Developmental changes in the hypoxia tolerance of the in vitro respiratory network of rats.

The functional relation between respiratory activity, extracellular potassium activity (aKe) and tissue oxygen pressure (pO2) was analyzed in vitro in the ventral respiratory group (VRG) of the neonatal brainstem-spinal cord (NB) and the perfused adult brainstem (AB) of rats. In the AB, an aKe increase of up to 35 mM and a reversible blockade of respiratory activity occurred during anoxia periods of 5-10 min. In the NB, respiratory activity persisted during a 60 min anoxia in CO2/HCO3(-)-buffered solutions and aKe increased by less than 1.5 mM. In both preparations, inhibition of glycolysis by iodoacetate led to an irreversible blockade of respiratory rhythm and a delayed increase of aKe by more than 15 mM. We conclude that anaerobic metabolism is sufficient for the maintenance of respiratory activity and potassium homeostasis in the brainstem of the neonatal rat, but not of the adult.