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

Patient-reported use of medical cannabis for pain, anxiety, and depression symptoms: Systematic review and meta-analysis

RATIONALE

Certifications for medical cannabis are generally restricted to a small number of specific medical conditions, yet patients frequently report symptoms of pain, anxiety, and depression as reasons for use. This is a critical concern for researchers, healthcare providers, and policymakers, yet research in this area is currently obstructed by the lack of a focused review or empirical synthesis on patient-reported reasons for medical cannabis use.

OBJECTIVES

AND METHOD: The first aim of this project was to conduct the first systematic review and meta-analysis of empirical studies of patient-reported symptoms of pain, anxiety, and depression as reasons for medical cannabis use. The second aim was to conduct an empirical assessment of the methodological quality of extant research, test for publication bias, and test sex composition and quality scores of individual studies as possible sources of observed heterogeneity.

RESULTS

Meta-analytic results indicated that pain (64%), anxiety (50%), and depression/mood (34%) were common reasons for medical cannabis use. No evidence for publication bias was detected, despite heterogeneity in prevalence rates. A comprehensive assessment of study quality identified a number of specific methodological limitations of the existing research, including challenges in patient recruitment, use of restrictive sampling frames, and a lack of randomized recruitment methods and validated assessment measures.

CONCLUSION

Findings are discussed with regard to possible explanations for current results, clinical considerations, and areas of future research that are needed to move the field forward.

Antinociceptive effects of JWH015 in female and male rats

Despite greater chronic pain prevalence in females compared with males, and the analgesic potential of cannabinoid receptor type 2 (CB2) agonists, CB2 agonists have rarely been tested in females. The aim of the present study was to compare the antinociceptive effects of a CB2-preferring agonist, (2-methyl-1-propyl-1H-indol-3-yl)-1-naphthalenylmethanone (JWH015), in female and male rats against acute pain and persistent inflammatory pain. JWH015 (5-20 mg/kg, intraperitoneally) produced dose-dependent and time-dependent increases in latency to respond on the tail withdrawal and paw pressure tests that did not differ statistically between the sexes. JWH015 dose-dependently decreased locomotor activity in both sexes, but was more potent in females than males. JWH015 produced little catalepsy in either sex. In females, the antinociceptive effects of JWH015 against acute pain were blocked by rimonabant and SR144528, whereas locomotor suppression was antagonized by rimonabant. When administered 3 days after intraplantar injection of complete Freund's adjuvant, JWH015 produced a significantly greater antiallodynic effect in females at the highest dose tested (10 mg/kg, intraperitoneally). Antiallodynic effects of JWH015 were antagonized by rimonabant and SR144528 in both sexes. These studies indicate that systemically administered JWH015 produced antinociception that was both CB1 and CB2 receptor-mediated in both sexes. Unlike [INCREMENT]-9-tetrahydrocannabinol and other nonselective cannabinoid agonists, the CB2-preferring agonist JWH015 may produce more equivalent antinociception in females and males.

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.

Δ9-tetrahydrocannabinol attenuates oxycodone self-administration under extended access conditions

Growing nonmedical use of prescription opioids is a global problem, motivating research on ways to reduce use and combat addiction. Medical cannabis ("medical marijuana") legalization has been associated epidemiologically with reduced opioid harms and cannabinoids have been shown to modulate effects of opioids in animal models. This study was conducted to determine if Δ⁹-tetrahydrocannabinol (THC) enhances the behavioral effects of oxycodone. Male rats were trained to intravenously self-administer (IVSA) oxycodone (0.15 mg/kg/infusion) during 1 h, 4 h or 8 h sessions. Following acquisition rats were exposed to THC by vapor inhalation (1 h and 8 h groups) or injection (0-10 mg/kg, i.p.; all groups) prior to IVSA sessions. Fewer oxycodone infusions were obtained by rats following vaporized or injected THC compared with vehicle treatment prior to the session. Follow-up studies demonstrated parallel dose-dependent effects of THC, i.p., on self-administration of different per-infusion doses of oxycodone and a preserved loading dose early in the session. These patterns are inconsistent with behavioral suppression. Additional groups of male and female Wistar rats were assessed for nociception following inhalation of vaporized THC (50 mg/mL), oxycodone (100 mg/mL) or the combination. Tail withdrawal latency was increased more by the THC/oxycodone combination compared to either drug alone. Similar additive antinociceptive effects were produced by injection of THC (5.0 mg/kg, i.p.) and oxycodone (2.0 mg/kg, s.c.). Together these data demonstrate additive effects of THC and oxycodone and suggest the potential use of THC to enhance therapeutic efficacy, and to reduce the abuse, of opioids.

The effects of alcohol and cannabinoid exposure during the brain growth spurt on behavioral development in rats

Cannabis is the most commonly used illicit drug among pregnant women. Moreover, over half of pregnant women who are consuming cannabis are also consuming alcohol; however, the consequences of combined prenatal alcohol and cannabis exposure on fetal development are not well understood. The current study examined behavioral development following exposure to ethanol (EtOH) and/or CP-55,940 (CP), a cannabinoid receptor agonist. From postnatal days (PD) 4-9, a period of brain development equivalent to the third trimester, Sprague-Dawley rats received EtOH (5.25 g/kg/day) or sham intubation, as well as CP (0.4 mg/kg/day) or vehicle. All subjects were tested on open field activity (PD 18-21), elevated plus maze (PD 25), and spatial learning (PD 40-46) tasks. Both EtOH and CP increased locomotor activity in the open field, and the combination produced more severe overactivity than either exposure alone. Similarly, increases in thigmotaxis in the Morris water maze were caused by either EtOH or CP alone, and were more severe with combined exposure, although only EtOH impaired spatial learning. Finally, developmental CP significantly increased time spent in the open arms on the elevated plus maze. Overall, these data indicate that EtOH and CP produce some independent effects on behavior, and that the combination produces more severe overactivity in the open field. Importantly, these data suggest that prenatal cannabis disrupts development and combined prenatal exposure to alcohol and cannabis may be particularly damaging to the developing fetus, which has implications for the lives of affected individuals and families and also for establishing public health policy.

Sex differences in antinociceptive response to Δ-9-tetrahydrocannabinol and CP 55,940 in the mouse formalin test

Cannabinoids have shown promise for the treatment of intractable pain states and may represent an alternative pharmacotherapy for pain management. A growing body of clinical evidence suggests a role for sex in pain perception and in cannabinoid response. We examined cannabinoid sensitivity and tolerance in male and female mice expressing a desensitization-resistant form (S426A/S430A) of the cannabinoid type 1 receptor (CB1R). Mice were assessed for acute and inflammatory nociceptive behaviors in the formalin test following pretreatment with either vehicle or mixed CB1R/CB2R agonists, Δ-9-tetrahydrocannabinol ([INCREMENT]-THC) (1-6 mg/kg) or CP 55,940 (0.06-0.2 mg/kg). Tolerance to the effects of 6 mg/kg [INCREMENT]-THC or 0.1 mg/kg CP 55,940 was examined by the formalin test following chronic daily dosing. Female mice showed decreased sensitivity to the effects of [INCREMENT]-THC and CP 55,940 compared with male mice. The S426A/S430A mutation increased the attenuation of nociceptive behaviors for both agonists in both sexes. Female mice displayed delayed tolerance to [INCREMENT]-THC compared with male mice, whereas the S426A/S430A mutation conferred a delay in tolerance to [INCREMENT]-THC in both sexes. Male S426A/S430A mutant mice also display resistance to tolerance to CP 55,940 compared with wild-type controls. This study demonstrates sex and genotype differences in response for two different cannabinoid agonists. The results underscore the importance of including both male and female mice in preclinical studies of pain and cannabinoid pharmacology.

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.

Cannabis Use: Neurobiological, Behavioral, and Sex/Gender Considerations

PURPOSE OF REVIEW

To summarize the current literature on the effects of cannabinoids in humans and to discuss the existing literature on the sex- and gender-related differences in the effects of cannabinoids.

RECENT FINDINGS

Cannabis and its constituent cannabinoids are associated with risk of addiction, cognitive deficits and mood/psychotic disorders. Preclinical and emerging clinical data suggest greater sensitivity to the effects of cannabinoids in women.

SUMMARY

Cannabis is one of the most commonly used drugs with increasing rates of use. Women in particular may be at a greater risk of adverse outcomes given the previously described "telescoping effect" of substance use in women. Human data examining the sex- and gender-related differences in the effects of cannabinoids and factors underlying these differences are very limited. This represents a critical gap in the literature and needs to be systematically examined in future studies.

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.

Medication overuse headache following repeated morphine, but not [INCREMENT]9-tetrahydrocannabinol administration in the female rat

The potential of [INCREMENT]-tetrahydrocannabinol (THC) as a treatment for migraine depends on antinociceptive efficacy with repeated administration. Although morphine has good antinociceptive efficacy, repeated administration causes medication overuse headache (MOH) - a condition in which the intensity/frequency of migraine increases. The present study compared the effect of repeated morphine or THC administration on the magnitude and duration of migraine-like pain induced by a microinjection of allyl isothiocyanate (AITC) onto the dura mater of female rats. Acute administration of THC or morphine prevented AITC-induced depression of wheel running. This antinociception was maintained in rats treated repeatedly with THC, but not following repeated administration of morphine. Moreover, repeated morphine, but not THC administration, extended the duration of AITC-induced depression of wheel running. These data indicate that tolerance and MOH develop rapidly to morphine administration. The lack of tolerance and MOH to THC indicates that THC may be an especially effective long-term treatment against migraine.

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.

Tolerance to hypothermic and antinoceptive effects of ∆9-tetrahydrocannabinol (THC) vapor inhalation in rats

RATIONALE

A reduced effect of a given dose of ∆⁹-tetrahydrocannabinol (THC) emerges with repeated exposure to the drug. This tolerance can vary depending on THC dose, exposure chronicity and the behavioral or physiological measure of interest. A novel THC inhalation system based on e-cigarette technology has been recently shown to produce the hypothermic and antinociceptive effects of THC in rats.

OBJECTIVE

To determine if tolerance to these effects can be produced with repeated vapor inhalation.

METHODS

Groups of male and female Wistar rats were exposed to 30 min of inhalation of the propylene glycol (PG) vehicle or THC (200 mg/mL in PG) two or three times per day for four days. Rectal temperature changes and nociception were assessed after the first exposure on the first and fourth days of repeated inhalation.

RESULTS

Female, but not male, rats developed tolerance to the hypothermic and antinociceptive effects of THC after four days of twice-daily THC vapor inhalation. Thrice daily inhalation for four days resulted in tolerance in both male and female rats. The plasma THC levels reached after a 30 min inhalation session did not differ between the male and female rats.

CONCLUSIONS

Repeated daily THC inhalation induces tolerance in female and male rats, providing further validation of the vapor inhalation method for preclinical studies.

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.

Cannabis Withdrawal: A Review of Neurobiological Mechanisms and Sex Differences

PURPOSE OF REVIEW

This report provides an updated overview of pre-clinical and clinical research on the etiology and biological substrates of the cannabis withdrawal syndrome.

RECENT FINDINGS

Long-term cannabis use is associated with downregulation of type-1 cannabinoid receptors (CB1). Reduced CB1 receptor density is related to increased withdrawal during early abstinence, and the reduction in CB1 receptor density reverses with extended abstinence. Females have been shown to have increased rate and severity of a subset of cannabis withdrawal symptoms compared with men.

SUMMARY

Recent studies have extended knowledge of the biological processes and individual difference variables that influence cannabis withdrawal. However, caveats include small sample sizes in clinical studies, participant samples that are predominantly male, and limited examinations of endocannabinoids, enzymes that degrade endocannabinoids, negative allosteric modulators, and other neurobiological systems that may directly impact cannabis withdrawal symptom expression.

Anti-nociceptive interactions between opioids and a cannabinoid receptor 2 agonist in inflammatory pain

The cannabinoid 1 receptor and cannabinoid 2 receptor can both be targeted in the treatment of pain; yet, they have some important differences. Cannabinoid 1 receptor is expressed at high levels in the central nervous system, whereas cannabinoid 2 receptor is found predominantly, although not exclusively, outside the central nervous system. The objective of this study was to investigate potential interactions between cannabinoid 2 receptor and the mu-opioid receptor in pathological pain. The low level of adverse side effects and lack of tolerance for cannabinoid 2 receptor agonists are attractive pharmacotherapeutic traits. This study assessed the anti-nociceptive effects of a selective cannabinoid 2 receptor agonist (JWH-133) in pathological pain using mice subjected to inflammatory pain using the formalin test. Furthermore, we examined several ways in which JWH-133 may interact with morphine. JWH-133 produces dose-dependent anti-nociception during both the acute and inflammatory phases of the formalin test. This was observed in both male and female mice. However, a maximally efficacious dose of JWH-133 (1 mg/kg) was not associated with somatic withdrawal symptoms, motor impairment, or hypothermia. After eleven once-daily injections of 1 mg/JWH-133, no tolerance was observed in the formalin test. Cross-tolerance for the anti-nociceptive effects of JWH-133 and morphine were assessed to gain insight into physiologically relevant cannabinoid 2 receptor and mu-opioid receptor interaction. Mice made tolerant to the effects of morphine exhibited a lower JWH-133 response in both phases of the formalin test compared to vehicle-treated morphine-naïve animals. However, repeated daily JWH-133 administration did not cause cross-tolerance for morphine, suggesting opioid and cannabinoid 2 receptor cross-tolerance is unidirectional. However, preliminary data suggest co-administration of JWH-133 with morphine modestly attenuates morphine tolerance. Isobolographic analysis revealed that co-administration of JWH-133 and morphine has an additive effect on anti-nociception in the formalin test. Overall these findings show that cannabinoid 2 receptor may functionally interact with mu-opioid receptor to modulate anti-nociception in the formalin test.

Sex-dependent effects of cannabis-induced analgesia

BACKGROUND

Preclinical studies demonstrate that cannabinoid-mediated antinociceptive effects vary according to sex; it is unknown if these findings extend to humans.

METHODS

This retrospective analysis compared the analgesic, subjective and physiological effects of active cannabis (3.56-5.60% THC) and inactive cannabis (0.00% THC) in male (N=21) and female (N=21) cannabis smokers under double-blind, placebo-controlled conditions. Pain response was measured using the Cold-Pressor Test (CPT). Participants immersed their hand in cold water (4°C); times to report pain (pain sensitivity) and withdraw the hand (pain tolerance) were recorded. Subjective drug ratings were also measured.

RESULTS

Among men, active cannabis significantly decreased pain sensitivity relative to inactive cannabis (p<0.01). In women, active cannabis failed to decrease pain sensitivity relative to inactive. Active cannabis increased pain tolerance in both men women immediately after smoking (p<0.001); a trend was observed for differences between men and women (p<0.10). Active cannabis also increased subjective ratings of cannabis associated with abuse liability ('Take again,' 'Liking,' 'Good drug effect'), drug strength, and 'High' relative to inactive in both men and women (p<0.01).

CONCLUSIONS

These results indicate that in cannabis smokers, men exhibit greater cannabis-induced analgesia relative to women. These sex-dependent differences are independent of cannabis-elicited subjective effects associated with abuse-liability, which were consistent between men and women. As such, sex-dependent differences in cannabis's analgesic effects are an important consideration that warrants further investigation when considering the potential therapeutic effects of cannabinoids for pain relief.

A Judicial Perspective on Expert Testimony in Marijuana Driving Cases

The decriminalization of marijuana and propagation of marijuana prescribed for medical reasons have resulted in an increase in driving while under the influence of marijuana. Currently, the legal definition of marijuana driving impairment varies by state across the United States. Expert witnesses such as drug recognition experts and medical toxicologists are needed during a discovery to educate attorneys and during a testimony to educate judges and juries. These proceedings provide an overview of the US case law about driving impairment, the current status of the legal thresholds used in the courts for the admission of the medical toxicologist as an expert witness in marijuana driving and related cases, and provides an understanding of evolving issues surrounding the admissibility of their scientific opinion testimony.

Marijuana, the Endocannabinoid System and the Female Reproductive System

Marijuana use among women is highly prevalent, but the societal conversation on marijuana rarely focuses on how marijuana affects female reproduction and endocrinology. This article reviews the current scientific literature regarding marijuana use and hypothalamic-pituitary-ovarian (HPO) axis regulation, ovarian hormone production, the menstrual cycle, and fertility. Evidence suggests that marijuana can reduce female fertility by disrupting hypothalamic release of gonadotropin releasing hormone (GnRH), leading to reduced estrogen and progesterone production and anovulatory menstrual cycles. Tolerance to these effects has been shown in rhesus monkeys, but the effects of chronic marijuana use on human female reproduction are largely unknown. Marijuana-induced analgesia, drug reinforcement properties, tolerance, and dependence are influenced by ovarian hormones, with estrogen generally increasing and progesterone decreasing sensitivity to marijuana. Carefully controlled regulation of the Endocannabinoid System (ECS) is required for successful reproduction, and the exogenous cannabinoids in marijuana may disrupt the delicate balance of the ECS in the female reproductive system.

Estrogen facilitates and the kappa and mu opioid receptors mediate antinociception produced by intrathecal (-)-pentazocine in female rats

Pentazocine, a mixed-action kappa opioid receptor (KOR) agonist, has high affinity for both KOR and the mu opioid receptor (MOR), and has been shown clinically to alleviate pain with a pronounced effect in women. However, whether local application of pentazocine in the spinal cord produces antinociception and the contribution of spinal KOR and MOR in mediating the effect of pentazocine in female rats remain unknown. Also, it is not known whether pentazocine-induced antinociception in females is estrogen-dependent. Hence, we investigated whether intrathecal (i.t.) (-)-pentazocine produces thermal antinociception and whether estrogen modulates the drug effect in female rats. Only the highest dose of pentazocine (500 nmol) was effective in producing antinociception in ovariectomized (OVX) rats. In contrast, pentazocine produced antinociception in estradiol-treated ovariectomized females (OVX+E) rats with the lowest effective dose being 250nmol. KOR or MOR mediated the effect of the lowest effective dose in OVX+E rats; however, MOR blockade extended the KOR-mediated effect of 500nmol pentazocine in both groups. In normally cycling females, the 250nmol dose was effective in producing antinociception at the proestrous, but not at the diestrous stage of the estrous cycle. Thus, estrogen facilitates and KOR or MOR mediates. the antinociceptive effect of i.t. (-)-pentazocine in female rats. Selective doses of (-)-pentazocine, with or without MOR blockade, may have a therapeutic benefit.

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.

Chronic Δ9-Tetrahydrocannabinol during Adolescence Differentially Modulates Striatal CB1 Receptor Expression and the Acute and Chronic Effects on Learning in Adult Rats

The purpose of this study was to determine whether chronic administration of Δ(9)-tetrahydrocannabinol (THC) during adolescence would (1) modify any sex-specific effects of THC on learning and (2) affect the development of tolerance to THC as an adult. Male and female rats received daily injections of saline or 5.6 mg/kg of THC from postnatal day 35-75, yielding four groups (female/saline, female/THC, male/saline, and male/THC). Rats were then trained on a procedure that assayed both learning and performance behavior and administered 0.32-18 mg/kg of THC acutely as adults (experiment 1). THC produced rate-decreasing and error-increasing effects in both sexes; however, female rats were more sensitive than male rats were to the rate-decreasing effects. Rats were then chronically administered 10 mg/kg of THC (experiment 2). Rats that received THC during adolescence developed tolerance to the rate-decreasing effects more slowly and less completely than did rats that received saline; in addition, females developed tolerance to the error-increasing effects of THC slower than males did. Western blot analysis of brain tissue indicated long-term changes in hippocampal and striatal cannabinoid type-1 receptor (CB1R) levels despite levels that were indistinguishable immediately after chronic treatment during adolescence. Striatal CB1R levels were increased in adult rats that received THC during adolescence; hippocampal CB1R levels varied by sex. In summary, female rats were more sensitive than male rats were to the acute and chronic effects of THC, and chronic administration of THC during adolescence produced long-term changes in CB1R levels that correlated with decreased tolerance development to the rate-decreasing effects of THC.

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.

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.

Antinociceptive effects of sinomenine in a rat model of neuropathic pain

Sinomenine is a principal ingredient of traditional Chinese medicine, Sinomenium Acutum, which has been reported to have various pharmacological effects including anti-rheumatism and immunomodulation. This study examined the effects of sinomenine in rats that received chronic constriction injury (CCI), a model of peripheral neuropathic pain. CCI injury on the right sciatic nerve led to long-lasting mechanical hyperalgesia. Acute sinomenine treatment (10-40 mg/kg, i.p.) significantly and dose-dependently reversed mechanical hyperalgesia. In addition, the antinociceptive effects of sinomenine remained stable during repeated daily treatment for up to 2 weeks. Although sinomenine did not alter the duration of immobility in the forced swimming test in healthy animals, it dose-dependently reversed the increased immobility time in rats receiving CCI, suggesting that sinomenine attenuated chronic pain-induced depressive-like behavior. The antinociceptive effects of sinomenine were blocked by the GABAa receptor antagonist bicuculine. The doses of sinomenine studied here did not significantly alter the spontaneous locomotor activity. Together, these results suggested that sinomenine exerts significant antinociceptive effects for neuropathic pain via GABAa-mediated mechanism, which suggests that sinomenine may be useful for the management of chronic painful conditions such as neuropathic pain.