Fetal locus coeruleus transplanted into the transected spinal cord of the adult rat: some observations and implications.

The 16-day-old fetal locus coeruleus can survive and grow, when transplanted into the spinal cavity created by transection of the adult spinal cord. The implants usually break up into smaller cell groups which become lodged in the host spinal cord, mainly in the caudal region. There was a marked proliferation of the damaged coerulospinal noradrenergic fibers in the rostral, ventral horn region of the cord. A neurotrophic substance produced by the locus coeruleus implants is probably responsible for this effect. Evidence for vigorous axonal growth of noradrenergic fibers derived from the implants in the caudal region of the cord was obtained. In 2/12 cases, the surviving locus coeruleus did not grow into the host tissue. Neosympathetic innervation of the caudal region of the cord occurred both in cases in which the implants survived, or did not survive. The survival rate of the transected, implanted animals is greater than 90%. The success rate of fusion of the implant with the host tissue is 40%. Based on these results, and other reports published recently, it is concluded: (1) that the purely technical difficulties of transplantation and survival of the fetal locus coeruleus in the transected spinal cord of the young adult rat on a long-term basis can be successfully solved. (2) For optimum reinnervation, the transplant should be placed in the lumbar intumescence, and not in the spinal cavity created by transection. (3) The spinal cavity created by transection must be bridged by some other method. The use of fetal spinal cord tissue on fetal mesencephalic tissue may prove to be useful for this purpose. (4) Transection of the cord must be done sub-pially, in order to minimize retraction and compression of the cord. The damaged pia must be resutured. (5) A second fetal locus coeruleus implant should be placed adjacent to the exposed surface of the rostral region of the cord. The results are discussed both in the context of recent efforts to try to restore functional activity to the damaged spinal cord, and in terms of efforts to try to understand the problems involved in fostering the growth of fetal brain tissue in the damaged spinal cord of an adult host animal.