The effect of 5-HT(2a/2c) receptor agonist microinjected into central amygdaloid nucleus and median preoptic area on maternal aggressive behavior in rats

Much evidence supports the hypothesis that 5-hydroxytryptamine (5-HT) activation is related to the inhibition of aggression. We examined potentially pro- and anti-aggressive effects of the 5-HT(2A/2C) receptor agonist on specific brain sites. Female Wistar rats on the 7th day postpartum were microinjected with the selective 5-HT(2A/2C) receptor agonist, alpha-methyl-5-hydroxytryptamine maleate (0.2 to 1.0 microg/0.2 microl) into the central amygdaloid nucleus and median preoptic nucleus. For each brain area studied, the frequency of the behaviors: locomotion, social investigation, lateral threat, attacks (frontal and lateral), and biting the intruder were compared among the various treatments by an Analysis of Variance, followed when appropriate, by Tukey's test. Microinjection of the selective 5-HT(2A/2C) receptor agonist, a-methyl-5-hydroxytryptamine maleate into central amygdaloid nucleus increased maternal aggression in the absence of concurrent changes in non-aggressive behavior. By contrast, microinjection of the selective 5-HT(2A/2C) receptor agonist at several dilutions into the median preoptic nucleus did not alter aggressive behavior. The current and earlier data with pro- and anti-aggressive effects of the 5-HT(2a/2c) receptor agonist, when microinjected into the median preoptic nucleus relative to the central amygdaloid nucleus, medial septum and periaqueductal grey area in female rats point to functionally separate serotonin receptor populations in the amygdaloid-septal-hypothalamic and periaqueductal gray matter areas controlling aggressive behavior. It is possible that amygdaloid 5-HT(2a/2c) receptors may increase aggressive behavior in lactating females as a result of changes in fear.