Convergence of multiple sensory inputs onto neurons in the dorsolateral medulla in cats

The dorsolateral medulla, including the nucleus reticularis parvicellularis, the cuneate nucleus, and the external cuneate nucleus, is an integrative 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 α-chloralose. Neurons were located in the nucleus reticularis parvicellularis (24 cells, 60%), the cuneate nucleus (10 cells, 25%), and the external cuneate nucleus (6 cells, 15%). All neurons were tested for responses to: electrical stimulation of afferents coursing through the left stellate ganglion and afferents in the left cervical vagus nerve, and somatic, auditory, and visual stimulation. No neurons responded to all five stimuli. Three cells (7.5%) responded to four stimuli, 11 (27.5%) responded to three stimuli, 10 (25.0%) responded to two stimuli, and 15 (37.5%) responded to only a single stimulus. The remaining cell was unresponsive to any stimulus. As a group, neurons in the nucleus reticularis parvicellularis received input from the greatest number of sensory modalities, and cuneate nucleus neurons received input predominantly from somatosensory afferents. 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 receive convergent inputs from different sensory modalities. The neuronal response patterns are consistent with the concept that the nucleus reticularis parvicellularis is an association region that coordinates motor and autonomic responses during orofacial motor behaviors.