Functional innervation of spinal cord tissue by fetal neocortical grafts in oculo: an electrophysiological study.

The ability of fetal neocortex transplants, to functionally innervate maturated cervical spinal cord grafts in oculo, was investigated in rats. We found that a neocortex co-graft will grow and develop in contact with a spinal cord graft, and will generate a functional input to maturated spinal cord tissue which can be activated by electrical stimulation of the neocortex graft. Our data suggest that orthodromic stimulation of this pathway causes short latency, transient excitations of spinal graft neurons. These appear to be mediated by an excitatory amino acid receptor since the response was noncompetitively antagonized by kynurenic acid. Kynurenic acid also noncompetitively antagonized the excitatory effects of glutamate superfused over single spinal cord grafts. The mechanism of the excitation probably does not involve an NMDA (N-methyl-D-aspartate) receptor since APV (2-amino-5-phosphonovalerate) did not alter the spinal graft neuronal responses to neocortical co-graft stimulation. These data suggest that fetal neocortex can functionally innervate maturated cervical spinal cord in the in oculo graft preparation. The in oculo spinal cord graft model may thus provide a unique test system for studies of the influence of drugs and other manipulations that might alter cortico-spinal pathway development as well as influence reestablishment of neuronal pathways after spinal cord injury.