Serotonergic influences on the social behavior of vervet monkeys (Cercopithecus aethiops sabaeus)

The behavioral effects of altering serotonin neurotransmission by chronic drug treatments in socially living vervet monkeys (Cercopithecus aethiops sabaeus) were examined. Animals received tryptophan (TRP, 20 mg/kg/day), parachlorophenylalanine (PCPA, 80 mg/kg/day), 5-hydroxytryptophan (5-HTP, 40 mg/kg/day), chlorgyline (10 mg/kg/day), or PCPA followed by concurrent PCPA and 5-HTP. Grooming, approaching, resting, and eating were increased by TRP and decreased by PCPA; TRP decreased and PCPA increased locomoting, avoiding, being solitary, and being vigilant. Grooming, being vigilant, and receiving aggression were increased by 5-HTP, and PCPA increased initiating aggression and decreased huddling. Concurrent administration of 5-HTP and PCPA reversed the effects of PCPA on approaching, grooming, and resting; augmented the PCPA effects on avoiding, being solitary, and aggression; and did not alter the PCPA effects on eating, locomoting, and huddling. Chlorgyline increased grooming, approaching, and being vigilant and decreased being solitary. No treatment significantly affected sexual behavior. These data suggest that serotonergic systems contribute relatively substantially to the mediation of grooming and approaching, participate less strongly in resting and locomoting, are implicated still more weakly in being solitary, avoiding, and being vigilant, and have little if any involvement in huddling, aggression, and sexual behavior.