The Enduring Consequences of Prenatal Opioid Exposure

Abstract

The opioid crisis has resulted in an unprecedented number of neonates born with prenatal opioid exposure; however, the long-term effects of opioid exposure on offspring behavior and neurodevelopment remain relatively unknown. I developed a translational mouse model of prenatal methadone exposure (PME) that resembles the typical pattern of opioid use by pregnant women who first use oxycodone then switch to methadone maintenance pharmacotherapy, and subsequently become pregnant while maintained on methadone. PME produced substantial impairments in offspring growth, sensorimotor milestone acquisition, and activity in an open field. Furthermore, these behavioral alterations were associated with significant disruptions in the primary motor cortex (M1). Notably, layer 5 pyramidal neurons of the M1 displayed significantly increased voltage sag which is primarily mediated by HCN1 channels. Interestingly, the α2-adrenergic receptor, a known modulator of HCN1 channels, displayed significantly increased expression in the M1 of PME animals. The locomotor activity in an open field was significantly reduced following in vivo pharmacological activation of the α2-adrenergic receptor with clonidine in PME offspring suggesting this may be therapeutic target for the hyperactivity associated with prenatal exposure to opioids. Previous work has also described an association between prenatal opioid exposure and alterations in opioid reward-related behavior; however, the effect of PME on alcohol reward remains undetermined. Given the widespread accessibility and usage, alcohol represents the most likely addictive substance the growing population of opioid exposed neonates will encounter as they age. I discovered that PME disrupts conditioned preference for alcohol, enhances the locomotor stimulating effects of alcohol, and increases alcohol consumption in a sex-dependent manner. This alcohol-reward phenotype in PME offspring was associated with altered excitatory neurotransmission and disrupted cannabinoid-mediated long-term depression (CB-LTD) in the dorsolateral striatum, an important substrate involved in compulsive drug use. Further work is required to determine the specific inputs at which CB-LTD is disrupted and if restoring this form of plasticity in PME animals prevents the enhanced alcohol addiction phenotype.