Periadolescent alcohol exposure has lasting effects on adult neurophysiological function in rats

Voluntary alcohol consumption during distinct phases of adolescence differentially alters adult fear acquisition, extinction and renewal in male and female rats

Alcohol use during adolescence coincides with elevated risks of stress-related impairment in adults, particularly via disrupted developmental trajectories of vulnerable corticolimbic and mesolimbic systems involved in fear processing. Prior work has investigated the impact of binge-like alcohol consumption on adult fear and stress, but less is known about whether voluntarily consumed alcohol imparts differential effects based on adolescence phases and biological sex. Here, adolescent male and female Long Evans rats were granted daily access to alcohol (15%) during either early (Early-EtOH; P25-45) or late adolescence (Late-EtOH; P45-55) using a modified drinking-in-the-dark design. Upon adulthood (P75-80), rats were exposed to a three-context (ABC) fear renewal procedure. We found that male and female Early-EtOH rats showed faster acquisition of fear but less freezing during early phases of extinction and throughout fear renewal. In the extinction period specifically, Early-EtOH rats showed normal levels of freezing in the presence of fear-associated cues, but abnormally low freezing immediately after cue offset, suggesting a key disruption in contextual processing and/or novelty seeking brought by early adolescent binge consumption. While the effects of alcohol were most pronounced in the Early-EtOH rats (particularly in females), Late-EtOH rats displayed some changes in fear behavior including slower fear acquisition, faster extinction, and reduced renewal compared with controls, but primarily in males. Our results suggest that early adolescence in males and females and, to a lesser extent, late adolescence in males is a particularly vulnerable period wherein alcohol use can promote stress-related dysfunction in adulthood. Furthermore, our results provide multiple bases for future research focused on developmental correlates of alcohol mediated disruption in the brain.

Voluntary alcohol consumption during distinct phases of adolescence differentially alters adult fear acquisition, extinction and renewal in male and female rats

Alcohol use during adolescence coincides with elevated risks of stress-related impairment in adults, particularly via disrupted developmental trajectories of vulnerable corticolimbic and mesolimbic systems involved in fear processing. Prior work has investigated the impact of binge-like alcohol consumption on adult fear and stress, but less is known about whether voluntarily consumed alcohol imparts differential effects based on adolescence phases and biological sex. Here, adolescent male and female Long Evans rats were granted daily access to alcohol (15%) during either early (Early-EtOH; P25-45) or late adolescence (Late-EtOH; P45-55) using a modified drinking-in-the-dark design. Upon adulthood (P75-80), rats were exposed to a three-context (ABC) fear renewal procedure. We found that male and female Early-EtOH rats showed faster acquisition of fear but less freezing during early phases of extinction and throughout fear renewal. In the extinction period specifically, Early-EtOH rats showed normal levels of freezing in the presence of fear-associated cues, but abnormally low freezing immediately after cue offset, suggesting a key disruption in contextual processing and/or novelty seeking brought by early adolescent binge consumption. While the effects of alcohol were most pronounced in the Early-EtOH rats (particularly in females), Late-EtOH rats displayed some changes in fear behavior including slower fear acquisition, faster extinction, and reduced renewal compared with controls, but primarily in males. Our results suggest that early adolescence in males and females and, to a lesser extent, late adolescence in males is a particularly vulnerable period wherein alcohol use can promote stress-related dysfunction in adulthood. Furthermore, our results provide multiple bases for future research focused on developmental correlates of alcohol mediated disruption in the brain.

Sex and Age Effects on Neurobehavioral Toxicity Induced by Binge Alcohol

Historically, most alcohol neurotoxicity studies were conducted in young adult males and focused on chronic intake. There has been a shift towards studying the effects of alcohol on the adolescent brain, due to alcohol consumption during this formative period disrupting the brain's developmental trajectory. Because the most typical pattern of adolescent alcohol intake is heavy episodic (binge) drinking, there has also been a shift towards the study of binge alcohol-induced neurobehavioral toxicity. It has thus become apparent that binge alcohol damages the adolescent brain and there is increasing attention to sex-dependent effects. Significant knowledge gaps remain in our understanding of the effects of binge alcohol on the female brain, however. Moreover, it is unsettling that population-level studies indicate that the prevalence of binge drinking is increasing among American women, particularly those in older age groups. Although study of adolescents has made it apparent that binge alcohol disrupts ongoing brain maturational processes, we know almost nothing about how it impacts the aging brain, as studies of its effects on the aged brain are relatively scarce, and the study of sex-dependent effects is just beginning. Given the rapidly increasing population of older Americans, it is crucial that studies address age-dependent effects of binge alcohol, and given the increase in binge drinking in older women who are at higher risk for cognitive decline relative to men, studies must encompass both sexes. Because adolescence and older age are both characterized by age-typical brain changes, and because binge drinking is the most common pattern of alcohol intake in both age groups, the knowledge that we have amassed on binge alcohol effects on the adolescent brain can inform our study of its effects on the aging brain. In this review, we therefore cover the current state of knowledge of sex and age-dependent effects of binge alcohol, as well as statistical and methodological considerations for studies aimed at addressing them.

Longitudinal Effects of Alcohol Consumption on the Hippocampus and Parahippocampus in College Students

BACKGROUND

The hazardous effects of alcohol consumption on both the hippocampus and memory have been well established. However, the longitudinal effects of ethanol on the developing brain and related consequences on memory are not well explored. Given the above, we investigated the longitudinal effects of college drinking on hippocampal volume in emerging college adults.

METHODS

Data were derived from the longitudinal Brain and Alcohol Research with College Students study. A subset of 146 freshmen (mean age at baseline = 18.5 years) underwent brain magnetic resonance imaging scans at baseline and 24 months later. Four drinking-related measures derived from monthly surveys were reduced to a single alcohol use index using principal component analysis. Gray matter volumetric change (GMV-c) data were derived using a longitudinal pipeline. Voxelwise hippocampal/para-hippocampal GMV-c associations with the drinking index were derived using a multiple regression framework within SPM12. Supplementary associations were assessed between GMV-c and memory scores computed from the California Verbal Learning Test-II (assessed at the end of the study), and between GMV-c and total alcohol-induced memory blackouts.

RESULTS

Larger alcohol use index was associated with an accelerated GMV decline in the hippocampus/para-hippocampus. Also, larger hippocampal volume decline was associated with poorer memory performance and more memory blackouts.

CONCLUSIONS

Our study extends prior cross-sectional literature by showing that a heavier drinking burden while in college is associated with greater hippocampal GMV decline that is in turn associated with poorer memory scores, all of which could ultimately have a significant impact on student success.

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.

Alcohol drinking during adolescence increases consumptive responses to alcohol in adulthood in Wistar rats

Binge drinking and the onset of alcohol-use disorders usually peak during the transition between late adolescence and early adulthood, and early adolescent onset of alcohol consumption has been demonstrated to increase the risk for alcohol dependence in adulthood. In the present study, we describe an animal model of early adolescent alcohol consumption where animals drink unsweetened and unflavored ethanol in high concentrations (20%). Using this model, we investigated the influence of drinking on alcohol-related appetitive behavior and alcohol consumption levels in early adulthood. Further, we also sought to investigate whether differences in alcohol-related drinking behaviors were specific to exposure in adolescence versus exposure in adulthood. Male Wistar rats were given a 2-bottle choice between 20% ethanol and water in one group and between two water bottles in another group during their adolescence (Postnatal Day [PD] 26-59) to model voluntary drinking in adolescent humans. As young adults (PD85), rats were trained in a paradigm that provided free access to 20% alcohol for 25 min after completing up to a fixed-ratio (FR) 16 lever press response. A set of young adult male Wistar rats was exposed to the same paradigm using the same time course, beginning at PD92. The results indicate that adolescent exposure to alcohol increased consumption of alcohol in adulthood. Furthermore, when investigating differences between adolescent high and low drinkers in adulthood, high consumers continued to drink more alcohol, had fewer FR failures, and faster completion of FR schedules in adulthood, whereas the low consumers were no different from controls. Rats exposed to ethanol in young adulthood also increased future intake, but there were no differences in any other components of drinking behavior. Both adolescent- and adult-exposed rats did not exhibit an increase in lever pressing during the appetitive challenge session. These data indicate that adolescent and early adult alcohol exposure can increase consumptive aspects of drinking but that adolescent exposure may preferentially influence the motivation to drink.

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.

Ethanol Induced Brain Lipid Changes in Mice Assessed by Mass Spectrometry

Alcohol abuse is a chronic disease characterized by the consumption of alcohol at a level that interferes with physical and mental health and causes serious and persistent changes in the brain. Lipid metabolism is of particular interest due to its high concentration in the brain. Lipids are the main component of cell membranes, are involved in cell signaling, signal transduction, and energy storage. In this study, we analyzed lipid composition of chronically ethanol exposed mouse brains. Juvenile (JUV) and adult (ADU) mice were placed on a daily limited-access ethanol intake model for 52 days. After euthanasia, brains were harvested, and total lipids were extracted from brain homogenates. Samples were analyzed using high resolution mass spectrometry and processed by multivariate and univariate statistical analysis. Significant lipid changes were observed in different classes including sphingolipids, fatty acids, lysophosphatidylcholines, and other glycerophospholipids.

The ontogeny of ethanol aversion

Recent work has suggested separate developmental periods within the broader framework of adolescence, with data suggesting distinct alterations and vulnerabilities within these intervals. While previous research has suggested reduced sensitivity to the aversive effects of alcohol in adolescence relative to adults, a more detailed ontogeny of this effect has yet to be conducted. The adolescent brain undergoes significant transitions throughout adolescence, including in regions linked with drug reward and aversion. The current study aimed to determine the ontogeny of ethanol aversion by utilizing a conditioned taste aversion procedure at six different ages to test the hypothesis that the transitions into, through, and out of adolescence are associated with ontogenetic alterations in sensitivity to the aversive properties of ethanol. Non-deprived animals given Boost® as the conditioned stimulus (CS) were used in Experiment 1, whereas Experiment 2 used water-restricted animals provided with a saccharin/sucrose solution as the CS. In both experiments, an attenuated sensitivity to the aversive properties of ethanol was evident in adolescents compared to adults, although more age differences were apparent in water deprived animals than when a highly palatable CS was given to ad libitum animals. Overall, the data suggest an attenuated sensitivity to the aversive properties of ethanol that is most pronounced during pre- and early adolescence, declining thereafter to reach the enhanced aversive sensitivity of adults.

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.

Heavy alcohol use, marijuana use, and concomitant use by adolescents are associated with unique and shared cognitive decrements

To assess recovery of cognitive effects, we investigated neuropsychological performance after 1 month of monitored abstinence in teens with histories of heavy episodic drinking, protracted marijuana use, or concomitant use of alcohol and marijuana. Adolescents (ages 16-18 years) with histories of heavy episodic drinking (HED; n=24), marijuana use (MJ; n=20), both heavy alcohol and marijuana use (HED+MJ; n=29), and socio-demographically similar control teens (CON; n=55) completed a neuropsychological battery following 4 weeks of monitored abstinence. Groups were similar on 5th grade standardized test scores, suggesting comparable academic functioning before onset of substance use. Relative to CON, HED showed poorer cognitive flexibility (p=.006), verbal recall (p=.024), semantic clustering (p=.011), and reading skills (p=.018). MJ performed worse than CON on inhibition task accuracy (p=.015), cued verbal memory (p=.031), and psychomotor speed (p=.027). Similar to HED youth, HED+MJ showed differences relative to CON on cognitive flexibility (p=.024) and verbal recall (p=.049). As with MJ teens, HED+MJ showed poorer task accuracy (p=.020). Unique to the HED+MJ group was poorer working memory (p=.012) relative to CON. For all substance using participants, worse performance across domains correlated with more lifetime use of alcohol and of marijuana, more withdrawal symptoms from alcohol, and earlier age of onset of marijuana use (ps<.05). Heavy alcohol use, marijuana use, and concomitant use of both substances during adolescence appear to be associated with decrements in cognitive functioning, and each substance (or combination of substances) may be linked to poorer performance in specific cognitive domains.

GABAergic contributions to alcohol responsivity during adolescence: insights from preclinical and clinical studies

There is a considerable body of literature demonstrating that adolescence is a unique age period, which includes rapid and dramatic maturation of behavioral, cognitive, hormonal and neurobiological systems. Most notably, adolescence is also a period of unique responsiveness to alcohol effects, with both hyposensitivity and hypersensitivity observed to the various effects of alcohol. Multiple neurotransmitter systems are undergoing fine-tuning during this critical period of brain development, including those that contribute to the rewarding effects of drugs of abuse. The role of developmental maturation of the γ-amino-butyric acid (GABA) system, however, has received less attention in contributing to age-specific alcohol sensitivities. This review integrates GABA findings from human magnetic resonance spectroscopy studies as they may translate to understanding adolescent-specific responsiveness to alcohol effects. Better understanding of the vulnerability of the GABA system both during adolescent development, and in psychiatric conditions that include alcohol dependence, could point to a putative mechanism, boosting brain GABA, that may have increased effectiveness for treating alcohol use disorders.

Adolescent heavy episodic drinking: neurocognitive functioning during early abstinence

The present study investigated the rate and pattern of neuropsychological recovery in heavy episodic drinking teens during the initial days to weeks of abstinence from alcohol. Adolescents (ages, 16-18 years) with histories of heavy episodic drinking (HED; N = 39) and socio-demographically similar control teens (CON; N = 26) were recruited from San Diego area schools. HED and CON were comparable on 5th grade standardized math and language arts test performance to ensure similar functioning before onset of substance use. Participants were administered three neuropsychological test batteries with 2-week intervals during a 4-week monitored abstinence period. HED teens performed worse overall than CON on tests of prospective memory (p = .005), cognitive switching (p = .039), inhibition task accuracy (p = .001), verbal memory (p's < .045), visuospatial construction (p's < .043), and language and achievement (p's < .008). The statistically significant group × time interaction for block design demonstrated normalization within the 4 weeks of abstinence for the HED (p = .009). This study identified cognitive performance deficits associated with heavy episodic drinking in adolescence during early abstinence and with sustained 4-week abstention. These findings suggest alcohol-related influences on several underlying brain systems that may predate the onset of alcohol abuse or dependence or take longer than 4 weeks to recover.

Event-related potential responses to the acute and chronic effects of alcohol in adolescent and adult Wistar rats

BACKGROUND

This study explored the hypothesis that adolescent ethanol (EtOH) exposure may cause long-lasting changes in EtOH sensitivity by exploring the age-related effects of acute alcohol on intoxication and on event-related potential (ERP) responses to acoustic stimuli in EtOH-naïve adolescent and adult male Wistar rats and in adult rats that were exposed to chronic EtOH/control conditions during adolescence.

METHODS

EtOH-naïve adolescent (postnatal day 32 [PD32]) and adult male rats (PD99) were included in the first study. In a second study, rats were exposed to 5 weeks of EtOH vapor (blood EtOH concentrations at 175 mg%) or air from PD24 to 59 and allowed to mature until PD90. In both studies, rats were implanted with cortical recording electrodes, and the effects of acute EtOH (0.0, 1.5, and 3.0 g/kg) on behavioral and ERP responses were assessed.

RESULTS

Adolescents were found to have higher amplitude and longer latency P3a and P3b components at baseline as compared to adult rats, and EtOH was found to produce a robust dose-dependent increase in the latency of the P3a and P3b components of the auditory ERP recorded in cortical sites in both adolescents and adults. However, EtOH produced significantly larger delays in P3a and P3b latencies in adults as compared to adolescents. Acute EtOH administration was also found to produce a robust dose-dependent increase in the latency of the P3a and P3b components in adult animals exposed to EtOH vapor as adolescents and air exposed controls; however, larger acute EtOH-induced increases in P3a and P3b latencies were seen in controls as compared to adolescent vapor exposed rats.

CONCLUSIONS

Adolescent rats have a less intense P3 latency response to acute EtOH administration when compared to adult rats. Exposure to chronic EtOH during adolescence can cause "retention" of the adolescent phenotype of reduced P3 latency sensitivity to EtOH.

Developmental differences in EEG and sleep responses to acute ethanol administration and its withdrawal (hangover) in adolescent and adult Wistar rats

Age-related differences in sensitivity to the acute effects of alcohol may play an important role in the increased risk for the development of alcoholism seen in teens that begin drinking at an early age. The present study evaluated the acute and protracted (hangover) effects of ethanol in adolescent (P33-P40) and adult (P100-P107) Wistar rats, using the cortical electroencephalogram (EEG). Six minutes of EEG was recorded during waking, 15 min after administration of 0, 1.5, or 3.0 g/kg ethanol, and for 3 h at 20 h post ethanol, during the rats' next sleep cycle. Significantly higher overall frontal and parietal cortical power was seen in a wide range of EEG frequencies in adolescent rats as compared to adult rats in their waking EEG. Acute administration of ethanol did not produce differences between adolescents and adults on behavioral measures of acute intoxication. However, it did produce a significantly less intense acute EEG response to ethanol in the theta frequencies in parietal cortex in the adolescents as compared to the adults. At 20 h following acute ethanol administration, during the rats' next sleep cycle, a decrease in slow-wave frequencies (1-4 Hz) was seen and the adolescent rats were found to display more reduction in the slow-wave frequencies than the adults did. The present study found that adolescent rats, as compared to adults, demonstrate low sensitivity to acute ethanol administration in the theta frequencies and more susceptibility to disruption of slow-wave sleep during hangover. These studies may lend support to the idea that these traits may contribute to increased risk for alcohol use disorders seen in adults who begin drinking in their early teenage years.

The effects of abused drugs on adolescent development of corticolimbic circuitry and behavior

Adolescence is a period of significant neurobiological change that occurs as individuals transition from childhood to adulthood. Because the nervous system is in a relatively labile state during this stage of development, it may be especially sensitive to experience-induced plasticity. One such experience that is relatively common to adolescents is the exposure to drugs of abuse, particularly alcohol and psychostimulants. In this review, we highlight recent findings on the long-lasting effects of exposure to these drugs during adolescence in humans as well as in animal models. Whenever possible, our focus is on studies that use comparison groups of adolescent- and adult-exposed subjects as this is a more direct test of the hypothesis that adolescence represents a period of enhanced vulnerability to the effects of drug-induced plasticity. Lastly, we suggest areas of future investigation that are needed and methodological concerns that should be addressed.

Brain structure in adolescents and young adults with alcohol problems: systematic review of imaging studies

AIMS

Alcohol-dependent people who are middle-aged or older have a widespread loss of cortical grey and white matter, particularly in the prefrontal cortex (PFC). We examine if brain abnormalities are detectable in alcohol use disorders before the fifth decade (i.e., <40), and the brain structural differences associated with alcohol abuse/dependence in adolescence.

METHODS

Case-control studies comparing brain structure in alcohol-abusing/-dependent individuals with normal controls in which the mean age of participants was <40 were identified using Medline, EMBASE and PsychInfo. Studies in which mean age was over and under 21 were considered separately.

RESULTS

Twelve papers fulfilled inclusion criteria, five in the adolescent (14-21) and seven in the young adult age range. Two independent groups reported hippocampal and prefrontal volume reductions in adolescents, although this was consistently observed only in females. In young adults (aged 21-40), there were grey matter deficits in the PFC in both sexes. Adult women appeared to, particularly, exhibit white matter differences, evident as reduced area of the corpus callosum. Hippocampal volume reduction was observed in one study of young adults study but not another.

CONCLUSION

The available data suggest that quantitative structural abnormalities of the brain are detectable in young alcohol abusers. There is overlap between the abnormalities seen in adolescents and young adults, although hippocampal volume loss is most consistently seen in the former group. The adolescent hippocampus may be particularly susceptible to alcohol, potentially because of an interaction between adolescent brain development and alcohol exposure.

Long-lasting neural circuit dysfunction following developmental ethanol exposure

Fetal Alcohol Spectrum Disorder (FASD) is a general diagnosis for those exhibiting long-lasting neurobehavioral and cognitive deficiencies as a result of fetal alcohol exposure. It is among the most common causes of mental deficits today. Those impacted are left to rely on advances in our understanding of the nature of early alcohol-induced disorders toward human therapies. Research findings over the last decade have developed a model where ethanol-induced neurodegeneration impacts early neural circuit development, thereby perpetuating subsequent integration and plasticity in vulnerable brain regions. Here we review our current knowledge of FASD neuropathology based on discoveries of long-lasting neurophysiological effects of acute developmental ethanol exposure in animal models. We discuss the important balance between synaptic excitation and inhibition in normal neural network function, and relate the significance of that balance to human FASD as well as related disease states. Finally, we postulate that excitation/inhibition imbalance caused by early ethanol-induced neurodegeneration results in perturbed local and regional network signaling and therefore neurobehavioral pathology.

Peri-adolescent ethanol vapor exposure produces reductions in hippocampal volume that are correlated with deficits in prepulse inhibition of the startle

BACKGROUND

Epidemiological studies suggest that excessive alcohol consumption is prevalent among adolescents and may have lasting neurobehavioral consequences. The use of animal models allows for the separation of the effects of adolescent ethanol (EtOH) exposure from genetic background and other environmental insults. In this study, the effects of moderate EtOH vapor exposure, during adolescence, on structural diffusion tensor imaging (DTI) and behavioral measures were evaluated in adulthood.

METHODS

A total of 53 Wistar rats were received at postnatal day (PD) 21 and were randomly assigned to EtOH vapor (14 hours on/10 hours off/day) or air exposure for 35 days from PD 23 to 58 (average blood ethanol concentration: 169 mg%). Animals were received in 2 groups that were subsequently sacrificed at 2 time points following withdrawal from EtOH vapor: (i) at 72 days of age, 2 weeks following withdrawal or (ii) at day 128, 10 weeks following withdrawal. In the second group, behavior in the light/dark box and prepulse inhibition (PPI) of the startle was also evaluated. Fifteen animals in each group were scanned, postmortem, for structural DTI.

RESULTS

There were no significant differences in body weight between EtOH and control animals. Volumetric data demonstrated that total brain, hippocampal, corpus callosum but not ventricular volume were significantly larger in the 128-day-sacrificed animals as compared to the 72 day animals. The hippocampus was smaller and the ventricles larger at 128 days as compared to 72 days, in the EtOH-exposed animals, leading to a significant group × time effect. EtOH-exposed animals sacrificed at 128 days also had diminished PPI, and more rears in the light box were significantly correlated with hippocampal size.

CONCLUSIONS

These studies demonstrate that DTI volumetric measures of hippocampus are significantly impacted by age and peri-adolescent EtOH exposure and withdrawal in Wistar rats.

Periadolescent ethanol vapor exposure persistently reduces measures of hippocampal neurogenesis that are associated with behavioral outcomes in adulthood

Excessive alcohol consumption is prevalent among adolescents and may result in lasting neurobehavioral consequences. The use of animal models to study adolescent alcohol exposure has the advantage of allowing for the control necessary in order to evaluate the effects of ethanol on the brain and separate such effects from genetic background and other environmental insults. In the present study the effects of moderate ethanol vapor exposure, during adolescence, on measures of neurogenesis and behavioral measures were evaluated at two different times following ethanol withdrawal, in adulthood. The two groups of Wistar rats were both exposed to intermittent ethanol vapor (14 h on/10h off/day) for 35-36 days from PD 23 to PD 58 (average blood ethanol concentration: 163 mg%). In the first group, after rats were withdrawn from vapor they were subsequently assessed for locomotor activity, conflict behavior in the open field, and behaviors in the forced swim test (FST) and then sacrificed at 72 days of age. The second group of rats were withdrawn from vapor and injected for 5 days with Bromo-deoxy-Uridine (BrdU). Over the next 8 weeks they were also assessed for locomotor activity, conflict behavior in the open field, and behaviors in the FST and then sacrificed at 113/114 days of age. All rats were perfused for histochemical analyses. Ethanol vapor-exposed rats displayed hypoactivity in tests of locomotion and less anxiety-like and/or more "disinhibitory" behavior in the open field conflict. Quantitative analyses of immunoreactivity revealed a significant reduction in measures of neurogenesis, progenitor proliferation, as indexed by doublecortin (DCX), Ki67, and increased markers of cell death as indexed by cleaved caspase-3, and Fluoro-Jade at 72 days, and decreases in DCX, and increases in cleaved caspase-3 at 114 days in the ethanol vapor-exposed rats. Progenitor survival, as assessed by BrdU+, was reduced in the vapor-exposed animals that were sacrificed at 114 days. The reduction seen in DCX labeled in cell counts was significantly correlated with hypoactivity at 24h after withdrawal as well as less anxiety-like and/or more "disinhibitory" behavior in the open field conflict test at 2 and 8 weeks following termination of vapor exposure. These studies demonstrate that behavioral measures of disinhibitory behavior correlated with decreases in neurogenesis are all significantly and persistently impacted by periadolescent ethanol exposure and withdrawal in Wistar rats.

Adolescent alcohol exposure alters the rat adult hypothalamic-pituitary-adrenal axis responsiveness in a sex-specific manner

Exposure to alcohol during adolescence exerts long-term effects on the adult brain stress circuits, causing many changes that persist into adulthood. Here we examined the consequences of adolescent intermittent ethanol (AIE, administered from postnatal day (PND) 28-42) on the hypothalamic-pituitary-adrenal (HPA) axis-related brain circuitry of rats challenged with intragastric (ig) administration of alcohol in adulthood (PND 70-71). Both male and female adolescent rats were exposed to alcohol vapors, while controls did not receive the drug, to assess whether AIE alters adult alcohol response in a sex-specific manner. We demonstrated that AIE increased paraventricular nucleus (PVN) Avp mRNA levels during late (PND 42) but not middle (PND 36) adolescence in males. While an alcohol challenge administered to 70-71-day-old rats increased Crf mRNA levels in males and Avp mRNA levels in females, AIE blunted both effects. These results suggest that AIE produced long-lasting changes in the responsiveness of the HPA axis to a subsequent alcohol challenge in a sex-specific manner. Furthermore, AIE altered adrenergic brain stem nuclei involved in stress responses in adulthood, resulting in increased numbers of phenylethanolamine N-methyltransferase (PNMT) neurons in male C2 and female C1 regions. This tended to enhance activation of the male C2 nucleus upon alcohol challenge. Collectively, these results suggest that AIE exerts long-term effects on the ability of the PVN to respond to an alcohol challenge in adulthood, possibly mediated by catecholaminergic input from the brain stem to the PVN.

Effects of adolescent onset voluntary drinking followed by ethanol vapor exposure on subsequent ethanol consumption during protracted withdrawal in adult Wistar rats

Epidemiological studies have demonstrated that heavy drinking and alcohol abuse and dependence peak during the transition between late adolescence and early adulthood. The objective of the present study was to determine whether a model of early onset adolescent ethanol drinking exposure that is followed by an ethanol vapor regimen during late adolescence and young adulthood leads to an increase in drinking in adulthood. In this model, initiation of voluntary ethanol drinking in adolescence, using a sweetened solution, was followed by an 8-wk intermittent ethanol vapor regimen in Wistar rats. A limited-access two-bottle choice paradigm was then used to measure intake of a 10% (w/v) ethanol solution. No differences in water intake (g/kg), total fluid intake (ml/kg) and body weight (g) were observed between air-exposed and ethanol-vapor exposed groups during the pre-vapor and post-vapor phases. The 8 weeks of ethanol vapor exposure was found to produce only a modest, but statistically significant, elevation of ethanol intake during the protracted withdrawal period, compared to air-exposed rats. A significant increase in ethanol preference ratio was also observed in ethanol-vapor exposed rats during the sucrose-fading phase, but not during the protracted withdrawal period. The findings from the present study suggest that in addition to alcohol exposure, environmental variables that impact appetitive as well as consumptive behaviors may be important in developing robust drinking effects that model, in animals, the increased risk for alcohol dependence seen in some human adolescents who begin drinking at an early age.

The effect of chronic intermittent ethanol exposure on spatial memory in adolescent rats: the dissociation of metabolic and cognitive tolerances

Using a rapid chronic intermittent ethanol (CIE) vapor exposure paradigm, we demonstrate the dissociability of metabolic tolerance from cognitive tolerance in adolescent rats. Adolescent rats were trained to spatially navigate in the Morris Water Maze and then exposed to CIE vapor or air 16 h a day for 4 days. After a final 28 h withdrawal, all rats received a saline or ethanol challenge, followed by a test of spatial memory 30 min after administration. Results indicate that CIE vapor exposure did not significantly impair adolescent spatial memory. Although CIE-exposed rats developed metabolic tolerance to a subsequent ethanol administration, CIE exposure did not alter dose-dependent ethanol-induced spatial memory impairments. These data indicate that metabolic ethanol tolerance can be distinguished from cognitive ethanol tolerance during adolescence and suggest that blood alcohol levels alone do not fully explain ethanol-induced spatial memory impairments.

Lithium prevents long-term neural and behavioral pathology induced by early alcohol exposure

Fetal alcohol exposure can cause developmental defects in offspring known as fetal alcohol spectrum disorder (FASD). FASD symptoms range from obvious facial deformities to changes in neuroanatomy and neurophysiology that disrupt normal brain function and behavior. Ethanol exposure at postnatal day 7 in C57BL/6 mice induces neuronal cell death and long-lasting neurobehavioral dysfunction. Previous work has demonstrated that early ethanol exposure impairs spatial memory task performance into adulthood and perturbs local and interregional brain circuit integrity in the olfacto-hippocampal pathway. Here we pursue these findings to examine whether lithium prevents anatomical, neurophysiological, and behavioral pathologies that result from early ethanol exposure. Lithium has neuroprotective properties that have been shown to prevent ethanol-induced apoptosis. Here we show that mice co-treated with lithium on the same day as ethanol exposure exhibit dramatically reduced acute neurodegeneration in the hippocampus and retain hippocampal-dependent spatial memory as adults. Lithium co-treatment also blocked ethanol-induced disruption in synaptic plasticity in slice recordings of hippocampal CA1 in the adult mouse brain. Moreover, long-lasting dysfunctions caused by ethanol in olfacto-hippocampal networks, including sensory-evoked oscillations and resting state coherence, were prevented in mice co-treated with lithium. Together, these results provide behavioral and physiological evidence that lithium is capable of preventing or reducing immediate and long-term deleterious consequences of early ethanol exposure on brain function.

Chronic ethanol exposure during adolescence alters the behavioral responsiveness to ethanol in adult mice

Alcohol exposure during early adolescence is believed to durably alter the behavioral properties of ethanol, increasing the likelihood of later alcohol-related disorders. The aim of the present experiments was to characterize changes in the behavioral effects of ethanol in adult female Swiss mice after a chronic ethanol exposure during adolescence, extending from postnatal day 28 to postnatal day 42. After a chronic ethanol exposure during adolescence (daily injections of 0, 2.5 or 4 g/kg ethanol for 14 consecutive days), adult mice were tested at postnatal day 63. The locomotor stimulant effects of ethanol, together with ethanol sensitization were tested in experiment 1. In experiment 2, the sedative effects of ethanol were assessed with the loss of righting reflex procedure. Finally, in experiment 3, the anxiolytic effects of ethanol were tested with the light/dark box test. Adult mice chronically exposed to ethanol during adolescence showed a lower basal locomotor activity, but higher locomotor stimulant effects of ethanol than non-exposed mice. Additionally, these adult mice developed higher rates of ethanol sensitization after chronic re-exposure to ethanol in adulthood. Adult mice exposed to ethanol during adolescence also had a stronger tolerance to the sedative effects of high ethanol doses, although they showed no evidence of changes in the anxiolytic effects of ethanol. These results are in agreement with the thesis that chronic alcohol consumption during adolescence, especially in high amounts, increases the risk of later alcohol-related disorders.

Periadolescent ethanol exposure reduces adult forebrain ChAT+IR neurons: correlation with behavioral pathology

Substance abuse typically begins in adolescence; therefore, the impact of alcohol during this critical time in brain development is of particular importance. Epidemiological data indicate that excessive alcohol consumption is prevalent among adolescents and may have lasting neurobehavioral consequences. Loss of cholinergic input to the forebrain has been demonstrated following fetal alcohol exposure and in adults with Wernicke-Korsakoff syndrome. In the present study, immunohistochemistry for choline acetyltransferase (ChAT) was determined to assess forebrain cholinergic neurons (Ch1-4), and behavioral changes following periadolescent alcohol exposure. Wistar rats were exposed to intermittent ethanol vapor (14 h on/10 h off/day) for 35 days from postnatal day (PD) 22 to PD 57 (average blood alcohol concentration (BAC): 163 mg%). Rats were withdrawn from vapor and assessed for locomotor activity, startle response, conflict behavior in the open field, and immobility in the forced swim test, as adults. Rats were then sacrificed at day 71/72 and perfused for histochemical analyses. Ethanol vapor-exposed rats displayed: increased locomotor activity 8 h after the termination of vapor delivery for that 24 h period at day 10 and day 20 of alcohol vapor exposure, significant reductions in the amplitude of their responses to prepulse stimuli during the startle paradigm at 24 h withdrawal, and at 2 weeks following withdrawal, less anxiety-like and/or more "disinhibitory" behavior in the open field conflict, and more immobility in the forced swim test. Quantitative analyses of ChAT immunoreactivity revealed a significant reduction in cell counts in the Ch1-2 and Ch3-4 regions of the basal forebrain in ethanol vapor-exposed rats. This reduction in cell counts was significantly correlated with less anxiety-like and/or more "disinhibitory" behavior in the open field conflict test. These studies demonstrate that behavioral measures of arousal, affective state, disinhibitory behavior, and ChAT+IR, are all significantly impacted by periadolescent ethanol exposure and withdrawal in Wistar rats.

Prolonged chronic ethanol exposure alters neuropeptide Y and corticotropin-releasing factor levels in the brain of adult Wistar rats

There is evidence to suggest that alterations in neuropeptide Y (NPY) and corticotropin-releasing factor (CRF) contribute to the escalated voluntary ethanol intake seen following long term chronic ethanol exposure. The present study assessed whether the duration of chronic ethanol exposure and abstinence alters brain levels of NPY and CRF in adult Wistar rats. NPY-like immunoreactivity (NPY-LI) and CRF-LI were determined in the amygdala (AMYG), frontal cortex (FCTX), hippocampus (HPC) and parietal cortex (PCTX) of adult Wistar rats after chronic ethanol exposure, and 24-h and 2-weeks following withdrawal (WD). Chronic ethanol exposure consisted of either a 2-week or an 8-week ethanol vapor regimen. No change in brain levels of NPY-LI, CRF-LI and the NPY-LI/CRF-LI ratio was observed 2-weeks following ethanol exposure, whereas, 8-weeks of ethanol exposure produced a significant effect on NPY-LI expression in the AMYG and FCTX. Moreover, an 8-week ethanol vapor regimen significantly increased CRF-LI levels in the HPC and PCTX. Findings from the present study suggest that a longer duration of ethanol vapor, similar to what is required to enhance voluntary drinking, is required to produce changes in NPY-LI and CRF-LI expression in the adult rat brain.

Adolescent binge drinking alters adult brain neurotransmitter gene expression, behavior, brain regional volumes, and neurochemistry in mice

BACKGROUND

Binge drinking is common in human adolescents. The adolescent brain is undergoing structural maturation and has a unique sensitivity to alcohol neurotoxicity. Therefore, adolescent binge ethanol may have long-term effects on the adult brain that alter brain structure and behaviors that are relevant to alcohol-use disorders.

METHODS

To determine whether adolescent ethanol (AE) binge drinking alters the adult brain, male C57BL/6 mice were treated with either water or ethanol during adolescence (5 g/kg/d, i.g., postnatal days P28 to P37) and assessed during adulthood (P60 to P88). An array of neurotransmitter-specific genes, behavioral tests (i.e., reversal learning, prepulse inhibition, and open field), and postmortem brain structure using magnetic resonance imaging (MRI) and immunohistochemistry, were employed to assess persistent alterations in adult brain.

RESULTS

At P38, 24 hours after AE binge, many neurotransmitter genes, particularly cholinergic and dopaminergic, were reduced by ethanol treatment. Interestingly, dopamine receptor type 4 mRNA was reduced and confirmed using immunohistochemistry. Normal control maturation (P38 to P88) resulted in decreased neurotransmitter mRNA, e.g., an average decrease of 56%. Following AE treatment, adults showed greater gene expression reductions than controls, averaging 73%. Adult spatial learning assessed in the Morris water maze was not changed by AE treatment, but reversal learning experiments revealed deficits. Assessment of adult brain region volumes using MRI indicated that the olfactory bulb and basal forebrain were smaller in adults following AE. Immunohistochemical analyses found reduced basal forebrain area and fewer basal forebrain cholinergic neurons.

CONCLUSIONS

Adolescent binge ethanol treatment reduces adult neurotransmitter gene expression, particularly cholinergic genes, reduces basal forebrain and olfactory bulb volumes, and causes a reduction in the density of basal forebrain acetylcholine neurons. Loss of cholinergic neurons and forebrain structure could underlie adult reversal learning deficits following adolescent binge drinking.

Alcohol inhibition of neurogenesis: a mechanism of hippocampal neurodegeneration in an adolescent alcohol abuse model

Adolescents diagnosed with an alcohol use disorder show neurodegeneration in the hippocampus, a region important for learning, memory, and mood regulation. This study examines a potential mechanism by which excessive alcohol intake, characteristic of an alcohol use disorder, produces neurodegeneration. As hippocampal neural stem cells underlie ongoing neurogenesis, a phenomenon that contributes to hippocampal structure and function, we investigated aspects of cell death and cell birth in an adolescent rat model of an alcohol use disorder. Immunohistochemistry of various markers along with Bromo-deoxy-Uridine (BrdU) injections were used to examine different aspects of neurogenesis. After 4 days of binge alcohol exposure, neurogenesis was decreased by 33 and 28% at 0 and 2 days after the last dose according to doublecortin expression. To determine whether this decrease in neurogenesis was due to effects on neural stem cell proliferation, quantification of BrdU-labeled cells revealed a 21% decrease in the dentate gyrus of alcohol-exposed brains. Cell survival and phenotype of BrdU-labeled cells were assessed 28 days after alcohol exposure and revealed a significant, 50% decrease in the number of surviving cells in the alcohol-exposed group. Reduced survival was supported by significant increases in the number of pyknotic-, FluoroJade B positive-, and TUNEL-positive cells. However, so few cells were TUNEL-positive that cell death is likely necrotic in this model. Although alcohol decreased the number of newborn cells, it did not affect the percentage of cells that matured into neurons (differentiation). Thus, our data support that in a model of an adolescent alcohol use disorder, neurogenesis is impaired by two mechanisms: alcohol-inhibition of neural stem cell proliferation and alcohol effects on new cell survival. Remarkably, alcohol inhibition of neurogenesis may outweigh the few dying cells per section, which implies that alcohol inhibition of neurogenesis contributes to hippocampal neurodegeneration in alcohol use disorders.

N-methyl-D-aspartate receptor subunit expression in adult and adolescent brain following chronic ethanol exposure

Substantial evidence suggests that glutamatergic neurotransmission is a critical mediator of the experience-dependent synaptic plasticity that may underlie alcohol dependence. Substance abuse typically begins in adolescence; therefore, the impact of alcohol on glutamatergic systems during this critical time in brain development is of particular importance. The N-methyl-d-aspartate receptor (NMDAR) is involved in developmental mechanisms underlying neuronal differentiation and synaptogenesis and as such may be a target system for alcohol effects during adolescence. In the present study quantitative biochemical determinations were made of the relative abundance of different protein expressions of NMDAR subunits in adolescents and adults after 2 weeks of ethanol vapor exposure, and 24 h and 2 weeks following withdrawal. After 2 weeks of ethanol vapor exposure N-methyl-d-aspartate receptor NR1 subunit (NR1), N-methyl-d-aspartate receptor NR2A subunit (NR2A), and N-methyl-d-aspartate receptor NR2B subunit (NR2B) subunit expression was found to be increased in hippocampus of the adults. In contrast, 2 weeks of ethanol exposure resulted in no significant changes in NR1 and NR2B subunits and a reduction NR2A subunit expression in hippocampus in adolescents. Twenty-four h and 2 weeks following withdrawal from ethanol vapor NR1 and NR2A subunit expression in hippocampus was decreased in adolescents, whereas in adults it had returned to control levels. In frontal cortex, 2 weeks of chronic ethanol exposure produced decreases in NR1 subunit expression in both adults and adolescents but also produced decreases in NR2A and NR2B subunit expression in adults that returned or exceeded control levels by 2 weeks following withdrawal from ethanol vapor. These results demonstrate that NMDAR subunit composition can be modulated differentially between adolescents and adults by chronic ethanol exposure and withdrawal. These developmental differences in NMDAR subunits composition may also be associated with the enhanced vulnerability of the adolescent brain to ethanol dependence.

Effects of adolescent ethanol exposure on event-related oscillations (EROs) in the hippocampus of adult rats

Electrophysiological studies have shown that adolescent ethanol (EtOH) exposure can produce long-term changes in hippocampal EEG and ERP activity. Recently, evidence has emerged suggesting that event-related oscillations (EROs) may be good indices of alcoholism risk in humans, however, have not been evaluated for their ability to index the effects of EtOH exposure. The objective of the present study was to characterize EROs generated in hippocampus in adult rats exposed to EtOH during adolescence. Adolescent male Sprague-Dawley rats were exposed to EtOH vapor for 12h/d for 10 days. A time-frequency representation method was used to determine delta, theta, alpha and beta ERO energy and the degree of phase variation in the hippocampus of adult rats exposed to EtOH and age-matched controls. The present results suggest that the decrease in P3 amplitudes, previously observed in adult rats exposed to EtOH during adolescence, is associated with increases in evoked theta ERO energy. These studies suggest that EROs are suitable for characterizing the long-term effects of adolescent EtOH exposure. Further studies are needed to determine the relationship between the mechanisms that regulate these neurophysiological endophenotypes and the consequences of adolescent EtOH exposure.

Adolescent ethanol exposure: does it produce long-lasting electrophysiological effects?

This review discusses evidence for long-lasting neurophysiological changes that may occur following exposure to ethanol during adolescent development in animal models. Adolescence is the time that most individuals first experience ethanol exposure, and binge drinking is not uncommon during adolescence. If alcohol exposure is neurotoxic to the developing brain during adolescence, not unlike it is during fetal development, then understanding how ethanol affects the developing adolescent brain becomes a major public health issue. Adolescence is a critical time period when cognitive, emotional, and social maturation occurs and it is likely that ethanol exposure may affect these complex processes. To study the effects of ethanol on adolescent brain, animal models where the dose and time of exposure can be carefully controlled that closely mimic the human condition are needed. The studies reviewed provide evidence that demonstrates that relatively brief exposure to high levels of ethanol, via ethanol vapors, during a period corresponding to parts of adolescence in the rat is sufficient to cause long-lasting changes in functional brain activity. Disturbances in waking electroencephalogram and a reduction in the P3 component of the event-related potential (ERP) have been demonstrated in adult rats that were exposed to ethanol vapor during adolescence. Adolescent ethanol exposure was also found to produce long-lasting reductions in the mean duration of slow-wave sleep (SWS) episodes and the total amount of time spent in SWS, a finding consistent with a premature aging of sleep. Further studies are necessary to confirm these findings, in a range of strains, and to link those findings to the neuroanatomical and neurochemical mechanisms potentially underlying the lasting effects of adolescent ethanol exposure.

Effects of ethanol on hippocampal function during adolescence: a look at the past and thoughts on the future

It has been demonstrated by several laboratories that ethanol, both acute and chronic, produces effects that are age dependent. Specifically, adolescent rats are less sensitive to the hypnotic and motor-impairing effects of ethanol but are more sensitive to the hypothermic effects of the drug. However, the results on hippocampal function are not as clear. For example, there have been mixed findings regarding adolescent sensitivity of hippocampal-dependent (spatial) memory in response to ethanol. The current review explores the present state of the field as it relates to ethanol's effects in the hippocampus, particularly as it relates to spatial memory. In addition, we review potential neurobiological mechanisms that might underlie the age-dependent effects of ethanol in the hippocampus. Finally, future directions are proposed that will advance the state of the field as it relates to ethanol's effect during this developmental period.

A preliminary study of functional magnetic resonance imaging response during verbal encoding among adolescent binge drinkers

Binge alcohol use is common among teenagers with 28% of 12th graders reporting getting drunk in the past month. Chronic heavy drinking has been associated with verbal learning and memory deficits in adolescents and adults, yet verbal encoding in less frequently drinking teens has not yet been studied. Here, we examined functional magnetic resonance imaging (fMRI) response during verbal encoding among adolescent binge drinkers. Participants recruited from local high schools were of ages 16-18 and consisted of 12 binge drinkers and 12 demographically similar nondrinkers. Participants were all nonsmokers, and drinkers were abstinent from alcohol for an average of 33 days at the time of scanning. Participants performed a verbal paired associates learning task during fMRI acquisition. Drinkers recalled marginally fewer words than nondrinkers (P=.07). Compared with nondrinkers, bingers showed more response in right superior frontal and bilateral posterior parietal cortices but less response in occipital cortex during novel encoding (Ps<.05, clusters >1,512microL). In addition, controls showed significant activation in the left hippocampus during novel encoding, whereas binge drinkers did not. Adolescent binge drinkers demonstrated (1) more response than nondrinkers in frontal and parietal regions, which could suggest greater engagement of working memory systems during encoding; (2) no hippocampal activation to novel word pairs; and (3) slightly poorer word pair recall, which could indicate disadvantaged processing of novel verbal information and a slower learning slope. Longitudinal studies will be needed to ascertain the degree to which emergence of binge drinking is linked temporally to these brain response patterns.

Chronic alcohol consumption from adolescence-to-adulthood in mice--effect on growth and social behavior

Experimentation with alcohol is common during adolescence. However the long-term consequences from moderate alcohol use during adolescence development are not clear. Using a two-bottle free-choice paradigm in the home-cage setting, we studied adolescent mice (4 weeks old) across a 6-week time span of the adolescence-to-adulthood development period. Adolescent mice readily reached a steady level of alcohol consumption and maintained this level throughout the 6-week period. Chronic alcohol consumption resulted in reduced growth in adolescent mice, as well as accelerated acclimation to a novel environment. During a social interaction test, similar levels of initial social investigation and subsequent habituation were observed in both the chronic alcohol and the water-only control groups. However, chronic alcohol self-administration resulted in impaired social recognition and decreased social play/fight behavior. Taken together, these results indicated that chronic alcohol consumption across adolescence development negatively impacted both physical growth and social behavior in mice, highlighting the detrimental consequences from prolonged alcohol drinking in adolescence.

Milk consumption during adolescence decreases alcohol drinking in adulthood

Early onset of alcohol consumption increases the risk for the development of dependence. Whether adolescent consumption of other highly palatable solutions may also affect alcohol drinking in adulthood is not known. The purpose of this study was to determine the effects of adolescent consumption of four solutions: water, sucrose, sucrose-milk and milk on ethanol drinking in adult rats. Rats had limited access to one of the four solutions from day PND 29 to PND 51 and were subsequently trained to consume ethanol (E) using a sucrose (S) fade-out procedure. Adolescent consumption of sucrose and sucrose-milk solutions increased intake of 2.5% E when it was combined with 10% S but it had no effect on the drinking of 10% E alone. Adolescent consumption of milk and sucrose-milk significantly decreased the intake of 10% E when it was combined with 10% S, and milk significantly reduced 10% E consumption alone and when it was combined with 5% S. Adolescent exposure to the sucrose-milk and sucrose solutions was also found to increase sucrose and sucrose-milk consumption. Our findings suggest adolescent exposure to sucrose increases, whereas, exposure to milk reduces ethanol consumption in adult rats. Our results may provide a new theoretical approach to the early prevention of alcoholism.

Effects of neonatal and peripubertal ethanol treatment on various aspects of adult rat behavior and brain anatomy

Exposure to ethanol during critical stages of brain development and maturation has adverse effects on behavioral and cognitive functions. So far, most animal models focused on the effects of either pre- or early postnatal ethanol treatment on behavior. We here used a multiple crossover design to investigate the effects of neonatal (postnatal day 7) ethanol treatment (2.5 g/kg b.i.d., dissolved in saline), subchronic peripubertal (postnatal days 40-65) ethanol treatment (1.0 g/kg, dissolved in saline) and the combination of both on the performance of adult Wistar rats in a variety of behavioral tasks. We also assessed anatomical changes in limbic and cortical brain areas. No effects of either single or combined neonatal and pubertal ethanol treatment was found on prepulse inhibition of startle (PPI, a measure of sensorimotor gating), or on the acoustic startle response in the absence of prepulses. Peripubertal ethanol treatment reduced the explorative behavior in the open field. The breakpoint in a progressive ratio operant response task was increased in those rats that had received both neonatal and pubertal ethanol treatment, while the preference for palatable food used as reinforcer in this task was not affected. No treatment effects were found on object recognition memory. No treatment effects on anxiety-related behavior in the elevated plus maze were found, however, the anxiolytic effect of the prototypical benzodiazepine diazepam was enhanced in rats that had received peripubertal ethanol treatment. Additive effects of neonatal and pubertal ethanol treatments were found on behaviors related to spontaneous locomotor activity. Combined neonatal and pubertal ethanol treatment lead to a reduction of myelin sheaths in the prefrontal cortex, and the neonatal ethanol treatment lead to a reduced number of parvalbumine-immunoreactive cells in the dorsal hippocampus. These findings suggest that neonatal ethanol exposure increases the risk of some but not all adverse behavioral and brain anatomical effects of pubertal ethanol consumption.

Effects of different concentrations of sugarcane alcohol on food intake and nutritional status of male and female periadolescent rats

The present study evaluated the effects of food and alcohol intake on the nutritional and metabolic status of male and female periadolescent rats submitted to single (15%) and multiple (10%, 20%, 30%) concentrations of hydroalcoholic solutions of sugar-based alcohol associated with a feed mixture. Thirty-six periadolescent Wistar rats were used and randomly arranged into three groups: Group A (control; 0% ethanol; six males and six females), Group B (15% ethanol; six males and six females), and Group C (10%, 20%, and 30% ethanol; six males and six females). Food consumption, body weight, water intake (mL), ethanol intake (g/kg/day), ethanol preference in relation to water and different concentrations, and serum biochemical dosages (glucose, total cholesterol, low-density lipoprotein cholesterol, high-density lipoprotein (HDL) cholesterol, very low-density lipoprotein fraction, triglycerides, cholesterol/HDL [CT/HDL], albumin) were analyzed. Males from Group C ingested more feed than females, which consumed reducing amounts throughout the weeks studied. Males also had heavier body weight, which increased throughout the experimental period. The animals ingested more water (females ingested more than males) in the first experimental week. Group C had a higher ethanol intake and greater preference for ethanol over water in both genders than Group B, which decreased over the subsequent weeks. Serum glucose was lower in Group A, whereas the CT/HDL ratio was lower in Group C. These findings allow the conclusion that nutritional and metabolic impact resulting from alcohol intake is different between genders and between the different forms in which the drug is offered. It is important to warn the population about the concentrations of alcohol intake, which may influence the growth and development of adolescents, thereby compromising their quality of life.

Effects of adolescent ethanol exposure on sleep in adult rats

Although adolescent ethanol (EtOH) exposure has been associated with long-lasting changes in brain function, little is known as to whether EtOH exposure during adolescence alters sleep and cortical arousal. This study examined protracted alterations in sleep in adult rats exposed to EtOH during adolescence. Adolescent male Wistar rats were exposed to EtOH vapor for 12 h/day for 5 weeks. Cortical electroencephalograms were obtained during 4-h recording sessions after 5 weeks of withdrawal from EtOH. Adolescent EtOH exposure significantly reduced the mean duration of slow-wave sleep (SWS) episodes and the total amount of time spent in SWS in EtOH-exposed rats, compared to controls. Spectral analysis revealed that adolescent EtOH exposure significantly increased cortical peak frequencies during SWS in the 2-4, 4-6, and 6-8 Hz bands. Taken together, our findings suggest that chronic EtOH exposure in adolescent rats reduces measures of SWS, an effect also seen as part of normal aging. Although the cellular and molecular mechanisms mediating the consequences of EtOH exposure on the aging process are not known, the similarities between adolescent EtOH exposure and aging merits further investigation.

Post-training ethanol disrupts trace conditioned fear in rats: effects of timing of ethanol, dose and trace interval duration

Ethanol has complex effects on memory performance, although hippocampus-dependent memory may be especially vulnerable to disruption by acute ethanol intoxication occurring during or shortly after a training episode. In the present experiments, the effects of post-training ethanol on delay and trace fear conditioning were examined in adolescent rats. In Experiment 1, 30-day-old Sprague-Dawley rats were given delay or trace conditioning trials in which a 10s flashing light CS was paired with a 0.5 mA shock US. For trace groups, the trace interval was 10 s. On days 31-33, animals were administered ethanol once daily (0.0 or 2.5 g/kg via intragastric intubation), and on day 34 animals were tested for CS-elicited freezing. Results showed that post-training ethanol affected the expression of trace, but had no effect on delay conditioned fear. Experiment 2 revealed that this effect was dose-dependent; doses lower than 2.5 g/kg were without effect. Experiment 3 evaluated whether proximity of ethanol to the time of training or testing was critical. Results show that ethanol administration beginning 24h after training was more detrimental to trace conditioned freezing than administration that was delayed by 48 h. Finally, in Experiment 4 animals were trained with one of three different trace intervals: 1, 3 or 10s. Results indicate that post-training administration of 2.5 g/kg ethanol disrupted trace conditioned fear in subjects trained with a 10s, but not with a 1 or 3s, trace interval. Collectively the results suggest that ethanol administration impairs post-acquisition memory processing of hippocampus-dependent trace fear conditioning.

Electrophysiological effects of dizocilpine (MK-801) in adult rats exposed to ethanol during adolescence

BACKGROUND

Despite evidence showing persistent changes in N-methyl-D-aspartate (NMDA)-receptor function following ethanol (EtOH) exposure, the contribution of NMDA systems to the long-term neurophysiological consequences of adolescent EtOH exposure is unclear. The aims of this study were the following: (1) to determine whether adolescent EtOH exposure produces neurophysiological changes after a prolonged withdrawal period in adult rats and (2) to assess protracted alterations in neurophysiological responses to the NMDA antagonist MK-801 in adult rats exposed to EtOH during adolescence.

METHODS

Adolescent male Wistar rats were exposed to EtOH vapor for 12 h/d for 5 weeks. The effects of MK-801 (0.0 to 0.1 mg/kg, intraperitoneally) on the electroencephalogram (EEG) and auditory event-related potentials (ERPs) were assessed after 8 weeks of abstinence from EtOH.

RESULTS

Experiments in aim 1 revealed that adolescent EtOH exposure reduced EEG variability in the frontal cortex in the 4 to 6 Hz band but had no effect on cortical and hippocampal EEG power and ERPs. Experiments in aim 2 showed that MK-801 significantly reduced EEG power in the parietal cortex (4 to 6 Hz, 6 to 8 Hz, 8 to 16 Hz, 16 to 32 Hz) and hippocampus (16 to 32 Hz) and EEG variability in the parietal cortex (6 to 8 Hz, 16 to 32 Hz) following adolescent EtOH exposure. MK-801 produced a significant decrease in hippocampal EEG variability (4 to 6 Hz, 8 to 16 Hz, 16 to 32 Hz) in control, but not in EtOH-exposed rats. MK-801 reduced frontal P1 ERP amplitude and latency in response to the rare tone in EtOH-exposed rats compared to controls. In contrast, MK-801 significantly reduced P3 ERP amplitude and latency in control, but not in EtOH-exposed rats.

CONCLUSIONS

The effects of MK-801 on hippocampal EEG variability and P3 ERP amplitude and latency are significantly attenuated after a prolonged withdrawal period following adolescent EtOH exposure. However, the inhibitory effects of MK-801 on cortical and hippocampal EEG power were enhanced in rats exposed to EtOH during adolescence. Taken together, these data suggest protracted changes in NMDA systems following adolescent EtOH exposure.

Differential effects of acute alcohol on EEG and sedative responses in adolescent and adult Wistar rats

Age-related developmental differences in sensitivity to the acute effects of alcohol may play an important role in the development of alcoholism. The present study was designed to evaluate the acute effects of alcohol on cortical electroencephalogram (EEG) in adolescent (P36) and adult (P78) Wistar rats. Five minutes of EEG was recorded after administration of 0, 0.75 or 1.5 g/kg alcohol. The righting reflex was performed to measure the sedative effects of alcohol (3.5 g/kg) and total sleeping time for each rat. Our results showed that alcohol (1.5 g/kg) increased power in the 1-2 Hz band and decreased the power in the 32-50 Hz band in the parietal cortical region of adolescent rats. Alcohol (1.5 g/kg) also increased stability of the EEG power in the slow-wave frequency bands (2-4 Hz, 4-6 Hz, and 6-8 Hz) of adolescent rats. In the frontal cortex of adult rats, but not in adolescent rats, alcohol (1.5 or 0.75 g/kg) decreased the power in the 16-32 Hz frequency band. Alcohol (1.5 g/kg) differentially increased power in a multiple of slow-wave frequency bands (2-4 Hz and 4-6 Hz) in the parietal cortex of adult rats as compared to adolescent rats. Adolescent rats were shown significantly shorter sleeping time and higher blood alcohol levels after regaining reflex than adult rats. Our results provide additional evidence of age-related differences in the effects of acute alcohol on cortical EEG, sedation and tolerance.

Neurobiological processes in adolescent addictive disorders

The purpose of this review is to summarize the neurobiological factors involved in the etiology of adolescent addiction and present evidence implicating various mechanisms in its development. Adolescents are at heightened risk for experimentation with substances, and early experimentation is associated with higher rates of SUD in adulthood. Both normative (e.g., immature frontal-limbic connections, immature frontal lobe development) and non-normative (e.g., lowered serotonergic function, abnormal hypothalamic-pituitary-adrenal axis function) neurobiological developmental factors can predispose adolescents to a heightened risk for SUD. In addition, a normative imbalance in the adolescent neurobiological motivational system may be caused by the relative underdevelopment of suppressive mechanisms when compared to stimulatory systems. These neurobiological liabilities may correspond to neurobehavioral impairments in decision-making, affiliation with deviant peers and externalizing behavior; these and other cognitive and behavioral traits converge with neurobiological factors to increase SUD risk. The progression to SUD acts as an amplifying feedback loop, where the development of SUD results in reciprocal impairments in neurobehavioral and neurobiological processes. A clearer understanding of adolescent neurobiology is a necessary step in the development of prevention and treatment interventions for adolescent SUD.

Chronic ethanol exposure during adolescence increases basal dopamine in the nucleus accumbens septi during adulthood

BACKGROUND

In humans, adolescent exposure to alcohol is associated with the onset of adult alcohol dependency and suggests that early use potentiates vulnerability to addiction. The aim of the present study was to address whether chronic ethanol exposure during adolescence would alter nucleus accumbens septi (NAcc) dopamine (DA) levels in the adult brain.

METHODS

Rats were injected daily from postnatal day (PND) 30 to 50 with either 0.75 g/kg/i.p. ethanol or saline followed by an ethanol-abstinent period from PND 51 to 65. Changes in extracellular DA levels in the anterior NAcc shell were measured via the no net flux (NNF) paradigm.

RESULTS

Extracellular DA levels were greater in rats chronically treated with ethanol during adolescence (6.5 nM DA) in comparison with saline-exposed controls (3.6 nM DA). There were no differences in extraction fraction (E(d)), an indirect measure of DA reuptake, between ethanol-treated (87%) and nontreated (68%) rats.

CONCLUSIONS

Together these findings suggest that changes in extracellular DA may be an underlying physiological mechanism in adolescent vulnerability to the rewarding properties of ethanol.

Increased expression of protein kinase A inhibitor alpha (PKI-alpha) and decreased PKA-regulated genes in chronic intermittent alcohol exposure

Intermittent models of alcohol exposure that mimic human patterns of alcohol consumption produce profound physiological and biochemical changes and induce rapid increases in alcohol self-administration. We used high-density oligonucleotide microarrays to investigate gene expression changes during chronic intermittent alcohol exposure in three brain regions that receive mesocorticolimbic dopaminergic projections and that are believed to be involved in alcohol's reinforcing actions: the medial prefrontal cortex, the nucleus accumbens and the amygdala. An independent replication of the experiment was used for RT-PCR validation of the microarray results. The protein kinase A inhibitor alpha (PKI-alpha, Pkia), a member of the endogenous PKI family implicated in reducing nuclear PKA activity, was found to be increased in all three regions tested. Conversely, we observed a downregulation of the expression of several PKA-regulated transcripts in one or more of the brain regions studied, including the activity and neurotransmitter-regulated early gene (Ania) - 1, -3, -7, -8, the transcription factors Egr1 and NGFI-B (Nr4a1) and the neuropeptide NPY. Reduced expression of PKA-regulated genes in mesocorticolimbic projection areas may have motivational significance in the rapid increase in alcohol self-administration induced by intermittent alcohol exposure.

P3 components and adolescent binge drinking in Southwest California Indians

In adolescence, consuming a large number of drinks over a short interval of time (e.g. binging) is not an uncommon occurrence. Since adolescence is an important neurodevelopmental period, the effect of binge drinking on brain and behavior has become a significant health concern. The present study evaluated event-related potentials (ERPs) in young adult Southwest California Indians who had a history of binge drinking during their adolescence. One hundred twenty five participants who were currently 18-25 yrs of age who were free of Axis I psychiatric diagnoses were categorized as: 1) reporting no binge drinking during adolescence (>5 drinks per occasion before age 18) or drug dependence diagnoses 2) reporting binge drinking during adolescence with no drug dependence diagnoses 3) reporting binge drinking during adolescence and drug dependence diagnoses. ERPs were collected using a facial discrimination task. Adolescent alcohol and drug exposure was found to be associated with decreases in the latency of an early P3 component (P350). Decreases in a later component amplitude (P450) were also found in young adults exposed to alcohol, and those exposed to alcohol and drugs. However, that finding appears to be a combined result of predisposing factors such as family history of alcoholism and presence of other externalizing diagnoses. Taken together these preliminary studies suggests that adolescent binge drinking may result in a decreases in P3 component latencies and amplitudes perhaps reflecting a loss or delay in the development of inhibitory brain systems.

Two-choice reaction time performance in Sprague-Dawley rats exposed to alcohol during adolescence or adulthood

Adolescent alcohol abusers display subtle attention impairments. This study used a two-choice reaction time task to examine the effects of ethanol on sustained attention following adult or adolescent exposure. Sprague-Dawley rats were exposed to ethanol vapor for 14 days starting on postnatal day 30 (adolescence) or 60-64 (adulthood) and were then trained to perform the two-choice reaction time task. Ethanol exposure resulted in blood ethanol levels averaging 215 mg/dl. Behavior following adult ethanol exposure was characterized by increased accuracy and omissions during the two-choice reaction time task, reduced fixed ratio lever pressing, and reductions in the highest fixed ratio completed on a progressive ratio schedule. Adolescent ethanol exposure transiently increased two-choice reaction time accuracy and slightly reduced fixed ratio lever presses. Improved accuracy was unexpected, but might be related to ethanol-induced increases in central nervous system arousal and/or mild behavioral perseveration. Increased omissions, reduced lever pressing, and reductions in the highest fixed ratios completed most likely reflect decreased 'motivation to work' and index generalized anhedonia. This study is the first to demonstrate that rats exposed to ethanol during adulthood are more sensitive to the effects of ethanol on sustained attention than rats exposed to ethanol during adolescence and to ethanol-induced anhedonia, as indexed by two-choice reaction time performance.

Chronic tolerance to the social consequences of ethanol in adolescent and adult Sprague-Dawley rats

Adolescence is a time when experimentation with ethanol becomes normative, with high levels of use becoming apparent in some adolescents. Little is known, however, as to whether ethanol adaptations emerging in adolescents with repeated ethanol use are similar to those emerging in adults. The presents study used a rodent model to investigate the development of chronic tolerance to ethanol-induced alterations in social behavior. The study focused both on ethanol-induced social facilitations, typically evident in adolescents but not adult animals at low doses of ethanol, as well as the inhibition of social behavior occurring at higher doses in both adolescent and adult rats. Adolescent and adult male and female Sprague-Dawley rats were injected intraperitoneally with either isotonic saline or 1 g/kg ethanol for 7 consecutive days: postnatal day (P) 27-33 for adolescents and P62-68 for adults. Acute effects of ethanol (0, 0.25, 0.5, 0.75, and 1 g/kg) on social behavior, social motivation (measured in terms of social preference), and locomotor activity were assessed 48 h after the last chronic exposure using a modified social interaction test in a familiar environment. Adolescents chronically exposed to ethanol developed tolerance to ethanol-induced social facilitation. Animals of both ages likewise developed chronic tolerance to ethanol-induced social inhibition. Metabolic tolerance emerged in adults, as indexed by a decrease in blood ethanol concentrations after chronic ethanol at this age, whereas only functional tolerance was evident in adolescents. Unexpectedly, chronic ethanol diminished baseline levels of social preference in adolescents, but made them more responsive to ethanol-induced enhancement of social preference. Chronic ethanol exposure in adulthood, however, only induced tolerance to the suppressing effects of higher ethanol doses on social preference. Thus, whereas adolescents and adult both develop adaptations following repeated exposure to ethanol, adolescents are more vulnerable to the disruptive effects of chronic ethanol exposure on social preference than their more mature counterparts.

Adolescent vulnerabilities to chronic alcohol or nicotine exposure: findings from rodent models

This article presents an overview of the proceedings from a symposium entitled "Is adolescence special? Possible age-related vulnerabilities to chronic alcohol or nicotine exposure," organized by Susan Barron and Linda Spear and held at the 2004 Research Society on Alcoholism Meeting in Vancouver, British Columbia. This symposium, co-sponsored by the Fetal Alcohol Syndrome Study Group and the Neurobehavioral Teratology Society, focused on our current knowledge regarding the long-term consequences of ethanol and/or nicotine exposure during adolescence with the emphasis on data from rodent models. The support from these two societies represents the understanding by these research groups that adolescence represents a unique developmental stage for the effects of chronic drug exposure and also marks an age in which many risky behaviors including alcohol consumption and smoking typically begin. The speakers included (1) Aaron White, who presented data on the effects of adolescent ethanol exposure on subsequent motor or cognitive response to an ethanol challenge in adulthood; (2) Richard Bell, who presented data suggesting that genetic differences could play a role in adolescent vulnerability to ethanol; (3) Craig Slawecki, who presented data looking at the effects of chronic exposure to alcohol or nicotine on neurophysiologic and behavioral end points; and (4) Ed Levin, who presented data on acute and long-term consequences of adolescent nicotine exposure. Finally, Linda Spear provided some summary points and recommendations regarding unresolved issues and future directions.