Impact of intermittent voluntary ethanol consumption during adolescence on the expression of endocannabinoid system and neuroinflammatory mediators

Assessment of Hippocampal-Related Behavioral Changes in Adolescent Rats of both Sexes Following Voluntary Intermittent Ethanol Intake and Noise Exposure: A Putative Underlying Mechanism and Implementation of a Non-pharmacological Preventive Strategy

Ethanol (EtOH) intake and noise exposure are particularly concerning among human adolescents because the potential to harm brain. Unfortunately, putative underlying mechanisms remain to be elucidated. Moreover, implementing non-pharmacological strategies, such as enriched environments (EE), would be pertinent in the field of neuroprotection. This study aims to explore possible underlying triggering mechanism of hippocampus-dependent behaviors in adolescent animals of both sexes following ethanol intake, noise exposure, or a combination of both, as well as the impact of EE. Adolescent Wistar rats of both sexes were subjected to an intermittent voluntary EtOH intake paradigm for one week. A subgroup of animals was exposed to white noise for two hours after the last session of EtOH intake. Some animals of both groups were housed in EE cages. Hippocampal-dependent behavioral assessment and hippocampal oxidative state evaluation were performed. Results show that different hippocampal-dependent behavioral alterations might be induced in animals of both sexes after EtOH intake and sequential noise exposure, that in some cases are sex-specific. Moreover, hippocampal oxidative imbalance seems to be one of the potential underlying mechanisms. Additionally, most behavioral and oxidative alterations were prevented by EE. These findings suggest that two frequently found environmental agents may impact behavior and oxidative pathways in both sexes in an animal model. In addition, EE resulted a partially effective neuroprotective strategy. Therefore, it could be suggested that the implementation of a non-pharmacological approach might also potentially provide neuroprotective advantages against other challenges. Finally, considering its potential for translational human benefit might be worth.

Consequences of adolescent drug use

Substance use in adolescence is a known risk factor for the development of neuropsychiatric and substance use disorders in adulthood. This is in part due to the fact that critical aspects of brain development occur during adolescence, which can be altered by drug use. Despite concerted efforts to educate youth about the potential negative consequences of substance use, initiation remains common amongst adolescents world-wide. Additionally, though there has been substantial research on the topic, many questions remain about the predictors and the consequences of adolescent drug use. In the following review, we will highlight some of the most recent literature on the neurobiological and behavioral effects of adolescent drug use in rodents, non-human primates, and humans, with a specific focus on alcohol, cannabis, nicotine, and the interactions between these substances. Overall, consumption of these substances during adolescence can produce long-lasting changes across a variety of structures and networks which can have enduring effects on behavior, emotion, and cognition.

Effects of Genetics and Sex on Acute Gene Expression Changes in the Hippocampus Following Neonatal Ethanol Exposure in BXD Recombinant Inbred Mouse Strains

Fetal alcohol spectrum disorders (FASD) are prevalent neurodevelopmental disorders. Genetics have been shown to have a role in the severity of alcohol's teratogenic effects on the developing brain. We previously identified recombinant inbred BXD mouse strains that show high (HCD) or low cell death (LCD) in the hippocampus following ethanol exposure. The present study aimed to identify gene networks that influence this susceptibility. On postnatal day 7 (3rd-trimester-equivalent), male and female neonates were treated with ethanol (5.0 g/kg) or saline, and hippocampi were collected 7hrs later. Using the Affymetrix microarray platform, ethanol-induced gene expression changes were identified in all strains with divergent expression sets found between sexes. Genes, such as Bcl2l11, Jun, and Tgfb3, showed significant strain-by-treatment interactions and were involved in many apoptosis pathways. Comparison of HCD versus LCD showed twice as many ethanol-induced genes changes in the HCD. Interestingly, these changes were regulated in the same direction suggesting (1) more perturbed effects in HCD compared to LCD and (2) limited gene expression changes that confer resistance to ethanol-induced cell death in LCD. These results demonstrate that genetic background and sex are important factors that affect differential cell death pathways after alcohol exposure during development that could have long-term consequences.

RNA m6A Modification Changes in Postmortem Nucleus Accumbens of Subjects with Alcohol Use Disorder: A Pilot Study

BACKGROUND

The nucleus accumbens (NAc) is a key brain structure mediating the rewarding effect of alcohol and drug abuse. Chronic alcohol consumption may alter RNA methylome (or epitranscriptome) in the NAc, leading to altered gene expression and thus behavioral neuroadaptation to alcohol.

METHODS

This pilot study profiled the epitranscriptomes of mRNAs, long noncoding RNAs (lncRNAs), and microRNAs (miRNAs) in postmortem NAc of three male Caucasian subjects with alcohol use disorder (AUD) and three matched male Caucasian control subjects using Arraystar's m6A-mRNA&lncRNA Epitranscriptomic Microarray assay. Differentially methylated (DM) RNAs and the function of DM RNAs were analyzed by biostatistics and bioinformatics programs.

RESULTS

26 mRNAs were hypermethylated and three mRNAs were hypomethylated in the NAc of AUD subjects (≥2-fold changes and p ≤ 0.05). Most of these 29 DM mRNAs are involved in immune-related pathways (e.g., IL-17 signaling). Moreover, four lncRNAs were hypermethylated and one lncRNA was hypomethylated in the NAc of AUD subjects (≥2-fold changes and p ≤ 0.05). Additionally, three miRNAs were hypermethylated in the NAc of AUD subjects (≥2-fold changes and p ≤ 0.05).

CONCLUSIONS

This study revealed RNA methylomic changes in the NAc of AUD subjects, suggesting that chronic alcohol consumption may lead to AUD through epitranscriptomic RNA modifications. Our findings need to be replicated in a larger sample.

Role of Cannabinoid CB2 Receptor in Alcohol Use Disorders: From Animal to Human Studies

Cumulative evidence has pointed out cannabinoid CB2 receptors (CB₂r) as a potential therapeutic key target for treating alcohol use disorder (AUD). This review provides the most relevant results obtained from rodent and human studies, including an integrative section focused on the involvement of CB₂r in the neurobiology of alcohol addiction. A literature search was conducted using the electronic databases Medline and Scopus for articles. The search strategy was as follows: “Receptor, Cannabinoid, CB2” AND “Alcohol-Related Disorders” AND “human/or patients”; “Receptor, Cannabinoid, CB2” AND “Alcohol” OR “Ethanol” AND “rodents/or mice/or rats”. Pharmacological approaches demonstrated that the activation or blockade of CB₂r modulated different alcohol-addictive behaviors. Rodent models of alcoholism revealed significant alterations of CB₂r in brain areas of the reward system. In addition, mice lacking CB₂r (CB₂KO) show increased alcohol consumption, motivation, and relapse alterations. It has been stressed that the potential neurobiological mechanisms underlying their behavioral effects involve critical elements of the alcohol reward system. Interestingly, recent postmortem studies showed CNR2 alterations in brain areas of alcoholic patients. Moreover, although the number of studies is limited, the results revealed an association between some genetic alterations of the CNR2 and an increased risk for developing AUD. This review provides evidence that CB₂r may play a role in alcohol addiction. Clinical studies are necessary to figure out whether CB₂r ligands may prove useful for the treatment of AUD in humans.

Acute stress and alcohol exposure during adolescence result in an anxious phenotype in adulthood: Role of altered glutamate/endocannabinoid transmission mechanisms

BACKGROUND

Stressful episodes and high alcohol consumption during adolescence are considered major risk factors for the development of psychiatric disorders in adulthood. Identification of mechanisms underlying these early events, which enhanced vulnerability to mental illness, is essential for both their prevention and treatment.

METHODS

Male Wistar rats were used to investigate the long-term effects of early restraint stress and intermittent alcohol exposure (intragastric administration of 3 g/kg ethanol; 4 days/week for 4 weeks during adolescence) on anxiety-like behavior and the expression of signaling systems associated with emotional behaviors [e.g., corticosterone, fatty acid-derived molecules and endocannabinoid enzymes, glutamate receptor subunits, corticotropin releasing hormone receptors (CRHR1 and CRHR2) and neuropeptide Y receptors (NPY1R and NPYR2)] in the blood and amygdala.

RESULTS

Overall, both stress and alcohol exposure during adolescence induced anxiogenic-like behaviors, increased plasma levels of corticosterone and increases in the amygdalar expression of the cannabinoid CB₂ receptor and certain subunits of glutamate receptors (i.e., mGluR1, mGluR5 and NMDAR1) in young adult rats. In addition, there were specific main effects of alcohol exposure on the expression of the cannabinoid CB₁ receptor, monoacylglycerol lipase (MAGL) and NPY2R in the amygdala, and significant increases were observed in rats exposed to alcohol. Interestingly, there were significant interaction effects between restraint stress and alcohol exposure on the expression of plasma 2-arachidonoyl glycerol (2-AG), and both CRHR1,2 and NPY1R in the amygdala. Thus, the restraint stress was associated with increased 2-AG levels, which was not observed in rats exposed to alcohol. The alcohol exposure was associated with an increased expression of CRHR1,2 but the restraint stress prevented these increases (stress alcohol rats). In contrast, NPY1R was only increased in rats exposed to stress and alcohol. Finally, we did not observe any potentiation of the behavioral and molecular effects by the combination of stress and alcohol, which is concordant with an overall ceiling effect on some of the variables.

CONCLUSION

Separate and combined early stress and alcohol induced a common anxious phenotype with increased corticosterone in adulthood. However, there were differences in the amygdalar expression of signaling systems involved in maladaptive changes in emotional behavior. Therefore, our results suggest the existence of partially different mechanisms for stress and alcohol exposures.

Endocannabinoid system contributions to sex-specific adolescent neurodevelopment

With an increasing number of countries and states adopting legislation permitting the use of cannabis for medical purposes, there is a growing interest among health and research professionals into the system through which cannabinoids principally act, the endocannabinoid system (ECS). Much of the seminal research into the ECS dates back only 30 years and, although there has been tremendous development within the field during this time, many questions remain. More recently, investigations have emerged examining the contributions of the ECS to normative development and the effect of altering this system during important critical periods. One such period is adolescence, a unique period during which brain and behaviours are maturing and reorganizing in preparation for adulthood, including shifts in endocannabinoid biology. The purpose of this review is to discuss findings to date regarding the maturation of the ECS during adolescence and the consequences of manipulations of the ECS during this period to normative neurodevelopmental processes, as well as highlight sex differences in ECS function, important technical considerations, and future directions. Because most of what we know is derived from preclinical studies on rodents, we provide relevant background of this model and some commentary on the translational relevance of the research in this area.

Repeated Restraint Stress and Binge Alcohol during Adolescence Induce Long-Term Effects on Anxiety-like Behavior and the Expression of the Endocannabinoid System in Male Rats

(1) Background: Negative experiences during adolescence increase the vulnerability to develop mental disorders later in life. A better understanding of the mechanisms underlying these long-term alterations could help to identify better therapeutic interventions. (2) Methods: Adolescent male Wistar rats were used to explore the effects of repeated stress and alcohol exposure on anxiety-like behaviors, plasma corticosterone levels and the gene expression of the endocannabinoid system (ECS) and other relevant signaling systems (glutamatergic, corticotropin-releasing hormone (CRH) and neuropeptide Y (NPY)) in the amygdala and the medial prefrontal cortex (mPFC). (3) Results: Overall, both stress and alcohol induced anxiety-like behaviors, but only the alcohol-exposed rats displayed increased plasma levels of corticosterone. In the amygdala, there was a general deficit in the gene expression of the ECS and increases in the mRNA levels of certain subunits of glutamate receptors. Interestingly, there were significant interaction effects between stress and alcohol on the expression of the NMDA receptor subunits. In addition, increased mRNA levels of the CRH receptor were observed in alcohol-exposed rats. In the mPFC, alcohol exposure was associated with an increase in the gene expression of the ECS. By contrast, the combination of stress and alcohol produced opposite effects. (4) Conclusions: In summary, early stress and alcohol exposure induced long-term anxiety-like behavior in male rats but different mechanisms are involved in these maladaptive changes in the brain.

Long-term consequences of alcohol use in early adolescent mice: Focus on neuroadaptations in GR, CRF and BDNF

Our aim was to assess the cognitive and emotional state, as well as related-changes in the glucocorticoid receptor (GR), the corticotropin-releasing factor (CRF) and the brain-derived neurotrophic factor (BDNF) expression of adolescent C57BL/6J male mice after a 5-week two-bottle choice protocol (postnatal day [pd]21 to pd52). Additionally, we wanted to analyse whether the behavioural and neurobiological effects observed in late adolescence (pd62) lasted until adulthood (pd84). Behavioural testing revealed that alcohol during early adolescence increased anxiety-like and compulsive-related behaviours, which was maintained in adulthood. Concerning cognition, working memory was only altered in late adolescent mice, whereas object location test performance was impaired in both ages. In contrast, novel object recognition remained unaltered. Immunohistochemical analysis showed that alcohol during adolescence diminished BDNF+ cells in the cingulate cortex, the hippocampal CA1 layer and the central amygdala. Regarding hypothalamic-pituitary-adrenal axis (HPA) functioning, alcohol abuse increased the GR and CRF expression in the hypothalamic paraventricular nucleus and the central amygdala. Besides this, GR density was also higher in the prelimbic cortex and the basolateral amygdala, regardless of the animals' age. Our findings suggest that adolescent alcohol exposure led to long-term behavioural alterations, along with changes in BDNF, GR and CRF expression in limbic brain areas involved in stress response, emotional regulation and cognition.

CB1 and CB2 receptors in the bed nucleus of the stria terminalis differently modulate anxiety-like behaviors in rats

The endocannabinoid system is implicated in anxiety, but the brain sites involved are not completely understood. The bed nucleus of the stria terminalis (BNST) has been related to anxiety and responses to aversive threats. Besides, endocannabinoid neurotransmission acting via CB₁ receptors was identified in the BNST. However, the presence of CB₂ receptors and the role of BNST endocannabinoid system in anxiety-like behaviors have never been reported. Therefore, this study investigated the presence of CB₁ and CB₂ receptors in the BNST and their role in anxiety-like behaviors. For this, gene expression of the endocannabinoid receptors was evaluated in samples from anterior and posterior BNST. Besides, behaviors were evaluated in the elevated plus-maze (EPM) in unstressed rats (trait anxiety-like behavior) and after exposure to restraint stress (restraint-evoked anxiety-like behavior) in rats treated with either the CB₁ receptor antagonist AM251 or the CB₂ receptor antagonist JTE907 into the anterior BNST. The presence of CB₁ and CB₂ receptors gene expression was identified in anterior and posterior divisions of the BNST. Bilateral microinjection of AM251 into the anterior BNST dose-dependently increased EPM open arms exploration in unstressed animals and inhibited the anxiety-like behavior in the EPM evoked by restraint. Conversely, intra-BNST microinjection of JTE907 decreased EPM open arms exploration in a dose-dependent manner and inhibited restraint-evoked behavioral changes in the EPM. Taken together, these results indicate that CB₁ and CB₂ receptors present in the BNST are involved in control of anxiety-like behaviors, and control by the latter is affected by previous stress experience.

Moderate adolescent chronic intermittent ethanol exposure sex-dependently disrupts synaptic transmission and kappa opioid receptor function in the basolateral amygdala of adult rats

Adolescent alcohol exposure is associated with many consequences in adulthood, including altered affective and reward-related behaviors. However, the long-term neurological disruptions underlying these behaviors are not fully understood. Shifts in the excitatory/inhibitory balance in the basolateral amygdala (BLA) relate to the expression of these behaviors and changes to BLA physiology are seen during withdrawal immediately following adolescent ethanol exposure, but no studies have examined whether these changes persist long-term. The kappa opioid receptor (KOR) neuromodulatory system mediates negative affective behaviors, and alterations of this system are implicated in behavioral changes following adult and adolescent chronic ethanol exposure. In the BLA, the KOR system undergoes functional changes across development, but whether BLA KOR function is disrupted by adolescent ethanol exposure is unknown. In this study, male and female Sprague-Dawley rats were exposed to a vapor model of moderate adolescent chronic intermittent ethanol (aCIE) and assessed for long-term effects on GABAergic and glutamatergic neurotransmission within the adult BLA and KOR modulation of these systems. aCIE exposure increased presynaptic glutamate transmission in females but had no effect in males or on GABA transmission in either sex. Additionally, aCIE exposure disrupted male KOR modulation of GABA release, with no effects in females or on glutamate transmission. These data suggest that aCIE produces sex-dependent and long-term changes to BLA physiology and KOR function. This is the first study to examine these persistent adaptations following adolescent alcohol exposure and opens a broad avenue for future investigation into other adolescent ethanol-induced disruptions of these systems.