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CSF 5-HIAA and nighttime activity in free-ranging primates
P T Mehlman1, G C Westergaard, B J Hoos
1Division of Research and Development, LABS of Virginia, Inc., Yemassee, SC 29945, USA.
Summary
Low serotonin activity in rhesus macaques is linked to disrupted sleep-wake cycles. Lower cerebrospinal fluid 5-hydroxyindoleacetic acid (CSF 5-HIAA) correlated with increased nighttime activity and daytime sleepiness.
Area of Science:
- Neuroscience
- Animal Behavior
- Chronobiology
Background:
- Central nervous system (CNS) serotonin turnover, indicated by cerebrospinal fluid 5-hydroxyindoleacetic acid (CSF 5-HIAA), is linked to circadian activity patterns in humans.
- Aberrant patterns include disrupted sleep and daytime hyperactivity.
Purpose of the Study:
- To investigate if similar relationships between CSF 5-HIAA and activity patterns exist in nonhuman primates.
- To examine the correlation between CSF 5-HIAA and nighttime activity in free-ranging rhesus macaques.
Main Methods:
- Cerebrospinal fluid (CSF) samples were collected from 16 adult male rhesus macaques.
- Radio-telemetry motion-detector collars monitored nighttime activity (2100-0600 hrs).
- Daytime behavior was observed by trained researchers.
Main Results:
- CSF 5-HIAA concentrations were inversely correlated with total nighttime activity duration and mean active event duration.
- Nighttime activity showed an inverse correlation with daytime activity.
- CSF 3-methoxy-hydroxyphenylglycol (MHPG) correlated positively with nighttime activity and inversely with daytime sleep frequency.
Conclusions:
- Male rhesus macaques with lower CSF 5-HIAA exhibited higher total nighttime activity and longer active periods.
- These animals also showed increased daytime sleep.
- Low serotonergic neurotransmission is associated with aberrant diurnal activity, including disrupted nighttime sleep and increased daytime inactivity.