Up-regulation of P2X7 Receptors Contributes to Spinal Microglial Activation and the Development of Pain Induced by BmK-I.

Previous work has demonstrated that the sensitization of spinal neurons and microglia is important in the development of pain behaviors induced by BmK I, a Na+ channel activator and a major peptide component of the venom of the scorpion Buthus martensi Karsch (BmK). We found that the expression of P2X7 receptors (P2X7Rs) was up-regulated in the ipsilateral spinal dorsal horn after BmK I injection in rats. P2X7R was selectively localized in microglia but not astrocytes or neurons. Similarly, interleukin 1β (IL-1β) was selectively up-regulated in microglia in the spinal dorsal horn after BmK I injection. Intrathecal injection of P2X7R antagonists largely reduced BmK I-induced spontaneous and evoked pain behaviors, and the up-regulation of P2X7R and IL-1β in the spinal cord. These data suggested that the up-regulation of P2X7Rs mediates microglial activation in the spinal dorsal horn, and therefore contributes to the development of BmK I-induced pain.