Strychnine-enhanced transsynaptic degeneration of dorsal horn neurons in rats with an experimental painful peripheral neuropathy.

A painful peripheral neuropathy was produced by loosely tying constrictive ligatures around the sciatic nerve of rats. Eight days after the nerve injury and after a series of injections a subconvulsive dose of strychnine, the animals were sacrificed and the spinal cord dorsal horn was examined for signs of transsynaptic degeneration. The presence of strychnine-enhanced transsynaptic degeneration was apparent from the presence of many pyknotic and hyperchromatic neurons (dark neurons). The dark neurons were seen in laminae I-IV bilaterally, but they were significantly more frequent ipsilateral to the nerve injury. The majority of the dark neurons were found within the medial two-thirds of laminae I-II; this region corresponds to the intraspinal territory of the sciatic nerve's small diameter afferents. The results suggest that a peripheral nerve injury that produces neuropathic pain induces morphological alterations of intraspinal somatosensory circuitry.