Maturational changes in pontine and medullary alpha-adrenoceptor influences on respiratory rhythm generation in neonatal rats

We examined developmental changes in α-adrenoceptor influences and descending pontine inputs on the medullary respiratory network in the neonatal rat in vitro brainstem-spinal cord preparation. Using a split bath preparation to isolate the pons from the medulla, antagonists for α1 and α2 adrenoreceptors were applied to only the medulla at postnatal days 0, 2 and 4, before and after transection of the pons. Blocking α1 and α2 receptors in the medulla in the absence of a pons reduced burst frequency at all ages with a more pronounced effect in younger animals. At all ages the presence of a pons diminished the effect of blocking α2 receptors in the medulla and eliminated the effect of blocking α1 receptors. These results indicate that there is a tonic release of catecholamines within the medulla that is under influence from the pons. Additionally, transection experiments indicated that during development, the net influence of the pons changed from one of excitation to one of inhibition.