Properties of medullary respiratory neurons

A summary of recently published results dealing with the intrinsic and extrinsic properties of medullary respiratory neurons is presented. These neurons are organized into two anatomically separate populations, one associated with the ventrolateral nucleus of the solitary tract and the other with nucleus ambiguus and retroambigualis. Procion yellow dye injection studies have shown that respiratory neurons are medium-sized cells, their dendrites are selectively oriented, there is considerable dendritic overlap, but axon collaterals could not be demonstrated. Axonal conduction velocities vary widely, and input resistance is higher than that of alpha motoneurons. Extrinsic properties reveal a variety of firing patterns and membrane potential trajectories. Evidence is presented and a model proposal suggesting that reciprocal inhibition as well as recurrent inhibition and excitation may be important extrinsic inputs onto medullary respiratory neurons.