Minocycline Attenuates the Development of Allodynia: An Immunohistochemical Study on CD11b, GFAP and c-Fos in the Spinal Dorsal Horn in SD Rat

ABSTRACT

BACKGROUND: Minocycline, a semisynthetic second-generation tetracycline, is an antibiotic that has excellent ability to penetration into the CNS via the brain-blood barrier. Minocycline has emerged as a potent inhibitor of microglial activation, and it is an effective neuroprotective agent in experimental brain ischemia. Glial cell activation and proliferation are known to be associated with neuropathic pain in the peripheral nerve injuries. METHODS: The fifty percent threshold of withdrawal responses was measured in the hindpaws of SD rats following tight ligation of left fifth lumbar spinal nerve. Rats were sacrificed at 1, 3, 5, and 7 days and at 0.5, 1, 2, and 4 h post ligation (n=5/group/time point). Immunohistochemistry for GFAP, CD11b and c-Fos was done on the spinal cord at the level of the fifth lumbar nerve. Minocycline (45 mg/kg) and normal saline (300-400 microL) were administered intraperitoneally, 1 day and 1 h before the operations, and every day postoperatively until the rats were sacrificed. RESULTS: Treatment with minocycline reduced allodynia and the expressions of CD11b at 5 days and c-Fos at 1 and 2 h post operation compared with the saline treatment (control). CONCLUSIONS: It was thought that minocycline reduced the allodynia induced by tight ligation of the fifth lumbar spinal nerve in rats through the inhibition of microglial activation and c-Fos expression.