Convergence of ventrolateral medulla and aortic baroreceptor inputs onto amygdala neurons

Experiments were done to investigate the effect of stimulation of neurons in ventrolateral medulla (VLM) and aortic baroreceptors on the discharge rate of amygdala neurons. The region of central nucleus of the amygdala (ACe) was explored for spontaneously active single units that altered their discharge rate to electrical stimulation of VLM in the alpha-chloralose anesthetized rat. Responsive units were also assessed for their response to electrical stimulation of the aortic depressor nerve (ADN). Stimulation of VLM altered the discharge rate of 47% (43/92) of the units tested in and around the region of ACe. Of these units, 60% (26/43) were excited (mean latency, 13.6 +/- 3.6 ms) and 40% (17/43) were inhibited (mean latency, 23.1 +/- 4.3 ms) by VLM stimulation. Of the 43 units that responded to stimulation of VLM, 19 (44%) also responded to ADN stimulation with a mean latency of 32.5 +/- 7.6 ms. These data demonstrate that inputs from VLM and ADN converge onto ACe neurons and suggest that VLM may function as a relay for cardiovascular afferent information to the amygdala.