PRETREATMENT WITH 5-HT1A RECEPTOR AGONIST FLESINOXAN ATTENUATES FOS PROTEIN IN RAT HYPOTHALAMUS

The 5-HT1A receptor agonist flesinoxan has anxiolytic activity and con currently enhances plasma corticosterone levels in rats. After a secon d injection of flesinoxan 24 h later, the corticosterone response disa ppears, but not the anxiolytic effects. Male rats received two injecti ons with either flesinoxan or vehicle within 24 h. Flesinoxan challeng e enhanced Fos immunoreactivity in the paraventricular nucleus of the hypothalamus, the central amygdala, and the dorsolateral part of the b ed nucleus of the stria terminalis and plasma corticosterone levels in the vehicle-pretreated rats. Flesinoxan pretreatment resulted in an a ttenuated response of plasma corticosterone levels and Fos-positive ne urons in the paraventricular nucleus of the hypothalamus, but not in t he central amygdala and the bed nucleus after a flesinoxan challenge. The differential desensitization levels for both behaviour and neuroen docrine responses after flesinoxan treatment seem to correspond to dif ferent organization levels in the brain, like limbic system and hypoth alamus. (C) 1997 Elsevier Science B.V.