CSF monoamines, age and impulsivity in wild grivet monkeys (Cercopithecus aethiops aethiops)

Brain monoaminergic activity has been associated with behaviors, such as im pulsive risk-taking, that tend to peak during adolescence in humans and non human primates. This study was designed to assess natural variation in mono amine neurotransmitter metabolism in relation to age and behavioral impulsi vity in grivet monkeys (Cercopithecus aethiops aethiops) living in their na tive habitat and subject to natural ecological pressures. Cisternal cerebro spinal fluid, collected from 22 animals living in the Awash National Park, Ethiopia, was assayed for the major metabolites of serotonin (5-hydroxyindo leacetic acid, 5-HIAA), dopamine (homovanillic acid, HVA) and norepinephrin e (3-methoxy-4-hydroxyphenylglycol, MHPG. Concentrations of HVA declined si gnificantly from one year of age to older adulthood. Further, a significant curvilinear relationship was identified between age and the 5-HIAA/HVA rat io, with the trough coinciding with the period of adolescence. Finally, beh avioral impulsivity, as measured by re-entering baited traps a second time after the animal had already been captured and sampled for CSF, was related to lower levels of MHPG. The results suggest that normal variation in cent ral monoaminergic activity may have functional consequences in wild populat ions.