Effect of isolation on dopaminergic agonist-induced penile erections and stretching and yawning in male rats.

Adult male rats reared in social isolation for 28 +/- 2 days were compared with animals housed in groups and pairs for frequency of penile erection (PE) and stretching and yawning (SY) elicited by dopaminergic (DA) autoreceptorial doses of B-HT 920 and n-N-propylnorapomorphine (NPA). PE and SY were consistently lower in the isolated group with respect to the other two groups, which did not differ significantly. The present experiments show the importance of housing conditions in modulating behavioural responses to DA agonists, a result that was confirmed when adult male rats, isolated or paired immediately after weaning until the day of tests (56 +/- 2 days), were treated with B-HT 920. In this case, however, not only isolated but also paired rats differed from grouped rats of the same age in their response to B-HT 920.