Prenatal methadone exposure leads to disruptions in adult-born dentate granule cell survival and female persistent fear responding

Abstract

Methadone is used for the treatment of opioid use disorder, including in pregnant patients. Research has established several consequences of prenatal opioid misuse, however little work has investigated the effects of prenatal methadone exposure (PME) on the offspring long-term, despite the continued prescription to pregnant individuals. The current study aimed to identify the long-term cognitive impairments arising from PME and assess hippocampal neurogenesis in these adult offspring. Pregnant Sprague Dawley rats were injected with methadone or sterile water twice daily from gestational day 3–20 or were left undisturbed as naïve controls. Adult offspring were tested in one of three behavioral tasks to assess pattern separation, spatial learning and memory, and contextual learning and memory, or were assigned to hippocampal tissue collection. For assessment of neurogenesis, offspring underwent injections of bromodeoxyuridine, and brains were collected at 24 h, 2wks, or 4wks for immunofluorescent staining. Methadone-exposed females, but not males, showed subtle impairments in pattern separation and heightened freezing during the extinction period in the fear conditioning task, and spatial memory in both sexes remained unaffected. Additionally, PME did not alter the rate of dentate granule cell proliferation but did significantly reduce the number of adult-born neuron surviving to a mature phenotype in the PME females at the 4wk timepoint. This work adds to the understanding of PME on offspring long-term and demonstrates female-specific sensitivity to these consequences. Future work is needed to fully investigate the neural disruptions arising from PME, with the goal of better supporting exposed individuals long-term.