Diffuse pathways convey efferent activity from rostral pontile pneumotaxic center to medullary respiratory regions

Studies were undertaken to evaluate the hypothesis that diffuse pathways serve to convey efferent activity from the rostral pontile pneumotaxic center to the respiratory regions of medulla. Activation of respiratory mechanisms within the pneumotaxic center was produced by electrical stimulation. In decerebrate, vagotomized, cerebellectomized, paralyzed and ventilated cats, stimulations of the pneumotaxic center produced a premature termination of activities of both phrenic nerves. Such a termination of neural activities was still obtained following hemisection of the brain stem at the pontomedullary junction either ipsilateral or contralateral to the site of stimulation. Likewise, both phrenic activities were terminated by stimulation of the pneumotaxic center after a midsagittal division of the brain stem from the intercollicular level to the medullary obex. These results demonstrate that efferent pathways from the pneumotaxic center must decussate in both the caudal pons and in the medulla. The finding of diffuse pathways from the pneumotaxic center to the medullary respiratory regions has implications for previous studies which reported a variety of respiratory patterns following a brain stem transection at the pontomedullary junction.