5-Hydroxytryptamine correlates of isolation-induced aggression in mice

Abstract

Drug regimens designed to enhance or impair serotonergic functioning were found to differentially affect isolation-induced fighting in mice. Male albino mice were isolated for at least 4 weeks. Number of fights, attack latencies, and average fight durations were recorded for 15 min every other day. On intervening days, the locomotor activity of each mouse was measured in stabilimeters. After the baseline for aggression and activity stabilized, drug procedures were instituted. While motility remained unaffected, mice injected with D,L-5-hydroxytryptophan in combination with a peripheral decarboxylase inhibitors (seryltrihydroxybenzine) engaged in fewer fights of shorter average duration which were precede by longer attack latencies. Biochemical analyses indicated that although serotonin levels were increased, catecholamine levels were reduced. A putative inhibitor of tryptophan hydroxylase, p-chloro-N-methylamphetamine (PCMA), was found to increase fighting frequency; attack latencies, average fight durations, and motility measurements did not differe significantly from non-injection performance. At time periods in which fighting was increased, levels of brain serotonin were reduced while catecholamine levels remained unaltered. Although PCMA did not affect motility at time intervals when fighting was increased, locomotor activity was increased for the first 8 hr after administration. Notwithstanding contributions by other putative neurotransmitters, these results suggest that serotonergic mechanisms are involved in the control of isolation-induced aggression in mice.