Third Trimester-Equivalent Alcohol Exposure Induces Sex-Dependent Alterations in Locomotor Activity, Anxiety-Risky Behaviors, and Enhances Mechanical Allodynia in Adulthood

ABSTRACT Prenatal alcohol exposure (PAE) causes fetal alcohol spectrum disorders (FASDs), which are neurodevelopmental conditions characterized by behavioral dysregulation, learning deficits, and cognitive inflexibilities. Alcohol exposure is harmful at all stages of human gestation, including the third trimester. This developmental window—characterized by rapid brain growth, myelination, and neural circuit formation—may be particularly vulnerable, yet the long-lasting behavioral and sensory consequences of exposure during this period remain poorly understood. In this study, neonatal mouse pups were exposed to ethanol (EtOH) or air vapor from postnatal day (P) 4 to P8, which is equivalent to a third-trimester alcohol exposure (TTAE) in humans. Blood ethanol concentrations measured at P8 reached approximately 250 mg/dL, consistent with binge-level exposure. Air- and EtOH-exposed mice were then assessed as adults at 5–6 months of age for locomotor activity, anxiety-related risky behaviors, recognition memory, and increased susceptibility to peripheral neuropathy, as indicated by sensitization to light touch following minor chronic constriction injury (mCCI) of the sciatic nerve. We found that TTAE was sufficient to produce long-lasting behavioral outcomes in a sex-dependent manner. Notably, EtOH-exposed males exhibited increased spontaneous locomotor activity and risky behavior, whereas EtOH-exposed females showed minimal or decreased changes compared to their respective controls. However, both EtOH-exposed male and female mice exhibited marked increases in light-touch sensitization, referred to as mechanical allodynia, following mCCI, a response absent in air-exposed controls. Together, these findings reveal that TTAE is highly detrimental to behavioral regulation and creates a vulnerability to developing neuropathic pain in adulthood.