Sexually dimorphic developmental changes in rat spinal cord pain pathways following neonatal inflammation.

Early-life inflammation has a long-lasting impact on pain behaviors, with neonatal inflammation resulting in altered pain behaviors throughout life. Possible mechanisms underlying these changes lie within the first and second order neurons in the pain neuroaxis. We investigated neuroinflammatory markers in dorsal root ganglia (DRGs) and spinal cords (SC) of Wistar rats (both sexes) following neonatal injection with either LPS or saline (postnatal days (P) 3 and 5) and isolated tissues in early postnatal development. RT-qPCR revealed acute neuroinflammation in the DRGs, with expression levels of four inflammatory mediators elevated at P7, two at P13, and none at P21 in LPS-treated rats. In contrast, the SC showed no change in inflammatory mediators at P7, elevation of two at P13 and four at P21 in LPS-treated rats. These differences were greater in female SCs, indicating sex-specific modulation even at these early stages of postnatal development. The SCs of P21 LPS-treated rats also showed sex-specific modulation of astrocytes (GFAP), with females showing an increase and males a decrease in GFAP. Together, these data indicate that during early postnatal development DRG neurons are more susceptible to acute inflammation whereas inflammation is delayed in the SC, with sex-specific modulation occurring only in the SC.