Effects of minocycline on Na ⁺ currents in rat dorsal root ganglion neurons

Minocycline is an inhibitor of microglial activation and proliferation. Minocycline suppresses pain-related behaviors in many different pain states, which correlates closely with its inhibition of microglial activation and subsequent release of pro-inflammatory mediators in the spinal cord. Na ⁺ channels in dorsal root ganglion (DRG) neurons are implicated in the generation of inflammatory and neuropathic pain. To elucidate a possible peripheral mechanism of minocycline analgesia, effects of minocycline on tetrodotoxin-sensitive and tetrodotoxin-resistant Na ⁺ currents in rat DRG neurons were investigated. Minocycline potently inhibited both types of Na ⁺ currents with IC ₅₀ values of 350 nM and 410 nM, respectively. The inhibition was accompanied by a depolarizing shift of the activation voltage. However, minocycline slowed the inactivation and speeded up the recovery from inactivation. These results suggest minocycline may exert analgesia peripherally thorough Na ⁺ channel inhibition in the primary afferent neurons as well as centrally through microglial inhibition in the spinal cord.