痛覚過敏における脊髄後角 N 型 Ca チャネルおよびプロテインキナーゼ C の役割

Abstract

Hyperalgesia following peripheral nociception may be mediated by up-regulated synaptic transmission of spinal cord. N-type Ca channel, which is ω-Conotoxin (ω-CgTx) sensitive, and the protein kinase C (PKC) localized at presynaptic terminal are possibly concerned in pain modulation. However, role of these synaptic regulation exerted by concurrent amino acids release and pain response is not fully understood. The purpose of the present study was to investigate whether manipulation by inhibitors for PKC and N-type Ca channel modulate similar pain-related response in relation to CSF amino acids following formalin-induced nociception in rats. In addition, we compared characteristics with morphine well-known as a potent pre-and post synaptic inhibitor in modulating hyperalgesia. Three days after intrathecal implantation of PE-10 catheter along with loop - type microdialysis probe in male Sprague-Dawley rats, 50 μl of 5% formalin was subcutaneously injected into left hind paw. Thereafter, simultaneous determinations of microdialysis at 10 min. -intervals for glutamate by HPLC-ECD and observation of flinches were performed for 60 min after intrathecal administration of either drugs (saline for control, the N-type Ca channel blocker ω-CgTx, the PKC inhibitor staurosporine (STU), STU combined with the PKC activator PDBu, the opioid receptor agonist morphine). Biphasic increases of flinches after injection of formalin were observed ; phase 1 (max. 13 flinches/min. at 1 min.) and phase 2 (max. 22 flinches/min. at 30-45 min.). ω-CgTx attenuated flinches during both phase 1 and 2 periods. STU attenuated flinches during phase 2 period and this inhibition was reversed by combined use of PDBu. CSF glutamate in saline group was transiently increased by 149±12% during first 10 min but this increase of glutamate was supressed by ω-CgTx and STU. With morphine, both increased CSF glutamate release and biphase of finchings after formalin injection were completely supressed. The present results clearly demonstrated that ω-CgTx inhibits the both phases of flinchings as shown with morphine, associated with supressed glutamate release, suggesting Ntype Ca channel may regulate neurotransmitter release evoked by C fiber activation. In contrast, the significant inhibition of second phase of flinches (hyperalgesia) with supression of glutamate release by PKC inhibitor, staurosporine, was reversed by combined use of PKC activator, suggesting possible contribution in developing hyperalgesia through the mechanism that PKC evokes both pre synaptic neurotransmitter release and activation of NMDA receptor at post synaptic event.