Transplantation of embryonic raphe cells regulates the modifications of the gabaergic phenotype occurring in the injured spinal cord

Transection of the spinal cord yields a permanent deficit due to the interr uption of descending and ascending tracts which subserve the supraspinal co ntrol of spinal cord functions. We have shown previously that transplantati on below the level of the section of embryonic monoaminergic neurons can pr omote the recovery of some segmental functions via a local serotonergic and noradrenergic reinnervation. Moreover, the up-regulation of the correspond ing receptors resulting from the section was corrected by the transplants. The aim of the present work was to determine whether such a graft could als o influence non-monoaminergic local neurons, the GABAergic interneurons of the spinal cord. Following spinal cord transection, the number of cells whi ch express glutamate decarboxylase (mol, wt 67,000) messenger RNA-a marker of GABA synthesis-increased significantly below the lesion compared with th e intact animal. In contrast, in lesioned animals which had been grafted on e week later with raphe neuroblasts, this number was close to control level . These post-grafting modifications were further associated with increased GABA immunoreactivity in the host tissue. These data suggest that the graft of embryonic raphe cells which compensate s the deficit of serotonin in the distal segment also regulates the express ion of the GABAergic phenotype in the host spinal cord. This regulation cou ld be mediated by the reestablishment of a local functional innervation by both serotonin and GABAergic transplanted neurons and/or by trophic factors released from the embryonic cells. It appears then that grafted cells infl uence the host tissue in a complex manner, through the release and/or regul ation of several neurotransmitter systems. (C) 1999 IBRO. Published by Else vier Science Ltd.