Perinatal opioid exposure leads to decreased social play in adolescent male and female rats: Potential role of oxytocin signaling in brain regions associated with social reward

Abstract

Over the last two decades, the number of infants exposed to opioids in utero has quadrupled in the United States, with some states reporting rates as high as 55 infants per 1000 births. Clinical studies report that children previously exposed to opioids during gestation show significant deficits in social behavior, including an inability to form friendships or other social relationships. To date, the neural mechanisms whereby developmental opioid exposure disrupts social behavior remain unknown. Using a novel paradigm of perinatal opioid administration, we tested the hypothesis that chronic opioid exposure during critical developmental periods would disrupt juvenile play. As oxytocin is a major regulator of sociability, the impact of perinatal morphine exposure on oxytocin peptide expression was also examined. Juvenile play was assessed in vehicle- or morphine-exposed male and female rats at P25, P35, and P45. Classical features of juvenile play were measured, including time spent engaged in social play, time not in contact, number of pins, and number of nape attacks. We report that morphine-exposed males and females spend less time engaged in play behavior than control males and females, with a corresponding increase in time spent alone. Morphine-exposed males and females also initiated fewer pins and nape attacks. Together, these data suggest that male and female rats exposed to morphine during critical developmental periods are less motivated to participate in social play, potentially due to alterations in oxytocin-mediated reward signaling.

Keywords: Juvenile play; Morphine; Neonatal opioid withdrawal syndrome; Social play.

Figure 1.

Schematic of the perinatal opioid exposure dosing paradigm. Created with Biorender.com.

Figure 2.

Perinatal opioid exposure does not lead to overt differences in litter characteristics or body weight. (A) Dams treated with morphine tend to weigh less later in pregnancy. Red arrow represents initiation of breeding. (B) Litter size was significantly reduced in morphine-treated dams. (C) No difference in sex balance between vehicle- and morphine-treated dams. (D) Male and female offspring exposed to morphine weigh less than vehicle-exposed offspring from P2-P10 but weigh more than vehicle-exposed offspring at weaning. E. No effect of perinatal opioid exposure on anogenital distance. N_{VEH M} = 36-43, N_{VEH F} = 23-35, N_{MOR M} = 16-20, N_{MOR F} = 9-19. Graphs represent mean ± SEM. * = significant at p < 0.05.

Figure 3.

Maternal morphine treatment leads to short-term differences in maternal behavior. Dams treated with morphine spent less time nursing (A), and more time grooming (B) when morphine was administered (P2 PM, P4 PM, and P6 PM; indicated by red arrows). N_VEH = 7, N_MOR = 4. Graphs represent mean ± SEM. Red arrows indicate timing of morphine dose.

Figure 4.

Adolescent weight (A) and nestlet shredding (B) do not differ between morphine- and vehicle-exposed male and female offspring. N_{VEH M} = 35, N_{VEH F} = 25, N_{MOR M} = 12, N_{MOR F} = 17. Graphs represent mean ± SEM.

Figure 5.

Morphine-exposed males and females show deficits in social behavior. (A) Morphine-exposed females play less than morphine-exposed males and vehicle-exposed male and females at P35 and P45 and (B) when averaged across all three ages. (C) Not-in-contact time was highest in morphine-exposed rats, regardless of sex and (D) when averaged across all three ages. (E) Vehicle-exposed males participate more in social exploration at P45, but there was no effect of treatment on average social exploration across all three ages (F). N_{VEH M} = 12 pairs, N_{VEH F} = 11 pairs, N_{MOR M} = 6 pairs, N_{MOR F} = 8 pairs. Graphs represent mean ± SEM. % represents change from sex-matched vehicle-exposed group.

Figure 6.

Morphine-exposed male and females display fewer characteristic features of social play. (A) Morphine-exposed females make the fewest nape attacks at P35 and P45 and (B) when averaged across all three ages. (C) Morphine-exposed males and females have significantly lower nape attack difference scores vs. vehicle-exposed males and females. (D) Morphine-exposed females make the fewest pins at P35 and P45 and (E) when averaged across all three ages. (F) Morphine-exposed males and females have significantly lower pin difference scores vs. vehicle-exposed males and females, particularly morphine-exposed females. Nape Attacks and Pins: N_{VEH M} = 24, N_{VEH F} = 22, N_{MOR M} =12, N_{MOR F} = 16. Difference Scores: N_{VEH M} = 11 pairs, N_{VEH F} = 8 pairs, N_{MOR M} = 6 pairs, N_{MOR F} = 6 pairs. Graphs represent mean ± SEM. % represents change from sex-matched vehicle-exposed group.

Figure 7.

Morphine-exposed rats show decreased oxytocin expression in the PVN and SON. (A) Representative images of OT staining in the PVN and SON. (B) OT+ cell counts were reduced in morphine-exposed rats in the PVN at P7, increased at P14, and comparable at P30. (C) Similar results were observed in the SON at P7, P14, and P30. N_VEH = 6-11, N_MOR = 6-14. (D) Cresyl violet staining in the hypothalamus of a subgroup of rats showed no differences in overall cell count. N_VEH = 3, N_MOR = 3. Graphs (panels B-C) represent median ± IQR and (panel D) represent mean ± SEM. *: significant (p<0.05) Sidak post hoc analysis.

Figure 8.

Model of proposed effect. Perinatal morphine exposure leads to decreased oxytocin expression in the PVN and SON in males and females. This suggests that perinatal morphine results in dysregulation of the oxytocin system during a critical period of social development, likely leading to long-term changes in juvenile play. Created with Biorender.com.