Effects of escalating versus fixed ethanol exposure on ∆FosB expression in the mesocorticolimbic pathway in adolescent and adult rats

Abstract

Background: We have reported induction of ∆FosB in adolescent rats that drank less ethanol than adults yet exhibited a progressive increase in ethanol intake.Objective: To test the hypothesis that an escalating pattern of ethanol exposure is more effective to induce ∆FosB expression [at prelimbic cortex (PrL), nucleus accumbens core and shell, striatum, basolateral amygdala (BLA) and central amygdala (CeC)] than a pattern equated for number of exposures yet employing a fixed ethanol dose.Methods: Adolescent and adult (Exp. 1, n = 48) male and female (n = 24 of each sex) or only adult male (Exp. 2, n = 36) Wistar rats were intermittently intubated with vehicle, escalating (from 0.5 to 2.5 g/kg) or fixed (2.0 g/kg) doses of ethanol, across 18 sessions. ∆FosB induction was assessed using immunohistochemistry. Ethanol intake, anxiety and risk-taking were assessed (in adults only) via two-bottles tests and the multivariate concentric square field.Results: Both patterns heightened ∆FosB levels similarly in adolescents and adults and in males and females. Fixed dosing induced ∆FosB in all areas (p < .05) except the CeC, whereas the escalating pattern induced ∆FosB in the PrL and BLA only (p < .05). Ethanol intake was initially lower in ethanol pre-exposed subjects than in control subjects (p < .05). Rats exposed to the fixed pattern exhibited enhanced risk-taking behavior (p < .05).Conclusions: The results agree with studies showing ethanol-mediated induction of ∆FosB in reward areas and indicate that, following ethanol intubations, this induction is similar in adolescents and adults. The induction of ∆FosB seems not necessarily associated with susceptibility for ethanol intake.