Sex differences in behavioral and brainstem transcriptomic neuroadaptations following neonatal opioid exposure in outbred mice

Abstract

The opioid epidemic led to an increase in the number of Neonatal Opioid Withdrawal Syndrome (NOWS) cases in infants born to opioid-dependent mothers. Hallmark features of NOWS include weight loss, severe irritability, respiratory problems, and sleep fragmentation. Mouse models provide an opportunity to identify brain mechanisms that contribute to NOWS. Neonatal outbred Swiss Webster Cartworth Farms White (CFW) mice were administered morphine (15mg/kg, s.c.) twice daily for postnatal days (P) 1-14, an approximate of the third trimester of human gestation. Male and female mice underwent behavioral testing on P7 and P14 to determine the impact of opioid exposure on anxiety and pain sensitivity. Ultrasonic vocalizations (USVs) and daily body weights were also recorded. Brainstems containing pons and medulla were collected during morphine withdrawal on P14 for RNA-sequencing. Morphine induced weight loss from P2-14, which persisted during adolescence (P21) and adulthood (P50). USVs markedly increased at P7 in females, emerging earlier than males. On P7 and P14, both morphine exposed female and male mice displayed hyperalgesia on the hot plate and tail flick assays, with females having greater hyperalgesia than males. Morphine-exposed mice exhibited increased anxiety-like behavior in the open-field arena at P21. Transcriptome analysis of the brainstem (medulla plus pons), an area implicated in opioid withdrawal and NOWS, identified pathways enriched for noradrenergic signaling in females and males. We also found sex-specific pathways related to mitochondrial function and neurodevelopment in females and circadian entrainment in males. Sex-specific transcriptomic neuroadaptations implicate unique neurobiological mechanisms underlying NOWS-like behaviors.

In utero exposure to morphine leads to sex-specific behavioral alterations that persist into adulthood in cross-fostered mice

“…Similar to our results, one study found that offspring from oxycodone-exposed dams have higher frequency USVs than control offspring (Zanni et al, 2021). Another study also found that neonate offspring injected with morphine from PND 1 – 14 had increased USV frequency parameters (Borrelli et al, 2021). Various studies and reviews have focused on understanding vocalizations and changes in their acoustic parameters, including how upward shifts in frequency modulation is usually associated with an increase in infant distress (Brudzynski, 2015; Castellucci, Calbick, & McCormick, 2019; Esposito, Nakazawa, Venuti, & Bornstein, 2013; Hahn & Lavooy, 2005; Kromkhun et al, 2013; Lingle, Wyman, Kotrba, Teichroeb, & Romanow, 2012; Parga et al, 2020; Wasz-Höckert, Michelsson, & Lind, 1985).…”