CSF5-HIAA and nighttime activity in free-ranging primates

Men with low CNS serotonin turnover, as measured by cerebrospinal fluid 5-h ydroxyindoleacetic acid (CSF 5-HIAA) concentrations, exhibit aberrant circa dian activity patterns characterized by disrupted sleep rhythms and daytime hyperactivity. To assess whether similar patterns are found in nonhuman pr imates we examined the relationship between CSF 5-HIAA and nighttime activi ty in free-ranging monkeys. CSF samples were obtained from 16 adult male rh esus macaques living on a 475 acre, heavily forested sea island. Each subje ct was captured, fitted with a radio-telemetry motion-detector collar, and then released back into its group. A receiver placed near the sleeping tree s of the study subjects recorded activity between 2100 hrs and 0600 hrs. Tr ained observers recorded a typical diurnal activity pattern, as they were a ctive 74% of the sampled time during the day and 37% of the sampled time du ring the night. CSF 5-HIAA concentrations were inversely correlated with to tal duration of nighttime activity as well as mean duration of all active e vents. Nighttime activity was inversely correlated with daytime activity. C SF 3-methoxy-hydroxyphenylglycol (MHPG) concentrations were positively corr elated with total nighttime activity, and inversely correlated with daytime sleep frequency. We conclude that male rhesus with low CSF 5-HIAA concentr ations have higher total nighttime activity, longer mean periods of nightti me activity, and sleep more during the day than do males with high CSF 5-HI AA concentrations. This suggests that low serotonergic neurotransmission is associated with aberrant diurnal activity, as evidenced by a disruption of nighttime sleep patterns and a compensatory higher rate of inactivity duri ng the day. Published by Elsevier Science Inc.