Effect of intrathecal administration of serotonin in chronic pain models in rats

The present study examined the effects of intrathecal (i.t.) administration of 5-hydroxytryptamine (5-HT; 0.1-100 mug) on mechanical hyperalgesia asso ciated with neuropathic pain (chronic constriction of the sciatic nerve mod el and diabetic model) and inflammatory pain (carrageenan and polyarthritic models) in rats. Results demonstrated that the hyperalgesia observed in th e mononeuropathic and diabetic rats was attenuated by 5-HT; the active dose , however, was 100- to 1000-fold higher than that required in normal rats, and was moderately effective. In the two experimental models of inflammator y pain, 5-HT was not markedly or similarly active. In the carrageenan model , 5-HT at the highest dose was only weakly effective whereas in the polyart hritic model it was inactive. Together, these results show that 5-HT has antinociceptive effects in sever al rat pain models, except in the model of diffuse pain (polyarthritic rats ). Its antinociceptive effects in these models, however, are slight and dif fer from those observed in normal rats. (C) 2000 Elsevier Science B.V. All rights reserved.