CONVERGENCE OF MULTIPLE SENSORY INPUTS ONTO NEURONS IN THE DORSOLATERAL MEDULLA IN CATS

The dorsolateral medulla, including the nucleus reticularis parvicellu laris, the cuneate nucleus, and the external cuneate nucleus, is an in tegrative region for a variety of sensory inputs. The purpose of this study was to determine whether individual neurons respond to a variety of different sensory modalities. To this end, responses of 40 neurons in the dorsolateral medulla to multiple sources of sensory input were assessed in cats anesthetized with alpha-chloralose. Neurons were loc ated in the nucleus reticularis parvicellularis (24 cells, 60%), the c uneate nucleus (10 cells, 25%), and the external cuneate nucleus (6 ce lls, 15%). All neurons were tested for responses to: electrical stimul ation of afferents coursing through the left stellate ganglion and aff erents in the left cervical vagus nerve; and somatic, auditory, and vi sual stimulation. No neurons responded to all five stimuli. Three cell s (7.5%) responded to four stimuli, 11 (27,5%) responded to three stim uli, 10 (25.0%) responded to two stimuli, and 15 (37.5%) responded to only a single stimulus. The remaining cell was unresponsive to any sti mulus. As a group, neurons in the nucleus reticularis parvicellularis received input from the greatest number of sensory modalities, and cun eate nucleus neurons received input predominantly from somatosensory a fferents. External cuneate nucleus neurons displayed response profiles intermediate between nucleus reticularis parvicellularis and cuneate nucleus. In addition, eight neurons (20% of the total) were sensitive to changes in blood pressure. Results of the present study support the hypothesis that neurons in the nucleus reticularis parvicellularis re ceive convergent inputs from different sensory modalities. The neurona l response patterns are consistent with the concept that the nucleus r eticularis parvicellularis is an association region that coordinates m otor and autonomic responses during orofacial motor behaviors.