights the progress made thus far in characterizing the behavioral and cellular mechanisms through which cannabinoids regulate energy homeostasis. We performed microstructural analysis of feeding behavior in gonadectomized guinea pigs and gonadally intact, transgenic CB1 receptor knockout mice to determine how cannabinoids affect circadian rhythms in food intake and meal pattern. We also implanted data loggers into the abdominal cavity to correlate the appetite-modulating properties of cannabinoids with changes in core body temperature. We then coupled the effects on feeding behavior and temperature regulation with synaptic changes in the hypothalamic feeding circuitry via whole-cell patch clamp electrophysiological recording from neurons in the arcuate nucleus (ARC), in order to gain a more global perspective on the cannabinoid modulation of energy homeostasis. We observed marked sex differences in cannabinoid effects on food intake and core body temperature--with male guinea pigs exhibiting a comparatively greater sensitivity to the hyperphagia and hypophagia, as well as the hypothermia and hyperthermia, produced by CB1 receptor agonists and antagonists, respectively. In addition, male but not female CB1 receptor knockout mice show a diminished nocturnal food intake and average daily body weight relative to their wildtype littermate controls. The disparity in the CB1 receptor-mediated hyperphagia is paralleled by sex differences in the cellular effects of cannabinoids at anorexigenic, guinea pig proopiomelanocortin (POMC) synapses. Postsynaptically, cannabinoids potentiate an A-type K+ current (I(A)) in POMC neurons from female guinea pigs, whereas in males the activation of an inwardly rectifying K+ current is observed. Presynaptically, while cannabinoids inhibit glutamatergic input onto POMC neurons in males and females to similar degrees, males are more refractory to the cannabinoid-induced inhibition of convergent GABAergic input than females. These data reveal pervasive sex differences in the cannabinoid regulation of energy homeostasis that are consistent with changes in the excitability of POMC neurons.

Sex differences in the cannabinoid modulation of appetite, body temperature and neurotransmission at POMC synapses

We sought to determine whether sex differences exist for the cannabinoid modulation of appetite, body temperature and neurotransmission at pro-opiomelanocortin (POMC) synapses. Gonadectomized male and female guinea pigs were outfitted to monitor core body temperature and injected with either the CB1 receptor agonist WIN 55,212-2 (1 mg/kg s.c.), antagonist AM251 (3 mg/kg s.c.) or vehicle (1 ml/kg s.c.) and evaluated for changes in six indices of feeding behavior under ad libitum conditions for 7 days. WIN 55,212-2 elicited an overt, sexually differentiated hyperphagia in which males displayed larger increases in hourly and daily intake, consumption/gram body weight, meal size and meal duration. The agonist also produced a more robust acute hypothermia in males than in females. In addition, males were more sensitive to the hypophagic effect of AM251, manifested by comparatively sizeable decreases in hourly intake, consumption/gram body weight, meal frequency and hyperthermia. To gain additional insight into the cellular mechanism underlying cannabinoid regulation of energy homeostasis, we performed whole-cell patch clamp recordings in hypothalamic slices prepared from gonadectomized male and female guinea pigs, and monitored miniature excitatory and inhibitory postsynaptic currents (mEPSCs and mIPSCs) in arcuate (ARC) neurons. ARC neurons from females exhibited a higher basal mEPSC frequency. WIN 55,212-2 dose-dependently reduced mEPSC and mIPSC frequency; however, cells from males were far less sensitive to the CB1 receptor-mediated decrease in mIPSC frequency. These effects were observed in neurons subsequently identified as POMC neurons. These data reveal pronounced sex differences in how cannabinoids influence the hypothalamic control of homeostasis.

Sex differences in the effects of delta9-tetrahydrocannabinol on spatial learning in adolescent and adult rats

Like other recreational drugs, cannabinoids may produce different effects in men and women. In this study we measured the effects of delta9-tetrahydrocannabinol (THC) on spatial learning in two groups that are underrepresented in drug research--females and adolescents. In the first experiment, adolescent (postnatal day 30) and adult (postnatal day 70) rats of both sexes were treated subchronically with 5.0 mg/kg THC or vehicle for five consecutive days. Thirty minutes after each daily injection, they were tested on the spatial version of the Morris water maze task. In the second experiment, a separate group of adolescent and adult rats of both sexes was treated with 5.0 mg/kg THC or vehicle daily for 21 days and tested, 4 weeks later, on the spatial version of the water maze. Subchronic THC impaired spatial learning, and this effect was dependent upon both the age and sex of the animals tested. Prior exposure to chronic THC, however, did not cause any long-lasting spatial learning deficits. On the basis of our previous studies in male rats the third experiment assessed the dose-response relationship for the effects of THC on spatial learning and memory in female animals. We found that subchronic THC treatment (2.5, 5.0, or 10.0 mg/kg, intraperitoneally) disrupted learning in both adolescents and adults, but with greater effects at higher doses in adolescents compared with adults. The developmental sensitivity to subchronic THC confirms previous work carried out in our laboratory, and the sex-dependent effects highlight the importance of including females in drug abuse and addiction research.