DELAYED DISPERSAL AND ELEVATED MONOAMINERGIC ACTIVITY IN FREE-RANGINGRHESUS-MONKEYS

Male rhesus monkeys typically disperse from their groups of birth when they are between 3 and 5 years of age. Some males, however, delay dis persal from their natal groups until after they are 5 years old. The c urrent study evaluated central monoaminergic neurotransmitter activity as a potential correlate of such ''delayed'' dispersal among 54 rando mly selected adolescent and adult male rhesus monkeys (Macaca mulatta) captured on Cayo Santiago during an annual trapping season. Specifica lly, cerebrospinal fluid (CSF) concentrations of 5-hydroxyindoleacetic acid (5-HIAA, a serotonin metabolite), 3-methoxy-4-hydroxyphenylglyco l (MHPG, a norepinephrine metabolite), and homovanillic acid (HVA, a d opamine metabolite) were compared in monkeys 60 months of age or more that had either dispersed (n = 33) or were still in their natal groups (n = 5). The monkeys still in their natal groups had higher CSF conce ntrations of both 5-HIAA and HVA (but not MHPG) than did the animals t hat had emigrated (Ps < 0.05). Subsequent analysis indicated that only 5-HIAA independently differentiated dispersing monkeys from delayed d ispersers. Of monkeys less than 60 months of age (n = 16), only two ha d dispersed from their natal groups; in this age class, there were no significant differences between dispersing and natal individuals in an y CSF monoaminergic metabolite (all Ps = NS). Finally, there was no di fference in the CSF 5-HIAA concentrations of the five delayed disperse rs and those of younger animals (P = NS), suggesting a failure to expe rience the frequently reported adolescent decline in serotonergic acti vity. In contrast, the CSF 5-HIAA concentrations of the dispersing ani mals were lower than those of the younger animals (P < 0.05), consiste nt with either an age-related decline or an effect of dispersal per se . (C) 1995 Wiley-Liss, Inc.