Increased levels of Met-enkephalin-like immunoreactivity in the spinal cord CSF of rats with adrenal medullary transplants

Recent work in our laboratory has demonstrated that the transplantation of adrenal medullary tissue into the spinal cord subarachnoid space can reduce pain sensitivity, particularly following nicotinic stimulation. This analgesia most likely results from the release of opioid peptides from the implanted chromaffin cells since it is blocked by the opiate antagonist naloxone. The purpose of the present study was to more directly measure opioid peptide release from adrenal medullary implants in the spinal cord using spinal cord superfusions. Basal levels of Met-enkephalin-like immunoreactivity (MELI) in spinal cord superfusates of animals with adrenal medullary implants was twice that in animals with control implants. The injection of nicotine further increased MELI release in adrenal medullary, but not control implanted animals. Both the basal MELI levels and the MELI levels following nicotine were correlated with reduced pain sensitivity in animals with adrenal medullary implants. Morphological studies revealed good long-term survival of grafted chromaffin cells. Results of this study suggest that it is possible to increase opioid peptide levels and concomitantly decrease pain sensitivity by the transplantation of adrenal medullary tissue into the spinal cord subarachnoid space.