RELEASE OF GLUTAMATE IN THE NUCLEUS TRACTUS SOLITARII IN RESPONSE TO BAROREFLEX ACTIVATION IN RATS

Abstract

Release of endogenous aspartate and glutamate from the region of the nucleus tractus solitarii was measured in vitro by perfusion methods and in vivo by microdialysis. Stimulation of the nucleus tractus solitarii with 35 mM potassium in vitro significantly increased extracellular concentrations of aspartate and glutamate. Glutamate and aspartate concentrations also increased with dialysis of 100 mM KCl into the nucleus tractus solitarii in vivo, but only changes in glutamate were significant. Experiments in vivo revealed that activation of the baroreflex by intravenous infusion of phenylephrine significantly increased glutamate in dialysates, while hypoventilation that accompanies baroreceptor activation and may activate chemoreceptors tended to increase aspartate but not glutamate.The demonstration that glutamate, but not aspartate, is released with activation of the baroreflex further supports the hypothesis that glutamate is a neurotransmitter of baroreceptor afferents terminating in the nucleus tractus solitarii.