[Mechanisms underlying depressor and bradycardia effects of A1-excitation in rats]

In chloral hydrate-anesthetized, tubocurarine-immobilized and artificially ventilated rats, the following results were observed: (1) Microinjection of sodium L-glutamate (Glu) into A1 area induced a significant fall in blood pressure and heart rate. (2) Bilateral vagotomy markedly reduced the magnitude of the depressor and bradycardia effects of Glu-injection into A1. (3) Injection of phentolamine or propranolol into bilateral RVL reduced the depressor effect of Glu-injection into A1. Naloxone-injection into RVL had no significant influence on cardiovascular effects of A1-excitation, but injecting bicuculline into RVL could reverse both depressor and bradycardia effects of A1 area. The results suggest that A1 exerts its cardiovascular effects mainly via RVL, and the alpha-, beta- and GABA-receptors within RVL (but not opiate receptors) mediate the hypotension effect of A1 area, while GABA-receptors play an important role in mediating the bradycardia effect of the A1 area.