Cerebrospinal fluid measures of neurotransmitter changes associated with pharmacological alteration of the despair response to social separation in rhesus monkeys.

Social separation is a risk factor for major depressions that can be modeled in nonhuman primates. Changes in central monoamine neurotransmission are also likely to be involved in major depression. This study examined the relationship between separation-induced depressive-like behavior and central monoamine neurotransmitter changes in rhesus monkeys. Measures of cerebrospinal fluid (CSF) norepinephrine (NE), 5-hydroxyindoleacetic acid (5HIAA), and homovanillic acid (HVA) were used to assess the neurobiological impact of social separation and drug treatments alone or in combination. alpha-Methyl-p-tyrosine exacerbated, and fusaric acid ameliorated, the depressive-like response to separation. Probenecid-induced accumulations of HVA and 5HIAA reflected changes in behavior, but were not consistently affected by drug treatment. In contrast, pretreatment CSF NE was comparatively stable across repeated sampling, and drug-induced changes in this measure were correlated with changes in behavior. Low CSF NE, whether drug-induced or naturally occurring, was associated with a more severe depressive-like response to separation.