Glia Dose not Participate in Antinociceptive Effects of Gabapentin in Rats with Trigeminal Neuropathic Pain

ABSTRACT

Previous clinical studies have demonstrated that gabapentin, a drug that binds to the voltage-gated calcium channel alpha2delta1 subunit proteins, is effective in the management of neuropathic pain, but there is limited evidence that addresses the participation of glial cells in the anti-allodynic effects of this drug. The present study investigated the participation of glial cells in the anti-nociceptive effects of gabapentin in rats with trigeminal neuropathic pain produced by mal-positioned dental implants. Under anesthesia, the left mandibular second molar was extracted and replaced by a miniature dental implant to induce injury to the inferior alveolar nerve. Mal-positioned dental implants significantly decreased the air-puff thresholds both ipsilateral and contralateral to the injury site. Gabapentin was administered intracisternally beginning on postoperative day (POD) 1 or on POD 7 for three days. Early or late treatment with 0.3, 3, or 30 microg of gabapentin produced significant anti-allodynic effect in the rats with mal-positioned dental implants. On POD 9, in the mal-positioned dental implants group, OX-42, a microglia marker, and GFAP, an astrocyte marker, were found to be up-regulated in the medullary dorsal horn, compared with the naive group. However, the intracisternal administration of gabapentin (30 microg) failed to reduce the number of activated microglia or astrocytes in the medullary dorsal horn. These findings suggest that gabapentin produces significant anti-nociceptive effects, which are not mediated by the inhibition of glial cell function in the medullary dorsal horn, in a rat model of trigeminal neuropathic pain.