Disruption of circadian rhythms is associated with cognitive impairment during gestation

Disruption of circadian rhythms is increasingly recognized as a contributor to cognitive dysfunction, but its role in gestation-associated cognitive changes remains unexplored. Here we combine human cognitive screening with a comprehensive longitudinal mouse model to investigate whether gestational cognitive impairment and postpartum recovery are coupled with disruption and restoration of hippocampal circadian rhythms. Cognitive function was assessed in pregnant and postpartum women using the Montreal Cognitive Assessment (MoCA) and Mini-Mental State Examination (MMSE). In mice, four reproductive stages were compared: control, gestation, 1 month postpartum, and 3 months postpartum. Serum gonadotropins and sex hormones levels were quantified using ELISA. Home-cage locomotor activity was recorded over 48 h under a 12 h:12 h light-dark cycle. Hippocampal-dependent memory was evaluated using the novel object recognition test and Barnes maze at Zeitgeber times ZT6 (day) and ZT18 (night). Hippocampal amyloid β (Aβ) deposition was visualized via immunofluorescence; protein expression of amyloid precursor protein (APP), β-site amyloid precursor protein cleaving enzyme-1 (BACE1), and phosphorylated tau was measured by Western blots. Hippocampal clock gene expression was quantified by RT-qPCR at six time points; circadian parameters (mesor, amplitude, acrophase) were derived by cosinor analysis and compared between groups. Human cognitive screening confirmed modest gestational decline with postpartum recovery. In mice, gestation disrupted daily locomotor activity rhythms and reduced nocturnal preference; both partially recovered by 1 month and fully by 3 months postpartum. Behaviourally, pregnancy impaired the normal day-night difference and performance in novel object exploration and Barnes maze, which recovered progressively. At the molecular level, gestation increased hippocampal APP and BACE1 expression, elevated Aβ42 deposition, and induced tau hyperphosphorylation at multiple sites-hallmarks of Alzheimer's disease-related pathology. These alterations partially reversed by 1 month postpartum and normalized by 3 months. Hippocampal clock genes maintained 24 h rhythmicity, but gestation induced gene-specific phase shifts, amplitude reductions, and mesor alterations. These parameters showed gradual, gene-dependent normalization postpartum. Gestational cognitive impairment and postpartum recovery are associated with reversible disruption and restoration of both hippocampal circadian rhythms and Alzheimer's disease-related molecular pathology. These findings are correlational in nature and provide a foundation for future causal investigations.