Perinatal morphine exposure leads to sex-dependent executive function deficits and microglial changes in mice

Abstract

Children exposed prenatally to opioids are at an increased risk for behavioral problems and executive function deficits. The prefrontal cortex (PFC) and amygdala (AMG) regulate executive function and social behavior and are sensitive to opioids prenatally. Opioids can bind to toll-like receptor 4 (TLR4) to activate microglia, which may be developmentally important for synaptic pruning. Therefore, we tested the effects of perinatal morphine exposure on executive function and social behavior in male and female mouse offspring, along with microglial and synaptic-related outcomes. Dams were injected once daily s.c. with saline (SAL, n = 8) or morphine (MO, 10 mg/kg, n = 12) throughout pre-gestation, gestation, and lactation until offspring were weaned on postnatal day (P)21. Male MO offspring had impairments in attention and accuracy in the 5-choice serial reaction time task (5CSRTT), while female MO offspring were less affected. Targeted gene expression analysis at P21 in the PFC identified alterations in microglial and TLR4 related genes, while immunohistochemical analysis in adult brains indicated decreased microglial Iba1 and phagocytic CD68 protein in the PFC and AMG in males but females had an increase. Further, both male and female MO offspring had increased social preference. Overall, these data demonstrate male vulnerability to executive function deficits in response to perinatal opioid exposure and evidence for disruptions in neuron-microglial signaling.

SIGNIFICANCE STATEMENT

This study demonstrates (1) construct validity for a mouse model of perinatal morphine exposure that results in executive function deficits and (2) evidence in support of alterations in neuron-microglial signaling that may underlie these behavioral deficits. The importance of this work is emphasized by the continually worsening opioid epidemic and the challenges of studying long-term behavioral health of exposed children. Our study found that male morphine-exposed offspring had delayed learning and reduced motivation in basic cognitive tasks, followed by executive function deficits in attention and accuracy. Females instead had an increase in impulsivity, but both sexes displayed heightened social preference. Transcriptional profiling identified altered neuron-microglial signaling as an important biological pathway affected by perinatal morphine.