CONVERGENCE OF VENTROLATERAL MEDULLARY AND AORTIC BARORECEPTOR INPUTSIN NUCLEUS OF THE SOLITARY TRACT

Experiments were done in alpha-chloralose anesthetized rats to investi gate the effect of stimulating the intermediate region of the ventrola teral medulla (VLM) on the response of single units in nucleus of the solitary tract (NTS) that altered their rate of discharge during aorti c baroreceptor stimulation. Of 178 units recorded within NTS. 65 respo nded orthodromically to VLM stimulation. An additional 16 units were a ctivated antidromically by VLM stimulation. The interaction between th e aortic depressor nerve and VLM orthodromic inputs was investigated i n 38 units that received converging inputs from VLM and the aortic dep ressor nerve. A conditioning stimulus applied to VLM, regardless of wh ether the NTS unit was excited by (n = 13) or did not respond to (n = 9) VLM stimulation, decreased the excitatory response of the unit to a ortic depressor nerve stimulation. These data suggest that VLM neurons are involved in the modulation of aortic baroreceptor afferent inform ation at the level of the NTS and that this interaction of inputs in N TS may involve both postsynaptic and presynaptic mechanisms.