[Elongation of mouse spinal cord axons in isogenic grafts of the sciatic nerve, skeletal muscle and submaxillary gland].

Isografts of sciatic nerve, skeletal muscle, submaxillary gland and, as control experiments, of optice nerve, were transplanted into the non transected spinal cord of young albino mice, through a punctiform pial aperture. Under these conditions, local cellular reactions were reduced and the sensori motor behavior of the operated animals remained apparently undisturbed throughout the experimental period. Within a few days, axonal sprouts issuing mainly from the terminal clubs of intraspinal nerve fibres severed by the grafting procedure were seen elongating and growing into--and presumably throughout--the nervous as well as the muscular and glandular transplants. The Schwann cells of these grafts, either sedentary or migrating towards the cord and intermingling with host reactive glial cells, appeared to guide the growth of the axonal sprouts they ensheathed (from day 3 to day 10) and generally myelinated (as early as day 6). Optic nerve transplants, lacking Schwann cells, were never reinnervated. Furthermore, in control microinjuries without grafting, limited growth of axonal sprouts was observed only when a few host Schwann cells were present. Mouse spinal neurons, therefore, demonstrate a marked capacity for regrowth when minimal damage to the spinal cord is associated with an adequate supply of Schwann cells. In contrast, host as well as transplanted glial cells, were unable, at least when they were not associated with Schwannian elements, to promote regenerative expression of these central neurons.