The role of inhibitory amino acids in control of respiratory motor output in an arterially perfused rat

Mechanisms of respiratory rhythm generation

In mammals, a three-phasic respiratory rhythm is generated by a network of various types of neurons in the lower brainstem. The cellular mechanisms of rhythmogenesis involve cooperative interactions between synaptic processes and specific membrane properties. The network seems to be driven by extrinsic sources in mature animals, whereas in the immature network pacemaker neurons might be involved.

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.