Novel-object place conditioning in adolescent and adult male and female rats: effects of social isolation

Abstract

Elevated levels of novelty seeking are often seen during adolescence. Recent studies using a conditioned place preference (CPP) paradigm have shown that novelty may be rewarding for adult rats. The present study explored the impact of age, sex, and isolation stress on novelty seeking and novelty reward by assessing novel object-induced CPP in adolescent and adult male and female Sprague-Dawley rats housed either socially or in isolation. Responding to the novel objects during conditioning was higher in adolescent animals than adults, and was suppressed by social isolation only in adulthood, particularly among males. Novel object CPP was strong among adolescent males, whereas only socially isolated adult males demonstrated preference for the compartment paired with the novel objects. This age difference was not evident in females, with both adolescent and adult group-housed females, but not their isolated counterparts, showing novel-object place conditioning. These dissociations between novelty-directed behaviors during conditioning and novelty reward in the CPP paradigm support the suggestion that mechanisms underlying novelty seeking are separable from those involved in the rewarding effects of novelty. High levels of novelty seeking demonstrated by adolescents do not necessarily predict high rewarding properties of novelty, with the latter also being influenced by environmental and gender-related factors.