In utero exposure to morphine leads to sex-specific behavioral alterations that persist into adulthood in cross-fostered mice
Authors: Fleites Vanessa C. , Markwalter Patrick S. , Johnson Keenan , De Biasi Mariella 
Published: March 2022

Introduction

The opioid epidemic has seen an increase in drug use among women of reproductive age. It is well established that Opioid Use Disorder (OUD) can have many negative consequences for the health of mothers and their babies, both during pregnancy and after delivery, but our understanding of the impact of fetal opioid exposure on behavior during adolescence and adulthood is less understood. Preclinical studies have unveiled some of the long-term effects of in utero morphine exposure primarily using injections as the route of drug delivery. Our study utilized a model for oral, voluntary morphine self-administration to investigate neonate, adolescent, and adult offspring’s behavioral phenotypes and subsequent ethanol misuse liability.

Methods

We first validated a paradigm for maternal oral intake of morphine, where female mice became morphine dependent pre-pregnancy, and continued to voluntarily consume morphine in the continuous two-bottle choice (C2BC) paradigm during pregnancy and up to offspring postnatal day 7 (PND 7). Offspring were cross-fostered to a drug-naïve dam at PND 7, to model first and second trimester in utero exposure in humans and to mimic the stress associated with NOWS. Bodyweight and ultrasonic vocalizations were assessed to determine alterations in the neonates. Offspring from control and morphine-exposed dams were then tested during adolescence and adulthood in a battery of behavioral tests to assess baseline behavioral phenotypes. We also computed a global behavioral score (GBS) to integrate offspring’s multiple behavioral outcomes into a composite score that could be used to identify potential vulnerable and resilient populations in offspring exposed prenatally to morphine. Offspring that were tested during adolescence were also evaluated during adulthood in the ethanol intermittent 2BC to assess ethanol misuse risk.

Results

Using an oral maternal morphine C2BC protocol, we demonstrated that morphine dams display signs of dependence, measured by somatic signs during withdrawal, and voluntarily drink morphine throughout gestation. Neonate cross-fostered offspring display changes in spontaneous activity, body weight, and ultrasonic vocalization parameters. During adolescence, offspring display both increased baseline anxiety-like/compulsive-like behavior, while in adulthood they display increased anxiety-like behavior. No changes were found for baseline physical signs, locomotion, and depressive-like behavior during adolescence or adulthood. In addition, a greater percentage of adult male offspring exposed to maternal morphine fell into moderate and high GBS classifications, signaling a more severe behavioral phenotype, compared to male control offspring. These effects were not observed in adult female offspring exposed to morphine in utero. Additionally, male adult offspring exposed to maternal morphine reduced their 2-hour ethanol intake in the intermittent two-bottle choice (I2BC) paradigm, although no changes in 24-hour ethanol intake and preference were found. No changes were observed in female offspring of morphine-exposed dams.

Conclusion

Overall, maternal morphine exposure leads to sex-specific changes in neonate, adolescent, and adult behavior, including ethanol intake.