ABSTRACT
Injection of Freund's complete adjuvant (FCA) into the plantar surface of the rat induces inflammatory responses with accompanying pain behaviors. Signs of pain behaviors observed in FCA-injected animals are reported to be similar to symptoms seen in patients with inflammatory pain. In the previous study, injection of FCA produced a significant mechanical allodynia over time. The role of substance-P and calcitonin gene-related peptide(CGRP) on allodynia induced by inflammation is still controversial. We investigated the change of spinal neuropeptides and nitric oxide (NO) in rats with inflammation induced by subcutaneous injection of FCA into hind paw. The results are: 1. The number of NADPH-diaphorase and substance P positive neurons increased at ipsilateral spinal ventral horn after FCA injection. No significant changes were found with L-NAME posttreatment. 2. Staining intensity of substance P-immunoreactive area increased at ipsilateral spinal dorsal horn after FCA injection. No significant changes were found with L-NAME posttreatment. 3. CGRP immunoreactivity changed in the same pattern with substance P in all group. The results suggest that spinal neuropeptide substance P and CGRP are involved in the mechanism of the development and maintenance of allodynia in a state of FCA-induced inflammaion. NO may be also involved in the regulation of the quantity of substance P and CGRP in spinal cord.