Periadolescent exposure to cannabinoids alters the striatal and hippocampal dopaminergic system in the adult rat brain

Neurological Disorders Induced by Drug Use: Effects of Adolescent and Embryonic Drug Exposure on Behavioral Neurodevelopment

Clinical studies demonstrate that the risk of developing neurological disorders is increased by overconsumption of the commonly used drugs, alcohol, nicotine and cannabis. These drug-induced neurological disorders, which include substance use disorder (SUD) and its co-occurring emotional conditions such as anxiety and depression, are observed not only in adults but also with drug use during adolescence and after prenatal exposure to these drugs, and they are accompanied by long-lasting disturbances in brain development. This report provides overviews of clinical and preclinical studies, which confirm these adverse effects in adolescents and the offspring prenatally exposed to the drugs and include a more in-depth description of specific neuronal systems, their neurocircuitry and molecular mechanisms, affected by drug exposure and of specific techniques used to determine if these effects in the brain are causally related to the behavioral disturbances. With analysis of further studies, this review then addresses four specific questions that are important for fully understanding the impact that drug use in young individuals can have on future pregnancies and their offspring. Evidence demonstrates that the adverse effects on their brain and behavior can occur: (1) at low doses with short periods of drug exposure during pregnancy; (2) after pre-conception drug use by both females and males; (3) in subsequent generations following the initial drug exposure; and (4) in a sex-dependent manner, with drug use producing a greater risk in females than males of developing SUDs with emotional conditions and female offspring after prenatal drug exposure responding more adversely than male offspring. With the recent rise in drug use by adolescents and pregnant women that has occurred in association with the legalization of cannabis and increased availability of vaping tools, these conclusions from the clinical and preclinical literature are particularly alarming and underscore the urgent need to educate young women and men about the possible harmful effects of early drug use and to seek novel therapeutic strategies that might help to limit drug use in young individuals.

The long-term effects of adolescent Δ9-tetrahydrocannabinol on brain structure and function assessed through neuroimaging techniques in male and female rats

Several studies performed on human subjects have examined the effects of adolescent cannabis consumption on brain structure or function using brain imaging techniques. However, the evidence from these studies is usually heterogenous and affected by several confounding variables. Animal models of adolescent cannabinoid exposure may help to overcome these difficulties. In this exploratory study, we aim to increase our understanding of the protracted effects of adolescent Δ9-tetrahydrocannabinol (THC) in rats of both sexes using magnetic resonance (MR) to obtain volumetric data, assess grey and white matter microstructure with diffusion tensor imaging (DTI) and measure brain metabolites with 1H-MR spectroscopy (MRS); in addition, we studied brain function using positron emission tomography (PET) with 2-deoxy-2-[18F]fluoro-d-glucose as the tracer. THC-exposed rats exhibited volumetric and microstructural alterations in the striatum, globus pallidus, lateral ventricles, thalamus, and septal nuclei in a sex-specific manner. THC administration also reduced fractional anisotropy in several white matter tracts, prominently in rostral sections, while in vivo MRS identified lower levels of cortical choline compounds. THC-treated males had increased metabolism in the cerebellum and olfactory bulb and decreased metabolism in the cingulate cortex. By contrast, THC-treated females showed hypermetabolism in a cluster of voxels comprising the entorhinal piriform cortices and in the cingulate cortex. These results indicate that mild THC exposure during adolescence leaves a lingering mark on brain structure and function in a sex-dependant manner. Some of the changes found here resemble those observed in human studies and highlight the importance of studying sex-specific effects in cannabinoid research.

Δ 9-Tetrahydrocannabinol During Adolescence Reprograms the Nucleus Accumbens Transcriptome, Affecting Reward Processing, Impulsivity, and Specific Aspects of Cocaine Addiction-Like Behavior in a Sex-Dependent Manner

BACKGROUND

Cannabis exposure during adolescence is associated with emotional and motivational alterations that may entail an enhanced risk of developing psychiatric disorders. In rodent models, exposure to cannabinoids during adolescence leads to increased self-administration of opiates and cocaine, however, the psychological and neural mechanisms and the sex-specificity of this phenomenon are largely unknown.

METHODS

We exposed male and female adolescent rats to Δ9-tetrahydrocannabinol (THC) and studied at adulthood the effects of such treatment on psychological processes related to reward, such as Pavlovian conditioned approach, Pavlovian to instrumental transfer, habit formation and waiting impulsivity. In the light of these data and given the involvement of the nucleus accumbens in the processes examined, we performed an RNASeq transcriptomic study and assessed cocaine addiction-like behavior.

RESULTS

THC exposure increased goal-tracking (in males and females) and enhanced Pavlovian to instrumental transfer (especially in males) but did not affect habit formation. THC-exposed rats exhibited subtle, state-dependent changes in premature responding in the 2-CSRTT task. RNASeq data showed gene expression alterations in a marked sex-specific manner. While no effects were found on the acquisition of cocaine self-administration or punished drug-seeking, rats exposed to THC self-administered more cocaine under a progressive ratio schedule (males), had a higher rebound upon returning to continuous access to the drug (females) and showed reduced drug-seeking after 30 days of withdrawal (females).

CONCLUSIONS

Adolescent THC affects specific aspects of reward- (and cocaine-) guided behavior and the function of a key brain region mediating these effects, in a remarkable sex-specific manner.

Adolescent cannabinoid exposure modulates the vulnerability to cocaine-induced conditioned place preference and DNMT3a expression in the prefrontal cortex in Swiss mice

RATIONALE

Cannabis sativa is the most widely used drug by adolescents globally. The recreational use of synthetic cannabinoids by teenagers has also grown in recent years. Despite the wrong perception that exposure to these drugs does not cause harm, repeated exposure to cannabinoids at early stages of life compromises important maturation processes and brain development. Chronic early cannabinoid use has been related to a higher risk of psychiatric outcomes, including cocaine addiction. Evidence suggests that exposure to natural and synthetic cannabinoids during adolescence modifies molecular and behavioral effects of cocaine in adulthood. Responses to cocaine are regulated by epigenetic mechanisms, such as DNA methylation, in the brain's reward regions. However, the involvement of these processes in modulation of the vulnerability to the effects of cocaine induced by prior exposure to cannabinoids remains poorly understood.

OBJECTIVES

Investigate whether exposure to the synthetic cannabinoid WIN55,212-2 during adolescence modulates anxiety- and depression-like behavior, memory, and cocaine reward in adult mice. We also evaluated whether exposure to cannabinoids during adolescence modulates the expression of enzymes that are involved in DNA methylation.

RESULTS

Exposure to WIN55,212-2 during adolescence did not alter anxiety- or depressive-like behavior. However, prior exposure to cannabinoids inhibited cocaine-induced conditioned place preference without modulating cocaine-induced hyperlocomotion, accompanied by an increase in expression of the enzyme DNA methyltransferase 3a (DNMT3a) in the prefrontal cortex.

CONCLUSIONS

Our findings suggest that exposure to WIN55,212-2 during adolescence leads to changes in DNMT3a expression, and this pathway appears to be relevant to modulating the rewarding effects of cocaine.

Effects of Cannabinoid Exposure during Neurodevelopment on Future Effects of Drugs of Abuse: A Preclinical Perspective

The endocannabinoid system plays a central role in the earliest stages of embryonic, postnatal and adolescent neurodevelopment. Aberrant activity of this system at key developmental phases has been shown to affect neural development. The aim of this review is to synthesise and analyse preclinical insights within rodent populations, focusing on the effects that perinatal (embryonic, gestational and early postnatal developmental stages) and adolescent (postnatal day 21–60) cannabinoid exposure impose across time on the subsequent activity of various drugs of abuse. Results in rodents show that exposure to cannabinoids during the perinatal and adolescent period can lead to multifaceted behavioural and molecular changes. In the perinatal period, significant effects of Δ⁹-THC exposure on subsequent opiate and amphetamine reward-related behaviours were observed primarily in male rodents. These effects were not extended to include cocaine or alcohol. In adolescence, various cannabinoid agonists were used experimentally. This array of cannabinoids demonstrated consistent effects on opioids across sex. In contrast, no significant effects were observed regarding the future activity of amphetamines and cocaine. However, these studies focused primarily on male rodents. In conclusion, numerous gaps and limitations are apparent in the current body of research. The sparsity of studies analysing the perinatal period must be addressed. Future research within both periods must also focus on delineating sex-specific effects, moving away from a male-centric focus. Studies should also aim to utilise more clinically relevant cannabinoid treatments.

Cannabis Use and Brain Volume in Adolescent and Young Adult Cannabis Users: Effects Moderated by Sex and Aerobic Fitness

OBJECTIVES

Studies examining the impact of adolescent and young adult cannabis use on structural outcomes have been heterogeneous. One already-identified moderator is sex, while a novel potential moderator is extent of aerobic fitness. Here, we sought to investigate the associations of cannabis use, sex, and aerobic fitness levels on brain volume. Second, we explored brain-behavior relationships to interpret these findings.

METHODS

Seventy-four adolescents and young adults (36 cannabis users and 38 controls) underwent 3 weeks of monitored cannabis abstinence, aerobic fitness testing, structural neuroimaging, and neuropsychological testing. Linear regressions examined cannabis use and its interaction with sex and aerobic fitness on whole-brain cortical volume and subcortical regions of interests.

RESULTS

No main-effect differences between cannabis users and nonusers were observed; however, cannabis-by-sex interactions identified differences in frontal, temporal, and paracentral volumes. Female cannabis users generally exhibited greater volume while male users exhibited less volume compared to same-sex controls. Positive associations between aerobic fitness and frontal, parietal, cerebellum, and caudate volumes were observed. Cannabis-by-fitness interaction was linked with left superior temporal volume. Preliminary brain-behavior correlations revealed that abnormal volumes were not advantageous in either male or female cannabis users.

CONCLUSIONS

Aerobic fitness was linked with greater brain volume and sex moderated the effect of cannabis use on volume; preliminary brain-behavior correlations revealed that differences in cannabis users were not linked with advantageous cognitive performance. Implications of sex-specific subtleties and mechanisms of aerobic fitness require large-scale investigation. Furthermore, present findings and prior literature on aerobic exercise warrant examinations of aerobic fitness interventions that aimed at improving neurocognitive health in substance-using youth.

Cocaine-induced Fos expression in the rat brain: Modulation by prior Δ9-tetrahydrocannabinol exposure during adolescence and sex-specific effects

It has been suggested that cannabis consumption during adolescence may be an initial step to cocaine use in adulthood. Indeed, previous preclinical data show that adolescent exposure to cannabinoids (both natural and synthetic) potentiates cocaine self-administration in rats. Here we aimed at gaining a deeper understanding of the cellular activation patterns induced by cocaine as revealed by Fos imaging and how these patterns may change due to adolescent exposure to THC. Male and female Wistar rats were administered every other day THC (3 mg/kg i.p.) or vehicle from postnatal day 28-44. At adulthood (PND90) they were given an injection of cocaine (20 mg/kg i.p.) or saline and sacrificed 90 min later. Cocaine-induced Fos activation was measured by immunohistochemistry as an index of cellular activation. We found that cocaine-induced activation in the motor cortex was stronger in THC-exposed rats. Moreover, there was significant sex-dependent interaction between cocaine and adolescent THC exposure in the dorsal hypothalamus, suggesting that cocaine induced a more robust cellular activation in THC-exposed females but not in THC-treated males. Other THC- and cocaine-induced effects were also evident. These results add to the previous literature suggesting that the behavioral, cellular, molecular, and brain-activating actions of cocaine are modulated by early experience with cannabinoids and provide additional knowledge that may explain the enhanced actions of cocaine in rats exposed to cannabinoids during their adolescence.

Dopamine D2R is Required for Hippocampal-dependent Memory and Plasticity at the CA3-CA1 Synapse

Dopamine receptors play an important role in motivational, emotional, and motor responses. In addition, growing evidence suggests a key role of hippocampal dopamine receptors in learning and memory. It is well known that associative learning and synaptic plasticity of CA3-CA1 requires the dopamine D1 receptor (D1R). However, the specific role of the dopamine D2 receptor (D2R) on memory-related neuroplasticity processes is still undefined. Here, by using two models of D2R loss, D2R knockout mice (Drd2-/-) and mice with intrahippocampal injections of Drd2-small interfering RNA (Drd2-siRNA), we aimed to investigate how D2R is involved in learning and memory as well as in long-term potentiation of the hippocampus. Our studies revealed that the genetic inactivation of D2R impaired the spatial memory, associative learning, and the classical conditioning of eyelid responses. Similarly, deletion of D2R reduced the activity-dependent synaptic plasticity in the hippocampal CA1-CA3 synapse. Our results demonstrate the first direct evidence that D2R is essential in behaving mice for trace eye blink conditioning and associated changes in hippocampal synaptic strength. Taken together, these results indicate a key role of D2R in regulating hippocampal plasticity changes and, in consequence, acquisition and consolidation of spatial and associative forms of memory.

Adolescent Exposure to WIN 55212-2 Render the Nigrostriatal Dopaminergic Pathway Activated During Adulthood

BACKGROUND

During adolescence, neuronal circuits exhibit plasticity in response to physiological changes and to adapt to environmental events. Nigrostriatal dopaminergic pathways are in constant flux during development. Evidence suggests a relationship between early use of cannabinoids and psychiatric disorders characterized by altered dopaminergic systems, such as schizophrenia and addiction. However, the impact of adolescent exposure to cannabinoids on nigrostriatal dopaminergic pathways in adulthood remains unclear. The aim of this research was to determine the effects of repeated activation of cannabinoid receptors during adolescence on dopaminergic activity of nigrostriatal pathways and the mechanisms underlying this impact during adulthood.

METHODS

Male Sprague-Dawley rats were treated with 1.2 mg/kg WIN 55212-2 daily from postnatal day 40 to 65. Then no-net flux microdialysis of dopamine in the dorsolateral striatum, electrophysiological recording of dopaminergic neuronal activity, and microdialysis measures of gamma-aminobutyric acid (GABA) and glutamate in substantia nigra par compacta were carried out during adulthood (postnatal days 72-78).

RESULTS

Repeated activation of cannabinoid receptors during adolescence increased the release of dopamine in dorsolateral striatum accompanied by increased population activity of dopamine neurons and decreased extracellular GABA levels in substantia nigra par compacta in adulthood. Furthermore, perfusion of bicuculline, a GABAa antagonist, into the ventral pallidum reversed the increased dopamine neuron population activity in substantia nigra par compacta induced by adolescent cannabinoid exposure.

CONCLUSIONS

These results suggest that adolescent exposure to cannabinoid agonists produces disinhibition of nigrostriatal dopamine transmission during adulthood mediated by decreased GABAergic input from the ventral pallidum.

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.

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.

Cannabis and development of dual diagnoses: A literature review

BACKGROUND

The use of cannabis has garnered more attention recently with ongoing efforts at marijuana legalization. The consequences of cannabis use are not clearly understood and remain a concern.

OBJECTIVES

To review the acute and persistent effects of cannabis use and associations with psychiatric disorders.

METHODS

Using Pubmed and PsychInfo, we conducted a narrative review of the literature on cannabis and psychiatric comorbidity using the keywords cannab*, marijuana, schizo*, psychosis, mood, depression, mania, bipolar, and anxiety.

RESULTS

There is substantial evidence of cannabis use leading to other illicit drug use and of an association between cannabis use and psychosis. A few reports suggest an association with bipolar disorder while the association with depression and anxiety disorders is mixed.

CONCLUSIONS

Whenever an association is observed between cannabis use and psychiatric disorders, the relationship is generally an adverse one. Age at the time of cannabis use appears to be an important factor with stronger associations observed between adolescent onset cannabis use and later onset of psychiatric disorders. Additional studies taking into account potential confounds (such as withdrawal symptoms, periods of abstinence, and other substance use) and moderators (such as age of initiation of cannabis use, the amount and frequency of drug use, prior history of childhood maltreatment, and gender) are needed to better understand the psychiatric consequences of cannabis use.

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.

Keep off the grass? Cannabis, cognition and addiction

In an increasing number of states and countries, cannabis now stands poised to join alcohol and tobacco as a legal drug. Quantifying the relative adverse and beneficial effects of cannabis and its constituent cannabinoids should therefore be prioritized. Whereas newspaper headlines have focused on links between cannabis and psychosis, less attention has been paid to the much more common problem of cannabis addiction. Certain cognitive changes have also been attributed to cannabis use, although their causality and longevity are fiercely debated. Identifying why some individuals are more vulnerable than others to the adverse effects of cannabis is now of paramount importance to public health. Here, we review the current state of knowledge about such vulnerability factors, the variations in types of cannabis, and the relationship between these and cognition and addiction.

Effects of Cannabinoid Exposure during Adolescence on the Conditioned Rewarding Effects of WIN 55212-2 and Cocaine in Mice: Influence of the Novelty-Seeking Trait

Adolescent exposure to cannabinoids enhances the behavioural effects of cocaine, and high novelty-seeking trait predicts greater sensitivity to the conditioned place preference (CPP) induced by this drug. Our aim was to evaluate the influence of novelty-seeking on the effects of adolescent cannabinoid exposure. Adolescent male mice were classified as high or low novelty seekers (HNS and LNS) in the hole-board test. First, we evaluated the CPP induced by the cannabinoid agonist WIN 55212-2 (0.05 and 0.075 mg/kg, i.p.) in HNS and LNS mice. Then, HNS and LNS mice were pretreated i.p. with vehicle, WIN 55212-2 (0.1 mg/kg), or cannabinoid antagonist rimonabant (1 mg/kg) and were subsequently conditioned with WIN 55212-2 (0.05 mg/kg, i.p.) or cocaine (1 or 6 mg/kg, i.p.). Only HNS mice conditioned with the 0.075 mg/kg dose acquired CPP with WIN 55212-2. Adolescent exposure to this cannabinoid agonist increased the rewarding effects of 1 mg/kg of cocaine in both HNS and LNS mice, and in HNS mice it also increased the reinstating effect of a low dose of cocaine. Our results endorse a role for individual differences such as a higher propensity for sensation-seeking in the development of addiction.

Changes in D1 but not D2 dopamine or mu-opioid receptor expression in limbic and motor structures after lateral hypothalamus electrical self-stimulation: A quantitative autoradiographic study

Intracranial self-stimulation (ICSS) of the lateral hypothalamus (LH) is involved in the activation of neuroanatomical systems that are also associated with the processing of natural and other artificial rewarding stimuli. Specific components of this behavior (hedonic impact, learning, and motor behavior) may involve changes in different neurotransmitters, such as dopamine and opioids. In this study, quantitative autoradiography was used to examine changes in mu-opioid and D1/D2-dopamine receptor expression in various anatomical regions related to the motor and mesolimbic reward systems after intracranial self-stimulation of the LH. Results of the behavioral procedure and subsequent radiochemical assays show selective changes in D1 but not D2 or mu receptors in Accumbens-Shell, Ventral Pallidum, Caudate-Putamen, and Medial Globus Pallidus. These findings are discussed in relation to the different psychobiological components of the appetitive motivational system, identifying some dissociation among them, particularly with respect to the involvement of the D1-dopamine subsystem (but not D2 or mu receptors) in goal-directed behaviors.

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, drugs, and adult neurogenesis: sex-dependent effects of escalating adolescent cannabinoid exposure on adult hippocampal neurogenesis, stress reactivity, and amphetamine sensitization

Cannabinoid exposure during adolescence has adverse effects on neuroplasticity, emotional behavior, cognition, and reward sensitivity in adult rats. We investigated whether escalating doses of the cannabinoid receptor 1 (CB1 R) agonist, HU-210, in adolescence would affect adult hippocampal neurogenesis and behavioral processes putatively modulated by hippocampal neurogenesis, in adult male and female Sprague-Dawley rats. Escalating doses of HU-210 (25, 50, and 100 µg/kg), or vehicle were administered from postnatal day (PND) 35 to 46. Animals were left undisturbed until PND 70, when they were treated with 5-bromo-2-deoxyuridine (BrdU; 200 mg/kg) and perfused 21 days later to examine density of BrdU-ir and BrdU/NeuN cells in the dentate gyrus. In another cohort, hypothalamic-pituitary-adrenal (HPA) axis reactivity to an acute restraint stress (30 min; PND 75) and behavioral sensitization to d-amphetamine sulfate (1-2 mg/kg; PND 105-134) were assessed in adulthood. Adolescent HU-210 administration suppressed the density of BrdU-ir cells in the dentate gyrus in adult male, but not adult female rats. Adolescent HU-210 administration also induced significantly higher peak corticosterone levels and reminiscent of the changes in neurogenesis, this effect was more pronounced in adult males than females. However, adolescent cannabinoid treatment resulted in significantly higher stereotypy scores in adult female, but not male, rats. Thus, adolescent CB1 R activation suppressed hippocampal neurogenesis and increased stress responsivity in adult males, but not females, and enhanced amphetamine sensitization in adult female, but not male, rats. Taken together, increased CB1 R activation during adolescence results in sex-dependent, long-term, changes to hippocampal structure and function, an effect that may shed light on differing vulnerabilities to developing disorders following adolescent cannabinoid exposure, based on sex.

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.

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.

Differential modulations of striatal tyrosine hydroxylase and dopamine metabolism by cannabinoid agonists as evidence for functional selectivity in vivo

It is generally assumed that cannabinoids induce transient modulations of dopamine transmission through indirect regulation of its release. However, we previously described a direct cannabinoid-mediated control of tyrosine hydroxylase (TH) expression, in vitro. We herein report on the influence of cannabinoid agonists on the expression of this key enzyme in catecholamine synthesis as well as on the modification of dopamine content in adult rats. As expected for cannabinoid agonists, the exposure to either Δ(9)-THC, HU 210 or CP 55,940 induced both catalepsy and hypolocomotion. Supporting a possible long-lasting control on dopaminergic activity, we noticed a significant HU 210-mediated increase in TH expression in the striatum that was concomitant with an increase in striatal dopamine content. Surprisingly, while a similar trend was reported with Δ(9)-THC, CP 55,940 completely failed to modulate TH expression or dopamine content. Nevertheless, the access of CP 55,940 to brain structures was validated by determinations of drug concentrations in the tissue and by ex vivo binding experiments. Furthermore, confirming the central activity of CP 55,940, the analysis of dopamine metabolites revealed a reduction in striatal DOPAC concentrations. Consistent with the involvement of the CB(1) cannabinoid receptor in these different responses, both HU 210- and CP 55,940-mediated effects were prevented by SR 141716A. Therefore, the present data suggest that both HU 210 and CP 55,940 cause a delayed/persistent regulation of the dopamine neurotransmission system. Nevertheless, these commonly used cannabinoid agonists endowed with similar pharmacodynamic properties clearly triggered distinct biochemical responses highlighting the existence of functional selectivity in vivo.

Sex-specific disturbances of the glutamate/GABA balance in the hippocampus of adult rats subjected to adolescent cannabinoid exposure

Adolescence is a period of active synaptic remodelling and plasticity and as such, a developmental phase of particular vulnerability to the effects of environmental insults. The endogenous cannabinoid system regulates central nervous system development and cannabinoid exposure during adolescence has been linked to several alterations to hippocampal-dependent processes such as cognition and emotion, which rely on intact glutamatergic and GABAergic systems. Here we show that K(+)-induced γ-amino butyric acid (GABA) release increases in the CA1 hippocampal field of Wistar rats of both sexes that were treated chronically with the cannabinoid agonist CP 55,940 (CP55940) during adolescence. GABA(B) receptors levels also increased in cannabinoid-exposed rats. In addition, CP55940-treated females exhibit reduced GABA transporter gene expression (GAT-1), increased GABA(A) receptor expression, as well as decreased K(+)-induced glutamate release and NMDA receptor levels. CP55940 administration did not affect the glial (EAAT2) or neuronal (EAAT3) glutamate transporter gene expression in either males or females, and nor were any changes in the mGlu5 receptor protein levels observed. Taken together, these results show that while the exacerbated GABA release induced by early cannabinoid exposure may be compensated by an increment in GABA(B) receptors, which normally function as inhibitory autoreceptors, adolescent cannabinoid exposure in the females disturbs the normal balance between glutamate and GABA transmission. These observations may provide important insight into the neuronal basis of the well-documented alterations in cognitive and emotional processes induced by adolescent cannabinoid exposure.

History of cannabis use is not associated with alterations in striatal dopamine D2/D3 receptor availability

Cannabis use in adolescence is emerging as a risk factor for the development of psychosis. In animal studies, Δ9-tetrahydrocannabinol (THC), the psychoactive component of cannabis, modulates striatal dopaminergic neurotransmission. Alterations in human striatal dopaminergic function have also been reported both in psychosis and in stimulant use. We sought to examine whether striatal dopamine D(2)/D(3) receptor availability was altered in volunteers with a history of cannabis use using a database of previously acquired [(11)C]-raclopride positron emission tomography (PET) scans. Ten [(11)C]-raclopride scans from volunteers with a history of cannabis use were compared to ten control scans using a functional striatal subdivision region of interest (ROI) analysis. No significant differences in either overall striatal BP(ND) values or BP(ND) values in any functional striatal subdivision were found between the two groups. There was also no correlation between lifetime frequency of cannabis use and BP(ND) values. Limbic striatal BP(ND) values were ten percent lower in current nicotine cigarette smokers. These findings suggest that, unlike other drugs of abuse, a history of cannabis use is not associated with alterations in striatal dopamine D(2)/D(3) receptor availability.

Adolescent exposure to cannabis as a risk factor for psychiatric disorders

Adolescence represents a critical period for brain development and the endocannabinoid system plays a crucial role in the regulation of neuronal refinement during this period. Cannabis is the most consumed drug among adolescent people and its heavy use may affect maturational refinement by disrupting the regulatory role of the endocannabinoid system. In animals, adolescent cannabinoid exposure has been reported to cause long-term impairment in specific components of learning and memory and to differentially affect emotional reactivity with milder effects on anxiety behaviour and more pronounced effects on depression-like behaviour. Moreover, adolescent exposure to cannabinoids might represent a risk factor for developing psychotic-like symptoms at adulthood. Also epidemiological studies suggest that heavy adolescent cannabis use may increase the risk of cognitive abnormalities, psychotic illness, mood disorders and other illicit substance use later in life. In conclusion, the available data point to the hypothesis that heavy cannabis use in adolescence could increase the risk of developing psychiatric disorders, especially in people who already have a vulnerability to develop a psychiatric syndrome. Only few papers have investigated the neurobiological substrates of this vulnerability, thus further studies are needed to clarify the molecular mechanisms underlying the effect of cannabis on the adolescent brain.