Three Position Controller for Tensile Regulation of Axon Length

Abstract

Some evidence suggests that mechanical tension is a regulator of axonal length in both growth and retraction. The last phase of axonal growth was described by Weiss (1941) as “towing.” The tension exerted by the migration of the neuron’s target cell in the expanding animal embryo causes the attached axon to elongate. Bray (1984) showed that a similar process of tension-induced axonal elongation would occur in cultured neurons whose neurites were attached to a towing motor. Elimination of supernumerary axons in the development of skeletal muscle innervation (Purves and Lichtman 1980) occurs by axonal retraction, not degeneration (Riley 1981), indicating the presence of axonal tension to withdraw the supernumerary axons. Campenot (1985) found evidence for tension regulation in neurite length by adding or substracting nerve growth factor to ifferent regions of cultured neurons.