Morphological characterization of dorsal horn spinal neurons in rats with unilateral constriction nerve injury: A preliminary study

A new animal model of neuropathic pain utilizing loose ligation of a peripheral nerve has been previously reported. In addition to displaying abnormal pain symptoms such as allodynia and hyperalgesia, physiologic and morphologic changes are seen in spinal cord dorsal horn neurons. Two weeks after ligation of the right common sciatic nerve, rat dorsal horn spinal cord neurons with signs of transsynaptic changes (dark neurons) were found on the side ipsilateral to the nerve injury. A few dark neurons were also found in the contralateral dorsal horn. The distribution of dark neurons in lumbar dorsal horn was limited to the superficial laminae (I-III). The following changes which suggest altered cellular activity were seen under the electron microscope. The nuclear envelope appeared ruffled while the mitochondria appeared normal. In addition, the dense cytoplasm was filled with rosettes of ribosomes as well as extensively developed rough endoplasmic reticulum and distended Golgi apparatus cisternae. While dark neurons had normal appearing somatic synapses, a few appeared atypical. The altered activity of these neurons may lead to abnormal sensory experiences and may be a consequence of central changes in response to persistent peripheral nerve injury. The purpose of the present study was to assess morphologic, hence functional, changes in spinal cord neurons in response to peripheral nerve constriction injury which evokes chronic pain-related behaviour.