Effects of Early Bisphenol A Exposure on Cortical Excitatory and Inhibitory Balance and Behaviour in Mice

Abstract

Exposure to endocrine-disrupting chemicals such as 4-[2-(4-hydroxyphenyl)propan-2-yl]phenol (BPA) during development has been linked to altered neurodevelopment and increased risk for autism spectrum disorder (ASD) (1-5). During pregnancy, BPA exposure occurs through ingestion of contaminated food or beverages from polycarbonate plastics and epoxy resin-lined containers, allowing it to enter maternal circulation and cross the placenta (6-7). A proposed neurobiological mechanism underlying ASD involves disruption of cortical excitatory/inhibitory (E/I) synaptic balance, critical for neural network function and behavioural regulation (3, 8-12). However, it remains unclear whether combined prenatal and early postnatal BPA exposure alters cortical E/I organization in a dose-dependent and sex-specific manner. This study will investigate how early-life BPA exposure influences cortical synaptic markers and ASD-relevant behaviours in C57BL/6J mice. Eighteen pregnant dams (n = 6 per group) will be randomly assigned to control (water), low-dose BPA, or high-dose BPA groups. Through oral gavage, BPA will be administered from gestational day 0 through postnatal day 21 (PND21), targeting a critical window of synaptogenesis. This study will include only full-term offspring. BPA doses will model environmentally relevant human exposure (13-15). The experiment will divide offspring into molecular and behavioural cohorts. Molecular analyses will quantify excitatory (VGLUT1, PSD-95) and inhibitory (GAD67) synaptic markers using immunohistochemistry and western blotting to calculate cortical E/I ratios at PND21. Adolescent offspring will undergo behavioural testing between PND35 and PND60, including the three-chamber social interaction and open-field tests to assess sociability and anxiety-related behaviours. The study expects to determine that early-life BPA exposure produces dose-dependent and sex-specific alterations in cortical E/I balance accompanied by ASD-relevant behavioural changes (1, 3, 16-21). By integrating molecular and behavioural outcomes, this study will clarify whether early-life BPA exposure disrupts cortical E/I balance, a neurobiological feature implicated in ASD. This link would strengthen mechanistic evidence that environmental chemicals influence neurodevelopment and guide public health strategies to reduce exposure during critical developmental periods