Microglia ablation is sufficient to prevent spontaneous withdrawal following perinatal morphine exposure

Populations affected by the opioid epidemic include pregnant women and their offspring. Infants exposed to opioids in utero are at risk of developing Neonatal Opioid Withdrawal Syndrome (NOWS), a combination of acute somatic withdrawal symptoms. In adult rodents, there is evidence that opioid exposure and withdrawal alter microglia, but few studies have examined the effects of in utero exposure and neonatal withdrawal specifically on microglia. Using a mouse model of perinatal morphine exposure that encompasses the entirety of gestation and spans into the postnatal period, we measured microglial alterations during exposure and withdrawal in neonates. Microglia number was increased on postnatal day (PND)14 (during morphine exposure) and normalized by PND15 (during spontaneous withdrawal). To determine if microglia mediate withdrawal behaviors, mice were treated with PLX3397 from PND7-PND12 to deplete microglia during morphine exposure. These mice showed a reduction in somatic signs of withdrawal and thermal hyperalgesia, indicating that microglia may play a role in the production of physical withdrawal symptoms. Perinatal morphine exposure or PLX3397 treatment alone did not produce any persisting behavioral alterations, and the combination of both produced minimal effects in adults. To better understand the underlying molecular mechanisms associated with mediating withdrawal, we isolated microglia for RNA sequencing. The microglial transcriptome was markedly altered at PND14, with considerable normalization at PND15. Overall, these data suggest that microglia are implicated in the production of withdrawal symptoms induced by perinatal morphine exposure, and early-life microglial modulation has potential as a therapeutic target for treatment of these symptoms.