Fractalkine and minocycline alter neuronal activity in the spinal cord dorsal horn

Fractalkine (FKN) evokes nociceptive behavior in naı¨ve rats, whereas minocycline attenuates pain acutely after neuronal injury. We show that, in naı¨ve rats, FKN causes hyperresponsiveness of lumbar wide dynamic range neurons to brush, pressure and pinch applied to the hindpaw. One day after spinal nerve ligation (SNL), minocycline attenuates after-discharge and responses to brush and pressure. In contrast, minocycline does not alter evoked neuronal responses 10 days after SNL or sciatic constriction, but increases spontaneous discharge. We speculate that microglia rapidly alter sensory neuronal activity in naı¨ve and neuropathic rats acutely, but not chronically, after injury.