Peripheral correlates of serotonergically-influenced behaviors in vervet monkeys (Cercopithecus aethiops sabaeus)

The associations among twelve behaviors and three potential peripheral markers of central serotonergic activity were investigated in vervet monkeys (Cercopithecus aethiops sabaeus). The behaviors monitored included approach, heterogroom, rest, eat, avoid, be solitary, be vigilant, huddle, initiate aggress, receive aggress, and engage in sexual behavior. The biochemical parameters measured were whole blood serotonin, plasma free tryptophan, and plasma total tryptophan. Throughout the study period, intraindividual variability in both the behavioral and the biochemical measures was small, although there was substantial interindividual variability in both sets of measures. Free and total tryptophan correlated positively with approach, heterogroom, and eat, and inversely with avoid and be solitary. Whole blood serotonin correlated inversely with avoid and be solitary. These data are compatible with previously reported observations on the behavioral consequences of manipulating serotonergic systems in vervet monkeys and suggest that in normal, drug naive monkeys, free and total tryptophan are better correlates of the central serotonergic activity influencing behavior than is whole blood serotonin.