Early Life Injury Alters Spinal Astrocyte Development

Neonatal injury alters synaptic transmission in the spinal superficial dorsal horn (SDH), resulting in aberrant amplification of ascending nociceptive transmission. Astrocytes orchestrate synapse development and function across the CNS and play a critical role in the emergence and maintenance of persistent pain. However, little is currently known about the postnatal development of spinal astrocytes, nor about how the maturation of SDH astrocytes is impacted by early life injury. Here, we used a hindpaw incision model of postsurgical pain in postnatal day (P) 3 mice of both sexes to elucidate the effects of neonatal injury on the maturation of SDH astrocytes. Three-dimensional morphological analysis of individual astrocytes revealed that incision elicits age-dependent changes to astrocyte structure. At P4, spinal astrocytes in incised mice show increased size and complexity compared with naive controls. This is reversed at P10 and P24, as astrocytes from incised mice are smaller and less ramified compared with their naive counterparts. Transcriptomic analysis of spinal astrocytes revealed acute changes to gene expression after neonatal injury, as 76 differentially expressed genes (DEGs) were identified at P4 (such as Thbs1, Efemp1, Acta1, Acta2, Tpm2, and Fgf14), which included genes related to cell motility and cytoskeletal organization, but very few DEGs were detected at P10 and P24. Lastly, we identified that microglial engulfment of astrocyte material occurs in the developing dorsal horn and this process is altered by neonatal incision in a sex-dependent manner. These data illustrate, for the first time, that neonatal injury alters the postnatal development of spinal astrocytes.