The functional expression of a pontine pneumotaxic centre in neonatal rats.

1. Our purpose was to determine whether a pneumotaxic centre could be localized to the rostral pons in newborn rats. We recorded efferent activity 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 electrolytic lesions. Neuronal activities were blocked by microinjections of the glutamate antagonist MK-801 and were destroyed by the neurotoxins kainic acid and domoic acid. 3. Unilateral ablation or lesions of the pontine tegmentum caused a significant prolongation of the duration of the phrenic burst in animals of all ages. This duration increased further 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 those following physical ablations or lesions were recorded after microinjections of MK-801 or neurotoxins. 5. A common region of ablation, lesion and microinjection was the parabrachialis and Köllicker-Fuse nucleus. 6. Exposure to anoxia resulted in an alteration from apnoeusis to gasping. 7. We conclude that from the day of birth, rostral pontine pneumotaxic mechanisms play a significant role in the definition of eupnoea. Moreover, from the day of birth, rats can exhibit the classical ventilatory patterns of eupnoea, apneusis and gasping.