Neuroprotective Effects of Fluoxetine on Molecular Markers of Circadian Rhythm, Cognitive Deficits, Oxidative Damage, and Biomarkers of Alzheimer's Disease-Like Pathology Induced under Chronic Constant Light Regime in Wistar Rats.

There is mounting evidence of circadian rhythm disruption in Alzheimer's disease (AD); however, the cause-and-effect relationship between them is not understood. Chronic constant light exposure effectively disrupts circadian rhythm in rats. On the basis of previous publications, we hypothesized that chronic constant light exposure might contribute significantly to development of AD-like-phenotype in rats and that fluoxetine (Flx) treatment might protect the brain against it. Adult male rats were exposed to normal light-dark cycles, constant light (LL), constant dark, and LL+Flx (5 mg/kg/day, ZT5) for four months. The expression of molecular markers of circadian rhythm: transcripts; and protein expression of peroxiredoxin-1 (PRX1) and hyperoxidized peroxiredoxins (PRX-SO) were significantly dysregulated in the suprachiasmatic nuclei (SCN) of LL rats, which was prevented with concomitant fluoxetine administration. The levels of glutamate and γ-aminobutyric acid were dysregulated, and oxidative damage was observed in the SCN and hippocampi of LL rats. Fluoxetine treatment conferred protection against oxidative damage in LL rats. Constant light exposure also impaired rats' performance on Y-maze, Morris maze, and novel object recognition test, which was prevented with fluoxetine administration. A significant elevation in soluble Aβ levels, which strongly correlated with upregulation of and transcripts was observed in the hippocampus of LL rats. Further, the expression of antiaging gene was downregulated, and neuronal damage indicator was upregulated in hippocampus. Fluoxetine rescued Aβ upregulation and AD-related genes' dysregulation. Our findings show that circadian disruption by exposure to chronic constant light may contribute to progression of AD, which can be prevented with fluoxetine treatment.