Early ontogeny of rhythm generation and control of breathing

The ability of central networks to produce rhythmic motor behaviours linked to the respiratory function, is a remarkably conserved property of the brainstem reticular formation in vertebrates. Conserved cellular and molecular mechanisms also underlie the early embryonic development of the brainstem, leading to a segmented rhombencephalon in all vertebrates. We have proposed that the neural network that controls breathing after birth, derives from a primordial rhythmic network first active in the segmented hindbrain of the embryo. Observations on transgenic mice support this hypothesis: homozygous inactivation of Krox-20, a gene governing segmentation, leads to a lower-than-normal respiratory frequency (fR), despite fetal maturation of the respiratory network and functional compensatory control after birth.