Inhibition of spinal protein kinase C blocks substance P-mediated hyperalgesia

Substance P (SP) is an important neuromediator in the spinal processing of nociceptive afferent information. Our previous study has shown that spinal (intrathecal, IT) application of SP produces thermal hyperalgesia that is mediated by activation of the G-protein coupled NK1 receptor. The activation of some classes of the G-protein coupled receptors is known to produce diacylglycerol with consequent activation of protein kinase C (PKC). In the present study, we have demonstrated that intrathecal administration of a selective PKC inhibitor GF109203X (GF, 0.73 nmol) in rats chronically implanted with intrathecal catheters 15 min prior to IT-SP (48 nmol) completely blocked the SP-induced thermal hyperalgesia. The effect of GF was dose-dependent (0.073-0.73 nmol). Bisindolymaleimide V, the inactive homolog of GF, had no effect. Pretreatment with GF 3 h, but not 24 h, prior to SP still produced antinociception. Moreover, intrathecal treatment with GF (0.73 nmol) attenuated the formalin paw injection-induced flinching, preferentially at the 2nd phase, that is known to be associated with the release of endogenous SP at the spinal cord. These data suggest that activation of spinal PKC is involved in the SP-mediated hyperalgesia. Thus, SP, which is released in the spinal cord subsequent to persistent stimulation of small sensory afferents after tissue injury, may contribute to spinal hyperexcitability and persistent pain by enhancement of PKC-mediated phosphorylation of target molecules such as NMDA receptors.