AIMTo determine the involvement of NO signal pathway in the development of hyperalgesia induced by activation of protein kinase C (PKC ), nociceptive responses and nitric oxide synthase(NOS) expression and nitric oxide (NO) content in the spinal cord were observed after administration of Phorbol 12-Myristate-Acetate (PMA), a PKC agonist, in rats.

METHODSNociceptive response was observed by behavioral approach. Pain threshold was assayed using thermal tail-flick test. NADPH-d histochemistry was used to investigate the changes of NOS expression. Nitrate/nitrite (NO3-/NO2-) was assayed to represent NO content of lumbar enlargement of spinal cord.

RESULTSNociceptive response was induced and pain threshold decreased after intrathecal injection of PMA. The number of NADPH-d positive cells increased significantly in the superficial layer of the spinal cord dorsal horn (Laminae I - II ) and the grey matter surrounding the central canal (Laminae X), and the reactive degree of NADPH-d positive soma and processes and NO content of the lumbar enlargement of the spinal cord increased significantly after intrathecal injection of PMA. Pretreatment of PKC inhibitor chelerythrine chloride blocked the changes induced by PMA.

CONCLUSIONThe activation of PKC in the spinal cord neurons might induce spontaneous nociceptive responses and hyperalgesia in rats, as well as promote NOS expression and NO production, suggesting that increase in NO production is one of mechanisms of hyperalgesia induced by activation of PKC.