Developmental differences in acute ethanol withdrawal in adolescent and adult rats

Abstract

Background: Withdrawal from an acute high ethanol dose induces behaviors reminiscent of withdrawal from chronic ethanol exposure. While such "hangover"-related anxiety has previously been shown to be considerably less pronounced in adolescent compared to adult male rats, ontogenetic studies are limited and few experiments have directly compared sex- and age-related differences in sensitivity to ethanol hangover.

Methods: The current experiments examined consequences of a previous ethanol challenge (4.0 g/kg i.p. injection, 20% v/v) on anxiety and exploratory behavior in the elevated plus-maze (EPM) and holeboard (HB) tests, respectively, in adolescent and adult male and female Sprague-Dawley rats.

Results: In Exp. 1, evidence of hangover-related anxiety and withdrawal-induced hypoactivity emerged at both ages and in both sexes. As several procedural variables were changed in Exp.1 relative to previous studies from our laboratory showing age-related differences in these hangover measures, Exp. 2 explored the possible contribution of 2 variables to ontogenetic expression of withdrawal-induced anxiogenesis: (1) isolation vs. social context during the postchallenge recovery period and (2) EPM testing alone or immediately following a 5 minute HB test. Results of Exp. 2 revealed few significant interactions of these variables with age- and ethanol exposure-related anxiety measures, although sequential testing (HB before EPM) notably suppressed activity in the EPM and altered the major underlying component of EPM behavior from anxiety to activity as revealed in factor analyses of these data. Additional analyses conducted on animals tested only in the EPM revealed attenuations in withdrawal anxiogenesis among adolescents, along with withdrawal-related decreases in activity at both ages.

Conclusions: Taken together, these results suggest that adolescents do show an attenuated sensitivity to hangover-induced anxiogenesis in the EPM, an age difference not evident under other pretest conditions. Therefore, caution should be exerted when using the EPM to index anxiety across age. The robustness of withdrawal-related hypoactivity at both ages suggests that adolescents may not be globally insensitive to the consequences of previous binge-like exposure to ethanol, but rather less likely to express certain hangover-related consequences.

Figure 1

Holeboard behaviors of both adolescent and adult male and female rats from Exp. 1 following prior challenge with either ethanol (EtOH, white bars) or saline (SAL, black bars). Although there were no significant interactions for any of the variables, main effects of both ethanol exposure and age were observed for both (a) frequency of head dips and (b) total number of line crosses during the 5 min session, with a main effect of sex also observed for line crosses. Inserts are included for each behavior (collapsed across age and sex) in order to show the main effect of ethanol pre-exposure. There was a general reduction in head dips and line crosses in the ethanol compared to the saline group, as shown by the asterisks. In this, and in all subsequent figures, bars depict the mean value for each group, with vertical lines representing standard error of the mean.

Figure 2

Elevated plus-maze behaviors of both adolescent and adult male and female rats from Exp. 1 following prior challenge with either ethanol (EtOH) or saline (SAL). For both (a) percent open arm time (%OAT) and (b) percent protected stretched attend postures (%PSAP), only a main effect of ethanol exposure emerged in these analyses, with elevated anxiety observed in ethanol-exposed compared to saline-exposed animals. A main effect of ethanol exposure was also observed for (c) number of closed arm entries (CAE), along with a main effect of sex. Inserts for each behavior are included to emphasize the overall withdrawal effect (collapsed across age and sex), with asterisks noting the increase in anxiety behaviors and decrease in activity following prior ethanol exposure.

Figure 3

Elevated plus-maze behavior of adolescent and adult rats from Exp. 2 that were tested only in the plus-maze and that entered the open arms at least once. Data are collapsed over sex given that this variable did not interact with age-related differences in withdrawal anxiogenesis. Rats were administered either an ethanol (EtOH) or saline (SAL) challenge and were tested 3 hr post-clearance of the ethanol injection, with saline-exposed animals tested at an equivalent time point. (a) An age × exposure interaction for percent open arm time (%OAT) revealed that adults but not adolescents exhibited significant reductions in open arm time (as shown by the asterisk), (b) An age × exposure interaction for percent protected stretched attend postures (%PSAP) showed that ethanol-exposed adults were significantly more anxious than their ethanol-exposed adolescent counterparts (as indicated by the pound sign, #) (c) Significant reductions in closed arm entries (CAE) were again exhibited during hangover, regardless of age (as marked with the asterisks).