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

The CRF/Urocortin systems as therapeutic targets for alcohol use disorders

Development and maintenance of alcohol use disorders have been proposed to recruit critical mechanisms involving Corticotropin Releasing Factor and Urocortins (CRF/Ucns). The CRF/Ucns system is comprised of a family of peptides (CRF, Ucn 1, Ucn 2, Ucn 3) which act upon two receptor subtypes, CRFR1 and CRFR2, each with different affinity profiles to the endogenous peptides and differential brain distribution. Activity of CRF/Ucn system is further modulated by CRF binding protein (CRF-BP), which regulates availability of CRF and Ucns to exert their actions. Extensive evidence in preclinical models support the involvement of CRF/Ucn targets in escalated alcohol drinking, as well as point to changes in CRF/Ucn brain function as a result of chronic alcohol exposure and/or withdrawal. It highlights the role of CRF and CRFR1-mediated signaling in conditions of excessive alcohol taking and seeking, including during various stages of withdrawal and relapse to alcohol. Besides its role in the hypothalamic-pituitary-adrenal (HPA) axis, the importance of extra-hypothalamic CRF pathways, especially in the extended amygdala, in the neurobiology of alcohol abuse and dependence is emphasized. Emerging roles for other targets of the CRF/Ucn system, such as CRF2 receptors, CRF-BP and Ucns in escalated alcohol drinking is also discussed. Finally, the limited translational value of CRF/Ucn interventions in stress-related and alcohol use disorders is discussed. So far, CRFR1 antagonists have shown little or no efficacy in human clinical trials, although a range of unexplored conditions and possibilities remain to be explored.

Sex-related differences in young binge drinkers on the neurophysiological response to stress in virtual reality

Background

Stress is one of the main environmental factors involved in the onset of different psychopathologies. In youth, stressful life events can trigger inappropriate and health-damaging behaviors, such as binge drinking. This behavior, in turn, can lead to long-lasting changes in the neurophysiological response to stress and the development of psychological disorders late in life, e.g., alcohol use disorder. Our aim was to analyze the pattern of neurophysiological responses triggered with the exposition to a stressful virtual environment in young binge drinkers.

Methods

AUDIT-3 (third question from the full AUDIT) was used to detect binge drinking (BD) in our young sample (age 18-25 years). According to the score, participants were divided into control (CO) and BD group. Next, a standardized virtual reality (VR) scenario (Richie's Plank) was used for triggering the stress response while measuring the following neurophysiological variables: brain electrical activity by electroencephalogram (EEG) and cortisol levels through saliva samples both measurements registered before and after the stressful situation. Besides, heart rate (HR) with a pulsometer and electrodermal response (EDA) through electrodes placed on fingers were analyzed before, during and after the VR task.

Results

Regarding the behavior assessed during the VR task, BD group spent significantly less amount of time walking forward the table and a tendency toward more time walking backwards. There was no statistically significant difference between the BD and the CO group regarding time looking down, but when we controlled the variable sex, the BD women group displayed higher amount of time looking down than the rest of the groups. Neurophysiological measurements revealed that there was not any statistically significant difference between groups in any of the EEG registered measures, EDA response and cortisol levels. Sex-related differences were found in HR response to VR scenario, in which BD women displayed the highest peak of response to the stressor. Also, the change in heartbeat was higher in BD women than men.

Conclusion

Unveiling the neurophysiological alterations associated with BD can help us to prevent and detect early onset of alcohol use disorder. Also, from our data we conclude that participants' sex can modulate some stress responses, especially when unhealthy behaviors such as BD are present. Nevertheless, the moment of registration of the neurophysiological variables respect to the stressor seems to be a crucial variable.

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.

Immersive virtual plus-maze to examine behavior and psychophysiological-related variables in young people with problematic alcohol and cannabis consumption

Stressful events appear to be risky situations that can precipitate the consumption of drugs. One way to recreate stressful contexts, in an ecological and controlled method, is through immersive virtual reality (VR). In our study, we designed the scenario of an elevated plus-maze (EPM) using VR, which is widely used in animal models to assess unconditioned anxiety. This task allowed us to analyze the behavioral, psychophysiological (heart rate and electrodermal activity), and hormonal response (salivary cortisol and Alpha-amylase) to this stressful situation in different moments (before VR task (anticipation), at the end of the task and 10 minutes later) in young people with problematic alcohol use (AU, n = 27), alcohol combined with cannabis consumption (AU + C, n = 10), as well as in a control group (CO, n = 33). Behavioral analysis revealed that the AU group displayed fewer entries into open arms than the CO group, whereas both experimental groups spent less time at the end of the open arms, as well as lower time by look down index compared to the CO group. Moreover, our VR EPM induced different psychophysiological responses in the different moments measured. In general, electrodermal activity seemed to be a good biomarker of recovery from a stressful situation, as once the exposure to the stressful situation ended, the AU + C group took longer to recover compared to the CO group. Regarding hormonal analyses, we observed a similar response pattern in all groups suggesting that our VR task was able to activate both stress systems. The alpha-amylase to cortisol ratio, proposed as a biomarker of stress systems dysregulation, was higher in the group of young participants with alcohol abuse. Interestingly, our VR EPM was able to induce a slight alcohol craving in both experimental groups. In conclusion, our results suggest certain subtle behavioral and physiological differences that could be used to detect young individuals at risk of future severe addictions or other stress-related comorbidities. Moreover, it could help us to develop prevention strategies focused on emotional, cognitive, and psychophysiological aspects.

Impact of environmental enrichment on the GABAergic neurons and glucocorticoid receptors in the hippocampus and nucleus accumbens of Wistar rats: pro-resilient effects

The unpredictable chronic mild stress (UCMS) model has been used to induce depressive-like symptoms in animal models. Our work aims to evaluate the impact of environmental enrichment on male Wistar rats in an animal model for depression. For this purpose, we aim to assess changes in GR and GABAergic (PV+) density in cerebral regions related to cognitive-affective processes associated with depressive disorder, such as the dorsal- ventral hippocampus and accumbens nuclei. Three groups of rats were used: UCMs (unpredictable chronic mild stress), EE+ UCMs (enrichment + stress) and CONT (behavioral tests only). Hedonic responses elicited by sucrose solution were examined by licking behavior analysis; the anxiety level was evaluated using the elevated zero maze and the forced swimming (passive coping) tests. The environmental enrichment reduced the effects of chronic stress, promoting greater resilience. Thus, the UCMs group showed an anhedonia response, more anxiety and immobility behavior than either the control or the EE+ UCMs groups. Regarding immunochemistry results, there was a reduction in GABAergic activity coupled with increased activation of GR in UCMs in the dorsal hippocampus, but there were no differences between groups in the ventral hippocampus. These results suggest environmental enrichment could enhance greater resilience, reducing the vulnerability of the subjects to develop disorders such as depression and anxiety.

Adolescent ethanol drinking promotes hyperalgesia, neuroinflammation and serotonergic deficits in mice that persist into adulthood

Adolescent alcohol use can permanently alter brain function and lead to poor health outcomes in adulthood. Emerging evidence suggests that alcohol use can predispose individuals to pain disorders or exacerbate existing pain conditions, but the underlying neural mechanisms are currently unknown. Here we report that mice exposed to adolescent intermittent access to ethanol (AIE) exhibit increased pain sensitivity and depressive-like behaviors that persist for several weeks after alcohol cessation and are accompanied by elevated CD68 expression in microglia and reduced numbers of serotonin (5-HT)-expressing neurons in the dorsal raphe nucleus (DRN). 5-HT expression was also reduced in the thalamus, anterior cingulate cortex (ACC) and amygdala as well as the lumbar dorsal horn of the spinal cord. We further demonstrate that chronic minocycline administration after AIE alleviated hyperalgesia and social deficits, while chemogenetic activation of microglia in the DRN of ethanol-naïve mice reproduced the effects of AIE on pain and social behavior. Chemogenetic activation of microglia also reduced tryptophan hydroxylase 2 (Tph2) expression and was negatively correlated with the number of 5-HT-immunoreactive cells in the DRN. Taken together, these results indicate that microglial activation in the DRN may be a primary driver of pain, negative affect, and 5-HT depletion after AIE.

The Influence of Sex on Hippocampal Neurogenesis and Neurotrophic Responses on the Persistent Effects of Adolescent Intermittent Ethanol Exposure into Adulthood

In the United States, approximately 90% of alcohol consumed by adolescents is binge drinking. Binge-like ethanol exposure during adolescence promotes dysregulation of neurotrophic responses and neurogenesis in the hippocampus. These effects include changes in proliferation, regulation, differentiation, and maturation of neurons, and there is indication that such effects may be disproportionate between sexes. This study determined whether sex impacts neurotrophic responses and neurogenesis in adulthood after adolescent intermittent ethanol (AIE) exposure. To determine this, adolescent rats underwent AIE with ethanol (5 g/kg). In adulthood, animals were euthanized, and immunohistochemical techniques and ELISAs were utilized to determine AIE effects on sex-specific neurogenesis factors and neurotrophic markers, respectively. AIE exposure led to a significant decrease in neurogenesis in the dentate gyrus of the hippocampal formation indicated by reductions in the numbers of DCX+, SOX2+ and Ki-67+ cells in male and female AIE-exposed rats. Additionally, AIE increased markers for the pro-inflammatory cytokines, TNF-α and IL-1β, in the hippocampus into adulthood in male AIE-exposed rats only. No significant AIE-induced differences were observed in the anti-inflammatory cytokines, IL-10 and TGF-β, nor in the neurotrophic factors BDNF and GDNF. Altogether, our findings indicate that although AIE did not have a persistent effect on hippocampal neurotrophic levels, there was still a reduction in neurogenesis. The neurogenic impairment was not sex specific, but the neurogenic deficits in males may be attributed to an increase in pro-inflammatory cytokine expression. A persistent impairment in neurogenesis may have an impact on both behavioral maladaptations and neurodegeneration in adulthood.

BDNF and its Role in the Alcohol Abuse Initiated During Early Adolescence: Evidence from Preclinical and Clinical Studies

Brain-derived neurotrophic factor (BDNF) is a crucial brain signaling protein that is integral to many signaling pathways. This neurotrophin has shown to be highly involved in brain plastic processes such as neurogenesis, synaptic plasticity, axonal growth, and neurotransmission, among others. In the first part of this review, we revise the role of BDNF in different neuroplastic processes within the central nervous system. On the other hand, its deficiency in key neural circuits is associated with the development of psychiatric disorders, including alcohol abuse disorder. Many people begin to drink alcohol during adolescence, and it seems that changes in BDNF are evident after the adolescent regularly consumes alcohol. Therefore, the second part of this manuscript addresses the involvement of BDNF during adolescent brain maturation and how this process can be negatively affected by alcohol abuse. Finally, we propose different BNDF enhancers, both behavioral and pharmacological, which should be considered in the treatment of problematic alcohol consumption initiated during the adolescence.

Altered gut microbiota and metabolites profile are associated with reduced bone metabolism in ethanol-induced osteoporosis

Objective

Chronic heavy drinking causes ethanol‐induced osteoporosis (EIO). The present study aimed to explore the role of GM in EIO.

Material and Methods

A rat EIO model was established by chronic ethanol intake. Taking the antibiotic application as the matched group of dysbacteriosis, an integrated 16S rRNA sequencing and liquid chromatography–tandem mass spectrometry‐based metabolomics in serum and faeces were applied to explore the association of differential metabolic phenotypes and screen out the candidate metabolites detrimental to ossification. The colon organoids were used to track the source of 5‐HT and the effect of 5‐HT on bone formation was examined in vitro.

Results

Compared with antibiotics application, ethanol‐gavaged decreased the BMD in rats. We found that both ethanol and antibiotic intake affected the composition of GM, but ethanol intake increased the ratio of Firmicutes to Bacteroidetes. Elevated serotonin was proved to be positively correlated with the changes of the composition of GM and faecal metabolites and inhibited the proliferation and mineralization of osteogenesis‐related cells. However, the direct secretory promotion of serotonin was absent in the colon organoids exposed to ethanol.

Conclusion

This study demonstrated that ethanol consumption led to osteoporosis and intestinal‐specific dysbacteriosis. Conjoint analysis of the genetic profiles of GM and metabolic phenotypes in serum and faeces allowed us to understand the endogenous metabolite, 5‐HT, as detrimental regulators in the gut‐bone axis to impair bone formation.