Antidromic mapping of descending axons of respiratory bulbospinal neurons in the nucleus tractus solitarius of the rabbit.

Antidromic mapping of the descending axons of the respiratory bulbospinal neurons in the region of the nucleus tractus solitarius (NTS) was performed on rabbits anesthetized with urethane. Among 177 units tested, 29 out of 87 inspiratory (I), 27 out of 84 expiratory (E) and 2 out of 6 phase-spanning units were identified as bulbospinal. A prominent feature of the bulbospinal pathway from the NTS in the rabbit is the abundance of ipsilateral descending axons. The axons rising from one side are situated in the ventrolateral and ventral funiculi of both sides. The axonal conduction velocities are about 25-35 m/s. Both I and E bulbospinal neurons can be divided into R alpha and R beta types according to 'no I inflation' and 'maintained E inflation' tests.