Topographically selective reinnervation of adult mammalian skeletal muscles

In 2 rat muscles, serratus anterior and the diaphragm, the rostrocaudal axis of the motor pool is mapped onto the rostrocaudal axis of the muscle's surface (Laskowski and Sanes, 1987a). One possible basis for this orderly topography is that motor axons and intramuscular structures bear labels that favor connectivity among positionally matched partners. To test for the existence of such labels, we asked whether axons would selectively reinnervate appropriate portions of the muscles following nerve transection. We found that, on average, rostral and caudal halves of each muscle were preferentially reinnervated by axons from the rostral and caudal halves of its motor pool, respectively. In the serratus anterior, reinnervation was more selective following denervation in neonates than following denervation in adults, although in neither case was the normal pattern of innervation reestablished completely. These results show that motor axons can selectively reinnervate adult rat muscles, and support the idea that positional cues play a role in organizing neuromuscular topography.