Axon Branching of Medullary Expiratory Neurons in the Sacral Spinal Cord of the Cat

Abstract

It has been described that bulbospinal expiratory neurons are located in the region of the caudal nucleus retroambigualis (7,9). Expiratory (E) neurons in the caudal nucleus retroambigualis have axon collaterals in the upper lumbar segments (8), and they have respiratory synaptic effects on internal intercostal motoneurons (6) and abdominal motoneurons (9). Our previous study has shown that the majority of E neurons extend their descending spinal axons to the lower lumbar (L6-L7) and the sacral spinal cord (S1-S3) (12). Anatomical study has shown the projection from the caudal nucleus retroambigualis to the nucleus of Onuf using autoradiographic techniques (5). In the present study, we investigated the location of axon collaterals in the sacral spinal gray matter of single E neurons. For this purpose, a microstimulation technique was employed and the distribution of effective sites of antidromic activation in axon collaterals was mapped (12,13,14).