Abstract
The current concept regarding the respiratory centre in mammals is that it is composed of two distinct rhythm-generating neuronal networks in the ventrolateral medulla. These two rhythm generators can be active independently but are normally coupled in newborn and juvenile rats. Detailed characteristics of each generator and the neuronal mechanisms of coupling during development remain to be elucidated. Here, we report a knockout mouse (Na(+),K(+)-ATPase alpha2 subunit gene (Atp1a2) knockout) that may be defective in functional coupling between the two respiration-related rhythm generators. We investigated respiration-related neuron activity in an en bloc brainstem-spinal cord preparation isolated from embryonic day 18.5 Atp1a2(-/)(-) mouse fetuses. In the presence of adrenaline, two different types of rhythm generators were identified. One produced inspiratory burst activity that correlated with C4 inspiratory activity and was thought to be the inspiratory rhythm generator on the basis of its location and sensitivity to a mu-opiate receptor agonist, [d-Ala2, N-Me-Phe4, Gly5-ol]-enkephalin (DAMGO). The other was presumed to be the preinspiratory rhythm generator because it was insensitive to DAMGO and correlated with facial nerve activity. Coupling between these rhythm generators did not function in the normal manner in Atp1a2(-/)(-) mice, as shown by disruption of the linkage between the preinspiratory burst and the inspiratory burst. Coupling was partially restored by repeated activation of the neurons within the networks, suggesting the involvement of an activity-dependent process in the prenatal development of this coupling.