Medullary axonal projections of respiratory neurons of pontile pneumotaxic center.

In decerebrate, cerebellectomized, vagotomized, paralyzed and ventilated cats, activities were recorded from the phrenic nerve and single respiratory neurons in the area of the nucleus parabrachialis medialis and Kölliker-Fuse nucleus. Stimuli were delivered in the medulla and cervical spinal cord to elicit antidromic action potentials for these neurons and, hence, establish their axonal projections. Antidromic activation was obtained for 18 of 193 neurons following medullary stimulations. Following spinal stimulations, only two respiratory neurons exhibited some responses characteristic of antidromic activation. In the same pontile areas, a number of neurons with no respiratory-modulated or spontaneous activities were antidromically activated by medullary or spinal stimulations. Results are considered in the context of neuroanatomical studies which have established possible interconnections within the brainstem respiratory control system, and hypotheses for functions of the pontile pneumotaxic center in ventilatory control.