Electrical stimulation of pneumotaxic center: activation of fibers and neurons.

Electrical stimulations of the pneumotaxic center can result in a phase-switch from neural inspiration to expiration or the reverse. Terminations of inspiration are also obtained from many loci ventral to the pneumotaxic center. We hypothesized that responses to some stimulations reflect an activation of fibers rather than neurons. Studies were conducted in decerebrate, vagotomized, paralyzed and ventilated cats. Activities of the phrenic and triangularis sterni nerves were recorded. A multibarreled pipette was inserted into the rostral pons. Electrical stimulation was delivered through two barrels; another contained kainic acid to destroy neurons. The threshold current for producing inspiratory termination was not altered in most regions following the injections of kainic acid. However, stimulation of neurons did appear to underlie the premature onset of phrenic activity. In addition, neurons in medial pontile regions regulate triangularis sterni activity. We conclude that some functions ascribed to the pneumotaxic center are, in fact, subserved by neurons in other regions of the central nervous system.