Methadone (MTD) is a commonly prescribed treatment for opioid use disorder in pregnancy, despite limited information on the effects of passive exposure on fetal brain development. Animal studies suggest a link between perinatal MTD exposure and impaired white matter development. In this study, we characterized the effect of perinatal MTD exposure through the evaluation of oligodendrocyte development and glial cell activation in the neonatal rat brain. Six pregnant Sprague Dawley rat dams were randomized to MTD (0.2 mL/L) or untreated drinking water from embryonic day 7. Pups were terminated at postnatal day 7 and tissue sections were harvested from six randomly selected pups (one male and one female per litter) of each experimental group for immunohistochemistry in areas of corpus callosum (CC), lateral CC, external capsule (EC), and cerebellar white matter. In the MTD-exposed rat pups, myelination was significantly decreased in the CC, lateral CC, EC, and arbor vitae compared with the controls. The increased density and percentage of oligodendrocyte precursor cells (OPCs) were observed in the CC and cerebellar white matter. The highly active proliferation of OPCs as well as decreased density and percentage of differentiated oligodendrocytes were found in the cerebellum but no differences in the cerebrum. Apoptotic activities of both differentiated oligodendrocytes and myelinating oligodendrocytes were significantly increased in all regions of the cerebrum and cerebellum after MTD exposure. There was no quantitative difference in astrocyte, however, cell density and/or morphologic difference consistent with activation were observed in microglia throughout MTD-exposed CC and cerebellum. Taken together, perinatal MTD exposure reveals global attenuation of myelination, accelerated apoptosis of both differentiated and myelinating oligodendrocytes, and microglia activation, supporting an association between antenatal MTD exposure and impaired myelination in the developing brain.
Keywords: Oligodendrocyte; brain; methadone; microglia; myelination; neonatal abstinence syndrome; neonatal opioid withdrawal syndrome; opioid use disorder; perinatal opioid exposure.