Attenuation of learned helplessness in rats after transplant of adrenal medulla into the spinal cord.

The influence of an adrenal medullary transplant into the lumbar subarachnoid space on learned helplessness, an animal model of depression, was examined. The transplanted rats were found to be less susceptible than sham-operated animals to become helpless after administration of inescapable shocks. The effect was attributed to release of opioid peptides by chromaffin cells as it was reversed by naloxone. The viability of the transplanted tissue was verified by electron microscopy.