A primordial rhythm-generating neural network emerges during the segmental
period of vertebrate hindbrain development, suggesting a common genetic basis
to both the structure and network activity of the region. We show here that
segmentation influenced a postsegmental developmental step by which a GABAergic
rhythm generator was incorporated into the primordial network and increased
rhythm frequency to near mature values. This process depended on specifications
in r3 and r5 that controlled, on the basis of a two-segment repeat, later
maturation of GABAergic inhibition.
