Involvement of capsaicin sensitive primary afferents in thymulin-induced hyperalgesia.

Intraplantar (5 ng) or intraperitoneal (50 ng) injections of thymulin, produced both thermal and mechanical hyperalgesia in rats. In this report, we show that ablation of capsaicin sensitive primary afferents (CSPA) can alter or abolish thymulin-induced hyperalgesia. Different groups of rats were subjected to either treatment with capsaicin or to surgical subdiaphragmatic vagotomy (SDV). Both capsaicin and SDV reduced significantly thymulin-induced hyperalgesia. On the other hand, these treatments elicited differential effects on the modulation by thymulin of the levels of nerve growth factor and interleukin 1beta. We conclude that the hyperalgesic effects of i.p. thymulin are mainly mediated through the CSPA fibers.