Structural and functional analysis of raphe neurone implants into denervated rat spinal cord.

The ability of grafts of embryonic raphe cells to the adult rat spinal cord to reverse the morphological, neurochemical and functional deficits caused by ablation of the serotoninergic afferents has been studied. After grafting, extensive reinnervation was observed by 5HT-immunoreactive fibres, many of which appeared to make contacts with host motoneurones. The neurotransmitter complement was apparently normal. There was also a reinstatement of 5HT levels in the denervated cord after transplantation, amounting to some 40% of normal at the level of the graft. Similarly, Na+-dependent uptake of [3H]-5HT into P3 fractions was over 40% of that recorded in unlesioned animals. Antidromic stimulation of the ventral roots of the spinal cord was used to assess the degree of motoneurone excitability. The field potential in the ventral horn of grafted animals was increased by electrical stimulation of discrete regions along the cord, probably corresponding to the graft loci. It is concluded that serotoninergic neurones transplanted to the denervated spinal cord survive and develop normally, reinnervating the host tissue extensively. Furthermore, the graft/host connections appear to be functionally viable.