Morphine acts via mu-opioid receptors to enhance spinal regeneration and synaptic reconstruction of primary afferent fibers injured by sciatic nerve crush

Brain Res. 2007 Jan 26;1130(1):108-13. doi: 10.1016/j.brainres.2006.10.079. Epub 2006 Dec 13.


The present study investigated whether morphine can promote regeneration and synaptic reconstruction of the terminals of injured primary afferent fibers in lamina II of the spinal cord in rats following sciatic nerve injury. Fluoride-resistant acid phosphatase (FRAP)-positive terminals in lamina II of the L4 spinal segment after sciatic nerve injury were assessed after treatment with vehicle, morphine, and naloxone plus morphine. Under the electron microscope, types I and II complex terminals of unmyelinated afferent fibers from the dorsal root, simple terminals of interneuronal axons, and terminals of descending axons at lamina II of the L4 spinal segment were documented in the different groups after injury. FRAP-positive terminals in lamina II were depleted after sciatic nerve injury in the vehicle group. Treatment with morphine increased the numbers of FRAP-positive terminals, and this was prevented by naloxone. The present study demonstrates that morphine may promote the regeneration and synaptic reconstruction of the terminals of injured primary unmyelinated afferent fibers in lamina II of spinal cord, by a process mediated by mu-opioid receptors.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Acid Phosphatase / metabolism
  • Afferent Pathways / cytology
  • Afferent Pathways / drug effects*
  • Afferent Pathways / metabolism
  • Animals
  • Male
  • Morphine / metabolism*
  • Nerve Crush
  • Nerve Fibers, Unmyelinated / drug effects
  • Nerve Fibers, Unmyelinated / metabolism
  • Nerve Regeneration / drug effects*
  • Nerve Regeneration / physiology
  • Neuroprotective Agents / metabolism
  • Protein Kinases / metabolism
  • Rats
  • Rats, Sprague-Dawley
  • Receptors, Opioid, mu / metabolism*
  • Sciatic Nerve / cytology
  • Sciatic Nerve / injuries
  • Sciatic Nerve / physiology
  • Spinal Cord / cytology
  • Spinal Cord / metabolism
  • Synapses / drug effects
  • Synapses / physiology
  • Synapses / ultrastructure*
  • TOR Serine-Threonine Kinases


  • Neuroprotective Agents
  • Receptors, Opioid, mu
  • Morphine
  • Protein Kinases
  • TOR Serine-Threonine Kinases
  • Acid Phosphatase