THE FUNCTIONAL EXPRESSION OF A PONTINE PNEUMOTAXIC CENTER IN NEONATALRATS

1. Our purpose was to determine whether a pneumotaxic centre could be localized to the rostral pons in newborn rats. We recorded efferent ac tivity of the phrenic nerve in decerebrate, paralysed, vagotomized and ventilated rats, whose age varied from the day of birth to 22 days. 2 . The rostral pontine tegmentum was ablated by aspiration and electrol ytic lesions. Neuronal activities were blocked by microinjections of t he glutamate antagonist MK-801 and were destroyed by the neurotoxins k ainic acid and domoic acid. 3. Unilateral ablation or lesions of the p ontine tegmentum caused a significant prolongation of the duration of the phrenic burst in animals of all ages. This duration increased furt her following contralateral destruction and apneusis was established. The period between phrenic bursts increased in most rats whereas peak phrenic height was not consistently altered. 4. Similar changes to tho se following physical ablations or lesions were recorded after microin jections of MK-801 or neurotoxins. 5. A common region of ablation, les ion and microinjection was the parabrachialis and Kollicker-Fuse nucle us. 6. Exposure to anoxia resulted in an alteration from apnoeusis to gasping. 7. We conclude that from the day of birth, rostral pontine pn eumotaxic mechanisms play a significant role in the definition of eupn oea. Moreover, from the day of birth, rats can exhibit the classical v entilatory patterns of eupnoea, apneusis and gasping.