Regulation of motor axon sprouting

Our studies on the amphibian and mammalian motor systems suggest that sprouting of intact motoneurons and synapse formation can be regulated by three mechanisms: peripheral, central, and transneuronal. Peripheral mechanisms provide the means of a direct mode of interaction between the periphery of the nerve cell and the target, to determine the extent of target innervation. The central mechanism enables target muscles to signal the cell bodies of their innervating motoneurons to regulate axonal growth and synapse formation, and thus again determine the extent of their innervation. The transneuronal mechanism provides a vehicle by which the pattern of innervation of a muscle can be altered by nerve cells that do not themselves innervate the muscle, but are an integral part of the entire system.