Primordial respiratory-like rhythm generation in the vertebrate embryo.

Respiration is a rhythmic motor behavior that appears in the fetus and acquires a vital importance at birth. It is generated centrally, within neuronal networks of the hindbrain. This region of the brain is of particular interest since it is the best understood with respect to the cellular and molecular mechanisms that underlie its development. Examination of hindbrain activities in the chick embryo has revealed that the central rhythm generator is active before fetal maturation and conforms to the rhombomeric organization of the embryonic hindbrain. Inactivation of genes required for the normal formation of rhombomeres in mice leads to perturbations of the reticular formation that affect respiration after birth and compromise the probability of survival. From studies of hindbrain development we might gain an understanding of how genes govern the early embryonic development of neuronal networks and how this might specify patterns of motor activities operating throughout life.