Sex differences in late behavioral response to subcutaneous formalin injection in mice

We investigated sex- or gender-dependent differences in nociception using the formalin test in mice. In addition to typical biphasic responses, a new, late phase (Phase 3) was observed. A local anesthetic QX-314 injected at the end of Phase 2 blocked Phase 3. Phase 3 in female mice was significantly greater than that in male mice regardless the stage of the estrus cycle.