5-HYDROXYTRYPTAMINE(3) RECEPTOR MODULATION OF EXCITATORY AMINO-ACID RELEASE IN THE RAT NUCLEUS-TRACTUS-SOLITARIUS

In vivo microdialysis was employed to measure release of endogenous L- glutamate (GLU) and L-aspartate (ASP) in the medial nucleus tractus so litarius of urethane anaesthetised rats. Basal extracellular levels of these amino acids were stable following a 90 min equilibration period (6.3 +/- 0.24 and 3.4 +/- 0.6 pmol/20 mu l sample of GLU and ASP, res pectively). Basal levels of endogenous extracellular GLU and ASP were increased over 2-fold and S-fold, respectively, following local admini stration of the selective 5-hydroxytryptamine (5-HT3) receptor agonist phenylbiguanide (300 mu M). Intracerebral administration of the selec tive 5-HT3 receptor antagonist ondansetron (30 mu M) blocked the effec t of phenylbiguanide on GLU release whilst the effect on ASP was varia ble and complex. These data suggest that 5-HT3 receptor activation in the rat nucleus tractus solitarius can affect excitatory amino acid ne urotransmission in this region of the medulla oblongata.