Pontine projections of pulmonary slowly adapting receptor relay neurons in the cat

Pontine projections of second-order neurons activated by vagal afferents originating from pulmonary slowly adapting receptors were studied electrophysiologically in Nembutal-anesthetized, paralyzed and artificially ventilated cats. Extracellular recordings from these neurons (referred to as P-cells) were made in the nucleus tractus solitarii. Antidromic mapping of the brain stem showed that many P-cells examined projected their axons to the ipsilateral pons as well as the medulla. Axonal arborizations were found in the parabrachial nucleus, i.e. in the area corresponding to the pontine respiratory group. In some P-cells, axonal arborizations were also found in the A5 area. The present results suggest that the P-cells are involved in pontine pneumotaxic mechanisms.