FUNCTIONAL AND MORPHOLOGICAL RESTORATION OF INTRACRANIAL BRACHIAL LESION OF THE RETINOCOLLICULAR PATHWAY BY PERIPHERAL-NERVE AUTOGRAFTS IN ADULT HAMSTERS

Axons of adult mammals can regenerate through peripheral nerve grafts and restore the retinocollicular pathway if lesioned proximal to the r etinal ganglion cell somata. Whether the grafting and subsequent reinn ervation of the superior colliculus (SC) is possible in distal axotomy in the brain is a question of clinical relevance. We have deafferente d the SC of adult hamsters at its brachium thus axotomizing the retina l ganglion cell axons rostral to its synaptic contact with the SC neur ons. After unilateral brachium transection, a short segment of the aut ologous sciatic nerve was grafted to bridge the lesioned site to the S C (n = 28). As controls the brachium was transected and left ungrafted (n = 12). Functional restoration was examined 3 to 75 weeks later in grafted (n = 16) and control (n = 5) animals by recording visual evoke d responses from the collicular cells. Prior to recording the grafts w ere visually evaluated and categorized into successfully (n = 8) and u nsuccessfully (n = 8) grafted groups. To diffuse flash stimuli applied to the contralateral eye, visual evoked held potentials were recorded from all successfully grafted, but not in unsuccessfully grafted (wit h the exception of one animal) nor control animals. Unitary spike resp onses to diffuse flash stimuli were recorded exclusively from three su ccessfully grafted animals. Morphological reinnervation was examined i n the remaining grafted (n = 12) and control (n = 7) animals by antero gradely labeling the regenerating retinal axons with WGA-HRP. Axons in the grafts and their terminals in the superficial layers of the SC we re clearly labeled in 8 of the grafted and none of the controls. From these results we conclude that the brachium of the SC is conducive to axonal regeneration and the peripheral nerve graft is indeed effective in restoring distally axotomized visual pathway in adult mammals. (C) 1996 Academic Press, Inc.