Dynorphin induces partially reversible paraplegia in the rat.

Endogenous opioids have previously been implicated in the pathophysiology of spinal cord injury, but the specific opioid(s) involved has not been determined. Here we report that dynorphin administered intrathecally causes dose-related, partially reversible, hindlimb paralysis in the unanesthetized rat. Other opioids, including mu-selective and delta-selective synthetic enkephalins or beta-endorphin, failed to induce motor dysfunction. These findings suggest that dynorphin or dynorphin-related peptides may play a role in spinal cord injury.