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

Abstract

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.

Keywords: Adolescence; Anxiety; Depression; Disinhibition; Ethanol vapor.

Figure 1

(A-D): Behavioral measures in the open field conflict test. Group 1: post-natal day (PD) 38; group 2: PD59; group 3: PD73 (open bars) and were compared to ethanol vapor controls (lined bars) at PD105-106. Ethanol vapor control animals (AIR) (lined bars) were also compared to adolescent intermittent ethanol vapor (AIE) rats (black bars) of same age (data previously published and included for reference to current study). (A) All ontogenic groups and AIE treated rats took significantly less time to enter the lit middle center of the open field and spent more time there (B) compared to older controls. (C) Controls were on average further from the food pellet than AIE treated and all ontogenic groups. (D) Controls ate less food than all ontogenic groups and AIE treated animals. All means are unadjusted. * p<0.01 AIE effect and co-varied by body weight, + p<0.01 ontogenic age effect (ANOVA, Dunnett’s test).