Synaptic terminals from an identified motoneuron in locust muscle: comparison between first instar larva and adult.

Dimensions and innervation of muscle fibers in locust jumping muscle from 1st instar larva and adult are compared. Fibers innervated by only one motoneuron were investigated. During postembryonic development, the size, but not the number, of muscle fibers increases. The number of synaptic contacts per fiber increases by at least one order of magnitude while the number per micron2 of surface membrane undergoes little change. Nerve terminals in the larva are on average shorter and separated by longer distances than in the adult. Synaptogenesis seems to be initiated by characteristic projections from the muscle attracting glial and axonal processes.