[Mechanisms underlying depressor and bradycardia effects of A5-excitation (compared with that of A1-excitation) in rats].

Experiments were performed under the same condition described in the accompanying paper. (1) Injection of sodium L-glutamate (Glu) into A5 area of rat induced depressor and bradycardia responses, as Glu-injection into A1 area did. (2) Bilateral vagotomy also markedly attenuated the cardiovascular effect of Glu-injection into A5. (3) Influences of the receptor blockers injected into rostral ventrolateral medulla (RVL) on the depressor and bradycardia responses of Glu-injection into A5 were slightly different from those of the same receptor blockers administered into RVL: phentolamine, propranolol, naloxone and bicuculline all markedly reduced the depressor and bradycardia effects of A5-excitation (propranolol and bicuculline even reversed these effects). These results indicate that not only alpha-, beta-, GABA receptors, but also opiate receptors mediate the depressor and bradycardia effects of A5.