Chronic Drinking During Adolescence Predisposes the Adult Rat for Continued Heavy Drinking: Neurotrophin and Behavioral Adaptation after Long-Term, Continuous Ethanol Exposure

Behavioral and Amygdala Biochemical Damage Induced by Alternating Mild Stress and Ethanol Intoxication in Adolescent Rats: Reversal by Argan Oil Treatment?

Adolescence is a critical period when the effects of ethanol and stress exposure are particularly pronounced. Argan oil (AO), a natural vegetable oil known for its diverse pharmacological benefits, was investigated for its potential to mitigate addictive-like behaviors and brain damage induced by adolescent intermittent ethanol intoxication (IEI) and unpredictable mild stress (UMS). From P30 to P43, IEI rats received a daily ip ethanol (3 g/kg) on a two-day on/two-day off schedule. On alternate days, the rats were submitted to UMS protocol. Next, a two-bottle free access paradigm was performed over 10 weeks to assess intermittent 20% ethanol voluntary consumption. During the same period, the rats were gavaged daily with AO (15 mL/kg). Our results show that IEI/UMS significantly increased voluntary alcohol consumption (from 3.9 g/kg/24 h to 5.8 g/kg/24 h) and exacerbated withdrawal signs and relapse-like drinking in adulthood. Although AO treatment slightly reduced ethanol intake, it notably alleviated withdrawal signs during abstinence and relapse-like drinking in adulthood. AO's effects were associated with its modulation of the HPA axis (elevated serum corticosterone), restoration of amygdala oxidative balance, BDNF levels, and attenuation of neurodegeneration. These findings suggest that AO's neuroprotective properties could offer a potential therapeutic avenue for reducing ethanol/stress-induced brain damage and addiction. Further research is needed to explore its mechanisms and therapeutic potential in alcohol use disorders.

Omega-3 fatty acids supplementation prevents learning and memory impairment induced by chronic ethanol consumption in adolescent male rats through restoration of inflammatory and oxidative responses

OBJECTIVE

Ethanol (Eth) intake is known to cause numerous detrimental effects on the structure and function of the brain, and it is commonly used as a psychostimulant drug by adolescents. Conversely, omega-3 (O3) can reduce the risk of cognitive decline and promote the maintenance of neurophysiological functions. In this study, we investigated the protective effects of O3 on behavioral alterations, oxidative stress, and interleukin-6 (IL-6) levels induced by chronic Eth intake during adolescence in rats.

MATERIALS AND METHODS

Adolescent male rats (21 days old) were divided as follows: (1) Vehicle, (2) Eth (Eth in drinking water [20%]), (3-5) Eth + O3 (50/100/150 mg/kg), and (6) O3 (150 mg/kg). After 5 weeks, Morris water maze (MWM) and passive avoidance (PA) tests were performed, and the hippocampal and cortical levels of oxidative stress markers and inflammatory indices were measured.

RESULTS

Adolescent Eth intake impairs learning and memory function in MWM and PA tests (groups × day, p < 0.05 and p < 0.001, respectively). It was shown that Eth induced oxidative stress and neuroinflammation. O3 improved learning and impairment induced by Eth by reducing the adverse effects of Eth on the oxidant/antioxidant balance in the hippocampi (for malondialdehyde [MDA]/thiol: p < 0.01, p < 0.001, respectively) and for superoxide dismutase (SOD)/catalase (CAT): p < 0.01 and p < 0.05, respectively). Furthermore, we found that O3 prevented the Eth-induced increase of hippocampal IL-6 (p < 0.001).

CONCLUSION

O3 supplementation acts as an effective approach to prevent learning and memory impairments induced by chronic Eth consumption during adolescence. In this respect, the antioxidant and anti-inflammatory properties of O3 seem to be the main underlying mechanisms of neuroprotection.

Pharmacologic hyperreactivity of kappa opioid receptors in periaqueductal gray matter during alcohol withdrawal syndrome in rats

BACKGROUND

Periaqueductal gray matter (PAG) is a brain region rich in kappa-opioid receptors (KOR). KOR in PAG mediates behavioral responses related to pain integration, and panic response, among others. Its participation in the addiction phenomena has been poorly studied. Hence, this preliminary study explored the pharmacological effects of KOR stimulation/blockade in dorsal-PAG (D-PAG) during alcohol withdrawal on anxiety-type behaviors and alcohol intake/preference.

METHODS

Juvenile male Wistar rats were unexposed (A-naïve group) or exposed to alcohol for 5 weeks and then restricted (A-withdrawal group). Posteriorly, animals received intra D-PAG injections of vehicle (10% DMSO), salvinorin A (SAL-A; a selective KOR agonist), or 2-Methyl-N-((2'-(pyrrolidin-1-ylsulfonyl)biphenyl-4-yl)methyl)propan-1-amine (PF-04455242; a highly selective KOR-antagonist). Subsequently, the defensive burying behavior (DBB) and alcohol intake/preference paradigms were evaluated.

RESULTS

SAL-A markedly increased burying time, the height of bedding, and alcohol consumption/preference in A-withdrawal, while slightly increased the height of bedding in A-näive rats. PF-04455242 decreased both burying and immobility duration, whereas increases latency to burying, frequency of rearing, and the number of stretches attempts with no action on alcohol intake/preference in A-withdrawal rats.

CONCLUSIONS

In general, stimulation/blockade of KOR in A-withdrawal animals exert higher responses compared to A-naïve ones. SAL-A produced anxiety-like behaviors and increased alcohol consumption/preference, especially/solely in the alcohol-withdrawal condition, while PF-04455242 augmented exploration with no effects on alcohol intake/preference. Our findings suggest a possible pharmacologic hyperreactivity of the KOR in PAG during alcohol withdrawal.

Schedule-induced alcohol intake during adolescence sex dependently impairs hippocampal synaptic plasticity and spatial memory

In a previous study, we demonstrated that intermittent ethanol administration in male adolescent animals impaired hippocampus-dependent spatial memory, particularly under conditions of excessive ethanol administration. In this current study, we subjected adolescent male and female Wistar rats an alcohol schedule-induced drinking (SID) procedure to obtain an elevated rate of alcohol self-administration and assessed their hippocampus-dependent spatial memory. We also studied hippocampal synaptic transmission and plasticity, as well as the expression levels of several genes involved in these mechanisms. Both male and female rats exhibited similar drinking patterns throughout the sessions of the SID protocol reaching similar blood alcohol levels in all the groups. However, only male rats that consumed alcohol showed spatial memory deficits which correlated with inhibition of hippocampal synaptic plasticity as long-term potentiation. In contrast, alcohol did not modify hippocampal gene expression of AMPA and NMDA glutamate receptor subunits, although there are differences in the expression levels of several genes relevant to synaptic plasticity mechanisms underlying learning and memory processes, related to alcohol consumption as Ephb2, sex differences as Pi3k or the interaction of both factors such as Pten. In conclusion, elevated alcohol intake during adolescence seems to have a negative impact on spatial memory and hippocampal synaptic plasticity in a sex dependent manner, even both sexes exhibit similar blood alcohol concentrations and drinking patterns.

Intermittent Exposure to a Single Bottle of Ethanol Modulates Stress Sensitivity: Impact of Age at Exposure Initiation

Alcohol use during adolescence is a serious public health problem, with binge drinking and high-intensity drinking being particularly harmful to the developing adolescent brain. To investigate the adverse consequences of binge drinking and high-intensity adolescent drinking, adolescent rodents were intermittently exposed to ethanol through intragastric gavage, intraperitoneal injection, or vapor inhalation. These models revealed the long-lasting behavioral and neural consequences of adolescent intermittent ethanol (AIE) exposure. The present study was designed to characterize a different AIE model, namely, intermittent exposure to a single bottle of 10% ethanol as the only source of fluids on a 2 days on/2 days off (water days) schedule, and to determine whether this AIE exposure model would produce changes in hormonal and neuroimmune responsiveness to challenges of differing modalities. Assessments of ethanol intake as well as blood and brain ethanol concentrations (BECs and BrECs, respectively) in adult male and female rats (Experiment 1) revealed that BECs and BrECs peaked following access to ethanol for a 2 h period when assessed 1 h into the dark cycle. Experiment 2 revealed age differences in ethanol intake, BECs, and BrECs following a 2 h access to ethanol (1 h into the dark cycle), with adolescents ingesting more ethanol and reaching higher BECs as well as BrECs than adults. In Experiment 3, intermittent exposure to a single bottle of 10% ethanol for 10 cycles of 2 days on/2 days off was initiated either in early or late adolescence, followed by an acute systemic immune challenge with lipopolysaccharide (LPS) in adulthood. LPS increased corticosterone and progesterone levels regardless of sex and prior ethanol history, whereas an LPS-induced increase in cytokine gene expression in the hippocampus was evident only in ethanol-exposed males and females, with females who underwent early exposure to ethanol being more affected than their later-exposed counterparts. In Experiment 4, intermittent ethanol exposure in females was initiated either in adolescence or adulthood and lasted for 12 ethanol exposure cycles. Then, behavioral (freezing behavior), hormonal (corticosterone and progesterone levels), and neuroimmune (cytokine gene expression in the PVN, amygdala, and hippocampus) responses to novel environments (mild stressors) and shock (intense stressors) were assessed. More pronounced behavioral and hormonal changes, as well as changes in cytokine gene expression, were evident in the shock condition than following placement in the novel environment, with prior history of ethanol exposure not playing a substantial role. Interleukin (IL)-1β gene expression was enhanced by shock in the PVN, whereas shock-induced increases in IL-6 gene expression were evident in the hippocampus. Together, these findings demonstrate that our intermittent adolescent exposure model enhances responsiveness to immune but not stress challenges, with females being more vulnerable to this AIE effect than males.

Age-related differences in the effect of chronic alcohol on cognition and the brain: a systematic review

Adolescence is an important developmental period associated with increased risk for excessive alcohol use, but also high rates of recovery from alcohol use-related problems, suggesting potential resilience to long-term effects compared to adults. The aim of this systematic review is to evaluate the current evidence for a moderating role of age on the impact of chronic alcohol exposure on the brain and cognition. We searched Medline, PsycInfo, and Cochrane Library databases up to February 3, 2021. All human and animal studies that directly tested whether the relationship between chronic alcohol exposure and neurocognitive outcomes differs between adolescents and adults were included. Study characteristics and results of age-related analyses were extracted into reference tables and results were separately narratively synthesized for each cognitive and brain-related outcome. The evidence strength for age-related differences varies across outcomes. Human evidence is largely missing, but animal research provides limited but consistent evidence of heightened adolescent sensitivity to chronic alcohol's effects on several outcomes, including conditioned aversion, dopaminergic transmission in reward-related regions, neurodegeneration, and neurogenesis. At the same time, there is limited evidence for adolescent resilience to chronic alcohol-induced impairments in the domain of cognitive flexibility, warranting future studies investigating the potential mechanisms underlying adolescent risk and resilience to the effects of alcohol. The available evidence from mostly animal studies indicates adolescents are both more vulnerable and potentially more resilient to chronic alcohol effects on specific brain and cognitive outcomes. More human research directly comparing adolescents and adults is needed despite the methodological constraints. Parallel translational animal models can aid in the causal interpretation of observed effects. To improve their translational value, future animal studies should aim to use voluntary self-administration paradigms and incorporate individual differences and environmental context to better model human drinking behavior.

Acute Ethanol Challenge Differentially Regulates Expression of Growth Factors and miRNA Expression Profile of Whole Tissue of the Dorsal Hippocampus

Acute ethanol exposure produces rapid alterations in neuroimmune gene expression that are both time- and cytokine-dependent. Interestingly, adolescent rats, who often consume binge-like quantities of alcohol, displayed reduced neuroimmune responses to acute ethanol challenge. However, it is not known whether growth factors, a related group of signaling factors, respond to ethanol similarly in adults and adolescents. Therefore, Experiment 1 aimed to assess the growth factor response to ethanol in both adolescents and adults. To test this, adolescent (P29-P34) and adult (P70-P80) Sprague Dawley rats of both sexes were injected with either ethanol (3.5 g/kg) or saline, and brains were harvested 3 h post-injection for assessment of growth factor, cytokine, or miRNA expression. As expected, acute ethanol challenge significantly increased IL-6 and IκBα expression in the hippocampus and amygdala, replicating our prior findings. Acute ethanol significantly decreased BDNF and increased FGF2 regardless of age condition. PDGF was unresponsive to ethanol, but showed heightened expression among adolescent males. Because recent work has focused on the PDE4 inhibitor ibudilast for treatment in alcohol use disorder, Experiment 2 tested whether ibudilast would alter ethanol-evoked gene expression changes in cytokines and growth factors in the CNS. Ibudilast (9.0 mg/kg s.c.) administration 1 h prior to ethanol had no effect on ethanol-induced changes in cytokine or growth factor changes in the hippocampus or amygdala. To further explore molecular alterations evoked by acute ethanol challenge in the adult rat hippocampus, Experiment 3 tested whether acute ethanol would change the miRNA expression profile of the dorsal hippocampus using RNASeq, which revealed a rapid suppression of 12 miRNA species 3 h after acute ethanol challenge. Of the miRNA affected by ethanol, the majority were related to inflammation or cell survival and proliferation factors, including FGF2, MAPK, NFκB, and VEGF. Overall, these findings suggest that ethanol-induced, rapid alterations in neuroimmune gene expression were (i) muted among adolescents; (ii) independent of PDE4 signaling; and (iii) accompanied by changes in several growth factors (increased FGF2, decreased BDNF). In addition, ethanol decreased expression of multiple miRNA species, suggesting a dynamic molecular profile of changes in the hippocampus within a few short hours after acute ethanol challenge. Together, these findings may provide important insight into the molecular consequences of heavy drinking in humans.

Alcohol-Drinking Under Limited-Access Procedures During Mature Adulthood Accelerates the Onset of Cognitive Impairment in Mice

A history of heavy drinking increases vulnerability to, and the severity of, Alzheimer’s disease (AD) and related dementias, with alcohol use disorder identified as the strongest modifiable risk factor for early-onset dementia. Heavy drinking has increased markedly in women over the past 10 years, particularly in mature adult women during the coronavirus (COVID-19) pandemic. This is concerning as women are more sensitive to many alcohol-related disease states, including AD and related dementias. Herein, we conducted two studies to determine if a 1-month period of binge drinking during mature adulthood (i.e., 5–9 months of age) impairs spatial and working memory to a greater extent in female vs. male C57BL/6J (B6J) mice. The anxiogenic and cognitive-impairing effects of binge drinking were also compared between mature adult and old B6J mice (18 months of age) in a third study. Throughout, females consumed more alcohol than males, indicating that a sex difference in binge drinking persists into old age. Despite the sex difference in intake, we detected no consistent sex difference in our measures of alcohol withdrawal-induced anxiety during a behavioral test battery. Although mature adult females exhibited more cognitive deficits than males, the precise outcome exhibiting a female-selective effect varied across studies. Old mice drank lower amounts of alcohol than mature adult mice, yet their blood ethanol concentrations (BECs) were within error of the 80 mg/dl criterion for binge drinking, indicative of an age-related slowing of alcohol metabolism. As expected, 18-month-old controls exhibited more signs of cognitive impairment than their 6-month-old counterparts, and binge drinking history impaired the Morris water maze performance of mice of both ages. In contrast, binge drinking history impaired the radial arm maze performance of 6-month-old mice only, and the extent of the impairment was comparable to the behavior exhibited by the older mice. We conclude from our studies that: (1) both biological sex and the age of drinking onset are subject factors that impact voluntary alcohol consumption by mice into old age; (2) binge drinking during later life elicits a negative affective state that is relatively sex-independent; (3) binge drinking during both mature adulthood and old age impairs spatial learning and memory; (4) binge drinking during mature adulthood accelerates deficits in working memory; and (5) mature adult females tend to exhibit more alcohol-induced cognitive impairments than males. If relevant to humans, these findings suggest that binge-like drinking by older adult men and women induces a negative affective state and cognitive decline, but that mature adult women, in particular, may be more sensitive to both the immediate and persistent cognitive-impairing effects of heavy drinking.

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.

Disinhibition-Like Behavior Correlates with Frontal Cortex Damage in an Animal Model of Chronic Alcohol Consumption and Thiamine Deficiency

Wernicke-Korsakoff syndrome (WKS) is induced by thiamine deficiency (TD) and mainly related to alcohol consumption. Frontal cortex dysfunction has been associated with impulsivity and disinhibition in WKS patients. The pathophysiology involves oxidative stress, excitotoxicity and inflammatory responses leading to neuronal death, but the relative contributions of each factor (alcohol and TD, either isolated or in interaction) to these phenomena are still poorly understood. A rat model was used by forced consumption of 20% (w/v) alcohol for 9 months (CA), TD hit (TD diet + pyrithiamine 0.25 mg/kg, i.p. daily injections the last 12 days of experimentation (TDD)), and both combined treatments (CA+TDD). Motor and cognitive performance and cortical damage were examined. CA caused hyperlocomotion as a possible sensitization of ethanol-induced excitatory effects and recognition memory deficits. In addition, CA+TDD animals showed a disinhibited-like behavior which appeared to be dependent on TDD. Additionally, combined treatment led to more pronounced alterations in nitrosative stress, lipid peroxidation, apoptosis and cell damage markers. Correlations between injury signals and disinhibition suggest that CA+TDD disrupts behaviors dependent on the frontal cortex. Our study sheds light on the potential disease-specific mechanisms, reinforcing the need for neuroprotective therapeutic approaches along with preventive treatments for the nutritional deficiency in WKS.

Markers of Neuroinflammation in the Serum of Prepubertal Children with Fetal Alcohol Spectrum Disorders

BACKGROUND

Fetal Alcohol Spectrum Disorders (FASD) are the manifestation of the damage caused by alcohol consumption during pregnancy. Children with Fetal Alcohol Syndrome (FAS), the extreme FASD manifestation, show both facial dysmorphology and mental retardation. Alcohol consumed during gestational age prejudices brain development by reducing, among others, the synthesis and release of neurotrophic factors and neuroinflammatory markers. Alcohol drinking also induces oxidative stress.

HYPOTHESIS/OBJECTIVE

The present study aimed to investigate the potential association between neurotrophins, neuroinflammation, and oxidative stress in 12 prepubertal male and female FASD children diagnosed as FAS or partial FAS (pFAS).

METHODS

Accordingly, we analyzed, in the serum, the level of BDNF and NGF and the oxidative stress, as Free Oxygen Radicals Test (FORT) and Free Oxygen Radicals Defense (FORD). Moreover, serum levels of inflammatory mediators (IL-1α, IL-2, IL-6, IL-10, IL-12, MCP-1, TGF-β, and TNF-α) involved in neuroinflammatory and oxidative processes have been investigated.

RESULTS

We demonstrated low serum levels of NGF and BDNF in pre-pubertal FASD children with respect to healthy controls. These changes were associated with higher serum presence of TNF- α and IL-1α. Quite interestingly, an elevation in the FORD was also found despite normal FORT levels. Moreover, we found a potentiation of IL-1α, IL-2, IL-10, and IL-1α1 in the analyzed female compared to male children.

CONCLUSION

The present investigation shows an imbalance in the peripheral neuroimmune pathways that could be used in children as early biomarkers of the deficits observed in FASD.

Translational opportunities in animal and human models to study alcohol use disorder

Animal and human laboratory paradigms offer invaluable approaches to study the complex etiologies and mechanisms of alcohol use disorder (AUD). We contend that human laboratory models provide a "bridge" between preclinical and clinical studies of AUD by allowing for well-controlled experimental manipulations in humans with AUD. As such, examining the consilience between experimental models in animals and humans in the laboratory provides unique opportunities to refine the translational utility of such models. The overall goal of the present review is to provide a systematic description and contrast of commonly used animal paradigms for the study of AUD, as well as their human laboratory analogs if applicable. While there is a wide breadth of animal species in AUD research, the paradigms discussed in this review rely predominately on rodent research. The overarching goal of this effort is to provide critical analysis of these animal models and to link them to human laboratory models of AUD. By systematically contrasting preclinical and controlled human laboratory models, we seek to identify opportunities to enhance their translational value through forward and reverse translation. We provide future directions to reconcile differences between animal and human work and to improve translational research for AUD.

Voluntary Adolescent-Onset Alcohol Drinking Fails to Influence Alcohol Consumption or Anxiety-Like Behaviour in Adulthood in Female Alcohol-Preferring Rats

AIMS

Alcohol exposure during adolescence is associated with both increased risk for alcohol use disorders and anxiety in adulthood. Our present experiments examined this association using alcohol-preferring AA (Alko Alcohol) rats selected for high voluntary alcohol drinking.

METHODS

Two groups of female AA rats acquired alcohol drinking at different ages. We gave the adolescent-onset group free choice to 10% alcohol and water for seven weeks, starting on post-natal day 42 (PND 42), whereas the adult-onset group started drinking alcohol on PND 112. After the 7-week drinking, we withdrew the adolescent group from alcohol for two weeks, followed by another voluntary 7-week drinking period, started at the same age as the adult-onset group. We assessed anxiety-like behaviour repeatedly during alcohol drinking with open field and elevated plus maze tests. At the end of alcohol drinking, we also tested the rats using the light/dark box, stress-induced body temperature test and social dominance test.

RESULTS

During the first 7-week alcohol drinking, adolescent rats exhibited significantly slower acquisition of alcohol drinking and lower alcohol preference than the adult-onset group. However, when tested at the same age as the adult-onset rats, they displayed identical alcohol intake and preference. We found no alcohol-induced effects on anxiety- or stress-related behaviour in the experimental groups at any time points.

CONCLUSIONS

These data show that the genetically determined phenotype of high alcohol drinking of the female alcohol-preferring AA rats is not associated with a predisposition to develop anxiety-like behaviour following voluntary alcohol exposure, even when initiated during adolescence.

Alcohol Consumption during Adulthood Does Not Impair Later Go/No-Go Reversal Learning in Male Rats

Reversal learning tasks are used to model flexible decision-making in laboratory animals, and exposure to drugs of abuse can cause long-term impairments in reversal learning. However, the long-term effects of alcohol on reversal learning have varied. We evaluated whether six weeks of voluntary alcohol consumption through chronic intermittent alcohol access (elevated by food restriction) in adult male rats would impair rats in a go/no-go reversal learning task when tested at an interval beyond acute withdrawal. In our go/no-go task, rats were reinforced for pressing one lever or withholding from pressing another lever, and the identities of the two levers were switched twice (once rats reached an accuracy criterion). We found no evidence that prior alcohol consumption altered discrimination or reversal learning in our task. This replicates previous patterns from our laboratory that higher alcohol consumption in food-restricted rats did not impair discrimination or reversal learning in a different go/no-go task and that alcohol consumption in free-fed adolescent/early adult rats did not impair go/no-go discrimination or reversal learning in the same task. It is unclear whether this represents an insensitivity of this task to alcohol exposure generally or whether an alcohol exposure procedure that leads to higher blood ethanol concentration (BEC) levels would impair learning. More research is needed to investigate these possibilities.

Preclinical methodological approaches investigating of the effects of alcohol on perinatal and adolescent neurodevelopment

Despite much evidence of its economic and social costs, alcohol use continues to increase. Much remains to be known as to the effects of alcohol on neurodevelopment across the lifespan and in both sexes. We provide a comprehensive overview of the methodological approaches to ethanol administration when using animal models (primarily rodent models) and their translational relevance, as well as some of the advantages and disadvantages of each approach. Special consideration is given to early developmental periods (prenatal through adolescence), as well as to the types of research questions that are best addressed by specific methodologies. The zebrafish is used increasingly in alcohol research, and how to use this model effectively as a preclinical model is reviewed as well.

Sex-dependent effects of chronic intermittent voluntary alcohol consumption on attentional, not motivational, measures during probabilistic learning and reversal

Background

Forced alcohol (ethanol, EtOH) exposure has been shown to cause significant impairments on reversal learning, a widely-used assay of cognitive flexibility, specifically on fully-predictive, deterministic versions of this task. However, previous studies have not adequately considered voluntary EtOH consumption and sex effects on probabilistic reversal learning. The present study aimed to fill this gap in the literature.

Methods

Male and female Long-Evans rats underwent either 10 weeks of voluntary intermittent 20% EtOH access or water only (H2O) access. Rats were then pretrained to initiate trials and learn stimulus-reward associations via touchscreen response, and subsequently required to select between two visual stimuli, rewarded with probability 0.70 or 0.30. In the final phase, reinforcement contingencies were reversed.

Results

We found significant sex differences on several EtOH-drinking variables, with females reaching a higher maximum EtOH consumption, exhibiting more high-drinking days, and escalating their EtOH at a quicker rate compared to males. During early abstinence, EtOH drinkers (and particularly EtOH-drinking females) made more initiation omissions and were slower to initiate trials than H2O drinking controls, especially during pretraining. A similar pattern in trial initiations was also observed in discrimination, but not in reversal learning. EtOH drinking rats were unaffected in their reward collection and stimulus response times, indicating intact motivation and motor responding. Although there were sex differences in discrimination and reversal phases, performance improved over time. We also observed sex-independent drinking group differences in win-stay and lose-shift strategies specific to the reversal phase.

Conclusions

Females exhibit increased vulnerability to EtOH effects in early learning: there were sex-dependent EtOH effects on attentional measures during pretraining and discrimination phases. We also found sex-independent EtOH effects on exploration strategies during reversal. Future studies should aim to uncover the neural mechanisms for changes in attention and exploration in both acute and prolonged EtOH withdrawal.

The effects of adolescent alcohol exposure on learning and related neurobiology in humans and rodents

Adolescent alcohol use is a widespread problem in the United States. In both humans and rodents, alcohol can impair learning and memory processes mediated by forebrain areas such as the prefrontal cortex (PFC) and hippocampus (HC). Adolescence is a period in which alcohol use often begins, and it is also a time that can be uniquely sensitive to the detrimental effects of alcohol. Exposure to alcohol during adolescence can cause persisting alterations in PFC and HC neurobiology that are linked to cognitive impairments, including changes in neurogenesis, inflammation, and various neurotransmitter systems in rodent models. Consistent with this, chronic adolescent alcohol exposure can cause PFC-dependent learning impairments that persist into adulthood. Deficits in adult HC-dependent learning after adolescent alcohol exposure have also been reported, but these findings are less consistent. Overall, evidence summarized in this review indicates that adolescent exposure to alcohol can produce long-term detrimental effects on forebrain-dependent cognitive processes.

Effect of alcohol use on the adolescent brain and behavior

Adolescence is a particularly vulnerable neurodevelopmental period marked by high rates of engagement with risky alcohol use. This review summarizes the cognitive and neural consequences following alcohol use during adolescence from longitudinal design studies in humans and animals. Findings from human adolescent studies suggest that binge drinking and heavy alcohol use is associated with poorer cognitive functioning on a broad range of neuropsychological assessments, including learning, memory, visuospatial functioning, psychomotor speed, attention, executive functioning, and impulsivity. Alcohol use during adolescence is associated with accelerated decreases in gray matter and attenuated increases in white matter volume, and aberrant neural activity during executive functioning, attentional control, and reward sensitivity tasks, when compared to non-drinking adolescents. Animal studies in rodents and non-human primates have replicated human findings, and suggest cognitive and neural consequences of adolescent alcohol use may persist into adulthood. Novel rodent studies demonstrate that adolescent alcohol use may increase reward responsiveness of the dopamine system to alcohol later in life, as well as disrupt adolescent neurogenesis, potentially through neuroinflammation, with long-lasting neural and behavioral effects into adulthood. Larger longitudinal human cognitive and neuroimaging studies with more diverse samples are currently underway which will improve understanding of the impact of polysubstance use, as well as the interactive effects of substance use, physical and mental health, and demographic factors on cognition and neurodevelopment.

Adolescent Ethanol Exposure: Anxiety-Like Behavioral Alterations, Ethanol Intake, and Sensitivity

Adolescence is a developmental period associated with rapid age-specific physiological, neural, and hormonal changes. Behaviorally, human adolescents are characterized by age-typical increases in novelty-seeking and risk-taking, including the frequent initiation of alcohol and drug use. Alcohol use typically begins during early adolescence, and older adolescents often report high levels of alcohol consumption, commonly referred to as high-intensity drinking. Early-onset and heavy drinking during adolescence are associated with an increased risk of developing alcohol use disorders later in life. Yet, long-term behavioral consequences of adolescent alcohol use that might contribute to excessive drinking in adulthood are still not well understood. Recent animal research, however, using different exposure regimens and routes of ethanol administration, has made substantial progress in identifying the consequences of adolescent ethanol exposure that last into adulthood. Alterations associated with adolescent ethanol exposure include increases in anxiety-like behavior, impulsivity, risk-taking, and ethanol intake, although the observed alterations differ as a function of exposure regimens and routes of ethanol administration. Rodent studies have also shown that adolescent ethanol exposure produces alterations in sensitivity to ethanol, with these alterations reminiscent of adolescent-typical ethanol responsiveness. The goal of this mini-review article is to summarize the current state of animal research, focusing on the long-term consequences related to adolescent ethanol exposure, with a special emphasis on the behavioral alterations and changes to ethanol sensitivity that can foster high levels of drinking in adulthood.

Timing Eclipses Amount: The Critical Importance of Intermittency in Alcohol Exposure Effects

Frequency and duration of ethanol (EtOH) exposures influence the consequences of those experiences, with evidence building from basic science studies in rats and mice that intermittent alcohol access (IAA) typically produces a greater escalation of EtOH intake than more continuous alcohol access (CAA). IAA also better simulates human use patterns where alcohol levels typically clear from the body between periods of use. A variety of mechanisms have been proposed to contribute to the enhanced intake of EtOH induced by IAA, including a possible attenuation in the aversive effects of EtOH, although further studies are needed to address this and other possibilities. Neural differences include indications of an IAA-associated increase in NR2B receptors that is not evident with CAA; although little studied, alterations in other neural and neurotransmitter systems are evident as well. Many gaps in understanding of IAA/CAA effects remain. Further work is needed to characterize neural mechanisms underlying these effects, consequences of IAA/CAA on EtOH effects beyond intake, and the impact of stress and environmental variables on these differences. IAA/CAA studies to date have also largely been limited to males and to adult animals, and hence, more studies examining IAA/CAA across sex and age are needed. Such additional work is essential to determine unique contributors to IAA-induced elevations in EtOH intake that may provide important insights for the development of new prevention/intervention strategies for heavy alcohol use and abuse.

The effects of social instability stress and subsequent ethanol consumption in adolescence on brain and behavioral development in male rats

Excessive drinking in adolescence continues to be a problem, and almost a quarter of young Canadians have reported consuming five or more alcoholic drinks in one occasion in recent surveys. The consequences of such drinking may be more pronounced when commenced in adolescence, given the ongoing brain development during this period of life. Here, we investigated the consequences of 3 weeks' intermittent access to ethanol in mid-adolescence to early adulthood in rats, and the extent to which a stress history moderated the negative consequences of ethanol access. In experiment 1, male rats that underwent adolescent social instability stress (SS; daily 1 h isolation + return to unfamiliar cage partner every day from postnatal day [PND] 30-45) did not differ from control (CTL) rats in intake of 10% ethanol sweetened with 0.1% saccharin (access period; PND 47-66). Ethanol drinking reduced proteins relevant for synaptic plasticity (αCaMKII, βCaMKII, and PSD-95) in the dorsal hippocampus, and in CTL rats only in the prefrontal cortex (αCaMKII and PSD 95), attenuating the difference between CTL and SS rats in the water-drinking group. In experiment 2, ethanol also attenuated the difference between SS and CTL rats in a social interaction test by reducing social interaction in SS rats; CTL rats, however, had a higher intake of ethanol than did SS rats during the access period. Ethanol drinking reduced baseline and fear recall recovery concentrations of corticosterone relative to those exposed only to water, although there was no effect of either ethanol or stress history on fear conditioning. Ethanol drinking did not influence intake after 9 days of withdrawal; however, ethanol-naïve SS rats drank more than did CTL rats when given a 24-h access in adulthood. These results reveal a complex relationship between stress history and ethanol intake in adolescence on outcomes in adulthood.

Age-dependent impairment of metabotropic glutamate receptor 2-dependent long-term depression in the mouse striatum by chronic ethanol exposure

Chronic alcohol exposure is associated with increased reliance on behavioral strategies involving the dorsolateral striatum (DLS), including habitual or stimulus-response behaviors. Presynaptic G protein-coupled receptors (GPCRs) on cortical and thalamic inputs to the DLS inhibit glutamate release, and alcohol-induced disruption of presynaptic GPCR function represents a mechanism by which alcohol could disinhibit DLS neurons and thus bias toward use of DLS-dependent behaviors. Metabotropic glutamate receptor 2 (mGlu₂) is a G_i/o-coupled GPCR that robustly modulates glutamate transmission in the DLS, inducing long-term depression (LTD) at both cortical and thalamic synapses. Loss of mGlu₂ function has recently been associated with increased ethanol seeking and consumption, but the ability of alcohol to produce adaptations in mGlu₂ function in the DLS has not been investigated. We exposed male C57Bl/6J mice to a 2-week chronic intermittent ethanol (CIE) paradigm followed by a brief withdrawal period, then used whole-cell patch clamp recordings of glutamatergic transmission in the striatum to assess CIE effects on mGlu₂-mediated synaptic plasticity. We report that CIE differentially disrupts mGlu₂-mediated long-term depression in the DLS vs. dorsomedial striatum (DMS). Interestingly, CIE-induced impairment of mGlu₂-LTD in the dorsolateral striatum is only observed when alcohol exposure occurs during adolescence. Incubation of striatal slices from CIE-exposed adolescent mice with a positive allosteric modulator of mGlu₂ fully rescues mGlu₂-LTD. In contrast to the 2-week CIE paradigm, acute exposure of striatal slices to ethanol concentrations that mimic ethanol levels during CIE exposure fails to disrupt mGlu₂-LTD. We did not observe a reduction of mGlu₂ mRNA or protein levels following CIE exposure, suggesting that alcohol effects on mGlu₂ occur at the functional level. Our findings contribute to growing evidence that adolescents are uniquely vulnerable to certain alcohol-induced neuroadaptations, and identify enhancement of mGlu₂ activity as a strategy to reverse the effects of adolescent alcohol exposure on DLS physiology.

Aging with alcohol-related brain damage: Critical brain circuits associated with cognitive dysfunction

Alcoholism is associated with brain damage and impaired cognitive functioning. The relative contributions of different etiological factors, such as alcohol, thiamine deficiency and age vulnerability, to the development of alcohol-related neuropathology and cognitive impairment are still poorly understood. One reason for this quandary is that both alcohol toxicity and thiamine deficiency produce brain damage and cognitive problems that can be modulated by age at exposure, aging following alcohol toxicity or thiamine deficiency, and aging during chronic alcohol exposure. Pre-clinical models of alcohol-related brain damage (ARBD) have elucidated some of the contributions of ethanol toxicity and thiamine deficiency to neuroinflammation, neuronal loss and functional deficits. However, the critical variable of age at the time of exposure or long-term aging with ARBD has been relatively ignored. Acute thiamine deficiency created a massive increase in neuroimmune genes and proteins within the thalamus and significant increases within the hippocampus and frontal cortex. Chronic ethanol treatment throughout adulthood produced very minor fluctuations in neuroimmune genes, regardless of brain region. Intermittent "binge-type" ethanol during the adolescent period established an intermediate neuroinflammatory response in the hippocampus and frontal cortex, that can persist into adulthood. Chronic excessive drinking throughout adulthood, adolescent intermittent ethanol exposure, and thiamine deficiency all led to a loss of the cholinergic neuronal phenotype within the basal forebrain, reduced hippocampal neurogenesis, and alterations in the frontal cortex. Only thiamine deficiency results in gross pathological lesions of the thalamus. The behavioral impairment following these types of treatments is hierarchical: Thiamine deficiency produces the greatest impairment of hippocampal- and prefrontal-dependent behaviors, chronic ethanol drinking ensues mild impairments on both types of tasks and adolescent intermittent ethanol exposure leads to impairments on frontocortical tasks, with sparing on most hippocampal-dependent tasks. However, our preliminary data suggest that as rodents age following adolescent intermittent ethanol exposure, hippocampal functional deficits began to emerge. A necessary requirement for the advancement of understanding the neural consequences of alcoholism is a more comprehensive assessment and understanding of how excessive alcohol drinking at different development periods (adolescence, early adulthood, middle-aged and aged) influences the trajectory of the aging process, including pathological aging and disease.

Intermittent-Excessive and Chronic-Moderate Ethanol Intake during Adolescence Impair Spatial Learning, Memory and Cognitive Flexibility in the Adulthood

Intermittent and excessive ethanol consumption over very short periods of time, known as binge drinking, is common in the adolescence, considered a vulnerable period to the effects of alcohol in terms of cognitive performance. One of the brain functions most drastically affected by ethanol in adolescent individuals seems to be spatial learning and memory dependent on the hippocampus. In the current study we have focused on the long-lasting effects on spatial learning and memory of intermittent and excessive alcohol consumption compared to chronic and moderate alcohol exposure during adolescence. Five-week old male Wistar rats consumed ethanol for 24 days following two different self-administration protocols that differed in the intake pattern. Spatial learning and memory were evaluated in the radial arm maze. Hippocampal synaptic plasticity was assessed by measuring field excitatory postsynaptic potentials. Hippocampal expression of AMPA and NMDA receptor subunits as well as levels of phosphorylated Ser⁹-GSK3β (the inactive form of GSK3β) were also quantified. Our results show that both patterns of ethanol intake during adolescence impair spatial learning, memory and cognitive flexibility in the adulthood in a dose-dependent way. Nevertheless, changes in synaptic plasticity, gene expression and levels of inactive GSK3β depended on the pattern of ethanol intake.

The intermittent administration of ethanol during the juvenile period produces changes in the expression of hippocampal genes and proteins and deterioration of spatial memory

BACKGROUND

Binge drinking is a pattern of alcohol intake characterized by excessive and intermittent alcohol consumption over a very short period of time that is more used during adolescence. We aim to compare the lasting effects of a chronic-moderate vs. this intermittent-excessive way of alcohol intake during adolescence in spatial memory and in the expression of glutamatergic receptors and GSK3β activity.

METHODS

Adolescent male Wistar rats were given ethanol/saline i.p. injections in four different groups: High-I (4 g/kg of a 25% (vol/vol) every 3 days), Low-I (1 g/kg of a 5% (vol/vol) every 3 days), M (0.3 g/kg of a 2.5% (vol/vol) daily) and Control (C, sterile isotonic saline daily). Rats received ethanol for up to five 3-day cycles. Spatial memory was measured by spontaneous alternation in the Y-Maze. Gene and protein expression of hippocampal proteins were also analysed.

RESULTS

Both high- and low-intermittent ethanol administration produced spatial memory impairment and changes in glutamatergic receptors gene expression were observed regardless of the pattern of exposure. High doses of intermittent alcohol administration produced an increase of phosphorylation of GSK3β Ser9. Moreover, moderate alcohol administration produced a down-regulation of the AMPAR 2/3 ratio despite lack of spatial memory deficits.

CONCLUSIONS

Excessive and intermittent ethanol exposure during adolescence impaired the spatial memory processes during adulthood regardless of the amount of alcohol administered. Moreover, chronic-moderate and intermittent pattern induced changes in the expression of glutamatergic receptors. In addition, high-intermittent ethanol exposure during adolescence inactivated GSK3β by increasing its phosphorylation in Ser9.

General anesthetic exposure in adolescent rats causes persistent maladaptations in cognitive and affective behaviors and neuroplasticity

Accumulating evidence indicates that exposure to general anesthetics during infancy and childhood can cause persistent cognitive impairment, alterations in synaptic plasticity, and, to a lesser extent, increased incidence of behavioral disorders. Unfortunately, the developmental parameters of susceptibility to general anesthetics are not well understood. Adolescence is a critical developmental period wherein multiple late developing brain regions may also be vulnerable to enduring general anesthetic effects. Given the breadth of the adolescent age span, this group potentially represents millions more individuals than those exposed during early childhood. In this study, isoflurane exposure within a well-characterized adolescent period in Sprague-Dawley rats elicited immediate and persistent anxiety- and impulsive-like responding, as well as delayed cognitive impairment into adulthood. These behavioral abnormalities were paralleled by atypical dendritic spine morphology in the prefrontal cortex (PFC) and hippocampus (HPC), suggesting delayed anatomical maturation, and shifts in inhibitory function that suggest hypermaturation of extrasynaptic GABA_A receptor inhibition. Preventing this hypermaturation of extrasynaptic GABA_A receptor-mediated function in the PFC selectively reversed enhanced impulsivity resulting from adolescent isoflurane exposure. Taken together, these data demonstrate that the developmental window for susceptibility to enduring untoward effects of general anesthetics may be much longer than previously appreciated, and those effects may include affective behaviors in addition to cognition.

Prefrontal cortex development and emergence of self-regulatory competence: the two cardinal features of adolescence disrupted in context of alcohol abuse

Adolescence is a tumultuous period in the lifetime of an individual confronted to major changes in emotional, social and cognitive appraisal. During this period of questioning and doubt, while the executive functions are still maturing, the abstract reasoning remains vague and the response inhibition loose; ultimately the adolescent scarcely resists temptation. Consequently, adolescence is often associated with uninhibited risk-taking, reckless behaviours, among which are alcohol and illicit drugs use. Here, we discuss how the development of the prefrontal cortex (which critically contributes to rational decision-making and temporal processing of complex events) can be associated with the idiosyncratic adolescent behaviour, and potentially uncontrolled alcohol use. Most importantly, we present clinical and preclinical evidence supporting that ethanol exposure has deleterious effects on the adolescent developing brain. Ultimately, we discuss why a late maturing prefrontal cortex represents a ripe candidate to environmental influences that contribute to shape the adolescent brain but, potentially, can also trigger lifelong maladaptive responses, including increased vulnerability to develop substance use disorder later in life.

Operant over-responding is more sensitive than reversal learning for revealing behavioral changes after withdrawal from alcohol consumption

In humans, prior alcohol use is linked with impulsivity and impaired decision-making, but the nature of this relationship is unclear. In a previous study in rats, we found that prior alcohol access led to over-responding in go/no-go discrimination training, but had no effect on discrimination learning. It was unclear whether this over-responding effect would occur in a reversal learning task, or whether prior alcohol would impair reversal learning in our task. In the present experiments, we determined whether six weeks of chronic intermittent alcohol access would induce over-responding or impair reversal learning in our task. Our task allowed for multiple responses/trial with limited reinforcement, so over-responding could be assessed. In Exp. 1, we gave three days of discrimination training prior to access to 20% alcohol or water, then reversed task contingencies starting 4 days after the end of alcohol access. In Exp. 2, we gave either three or six days of discrimination training prior to the same alcohol access and reversal learning procedures to determine if the original training length would affect alcohol's behavioral effects. We found no reversal learning deficits in either experiment. Across both experiments, we found that the Alcohol group exhibited over-responding to the active lever, but this effect was smaller than in our previous discrimination experiments. Our data suggest that there are behavioral changes after voluntary alcohol access that can be missed by some discrimination/reversal learning assessments, and our over-responding task can detect these transient changes. However, over-responding is more pronounced in discrimination than reversal learning.

The long-term cognitive consequences of adolescent exposure to recreational drugs of abuse

During adolescence, the brain continues to undergo vital developmental processes. In turn, complex behavioral and cognitive skills emerge. Unfortunately, neurobiological development during adolescence can be influenced by environmental factors such as drug exposure. Engaging in drug use during adolescence has been a long-standing health concern, especially how it predicts or relates to drug using behavior later in life. However, recent findings suggest that other behavioral domains, such as learning and memory, are also vulnerable to adolescent drug use. Moreover, it is becoming increasingly apparent that deficits in learning and memory following adolescent drug use endure into adulthood, well after drug exposure has subsided. Although persistent effects suggest an interaction between drug exposure and ongoing development during adolescence, the exact acute and long-term consequences of adolescent drug exposure on substrates of learning and memory are not fully understood. Thus, this review will summarize human and animal findings on the enduring cognitive deficits due to adolescent drug exposure. Moreover, due to the fact that adolescents are more likely to consume drugs of abuse legally available to adults, this review will focus on alcohol, nicotine, and marijuana. Further, given the critical role of the frontal cortex and hippocampus in various learning and memory domains, the impact adolescent use of the previous listed drugs on the neurobiology within these regions will also be discussed.

Binge Drinking and Intergenerational Implications: Parental Preconception Alcohol Impacts Offspring Development in Rats

Preconception behaviors and experiences of mothers and fathers can affect future offspring. Recently, our laboratory showed that alcohol-naive offspring of parents who were exposed to repeated binge alcohol during adolescence showed altered DNA methylation patterns in the hypothalamus, a brain region involved in regulation of pubertal development, stress, and behavior. These observations have potentially far-reaching consequences for human health, as more than 4.6 million Americans under the age of 21 years report engaging in the rapid intoxication behavior of binge-pattern alcohol (EtOH) drinking. Therefore, we tested the hypothesis that offspring of binge EtOH‒exposed parents would have altered hypothalamic function manifested phenotypically as improper pubertal development, impaired socialization, and dysregulated stress response. In addition, we tested the hypothesis that parental EtOH exposure would confer adaptive protection from the negative effects of EtOH when offspring were themselves exposed to EtOH. Rats received EtOH via oral gavage once daily for 6 days at both early [postnatal day (PND) 37] and late puberty (PND 67). Animals were paired (EtOH-EtOH, vehicle-vehicle) for mating 24 hours after the last EtOH dose. After weaning, offspring were randomized to vehicle treatment to assess changes in normal development or to EtOH treatment to assess the effect of parental EtOH exposure on offspring response to this treatment. We found that offspring had smaller body weights and displayed fewer play behaviors when parents had been exposed to EtOH before conception. In addition, offspring showed a reduction in pubertal development markers that could indicate that parental preconception EtOH exposure confers maladaptive epigenetic traits in first-generation offspring.

Effects of adolescent alcohol consumption on the brain and behaviour

Per occasion, alcohol consumption is higher in adolescents than in adults in both humans and laboratory animals, with changes in the adolescent brain probably contributing to this elevated drinking. This Review examines the contributors to and consequences of the use of alcohol in adolescents. Human adolescents with a history of alcohol use differ neurally and cognitively from other adolescents; some of these differences predate the commencement of alcohol consumption and serve as potential risk factors for later alcohol use, whereas others emerge from its use. The consequences of alcohol use in human adolescents include alterations in attention, verbal learning, visuospatial processing and memory, along with altered development of grey and white matter volumes and disrupted white matter integrity. The functional consequences of adolescent alcohol use emerging from studies of rodent models of adolescence include decreased cognitive flexibility, behavioural inefficiencies and elevations in anxiety, disinhibition, impulsivity and risk-taking. Rodent studies have also showed that adolescent alcohol use can impair neurogenesis, induce neuroinflammation and epigenetic alterations, and lead to the persistence of adolescent-like neurobehavioural phenotypes into adulthood. Although only a limited number of studies have examined comparable measures in humans and laboratory animals, the available data provide evidence for notable across-species similarities in the neural consequences of adolescent alcohol exposure, providing support for further translational efforts in this context.

Age-Related Differences in Alcohol Intake and Control Over Alcohol Seeking in Rats

Alcohol use disorder (AUD) is characterized by excessive and persistent alcohol use, despite adverse consequences. AUD often originates during adolescence, as do other substance use disorders. However, despite periods of excessive alcohol intake, many adolescents reduce their alcohol use by early adulthood. Brain development, social context, personality traits, and genetic makeup are thought to play an important role in these age-dependent fluctuations in alcohol use. However, studies that directly investigate age-related differences in the effects of alcohol exposure on brain and behavior are sparse. Therefore, to better understand the relationship between adolescent alcohol consumption and AUD-like behavior, this study compared the degree of control over alcohol seeking in rats that differed in terms of age of onset of alcohol drinking and in their level of alcohol consumption. We hypothesized that control over alcohol seeking is more prominent in adolescent-onset rats than in adult-onset rats, and that control over alcohol seeking is related to the consumed amount of alcohol. To test this hypothesis, alcohol seeking in the presence of a conditioned aversive stimulus was assessed after 2 months of intermittent alcohol access (IAA) in rats that consumed alcohol from postnatal day 42 (adolescence) or day 77 (adulthood). The rats were subdivided into low (LD), medium (MD), or high (HD) alcohol drinking rats, in order to assess the impact of the extent of alcohol intake on control over alcohol seeking. The adolescent-onset animals consumed slightly, but significantly less alcohol compared to the adult-onset rats. In adult-onset rats, we found that conditioned suppression of alcohol seeking, i.e., reduction of alcohol seeking by presentation of a conditioned aversive stimulus, was most pronounced in LD. By contrast, in the adolescent-onset rats, MD and HD showed increased alcohol seeking compared to LD, which was suppressed by conditioned aversive stimuli. Taken together, these findings reveal a complex relationship between the age of onset and level of alcohol intake with control over alcohol seeking, whereby adolescent rats consume less alcohol than adults. In adult rats, control over alcohol seeking is negatively related to preceding levels of alcohol intake. By contrast, adolescent rats appear to retain control over alcohol seeking, even after a history of high levels of alcohol intake.

Age-Dependent Effects of Acute Alcohol Administration in the Hippocampal Phosphoproteome

Alcohol consumption during adolescence is deleterious to the developing brain and leads to persistent deficits in adulthood. Several results provide strong evidence for ethanol-associated alterations in glutamatergic signaling and impaired synaptic plasticity in the hippocampus. Protein phosphorylation is a well-known and well-documented mechanism in memory processes, but information on phosphoprotein alterations in hippocampus after ethanol exposure is limited. This study focuses on age-related changes in the hippocampal phosphoproteome after acute alcohol administration. We have compared the phosphoprotein expression in the hippocampus of adult and adolescent Wistar rats treated with a single dose of ethanol (5 g/kg i.p.), using a proteomic approach including phosphoprotein enrichment by immobilized metal affinity chromatography (IMAC). Our proteomic analysis revealed that 13 proteins were differentially affected by age, ethanol administration, or both. Most of these proteins are involved in neuroprotection and are expressed less in young rats treated with ethanol. We conclude that acute alcohol induces important changes in the expression of phosphoproteins in the hippocampus that could increase the risk of neurodegenerative disorders, especially when the alcohol exposure begins in adolescence.

Voluntary alcohol intake after noise exposure in adolescent rats: Hippocampal-related behavioral alterations

Different physical or chemical agents, such as noise or alcohol, can induce diverse behavioral and biochemical alterations. Considering the high probability of young people to undergo consecutive or simultaneous exposures, the aim of the present work was to investigate in an animal model if noise exposure at early adolescence could induce hippocampal-related behavioral changes that might be modified after alcohol intake. Male Wistar rats (28-days-old) were exposed to noise (95-97 dB, 2 h). Afterwards, animals were allowed to voluntarily drink alcohol (10% ethanol in tap water) for three consecutive days, using the two-bottle free choice paradigm. After that, hippocampal-related memory and anxiety-like behavior tests were performed. Results show that whereas noise-exposed rats presented deficits in habituation memory, those who drank alcohol exhibited impairments in associative memory and anxiety-like behaviors. In contrast, exposure to noise followed by alcohol intake showed increases in exploratory and locomotor activities as well as in anxiety-like behaviors, unlike what was observed using each agent separately. Finally, lower levels of alcohol intake were measured in these animals when compared with those that drank alcohol and were not exposed to noise. Present findings demonstrate that exposure to physical and chemical challenges during early adolescence might induce behavioral alterations that could differ depending on the schedule used, suggesting a high vulnerability of rat developing brain to these socially relevant agents.

Adolescent binge ethanol exposure alters specific forebrain cholinergic cell populations and leads to selective functional deficits in the prefrontal cortex

Adolescence has been identified as a vulnerable developmental time period during which exposure to drugs can have long-lasting, detrimental effects. Although adolescent binge-like ethanol (EtOH) exposure leads to a significant reduction in forebrain cholinergic neurons, EtOH's functional effect on acetylcholine (ACh) release during behavior has yet to be examined. Using an adolescent intermittent ethanol exposure model (AIE), rats were exposed to binge-like levels of EtOH from postnatal days (PD) 25 to 55. Three weeks following the final EtOH exposure, cholinergic functioning was assessed during a spontaneous alternation protocol. During maze testing, ACh levels increased in both the hippocampus and prefrontal cortex. However, selectively in the prefrontal cortex, AIE rats displayed reduced levels of behaviorally relevant ACh efflux. We found no treatment differences in spatial exploration, spatial learning, spatial reversal, or novel object recognition. In contrast, AIE rats were impaired during the first attentional set shift on an operant set-shifting task, indicative of an EtOH-mediated deficit in cognitive flexibility. A unique pattern of cholinergic cell loss was observed in the basal forebrain following AIE: Within the medial septum/diagonal band there was a selective loss (30%) of choline acetyltransferase (ChAT)-positive neurons that were nestin negative (ChAT+/nestin-); whereas in the Nucleus basalis of Meynert (NbM) there was a selective reduction (50%) in ChAT+/nestin+. These results indicate that early adolescent binge EtOH exposure leads to a long-lasting frontocortical functional cholinergic deficit, driven by a loss of ChAT+/nestin+ neurons in the NbM, which was associated with impaired cognitive flexibility during adulthood.

Chronic intermittent ethanol exposure leads to alterations in brain-derived neurotrophic factor within the frontal cortex and impaired behavioral flexibility in both adolescent and adult rats

Chronic intermittent exposure to ethanol (EtOH; CIE) that produces binge-like levels of intoxication has been associated with age-dependent deficits in cognitive functioning. Male Sprague-Dawley rats were exposed to CIE (5g/kg, 25% EtOH, 13 intragastric gavages) beginning at three ages: early adolescence (postnatal day [PD] 28), mid-adolescence (PD35) and adulthood (PD72). In experiment 1, rats were behaviorally tested following CIE. Spatial memory was not affected by CIE, but adult CIE rats were impaired at acquiring a non-spatial discrimination task and subsequent reversal tasks. Rats exposed to CIE during early or mid-adolescence were impaired on the first reversal, demonstrating transient impairment in behavioral flexibility. Blood EtOH concentrations negatively correlated with performance on reversal tasks. Experiment 2 examined changes in brain-derived neurotrophic factor (BDNF) levels within the frontal cortex (FC) and hippocampus (HPC) at four time points: during intoxication, 24 h after the final EtOH exposure (acute abstinence), 3 weeks following abstinence (recovery) and after behavioral testing. HPC BDNF levels were not affected by CIE at any time point. During intoxication, BDNF was suppressed in the FC, regardless of the age of exposure. However, during acute abstinence, reduced FC BDNF levels persisted in early adolescent CIE rats, whereas adult CIE rats displayed an increase in BDNF levels. Following recovery, neurotrophin levels in all CIE rats recovered. Our results indicate that intermittent binge-like EtOH exposure leads to acute disruptions in FC BDNF levels and long-lasting behavioral deficits. However, the type of cognitive impairment and its duration differ depending on the age of exposure.

The Prefrontal Cortex as a Critical Gate of Negative Affect and Motivation in Alcohol Use Disorder

The prefrontal cortex (PFC) represents and executes the highest forms of goal-directed behavior, and has thereby attained a central neuroanatomical position in most pathophysiological conceptualizations of motivational disorders, including alcohol use disorder (AUD). Excessive, intermittent exposure to alcohol produces an allostatic dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis along with heightened forebrain glucocorticoid signaling that can damage PFC architecture and function. Negative affective states intimately associated with the transition to alcohol dependence result not only from a dysregulated HPA axis, but also from the inability of a damaged PFC to regulate subcortical stress and reinforcement centers, including the ventral striatum and amygdala. Several cognitive symptoms commonly associated with severe AUD, ranging from poor risk management to the cognitive/affective dimension of pain, are likely mediated by altered function of key anatomical elements that modulate PFC executive function, including contributions from the cingulate cortex and insula. Future therapeutic strategies for severe AUD should focus on attenuating the deleterious effects of excessive stress hormone activity on cognitive/affective and motivational behaviors gated by the PFC.

Voluntary ethanol consumption changes anticipatory ultrasonic vocalizations but not novelty response

Novelty and sensation seeking (NSS) and affective disorders are correlated with earlier ethanol (ETOH) consumption, and sustained drinking into adulthood. Understanding the NSS response and affective response before and after voluntary ETOH consumption could elucidate important individual differences promoting sustained ETOH consumption. This study determined that NSS and affective response to rewarding stimulation-measured by ultrasonic vocalizations (USVs)-change after adolescent ETOH voluntary drinking. Rats were tested for their NSS response using the inescapable novelty test. Then rats were tested for their affective response to a natural reward and USVs were measured. The natural reward was experimenter-induced play behavior. Rats were exposed to ETOH for 8 weeks using an intermittent two bottle paradigm. After 8 weeks of voluntary consumption, rats were retested for their response to NSS and affective response to natural reward. Results indicate that voluntary ETOH consumption did not change the response to novelty. Control and ETOH exposed rats decreased their novelty response equally after ETOH consumption, suggesting the decrease was due to age. Importantly, voluntary ETOH consumption changed affective USVs. Compared to water-drinking control rats, ETOH-consuming rats elicited greater anticipatory trill USVs to a natural reward-associated context during a post-drinking probe test. Tickle-induced trill USVs did not change differently between ETOH and control rats. These results provide evidence that voluntary intermittent ETOH exposure increases the anticipation of reward and may represent a form of incentive salience. We postulate these diverging effects could be due to differences in incentive salience or reward processing. Together, these results suggest that voluntary ETOH consumption changes the affective response to conditioned and unconditioned natural rewards and offers a behavioral mechanism for studying affective reward processing after ETOH consumption.