| Abstract: | 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 μg), 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. |
