Altered behavioral responses to intense foot shock in socially-isolated rats

Male Wistar rats were isolated immediately after weaning for 12 weeks and exposed to electric foot shock of various intensities. The shock-elicited jumping behavior was measured every ten minutes for one hr. The frequency of jumping in isolated rats was lower than that in grouped and the difference between two groups was the greatest with the most intense shock. In these experimental situations, there was no significant difference in monoamine turnover rate between the two groups while noradrenaline turnover markedly increased in both groups. Chlorpromazine suppressed the jumping in a dose-dependent manner in both groups with stronger suppression in isolated rats. Methamphetamine facilitated the jumping in grouped rats dose-dependently while the drug rather depressed it in the isolated. From these results and the behavioral similarity between the isolated and 6-hydroxydopamine treated rats under foot shock situation, it was suggested that the receptor supersensitivity of central catecholaminergic neurons was involved in the behavioral change in isolated rats.