EVIDENCE FOR L-DOPA SYSTEMS RESPONSIBLE FOR CARDIOVASCULAR CONTROL IN THE NUCLEUS-TRACTUS-SOLITARII OF THE RAT

Microinjections of L-DOPA (10-100 ng) into the medial area of the nucleus tractus solitarii (NTS) led to dose-dependent decreases in arterial blood pressure and heart rate in rats treated with i.p. 3-hydroxybenzylhydrazine, a central inhibitor of DOPA decarboxylase, or similarly with intraventricular 6-hydroxydopamine. D-DOPA, dopamine or noradrenaline (100 ng) produced no effect. L-DOPA methyl ester (1-mu-g), a competitive antagonist for L-DOPA, microinjected into NTS. blocked the depressor and bradycardic responses to L-DOPA. High K+ (40 mM) released endogenous DOPA in a Ca2+-dependent manner from slices of the rat dorsomedial medulla including NTS. These results support the hypothesis that there exist systems Of L-DOPA itself responsible for cardiovascular regulation in NTS of rats. This regulatory action Of L-DOPA seems to be postsynaptic in nature.