A MICRODIALYSIS EXAMINATION OF SEROTONIN RELEASE IN THE RAT FOREBRAININDUCED BY BEHAVIORAL ENVIRONMENTAL MANIPULATIONS

Serotonin (5-HT) has been implicated in a variety of behavioral and ph ysiological processes mediated by the central nervous system. However, the exact nature of 5-HT release under naturalistic or physiologic co nditions remains unclear. The present study investigated this issue by employing in vivo microdialysis to examine 5-HT release in the hippoc ampus, corpus striatum, amygdala, and prefrontal cortex of the rat dur ing manipulations that induced varying behavioral and physiological re sponses. In each rat, two sites were examined simultaneously during tw o of the following manipulations: tail pinch, tail pinch with food pre sent, feeding, cat exposure, floating, and swimming. Results indicate that 5-HT levels increased 20-65% above baseline levels in response to each manipulation in all forebrain areas examined. The only significa nt difference found across manipulations was that tail pinch with food present produced a greater increase in 5-HT than cat exposure, which may be attributable to differences in the degree of general activation induced by these manipulations rather than to specific physiological or behavioral aspects. Furthermore, there was a strong positive correl ation between 5-HT release and time spent in alert waking. Finally, th ere was an overall significantly smaller increase in 5-HT release in t he corpus striatum compared to the other three sites. These data sugge st that the release of 5-HT in the forebrain is closely related to beh avioral state, not to specific behaviors, and that the magnitude of 5- HT release may reflect the degree of activation. In addition, this stu dy suggests there can be some degree of differential pattern of releas e of 5-HT in the forebrain.