It has been suggested that the
opioid dynorphin, an endogenous agonist for kappa-
opiate receptors, contributes to secondary tissue damage after
spinal cord injury. To evaluate this hypothesis further, effects of intrathecally administered
dynorphin (Dyn) A-(1-17),
dynorphin antiserum, or the kappa-selective
opiate antagonist
nor-binaltorphimine (
nor-BNI) were studied in rats subjected to standardized impact
trauma to the thoracic spinal cord. Effects of intrathecal Dyn A-(1-17) were also compared to those of Dyn A-(2-17), which is inactive at
opiate receptors, in uninjured and injured animals. Both Dyn A-(1-17) and Dyn A-(2-17) produced motor dysfunction in uninjured rats, but Dyn A-(1-17) was approximately 2.5 times more potent. At lower doses of Dyn A-(1-17),
paraparesis was markedly attenuated by
nor-BNI;
nor-BNI was less effective at higher doses of Dyn A-(1-17) and did not modify the motor dysfunction produced by Dyn A-(2-17). Treatment with
dynorphin antiserum significantly improved outcome after
trauma as compared to control treatment with normal rabbit serum or
leucine-enkephalin antiserum. Dyn A-(1-17), but not Dyn A-(2-17) at similar doses, exacerbated neurological dysfunction after
spinal cord injury. Pretreatment with
nor-BNI attenuated neurological dysfunction after traumatic
spinal cord injury to a similar degree in rats administered saline or Dyn A-(1-17). These observations support the hypothesis that
dynorphin contributes to certain pathophysiological changes after traumatic
spinal cord injury through both
opiate-receptor (
kappa-receptor)-mediated and nonopioid mechanisms.