Adolescent alcohol exposure and persistence of adolescent-typical phenotypes into adulthood: a mini-review

Binge ethanol drinking during adolescence modifies cocaine responses in mice

Binge ethanol drinking is an emerging pattern of excessive consumption among adolescents and young adults. Repeated ethanol intoxication has negative consequences during critical periods of brain development. Therefore, binge ethanol intake represents a vulnerability factor that promotes subsequent manifestations of neuropsychiatric disorders. In this study, we investigated the effects of oral binge ethanol intake during adolescence on the subsequent effects of cocaine in C57BL/6 mice. Firstly, we evaluated the oral ethanol intake of two binge ethanol procedures with different ethanol concentrations (20% v/v versus 30%, v/v). The highest ethanol intake was found in mice exposed to the lower ethanol concentration (20% v/v). In a second experiment, mice exposed to binge ethanol procedure were evaluated to study the effects of cocaine on locomotor activity, behavioural sensitization, and the reinforcing effects of cocaine in the self-administration paradigm. Mice exposed to ethanol binging showed discrete detrimental effects in responses to cocaine in the different experiments evaluated. Our findings revealed that the pattern of binge ethanol consumption in adolescent mice here evaluated produced a weak facilitation of cocaine responses. The present study highlights the importance of interventions to limit the deleterious effects of binge ethanol drinking during adolescence.

Gender Differences in Risk Factors for Adolescent Binge Drinking and Implications for Intervention and Prevention

Alcohol use, particularly binge drinking (BD), is a major public health concern among adolescents. Recent national data show that the gender gap in alcohol use is lessening, and BD among girls is rising. Considering the increase in BD among adolescent girls, as well as females' increased risk of experiencing more severe biopsychosocial negative effects and consequences from BD, the current review sought to examine gender differences in risk factors for BD. The review highlights gender differences in (1) developmental-related neurobiological vulnerability to BD, (2) psychiatric comorbidity and risk phenotypes for BD, and (3) social-related risk factors for BD among adolescents, as well as considerations for BD prevention and intervention. Most of the information gleaned thus far has come from preclinical research. However, it is expected that, with recent advances in clinical imaging technology, neurobiological effects observed in lower mammals will be confirmed in humans and vice versa. A synthesis of the literature highlights that males and females experience unique neurobiological paths of development, and although there is debate regarding the specific nature of these differences, literature suggests that these differences in turn influence gender differences in psychiatric comorbidity and risk for BD. For one, girls are more susceptible to stress, depression, and other internalizing behaviors and, in turn, these symptoms contribute to their risk for BD. On the other hand, males, given gender differences across the lifespan as well as gender differences in development, are driven by an externalizing phenotype for risk of BD, in part, due to unique paths of neurobiological development that occur across adolescence. With respect to social domains, although social and peer influences are important for both adolescent males and females, there are gender differences. For example, girls may be more sensitive to pressure from peers to fit in and impress others, while male gender role stereotypes regarding BD may be more of a risk factor for boys. Given these unique differences in male and female risk for BD, further research exploring risk factors, as well as tailoring intervention and prevention, is necessary. Although recent research has tailored substance use intervention to target males and females, more literature on gender considerations in treatment for prevention and intervention of BD in particular is warranted.

Differential Sensitivity to Ethanol-Induced Circadian Rhythm Disruption in Adolescent and Adult Mice

BACKGROUND

Growing evidence supports a central role for the circadian system in alcohol use disorders, but few studies have examined this relationship during adolescence. In mammals, circadian rhythms are regulated by the suprachiasmatic nucleus, a biological clock whose timing is synchronized (reset) to the environment primarily by light (photic) input. Alcohol (ethanol [EtOH]) disrupts circadian timing in part by attenuating photic phase-resetting responses in adult rodents. However, circadian rhythms change throughout life and it is not yet known whether EtOH has similar effects on circadian regulation during adolescence.

METHODS

General circadian locomotor activity was monitored in male C57BL6/J mice beginning in adolescence (P27) or adulthood (P61) in a 12-hour light, 12-hour dark photocycle for ~2 weeks to establish baseline circadian activity measures. On the day of the experiment, mice received an acute injection of EtOH (1.5 g/kg, i.p.) or equal volume saline 15 minutes prior to a 30-minute light pulse at Zeitgeber Time 14 (2 hours into the dark phase) and then were released into constant darkness (DD) for ~2 weeks to assess phase-resetting responses. Control mice of each age-group received injections but no light pulse prior to DD.

RESULTS

While adults showed the expected decrease in photic phase-delays induced by acute EtOH, this effect was absent in adolescent mice. Adolescents also showed baseline differences in circadian rhythmicity compared to adults, including advanced photocycle entrainment, larger photic phase-delays, a shorter free-running (endogenous) circadian period, and greater circadian rhythm amplitude.

CONCLUSIONS

Collectively, our results indicate that adolescent mice are less sensitive to the effect of EtOH on circadian photic phase-resetting and that their daily activity rhythms are markedly different than those of adults.

Post-weaning Environmental Enrichment, But Not Chronic Maternal Isolation, Enhanced Ethanol Intake during Periadolescence and Early Adulthood

This study analyzed ethanol intake in male and female Wistar rats exposed to maternal separation (MS) during infancy (postnatal days 1-21, PD1-21) and environmental enrichment (EE) during adolescence (PD 21-42). Previous work revealed that MS enhances ethanol consumption during adulthood. It is still unknown if a similar effect is found during adolescence. Several studies, in turn, have revealed that EE reverses stress experiences, and reduces ethanol consumption and reinforcement; although others reported greater ethanol intake after EE. The interactive effects between these treatments upon ethanol's effects and intake have yet to be explored. We assessed chronic ethanol intake and preference (12 two-bottle daily sessions, spread across 30 days, 1st session on PD46) in rats exposed to MS and EE. The main finding was that male - but not female - rats that had been exposed to EE consumed more ethanol than controls given standard housing, an effect that was not affected by MS. Subsequent experiments assessed several factors associated with heightened ethanol consumption in males exposed to MS and EE; namely taste aversive conditioning and hypnotic-sedative consequences of ethanol. We also measured anxiety response in the light-dark box and in the elevated plus maze tests; and exploratory patterns of novel stimuli and behaviors indicative of risk assessment and risk-taking, via a modified version of the concentric square field (CSF) test. Aversive conditioning, hypnosis and sleep time were similar in males exposed or not to EE. EE males, however, exhibited heightened exploration of novel stimuli and greater risk taking behaviors in the CSF test. It is likely that the promoting effect of EE upon ethanol intake was due to these effects upon exploratory and risk-taking behaviors.

Adolescent Alcohol Exposure Persistently Impacts Adult Neurobiology and Behavior

Adolescence is a developmental period when physical and cognitive abilities are optimized, when social skills are consolidated, and when sexuality, adolescent behaviors, and frontal cortical functions mature to adult levels. Adolescents also have unique responses to alcohol compared with adults, being less sensitive to ethanol sedative-motor responses that most likely contribute to binge drinking and blackouts. Population studies find that an early age of drinking onset correlates with increased lifetime risks for the development of alcohol dependence, violence, and injuries. Brain synapses, myelination, and neural circuits mature in adolescence to adult levels in parallel with increased reflection on the consequence of actions and reduced impulsivity and thrill seeking. Alcohol binge drinking could alter human development, but variations in genetics, peer groups, family structure, early life experiences, and the emergence of psychopathology in humans confound studies. As adolescence is common to mammalian species, preclinical models of binge drinking provide insight into the direct impact of alcohol on adolescent development. This review relates human findings to basic science studies, particularly the preclinical studies of the Neurobiology of Adolescent Drinking in Adulthood (NADIA) Consortium. These studies focus on persistent adult changes in neurobiology and behavior following adolescent intermittent ethanol (AIE), a model of underage drinking. NADIA studies and others find that AIE results in the following: increases in adult alcohol drinking, disinhibition, and social anxiety; altered adult synapses, cognition, and sleep; reduced adult neurogenesis, cholinergic, and serotonergic neurons; and increased neuroimmune gene expression and epigenetic modifiers of gene expression. Many of these effects are specific to adolescents and not found in parallel adult studies. AIE can cause a persistence of adolescent-like synaptic physiology, behavior, and sensitivity to alcohol into adulthood. Together, these findings support the hypothesis that adolescent binge drinking leads to long-lasting changes in the adult brain that increase risks of adult psychopathology, particularly for alcohol dependence.

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

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

Neurodevelopmental Precursors and Consequences of Substance Use during Adolescence: Promises and Pitfalls of Longitudinal Neuroimaging Strategies

Neurocognitive and emotional regulatory deficits in substance users are often attributed to misuse; however most studies do not include a substance-naïve baseline to justify that conclusion. The etiological literature suggests that pre-existing deficits may contribute to the onset and escalation of use that are then exacerbated by subsequent use. To address this, there is burgeoning interest in conducting prospective, longitudinal neuroimaging studies to isolate neurodevelopmental precursors and consequences of adolescent substance misuse, as reflected in recent initiatives such as the NIH-led Adolescent Brain Cognitive Development (ABCD) study and the National Consortium on Alcohol and Neurodevelopment (NCANDA). To distinguish neurodevelopmental precursors from the consequences of adolescent substance use specifically, prospective, longitudinal neuroimaging studies with substance-naïve pre-adolescents are needed. The exemplar described in this article—i.e., the ongoing Adolescent Development Study (ADS)—used a targeted recruitment strategy to bolster the numbers of pre-adolescent individuals who were at increased risk of substance use (i.e., “high-risk”) in a sample that was relatively small for longitudinal studies of similar phenomena, but historically large for neuroimaging (i.e., N = 135; 11–13 years of age). At baseline participants underwent MRI testing and a large complement of cognitive and behavioral assessments along with genetics, stress physiology and interviews. The study methods include repeating these measures at three time points (i.e., baseline/Wave 1, Wave 2 and Wave 3), 18 months apart. In this article, rather than outlining specific study outcomes, we describe the breadth of the numerous complexities and challenges involved in conducting this type of prospective, longitudinal neuroimaging study and “lessons learned” for subsequent efforts are discussed. While these types of large longitudinal neuroimaging studies present a number of logistical and scientific challenges, the wealth of information obtained about the precursors and consequences of adolescent substance use provides unique insights into the neurobiological bases for adolescent substance use that will lay the groundwork for targeted interventions.

Does our legal minimum drinking age modulate risk of first heavy drinking episode soon after drinking onset? Epidemiological evidence for the United States, 2006-2014

Background. State-level 'age 21' drinking laws conform generally with the United States National Minimum Drinking Age Act of 1984 (US), and are thought to protect young people from adverse drinking experiences such as heavy episodic drinking (HED, sometimes called 'binge drinking'). We shed light on this hypothesis while estimating the age-specific risk of transitioning from 1st full drink to 1st HED among 12-to-23-year-old newly incident drinkers, with challenge to a "gender gap" hypothesis and male excess described in HED prevalence reports. Methods. The study population consisted of non-institutionalized civilians in the United States, with nine independently drawn nationally representative samples of more than 40,000 12-to-23-year-olds (2006-2014). Standardized audio computer-assisted self-interviews identified 43,000 newly incident drinkers (all with 1st HED evaluated within 12 months of drinking onset). Estimated age-specific HED risk soon after first full drink is evaluated for males and females. Results. Among 12-to-23-year-old newly incident drinkers, an estimated 20-30% of females and 35-45% of males experienced their 1st HED within 12 months after drinking onset. Before mid-adolescence, there is no male excess in such HED risk. Those who postponed drinking to age 21 are not spared (27% for 'postponer' females; 95% CI [24-30]; 42% for 'postponer' males; 95% CI [38-45]). An estimated 10-18% females and 10-28% males experienced their 1st HED in the same month of their 1st drink; peak HED risk estimates are 18% for 'postponer' females (95% CI [15-21]) and 28% for 'postponer' males (95% CI [24-31]). Conclusions. In the US, one in three young new drinkers transition into HED within 12 months after first drink. Those who postpone the 1st full drink until age 21 are not protected. Furthermore, 'postponers' have substantial risk for very rapid transition to HED. A male excess in this transition to HED is not observed until after age 14.

Adolescent Alcohol Exposure: Burden of Epigenetic Reprogramming, Synaptic Remodeling, and Adult Psychopathology

Adolescence represents a crucial phase of synaptic maturation characterized by molecular changes in the developing brain that shape normal behavioral patterns. Epigenetic mechanisms play an important role in these neuromaturation processes. Perturbations of normal epigenetic programming during adolescence by ethanol can disrupt these molecular events, leading to synaptic remodeling and abnormal adult behaviors. Repeated exposure to binge levels of alcohol increases the risk for alcohol use disorder (AUD) and comorbid psychopathology including anxiety in adulthood. Recent studies in the field clearly suggest that adolescent alcohol exposure causes widespread and persistent changes in epigenetic, neurotrophic, and neuroimmune pathways in the brain. These changes are manifested by altered synaptic remodeling and neurogenesis in key brain regions leading to adult psychopathology such as anxiety and alcoholism. This review details the molecular mechanisms underlying adolescent alcohol exposure-induced changes in synaptic plasticity and the development of alcohol addiction-related phenotypes in adulthood.

Impaired fear extinction in adolescent rodents: Behavioural and neural analyses

Despite adolescence being a developmental window of vulnerability, up until very recently there were surprisingly few studies on fear extinction during this period. Here we summarise the recent work in this area, focusing on the unique behavioural and neural characteristics of fear extinction in adolescent rodents, and humans where relevant. A prominent hypothesis posits that anxiety disorders peak during late childhood/adolescence due to the non-linear maturation of the fear inhibition neural circuitry. We discuss evidence that impaired extinction retention in adolescence is due to subregions of the medial prefrontal cortex and amygdala mediating fear inhibition being underactive while other subregions that mediate fear expression are overactive. We also review work on various interventions and surprising circumstances which enhance fear extinction in adolescence. This latter work revealed that the neural correlates of extinction in adolescence are different to that in younger and older animals even when extinction retention is not impaired. This growing body of work highlights that adolescence is a unique period of development for fear inhibition.

Chronic intermittent ethanol exposure during adolescence: Effects on stress-induced social alterations and social drinking in adulthood

We previously observed lasting and sex-specific detrimental consequences of early adolescent intermittent ethanol exposure (AIE), with male, but not female, rats showing social anxiety-like alterations when tested as adults. The present study used Sprague Dawley rats to assess whether social alterations induced by AIE (3.5g/kg, intragastrically, every other day, between postnatal days [P] 25-45) are further exacerbated by stressors later in life. Another aim was to determine whether AIE alone or in combination with stress influenced intake of a sweetened ethanol solution (Experiment 1) or a sweetened solution ("supersac") alone (Experiment 2) under social circumstances. Animals were exposed to restraint on P66-P70 (90min/day) or left nonstressed, with corticosterone (CORT) levels assessed on day 1 and day 5 in Experiment 2. Social anxiety-like behavior emerged after AIE in non-stressed males, but not females, whereas stress-induced social anxiety was evident only in water-exposed males and females. Adult-typical habituation of the CORT response to repeated restraint was not evident in adult animals after AIE, a lack of habituation reminiscent of that normally evident in adolescents. Neither AIE nor stress affected ethanol intake under social circumstances, although AIE and restraint independently increased adolescent-typical play fighting in males during social drinking. Among males, the combination of AIE and restraint suppressed "supersac" intake; this index of depression-like behavior was not seen in females. The results provide experimental evidence associating adolescent alcohol exposure, later stress, anxiety, and depression, with young adolescent males being particularly vulnerable to long-lasting adverse effects of repeated ethanol. This article is part of a Special Issue entitled SI: Adolescent plasticity.

Clinical characteristics of alcohol combined with other substance use disorders in an American Indian community sample

BACKGROUND

Alcohol and other substance use disorders (SUD) pose major problems of morbidity and mortality in some American Indian communities, but little is known about the clinical characteristics, risk factors, and consequences of combined alcohol and other substance use disorders (multi-substance use disorder, MSUD) in those communities.

METHODS

Using the Semi-Structured Assessment for the Genetics of Alcoholism (SSAGA), in a community sample of 876 American Indians, the clinical characteristics of lifetime DSM-5 moderate or severe alcohol use disorder alone (AUD alone) (n=146) and MSUD (defined as alcohol and ≥1 other SUD) (n=284) were evaluated and compared to 347 participants with no lifetime SUD (no SUD).

RESULTS

The majority (57%) of participants with a SUD had multi-substance use disorder and 94% of those were with AUD. Stimulants (cocaine and/or amphetamine) and/or cannabis were the most common other SUDs. Participants with AUD alone were more likely to be male and have an earlier age of first alcohol intoxication than those with no SUD. Those with MSUD were more likely to have dropped out of high school, have antisocial personality disorder (ASPD) or conduct disorder (CD), have earlier ages of first alcohol intoxication and first use of cannabis and stimulants, an earlier age of onset of AUD, and more of several AUD symptoms than those with AUD alone, but the same temporal course and time to remission of AUD.

CONCLUSIONS

MSUD is prevalent in this sample, is associated with multiple comorbidities and denotes a more severe alcohol syndrome than AUD alone.

Age-related effects of chronic restraint stress on ethanol drinking, ethanol-induced sedation, and on basal and stress-induced anxiety response

Adolescents are sensitive to the anxiolytic effect of ethanol, and evidence suggests that they may be more sensitive to stress than adults. Relatively little is known, however, about age-related differences in stress modulation of ethanol drinking or stress modulation of ethanol-induced sedation and hypnosis. We observed that chronic restraint stress transiently exacerbated free-choice ethanol drinking in adolescent, but not in adult, rats. Restraint stress altered exploration patterns of a light-dark box apparatus in adolescents and adults. Stressed animals spent significantly more time in the white area of the maze and made significantly more transfers between compartments than their non-stressed peers. Behavioral response to acute stress, on the other hand, was modulated by prior restraint stress only in adults. Adolescents, unlike adults, exhibited ethanol-induced motor stimulation in an open field. Stress increased the duration of loss of the righting reflex after a high ethanol dose, yet this effect was similar at both ages. Ethanol-induced sleep time was much higher in adult than in adolescent rats, yet stress diminished ethanol-induced sleep time only in adults. The study indicates age-related differences that may increase the risk for initiation and escalation in alcohol drinking.

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

Previous research has found that adolescent ethanol (EtOH) exposure alters drug seeking behaviors, cognition and neuroplasticity. Using male Sprague Dawley rats, differences in spatial working memory, non-spatial discrimination learning and behavioral flexibility were explored as a function of age at the onset (mid-adolescent vs. adult) of chronic EtOH exposure (CET). Concentrations of mature brain-derived neurotrophic factor (mBDNF) and beta-nerve growth factor (β-NGF) in the prefrontal cortex and hippocampus were also assessed at different time-points: during CET, following acute abstinence (48-hrs), and after protracted abstinence (6-8 wks). Our results revealed that an adolescent onset of CET leads to increased EtOH consumption that persisted into adulthood. In both adult and adolescent onset CET groups, there were significant long-term reductions in prefrontal cortical mBDNF and β-NGF levels. However, only adult onset CET rats displayed decreased hippocampal BDNF levels. Spatial memory, assessed by spontaneous alternation and delayed alternation, was not significantly affected by CET as a function of age of drinking onset, but higher blood-EtOH levels were correlated with lower spontaneous alternation scores. Regardless of the age of onset, EtOH exposed rats were impaired on non-spatial discrimination learning and displayed inflexible behavioral patterns upon reversal learning. Our results indicate that adolescent EtOH exposure changes long-term consumption patterns producing behavioral and neural dysfunctions that persist across the lifespan.

Baclofen blocks yohimbine-induced increases in ethanol-reinforced responding in rats

Chronic or repeated stress increases alcohol consumption. The GABA-B agonist baclofen decreases alcohol consumption and may be most effective for individuals with comorbid anxiety/stress disorders. The present study sought to determine if baclofen blocks stress-induced increases in ethanol self-administration as modeled by repeated yohimbine injections in rats. Rats were trained to respond for 15% w/v ethanol in operant chambers using a method that applies neither water deprivation nor saccharin/sucrose fading. Following training, the rats received 6 injections of 1.25mg/kg yohimbine were given immediately prior to the operant sessions during a 2-week time period. Subsequently, some rats were pair-matched to receive either 1.25mg/kg yohimbine or saline in the presence of 0.3, 1, and 3mg/kg baclofen prior to sessions. Acquisition of ethanol self-administration was poor. Pretreatment with yohimbine consistently increased responding across repeated injections. Yohimbine's effect on ethanol intake unexpectedly diverged from the effect on responding as the rats failed to consume all reinforcers earned. Smaller doses of baclofen paired with saline injections had no effect on ethanol responding; only 3mg/kg baclofen reduced ethanol self-administration. The smallest baclofen dose of 0.3mg/kg failed to block the yohimbine-induced increase in self-administration. The large baclofen dose of 3mg/kg continued to suppress ethanol self-administration when given with yohimbine. Baclofen 1mg/kg blocked the effect of yohimbine even though it had no effect when given in the absence of yohimbine. Exposure to high ethanol concentrations may induce self-administration only in certain conditions. The dissociation between responding and intake suggests that repeated yohimbine injections may initiate other behavioral or physiological mechanisms that confound its effects as a pharmacological stressor. Furthermore, an optimal baclofen dose range may specifically protect against stress-induced alcohol self-administration, highlighting a specific contribution of GABA-B receptors and a potential therapeutic efficacy of GABA-B agonists at a non-sedating dose.

Sex Differences in Behavioral Dyscontrol: Role in Drug Addiction and Novel Treatments

The purpose of this review is to discuss recent findings related to sex differences in behavioral dyscontrol that lead to drug addiction, and clinical implications for humans are discussed. This review includes research conducted in animals and humans that reveals fundamental aspects of behavioral dyscontrol. The importance of sex differences in aspects of behavioral dyscontrol, such as impulsivity and compulsivity, is discussed as major determinants of drug addiction. Behavioral dyscontrol during adolescence is also an important consideration, as this is the time of onset for drug addiction. These vulnerability factors additively increase drug-abuse vulnerability, and they are integral aspects of addiction that covary and interact with sex differences. Sex differences in treatments for drug addiction are also reviewed in terms of their ability to modify the behavioral dyscontrol that underlies addictive behavior. Customized treatments to reduce behavioral dyscontrol are discussed, such as (1) using natural consequences such as non-drug rewards (e.g., exercise) to maintain abstinence, or using punishment as a consequence for drug use, (2) targeting factors that underlie behavioral dyscontrol, such as impulsivity or anxiety, by repurposing medications to relieve these underlying conditions, and (3) combining two or more novel behavioral or pharmacological treatments to produce additive reductions in drug seeking. Recent published work has indicated that factors contributing to behavioral dyscontrol are an important target for advancing our knowledge on the etiology of drug abuse, intervening with the drug addiction process and developing novel treatments.

Sex differences in behavior and neural development and their role in adolescent vulnerability to substance use

Adolescents are especially prone to risky behavior and to the emergence of psychological disorders like substance abuse, anxiety and depression. However, there is a sex (or gender) difference in this vulnerability, with females being more prone to developing internalizing disorders and males being more likely to engage in risky behavior and drug use. While several researchers have proposed that there is a relationship between corticolimbic circuit development and adolescent vulnerability, the current proposed models do not take sex differences into account. In this review, we explore recent findings from both human and rodent studies of sex differences during adolescence. In particular, we consider epidemiological studies on the factors that contribute to the development of substance abuse and internalizing disorders, laboratory studies on reward-related and decision-making behavior, and neuroanatomical studies on the development of several structures in the corticolimbic circuit (i.e., prefrontal cortex [PFC], amygdala and striatum). We then integrate these recent findings into models of adolescent vulnerability to substance use that have previously not addressed sex differences. Lastly, we discuss methodological considerations for the interpretation and design of studies on sex (or gender) differences during adolescence while highlighting some opportunities for future investigations.

Adolescent binge-like alcohol alters sensitivity to acute alcohol effects on dopamine release in the nucleus accumbens of adult rats

Rationale: Early onset of alcohol drinking has been associated with alcohol abuse in adulthood. The neurobiology of this phenomenon is unclear, but mesolimbic dopamine pathways, which are dynamic during adolescence, may play a role.

OBJECTIVES

We investigated the impact of adolescent binge-like alcohol on phasic dopaminergic neurotransmission during adulthood.

METHODS

Rats received intermittent intragastric ethanol, water, or nothing during adolescence. In adulthood, electrically evoked dopamine release and subsequent uptake were measured in the nucleus accumbens core at baseline and after acute challenge of ethanol or saline.

RESULTS

Adolescent ethanol exposure did not alter basal measures of evoked dopamine release or uptake. Ethanol challenge dose-dependently decreased the amplitude of evoked dopamine release in rats by 30–50 % in control groups, as previously reported, but did not alter evoked release in ethanol-exposed animals. To address the mechanism by which ethanol altered dopamine signaling, the evoked signals were modeled to estimate dopamine efflux per impulse and the velocity of the dopamine transporter. Dopamine uptake was slower in all exposure groups after ethanol challenge compared to saline, while dopamine efflux per pulse of electrical stimulation was reduced by ethanol only in ethanol-naive rats.

CONCLUSIONS

The results demonstrate that exposure to binge levels of ethanol during adolescence blunts the effect of ethanol challenge to reduce the amplitude of phasic dopamine release in adulthood. Large dopamine transients may result in more extracellular dopamine after alcohol challenge in adolescent-exposed rats and may be one mechanism by which alcohol is more reinforcing in people who initiated drinking at an early age.

Drinking Over the Lifespan: Focus on Early Adolescents and Youth

Historical trends in alcohol use among U.S. adolescents, as well as data regarding alcohol-related traffic fatalities among youth, indicate decreases in alcohol use. Nevertheless, alcohol use patterns still indicate high rates of binge drinking and drunkenness and the co-occurrence of alcohol use among youth with risky sexual activity, illicit substance use, and poor school performance. This article discusses unique elements of alcohol use among adolescents relative to adults that pose risks for alcohol misuse and alcohol-related problems. These differences range from patterns of drinking to differential sensitivity to alcohol. Developmental differences between adolescents and adults also are discussed with regard to age-normative developmental tasks and distinctions in brain development that may affect differences in drinking patterns. Epidemiologic findings on sexual-minority youth are provided, as are global trends in alcohol use among early adolescents and youth. It is proposed that using information about differences between youth and adults will be helpful in directing future etiologic and intervention research by capitalizing on unique biological, psychological, and social factors that may affect the success of efforts to reduce alcohol use among early adolescents and youth.

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

BACKGROUND

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

METHODS

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

RESULTS

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

CONCLUSIONS

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

Adolescent Intermittent Alcohol Exposure: Deficits in Object Recognition Memory and Forebrain Cholinergic Markers

The long-term effects of intermittent ethanol exposure during adolescence (AIE) are of intensive interest and investigation. The effects of AIE on learning and memory and the neural functions that drive them are of particular interest as clinical findings suggest enduring deficits in those cognitive domains in humans after ethanol abuse during adolescence. Although studies of such deficits after AIE hold much promise for identifying mechanisms and therapeutic interventions, the findings are sparse and inconclusive. The present results identify a specific deficit in memory function after AIE and establish a possible neural mechanism of that deficit that may be of translational significance. Male rats (starting at PND-30) received exposure to AIE (5g/kg, i.g.) or vehicle and were allowed to mature into adulthood. At PND-71, one group of animals was assessed using the spatial-temporal object recognition (stOR) test to evaluate memory function. A separate group of animals was used to assess the density of cholinergic neurons in forebrain areas Ch1-4 using immunohistochemistry. AIE exposed animals manifested deficits in the temporal component of the stOR task relative to controls, and a significant decrease in the number of ChAT labeled neurons in forebrain areas Ch1-4. These findings add to the growing literature indicating long-lasting neural and behavioral effects of AIE that persist into adulthood and indicate that memory-related deficits after AIE depend upon the tasks employed, and possibly their degree of complexity. Finally, the parallel finding of diminished cholinergic neuron density suggests a possible mechanism underlying the effects of AIE on memory and hippocampal function as well as possible therapeutic or preventive strategies for AIE.

The reinforcing properties of ethanol are quantitatively enhanced in adulthood by peri-adolescent ethanol, but not saccharin, consumption in female alcohol-preferring (P) rats

Alcohol drinking during adolescence is associated in adulthood with heavier alcohol drinking and an increased rate of alcohol dependence. Past research in our laboratory has indicated that peri-adolescent ethanol consumption can enhance the acquisition and reduce the rate of extinction of ethanol self-administration in adulthood. Caveats of the past research include reinforcer specificity, increased oral consumption during peri-adolescence, and a lack of quantitative assessment of the reinforcing properties of ethanol. The current experiments were designed to determine the effects of peri-adolescent ethanol or saccharin drinking on acquisition and extinction of oral ethanol self-administration and ethanol seeking, and to quantitatively assess the reinforcing properties of ethanol (progressive ratio). Ethanol or saccharin access by alcohol-preferring (P) rats occurred during postnatal day (PND) 30-60. Animals began operant self-administration of ethanol or saccharin after PND 85. After 10 weeks of daily operant self-administration, rats were tested in a progressive ratio paradigm. Two weeks later, self-administration was extinguished in all rats. Peri-adolescent ethanol consumption specifically enhanced the acquisition of ethanol self-administration, reduced the rate of extinction for ethanol self-administration, and quantitatively increased the reinforcing properties of ethanol during adulthood. Peri-adolescent saccharin consumption was without effect. The data indicate that ethanol consumption during peri-adolescence results in neuroadaptations that may specifically enhance the reinforcing properties of ethanol during adulthood. This increase in the reinforcing properties of ethanol could be a part of biological sequelae that are the basis for the effects of adolescent alcohol consumption on the increase in the rate of alcoholism during adulthood.

Sex differences in the long-lasting consequences of adolescent ethanol exposure for the rewarding effects of cocaine in mice

RATIONALE

The practice of binge drinking is very common among adolescents of both sexes. It can have long-term consequences with respect to drug consumption during adulthood, but knowledge on these effects in females is limited.

OBJECTIVES

The long-lasting effects of intermittent exposure to ethanol (EtOH) during adolescence on different cocaine-elicited behaviours, including locomotor reactivity, conditioned place preference (CPP) and intravenous self-administration, were evaluated in male and female adult mice. It was hypothesized that an EtOH binge during adolescence would increase sensitivity to the effects of a sub-threshold dose of cocaine and has a differential impact on the drug's effects in males and females.

METHODS

Adolescent OF1 mice (postnatal day (PND) 26) underwent a 2-week pre-treatment schedule consisting of 16 doses of EtOH (2.5 g/kg) or saline (twice daily administrations separated by a 4-h interval i.p.) administered on two consecutive days separated by an interval of 2 days. Three weeks later (PND > 60), we assessed locomotor activity responses induced by an acute injection of different doses of cocaine in experiment 1 and the rewarding effects of cocaine on the CPP (1 mg/kg) and intravenous self-administration (1 mg/kg/infusion) paradigms in experiment 2.

RESULTS

Pre-exposure to EtOH during adolescence altered motor reactivity to cocaine in a dose- and sex-dependent manner, increased sensitivity to cocaine in CPP and enhanced self-administration in adult mice.

CONCLUSIONS

The effects of intermittent exposure to ethanol during adolescence are evident in adulthood, during which greater sensitivity and intake of cocaine is observed and differ in each sex.

Disruption of peri-adolescent endocannabinoid signaling modulates adult neuroendocrine and behavioral responses to stress in male rats

The endocannabinoid (eCB) system is known to regulate neural, endocrine and behavioral responses to stress in adults; however there is little knowledge regarding how this system governs the development and maturation of these responses. Previous work has reported dynamic and time-specific changes in CB1 receptor expression, N-arachidonylethanolamine (AEA) content and fatty acid amide hydrolase (FAAH) activity within corticolimbic structures throughout the peri-adolescent period. To examine whether fluctuations in adolescent eCB activity contribute to the development of adult stress responsivity and emotionality, we treated male Sprague-Dawley rats daily with the CB1R antagonist, AM-251 (5 mg/kg), or vehicle between post-natal days (PND) 35-45. Following this treatment, emotional behavior, HPA axis stress reactivity and habituation to repeated restraint stress, as well as corticolimbic eCB content were examined in adulthood (PND 75). Behaviorally, AM-251-treated males exhibited more active stress-coping behavior in the forced swim test, greater risk assessment behavior in the elevated plus maze and no significant differences in general motor activity. Peri-adolescent AM-251 treatment modified corticosterone habituation to repeated restraint exposure compared to vehicle. Peri-adolescent CB1R antagonism induced moderate changes in adult corticolimbic eCB signaling, with a significant decrease in amygdalar AEA, an increase in hypothalamic AEA and an increase in prefrontal cortical CB1R expression. Together, these data indicate that peri-adolescent endocannabinoid signaling contributes to the maturation of adult neurobehavioral responses to stress.

Adolescent nicotine induces persisting changes in development of neural connectivity

Adolescent nicotine induces persisting changes in development of neural connectivity. A large number of brain changes occur during adolescence as the CNS matures. These changes suggest that the adolescent brain may still be susceptible to developmental alterations by substances which impact its growth. Here we review recent studies on adolescent nicotine which show that the adolescent brain is differentially sensitive to nicotine-induced alterations in dendritic elaboration, in several brain areas associated with processing reinforcement and emotion, specifically including nucleus accumbens, medial prefrontal cortex, basolateral amygdala, bed nucleus of the stria terminalis, and dentate gyrus. Both sensitivity to nicotine, and specific areas responding to nicotine, differ between adolescent and adult rats, and dendritic changes in response to adolescent nicotine persist into adulthood. Areas sensitive to, and not sensitive to, structural remodeling induced by adolescent nicotine suggest that the remodeling generally corresponds to the extended amygdala. Evidence suggests that dendritic remodeling is accompanied by persisting changes in synaptic connectivity. Modeling, electrophysiological, neurochemical, and behavioral data are consistent with the implication of our anatomical studies showing that adolescent nicotine induces persisting changes in neural connectivity. Emerging data thus suggest that early adolescence is a period when nicotine consumption, presumably mediated by nicotine-elicited changes in patterns of synaptic activity, can sculpt late brain development, with consequent effects on synaptic interconnection patterns and behavior regulation. Adolescent nicotine may induce a more addiction-prone phenotype, and the structures altered by nicotine also subserve some emotional and cognitive functions, which may also be altered. We suggest that dendritic elaboration and associated changes are mediated by activity-dependent synaptogenesis, acting in part through D1DR receptors, in a network activated by nicotine. The adolescent nicotine effects reviewed here suggest that modification of late CNS development constitutes a hazard of adolescent nicotine use.

Adolescent intermittent ethanol exposure enhances ethanol activation of the nucleus accumbens while blunting the prefrontal cortex responses in adult rat

The brain continues to develop through adolescence when excessive alcohol consumption is prevalent in humans. We hypothesized that binge drinking doses of ethanol during adolescence will cause changes in brain ethanol responses that persist into adulthood. To test this hypothesis Wistar rats were treated with an adolescent intermittent ethanol (AIE; 5 g/kg, i.g. 2 days on-2 days off; P25-P54) model of underage drinking followed by 25 days of abstinence during maturation to young adulthood (P80). Using markers of neuronal activation c-Fos, EGR1, and phophorylated extracellar signal regulated kinase (pERK1/2), adult responses to a moderate and binge drinking ethanol challenge, e.g., 2 or 4 g/kg, were determined. Adult rats showed dose dependent increases in neuronal activation markers in multiple brain regions during ethanol challenge. Brain regional responses correlated are consistent with anatomical connections. AIE led to marked decreases in adult ethanol PFC (prefrontal cortex) and blunted responses in the amygdala. Binge drinking doses led to the nucleus accumbens (NAc) activation that correlated with the ventral tegmental area (VTA) activation. In contrast to other brain regions, AIE enhanced the adult NAc response to binge drinking doses. These studies suggest that adolescent alcohol exposure causes long-lasting changes in brain responses to alcohol that persist into adulthood.

Adolescent intermittent alcohol exposure: persistence of structural and functional hippocampal abnormalities into adulthood

BACKGROUND

Human adolescence is a crucial stage of neurological development during which ethanol (EtOH) consumption is often at its highest. Alcohol abuse during adolescence may render individuals at heightened risk for subsequent alcohol abuse disorders, cognitive dysfunction, or other neurological impairments by irreversibly altering long-term brain function. To test this possibility, we modeled adolescent alcohol abuse (i.e., intermittent EtOH exposure during adolescence [AIE]) in rats to determine whether adolescent exposure to alcohol leads to long-term structural and functional changes that are manifested in adult neuronal circuitry.

METHODS

We specifically focused on hippocampal area CA1, a brain region associated with learning and memory. Using electrophysiological, immunohistochemical, and neuroanatomical approaches, we measured post-AIE changes in synaptic plasticity, dendritic spine morphology, and synaptic structure in adulthood.

RESULTS

We found that AIE-pretreated adult rats manifest robust long-term potentiation, induced at stimulus intensities lower than those required in controls, suggesting a state of enhanced synaptic plasticity. Moreover, AIE resulted in an increased number of dendritic spines with characteristics typical of immaturity. Immunohistochemistry-based analysis of synaptic structures indicated a significant decrease in the number of co-localized pre- and postsynaptic puncta. This decrease is driven by an overall decrease in 2 postsynaptic density proteins, PSD-95 and SAP102.

CONCLUSIONS

Taken together, these findings reveal that repeated alcohol exposure during adolescence results in enduring structural and functional abnormalities in the hippocampus. These synaptic changes in the hippocampal circuits may help to explain learning-related behavioral changes in adult animals preexposed to AIE.

The IFNγ-PKR pathway in the prefrontal cortex reactions to chronic excessive alcohol use

BACKGROUND

Brain cell death is a major pathological consequence of alcohol neurotoxicity. However, the molecular cascades in alcohol-induced brain tissue injury are unclear.

METHODS

Using Western blot and double immunofluorescence, we examined the expression of interferon (IFN)-induced protein kinase R (PKR), phosphorylated-PKR (p-PKR), and IFN gamma (IFNγ) in the prefrontal cortex (PFC) of postmortem brains from subjects with alcohol use disorders (AUD).

RESULTS

The protein levels of PKR, p-PKR, and IFNγ were significantly increased in subjects with AUD compared with control subjects without AUD, and a younger age of onset of AUD was significantly correlated with higher protein levels of p-PKR. In addition, elevated PKR- and p-PKR-IR were observed in both neurons and astrocytes in the PFC of subjects with AUD compared to subjects without AUD.

CONCLUSIONS

The activation of the IFNγ-PKR pathway in PFC of humans is associated with chronic excessive ethanol use with an age of onset dependent manner, and activation of this pathway may play a pivotal role in AUD-related brain tissue injury. This study provides insight into neurodegenerative key factors related to AUD and identifies potential targets for the treatment of alcohol-induced neurotoxicity.

Consequences of repeated ethanol exposure during early or late adolescence on conditioned taste aversions in rats

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Adolescent Intermittent Ethanol (AIE) resulted in attenuated CTA in adulthood.

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AIE in late adolescence resulted in greater CTA attenuation 2 days post-exposure.

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All AIE animals were equally insensitive when tested 3 weeks post-exposure.

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No metabolic tolerance was noted following AIE.

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AIE results in a decreased sensitivity to aversive effects of ethanol in adulthood.

Alcohol use is prevalent during adolescence, yet little is known about possible long-lasting consequences. Recent evidence suggests that adolescents are less sensitive than adults to ethanol's aversive effects, an insensitivity that may be retained into adulthood after repeated adolescent ethanol exposure. This study assessed whether intermittent ethanol exposure during early or late adolescence (early-AIE or late-AIE, respectively) would affect ethanol conditioned taste aversions 2 days (CTA1) and >3 weeks (CTA2) post-exposure using supersaccharin and saline as conditioning stimuli (CS), respectively. Pair-housed male Sprague-Dawley rats received 4 g/kg i.g. ethanol (25%) or water every 48 h from postnatal day (P) 25–45 (early AIE) or P45-65 (late AIE), or were left non-manipulated (NM). During conditioning, 30 min home cage access to the CS was followed by 0, 1, 1.5, 2 or 2.5 g/kg ethanol i.p., with testing 2 days later. Attenuated CTA relative to controls was seen among early and late AIE animals at both CTA1 and CTA2, an effect particularly pronounced at CTA1 after late AIE. Thus, adolescent exposure to ethanol was found to induce an insensitivity to ethanol CTA seen soon after exposure and lasting into adulthood, and evident with ethanol exposures not only early but also later in adolescence.

Adolescent alcohol exposure: Are there separable vulnerable periods within adolescence?

There are two key alcohol use patterns among human adolescents that confer increased vulnerability for later alcohol abuse/dependence, along with neurocognitive alterations: (a) early initiation of use during adolescence, and (b) high rates of binge drinking that are particularly prevalent late in adolescence. The central thesis of this review is that lasting neurobehavioral outcomes of these two adolescent exposure patterns may differ. Although it is difficult to disentangle consequences of early use from later binge drinking in human studies given the substantial overlap between groups, these two types of problematic adolescent use are differentially heritable and hence separable to some extent. Although few studies using animal models have manipulated alcohol exposure age, those studies that have have typically observed timing-specific exposure effects, with more marked (or at least different patterns of) lasting consequences evident after exposures during early-mid adolescence than late-adolescence/emerging adulthood, and effects often restricted to male rats in those few instances where sex differences have been explored. As one example, adult male rats exposed to ethanol during early-mid adolescence (postnatal days [P] 25-45) were found to be socially anxious and to retain adolescent-typical ethanol-induced social facilitation into adulthood, effects that were not evident after exposure during late-adolescence/emerging adulthood (P45-65); exposure at the later interval, however, induced lasting tolerance to ethanol's social inhibitory effects that was not evident after exposure early in adolescence. Females, in contrast, were little influenced by ethanol exposure at either interval. Exposure timing effects have likewise been reported following social isolation as well as after repeated exposure to other drugs such as nicotine (and cannabinoids), with effects often, although not always, more pronounced in males where studied. Consistent with these timing-specific exposure effects, notable maturational changes in brain have been observed from early to late adolescence that could provide differential neural substrates for exposure timing-related consequences, with for instance exposure during early adolescence perhaps more likely to impact later self-administration and social/affective behaviors, whereas exposures later in adolescence may be more likely to influence cognitive tasks whose neural substrates (such as the prefrontal cortex [PFC]) are still undergoing maturation at that time. More work is needed, however to characterize timing-specific effects of adolescent ethanol exposures and their sex dependency, determine their neural substrates, and assess their comparability to and interactions with adolescent exposure to other drugs and stressors. Such information could prove critical for informing intervention/prevention strategies regarding the potential efficacy of efforts directed toward delaying onset of alcohol use versus toward reducing high levels of use and risks associated with that use later in adolescence.

Adolescent rats are resistant to forming ethanol seeking habits

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Adult rats develop ethanol-seeking habits more rapidly than adolescents.

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Adolescents appear resistant to the habit promoting effects of ethanol.

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Adolescent rats self-administer more ethanol than adults.

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Adolescent onset ethanol self-administration results in greater self-administration in adulthood.

Early age of onset alcohol drinking is significantly more likely to lead to alcohol use disorders (AUDs) than alcohol drinking that begins after the age of 18. Unfortunately, the majority of people in the United States begin drinking in adolescence. Therefore, it is important to understand how early alcohol drinking leads to increased risk for AUDs so that better treatments and prevention strategies can be developed. Adolescents perceive greater rewarding properties of alcohol, and adolescents may be more likely to form alcohol-seeking habits that promote continued use throughout the lifetime. Therefore, we compared the development of alcohol seeking habits in adolescent and adult male, Sprague-Dawley rats. Rats were trained to lever press to receive 10% ethanol + 0.1% saccharin on a schedule that promotes habit formation. Rats were tested using a contingency degradation procedure at different points in training. Adult rats formed ethanol-seeking habits with only moderate training, while adolescents remained goal-directed even with extended training. Nevertheless, adolescents consumed more ethanol than adults throughout the experiment and continued to consume more ethanol than adults when they reached adulthood. Therefore, early onset alcohol use may promote AUD formation through establishment of high levels of drinking that becomes habitual in adulthood.

Social consequences of ethanol: Impact of age, stress, and prior history of ethanol exposure

The adolescent period is associated with high significance of interactions with peers, high frequency of stressful situations, and high rates of alcohol use. At least two desired effects of alcohol that may contribute to heavy and problematic drinking during adolescence are its abilities to both facilitate interactions with peers and to alleviate anxiety, perhaps especially anxiety seen in social contexts. Ethanol-induced social facilitation can be seen using a simple model of adolescence in the rat, with normal adolescents, but not their more mature counterparts, demonstrating this ethanol-related social facilitation. Prior repeated stress induces expression of ethanol-induced social facilitation in adults and further enhances socially facilitating effects of ethanol among adolescent rats. In contrast, under normal circumstances, adolescent rats are less sensitive than adults to the social inhibition induced by higher ethanol doses and are insensitive to the socially anxiolytic effects of ethanol. Sensitivity to the socially anxiolytic effects of ethanol can be modified by prior stress or ethanol exposure at both ages. Shortly following repeated restraint or ethanol exposure, adolescents exhibit social anxiety-like behavior, indexed by reduced social preference, and enhanced sensitivity to the socially anxiolytic effects of ethanol, indexed through ethanol-associated reinstatement of social preference in these adolescents. Repeated restraint, but not repeated ethanol, induces similar effects in adults as well, eliciting social anxiety-like behavior and increasing their sensitivity to the socially anxiolytic effects of acute ethanol; the stressor also decreases sensitivity of adults to ethanol-induced social inhibition. The persisting consequences of early adolescent ethanol exposure differ from its immediate consequences, with males exposed early in adolescence, but not females or those exposed later in adolescence, showing social anxiety-like behavior when tested in adulthood. Adult males exposed to ethanol early in adolescence also show enhanced sensitivity to the socially facilitating effects of ethanol, whereas adult males exposed to ethanol during late adolescence demonstrate insensitivity to the socially suppressing effects of ethanol. To the extent that these results are applicable to humans, stressful live events may make alcohol more attractive for stressed adolescents and adults due to its socially facilitating and socially anxiolytic properties, therefore fostering high levels of drinking. Retention of adolescent-typical responsiveness to alcohol in adult males following adolescent alcohol exposure, including enhanced sensitivity to the socially facilitating effects of ethanol following early exposure and insensitivity to the socially inhibiting effects following late adolescent exposure, may put these males at risk for the development of alcohol-related disorders later in life.

Distinct neurobehavioral dysfunction based on the timing of developmental binge-like alcohol exposure

Gestational exposure to alcohol can result in long-lasting behavioral deficiencies generally described as fetal alcohol spectrum disorder (FASD). FASD-modeled rodent studies of acute ethanol exposure typically select one developmental window to simulate a specific context equivalent of human embryogenesis, and study consequences of ethanol exposure within that particular developmental epoch. Exposure timing is likely a large determinant in the neurobehavioral consequence of early ethanol exposure, as each brain region is variably susceptible to ethanol cytotoxicity and has unique sensitive periods in their development. We made a parallel comparison of the long-term effects of single-day binge ethanol at either embryonic day 8 (E8) or postnatal day 7 (P7) in male and female mice, and here demonstrate the differential long-term impacts on neuroanatomy, behavior and in vivo electrophysiology of two systems with very different developmental trajectories. The significant long-term differences in odor-evoked activity, local circuit inhibition, and spontaneous coherence between brain regions in the olfacto-hippocampal pathway that were found as a result of developmental ethanol exposure, varied based on insult timing. Long-term effects on cell proliferation and interneuron cell density were also found to vary by insult timing as well as by region. Finally, spatial memory performance and object exploration were affected in P7-exposed mice, but not E8-exposed mice. Our physiology and behavioral results are conceptually coherent with the neuroanatomical data attained from these same mice. Our results recognize both variable and shared effects of ethanol exposure timing on long-term circuit function and their supported behavior.