THE EFFECTS OF A 5-HT1A RECEPTOR AGONIST AND ANTAGONIST ON THE 5-HYDROXYTRYPTAMINE RELEASE IN THE CENTRAL NUCLEUS OF THE AMYGDALA - A MICRODIALYSIS STUDY WITH FLESINOXAN AND WAY-100635

The modulation of extracellular 5-hydroxytryptamine (5-HT) in the cent ral nucleus of the amygdala (CeA) by 5-HT1A receptors was studied by i ntracerebral microdialysis in awake and freely moving rats. Local admi nistration of 1 mu M tetrodotoxin (TTX), 60 mM K+ and perfusion with C a2+-free Ringer containing EGTA confirmed that the major part of dialy sate 5-HT levels from the CeA is of neuronal origin. Administration of 300 nM of RU 24969, a 5-HT1B receptor agonist, through the probe into the CeA decreased dialysate 5-HT levels to 67.2% of the baseline valu e. Systemic administration of the 5-HT1A receptor agonists 8-OH-DPAT a nd flesinoxan dose-dependently decreased 5-HT levels in the CeA. The e ffect of 0.3 mg/kg of flesinoxan could be completely antagonized by sy stemic administration of 0.05 mg/kg WAY 100635, a 5-HT1A receptor anta gonist. WAY 100635 alone had only minimal effects at this dose, These data show that a major part of the extracellular 5-HT in the CeA stems from 5-HT neurons and that the amount of 5-HT released into this brai n region can be modulated by 5-HT1A receptors.