Sex-Dependent Glial Signaling in Pathological Pain:Distinct Roles of Spinal Microglia and Astrocytes

Increasing evidence suggests that spinal micro- glia regulate pathological pain in males. In this study, we investigated the effects of several microglial and astroglial modulators on inflammatory and neuropathic pain follow- ing intrathecal injection in male and female mice. These modulators were the microglial inhibitors minocycline and ZVEID （a caspase-6 inhibitor） and the astroglial inhibitors L-α-aminoadipate （L-AA, an astroglial toxin） and car- benoxolone （a connexin 43 inhibitor）, as well as U0126 （an ERK kinase inhibitor） and D-JNKI-1 （a c-Jun N-terminal kinase inhibitor）. We found that spinal administration of minocycline or ZVEID, or Caspase6 deletion, reduced formalin-induced inflammatory and nerve injury-induced neuropathic pain primarily in male mice. In contrast, intrathecal L-AA reduced neuropathic pain but not inflam- matory pain in both sexes. Intrathecal U0126 and D-JNKI- 1 reduced neuropathic pain in both sexes. Nerve injury caused spinal upregulation of the astroglial markers GFAP and Connexin 43 in both sexes. Collectively, our data confirmed male-dominant microglial signaling but also revealed sex-independent astroglial signaling in the spinal cord in inflammatory and neuropathic pain.