Neocortical grafts receive functional afferents from the same neurons of the thalamus which have innervated the visual cortex replaced by the graft in adult rats.

Electrophysiological and anatomical studies were carried out in parallel to investigate the ability of lateral geniculate body neurons to regenerate axons damaged by the removal of the primary visual cortex and to innervate graft neurons functionally after transplantation of fetal neocortical tissue to a lesion cavity in the brain of adult rats. In electrophysiological experiments neurons of a large portion of the transplants (14/35) displayed visual responses with characteristics resembling closely those of normal primary visual cortex; these transplants also displayed a different degree of restoration of topographically organized visual field representations on them. To demonstrate anatomical regeneration of inputs from the host lateral geniculate body to the graft, injections of FluoroGold were made before grafting into the intact visual cortex for retrograde labeling of the lateral geniculate body neurons. After completion of the microelectrode recordings from the transplants a second dye, Bisbenzimide, was injected into the transplants. The rats with transplants whose neurons displayed responses to visual stimulations contained in the lateral geniculate body neurons with FluoroGold-labeled cytoplasm and Bisbenzimide-labeled nuclei. The presence of double-labeled neurons suggests that the same neurons, the axons of which have terminated in area 17 of the cortex, innervated the transplants functionally through the regeneration of damaged axons.