Convergence of sympathetic, vagal, and other sensory inputs onto neurons in feline ventrolateral medulla

Abstract

Responses of 80 neurons in rostral and caudal ventrolateral medulla to multiple sources of sensory input were assessed in cats anesthetized with alpha-chloralose. Sixty-one of eighty-one neurons (76%) were excited by stimulation of the stellate ganglion, and one neuron exhibited inhibition followed by excitation. In response to vagal stimulation, 12% of the neurons were excited and 29% inhibited. Vagal stimulation reduced the responses of 13 of 39 (33%) neurons to sympathetic stimulation. Overall, one-third of the neurons responded to both sympathetic and vagal stimulation. There was no difference in proportion of responsive neurons in rostral versus caudal ventrolateral reticular formation. Cells were also tested for auditory, visual, and natural somatic stimuli. Ten percent of the neurons responded to all five stimuli, and another 25% responded to four stimuli. Twelve percent of neurons were unresponsive to any stimulus. Twenty cells were tested for responses to changes in blood pressure elicited with phenylephrine and nitroglycerin. Seven neurons were inhibited by increases or excited by decreases in pressure, four had the opposite responses, and nine were unresponsive. In general, blood pressure-sensitive cells exhibited comparable convergence of other inputs as the overall cell population. However, three times as many pressure-insensitive neurons received vagal input as did pressure sensitive neurons. In conclusion, neurons in the ventrolateral medulla, including the vasopressor and vasodepressor regions, receive and integrate convergent input from multiple sensory origins. Since the regions of the reticular formation studied are functionally heterogeneous, the precise functions of these neurons are not known.