Thymulin induces c-fos expression in the spinal cord of rats which is reversed by meloxicam and morphine

Intraplantar (i.pl.) injections of thymulin have been shown to produce hype ralgesia in rats through a prostaglandin E-2-dependent mechanism. This stud y aimed at investigating if such injections can produce sustained activatio n of spinal neurons by mapping the fos-like-immunoreactivity (FLI) as a mar ker for this activation. Our results showed that thymulin produces signific ant and sustained FLI in neurons located in spinal laminae known to be invo lved in nociception. Pretreatment with either morphine or meloxicam (a cycl ooxygenase inhibitor) revealed differential effects on FLI and the hyperalg esia induced by thymulin, These findings support the hypothesis that thymul in can affect central neurons either directly or through the peripheral ner ve terminals. (C) 1999 Elsevier Science B.V. All rights reserved.