Enhanced cocaine self-administration in adult rats with adolescent isolation experience

It is widely accepted that early environmental influences may affect the behavior of adult animals and their responses to psychotropic drugs. Rearing animals in isolation is a relevant paradigm for studying early life stress and for understanding the development of certain neurological and psychiatric diseases. The present study evaluated the effect of adolescent isolation on intravenous cocaine self-administration in adult rats. Male Sprague-Dawley rats were raised from postnatal day 22 to 55 either alone (isolated) or in groups of four per cage (grouped). Then, rats were trained for cocaine self-administration. Our results showed that both isolated and grouped rats acquired stable cocaine self-administration during 5 days of self-administration training. Numbers of both lever presses and cocaine infusions in isolated rats were significantly more than those in grouped rats. Especially, numbers of incorrect lever presses in isolated rats were significantly more than those in grouped rats. In addition, the intervals of inter-reinforcement for cocaine in isolated rats were significantly shorter as compared with grouped rats. These results indicate that rats with adolescent isolation experience have enhanced cocaine self-administration behavior.