These results suggest that the antiallodynic effect of Neurotropin is mediated via activation of descending pain inhibitory systems, such as the noradrenergic and serotonergic systems, which project from supraspinal sites to the spinal dorsal horn. In addition, activation of inhibitory GABAergic interneurons via 5-HT(3) receptors by serotonin released in the spinal dorsal horn may also be involved in the antiallodynic action of Neurotropin.

Abstract. Neurotropin ® , a non-protein extract from the inflamed skin of rabbits inoculated with vaccinia virus, has been clinically used as an analgesic drug for treatment of chronic pain. In this study, we investigated the analgesic mechanisms of Neurotropin in the adjuvant-induced arthritic rat, a chronic pain model with inflammation. Neurotropin caused dose-dependent inhibition of hyperalgesia in the adjuvant-induced arthritic rat after single intravenous (10 -100 NU / kg) and oral (30 -200 NU / kg) administration. The analgesic effect of Neurotropin (intravenous 100 NU / kg and oral 200 NU/ kg) was significantly inhibited by intrathecal injections of the a 2 -adrenoceptor antagonist yohimbine (30 nmol / animal) and the selective 5-HT 3 serotonin receptor antagonist MDL72222 (30 nmol / animal), and slightly inhibited by the non-selective serotonin receptor antagonist methysergide (100 nmol / animal). The results suggest that the analgesic action of Neurotropin is at least in part due to the enhancement of noradrenergic and serotonergic descending pain inhibitory pathways. Neurotropin may be useful for the clinical management of chronic pain diseases such as a rheumatoid arthritis and osteoarthritis.

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