Chronic treatment with CP 55,940 during the peri-adolescent period differentially affects the behavioural responses of male and female rats in adulthood

Alcohol and cannabis use for pain management: Translational findings of relative risks, benefits, and interactions

Chronic pain affects over 20% of the global population and contributes to the vast burden of psychiatric illness. While effective treatments for chronic pain remain limited, both alcohol and cannabis have been used for centuries to manage pain and closely associated negative affective symptoms. However, persistent misuse of alcohol and/or cannabis in such a negative reinforcement fashion is hypothesized to increase the risk of severity of substance use disorders (SUDs). The current review describes neurobiological evidence for the analgesic efficacy of alcohol and primary cannabis constituents and how use or co-use of these substances may influence SUD risk.

Maternal cannabis use in pregnancy, perinatal outcomes, and cognitive development in offspring: a longitudinal analysis of the ALSPAC cohort using paternal cannabis use as a negative control exposure

Maternal cannabis use in pregnancy is reported to be associated with perinatal and neurodevelopmental outcomes in offspring. Such associations, however, may be biased by residual confounding by socioeconomic position (SEP). To assess confounding, we use paternal cannabis use in pregnancy as a negative control exposure. We use data from 15,013 mother-father-child trios from the ALSPAC birth cohort, with participants initially recruited between 1990 and 1992. Exposures were maternal and paternal cannabis use during pregnancy. Neonatal anthropometry, perinatal, cognitive, and neurodevelopmental outcomes were modelled as a function of maternal and paternal cannabis use in pregnancy, adjusting for household-level SEP markers and maternal and paternal tobacco, alcohol, and drug use in pregnancy. We compared the strength of the association between maternal and paternal cannabis on outcomes using Wald tests. 5 and 13% of mothers and fathers reported cannabis use, which was inversely related to measures of SEP. Maternal cannabis use during pregnancy was associated with decreased infant birth weight (b = - 110.2 g, 95% CI - 185.1 to - 35.3 for any cannabis use) and length (b = - 0.45 cm, 95% CI - 0.84 to - 0.07). Maternal cannabis during pregnancy was also associated with neonatal special care admission (odds ratio 1.64, 95% CI 1.05 to 2.56) and lower education achievement scores at age 16 (b = - 19.2, 95% CI - 32.0 to - 6.3). Maternal cannabis use in pregnancy was modestly associated with perinatal outcomes and markers of cognitive development. However, most associations were attenuated after controlling for potential confounders, including SEP, and associations were not quantitatively different from paternal cannabis use. The association of maternal cannabis use in pregnancy with perinatal or cognitive outcomes in offspring may be driven by residual confounding, including SEP, rather than causal biological effects.

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

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

Age-dependent memory impairment induced by co-exposure to nicotine and a synthetic cannabinoid in mice

Co-use of marijuana and tobacco products is the second most common drug combination among adolescents. Nicotine (NIC) and cannabinoid use during adolescence induce similar detrimental changes, raising the hypothesis that simultaneous exposure could result in even more severe outcomes. Thus, we investigated whether the co-exposure to NIC and the synthetic cannabinoid WIN 55,212-2 (WIN) in adolescent mice causes behavioral outcomes different from those observed after exposure to a single drug. Male Swiss mice were exposed twice daily to NIC, WIN, or NIC + WIN during adolescence (PND28-47) or adulthood (PND70-89). Drug combination led to a greater reduction in weight gain in adolescent mice, while NIC-induced weight loss was observed in adults. During administration, NIC provoked hypothermia, and WIN produced hyperlocomotion in adolescent and adult mice. Animals exposed to NIC + WIN presented a profile of changes similar to those exposed to NIC. After drug exposure, changes in locomotion, thigmotaxis, social preference, prepulse inhibition, and working and recognition memory were evaluated. Adolescent but not adult mice exposed to NIC showed withdrawal-related hyperlocomotion unaffected by WIN co-administration. An age-specific impairment in object recognition memory was induced only by drug co-exposure during adolescence, which resolved spontaneously before reaching early adulthood. A transient decrease in hippocampal α7 nAChR subunit and CB1 receptor mRNA levels was induced by NIC exposure, which may be involved but is not enough to explain the memory impairment. Our work confirms the potential of NIC and cannabinoids association to aggravate some of the individual drug effects during critical neurodevelopmental periods.

Investigating the "two-hit hypothesis": Effects of prenatal maternal immune activation and adolescent cannabis use on neurodevelopment in mice

Prenatal exposure to maternal immune activation (MIA) and chronic adolescent cannabis use are both risk factors for neuropsychiatric disorders. However, exposure to a single risk factor may not result in major mental illness, indicating that multiple exposures may be required for illness onset. Here, we examine whether combined exposure to prenatal MIA and adolescent delta-9-tetrahydrocannabinol (THC), the main psychoactive component of cannabis, lead to enduring neuroanatomical and behavioural changes in adulthood. Mice were prenatally exposed to viral mimetic, poly I:C (5 mg/kg), or vehicle at gestational day (GD) 9, and postnatally exposed to chronic THC (5 mg/kg, intraperitoneal) or vehicle during adolescence (postnatal day [PND]28-45). Longitudinal magnetic resonance imaging (MRI) was performed pre-treatment, PND 25, post-treatment, PND 50, and in adulthood, PND85, followed by behavioural tests for anxiety-like, social, and sensorimotor gating. Post-mortem assessment of cannabinoid (CB)1 and 2 receptor expressing cells was performed in altered regions identified by MRI (anterior cingulate and somatosensory cortices, striatum, and hippocampus). Subtle deviations in neurodevelopmental trajectory and subthreshold anxiety-like behaviours were observed in mice exposed to both risk factors. Sex-dependent effects were observed in patterns of shared brain-behaviour covariation, indicative of potential sex differences in response to MIA and THC. Density of CB1 and CB2 receptor positive cells was significantly decreased in all mice exposed to MIA, THC, or both. These findings suggest that there may be a cumulative effect of risk factor exposure on gross neuroanatomical development, and that the endocannabinoid system may be sensitive to both prenatal MIA, adolescent THC, or the combination.

How High? Trends in Cannabis Use Prior to First Admission to Inpatient Psychiatry in Ontario, Canada, between 2007 and 2017

OBJECTIVES

To examine the trends in cannabis use within 30 days of first admission to inpatient psychiatry in Ontario, Canada, between 2007 and 2017, and the characteristics of persons reporting cannabis use.

METHODS

A retrospective cross-sectional analysis was conducted for first-time admissions to nonforensic inpatient psychiatric beds in Ontario, Canada, between January 1, 2007, and December 31, 2017, using data from the Ontario Mental Health Reporting System (N = 81,809).

RESULTS

Across all years, 20.1% of patients reported cannabis use within 30 days of first admission. Use increased from 16.7% in 2007 to 25.9% in 2017, and the proportion with cannabis use disorders increased from 3.8% to 6.0%. In 2017, 47.9% of patients aged 18 to 24 and 39.2% aged 25 to 34 used cannabis, representing absolute increases of 8.3% and 10.7%, respectively. Increases in cannabis use were found across almost all diagnostic groups, with the largest increases among patients with personality disorders (15% increase), schizophrenia or other psychotic disorders (14% increase), and substance use disorders (14% increase). A number of demographic and clinical factors were significantly associated with cannabis use, including interactions between schizophrenia and gender (area under the curve = 0.88).

CONCLUSIONS

As medical cannabis policies in Canada have evolved, cannabis use reported prior to first admission to inpatient psychiatry has increased. The findings of this study establish a baseline for evaluating the impact of changes in cannabis-related policies in Ontario on cannabis use prior to admission to inpatient psychiatry.

A review of the effects of acute and chronic cannabinoid exposure on the stress response

While cannabis has been used for centuries for its stress-alleviating properties, the effects of acute and chronic cannabinoid exposure on responses to stress remain poorly understood. This review provides an overview of studies that measured stress-related endpoints following acute or chronic cannabinoid exposure in humans and animals. Acute cannabinoid exposure increases basal concentrations of stress hormones in rodents and humans and has dose-dependent effects on stress reactivity in humans and anxiety-like behavior in rodents. Chronic cannabis exposure is associated with dampened stress reactivity, a blunted cortisol awakening response (CAR), and flattened diurnal cortisol slope in humans. Sex differences in these effects remain underexamined, with limited evidence for sex differences in effects of cannabinoids on stress reactivity in rodents. Future research is needed to better understand sex differences in the effects of cannabis on the stress response, as well as downstream impacts on mental health and stress-related disorders.

Effects of repeated adolescent exposure to cannabis smoke on cognitive outcomes in adulthood

BACKGROUND

Cannabis (marijuana) is the most widely used illicit drug in the USA, and consumption among adolescents is rising. Some animal studies show that adolescent exposure to delta 9-tetrahydrocannabinol or synthetic cannabinoid receptor 1 agonists causes alterations in affect and cognition that can persist into adulthood. It is less clear, however, whether similar alterations result from exposure to cannabis via smoke inhalation, which remains the most frequent route of administration in humans.

AIMS

To begin to address these questions, a rat model was used to determine how cannabis smoke exposure during adolescence affects behavioral and cognitive outcomes in adulthood.

METHODS

Adolescent male Long-Evans rats were assigned to clean air, placebo smoke, or cannabis smoke groups. Clean air or smoke exposure sessions were conducted daily during adolescence (from P29-P49 days of age ) for a total of 21 days, and behavioral testing began on P70.

RESULTS

Compared to clean air and placebo smoke conditions, cannabis smoke significantly attenuated the normal developmental increase in body weight, but had no effects on several measures of either affect/motivation (open field activity, elevated plus maze, instrumental responding under a progressive ratio schedule of reinforcement) or cognition (set shifting, reversal learning, intertemporal choice). Surprisingly, however, in comparison to clean air controls rats exposed to either cannabis or placebo smoke in adolescence exhibited enhanced performance on a delayed response working memory task.

CONCLUSIONS

These findings are consistent with a growing body of evidence for limited long-term adverse cognitive and affective consequences of adolescent exposure to relatively low levels of cannabinoids.

Inhibition of Fatty Acid Amide Hydrolase (FAAH) During Adolescence and Exposure to Early Life Stress may Exacerbate Depression-like Behaviors in Male and Female Rats

Early-life stress (ELS) is associated with later onset of depression. Early cannabis use may be a risk factor that interacts with environmental factors to increase the risk of psychopathologies. We aimed to examine the long-term effects of ELS on depression- and anxiety-like behavior, and examine whether chronic fatty acid amide hydrolase (FAAH) inhibition during mid-adolescence could ameliorate or exacerbate ELS effects on behavior. Male and female rats were exposed to ELS during post-natal days (P) 7-14, injected with the FAAH inhibitor URB597 (0.4 mg/kg, i.p.) or vehicle for 2 weeks during mid-adolescence (P30-45) or late-adolescence (P45-60). Rats were tested in adulthood for behavior and alterations in CB1 receptors (CB1r) and glucocorticoid receptors (GRs) in the brains' stress circuit. ELS produced decreased social preference, impaired social recognition, increased learned helplessness and anxiety-like behavior. Administering URB597 during mid-adolescence did not prevent the deleterious long-term effects of ELS on behavior in males and females. When URB597 was administered during late-adolescence, it ameliorated ELS-induced depression- and anxiety-like behavior. Moreover, in males, ELS and URB597 decreased CB1r levels in the prefrontal cortex (PFC) and CA1 and GRs in the PFC and basolateral amygdala (BLA). In females, ELS and URB decreased CB1r in the BLA and GRs in the CA1 and BLA. The findings suggest that mid-adolescence, as opposed to late-adolescence, may not be a potential developmental period for chronic treatment with FAAH inhibitors and that sex-dependent alterations in CB1r and GRs expression in the BLA-PFC-CA1 circuit may contribute to the depressive behavioral phenotype.

Antidepressant-like effects of URB597 and JZL184 in male and female rats exposed to early life stress

Early life stress (ELS) may increase predisposition to depression. Despite extensive research, there is still a lack of knowledge of how to optimally treat depression. We aimed to establish a role for the endocannabinoid (ECB) system within the hippocampal-nucleus accumbens (NAc) network as a possible effective target in combating the pathophysiological development of depression-like behavior and neuronal alterations that are precipitated by ELS. Male and female rats were exposed to ELS during post-natal days (P) 7-14, injected with the fatty acid amide hydrolase (FAAH) inhibitor URB597 or the monoacylglycerol lipase (MAGL) inhibitor JZL184 for 2 weeks during late-adolescence (P45-60). Rats were tested starting at P90 for depressive- and anxiety-like behaviors as well as social preference and recognition; alterations in FAAH and MAGL activity; the expression of brain-derived neurotrophic factor (BDNF); and plasticity in the hippocampal-NAc pathway. FAAH and MAGL inhibitors during late-adolescence prevented: (i) the long-term effects of ELS on depression- and anxiety-like behavior and the impairment in social behavior and neuronal plasticity in males and females; (ii) ELS-induced alterations in MAGL activity in males' hippocampus and females' hippocampus and NAc; and (iii) ELS-induced alterations in BDNF in males' hippocampus and NAc and females' hippocampus. Significant correlations were observed between alterations in MAGL and BDNF levels and the behavioral phenotype. The findings suggest that alterations in MAGL activity and BDNF expression in the hippocampal-NAc network contribute to the depressive-like behavioral phenotype in ELS males and females. Moreover, the study suggests FAAH and MAGL inhibitors as potential intervention drugs for depression.

Effects of cannabis exposure in the prenatal and adolescent periods: Preclinical and clinical studies in both sexes

Cannabis is the most commonly used illicit drug among adolescents and young adults, including pregnant women. There is substantial evidence for a significant association between prenatal cannabis exposure and lower birth weight in offspring, and mixed results regarding later behavioural outcomes in the offspring. Adolescent cannabis use, especially heavy use, has been associated with altered executive function, depression, psychosis and use of other drugs later in life. Human studies have limitations due to several confounding factors and have provided scarce information about sex differences. In general, animal studies support behavioural alterations reported in humans and have revealed diverse sex differences and potential underlying mechanisms (altered mesolimbic dopaminergic and hippocampal glutamatergic systems and interference with prefrontal cortex maturation). More studies are needed that analyse sex and gender influences on cannabis-induced effects with great clinical relevance such as psychosis, cannabis use disorder and associated comorbidities, to achieve more personalized and accurate treatments.

Adolescent drug exposure: A review of evidence for the development of persistent changes in brain function

Over the past decade, many studies have indicated that adolescence is a critical period of brain development and maturation. The refinement and maturation of the central nervous system over this prolonged period, however, makes the adolescent brain highly susceptible to perturbations from acute and chronic drug exposure. Here we review the preclinical literature addressing the long-term consequences of adolescent exposure to common recreational drugs and drugs-of-abuse. These studies on adolescent exposure to alcohol, nicotine, opioids, cannabinoids and psychostimulant drugs, such as cocaine and amphetamine, reveal a variety of long-lasting behavioral and neurobiological consequences. These agents can affect development of the prefrontal cortex and mesolimbic dopamine pathways and modify the reward systems, socio-emotional processing and cognition. Other consequences include disruption in working memory, anxiety disorders and an increased risk of subsequent drug abuse in adult life. Although preventive and control policies are a valuable approach to reduce the detrimental effects of drugs-of-abuse on the adolescent brain, a more profound understanding of their neurobiological impact can lead to improved strategies for the treatment and attenuation of the detrimental neuropsychiatric sequelae.

Disrupting the endocannabinoid system in early adolescence negatively impacts sociability

Animal models suggest that the endocannabinoid system (eCS) helps regulate various aspects of social behavior, including play behavior and social reward, during adolescence. Properly tuned endocannabinoid signaling may be a critical developmental component in the emergence of normal adult sociability. In the current experiment, we attempted to pharmacologically disrupt endocannabinoid tone during early adolescence, and then measure the behavioral effects at two subsequent time points. 36 male and 36 female Long Evans rats received daily injections of one of three treatments between post-natal day (PND) 25-39: 1) vehicle treatment, 2) 0.4 mg/kg CP55,940 (a potent CB1/CB2 receptor agonist), or 3) 0.5 mg/kg AM251 (a CB1 receptor antagonist/inverse agonist). Both soon after treatment (PND 40-44) and several weeks later (PND 66-70), subjects were tested in an elevated plus maze (EPM) for anxiety and in a three-chambered apparatus for sociability. For the latter test, the number of entries into each chamber and the amount of time spent investigating each target were measured. Analyses revealed significant main effects of both sex and age on sociability: males expressed greater sociability compared to females, and sociability was higher in adolescence than adulthood. Most importantly, drug treatment (both CP55,940 and AM251) attenuated sociability in adolescence without having a significant effect on anxiety in the EPM. However, this effect did not persist into adulthood. These results indicate that pharmacological disruption of endocannabinoid tone - through either chronic agonism or antagonism of cannabinoid receptors - during early adolescence has a detrimental effect on sociability. This effect may be caused by transient, compensatory alterations in the eCS.

An Investigation of Neurochemical Changes in Chronic Cannabis Users

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

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.

Cannabinoid and nicotine exposure during adolescence induces sex-specific effects on anxiety- and reward-related behaviors during adulthood

Nicotine and cannabis use during adolescence has the potential to induce long lasting changes on affective and cognitive function. Here, we examined whether adolescent exposure to nicotine, the cannabinoid agonist WIN55-212,2 (WIN), or co-exposure to both would alter operant learning, locomotion, and anxiety- and reward-related behaviors in male and female mice during adulthood. Males exposed to a moderate dose of WIN (2 mg/kg) or co-exposed to nicotine and the moderate dose of WIN exhibited decreased anxiety-associated behaviors and increased cognitive flexibility, but did not differ in operant learning or generalized locomotion. In contrast, differences were not found among the females in these measures at the moderate WIN dose or in both sexes with exposure to a low WIN dose (0.2 mg/kg). Furthermore, a sex-dependent dissociative effect was found in natural reward consumption. Males exposed to the moderate dose of WIN or co-exposed to nicotine and the moderate dose of WIN demonstrated increased sucrose consumption. In contrast, females exposed to the moderate dose of WIN exhibited a decrease in sucrose consumption, which was ameliorated with co-administration of nicotine. Together, these novel findings demonstrate that adolescent exposure to cannabinoids in the presence or absence of nicotine results in altered affective and reward-related behaviors during adulthood.

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

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

The Modulating Role of Sex and Anabolic-Androgenic Steroid Hormones in Cannabinoid Sensitivity

Cannabis is the most commonly used illicit drug worldwide. Although its use is associated with multiple adverse health effects, including the risk of developing addiction, recreational and medical cannabis use is being increasing legalized. In addition, use of synthetic cannabinoid drugs is gaining considerable popularity and is associated with mass poisonings and occasional deaths. Delineating factors involved in cannabis use and addiction therefore becomes increasingly important. Similarly to other drugs of abuse, the prevalence of cannabis use and addiction differs remarkably between males and females, suggesting that sex plays a role in regulating cannabinoid sensitivity. Although it remains unclear how sex may affect the initiation and maintenance of cannabis use in humans, animal studies strongly suggest that endogenous sex hormones modulate cannabinoid sensitivity. In addition, synthetic anabolic-androgenic steroids alter substance use and further support the importance of sex steroids in controlling drug sensitivity. The recent discovery that pregnenolone, the precursor of all steroid hormones, controls cannabinoid receptor activation corroborates the link between steroid hormones and the endocannabinoid system. This article reviews the literature regarding the influence of endogenous and synthetic steroid hormones on the endocannabinoid system and cannabinoid action.

Adolescent cannabinoid exposure effects on natural reward seeking and learning in rats

RATIONALE

Adolescence is characterized by endocannabinoid (ECB)-dependent refinement of neural circuits underlying emotion, learning, and motivation. As a result, adolescent cannabinoid receptor stimulation (ACRS) with phytocannabinoids or synthetic agonists like "Spice" cause robust and persistent changes in both behavior and circuit architecture in rodents, including in reward-related regions like medial prefrontal cortex and nucleus accumbens (NAc).

OBJECTIVES AND METHODS

Here, we examine persistent effects of ACRS with the cannabinoid receptor 1/2 specific agonist WIN55-212,2 (WIN; 1.2 mg/kg/day, postnatal day (PD) 30-43), on natural reward-seeking behaviors and ECB system function in adult male Long Evans rats (PD 60+).

RESULTS

WIN ACRS increased palatable food intake, and altered attribution of incentive salience to food cues in a sign-/goal-tracking paradigm. ACRS also blunted hunger-induced sucrose intake, and resulted in increased anandamide and oleoylethanolamide levels in NAc after acute food restriction not seen in controls. ACRS did not affect food neophobia or locomotor response to a novel environment, but did increase preference for exploring a novel environment.

CONCLUSIONS

These results demonstrate that ACRS causes long-term increases in natural reward-seeking behaviors and ECB system function that persist into adulthood, potentially increasing liability to excessive natural reward seeking later in life.

Preclinical Studies of Cannabinoid Reward, Treatments for Cannabis Use Disorder, and Addiction-Related Effects of Cannabinoid Exposure

Cannabis use has become increasingly accepted socially and legally, for both recreational and medicinal purposes. Without reliable information about the effects of cannabis, people cannot make informed decisions regarding its use. Like alcohol and tobacco, cannabis can have serious adverse effects on health, and some people have difficulty discontinuing their use of the drug. Many cannabis users progress to using and becoming addicted to other drugs, but the reasons for this progression are unclear. The natural cannabinoid system of the brain is complex and involved in many functions, including brain development, reward, emotion, and cognition. Animal research provides an objective and controlled means of obtaining information about: (1) how cannabis affects the brain and behavior, (2) whether medications can be developed to treat cannabis use disorder, and (3) whether cannabis might produce lasting changes in the brain that increase the likelihood of becoming addicted to other drugs. This review explains the tactics used to address these issues, evaluates the progress that has been made, and offers some directions for future research.

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.

Chronic Δ⁸-THC Exposure Differently Affects Histone Modifications in the Adolescent and Adult Rat Brain

Adolescence represents a vulnerable period for the psychiatric consequences of delta9-tetrahydrocannabinol (Δ⁸-THC) exposure, however, the molecular underpinnings of this vulnerability remain to be established. Histone modifications are emerging as important epigenetic mechanisms involved in the etiopathogenesis of psychiatric diseases, thus, we investigated the impact of chronic Δ⁸-THC exposure on histone modifications in different brain areas of female rats. We checked histone modifications associated to both transcriptional repression (H3K9 di- and tri-methylation, H3K27 tri-methylation) and activation (H3K9 and H3K14 acetylation) after adolescent and adult chronic Δ⁸-THC exposure in the hippocampus, nucleus accumbens, and amygdala. Chronic exposure to increasing doses of Δ⁸-THC for 11 days affected histone modifications in a region- and age-specific manner. The primary effect in the adolescent brain was represented by changes leading to transcriptional repression, whereas the one observed after adult treatment led to transcriptional activation. Moreover, only in the adolescent brain, the primary effect was followed by a homeostatic response to counterbalance the Δ⁸-THC-induced repressive effect, except in the amygdala. The presence of a more complex response in the adolescent brain may be part of the mechanisms that make the adolescent brain vulnerable to Δ⁸-THC adverse effects.

Evidence for the Risks and Consequences of Adolescent Cannabis Exposure

OBJECTIVE

This review of the scientific literature examines the potential adult sequelae of exposure to cannabis and related synthetic cannabinoids in adolescence. We examine the four neuropsychiatric outcomes that are likely most vulnerable to alteration by early cannabinoid use, as identified within both the clinical and preclinical research: cognition, emotional functioning, risk for psychosis, and addiction.

METHOD

A literature search was conducted through PubMed, PsychInfo, and Google Scholar with no publication date restrictions. The search terms used were "adolescent" and "adult," and either "cannabis," "marijuana," "delta-9-tetra-hydrocannabinol," or "cannabinoid," which was then crossed with one or more of the following terms: "deficit," "impairment," "alteration," "long-term," "persistent," "development," "maturation," and "pubescent."

RESULTS

The majority of the clinical and preclinical data point to a strong correlation between adolescent cannabinoid exposure and persistent, adverse neuropsychiatric outcomes in adulthood. Although the literature supports the hypothesis that adolescent cannabis use is connected to impaired cognition and mental health in adults, it does not conclusively demonstrate that cannabis consumption alone is sufficient to cause these deficits in humans. The animal literature, however, clearly indicates that adolescent-onset exposure to cannabinoids can catalyze molecular processes that lead to persistent functional deficits in adulthood, deficits that are not found to follow adult-onset exposure and that model some of the adverse outcomes reported in humans among adult populations of early-onset cannabis users.

CONCLUSION

Based on the data in the current literature, a strong association is found between early, frequent, and heavy adolescent cannabis exposure and poor cognitive and psychiatric outcomes in adulthood, yet definite conclusions cannot yet be made as to whether cannabis use alone has a negative impact on the human adolescent brain. Future research will require animal models and longitudinal studies to be carefully designed with a focus on integrating assessments of molecular, structural, and behavioral outcomes in order to elucidate the full range of potential adverse and long-term consequences of cannabinoid exposure in adolescence.

Consequences of adolescent use of alcohol and other drugs: Studies using rodent models

Studies using animal models of adolescent exposure to alcohol, nicotine, cannabinoids, and the stimulants cocaine, 3,4-methylenedioxymethampethamine and methamphetamine have revealed a variety of persisting neural and behavioral consequences. Affected brain regions often include mesolimbic and prefrontal regions undergoing notable ontogenetic change during adolescence, although it is unclear whether this represents areas of specific vulnerability or particular scrutiny to date. Persisting alterations in forebrain systems critical for modulating reward, socioemotional processing and cognition have emerged, including apparent induction of a hyper-dopaminergic state with some drugs and/or attenuations in neurons expressing cholinergic markers. Disruptions in cognitive functions such as working memory, alterations in affect including increases in social anxiety, and mixed evidence for increases in later drug self-administration has also been reported. When consequences of adolescent and adult exposure were compared, adolescents were generally found to be more vulnerable to alcohol, nicotine, and cannabinoids, but generally not to stimulants. More work is needed to determine how adolescent drug exposure influences sculpting of the adolescent brain, and provide approaches to prevent/reverse these effects.

What Can Rats Tell Us about Adolescent Cannabis Exposure? Insights from Preclinical Research

Marijuana is the most widely used drug of abuse among adolescents. Adolescence is a vulnerable period for brain development, during which time various neurotransmitter systems such as the glutamatergic, GABAergic, dopaminergic, and endocannabinoid systems undergo extensive reorganization to support the maturation of the central nervous system (CNS). ▵-9-tetrahydrocannabinol (THC), the psychoactive component of marijuana, acts as a partial agonist of CB1 cannabinoid receptors (CB1Rs). CB1Rs are abundant in the CNS and are central components of the neurodevelopmental changes that occur during adolescence. Thus, overactivation of CB1Rs by cannabinoid exposure during adolescence has the ability to dramatically alter brain maturation, leading to persistent and enduring changes in adult cerebral function. Increasing preclinical evidence lends support to clinical evidence suggesting that chronic adolescent marijuana exposure may be associated with a higher risk for neuropsychiatric diseases, including schizophrenia. In this review, we present a broad overview of current neurobiological evidence regarding the long-term consequences of adolescent cannabinoid exposure on adult neuropsychiatric-like disorders.

The Impact of Exposure to Cannabinoids in Adolescence: Insights From Animal Models

The regular use of cannabis during adolescence is of particular concern because use by this age group seems to be associated with an increased likelihood of deleterious consequences, as reported by several epidemiologic studies. However, despite their unquestionable value, epidemiologic data are inconclusive. Modeling the adolescent phase in animals appears to be a useful approach to investigate the impact of cannabis use on the adolescent brain. In these models, adolescent cannabinoid exposure has been reported to cause long-term impairment in specific components of learning and memory and to have differential effects on anxiety, social behavior, and depressive-like signs. These findings suggest that it may represent, per se or in association with other hits, a risk factor for developing psychotic-like symptoms in adulthood. The neurobiological bases of this association include the induction of alterations in the maturational events of the endocannabinoid system occurring in the adolescent brain. Alterations in the endocannabinoid system may profoundly dysregulate developmental processes in some neurotransmitter systems, such as gamma-aminobutyric acid and glutamate, mainly in the cortex. The resulting picture strongly resembles the one present in schizophrenic patients, highlighting the translational value of this experimental approach.

Sex and age specific effects of delta-9-tetrahydrocannabinol during the periadolescent period in the rat: The unique susceptibility of the prepubescent animal

Adolescents who use marijuana are more likely to exhibit anxiety, depression, and other mood disorders, including psychotic-like symptoms. Additionally, the age at onset of use and the stress history of the individual can affect responses to cannabis. To examine the effect of early life experience on adolescent Δ-9-tetrahydrocannabinol (THC) exposure, we exposed adolescent (postnatal day (P) 29-38) male and female rats, either shipped from a supplier or born in our vivarium, to once daily injections of 3mg/kg THC. Our findings suggest that males are more sensitive to the anxiolytic and antidepressant effects of THC, as measured by the elevated plus maze (EPM) and forced swim test (FST), respectively, than females. Exposure to the FST increased plasma corticosterone levels, regardless of drug treatment or origin and females had higher levels than males overall. Shipping increased THC responses in females (acoustic startle habituation) and in males (latency to immobility in FST). No significant effects of THC or shipping on pre-pulse inhibition were observed. Due to differences in timing of puberty in males and females during the P29-38 period of THC treatment, we also dosed female rats between P21-30 (pre-puberty) and male rats between P39-48 (puberty). Pre-pubertal animals showed reductions in anxiety on the EPM, an effect that was not seen in animals treated during puberty. These results suggest that both sexes are more susceptible to changes in emotional behavior when THC exposure occurs just prior to the onset of puberty. Within the animals dosed from P29-38, THC increased cannabinoid receptor 1 (CB1R) mRNA expression and tended to decrease CP55,940 stimulated [³⁵S]GTPγS binding in the central amygdala only of females. Therefore, early stress enhances THC responses in males (in FST) and females (ASR habituation), THC alters CB1R expression and function in females only and prepubescent rats are generally more responsive to THC than pubertal rats. In summary, THC and stress interact with the developing endocannabinoid system in a sex specific manner during the peri-pubertal period.

Developmental regulation of fear learning and anxiety behavior by endocannabinoids

The developing brain undergoes substantial maturation into adulthood and the development of specific neural structures occurs on differing timelines. Transient imbalances between developmental trajectories of corticolimbic structures, which are known to contribute to regulation over fear learning and anxiety, can leave an individual susceptible to mental illness, particularly anxiety disorders. There is a substantial body of literature indicating that the endocannabinoid (eCB) system critically regulates stress responsivity and emotional behavior throughout the life span, making this system a novel therapeutic target for stress- and anxiety-related disorders. During early life and adolescence, corticolimbic eCB signaling changes dynamically and coincides with different sensitive periods of fear learning, suggesting that eCB signaling underlies age-specific fear learning responses. Moreover, perturbations to these normative fluctuations in corticolimbic eCB signaling, such as stress or cannabinoid exposure, could serve as a neural substrate contributing to alterations to the normative developmental trajectory of neural structures governing emotional behavior and fear learning. In this review, we first introduce the components of the eCB system and discuss clinical and rodent models showing eCB regulation of fear learning and anxiety in adulthood. Next, we highlight distinct fear learning and regulation profiles throughout development and discuss the ontogeny of the eCB system in the central nervous system, and models of pharmacological augmentation of eCB signaling during development in the context of fear learning and anxiety.

Adolescent delta-9-tetrahydrocannabinol (THC) exposure fails to affect THC-induced place and taste conditioning in adult male rats

BACKGROUND

Adolescent initiation of drug use has been linked to problematic drug taking later in life and may represent an important variable that changes the balance of the rewarding and/or aversive effects of abused drugs which may contribute to abuse vulnerability. The current study examined the effects of adolescent THC exposure on THC-induced place preference (rewarding effects) and taste avoidance (aversive effects) conditioning in adulthood.

METHODS

Forty-six male Sprague-Dawley adolescent rats received eight injections of an intermediate dose of THC (3.2mg/kg) or vehicle. After these injections, animals were allowed to mature and then trained in a combined CTA/CPP procedure in adulthood (PND ~90). Animals were given four trials of conditioning with intervening water-recovery days, a final CPP test and then a one-bottle taste avoidance test.

RESULTS

THC induced dose-dependent taste avoidance but did not produce place conditioning. None of these effects was impacted by adolescent THC exposure.

CONCLUSIONS

Adolescent exposure to THC had no effect on THC taste and place conditioning in adulthood. The failure to see an effect of adolescent exposure was addressed in the context of other research that has assessed exposure of drugs of abuse during adolescence on drug reactivity in adulthood.

Evidence for a Role of Adolescent Endocannabinoid Signaling in Regulating HPA Axis Stress Responsivity and Emotional Behavior Development

Adolescence is a period characterized by many distinct physical, behavioral, and neural changes during the transition from child- to adulthood. In particular, adolescent neural changes often confer greater plasticity and flexibility, yet with this comes the potential for heightened vulnerability to external perturbations such as stress exposure or recreational drug use. There is substantial evidence to suggest that factors such as adolescent stress exposure have longer lasting and sometimes more deleterious effects on an organism than stress exposure during adulthood. Moreover, the adolescent neuroendocrine response to stress exposure is different from that of adults, suggesting that further maturation of the adolescent hypothalamic-pituitary-adrenal (HPA) axis is required. The endocannabinoid (eCB) system is a potential candidate underlying these age-dependent differences given that it is an important regulator of the adult HPA axis and neuronal development. Therefore, this review will focus on (1) the functionality of the adolescent HPA axis, (2) eCB regulation of the adult HPA axis, (3) dynamic changes in eCB signaling during the adolescent period, (4) the effects of adolescent stress exposure on the eCB system, and (5) modulation of HPA axis activity and emotional behavior by adolescent cannabinoid treatment. Collectively, the emerging picture suggests that the eCB system mediates interactions between HPA axis stress responsivity, emotionality, and maturational stage. These findings may be particularly relevant to our understanding of the development of affective disorders and the risks of adolescent cannabis consumption on emotional health and stress responsivity.

Strain and sex differences in puberty onset and the effects of THC administration on weight gain and brain volumes

The use of recreational marijuana is widespread and frequently begins and persists through adolescence. Some research has shown negative consequences of adolescent marijuana use, but this is not seen across studies, and certain factors, like genetic background and sex, may influence the results. It is critical to identify which characteristics predispose an individual to be susceptible to the negative consequences of chronic exposure to marijuana in adolescence on brain health and behavior. To this end, using males and females of two strains of rats, Long-Evans hooded (LER) and Wistar (WR) rats, we explored whether these anatomically and behaviorally dimorphic strains demonstrated differences in puberty onset and strain-specific effects of adolescent exposure to Δ9-tetrahydrocannabinol (THC), the main psychoactive component of marijuana. Daily 5 mg/kg treatment began on the day of puberty onset and continued for 14 days. Of particular interest were metrics of growth and volumetric estimates of brain areas involved in cognition that contain high densities of cannabinoid receptors, including the hippocampus and its subregions, the amygdala, and the frontal cortex. Brain volumetrics were analyzed immediately following the treatment period. LER and WR females started puberty at different ages, but no strain differences were observed in brain volumes. THC decreased weight gain throughout the treatment period for all groups. Only the hippocampus and some of its subregions were affected by THC, and increased volumes with THC administration was observed exclusively in females, regardless of strain. Long-term treatment of THC did not affect all individuals equally, and females displayed evidence of increased sensitivity to the effects of THC, and by extension, marijuana. Identifying differences in adolescent physiology of WR and LER rats could help determine the cause for strain and sex differences in brain and behavior of adults and help to refine the use of animal models in marijuana research.

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.

Sex-specific alterations in hippocampal cannabinoid 1 receptor expression following adolescent delta-9-tetrahydrocannabinol treatment in the rat

Marijuana use by adolescents has been on the rise since the early 1990s. With recent legalization and decriminalization acts passed, cannabinoid exposure in adolescents will undoubtedly increase. Human studies are limited in their ability to examine underlying changes in brain biochemistry making rodent models valuable. Studies in adult and adolescent animals show region and sex specific downregulation of the cannabinoid 1 (CB1) receptor following chronic cannabinoid treatment. However, although sex-dependent changes in behavior have been observed during the drug abstinence period following adolescent cannabinoid exposure, little is known about CB1 receptor expression during this critical time. In order to characterize CB1 receptor expression following chronic adolescent Δ-9-tetrahydrocannabinol (THC) exposure, we used [(3)H] CP55,940 binding to assess CB1 receptor expression in the dentate gyrus and areas CA1, CA2, and CA3 of the hippocampus in both male and female adolescent rats at both 24h and 2 weeks post chronic THC treatment. Consistent with other reported findings, we found downregulation of the CB1 receptor in the hippocampal formation at 24h post treatment. While this downregulation persisted in both sexes following two weeks of abstinence in the CA2 region, in females, this downregulation also persisted in areas CA1 and CA3. Expression in the dentate gyrus returned to the normal range by two weeks. These data suggest that selective regions of the hippocampus show persistent reductions in CB1 receptor expression and that these reductions are more widespread in female compared to male adolescents.

Long-term consequences of perinatal and adolescent cannabinoid exposure on neural and psychological processes

Marihuana is the most widely consumed illicit drug, even among adolescents and pregnant women. Given the critical developmental processes that occur in the adolescent and fetal nervous system, marihuana consumption during these stages may have permanent consequences on several brain functions in later adult life. Here, we review what is currently known about the long-term consequences of perinatal and adolescent cannabinoid exposure. The most consistent findings point to long-term impairments in cognitive function that are associated with structural alterations and disturbed synaptic plasticity. In addition, several neurochemical modifications are also evident after prenatal or adolescent cannabinoid exposure, especially in the endocannabinoid, glutamatergic, dopaminergic and opioidergic systems. Important sexual dimorphisms are also evident in terms of the long-lasting effects of cannabinoid consumption during pregnancy and adolescence, and cannabinoids possibly have a protective effect in adolescents who have suffered traumatic life challenges, such as maternal separation or intense stress. Finally, we suggest some future research directions that may encourage further advances in this exciting field.

Sex-dependent vulnerability to cannabis abuse in adolescence

The goal of this review is to summarize current evidence for sex differences in the response to cannabinoid compounds, focusing mainly on a specific age of exposure, i.e., adolescence. Preclinical as well as clinical studies are examined. Among the different possible underlying mechanisms, the consistent dimorphism in the endocannabinoid system and delta9-tetrahydrocannabinol metabolism may play a part. All the collected data point to the need of including females in basic research as well as of analyzing results for sex differences in epidemiological studies.

Chronic Δ⁹-tetrahydrocannabinol administration may not attenuate simian immunodeficiency virus disease progression in female rhesus macaques

Persons living with HIV/AIDS (PLWHA) frequently use cannabinoids, either recreationally by smoking marijuana or therapeutically (delta-9-tetrahydrocannabinol; Δ(9)-THC dronabinol). Previously, we demonstrated that chronic Δ(9)-THC administration decreases early mortality in male simian immunodeficiency virus (SIV)-infected macaques. In this study, we sought to examine whether similar protective effects resulted from chronic cannabinoid administration in SIV-infected female rhesus macaques. Clinical and viral parameters were evaluated in eight female rhesus macaques that received either Δ(9)-THC (0.18-0.32 mg/kg, intramuscularly, twice daily) or vehicle (VEH) starting 28 days prior to intravenous inoculation with SIVmac251. SIV disease progression was assessed by changes in body weight, mortality, viral levels in plasma and mucosal sites, and lymphocyte subsets. In contrast to our results in male animals, chronic Δ(9)-THC did not protect SIV-infected female rhesus macaques from early mortality. Markers of SIV disease, including viral load and CD4(+)/CD8(+) ratio, were not altered by Δ(9)-THC compared to control females; however, females that received chronic Δ(9)-THC did not gain as much weight as control animals. In addition, Δ(9)-THC administration increased total CXCR4 expression in both peripheral and duodenal CD4(+) and CD8(+) T lymphocytes prior to SIV inoculation. Although protection from early mortality was not evident, chronic Δ(9)-THC did not affect clinical markers of SIV disease progression. The contrasting effects of chronic Δ(9)-THC in males versus females remain to be explained, but highlight the need for further studies to explore the sex-dependent effects of Δ(9)-THC and other cannabinoids on the HIV disease course and their implications for virus transmission.

Long-term consequences of adolescent cannabinoid exposure in adult psychopathology

Marijuana is the most widely used illicit drug among adolescents and young adults. Unique cognitive, emotional, and social changes occur during this critical period of development from childhood into adulthood. The adolescent brain is in a state of transition and differs from the adult brain with respect to both anatomy (e.g., neuronal connections and morphology) and neurochemistry (e.g., dopamine, GABA, and glutamate). These changes are thought to support the emergence of adult cerebral processes and behaviors. The endocannabinoid system plays an important role in development by acting on synaptic plasticity, neuronal cell proliferation, migration, and differentiation. Delta-9-tetrahydrocanabinol (THC), the principal psychoactive component in marijuana, acts as a partial agonist of the cannabinoid type 1 receptor (CB1R). Thus, over-activation of the endocannabinoid system by chronic exposure to CB1R agonists (e.g., THC, CP-55,940, and WIN55,212-2) during adolescence can dramatically alter brain maturation and cause long-lasting neurobiological changes that ultimately affect the function and behavior of the adult brain. Indeed, emerging evidence from both human and animal studies demonstrates that early-onset marijuana use has long-lasting consequences on cognition; moreover, in humans, this use is associated with a two-fold increase in the risk of developing a psychotic disorder. Here, we review the relationship between cannabinoid exposure during adolescence and the increased risk of neuropsychiatric disorders, focusing on both clinical and animal studies.

Chronic THC during adolescence increases the vulnerability to stress-induced relapse to heroin seeking in adult rats

Cannabis derivatives are among the most widely used illicit substances among young people. The addictive potential of delta-9-tetrahydrocannabinol (THC), the major active ingredient of cannabis is well documented in scientific literature. However, the consequence of THC exposure during adolescence on occurrence of addiction for other drugs of abuse later in life is still controversial. To explore this aspect of THC pharmacology, in the present study, we treated adolescent rats from postnatal day (PND) 35 to PND-46 with increasing daily doses of THC (2.5-10mg/kg). One week after intoxication, the rats were tested for anxiety-like behavior in the elevated plus maze (EPM) test. One month later (starting from PND 75), rats were trained to operantly self-administer heroin intravenously. Finally, following extinction phase, reinstatement of lever pressing elicited by the pharmacological stressor, yohimbine (1.25mg/kg) was evaluated. Data revealed that in comparison to controls, animals treated with chronic THC during adolescence showed a higher level of anxiety-like behavior. When tested for heroin (20μg per infusion) self-administration, no significant differences were observed in both the acquisition of operant responding and heroin intake at baseline. Noteworthy, following the extinction phase, administration of yohimbine elicited a significantly higher level of heroin seeking in rats previously exposed to THC. Altogether these findings demonstrate that chronic exposure to THC during adolescence is responsible for heightened anxiety and increased vulnerability to drug relapse in adulthood.

Sex-dependent long-term effects of adolescent exposure to THC and/or MDMA on neuroinflammation and serotoninergic and cannabinoid systems in rats

BACKGROUND AND PURPOSE

Many young people consume ecstasy as a recreational drug and often in combination with cannabis. In this study, we aimed to mimic human consumption patterns and investigated, in male and female animals, the long-term effects of Δ(9) -tetrahydrocannabinol (THC) and 3,4-methylenedioxymethamphetamine (MDMA) on diverse neuroinflammation and neurotoxic markers.

EXPERIMENTAL APPROACH

Male and female Wistar rats were chronically treated with increasing doses of THC and/or MDMA during adolescence. The effects of THC and/or MDMA on glial reactivity and on serotoninergic and cannabinoid systems were assessed by immunohistochemistry in the hippocampus and parietal cortex.

KEY RESULTS

THC increased the area staining for glial fibrilar acidic protein in both sexes. In males, both drugs, either separately or in combination, increased the proportion of reactive microglia cells [ionized calcium binding adaptor molecule 1 (Iba-1)]. In contrast, in females, each drug, administered alone, decreased of this proportion, whereas the combination of both drugs resulted in a 'normalization' to control values. In males, MDMA reduced the number of SERT positive fibres, THC induced the opposite effect and the group receiving both drugs did not significantly differ from the controls. In females, MDMA reduced the number of SERT positive fibres and the combination of both drugs counteracted this effect. THC also reduced immunostaining for CB1 receptors in females and this effect was aggravated by the combination with MDMA.

CONCLUSIONS AND IMPLICATIONS

Adolescent exposure of rats to THC and/or MDMA induced long-term, sex-dependent neurochemical and glial alterations, and revealed interactions between the two drugs.

LINKED ARTICLES

This article is part of a themed section on Cannabinoids 2013. To view the other articles in this section visit http://dx.doi.org/10.1111/bph.2014.171.issue-6.

The Directive 2010/63/EU on animal experimentation may skew the conclusions of pharmacological and behavioural studies

All laboratory animals shall be provided some form of environmental enrichment (EE) in the nearest future (Directive 2010/63/EU). Displacing standard housing with EE entails the possibility that data obtained under traditional housing may be reconsidered. Specifically, while EE often contrasts the abnormalities of consolidated disease models, it also indirectly demonstrates that their validity depends on housing conditions. We mimicked a situation in which the consequences of a novel pharmacological compound were addressed before and after the adoption of the Directive. We sub-chronically exposed standard- or EE-reared adolescent CD1 mice (postnatal days 23-33) to the synthetic compound JWH-018, and evaluated its short- and long-term potential cannabinoid properties on: weight gain, locomotion, analgesia, motor coordination, body temperature, brain metabolism (¹H MRI/MRS), anxiety- and depressive-related behaviours. While several parameters are modulated by JWH-018 independently of housing, other effects are environmentally mediated. The transition from standard housing to EE shall be carefully monitored.

Chronic administration during early adulthood does not alter the hormonally-dependent disruptive effects of delta-9-tetrahydrocannabinol (Δ9-THC) on complex behavior in female rats

This study examined whether chronic Δ(9)-THC during early adulthood would produce the same hormonally-dependent deficits in learning that are produced by chronic Δ(9)-THC during adolescence. To do this, either sham-operated (intact) or ovariectomized (OVX) female rats received daily saline or 5.6 mg/kg of Δ(9)-THC i.p. for 40 days during early adulthood. Following chronic administration, and a drug-free period to train both a learning and performance task, acute dose-effect curves for Δ(9)-THC (0.56-10 mg/kg) were established in each of the four groups (intact/saline, intact/THC, OVX/saline and OVX/THC). The dependent measures of responding under the learning and performance tasks were the overall response rate and the percentage of errors. Although the history of OVX and chronic Δ(9)-THC in early adulthood did not significantly affect non-drug or baseline behavior under the tasks, acute administration of Δ(9)-THC produced both rate-decreasing and error-increasing effects on learning and performance behavior, and these effects were dependent on their hormone condition. More specifically, both intact groups were more sensitive to the rate-decreasing and error-increasing effects of Δ(9)-THC than the OVX groups irrespective of chronic Δ(9)-THC administration, as there was no significant main effect of chronic treatment and no significant interaction between chronic treatment (saline or Δ(9)-THC) and the dose of Δ(9)-THC administered as an adult. Post mortem examination of 10 brain regions also indicated there were significant differences in agonist-stimulated GTPγS binding across brain regions, but no significant effects of chronic treatment and no significant interaction between the chronic treatment and cannabinoid signaling. Thus, acute Δ(9)-THC produced hormonally-dependent effects on learning and performance behavior, but a period of chronic administration during early adulthood did not alter these effects significantly, which is contrary to what we and others have shown for chronic administration during adolescence.

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

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

Cannabis Use during Adolescent Development: Susceptibility to Psychiatric Illness

Cannabis use is increasingly pervasive among adolescents today, even more common than cigarette smoking. The evolving policy surrounding the legalization of cannabis reaffirms the need to understand the relationship between cannabis exposure early in life and psychiatric illnesses. cannabis contains psychoactive components, notably Δ(9)-tetrahydrocannabinol (THC), that interfere with the brain's endogenous endocannabinoid system, which is critically involved in both pre- and post-natal neurodevelopment. Consequently, THC and related compounds could potentially usurp normal adolescent neurodevelopment, shifting the brain's developmental trajectory toward a disease-vulnerable state, predisposing early cannabis users to motivational, affective, and psychotic disorders. Numerous human studies, including prospective longitudinal studies, demonstrate that early cannabis use is associated with major depressive disorder and drug addiction. A strong association between schizophrenia and cannabis use is also apparent, especially when considering genetic factors that interact with this environmental exposure. These human studies set a foundation for carefully controlled animal studies which demonstrate similar patterns following early cannabinoid exposure. Given the vulnerable nature of adolescent neurodevelopment and the persistent changes that follow early cannabis exposure, the experimental findings outlined should be carefully considered by policymakers. In order to fully address the growing issues of psychiatric illnesses and to ensure a healthy future, measures should be taken to reduce cannabis use among teens.

Trajectory of adolescent cannabis use on addiction vulnerability

The adolescent brain is a period of dynamic development making it vulnerable to environmental factors such as drug exposure. Of the illicit drugs, cannabis is most used by teenagers since it is perceived by many to be of little harm. This perception has led to a growing number of states approving its legalization and increased accessibility. Most of the debates and ensuing policies regarding cannabis were done without consideration of its impact on one of the most vulnerable population, namely teens, or without consideration of scientific data. We provide an overview of the endocannabinoid system in relation to adolescent cannabis exposure and provide insights regarding factors such as genetics and behavioral traits that confer risk for subsequent addiction. While it is clear that more systematic scientific studies are needed to understand the long-term impact of adolescent cannabis exposure on brain and behavior, the current evidence suggests that it has a far-reaching influence on adult addictive behaviors particularly for certain subsets of vulnerable individuals. This article is part of a Special Issue entitled 'NIDA 40th Anniversary Issue'.

Drugs of abuse and increased risk of psychosis development

OBJECTIVE

There is considerable evidence to suggest that the abuse of illicit drugs, particularly cannabis and methamphetamine, has aetiological roles in the pathogenesis of psychosis and schizophrenia. Factors that may increase susceptibility to the propsychotic effects of these drugs include the age at which the abuse starts as well as family history of genetic polymorphisms relevant to the pathophysiology of this disorder. However, the neurobiological mechanisms involved in drug abuse-associated psychosis remain largely unclear.

METHODS AND RESULTS

This paper presents an overview of the available evidence, including clinical, animal model, and molecular studies, with a focus on brain regions and neurotransmitters systems, such as dopamine and glutamate, previously implicated in psychosis.

CONCLUSION

It is clear that further studies are urgently needed to provide a greater insight into the mechanisms that mediate the long-term and neurodevelopmental effects of cannabis and methamphetamine. A dialogue between basic science and clinical research may help to identify at-risk individuals and novel pathways for treatment and prevention.