Analysis of the proportion and neuronal activity of excitatory and inhibitory neurons in the rat dorsal spinal cord after peripheral nerve injury.

The dorsal spinal cord contains projection neurons that transmit somatosensory information to the brain and interneurons which then modulate neuronal activity of these projection neurons and/or other interneurons. Interneurons can be subdivided into two groups: excitatory and inhibitory neurons. While inhibitory interneurons are thought to play a crucial role in analgesia, it is unclear whether they are involved in neuropathic pain. In the present study, we aimed to assess the proportion and neuronal activity of excitatory/inhibitory neurons in the dorsal spinal cord using a neuropathic pain model in rats. Following partial sciatic nerve ligation (PSNL), rats showed significant mechanical hyperalgesia, and subsequent immunohistochemical studies were conducted in laminae I-III of the dorsal spinal cord. We found that the number of FosB-immunoreactive cells was significantly higher; there was no change in the percentage of Pax2 positive/negative neurons in NeuN positive neurons; Pax2 negative neurons, but not Pax2 positive neurons, were predominantly activated in PSNL rats; and the immunofluorescence intensity of the calcium channel α2δ1 subunit was significantly higher. These results indicate that while peripheral nerve injury might not affect the proportion of excitatory and inhibitory neurons, it predominantly activates excitatory neurons in laminae I-III of the rat dorsal spinal cord.