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

A multicomponent ethanol response battery across a cumulative dose ethanol challenge reveals diminished adolescent rat ethanol responsivity relative to adults

Adolescence is a conserved developmental period associated with low alcohol responsivity, which can contribute to heavy drinking and development of an alcohol use disorder (AUD) later in life. To investigate ethanol responsivity between adolescent and adult rats, we developed an ethanol response battery (ERB) to assess acute ethanol responses across cumulative doses of ethanol during the rising phase of the blood ethanol curve. We tested the hypothesis that adolescent male and female rats would exhibit lower ethanol responsivity to a cumulative ethanol challenge relative to adults. Male and female adolescent (postnatal day [P]40) and adult (P85) Wistar rats underwent ERB assessment following consecutive doses of ethanol (i.e., 1.0, 1.0, and 1.0 g/kg) to produce cumulative ethanol doses of 0.0, 1.0, 2.0, and 3.0 g/kg. The ERB consisted of (1) the 6-point behavioral intoxication rating scale, (2) body temperature assessment, (3) tail blood collection, (4) accelerating rotarod assessment, (5) tilting plane assessment, and (6) loss of righting reflex (LORR) assessment. Across cumulative ethanol doses, adolescent and adult rats evidenced progressive changes in ERB measures. On the ERB, adolescent rats of both sexes evidenced (1) lower intoxication rating, (2) blunted hypothermic responses, particularly in females, (3) longer latencies to fall from the accelerating rotarod, and (4) less tilting plane impairment relative to adults despite comparable BECs. All adult rats, regardless of sex, displayed a LORR at the 3.0 g/kg cumulative ethanol dose while among the adolescent rats, only one male rat and no females showed the LORR. These data reveal decreased adolescent ethanol responsivity across body temperature, intoxication, balance, and coordination responses to a cumulative ethanol challenge as assessed using the novel ERB relative to adults. The results of this study suggest that adolescent-specific low ethanol responsivity may contribute to adolescent binge drinking and increased risk for development of an AUD.

Intoxicating effects of alcohol depend on acid-sensing ion channels

Persons at risk for developing alcohol use disorder (AUD) differ in their sensitivity to acute alcohol intoxication. Alcohol effects are complex and thought to depend on multiple mechanisms. Here, we explored whether acid-sensing ion channels (ASICs) might play a role. We tested ASIC function in transfected CHO cells and amygdala principal neurons, and found alcohol potentiated currents mediated by ASIC1A homomeric channels, but not ASIC1A/2 A heteromeric channels. Supporting a role for ASIC1A in the intoxicating effects of alcohol in vivo, we observed marked alcohol-induced changes on local field potentials in basolateral amygdala, which differed significantly in Asic1a-/- mice, particularly in the gamma, delta, and theta frequency ranges. Altered electrophysiological responses to alcohol in mice lacking ASIC1A, were accompanied by changes in multiple behavioral measures. Alcohol administration during amygdala-dependent fear conditioning dramatically diminished context and cue-evoked memory on subsequent days after the alcohol had cleared. There was a significant alcohol by genotype interaction. Context- and cue-evoked memory were notably worse in Asic1a-/- mice. We further examined acute stimulating and sedating effects of alcohol on locomotor activity, loss of righting reflex, and in an acute intoxication severity scale. We found loss of ASIC1A increased the stimulating effects of alcohol and reduced the sedating effects compared to wild-type mice, despite similar blood alcohol levels. Together these observations suggest a novel role for ASIC1A in the acute intoxicating effects of alcohol in mice. They further suggest that ASICs might contribute to intoxicating effects of alcohol and AUD in humans.

Development of network oscillations through adolescence in male and female rats

The primary aim of this research was to study the developmental trajectory of oscillatory synchronization in neural networks of normal healthy rats during adolescence, corresponding to the vulnerable age of schizophrenia prodrome in human. To monitor the development of oscillatory networks through adolescence we used a "pseudo-longitudinal" design. Recordings were performed in terminal experiments under urethane anesthesia, every day from PN32 to PN52 using rats-siblings from the same mother, to reduce individual innate differences between subjects. We found that hippocampal theta power decreased and delta power in prefrontal cortex increased through adolescence, indicating that the oscillations in the two different frequency bands follow distinct developmental trajectories to reach the characteristic oscillatory activity found in adults. Perhaps even more importantly, theta rhythm showed age-dependent stabilization toward late adolescence. Furthermore, sex differences was found in both networks, more prominent in the prefrontal cortex compared with hippocampus. Delta increase was stronger in females and theta stabilization was completed earlier in females, in postnatal days PN41-47, while in males it was only completed in late adolescence. Our finding of a protracted maturation of theta-generating networks in late adolescence is overall consistent with the findings of longitudinal studies in human adolescents, in which oscillatory networks demonstrated a similar pattern of maturation.

Sex Differences in the Alcohol-Mediated Modulation of BLA Network States

Alcohol use, reported by 85% of adults in the United States, is highly comorbid with mood disorders, like generalized anxiety disorder and major depression. The basolateral amygdala (BLA) is an area of the brain that is heavily implicated in both mood disorders and alcohol use disorder. Importantly, the modulation of BLA network/oscillatory states via parvalbumin (PV)-positive GABAergic interneurons has been shown to control the behavioral expression of fear and anxiety. Further, PV interneurons express a high density of δ subunit-containing GABAA receptors (GABAARs), which are sensitive to low concentrations of alcohol. Therefore, we hypothesized that the effects of alcohol may modulate BLA network states that have been associated with fear and anxiety behaviors via δ-GABAARs on PV interneurons in the BLA. Given the impact of ovarian hormones on the expression of δ-GABAARs, we also examined the ability of alcohol to modulate local field potentials in the BLA from male and female C57BL/6J and Gabrd-/- mice after acute and repeated exposure to alcohol. Here, we demonstrate that acute and repeated alcohol can differentially modulate oscillatory states in male and female C57BL/6J mice, a process that involves δ-GABAARs. This is the first study to demonstrate that alcohol is capable of altering network states implicated in both anxiety and alcohol use disorders.

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.

Adolescent Vulnerability to Alcohol Use Disorder: Neurophysiological Mechanisms from Preclinical Studies

Adolescent alcohol use in human populations dramatically increases the likelihood of adult alcohol use disorder. This adolescent vulnerability is recapitulated in preclinical models which provide important opportunities to understand basic neurobiological mechanisms. We provide here an overview of GABAergic and glutamatergic neurotransmission and our current understanding of the sensitivity of these systems to adolescent ethanol exposure. As a whole, the preclinical literature suggests that adolescent vulnerability may be directly related to region-specific neurobiological processes that continue to develop during adolescence. These processes include the activity of intrinsic circuits within diverse brain regions (primarily represented by GABAergic neurotransmission) and activity-dependent regulation of synaptic strength at glutamatergic synapses. Furthermore, GABAergic and glutamatergic neurotransmission within regions/circuits that regulate cognitive function, emotion, and their integration appears to be the most vulnerable to adolescent ethanol exposure. Finally, using documented behavioral differences between adolescents and adults with respect to acute ethanol, we highlight additional circuits and regions for future study.

Altered brain activity during withdrawal from chronic alcohol is associated with changes in IL-6 signal transduction and GABAergic mechanisms in transgenic mice with increased astrocyte expression of IL-6

Interleukin-6 (IL-6) is an important neuroimmune factor that is increased in the brain by alcohol exposure/withdrawal and is thought to play a role in the actions of alcohol on the brain. To gain insight into IL-6/alcohol/withdrawal interactions and how these interactions affect the brain, we are studying the effects of chronic binge alcohol exposure on transgenic mice that express elevated levels of IL-6 in the brain due to increased astrocyte expression (IL-6 tg) and their non-transgenic (non-tg) littermate controls. IL-6/alcohol/withdrawal interactions were identified by genotypic differences in spontaneous brain activity in electroencephalogram (EEG) recordings from the mice, and by Western blot analysis of protein activation or expression in hippocampus obtained from the mice after the final alcohol withdrawal period. Results from EEG studies showed frequency dependent genotypic differences in brain activity during withdrawal. For EEG frequencies that were affected by alcohol exposure/withdrawal in both genotypes, the nature of the effect was similar, but differed across withdrawal cycles. Differences between IL-6 tg and non-tg mice were also observed in Western blot studies of the activated form of STAT3 (phosphoSTAT3), a signal transduction partner of IL-6, and subunits of GABA_A receptors (GABA_AR). Regression analysis revealed that pSTAT3 played a more prominent role during withdrawal in the IL-6 tg mice than in the non-tg mice, and that the role of GABA_AR alpha-5 and GABA_AR alpha-1 in brain activity varied across genotype and withdrawal. Taken together, our results suggest that IL-6 can significantly impact mechanisms involved in alcohol withdrawal.

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.

Transgenic mice with increased astrocyte expression of IL-6 show altered effects of acute ethanol on synaptic function

A growing body of evidence has revealed that resident cells of the central nervous system (CNS), and particularly the glial cells, comprise a neuroimmune system that serves a number of functions in the normal CNS and during adverse conditions. Cells of the neuroimmune system regulate CNS functions through the production of signaling factors, referred to as neuroimmune factors. Recent studies show that ethanol can activate cells of the neuroimmune system, resulting in the elevated production of neuroimmune factors, including the cytokine interleukin-6 (IL-6). Here we analyzed the consequences of this CNS action of ethanol using transgenic mice that express elevated levels of IL-6 through increased astrocyte expression (IL-6-tg) to model the increased IL-6 expression that occurs with ethanol use. Results show that increased IL-6 expression induces neuroadaptive changes that alter the effects of ethanol. In hippocampal slices from non-transgenic (non-tg) littermate control mice, synaptically evoked dendritic field excitatory postsynaptic potential (fEPSP) and somatic population spike (PS) at the Schaffer collateral to CA1 pyramidal neuron synapse were reduced by acute ethanol (20 or 60 mM). In contrast, acute ethanol enhanced the fEPSP and PS in hippocampal slices from IL-6 tg mice. Long-term synaptic plasticity of the fEPSP (i.e., LTP) showed the expected dose-dependent reduction by acute ethanol in non-tg hippocampal slices, whereas LTP in the IL-6 tg hippocampal slices was resistant to this depressive effect of acute ethanol. Consistent with altered effects of acute ethanol on synaptic function in the IL-6 tg mice, EEG recordings showed a higher level of CNS activity in the IL-6 tg mice than in the non-tg mice during the period of withdrawal from an acute high dose of ethanol. These results suggest a potential role for neuroadaptive effects of ethanol-induced astrocyte production of IL-6 as a mediator or modulator of the actions of ethanol on the CNS, including persistent changes in CNS function that contribute to cognitive dysfunction and the development of alcohol dependence.

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

Alcohol use is typically initiated during adolescence, which, along with young adulthood, is a vulnerable period for the onset of high-risk drinking and alcohol abuse. Given across-species commonalities in certain fundamental neurobehavioral characteristics of adolescence, studies in laboratory animals such as the rat have proved useful to assess persisting consequences of repeated alcohol exposure. Despite limited research to date, reports of long-lasting effects of adolescent ethanol exposure are emerging, along with certain common themes. One repeated finding is that adolescent exposure to ethanol sometimes results in the persistence of adolescent-typical phenotypes into adulthood. Instances of adolescent-like persistence have been seen in terms of baseline behavioral, cognitive, electrophysiological and neuroanatomical characteristics, along with the retention of adolescent-typical sensitivities to acute ethanol challenge. These effects are generally not observed after comparable ethanol exposure in adulthood. Persistence of adolescent-typical phenotypes is not always evident, and may be related to regionally specific ethanol influences on the interplay between CNS excitation and inhibition critical for the timing of neuroplasticity.

Ontogeny and adolescent alcohol exposure in Wistar rats: open field conflict, light/dark box and forced swim test

Epidemiological studies have demonstrated that heavy drinking and alcohol abuse and dependence peak during the transition between late adolescence and early adulthood. Studies in animal models have demonstrated that alcohol exposure during adolescence can cause a modification in some aspects of behavioral development, causing the "adolescent phenotype" to be retained into adulthood. However, the "adolescent phenotype" has not been studied for a number of behavioral tests. The objective of the present study was to investigate the ontogeny of behaviors over adolescence/young adulthood in the light/dark box, open field conflict and forced swim test in male Wistar rats. These data were compared to previously published data from rats that received intermittent alcohol vapor exposure during adolescence (AIE) to test whether they retained the "adolescent phenotype" in these behavioral tests. Three age groups of rats were tested (post-natal day (PD) 34-42; PD55-63; PD69-77). In the light/dark box test, younger rats escaped the light box faster than older adults, whereas AIE rats returned to the light box faster and exhibited more rears in the light than controls. In the open field conflict test, both younger and AIE rats had shorter times to first enter the center, spent more time in the center of the field, were closer to the food, and consumed more food than controls. In the forced swim test no clear developmental pattern emerged. The results of the light/dark box and the forced swim test do not support the hypothesis that adolescent ethanol vapor exposure can "lock-in" all adolescent phenotypes. However, data from the open field conflict test suggest that the adolescent and the AIE rats both engaged in more "disinhibited" and food motivated behaviors. These data suggest that, in some behavioral tests, AIE may result in a similar form of behavioral disinhibition to what is seen in adolescence.

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.

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.

The influence of acute and chronic alcohol consumption on response time distribution in adolescent rhesus macaques

BACKGROUND

Analysis of the distribution of reaction times (RTs) in behavioral tasks can illustrate differences attributable to changes in attention, even when no change in mean RT is observed. Detrimental attentional effects of both acute and chronic exposure to alcohol may therefore be revealed by fitting RT data to an ex-Gaussian probability density function which identifies the proportion of long-RT responses.

METHODS

Adolescent male rhesus macaques completed a 5-choice serial reaction time task (5CSRT) after acute alcohol consumption (up to 0.0, 1.0 and 1.5 g/kg). Monkeys were next divided into chronic alcohol (N = 5) and control groups (N = 5); the experimental group consumed 1.5-3.0 g/kg alcohol for 200 drinking sessions. Unintoxicated performance in the 5CSRT task was determined systematically across the study period and the effect of acute alcohol was redetermined after the 180th drinking session. The effect of extended abstinence from chronic alcohol was determined across 90 days.

RESULTS

Acute alcohol exposure dose-dependently reduced the probability of longer RT responses without changing the mean or the standard deviation of the RT distribution. The RT distribution of control monkeys tightened across 10 months whereas that of the chronic alcohol group was unchanged. Discontinuation from chronic alcohol increased the probability of long RT responses with a difference from control animals observed after 30 days of discontinuation.

CONCLUSIONS

Alcohol consumption selectively affected attention as reflected in the probability of long RT responses. Acute alcohol consumption focused attention, chronic alcohol consumption impaired the maturation of attention across the study period and alcohol discontinuation impaired attention.

Hazardous alcohol levels in adolescents are underestimated by barkeepers and security personnel

Drunkenness among adolescents represents a significant problem and is associated with adverse consequences. A Licensing Act, which prohibits the dispensing of alcoholic beverages to visibly intoxicated individuals, was introduced in Germany to curb excessive drinking. The objective of the study was to explore whether it is possible for barkeepers and security personnel to correctly estimate the alcohol level (AL) of adolescents merely based on their outer appearance and self-report. In a commercial dance club, 89 adolescents reported their past and current alcohol consumption and estimated their own AL. Their breath alcohol level was measured with a breathalyzer. The sample was divided into "moderate drinkers" and "binge drinkers." Barkeepers and security personnel spoke to and examined the adolescents in order to estimate the adolescents' AL. Professional staff underestimated the ALs of adolescents in 60.7 % of all cases. Estimates of the personnel showed greater deviations from the measured AL of the adolescents as compared to estimates of the adolescents themselves, especially in the group of binge drinkers (t = 2.764; p = 0.009).

CONCLUSION

It seems that adolescents suffer less from observable effects of alcohol, such as sedation or impairment of motor function. Consequently, we do not recommend the application of the Licensing Act to adolescents, but suggest its replacement by other restrictions and prevention measures.

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.

Low and moderate doses of acute ethanol do not impair spatial cognition but facilitate accelerating rotarod performance in adolescent and adult rats

Adolescents and adult rodents have differing sensitivities to the acute effects of ethanol on a variety of behavioral and electrophysiological measures. Often, these differences are revealed using high ethanol doses and consequently little is known about these age-related effects using lower ethanol doses. We sought to determine if low-dose ethanol produces differential effects on cognition and motor behavior in adolescent and adult rats. Adolescent (postnatal day PD 30-32) and adult (PD 70-72) male Sprague Dawley rats were trained on the standard version of the Morris Water Maze (MWM) for 5 days or received 5 training trials on an accelerating rotarod (ARR). Adolescents learned the location of the submerged platform in the MWM significantly slower than adults during training and, acute ethanol administration (0.5 g/kg, 0.75 g/kg, or 1.0 g/kg) 30 min before testing did not impair spatial memory in either age group. On the ARR test, adolescent rats spent significantly more time on the rotarod compared to adults and, alcohol exposure (1.0 g/kg) significantly increased ARR performance 30 min following administration. Our findings address the utility of investigating low and moderate doses of ethanol during different developmental stages in rats.

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.

Effect of acute ethanol and acute allopregnanolone on spatial memory in adolescent and adult rats

The effects of ethanol differ in adolescent and adult rats on a number of measures. The evidence of the effects of ethanol on spatial memory in adolescents and adults is equivocal. Whether adolescents are more or less sensitive to ethanol-induced impairment of spatial memory acquisition remains unclear; with regard to the effects of acute ethanol on spatial memory retrieval there is almost no research looking into any age difference. Thus, we examined the effects of acute ethanol on spatial memory in the Morris Watermaze in adolescents and adults. Allopregnanolone (ALLO) is a modulator of the GABA(A) receptor and has similar behavioral effects as ethanol. We sought to also determine the effects of allopreganolone on spatial memory in adolescent and adults. Male adolescent (post natal [PN]28-30) and adult (PN70-72) rats were trained in the Morris Watermaze for 6 days and acute doses of ethanol (saline, 1.5 and 2.0 g/kg) or ALLO (vehicle, 9 and 18 mg/kg) were administered on Day 7. A probe trial followed on Day 8. As expected, there were dose effects; higher doses of both ethanol and ALLO impaired spatial memory. However, in both the ethanol and ALLO conditions adolescents and adults had similar spatial memory impairments. The current results suggest that ethanol and ALLO both impair hippocampal-dependent spatial memory regardless of age in that once learning has occurred, ethanol or ALLO does not differentially impair the retrieval of spatial memory in adolescents and adults. Given the mixed results on the effect of ethanol on cognition in adolescent rats, additional research is needed to ascertain the factors critical for the reported differential results.

Immediate and prolonged effects of alcohol exposure on the activity of the hypothalamic-pituitary-adrenal axis in adult and adolescent rats

Alcohol stimulates the hypothalamic-pituitary-adrenal (HPA) axis. Part of this influence is likely exerted directly at the level of the corticotropin-releasing factor (CRF) gene, but intermediates may also play a role. Here we review the effect of alcohol on this axis, provide new data on the effects of binge drinking during adolescence, and argue for a role of catecholaminergic circuits. Indeed, acute injection of this drug activates brain stem adrenergic and noradrenergic circuits, and their lesion, or blockade of α1 adrenergic receptors significantly blunts alcohol-induced ACTH release. As alcohol can influence the HPA axis even once discontinued, and alcohol consumption in young people is associated with increased adult drug abuse (a phenomenon possibly mediated by the HPA axis), we determined whether alcohol consumption during adolescence modified this axis. The number of CRF-immunoreactive (ir) cells/section was significantly decreased in the central nucleus of the amygdala of adolescent self-administering binge-drinking animals, compared to controls. When another group of adolescent binge-drinking rats was administered alcohol in adulthood, the number of colocalized c-fos-ir and PNMT-ir cells/brain stem section in the C3 area was significantly decreased, compared to controls. As the HPA axis response to alcohol is blunted in adult rats exposed to alcohol vapors during adolescence, a phenomenon which was not observed in our model of self-administration, it is possible that the blood alcohol levels achieved in various models play a role in the long-term consequences of exposure to alcohol early in life. Collectively, these results suggest an important role of brain catecholamines in modulating the short- and long-term consequences of alcohol administration.

Adolescent alcohol exposure alters the central brain circuits known to regulate the stress response

Adolescent alcohol exposure (AAE) may exert long-term effects on the adult brain. Here, we tested the hypothesis that the brain regions affected include the rat hypothalamic-pituitary-adrenal (HPA) axis. Specifically, we examined the consequences of AAE [postnatal days (PND) 28-42] on the HPA axis-related brain circuitry of male rats challenged with an intragastric (ig) administration of alcohol in young adulthood (PND 61-62). Adolescent rats were exposed to alcohol vapors, while controls did not receive the drug. The mean blood alcohol level in adolescence on PND 40 was 212.8±5.7 mg %. Using immunohistochemistry and in situ hybridization procedures, we measured signals for c-fos and corticotropin releasing factor (CRF) in the paraventricular nucleus (PVN) of the hypothalamus, as well as signals for c-fos and phenylethanolamine N-methyltransferase (PNMT) in the adrenergic brain stem regions (C1 and C2). PVN CRF mRNA expression was significantly blunted in AAE rats tested at PND 61-62, compared to their controls. These animals also displayed a significant increase in the mean number of PNMT-ir cells/brain stem section in the C2 area. Collectively, these results suggest that exposure to alcohol vapors during adolescence exerts long-term effects on the ability of the PVN to mount a response to an acute alcohol administration in young adulthood, possibly mediated by medullary catecholamine input to the PVN.

The acute impact of ethanol on cognitive performance in rhesus macaques

Decreased cognitive control over prepotent responses has been hypothesized to contribute to ethanol-induced behavioral disinhibition. However, the effects of ethanol on specific cognitive domains associated with decision making have not been extensively studied. We examined the impact of acute ethanol administration on cognitive performance of nonhuman primates. Studies were conducted using 0.2, 0.5, and 1 g/kg intravenous ethanol in rhesus macaques performing touch screen-based tasks examining stimulus discrimination, stimulus reversal, and stimulus response performance. The impact on attentional processing was also evaluated. Ethanol reduced the accuracy of reversal performance marginally at 0.2 g/kg and significantly at 0.5 g/kg. This effect was selective given an absence of impairment on the stimulus discrimination and stimulus response tasks at these doses. Performance on stimulus discrimination was impaired at 1.0 g/kg, which prevented determination of reversal performance. Analysis of post-error response times demonstrated that error processing was impaired at both 0.2 and 0.5 g/kg. Ethanol also increased the number of omissions and delayed responses on an attentional task, suggesting more frequent attentional lapses. These data demonstrate that cognitive function mediated by specific prefrontal cortical brain regions is particularly sensitive to ethanol and suggest specific cognitive mechanisms that may underlie harmful decisions made at low doses of ethanol.

Ontogeny of the stimulant and sedative effects of ethanol in male and female Swiss mice: gradual changes from weaning to adulthood

RATIONALE

The adolescent period is characterized by a specific sensitivity to the effects of alcohol, which is believed to contribute to the enhanced risks of alcohol dependence when drinking is initiated early during adolescence. In adolescent rodents, while the reduced sensitivity to the sedative effects of ethanol has been well characterized, its stimulant effects have not yet been extensively studied.

OBJECTIVES

The present study characterized the development of the stimulant and the sedative effects of acute ethanol in male and female Swiss mice from weaning to early adulthood and tested whether both effects are interrelated.

METHODS

In a first experiment, mice aged 21, 28, 35, 42, and 60 days were injected with various ethanol doses and tested for ethanol-induced locomotor activity. In an independent experiment, mice of the same groups of age were injected with 4 g/kg ethanol and ethanol-induced sedation was quantified with the loss of righting reflex procedure.

RESULTS

In male and female mice, the stimulant effects of ethanol gradually decreased, whereas its sedative effects increased with age. When the sedation was statistically controlled using a covariance analysis, the differences between adult and juvenile mice in the locomotor stimulation were significantly reduced.

CONCLUSIONS

From weaning to early adulthood, the acute stimulant and sedative effects of ethanol show gradual changes that are similar in male and female mice. Although the initial tolerance to the sedative effects of ethanol contributes to the changes in ethanol-induced locomotor activity, young mice also show a higher sensitivity to the stimulant effects of ethanol.

Behavioral effects of ethanol in cerebellum are age dependent: potential system and molecular mechanisms

BACKGROUND

Adolescent rats are less sensitive to the motor-impairing effects of ethanol than adults. However, the cellular and molecular mechanisms underlying this age-dependent effect of ethanol have yet to be fully elucidated.

METHOD

Male rats of various ages were used to investigate ethanol-induced ataxia and its underlying cellular correlates. In addition, Purkinje neurons from adolescent and adult rats were recorded both in vivo and in vitro. Finally, protein kinase C (PKCγ) expression was determined in 3 brain regions in both adolescent and adult rats.

RESULTS

The present multi-methodological investigation confirms that adolescents are less sensitive to the motor-impairing effects of ethanol, and this differential effect is not because of differential blood ethanol levels. In addition, we identify a particular cellular correlate that may underlie the reduced motor impairment. Specifically, the in vivo firing rate of cerebellar Purkinje neurons recorded from adolescent rats was insensitive to an acute ethanol challenge, while the firing rate of adult cerebellar Purkinje neurons was significantly depressed. Finally, it is demonstrated that PKCγ expression in the cortex and cerebellum mirrors the age-dependent effect of ethanol: adolescents have significantly less PKCγ expression compared to adults.

CONCLUSIONS

Adolescents are less sensitive than adults to the motor-impairing effects of ethanol, and a similar effect is seen with in vivo electrophysiological recordings of cerebellar Purkinje neurons. While still under investigation, PKCγ expression mirrors the age effect of ethanol and may contribute to the age-dependent differences in the ataxic effects of ethanol.

Human and laboratory rodent low response to alcohol: is better consilience possible?

If people are brought into the laboratory and given alcohol, there are pronounced differences among individuals in many responses to the drug. Some participants in alcohol challenge protocols show a cluster of 'low level of responses to alcohol' determined by observing post-drinking-related changes in subjective, motor and physiological effects at a given dose level. Those individuals characterized as having low level of response (LR) to alcohol have been shown to be at increased risk for a lifetime diagnosis of alcohol dependence (AD), and this relationship between low LR and AD appears to be in part genetic. LR to alcohol is an area where achieving greater consilience between the human and the rodent phenotypes would seem to be highly likely. However, despite extensive data from both human and rodent studies, few attempts have been made to evaluate the human and animal data systematically in order to understand which aspects of LR appear to be most directly comparable across species and thus the most promising for further study. We review four general aspects of LR that could be compared between humans and laboratory animals: (1) behavioral measures of subjective intoxication; (2) body sway; (3) endocrine responses; and (4) stimulant, autonomic and electrophysiological responses. None of these aspects of LR provide completely face-valid direct comparisons across species. Nevertheless, one of the most replicated findings in humans is the low subjective response, but, as it may reflect either aversively valenced and/or positively valenced responses to alcohol as usually assessed, it is unclear which rodent responses are analogous. Stimulated heart rate appears to be consistent in animal and human studies, although at-risk subjects appear to be more rather than less sensitive to alcohol using this measure. The hormone and electrophysiological data offer strong possibilities of understanding the neurobiological mechanisms, but the rodent data in particular are rather sparse and unsystematic. Therefore, we suggest that more effort is still needed to collect data using refined measures designed to be more directly comparable in humans and animals. Additionally, the genetically mediated mechanisms underlying this endophenotype need to be characterized further across species.

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.

Impact of age at first drink on vulnerability to alcohol-related problems: testing the marker hypothesis in a prospective study of young adults

There is ample evidence that the early initiation of alcohol use is a risk factor for the development of later alcohol-related problems. The purpose of the current study was to examine whether this association can be explained by indicators of a common underlying susceptibility or whether age at drinking onset may be considered as an independent predictor of later drinking behavior, suggesting a potential causal relationship. Participants were drawn from a prospective cohort study of the long-term outcomes of early risk factors followed up from birth onwards. Structured interviews were administered to 304 participants to assess age at first drink and current drinking behavior. Data on risk factors, including early family adversity, parental alcohol use, childhood psychopathology and stressful life events, were repeatedly collected during childhood using standardized parent interviews. In addition, information on genotype was considered. Results confirmed previous work demonstrating that hazardous alcohol consumption is related to early-adolescent drinking onset. A younger age of first drink was significantly predicted by 5-HTTLPR genotype and the degree of preceding externalizing symptoms, and both factors were related to increased consumption or harmful alcohol use at age 19. However, even after controlling for these potential explanatory factors, earlier age at drinking onset remained a strong predictor of heavy alcohol consumption in young adulthood. The present longitudinal study adds to the current literature indicating that the early onset - adult hazardous drinking association cannot solely be attributed to shared genetic and psychopathologic risk factors as examined in this study.

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.

Age-related differences in the blood alcohol levels of Wistar rats

Knowledge of blood alcohol levels (BALs) that are achieved following ethanol administration is critical for contemporary efforts to develop animal models of alcoholism. Adolescent and adult male Wistar rats were administered varying doses of ethanol (0.75, 1.5 and 3.0 g/kg) via gavage or intraperitoneal injection and BALs were measured over a two hour period. The results showed that adolescent animals had lower BALs across all time points in comparison to adults following administration of 0.75 g/kg ethanol and that 1 h after administration of 1.5 g/kg ethanol, adolescent animals showed an enhanced rate of elimination. The highest dose of ethanol (3.0 g/kg) produced comparable BALs for both adolescents and adults during the two-hour sampling period; however, the BALs for both ages were lower following administration of ethanol by gavage at this dose. Furthermore, an order effects analysis highlights that depending on the route of administration, initial dose size can influence the BALs produced by lower doses of ethanol. The current data identify the importance of measuring the level of alcohol in the blood to confirm that target BALs are achieved for adolescents and equivalent BALs are being reached for both adolescent and adult animals when such comparisons are made.

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.

Differential effects of acute alcohol on prepulse inhibition and event-related potentials in adolescent and adult Wistar rats

BACKGROUND

Previous studies have demonstrated that adolescent and adult rats show differential sensitivity to many of the acute effects of alcohol. We recently reported evidence of developmental differences in the effects of acute alcohol on the cortical electroencephalogram. However, it is unclear whether developmental differences are also observed in other neurophysiological and neurobehavioral measurements known to be sensitive to alcohol exposure. The present study determined the age-related effects of acute alcohol on behavioral and event-related potential (ERP) responses to acoustic startle (AS) and prepulse inhibition (PPI).

METHODS

Male adolescent and adult Wistar rats were implanted with cortical recording electrodes. The effects of acute alcohol (0.0, 0.75, and 1.5 g/kg) on behavioral and ERP responses to AS and PPI were assessed.

RESULTS

Acute alcohol (0.75 and 1.5 g/kg) significantly reduced the behavioral and electrophysiological response to AS in adolescent and adult rats. Both 0.75 and 1.5 g/kg alcohol significantly enhanced the behavioral response to PPI in adolescent, but not in adult rats. During prepulse + pulse trials, 1.5 g/kg alcohol significantly increased the N10 pulse response in the adolescent frontal cortex. Acute alcohol (0.75 and 1.5 g/kg) also increased the N1 ERP pulse response to prepulse stimuli in frontal and parietal cortices in adult rats, but not in adolescent rats.

CONCLUSIONS

These data suggest that alcohol's effect on behavioral and electrophysiological indices of AS do not differ between adults and adolescents whereas developmental stage does appear to significantly modify alcohol-influenced response to PPI.