Responses of simultaneously recorded respiratory-related medullary neuronsto stimulation of multiple sensory modalities

Responses of simultaneously recorded respiratory-related medullary neurons to stimulation of multiple sensory modalities. J. Neurophysiol. 82: 176-187 , 1999. This study addresses the hypothesis that multiple afferent systems share elements of a distributed brain stem network that modulates the respi ratory motor pattern. Data were collected from 18 decerebrate, bilaterally vagotomized, paralyzed, artificially ventilated cats. Up to 28 neurons dist ributed in the rostral and caudal ventral respiratory group, nucleus tractu s solitarius, and raphe obscurus were recorded simultaneously with microele ctrode arrays. Phases of the respiratory cycle and inspiratory drive were a ssessed from integrated efferent phrenic nerve activity. Carotid chemorecep tors were stimulated by injection of CO2-saturated saline solution via the external carotid artery. Baroreceptors were stimulated by increased blood p ressure secondary to inflation of an embolectomy catheter in the descending aorta. Cutaneous nociceptors were stimulated by pinching a footpad. Four h undred seventy-four neurons were tested for respiratory modulated firing ra tes and responses; 403 neurons were tested with stimulation of all 3 modali ties. Chemoreceptor stimulation and pinch, perturbations that tend to incre ase; respiratory drive, caused similar responses in 52 neurons; 28 responde d oppositely. Chemoreceptor and baroreceptor stimulation resulted in simila r primary responses in 45 neurons; 48 responded oppositely. Similar respons es to baroreceptor stimulation and pinch were recorded for 38 neurons; oppo site effects were measured in 26 neurons. Among simultaneously recorded neu rons, distinct combinations of firing rate changes were evoked in response to stimulation of the different modalities. The results show a functional c onvergence of information from carotid chemoreceptors, baroreceptors, and c utaneous nociceptors on respiratory-modulated neurons distributed in the me dulla. The data are consistent with the hypothesis that brain stem neurons have overlapping memberships in multifunctional groups that influence the r espiratory motor pattern.