Dynorphin A-induced rat hindlimb paralysis and spinal cord injury are not altered by the κ opioid antagonist nor-binaltorphimine

Abstract

The selective κ opioid receptor antagonist nor-binaltorphimine (nor-BNI) was used to distinguish a κ opioid component in the mechanisms underlying the hindlimb paralysis, ischemia, and neuronal injury induced in the rat by the κ opioid agonist dynorphin A. Spinal intrathecal (i.t.) injection of nor-BNI (20 nmol) either 15 min or immediately before i.t. injections of 5 or 20 nmol of dynorphin A failed to alter the dynorphin A-induced disruption of hindlimb motor function and nociceptive responsiveness. Nor-BNI also did not change the 3-fold increases in cerebrospinal fluid lactate concentrations produced by 20 nmol of dynorphin A. Neuroanatomical evaluations revealed that the cell loss, fiber degeneration, and central gray necrosis in lumbosacral spinal cords of rats treated with 20 nmol of dynorphin A were not altered by nor-BNI (20 nmol, i.t.). Thus, the spinal cord injury and associated neurological deficits resulting from i.t. injection of dynorphin A appear to be primarily, if not totally, attributable to its non-κ opioid action(s).