Anxiogenic effects during withdrawal from acute ethanol in adolescent and adult rats

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.

Single, intense prenatal stress decreases emotionality and enhances learning performance in the adolescent rat offspring: interaction with a brief, daily maternal separation

Perinatal manipulations can lead to neurobehavioural changes in the progeny. In this study we investigated, in adolescent male rat offspring, the consequences of a single, intense prenatal stress induced by a 120 min-maternal immobilization at gestational day 16, and of a daily, brief maternal separation from postnatal day 2 until 21, on: unconditioned fear/anxiety-like behaviour in open field and in elevated plus-maze; learning performance in the "Can test", a non-aversive spatial and tactile/visual task; corticosterone plasma levels under basal and stress-induced conditions. Our results indicate that both prenatal stress and maternal separation procedures decrease emotionality and enhance learning performance. Maternal separation potentiates prenatal stress-induced effects in enhancing learning performance. Both basal and stress-induced corticosterone plasma levels are reduced following prenatal stress, maternal separation and the combination of two procedures. These findings suggest that a single, intense prenatal stress can enhance the adaptive stress-related responses in the progeny, probably due to the involvement of maternal factors. The synergistic effect of prenatal stress and maternal separation on learning performance may be due to a further damping of hypothalamic-pituitary-adrenal axis response in the progeny that better cope with the task administered.

Differences in the social consequences of ethanol emerge during the course of adolescence in rats: Social facilitation, social inhibition, and anxiolysis

The present experiments explored social consequences of ethanol during adolescence by examining dose-dependent ethanol-induced social facilitation and inhibition in a non-anxiogenic (familiar) environment, and ethanol-related anxiolysis in an anxiogenic (unfamiliar) environment in early (P28) and late (P42) adolescent rats. Pronounced age-related differences in the social consequences of ethanol emerged during the course of adolescence, with early adolescents being uniquely sensitive to activating effects of low doses of ethanol when tested in the familiar context in terms of play fighting-an adolescent-characteristic form of social interactions, but conversely less sensitive than late adolescents to ethanol-associated social suppression when tested at higher ethanol doses in this context. Early adolescents were also less sensitive than late adolescents to the anxiolytic effects of ethanol revealed in the unfamiliar test situation, when indexed in terms of increases in social investigation and the ethanol-induced transformation of social avoidance into social preference. Anti-anxiety properties of ethanol were found to be sex-dependent in older animals, with late adolescent females being more sensitive to ethanol anxiolysis than their male counterparts. Considerable ontogenetic differences in the social consequences of ethanol are evident even within the adolescent period, with early adolescence being a time of particularly pronounced adolescent-typical sensitivities to ethanol.

Effect of stress on the voluntary intake of a sweetened ethanol solution in pair-housed adolescent and adult rats

BACKGROUND

Data regarding the effects of stressors on ethanol intake are mixed. Previous experiments reporting greater voluntary intake of ethanol in adolescent than adult rats have examined intake in isolate-housed animals. Given that the stress of isolate housing may differ ontogenetically as well as confound interpretation of other stressor effects, the present study examined stressor/ethanol interactions among pair-housed adolescent and adult rats.

METHODS

Sprague-Dawley male rats were implanted with identification tags that allowed individual monitoring of home cage intake of water and either a 10% (v/v) ethanol solution containing 0.1% (w/v) saccharin or saccharin alone over a 14-day access period. Animals were given zero, one, or eight daily 15-min footshock sessions, with shock-induced freezing and pre-, post-, and recovery corticosterone levels determined on the first and last footshock exposure days. After the access period, withdrawal was assessed with a plus maze, and tolerance to ethanol-induced loss of righting reflex was examined.

RESULTS

Nonstressed adolescents drank considerably more sweetened ethanol than did adults, with chronic stress suppressing this adolescent consumption. Ethanol access in adolescents disrupted within-session adaptation to footshock in terms of freezing behavior, although no such disruption was evident at either age when indexed hormonally. Despite relatively high ethanol intakes (up to 6 g/kg/day in the adolescents), no evidence for withdrawal-associated anxiogenesis emerged. Evidence for tolerance was mixed and, to the extent that it was present, was metabolic in nature.

CONCLUSIONS

Previous reports of heightened voluntary ethanol intake among adolescent rats are not a function of isolate stress but are evident in pair-housed animals. Adolescents were more sensitive to ethanol/stress interactions than were adults, with the elevated ethanol intake of pair-housed adolescents selectively disrupted by chronic stress, a stress-induced disruption not evident in adults. Likewise, ethanol disrupted behavioral adaptation to the footshock stressor among adolescents but not adults.

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.

Sensitivity and tolerance to autonomic effects of ethanol in adolescent and adult rats during repeated vapor inhalation sessions

BACKGROUND

It is during adolescence that most drinkers initiate ethanol intake, with some of this use being excessive. One possible contributor to the increased ethanol consumption often seen during adolescence in humans and in various animal models is age differences in ethanol sensitivity and tolerance. The present study examined the impact of age on ethanol-related alterations in the autonomic nervous system.

METHODS

Sensitivity to the initial ethanol challenge and chronic tolerance as well as acute and protracted withdrawal-like phenomena were assessed in male adolescent and adult Sprague-Dawley rats, using implanted telemetry probes with ethanol delivered via vapor inhalation.

RESULTS

Both ages showed similar ethanol-induced tachycardia and activity suppression; however, adolescents were found to be more sensitive than adults to the hypothermic effect of ethanol, data opposite other results from our laboratory and elsewhere using intragastric intubations or intraperitoneal administrations of ethanol. Although little tolerance to ethanol's tachycardic or activity suppressant effects was seen after repeated ethanol inhalation sessions, chronic tolerance to ethanol's hypothermic effect developed faster in adults than in adolescents. A withdrawal-like syndrome, characterized by bradycardia and hypoactivity, typically emerged during the dark phase of the diurnal cycle after ethanol vapor exposure sessions. These effects were observed in animals of both ages, with the bradycardic effect more pronounced in adolescents.

CONCLUSIONS

In contrast to results indicating that adolescents may be less sensitive than adults to ethanol's hypothermic effect when ethanol is administered via bolus injection/intubation, adolescents appear more sensitive and develop tolerance to ethanol's hypothermic effects more slowly than adults when ethanol is administered at a more moderate rate via vapor inhalation.

Enhanced prepulse inhibition following adolescent ethanol exposure in Sprague-Dawley rats

OBJECTIVES

Recent studies have demonstrated that ethanol exposure differentially affects adolescents and adults. The current studies were designed to compare the effects of 2-week exposure to ethanol during adolescence or adulthood on the acoustic startle response (ASR) and prepulse inhibition (PPI) METHODS: Male Sprague-Dawley rats were exposed to ethanol vapor 12 hr/d (on from 6 pm to 6 am) for 14 days during adolescence or adulthood. Six days after the cessation of ethanol vapor exposure, the ASR and PPI were assessed.

RESULTS

During ethanol treatment, overall blood alcohol levels averaged 230 to 250 mg/dl in the adolescent and adult treatment groups. Assessment of the ASR revealed that latency to startle was more rapid in adolescents than in adults, but ASR latency was not altered by ethanol exposure. In addition, ASR magnitude was lower in adolescents and was decreased in ethanol-exposed rats on startle trials. Ethanol exposure significantly enhanced PPI, but only after adolescent exposure

CONCLUSIONS

These data further demonstrate a differential sensitivity of adolescents and adults to the effects of ethanol exposure. Specifically, a 2-week period of ethanol exposure during adolescence selectively enhanced PPI, a neurobehavioral index of sensorimotor gating. However, ASR magnitude was decreased by ethanol exposure regardless of age. On the basis of previous studies, the effects of ethanol exposure on PPI data could indicate that adolescent rats exposed to ethanol are more likely to exhibit behavioral inflexibility and that ethanol exposure acts as a more potent physical stressor in adolescent rats.

Factors Influencing Elevated Ethanol Consumption in Adolescent Relative to Adult Rats

BACKGROUND

Many teenagers report frequent alcohol use during the adolescent period. Animal models may be an important tool for exploring factors that contribute to alcohol consumption during this critical period.

METHODS

Using a 24-hour, free-access, two-bottle-choice procedure between water and a sweetened solution with or without ethanol in nondeprived rats, the present series of experiments examined the contribution of a variety of contextual and experimental variables (i.e., isolate-housing versus pair-housing, type of sipper tube, caloric value of solution, prior experimental perturbations) on alcohol consumption in both adolescent and adult Sprague-Dawley rats.

RESULTS

Ethanol consumption was particularly magnified among adolescent rats using ball bearing-containing ball-point (BP) sipper tubes, with this exacerbated intake not due to caloric content of the ethanol solution. Isolation housing for 12 days did not alter ethanol consumption of adolescents relative to their socially housed counterparts while suppressing consumption of isolated adults. An examination of differences in the relative magnitude of adolescent ethanol consumption across experiments in this series revealed that ethanol intake among adolescents was elevated not only by the inclusion of BP sipper tubes but also by staggering the timing of isolate housing relative to the presentation of the novel ethanol solution.

CONCLUSIONS

The results of this experimental series demonstrate that adolescent animals consume significantly more ethanol than adult animals under a variety of home cage continuous-access circumstances, with the relatively greater intake of adolescents further magnified by a number of test conditions. Subtle experimental details often thought to be innocuous can have a substantial impact on overall amount of voluntary ethanol consumption observed in both adolescent and adult animals.

Anxiety-like behaviors following chronic ethanol exposure

Rodent models of ethanol withdrawal-induced anxiety have been used to explore the neurobiology underlying withdrawal and to evaluate the utility of therapeutic agents aimed at reducing withdrawal severity. Of the many tests of anxiety-like behavior, the elevated plus maze, light/dark box, and open field are the most commonly used. In general, ethanol withdrawal decreases most or all of the individual behaviors recorded in these tasks, indicating the occurrence of an anxiogenic-like effect of withdrawal in rodents, although these effects of withdrawal have not always been found. Potential problems with interpreting the effects of withdrawal as being indicative of an anxiety-like state include the effects of withdrawal on motivation to explore an apparatus, non-specific effects of withdrawal on locomotion, and the use of test parameters that have not been pharmacologically validated. For example, most of the published studies interpreted as having shown increased anxiety-like behavior during ethanol withdrawal have also observed concurrent decreases in locomotion. At a minimum, a given test of anxiety-like behavior during withdrawal should be responsive to the dose and duration of ethanol exposure that was used to produce physical dependence, and should not non-specifically decrease locomotion. In addition, standard anxiolytic drugs should ameliorate the anxiogenic-like effects of withdrawal, preferably in multiple tests of anxiety-like behavior.

Age-related differences in elevated plus maze behavior between adolescent and adult rats

Adolescence is a time of considerable transformations, often associated with increases in risk taking and novelty-seeking behaviors. Little is known of a possible age-dependent expression of anxiety-related behaviors in novel or potentially dangerous situations. The present study explored age differences in anxiogenic and anxiolytic stimuli between adolescent and adult Sprague-Dawley rats using the elevated plus maze (EPM). Data were compared across several experiments using factor analysis of multiple EPM measures. Under some circumstances, adolescents revealed a relatively low behavioral anxiety profile compared to adults, whereas in other situations results revealed the opposite pattern. Characteristics of the pretest circumstances altered considerably the nature of the conclusions reached regarding age-related changes in anxiogenic and anxiolytic stimuli. In general, anxiety measures in adolescents were less affected by variations in pretest conditions compared to the same variables in adults, suggesting possible adolescent immaturity of brain mechanisms involved in the regulation of anxiety.

Adolescence and the trajectory of alcohol use: introduction to part VI

Research in the area of adolescent alcohol use is progressing rapidly, as exemplified by the chapters in this section. Basic animal research in rodents has revealed adolescents to be more sensitive than adults to ethanol-induced disruptions in brain plasticity, although adolescents conversely are relatively insensitive to ethanol cues that serve to moderate intake. Risks for excessive alcohol consumption due to genetic background have been shown in primate research to be exacerbated by adverse early life experiences. Studies in clinical populations have revealed neurocognitive deficits evident years following adolescent alcohol abuse, along with evidence that some neural changes may predate adolescent alcohol abuse, whereas others appear to be a consequence of this abuse. Further research is needed to detail determinants and consequences of adolescent alcohol abuse and to identify potential protective factors to diminish the propensity for excessive use of alcohol during this critical developmental period.

Acute ethanol withdrawal (hangover) and social behavior in adolescent and adult male and female Sprague-Dawley rats

BACKGROUND

The extensive use of alcohol during adolescence may be facilitated by an age-specific attenuation in sensitivity to adverse effects of ethanol. Adolescent rats are less sensitive than adults to some delayed effects of acute ethanol, including hangover-related anxiety on an elevated plus maze. The purpose of this study was to determine whether adolescent rats are also less sensitive than adults to hangover-related anxiogenesis when indexed in terms of social inhibition.

METHODS

Anxiety during ethanol hangover was indexed in adolescent and adult Sprague-Dawley rats of both genders by assessing the suppression in social behavior during a social interaction test. Animals were tested 18 hr after intraperitoneal administration of 0 g/kg (saline) or 4 g/kg ethanol (experiment 1) or at test intervals chosen on the basis of assessments of ethanol clearance time (experiment 2) to equate clearance-to-test intervals across age and gender (experiments 3-5).

RESULTS

Adults showed more hangover-related social suppression and slower postclearance recovery than adolescents. Sex differences were more pronounced in adults than adolescents, with males being more affected than females. Ethanol clearance time was considerably longer in adult males than in adolescent animals and adult females. In contrast to the modest decreases in social activity observed in adolescent animals shortly after ethanol clearance, adolescents showed a surprising increase in play fighting later in the recovery period- a hangover-related social facilitation that was not evident in adults.

CONCLUSIONS

The attenuated anxiety and increase in social interactions seen in adolescents during hangover are less likely to serve as deterrents for further drinking than the aversive increase in anxiety seen in adults. A facilitation of social interactions not only during a drinking episode, but also during the postalcohol recovery period, could help to establish a persisting cycle of drinking in at-risk adolescents, leading to dependency and a lifelong history of alcohol-related problems.