EFFECTS OF NITRIC-OXIDE ON SYMPATHETIC BAROREFLEX TRANSMISSION IN THENUCLEUS-TRACTUS-SOLITARII AND CAUDAL VENTROLATERAL MEDULLA IN CATS

We have previously shown that nitric oxide (NO) attenuates baseline sy mpathetic tone in the rostral ventrolateral medulla (RVLM), while havi ng no effects on baroreflex transmission in this region in cats. In th e present study, we tested the effects of microinjections (500 nl) of N-G-nitro-L-arginine (L-NNA, 0.3 mM) or the NO donor S-nitroso-N-acety lpenicillamine (SNAP, 10 mu M) in the nucleus tractus solitarii (NTS) and in the caudal ventrolateral medulla (CVLM) which are the two other relays of the sympathetic baroreflex within the brainstem, Neither L- NNA nor SNAP significantly changed the length of inhibition of renal s ympathetic nerve activity (SNA) evoked by electrical stimulation of th e ipsilateral carotid sinus nerve. In contrast, glutamate (1 mM) in th e NTS markedly increased baroreflex inhibition of SNA and the glutamat e receptor antagonist kynurenate (5 mM) in the CVLM significantly decr eased baroreflex transmission in the same experiments. These results s uggest that sympathetic baroreflex function is preserved during both i mpaired endogenous synthesis and excess exogenous supply of NO in the brainstem.