Inhibition of neurons in commissural nucleus of solitary tract reduces sympathetic nerve activity in SHR

Neurons in the commissural nucleus of the solitary tract (commNTS) play an important role in certain cardiovascular responses dependent on sympathetic vasoconstrictor activation, including the arterial chemoreceptor reflex. Electrolytic lesions of the commNTS elicit a fall in arterial pressure (AP) in spontaneously hypertensive rats (SHR). To determine whether the latter result 1) arose from elimination of commNTS neuronal activity rather than en passant axons and 2) was accompanied by a reduction in sympathetic nerve activity, we evaluated the effect of inhibition of neurons in the commNTS on basal splanchnic sympathetic nerve activity (SNA), AP, and heart rate (HR) in SHR, Wistar-Kyoto (WKY), and Sprague-Dawley (SD) rats. In chloralose-anesthetized, paralyzed, and artificially ventilated SHR, microinjection of GABA into the commNTS markedly decreased splanchnic SNA, AP, and HR. The reductions in SNA and AP following similar microinjections in WKY and SD rats were significantly less than those in SHR. Our findings suggest that tonically active neurons in the commNTS contribute to the maintenance of SNA and the hypertension in SHR. The level of tonic discharge of these commNTS neurons in normotensive WKY and SD rats may be lower than in SHR.