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Circadian rhythms of occipital-cortex temperature and motor activity in young and old rats under chronic protein malnutrition

The circadian rhythm of cortical temperature registered in the right occipital cortex and the circadian rhythm of motor activity were studied in young and old rats submitted to a chronic malnutrition paradigm. Circadian rhythms of cortical temperature and motor activity in Control (25% casein) and Malnourished (6% casein) Sprague-Dawley male rats were registered by telemetry along different lighting conditions. Results indicate that: (1) there are masking effects of light upon the period of cortical temperature in malnourished-old rats, (2) cortical temperature and motor-activity rhythms, show endogenous periods different from 24-h under free-running conditions, (3) protein malnutrition increases the amplitude and the mean value of cortical-temperature rhythm in malnourished-young rats, (4) aging decreases the amplitude and mean value of the motor-activity rhythm, (5) the acrophase of cortical temperature is delayed in malnourished-old rats, and (6) the temporal relationship between cortical temperature and motor-activity circadian rhythms is altered in malnourished-young and old rats. Therefore, this study provides evidence that protein malnutrition produces long-lasting alterations in the architecture of the circadian system, particularly affecting cortical-temperature oscillation. These changes might indicate thermoregulatory differences in the brain of malnourished rats that could be related to metabolic and behavioral alterations due to protein malnutrition.