Changes in glutamine synthetase activity under conditions of artificial light-induced circadian disruption

The activity of glutamine synthetase (GS), a key enzyme in glutamate metabolism that protects nerve cells from glutamate toxicity and performs a detoxification function for ammonia, was studied in various brain regions (cortex, cerebellum, hypothalamus, hippocampus, midbrain, and medulla oblongata) of three-month-old male Wistar rats under conditions of exposure to constant light (altered lighting conditions). All animals used in the experiment were randomly divided into two groups (n = 10 per group): experimental and control. A model of constant illumination was established by housing animals under constant light conditions: natural daylight during the day and artificial light at night using a daylight lamp. It was found that under conditions of constant illumination, there was a statistically significant reduction in GS activity in all examined brain structures compared to the control group, likely as a consequence of stress experienced by the experimental animals. Prolonged illumination, acting as a stress-inducing factor, may increase the brain's oxygen demand. These conditions are often associated with suppression of antioxidant system activity and reduced melatonin secretion, which, in turn, may disrupt enzymatic homeostasis and lead to functional alterations. The observed reduction in GS activity is presumably related to the enzyme's sensitivity to cellular environmental changes. These alterations may be attributed to the suppression of pineal gland function under conditions of constant light exposure.