Intrathecal dynorphin(1-13) results in an irreversible loss of the tail-flick reflex in rats

Brain Res. 1987 Dec 1;435(1-2):1-6. doi: 10.1016/0006-8993(87)91579-4.


Intrathecal injection of dynorphin produced a loss of the tail-flick reflex that lasted throughout the 14-day experimental period whereas, the inclined plane test of motor function and tail-shock vocalization recovered within an hour. An important aspect of the loss of the tail-flick reflex was that it was an all-or-none event. At any dose of tail-flick latency either remained unchanged when compared with pre-injection latencies or the latency was elevated to the cut off time of 14 s. The ED50's +/- S.E.M. for tail-flick, inclined plane and tail-shock vocalization were 65.4 +/- 5.0, 67.7 +/- 5.0 and 68.0 +/- 3.9 nmol respectively. Results from the hot-plate test revealed no statistical difference between saline and dynorphin injected animals one day following the injection. Animals injected with morphine sulphate s.c. lost the tail-flick reflex but completely recovered by 24 h. Histology of the spinal cord of animals treated with dynorphin 24 h prior to sacrifice revealed dead neurons primarily in the ventral horn with little or no damage in the dorsal horn. These data demonstrate that dynorphin(1-13) injected intrathecally results in a rather specific neurotoxic action in the spinal cord.

MeSH terms

  • Animals
  • Dynorphins / administration & dosage
  • Dynorphins / pharmacology*
  • Dynorphins / toxicity
  • Injections, Spinal
  • Male
  • Neurons / drug effects
  • Pain / physiopathology
  • Peptide Fragments / administration & dosage
  • Peptide Fragments / pharmacology*
  • Peptide Fragments / toxicity
  • Rats
  • Rats, Inbred Strains
  • Reflex / drug effects*
  • Spinal Cord / drug effects
  • Spinal Cord / pathology
  • Vocalization, Animal


  • Peptide Fragments
  • dynorphin (1-13)
  • Dynorphins