Unilateral hindpaw inflammation produces a bilateral increase in NADPH-diaphorase histochemical staining in the rat lumbar spinal cord.

Tissue injury results in several changes in spinal cord neurons that contribute to hyperalgesia arising from the injured tissue. In models of unilateral hindpaw inflammation, changes in the neurochemistry and electrophysiology of dorsal horn neurons ipsilateral, and to a much lesser extent contralateral, to the inflamed paw have been reported. For example, the excitability of dorsal horn neurons increases, receptive field size increases, and the content of various proteins and neuropeptides in the dorsal horn (e.g. FOS, dynorphin, enkephalin) are affected following peripheral inflammatory insult. These changes are typically interpreted on the basis of their relevance to nociception.