Sympathoinhibition from ventrolateral periaqueductal gray mediated by 5-HT1A receptors in the RVLM

The role of 5-hydroxytryptamine 1A (5-HT1A) receptors located in the rostra l ventrolateral medulla (RVLM) in the mediation of a sympathoinhibitory and depressor response elicited from the ventrolateral periaqueductal gray (vl PAG) matter of the midbrain was examined in pentobarbital sodium-anesthetiz ed rats. Activation of neurons in the vlPAG evoked a decrease in renal and lumbar sympathetic nerve activities and a decrease in arterial blood pressu re. After microinjection of the specific 5-HT1A-receptor antagonist WAY-100 635 into the pressor area of the RVLM, the vlPAG-evoked sympathoinhibition and hypotension was attenuated to control levels (7 of 15 animals) or conve rted into a sympathoexcitation and pressor response (8 of 15 animals). Baro reflex inhibition of sympathetic nerve activity was not impaired by microin jection of WAY into the sympathoexcitatory region of the RVLM. These data s uggest that sympathoinhibition and hypotension elicited by activation of ne urons in the vlPAG are mediated by 5-HT1A receptors in the RVLM.