Dynorphin A-(1-17) induces alterations in free fatty acids, excitatory amino acids, and motor function through an opiate-receptor-mediated mechanism

The endogenous opioid dynorphin A-(1-17) (Dyn A) has been implicated as a mediator of tissue damage after traumatic spinal cord injury (TSCI) and causes hindlimb paralysis when administered intrathecally. Motor impairment following intrathecal Dyn A is attenuated by antagonists of excitatory amino acids (EAAs); whether opioid receptors mediate such injury has been questioned. TSCI causes various biochemical changes associated with secondary tissue damage, including alterations in tissue amio acids, phospholipids, and fatty acids. Such changes reflect injury severity and correlate with motor dysfunction. The present studies examined whether dynorphin administration causes similar biochemical alterations and whether effects of Dyn A can be modified by treatment with opioid-receptor antagonists. At 24 hr after intrathecal Dyn A, there were significant declines in tissue levels of glutamate, aspartate, and glycine. Increases in total free fatty acids were found at 2 and 24 hr, reflecting changes in both saturated and unsaturated components, which were associated with significant decreases in tissue cholesterol and phospholipid phosphorus at the earlier time point. Each of these neurochemical changes, as well as corresponding motor deficits, were limited by pretreatment with the opioid antagonist nalmefene. In separate experiments, both nalmefene and the selective kappa-opioid antagonist nor-binaltorphimine (nor-BNI) limited dynorphin- induced motor dysfunction; effects of nor-BNI were dose related, and those of nalmefene were stereospecific. Therefore, behavioral and neurochemical consequences of Dyn A administration are mediated in part through opiate receptors, most likely kappa-receptors.(ABSTRACT TRUNCATED AT 250 WORDS)