Alterations in excitatory and inhibitory synaptic development within the mesolimbic dopamine pathway in a mouse model of prenatal drug exposure

Abstract

The rise in rates of opioid abuse in recent years has led to an increase in the incidence of neonatal abstinence syndrome (NAS). Despite having a greater understanding of NAS and its symptoms, there still remains a lack of information surrounding the long-term effects of prenatal exposure to drugs of abuse on neurological development. One potential outcome of prenatal drug exposure that has been increasingly explored is disruption in normal synaptogenesis within the central nervous system. Both opioids and gabapentin, an antiepileptic drug commonly co-abused by opioid abuse disorder patients, have been shown to interfere with the normal functioning of astrocytes, non-neuronal glial cells known to serve many functions, including regulation of synaptic development. The goal of this study was to investigate the effects of prenatal drug exposure on synaptogenesis within brain regions associated with the mesolimbic dopamine pathway, the primary reward pathway within the brain associated with drug abuse and addiction, in a pregnant mouse model. Immunohistochemistry (IHC) and confocal fluorescence microscopy imaging studies on the brains of postnatal day 21 (P21) mouse pups revealed a significant increase in the mean number of excitatory synapses within the anterior cingulate cortex (ACC), nucleus accumbens (NAc), and prefrontal cortex (PFC) in mice that were prenatally exposed to either the opioid drug buprenorphine or gabapentin. These studies also revealed a significant decrease in the mean number of inhibitory synapses within the NAc and PFC of mice treated with buprenorphine. This observed net increase in excitatory signaling capability within the developing mesolimbic dopamine pathway suggests that exposure to drugs of abuse in utero can trigger maladaptive neuronal connectivity that persists beyond the earliest stages of life.