Chronic-Intermittent Ethanol Exposure During Adolescence Prevents Normal Developmental Changes in Sensitivity to Ethanol-Induced Motor Impairments

Chronic intermittent ethanol exposure in early adolescent and adult male rats: effects on tolerance, social behavior, and ethanol intake

BACKGROUND

Given the prevalence of alcohol use in adolescence, it is important to understand the consequences of chronic ethanol exposure during this critical period in development. The purpose of this study was to assess possible age-related differences in susceptibility to tolerance development to ethanol-induced sedation and withdrawal-related anxiety, as well as voluntary ethanol intake after chronic exposure to relatively high doses of ethanol during adolescence or adulthood.

METHODS

Juvenile/adolescent and adult male Sprague-Dawley rats were assigned to one of five 10-day exposure conditions: chronic ethanol (4 g/kg every 48 hours), chronic saline (equivalent volume every 24 hours), chronic saline/acutely challenged with ethanol (4 g/kg on day 10), nonmanipulated/acutely challenged with ethanol (4 g/kg on day 10), or nonmanipulated. For assessment of tolerance development, duration of the loss of righting reflex (LORR) and blood ethanol concentrations (BECs) upon regaining of righting reflex (RORR) were tested on the first and last ethanol exposure days in the chronic ethanol group, with both saline and nonmanipulated animals likewise challenged on the last exposure day. Withdrawal-induced anxiety was indexed in a social interaction test 24 hours after the last ethanol exposure, with ethanol-naïve chronic saline and nonmanipulated animals serving as controls. Voluntary intake was assessed 48 hours after the chronic exposure period in chronic ethanol, chronic saline and nonmanipulated animals using an 8-day 2 bottle choice, limited-access ethanol intake procedure.

RESULTS

In general, adolescent animals showed shorter durations of LORR and higher BECs upon RORR than adults on the first and last ethanol exposure days, regardless of chronic exposure condition. Adults, but not adolescents, developed chronic tolerance to the sedative effects of ethanol, tolerance that appeared to be metabolic in nature. Social deficits were observed after chronic ethanol in both adolescents and adults. Adolescents drank significantly more ethanol than adults on a gram per kilogram basis, with intake uninfluenced by prior ethanol exposure at both ages.

CONCLUSIONS

Adolescents and adults may differ in their ability and/or propensity to adapt to chronic ethanol exposure, with adults, but not adolescents, developing chronic metabolic tolerance. However, this chronic exposure regimen was sufficient to disrupt baseline levels of social behavior at both ages. Taken together, these results suggest that, despite the age-related differences in tolerance development, adolescents are as susceptible as adults to consequences of chronic ethanol exposure, particularly in terms of disruptions in social behavior. Whether these effects would last into adulthood remains to be determined.

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.

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.

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.

The role of GABA(A) receptors in the acute and chronic effects of ethanol: a decade of progress

The past decade has brought many advances in our understanding of GABA(A) receptor-mediated ethanol action in the central nervous system. We now know that specific GABA(A) receptor subtypes are sensitive to ethanol at doses attained during social drinking while other subtypes respond to ethanol at doses attained by severe intoxication. Furthermore, ethanol increases GABAergic neurotransmission through indirect effects, including the elevation of endogenous GABAergic neuroactive steroids, presynaptic release of GABA, and dephosphorylation of GABA(A) receptors promoting increases in GABA sensitivity. Ethanol's effects on intracellular signaling also influence GABAergic transmission in multiple ways that vary across brain regions and cell types. The effects of chronic ethanol administration are influenced by adaptations in GABA(A) receptor function, expression, trafficking, and subcellular localization that contribute to ethanol tolerance, dependence, and withdrawal hyperexcitability. Adolescents exhibit altered sensitivity to ethanol actions, the tendency for higher drinking and longer lasting GABAergic adaptations to chronic ethanol administration. The elucidation of the mechanisms that underlie adaptations to ethanol exposure are leading to a better understanding of the regulation of inhibitory transmission and new targets for therapies to support recovery from ethanol withdrawal and alcoholism.

Discriminative stimulus effects of ethanol, pregnanolone, and dehydroepiandrosterone (DHEA) in rats administered ethanol or saline as adolescents

Adolescent alcohol use may produce long-term changes in the receptors and neurosteroids that putatively mediate alcohol's effects and consequently contribute to alcohol abuse and dependence as an adult. To test this possibility, ethanol (0.18-1.8 g/kg) and two neurosteroids, pregnanolone (1-10 mg/kg) and dehydroepiandrosterone (DHEA, 1-100 mg/kg), were administered alone and in combination to adult, male Long-Evans rats discriminating 1 g/kg ethanol (15% v/v) under a fixed ratio (FR) 20 schedule of food presentation after adolescent treatment with 15 injections of ethanol (n = 9, 2 g/kg, 20% v/v) or saline (n = 7). When compared as adults, ethanol-treated adolescents (as opposed to saline-treated adolescents) had higher percentages of ethanol-lever responding at doses smaller than the training dose, and higher response rates after both control and ethanol injections. Neither pregnanolone nor DHEA substituted for ethanol in either adolescent-treated group up to doses that substantially decreased response rates. When administered with ethanol, 1 and 3.2 mg/kg of pregnanolone enhanced the discriminative stimulus effects of small ethanol doses more in saline-treated adolescents than in ethanol-treated adolescents. Unlike pregnanolone, 32 and 100 mg/kg of DHEA attenuated the discriminative stimulus effects of ethanol modestly in both adolescent-treated groups. These results in adult rats suggest that adolescent ethanol administration can enhance the discriminative stimulus effects of small ethanol doses and affect the capacity of pregnanolone, but not DHEA, to interact with ethanol's discriminative stimulus effects.

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.

Sensitization, duration, and pharmacological blockade of anxiety-like behavior following repeated ethanol withdrawal in adolescent and adult rats

BACKGROUND

Repeated ethanol withdrawal sensitizes anxiety-like behavior in adult rats and causes anxiety-like behavior and decreased seizure thresholds in adolescent rats. Current experiments determined if adolescent rats exhibit sensitized anxiety-like behavior, the duration of this effect, if drug pretreatments blocked these effects, and if these effects differed from those seen in adults.

METHODS

Male adolescent rats received three 5-day cycles of 2.5% ethanol diet (ED) separated by two 2-day withdrawal periods, continuous 15 days of 2.5%ED, or a single 5-day cycle of 2.5%ED. Male adult rats received three 5-day cycles of either 2.5% or 3.5%ED. These groups were tested 5 hours into the final withdrawal for social interaction (SI) deficits (an index of anxiety-like behavior). Ethanol intake was monitored throughout and blood concentrations were obtained from separate groups of rats. Additionally, adolescent rats were tested for SI 1, 2, 7, 14, and 18 days and adults 1 and 2 days after the final withdrawal. Some adolescent rats were also pretreated with the CRF(1) antagonist CP-154,526, the 5-HT(1A) agonist buspirone, or the benzodiazepine receptor antagonist flumazenil during the first 2 withdrawals.

RESULTS

SI was reduced in adolescent rats following repeated withdrawals of 2.5%ED while neither a continuous or single cycle ED exposure caused this effect. Adult rats also had reduced SI following repeated withdrawals from both 2.5% and 3.5%ED. This effect was present up to 1 week following the final withdrawal in adolescents but returned to baseline by 1 day in adults. CP-154,526, buspirone, or flumazenil prevented this reduction in SI in adolescent rats.

CONCLUSIONS

Adolescent rats exhibit sensitized anxiety-like behavior following repeated withdrawals at ED concentrations similar to those used in adults. However, this effect is longer lasting in adolescent rats. Drugs modulating CRF, 5-HT, or GABA systems during initial withdrawals prevent the development of anxiety-like behavior otherwise manifest during a final withdrawal in adolescent rats.

Chronic intermittent exposure to ethanol during adolescence produces tolerance to the hypnotic effects of ethanol in male rats: a dose-dependent analysis

Adolescence is a time period when distinct behavioral and neurophysiological changes occur. Novelty seeking is common during this developmental period, and binge alcohol consumption by adolescents is prevalent. Adolescents, as compared to adults, have been shown to display decreased sensitivity to many effects of ethanol, including effects that may serve as cues to moderate consumption. Consequently, reduction of these factors could facilitate drinking behaviors in adolescents, which may disrupt normal developmental processes. Chronic intermittent ethanol exposure (CIEE) to high doses of ethanol in rats has been shown to prevent normal developmental increases in sensitivity to ethanol-induced loss of righting reflex (LORR). However, it is unknown whether the same disruptions would occur following CIEE to more moderate and low alcohol doses. The present study was designed to evaluate the effects of CIEE in rats to several different doses during adolescence on ethanol-induced LORR in adulthood. Male rats were weighed and treated intraperitoneal with 1.0, 2.0, 3.0, or 4.0 g/kg ethanol or equivolume saline (equivalent to 4.0 g/kg dosings) every 48 hours for 20 days beginning on postnatal day (PN) 30. LORR was measured following each ethanol exposure. Finally, LORR was measured in both ethanol and saline-exposed animals following 4.0 g/kg ethanol challenge on PN 50 and following a 12-day withdrawal period (PN62). Duration of LORR remained unchanged throughout the adolescent exposure period. However, when LORR was measured on PN50 and PN62, 4.0 and 3.0 g/kg treatment groups displayed significantly less LORR compared to the free feeding and 1.0 g/kg ethanol treated groups. Animals displayed no tolerance development to LORR throughout the chronic exposure period even though moderate and high doses of ethanol were used. CIEE to high (3.0 or 4.0 g/kg) doses of ethanol disrupted the expected developmental increase in sensitivity to ethanol-induced LORR. These results may have implications for human adolescent drinkers. Specifically due to adolescents' relative resistance to the hypnotic effects of alcohol and their tendency to intake alcohol in an intermittent, or binge-like, manner such tolerance might lead to increases in alcohol abuse in this population of drinkers.

Risk and speed of transitions to first alcohol dependence symptoms in adolescents: a 10-year longitudinal community study in Germany

BACKGROUND

Although in many western countries alcohol use (AU) and symptoms of alcohol dependence (AD) are frequent in adolescence, temporal patterns and trajectories remain understudied. It is unclear whether early onset of AU is associated with the speed of transition to first AD symptoms and whether specific first AD symptoms and their timing are associated with AD.

AIMS

To examine (i) the incidence patterns of self-reported first AD symptoms; (ii) whether early AU is associated with the risk and speed of transition to first AD symptoms; and (iii) whether first AD symptoms and their timing are associated with AD.

DESIGN

A total of 3021 community subjects from Germany aged 14-24 years at baseline followed prospectively over 10 years. AU, AD symptoms and AD were assessed using the Munich-Composite International Diagnostic Interview (DIA-X/M-CIDI).

FINDINGS

Among first AD symptoms, tolerance (13.1%) and much time spent (5.0%) were most prevalent. Five to 30% of all first AD symptoms occurred during the first year after first AU. Early AU was not related to the risk of first AD symptoms. The speed of transition to first AD symptoms was greater among those with AU onset in later adolescence. Tolerance and loss of control were associated with AD development (risk difference 3.9% and 15.4%), as was early onset of tolerance, much time spent and loss of control.

CONCLUSION

Early AU and early AD symptoms are frequent among adolescents. Early self-reported tolerance, much time spent and loss of control are particularly predictive for AD and important targets for early preventive interventions.

Differential dietary ethanol intake and blood ethanol levels in adolescent and adult rats: effects on anxiety-like behavior and seizure thresholds

BACKGROUND

Adult rats exhibit increased anxiety-like behavior after exposure to repeated cycles of chronic ethanol and withdrawal. While adolescent rats have differential responses to both acute and chronic ethanol treatments, the potential differences in the effects of repeated withdrawals in this population have yet to be determined.

METHODS

Male adult and adolescent rats received three 5-day cycles of either a 4.5% or 7% ethanol diet (ED) separated by two 2-day withdrawal periods. Five hours into the final withdrawal, rats were tested for social interaction (SI) deficits (an index of anxiety-like behavior) and then assessed for seizure thresholds (audiogenic and bicuculline-induced). Ethanol intake was monitored throughout, and blood ethanol concentrations (BEC) were obtained from a separate group of rats.

RESULTS

Adolescent rats have reduced SI during the final withdrawal from either ED and exhibit a greater reduction in SI compared to adult rats when exposed to a 7%ED. Audiogenic seizures were not increased during withdrawal from either ED in adult rats, but adolescent rats that received 7%ED displayed increased seizures. The bicuculline seizure thresholds were decreased in both ages exposed to a 7%ED, but only adolescent rats showed this decreased threshold after 4.5%ED. Ethanol intakes and BECs were higher in adolescent rats compared to similarly treated adults. However, ethanol intakes and BECs were comparable between 4.5%ED-treated adolescent and 7%ED-treated adult rats.

CONCLUSIONS

Behavioral results from the 7%ED-treated groups suggested that adolescent rats may be more vulnerable to repeated withdrawals from ethanol than adults; however, differences in ethanol intake and BECs may be at least in part responsible. When ethanol intakes and BECs were similar between 4.5%ED-treated adolescent and 7%ED-treated adult rats, behavioral effects were not different. Importantly, these data illustrated that adolescent rats can exhibit anxiety and reduced seizure thresholds following this repeated withdrawal paradigm.

Prefrontal cortex volumes in adolescents with alcohol use disorders: unique gender effects

BACKGROUND

Adolescents with alcohol use disorders (AUD) have shown smaller prefrontal cortex (PFC) volumes compared with healthy controls; however, differences may have been due to comorbid disorders. This study examined PFC volumes in male and female adolescents with AUD who did not meet criteria for comorbid mood or attention disorders.

METHODS

Participants were adolescents aged 15 to 17 who met criteria for AUD (n = 14), and demographically similar healthy controls (n = 17). Exclusions included any history of a psychiatric or neurologic disorder other than AUD or conduct disorder. Magnetic resonance imaging scans occurred after at least 5 days of abstinence from alcohol or drugs. Overall PFC volumes and white matter PFC volumes were compared between groups.

RESULTS

After controlling for conduct disorder, gender, and intracranial volume, AUD teens demonstrated marginally smaller anterior ventral PFC volumes (p = 0.09) than controls, and significant interactions between group and gender were observed (p < 0.001 to p < 0.03). Compared with same-gender controls, females with AUD demonstrated smaller PFC volumes, while males with AUD had larger PFC volumes. The same pattern was observed for PFC white matter volumes.

CONCLUSIONS

Consistent with adult literature, alcohol use during adolescence is associated with prefrontal volume abnormalities, including white matter differences. However, adolescents with AUD demonstrated gender-specific morphometric patterns. Thus, it is possible that gender may moderate the impact of adolescent alcohol use on prefrontal neurodevelopment, and the neurodevelopmental trajectories of heavy drinking boys and girls should be evaluated separately in longitudinal studies.

A developmental perspective on alcohol and youths 16 to 20 years of age

Late adolescence (ie, 16-20 years of age) is a period characterized by escalation of drinking and alcohol use problems for many and by the onset of an alcohol use disorder for some. This heightened period of vulnerability is a joint consequence of the continuity of risk from earlier developmental stages and the unique neurologic, cognitive, and social changes that occur in late adolescence. We review the normative neurologic, cognitive, and social changes that typically occur in late adolescence, and we discuss the evidence for the impact of these transitions on individual drinking trajectories. We also describe evidence linking alcohol abuse in late adolescence with neurologic damage and social impairments, and we discuss whether these are the bases for the association of adolescent drinking with increased risks of mental health, substance abuse, and social problems in adulthood. Finally, we discuss both the challenges and successes in the treatment and prevention of adolescent drinking problems.

Differential expression of ethanol-induced hypothermia in adolescent and adult rats induced by pretest familiarization to the handling/injection procedure

BACKGROUND

Previous work examining ethanol's autonomic effects has found contrasting patterns of age-related differences in ethanol-induced hypothermia between adolescent and adult rats. Most studies have found adolescents to be less sensitive than adults to this effect, although other work has indicated that adolescents may be more sensitive than adults under certain testing conditions. To test the hypothesis that adolescents show more ethanol hypothermia than adults when the amount of disruption induced by the test procedures is low, but less hypothermia when the experimental perturbation is greater, the present study examined the consequences of manipulating the amount of perturbation at the time of testing on ethanol-induced hypothermia in adolescent and adult rats.

METHODS

The amount of test disruption was manipulated by administering ethanol through a chronically indwelling gastric cannula (low perturbation) versus via intragastric intubation (higher perturbation) in Experiment 1 or by either familiarizing animals to the handling and injection procedure for several days pretest or leaving them unmanipulated before testing in Experiment 2.

RESULTS

The results showed that the handling manipulation, but not the use of gastric cannulae, altered the expression of ethanol-induced hypothermia differentially across age. When using a familiarization protocol sufficient to reduce the corticosterone response to the handling and injection procedure associated with testing, adolescents showed greater hypothermia than adults. In contrast, the opposite pattern of age differences in hypothermia was evident in animals that were not manipulated before the test day. Surprisingly, however, this difference across testing circumstances was driven by a marked reduction in hypothermia among adults who had been handled before testing, with handling having relatively little impact on ethanol hypothermia among adolescents.

CONCLUSIONS

Observed differences between adolescents and adults in the autonomic consequences of ethanol were dramatically influenced by whether animals were familiarized with the handling/injection process before testing. Under these circumstances, adolescents were less susceptible than adults to the impact of experimental perturbation on ethanol-induced hypothermia. These findings suggest that seemingly innocuous aspects of experimental design can influence conclusions reached on ontogenetic differences in sensitivity to ethanol, at least when indexed by ethanol-induced hypothermia.

The International society for developmental psychobiology 39th annual meeting symposium: Alcohol and development: beyond fetal alcohol syndrome

As has been repeatedly demonstrated, alcohol can exert deleterious morphological and physiological effects during early stages in development. The present review examines nonteratological links existing between alcohol and ontogeny. Human and animal studies are taken into consideration for the analysis of fetal, neonatal, infantile, adolescent, and adult responsiveness to the drug. Sensitivity to alcohol's chemosensory and postabsorptive properties, as well as learning and memory processes mediated by such properties, are examined from this developmental perspective. The studies under discussion indicate that, within each stage in development, we can trace alcohol-related experiences capable of determining or modulating alcohol seeking and intake patterns.

Age-dependent variation in behavior following acute ethanol administration in male and female adolescent rhesus macaques (Macaca mulatta)

BACKGROUND

There has been considerable focus on the adolescent stage of development in the study of alcohol use and the etiology of alcohol-related problems. Because adolescence is a process of dynamic change rather than a discrete or static stage of development, it is important to consider ontogenetic changes in the response to ethanol within the adolescent time period. In rodents, levels of ethanol-induced motor impairment have been shown to increase from early to late adolescence. This study investigated associations between behavior following acute ethanol administration and age, rearing condition (mother-reared vs nursery-reared), and serotonin transporter (rh5-HTTLPR) genotype in a sample of alcohol-naïve adolescent rhesus macaques.

METHODS

Rhesus macaques (n=97; 41 males, 56 females), ranging in age from 28 to 48 months, were administered intravenous (IV) doses of ethanol (2.2 g/kg for males, 2.0 g/kg for females) twice in 2 separate testing sessions. A saline/ethanol group (n=16; 8 males, 6 females) was administered saline in 1 testing session and ethanol in the second session. Following each IV injection, subjects underwent a 30-minute general motor behavioral assessment. Behavior in the saline/ethanol group was compared between the saline and ethanol-testing sessions using analysis of variance. Behavioral data for the larger study sample were averaged between the 2 testing sessions and summarized using factor analysis. Rotated factor scores were used as dependent variables in multiple regression analyses to test for relationships between behavior and age, rearing condition, and rh5-HTTLPR genotype.

RESULTS

During the ethanol-testing session, behaviors indicative of motor impairment (stumbles, falls, sways, bumping the wall, and unsuccessful jumps) were frequently observed in the saline/ethanol group, while they did not occur under the saline-testing session. Factor analysis of behavior following ethanol administration in the larger study sample yielded 3 factors: Ataxia, Impaired Jumping Ability, and Stimulation. Significant negative correlations between age and Ataxia were found for both males and females. Females also exhibited positive correlations between age and Impaired Jumping Ability and age and Stimulation. No significant correlations were found with either rearing condition or rh5-HTTLPR genotype.

CONCLUSIONS

These findings suggest that ontogenetic changes during adolescence in the behavioral response to ethanol differ between rodents and primates. Furthermore, sex differences in the behavioral response to ethanol appear to develop during adolescence.

Effects of alcohol and combined marijuana and alcohol use during adolescence on hippocampal volume and asymmetry

BACKGROUND

Converging lines of evidence suggest that the hippocampus may be particularly vulnerable to deleterious effects of alcohol and marijuana use, especially during adolescence. The goal of this study was to examine hippocampal volume and asymmetry in adolescent users of alcohol and marijuana.

METHODS

Participants were adolescent (aged 15-18) alcohol (ALC) users (n=16), marijuana and alcohol (MJ+ALC) users (n=26), and demographically similar controls (n=21). Extensive exclusionary criteria included prenatal toxic exposure, left handedness, and psychiatric and neurologic disorders. Substance use, cognitive, and anatomical measures were collected after at least 2 days of abstinence from all substances.

RESULTS

Adolescent ALC users demonstrated a significantly different pattern of hippocampal asymmetry (p<.05) and reduced left hippocampal volume (p<.05) compared to MJ+ALC users and non-using controls. Increased alcohol abuse/dependence severity was associated with increased right>left (R>L) asymmetry and smaller left hippocampal volumes while marijuana abuse/dependence was associated with increased L>R asymmetry and larger left hippocampal volumes. Although MJ+ALC users did not differ from controls in asymmetry, functional relationships with verbal learning were found only among controls, among whom greater right than left hippocampal volume was associated with superior performance (p<.05).

CONCLUSIONS

Aberrations in hippocampal asymmetry and left hippocampal volumes were found for adolescent heavy drinkers. Further, the functional relationship between hippocampal asymmetry and verbal learning was abnormal among adolescent substance users compared to healthy controls. These findings suggest differential effects of alcohol and combined marijuana and alcohol use on hippocampal morphometry and the relationship between hippocampal asymmetry and verbal learning performance among adolescents.

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.

Periadolescent exposure to ethanol and diazepam alters the aversive properties of ethanol in adult mice

Evidence suggests that the developing adolescent brain may be especially vulnerable to long-term neurobehavioral consequences following ethanol exposure and withdrawal. In the present study, we examined the long-term effect of adolescent ethanol withdrawal on a subsequent EtOH-induced conditioned taste aversion (CTA). Periadolescent and adult C3H mice were exposed to 64 h of continuous (single withdrawal) or intermittent (multiple withdrawal) ethanol vapor. Following each ethanol exposure, animals received either 0, 1, 2, or 3 mg/kg diazepam (DZP) in an attempt to counteract the possible effect of ethanol withdrawal. About 6 weeks following ethanol and DZP treatment, animals were tested for an EtOH-induced CTA. As expected, exposure to EtOH during adolescence attenuated the EtOH-induced CTA as compared to controls. Unexpectedly, administration of DZP during withdrawal did not spare but rather mimicked the attenuation of the EtOH-induced CTA seen in animals exposed to ethanol in adolescence. This attenuation was not evident when EtOH and/or DZP was administered in adulthood. Given the similar mode of action of EtOH and DZP on the GABA system, the principal implication of the present findings is that the intoxicating effect of ethanol on the developing brain can result in long-term changes in the aversive properties of EtOH.

Chronic intermittent ethanol exposure during adolescence reduces the effect of ethanol challenge on hippocampal allopregnanolone levels and Morris water maze task performance

Chronic intermittent ethanol exposure (CIEE) in adolescent rats has been shown to produce long-lasting hypnotic, metabolic, and functional tolerance. Recently, it has been hypothesized that allopregnanolone mediates some effects of ethanol, including ethanol-induced impairments in the performance of the Morris Water Maze Task (MWMT). The current studies explore the relationship between cortical and hippocampal allopregnanolone levels and ethanol-induced impairments in the MWMT following CIEE treatment in adolescent rats. Adolescent rats were administered 5.0 g/kg ethanol or saline every 48 h for a 20-day period beginning on postnatal day (P) 30. Training in the spatial version of the MWMT occurred on nontreatment days. Following completion of CIEE treatment and training, MWMT performance was tested 30 min after ethanol (2.0 g/kg) or saline challenge on P 50 and P 62. A separate group of rats were CIEE treated and received an ethanol (2.0 g/kg) or saline challenge on P 50 or 62, and were used for hippocampal and cortical allopregnanolone determination. CIEE during adolescence produced tolerance to both ethanol-induced impairments in the MWMT and ethanol-induced allopregnanolone levels in the hippocampus on P 50. However, when animals were tested at P 62, the reduction in ethanol-induced MWMT impairments found in CIEE rats was reversed and allopregnanolone levels from both saline or ethanol challenge were increased above levels found in control animals. Taken together, these results suggest that CIEE during adolescence produces tolerance to ethanol-induced impairments in MWMT and corresponding changes in ethanol-induced allopregnanolone levels in the hippocampus. Furthermore, cognitive tolerance is reversible and time dependent, but the reversal of cognitive tolerance is not correlated with normalization of hippocampal allopregnanolone levels.

Sedative and GABAergic effects of ethanol on male and female rats

BACKGROUND

Women consume less alcohol than men, and yet they are more susceptible than men to the negative medical consequences of alcohol use, such as cirrhosis of the liver, cardiac disease, and cognitive impairments. This sex difference is also reflected in animal studies, in which male and female rats differ on both behavioral and electrophysiological measures. Given that one significant difference between males and females is the cycling fluctuations of the sex hormones, this study aimed to compare the relative sensitivity of adolescent and adult rats of both sexes and varying estrous stages to the behavioral and electrophysiological effects of ethanol.

METHODS

Adult female rats were lavaged daily for estrous cycle assessment. Following administration of 5 g/kg ethanol, adolescent and adult male and female animals were observed for loss of the righting reflex. Then, using whole-cell recording, we tested the response of spontaneous, gamma-aminobutyric acid (GABA(A)) receptor-mediated inhibitory postsynaptic currents (sIPSCs) in hippocampal slices from drug-naïve adult male and female rats.

RESULTS

Consistent with previous findings, adolescent animals were less sensitive than adults to the effect of ethanol on the righting reflex. In addition, adult proestrous and diestrous female rats were less sensitive than male rats to the sedative effects of ethanol. Finally, ethanol increased the frequency of sIPSCs in hippocampal pyramidal neurons and did so more potently in cells from male rats than in those from female rats.

CONCLUSIONS

Female animals are less sensitive to the behavioral sedative effects of ethanol than adult male rats, and the effect is pronounced in the proestrous and diestrous states. This sex difference may be related to differential sensitivity of GABA receptor-mediated central nervous system function to ethanol in females.

Chronic intermittent ethanol exposure during adolescence blocks ethanol-induced inhibition of spontaneously active hippocampal pyramidal neurons

BACKGROUND

Binge alcohol drinking among adolescents has been a serious public health problem. A model of binge alcohol, chronic intermittent ethanol exposure (CIEE), during adolescence significantly attenuates ethanol-induced spatial memory deficits in rats. However, the attenuation was absent following a 12-day ethanol-free period. Since spatial memory is hippocampal dependent, a reduction in ethanol-induced spatial memory impairments may be due to a reduction in the ability of ethanol to inhibit the firing rate of single hippocampal pyramidal neurons following CIEE.

METHODS

Beginning on postnatal day 30 (P30), male adolescent Sprague-Dawley rats (Harlan) were administered 5.0 g/kg ethanol (n = 10, CIEE-treated group) or an equivolume saline (n = 10, CISE-treated group) every 48 hours for 20 days. Single hippocampal pyramidal neurons from 5 CIEE-treated rats and 5 CISE-treated rats were recorded on the day following completion of the chronic intermittent exposure procedure (animals now P50). Additionally, neurons from 5 CIEE-treated rats and 5 CISE-treated rats were recorded 12 days after the completion of the chronic intermittent exposure procedure (animals now P62).

RESULTS

Ethanol exposure during adolescence completely blocked ethanol-induced inhibition of hippocampal pyramidal neurons in rats that were CIEE exposed. However, the effect of CIEE on hippocampal neurophysiology was time dependent. Specifically, neurons recorded from CIEE-treated rats after a 12-day ethanol-free period had similar maximal inhibition as neurons from CISE-treated animals, although the time to reach inhibition was significantly greater in neurons from CIEE-treated rats.

CONCLUSION

Chronic ethanol exposure during adolescence produces a reduction, or tolerance, to ethanol-induced inhibition of hippocampal pyramidal neural activity. Although the tolerance was greatly reversed after a 12-day ethanol-free period, neurons from CIEE animals inhibited slower than neurons from CISE animals. Since the hippocampus is known to be involved not only in spatial memory, but also in many other types of memory formation, the altered hippocampal functions because of CIEE during adolescence should be taken as a serious warning for society.

Comparison of anxiety-like behavior in adolescent and adult Sprague-Dawley rats

The conditions under which age differences in anxiety are observed in rodents are unclear. These studies explored the influence of test condition on anxiety-like behavior in adolescent and adult rats using the light-dark box. Behavior was assessed under different illumination levels (30 or 60 lux) and after brief stress (restraint or bright light). Anxiety-like behavior did not differ in the 30-lux test but was increased in adolescents in the 60-lux test. Restraint increased anxiety-like behavior in adolescents, resulting in elevated anxiety-like behavior relative to adults. Bright light decreased anxiety-like behavior, possibly because of negative contrast or novelty-induced anxiolysis. These studies demonstrate that adolescents display increased anxiety-like behavior when test conditions are more aversive and following exposure to stress.

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.

Age-related effects of alcohol on memory and memory-related brain function in adolescents and adults

As detailed in this brief review, there is now clear evidence that adolescence represents a unique stage of brain development. Changes in brain organization and function during adolescence are widespread, and include intense rewiring in the frontal lobes and other neorcortical regions, as well as changes in a litany of subcortical structures. Recent research suggests that, because of these changes in brain function, drugs like alcohol affect adolescents and adults differently. The available evidence, much of it from research with animal models, suggests that adolescents might be more sensitive than adults to the memory impairing effects of alcohol, as well as the impact of alcohol on the brain function that underlies memory formation. For instance, when treated with alcohol, adolescent rats perform worse than adults in spatial learning tasks that are known to require the functioning of the hippocampus. Alcohol disrupts hippocampal function, and does so more potently in adolescents than adults. In contrast, adolescents appear to be far less sensitive than adults to both the sedative and motor impairing effects of alcohol. While research on this topic is still in its infancy, the findings clearly suggest that adolescence represents a unique stage of sensitivity to the impact of alcohol on behavior and brain function.

Blood Oxygen Level Dependent Response and Spatial Working Memory in Adolescents With Alcohol Use Disorders

BACKGROUND

Previous studies have suggested neural disruption and reorganization in young and older adults with alcohol use disorders (AUD). However, it remains unclear at what age and when in the progression of AUD changes in brain functioning might occur.

METHODS

Alcohol use disordered (n = 15) and nonabusing (n = 19) boys and girls aged 15 to 17 were recruited from local high schools. Functional magnetic resonance imaging data were collected after a minimum of 5 days' abstinence as participants performed spatial working memory and simple motor tasks.

RESULTS

Adolescents with AUD showed greater brain response to the spatial working memory task in bilateral parietal cortices and diminished response in other regions, including the left precentral gyrus and bilateral cerebellar areas (clusters > or =943 microl; p < 0.05), although groups did not differ on behavioral measures of task performance. No brain response differences were observed during a simple finger-tapping task. The degree of abnormality was greater for teens who reported experiencing more withdrawal or hangover symptoms and who consumed more alcohol.

CONCLUSIONS

Adolescents with AUD show abnormalities in brain response to a spatial working memory task, despite adequate performance, suggesting that subtle neuronal reorganization may occur early in the course of AUD.

Adolescent exposure to cannabinoids induces long-lasting changes in the response to drugs of abuse of rat midbrain dopamine neurons

BACKGROUND

Recent studies have raised concerns about subtle long-lasting neurobiological changes that might be triggered by exposure to Cannabis derivatives, especially in a critical phase of brain maturation, such as puberty. The mesolimbic dopamine (DA) system, involved in the processing of drug-induced reward, is a locus of action of cannabinoids and endocannabinoids. Thus, we compared the effects of repeated cannabinoid administration in adolescent and adult rats on DA neuronal functions and responses to drugs of abuse.

METHODS

Single-unit extracellular recordings from antidromically identified mesoaccumbens DA neurons and from their target cells in the nucleus accumbens were carried out in urethane-anesthetized rats. Animals were pretreated during adolescence or adulthood, for 3 days, with the cannabinoid agonist WIN55212.2 (WIN) or vehicle and allowed a 2-week interval.

RESULTS

In cannabinoid-administered rats, DA neurons were significantly less responsive to the stimulating action of WIN, regardless of the age of pretreatment; however, in the adolescent group, but not in the adult, long-lasting cross-tolerance developed to morphine, cocaine, and amphetamine.

CONCLUSIONS

Our study suggests that an enduring form of neuronal adaptation occurs in DA neurons after subchronic cannabinoid intake at a young age, affecting subsequent responses to drugs of abuse.

Chronic intermittent injections of high-dose ethanol during adolescence produce metabolic, hypnotic, and cognitive tolerance in rats

BACKGROUND

Many humans are first exposed to ethanol during adolescence, the time at which they are most likely to binge drink ethanol. Chronic intermittent ethanol (CIE) exposure produces ethanol tolerance in adolescent rodents. Recent studies suggested that adolescent animals administered CIE experienced increased cognitive impairment following an ethanol challenge. These studies further explore development of ethanol tolerance caused by CIE in adolescence, and whether CIE during adolescence leads to altered ethanol response in adulthood.

METHODS

Beginning postnatal day (P) 30, adolescent rats were administered 5.0 g/kg ethanol or saline every 48 hours for 20 days. In experiment I, animals were tested for differential weight gain. In experiment II, loss of righting reflex (LORR) was observed after each injection, then at completion of pretreatment all animals were tested with 5.0 g/kg ethanol and LORR was observed. In experiment III, blood ethanol levels were observed and elimination rates calculated after the first and fifth pretreatments. All animals were tested with 5.0 g/kg at completion of pretreatment and elimination rates were recalculated. In experiment IV, animals were trained on the spatial version of the Morris Water Maze Task (MWMT) on non-treatment days. Following completion of pretreatment and training, animals were tested after receiving an ethanol (1.0, 1.5, or 2.0 g/kg), or saline. Tests for experiments II, III, and IV were repeated in the same animals following 12 ethanol-free days.

RESULTS

Chronic intermittent ethanol exposure during adolescence caused differential weight gain (experiment I). Adolescent rats developed tolerance to ethanol-induced LORR (experiment II) and metabolic tolerance to ethanol (experiment III). This tolerance was seen after 12 ethanol-free days. CIE also attenuated ethanol-induced spatial memory deficits in the MWMT (experiment IV). This effect was not long-lasting.

CONCLUSIONS

Following CIE pretreatment during adolescence, tolerance developed to the hypnotic and cognitive impairing effects of ethanol, along with increased metabolic rate and decreased weight gain. These results further emphasize the ability of CIE to produce a variety of effects during adolescence, some having long-lasting consequences.

Hippocampal Function during Adolescence: A Unique Target of Ethanol Effects

Behaviors mediated by the hippocampus have long been known to be sensitive to the acute, chronic, and prenatal effects of ethanol. It has recently become clear that hippocampal function is uniquely responsive to ethanol during periadolescent development, and that alcohol affects behavior and brain function differently in adolescents and adults. We have used behavioral techniques, as well as extracellular and whole-cell electrophysiological techniques, to assess the effects of acute and chronic ethanol exposure on hippocampal function during adolescence and adulthood. Our results are consistent with the view that the hippocampus is more sensitive to the acute effects of ethanol during adolescence and may be more susceptible to the neurotoxic effects of ethanol during this developmental period. Studies of this type have yielded valuable information for prevention, education, and public policy efforts related to underage drinking.