Large-Scale In Vivo Electrophysiology and Dimensionality-Reduction Analysis Reveal Opposing Thalamic and Hippocampal Excitability After Third-Trimester-Equivalent Alcohol Exposure in Mice

Abstract

Acute, binge-like alcohol exposure during the third-trimester-equivalent period (TTAE) produces apoptotic neurodegeneration in brain regions critical for spatial learning and memory, including the anterior thalamic nuclei (ATN), which are necessary for contextual learning and memory. To investigate the neural mechanisms underlying spatial cognition deficits following developmental alcohol exposure, we performed high-density electrophysiological recordings in and around the ATN of behaving mice, sampling 7,490 neurons across multiple, predominantly thalamic depths. To model acute binge-like TTAE, C57BL/6J mice received two injections of 2.5 g/kg ethanol (or saline) on postnatal day (PND) 7. In young adulthood (>PND 60), mice were implanted with silicon or multi-wire electrode arrays and allowed to explore a circular arena (40 cm diameter) under dim red light with two wall-mounted LED cues that rotated pseudo-randomly. Spike timing and waveform features were extracted from each putative single unit. Across the recorded population, firing rates were generally reduced following TTAE, although responses were heterogeneous. To characterize this variability, neuronal features were embedded using uniform manifold approximation and projection (UMAP). Logistic regression classified saline- and TTAE-exposed neurons based on electrophysiological properties and UMAP coordinates, achieving 80% accuracy. Cluster-based comparisons showed weak correspondence between physiological similarity and treatment response, suggesting TTAE effects are driven primarily by anatomical location. This study presents the first large-scale in vivo electrophysiological recordings in a freely behaving mouse model of fetal alcohol spectrum disorders, revealing divergent circuit adaptations marked by hippocampal hyperexcitability and thalamic dysfunction.