Postweaning isolation affects responses to incentive contrast in adulthood

Adolescence is a time involving a series of changes in the use of appetitive reinforcers like food, as well as neuroendocrine changes like those taking place in the mesolimbic dopamine function. Social isolation from postnatal day 21 to 36 in rats leads to behavioral and neurophysiological alterations such as increased consumption of appetitive reinforcers. The work is focused on studying how exposure to chronic stress induced by social isolation during adolescence can have a long-lasting effect on responses to reinforcement shifts in adulthood. Two experiments were performed in rats in order to analyze the effect of adolescent isolation on the responses to unanticipated shifts in reinforcement during adulthood, in reinforcement devaluation (32-4% of sucrose solution), increase (4-32% of sucrose solution), and extinction (32-0% of sucrose solution) procedures. Adolescent isolation intensified the intake response resulting from a reinforcement increase (i.e., greater positive contrast), but had no effect on the response to reinforcement devaluation and omission. The implications of this procedure are discussed, along with the underlying behavioral and neurochemical mechanisms.