Convergence of ventrolateral medullary and aortic baroreceptor inputs in nucleus of the solitary tract.

Experiments were done in alpha-chloralose anesthetized rats to investigate the effect of stimulating the intermediate region of the ventrolateral medulla (VLM) on the response of single units in nucleus of the solitary tract (NTS) that altered their rate of discharge during aortic baroreceptor stimulation. Of 178 units recorded within NTS, 65 responded orthodromically to VLM stimulation. An additional 16 units were activated antidromically by VLM stimulation. The interaction between the aortic depressor nerve and VLM orthodromic inputs was investigated in 38 units that received converging inputs from VLM and the aortic depressor nerve. A conditioning stimulus applied to VLM, regardless of whether 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 aortic depressor nerve stimulation. These data suggest that VLM neurons are involved in the modulation of aortic baroreceptor afferent information at the level of the NTS and that this interaction of inputs in NTS may involve both postsynaptic and presynaptic mechanisms.