Emerging evidence links environmental exposures and circadian dysregulation to autism spectrum disorder (ASD), yet whether circadian phase modulates vulnerability to developmental toxicants remains unclear. Here, we investigated whether embryonic bisphenol A (BPA) exposure induces circadian phase-dependent ASD-related behavioral alterations via disruption of nr1d1 rhythmicity in zebrafish. In control larvae, nr1d1 exhibited significant circadian oscillation, whereas BPA exposure reduced expression levels and dampened oscillation amplitude. Two-way ANOVA revealed significant treatment × phase interactions in nr1d1 expression. Pharmacological activation of Nr1d1 partially restored rhythmic expression. Behavioral assessments conducted at defined circadian phases demonstrated a significant treatment × phase interaction in social preference. BPA-exposed larvae exhibited reduced social preference selectively at circadian time 15 (CT15), corresponding to the trough phase of nr1d1 expression, whereas no differences were observed at circadian time 3 (CT3). In contrast, tactile hyper-responsiveness showed a significant treatment effect but no phase interaction. BPA exposure also induced phase-dependent alterations in ASD-related genes, including α-nrxn2a and β-nrxn3a, with significant treatment × phase interactions. At the molecular level, BPA increased reactive oxygen species, impaired antioxidant defense, enhanced neuroinflammatory responses, and disrupted excitatory–inhibitory balance. Several of these endpoints exhibited phase-dependent modulation and were partially attenuated by Nr1d1 activation. These findings indicate that circadian phase modulates embryonic susceptibility to BPA-induced ASD-related behavioral and molecular alterations. Disruption of nr1d1 rhythmicity may contribute to time-of-day-specific neurodevelopmental vulnerability following environmental exposure.
Wu et al. (2026) studied this question.