INTERACTION BETWEEN CHEMORECEPTOR AND STRETCH-RECEPTOR INPUTS AT MEDULLARY RESPIRATORY NEURONS

The interaction between afferent inputs from carotid body chemorecepto rs (CCRs) and from slowly adapting pulmonary stretch receptors (PSRs) on the discharge patterns of medullary inspiratory (I) and expiratory (E) neurons was characterized in thiopental sodium-anesthetized, paral yzed, ventilated dogs. A cycle-triggered ventilator was used to produc e control and test pulmonary afferent input patterns. The CCRs were st imulated by phase-synchronized bolus injections of CO2-saturated salin e into the common carotid arteries. Only those neurons whose discharge time course was altered by both inflation and CCR activation were stu died. The dorsal respiratory-group (DRG) I inflation-insensitive neuro ns were also included. Cycle-triggered histograms of unit activity wer e obtained for the neuronal responses to inflation, CO2 bolus, and the ir combination, as well as for the spontaneous control condition. Line arity of the interaction was tested by comparing the sum of the net in dividual responses to the net response of the combined afferent inputs . The results suggest that a linear (additive) interaction between CCR and PSR inputs exists for the DRG I inflation-sensitive neurons, the ventral respiratory group (VRG) I decrementing, and caudal VRG E augme nting neurons, while a nonadditive interaction exists for caudal VRG E decrementing bulbospinal neurons. The implications of these findings are discussed.