Developmental changes in pontine influence on respiratory rhythm generation in neonatal rats: effect of age versus tissue oxygenation

Abstract

Pontine ablation depressed respiratory frequency in in vitro rat brainstem spinal cord preparations from postnatal rat pups on the day of birth (P0) but increased burst frequency in 2 and 4 day old (P2, P4) preparations. To examine the extent to which the response to pontine removal and the effects of age on this response represented developmental changes versus changes in tissue mass and oxygenation of the preparation, we first examined the effect of chemical rather than physical lesion of the pons with tetrodotoxin (0.5μM) in a split bath preparation to inactivate the pons without reducing tissue mass. We found chemical lesions had a similar effect as physical ablation. Next, using an O2 sensing microelectrode, we found that pontine ablation did not affect PO2 in the medulla at the level of the PreBötzinger Complex. PO2 reached zero around 1mm from the ventral surface in the absence and presence of the pons, suggesting adequate oxygenation of the ventral respiratory group. These data confirm that the role of the pons and the changes seen in pontine influence on respiratory rhythm over early development are not an artifact of changes in tissue mass or oxygenation. Supported by the NSERC of Canada.