The Cost Of Disturbed Circadian Rhythms

Researchers from India have shown that long-term circadian rhythm disruption causes Alzheimer’s-like symptoms in rats.

AsianScientist (Dec. 27, 2021) –While it may be tempting to stay up all night over the holidays binging the latest Netflix hit, you may want to rethink that. According to a study from ACS Chemical Neuroscience, disruptions to the circadian rhythm—from causes such as stress, jetlag or irregular sleeping hours—can have serious effects like hyperactivity and anxiety to memory deficits and an increased risk of neurological disorders.

Recent studies in rats have shown that even chronic light exposure can disrupt the circadian rhythm, causing memory deficits much like those seen in neurological disorders such as Alzheimer’s disease (AD). However, the cause-and-effect relationship between AD and circadian rhythm disruption remains unclear.

A research team from Shoolini University in India had previously discovered that rats exposed to light for two months showed both cognitive deficits and the accumulation of amyloid β (Aβ), the protein known to form harmful plaques in the brains of AD patients. This made them speculate that longer light exposure may result in circadian rhythm disruptions that cause AD-like symptoms.

To test this hypothesis, they disturbed the circadian rhythm of adult rats by exposing them to constant light conditions for four months.

“Cells of various organs in the body are synchronized to the day-night cycle, and release different biochemical substances including hormones in a time-specific manner. Untimely expression of these hormones can trigger anxiety, cognitive impairment and memory loss, all symptoms of brain disorders such as AD,” said lead author Professor Rohit Goyal of  Shoolini University.

Sure enough, the researchers found that the rats exposed to constant light conditions showed memory and cognitive deficits compared to rats subjected to a normal light-dark cycle.

On the biological level, the researchers found that the chronic light exposure disrupted the expression of genes like Per2 that follow circadian rhythms. The rats also displayed dysregulated neurotransmitters and  signs of oxidative stress in the brain region that controls circadian rhythms. The level of soluble Aβ was also significantly higher in the brains of these rats.

The researchers’ next hypothesis was that fluoxetine, a drug used for treating anxiety and hyperactivity, could alleviate physiological and functional abnormalities associated with circadian rhythm disruption. When they administered the drug to the light-exposed rats, it managed to prevent oxidative damage, Aβ accumulation, and rescued memory and cognitive deficits.

The study demonstrates that elevation in Aβ and disturbed circadian rhythms can each trigger the other, setting the stage for neurological conditions like AD. Fortunately, preventative steps that regulate the circadian rhythm may protect against that, said the researchers.

“Lifestyle changes that support exposure to natural light followed by ample rest at night may thus be key to limiting the risk of neurological disorders. Therapeutic strategies to optimize circadian timing in prospective patients hold great promise to restrain the prevalence of AD,” concluded Goyal.

The article can be found at: Sharma et al. (2021) 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.


Source: Shoolini University; Photo: Unsplash.
Disclaimer: This article does not necessarily reflect the views of AsianScientist or its staff.

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