Segmental motor projections to rat muscles during the loss of polyneuronal innervation.

The pattern of innervation of three muscles from rat (lateral gastrocnemius, biceps brachii, pectoralis minor) has been ascertained in the neonatal period (birth to 4 days) and from two to three weeks postnatal. Contraction, electrophysiological and histological methods were used to determine the pattern of innervation. There is a change in the segmental innervation during development which establishes the topographical projection of different segmental nerves found in mature muscles. Development of such topographical projections by different segmental nerves onto the muscles studied emerges as a consequence of elimination of terminals arising from the inappropriate segmental nerve.