At present, effective
drug for treatment of
neuropathic pain is still lacking. Recent studies have shown that the
ligands of translocator
protein (TSPO, 18 kDa), a peripheral receptor for
benzodiazepine, modulate inflammatory
pain. Here, we report that TSPO was upregulated in astrocytes and microglia in the ipsilateral spinal dorsal horn of rats following L5 spinal nerve
ligation (L5 SNL), lasting until the vanishing of the behavioral signs of
neuropathic pain (∼50 d). Importantly, a single
intrathecal injection of specific TSPO agonists
Ro5-4864 or
FGIN-1-27 at 7 and 21 d after L5 SNL depressed the established
mechanical allodynia and
thermal hyperalgesia dramatically, and the effect was abolished by pretreatment with AMG, a
neurosteroid synthesis inhibitor. Mechanically,
Ro5-4864 substantially inhibited spinal astrocytes but not microglia, and reduced the production of
tumor necrosis factor-α (TNF-α) in vivo and in vitro. The anti-neuroinflammatory effect was also prevented by AMG. Interestingly, TSPO expression returned to control levels or decreased substantially, when
neuropathic pain healed naturally or was reversed by
Ro5-4864, suggesting that the role of TSPO upregulation might be to promote recovery from the
neurological disorder. Finally, the
neuropathic pain and the upregulation of TSPO by L5 SNL were prevented by pharmacological blockage of
Toll-like receptor 4 (TLR4). These data suggested that TSPO might be a novel therapeutic target for the treatment of
neuropathic pain.