LONG-TERM EFFECTS OF CHRONIC SOCIAL STRESS ON SEROTONERGIC INDEXES INTHE PREFRONTAL CORTEX OF ADULT MALE CYNOMOLGUS MACAQUES

We examined the effects of chronic social stress and social rank on mo noamine concentrations in the prefrontal cortex (PFC) in adult male cy nomolgus macaques (Macaca fascicularis). Seventy-five animals were hou sed in five-member social groups for 28 months and were exposed to thr ee experimental conditions. A 'no-stress' condition was comprised of a nimals housed in groups of stable membership throughout the study. Ani mals assigned to a 'past-stress' condition had their group memberships reorganized at monthly intervals during the first (but not last) 14 m onths of the study, and a third 'recent-stress' condition consisted of social groups reorganized only during the last 14 months. At necropsy , the brains were collected and frozen at -70 degrees C until analyzed . Prefrontal orbital cortex was assayed for monoamines (serotonin (5-H T), dopamine (DA), norepinephrine (NE)), metabolites (5-hydroxyindolea cetic acid (5-HIAA), homovanillic acid (HVA), 3-methoxy-4-hydroxyphene thyleneglycol (MHPG)), and tryptophan using high-performance liquid ch romatography with electrochemical detection. Animals in the past-stres s condition had significantly lower PFC 5-HIAA concentrations compared to those in the no-stress condition (P < 0.05). PFC 5-HT concentratio ns of animals in the past-stress condition were significantly lower th an those in the no-stress and recent-stress conditions (P < 0.01). The concentrations of DA, HVA, NE and MHPG were not altered. These data s uggest that exposure to chronic social stress is associated with long- term selective reductions in serotonergic activity in the PFC. This ef fect may underlie the association in human beings between reduced sero tonergic function and conditions such as pathological grief and posttr aumatic stress disorder.