Effect of Food Schedule on the Hypothalamus and Development of Metabolic Syndrome in Rats Submitted to Night Work Model

*Corresponding author e-mail; robertosalgado@yahoo.com Introduction: The light-dark cycle provides the most powerful environmental cyclic stimulus, under which practically all organisms have evolved and adapted. To survive in a cyclic environment the organisms developed a circadian system that induces cyclic changes in the physiology and behavior. In mammals this system consists of a biological clock and multiple organs that constitute peripheral oscillators. The circadian system allows the organisms to express physiological processes and feeding at the appropriate time of the day or night. Nevertheless, recent studies report evidence that the type and the time of food can drive peripheral oscillators out of phase from the biological clock causing a internal desynchronization (ID), characterized by the loss of phase relation between behavioral, hormonal and metabolic rhythms. Shiftand night —work lead to ID and at long term lead to cardiovascular and gastric disorders, propensity to obesity, metabolic syndrome and cancer. To better understand the mechanisms underlying ID and in order to propose strategies to prevent this disturbance, we have developed an experimental model of night-work in rats based on schedules of forced activity. Methods: From Monday to Friday rats are placed for 8 hours in slow rotating wheels during their inactivity phase. During the remaining hours of the day and during weekends rats are returned to their individual home cages placed in a monitoring system in order to register their activity, and their feeding patterns. Results: After 4 weeks under this “working” schedule rats diminished their nocturnal activity and voluntarily shifted their food ingestion towards “working” hours. Metabolic rhythms were dampened or uncoupled from the suprachiasmatic nucleus (SCN) activity, which remained fixed to the LD cycle and promoted increased body weight and abdominal fat accumulation. Follow up of Fos and Perl daily cycles indicated that in hypothalamic structures activity had shifted to the “working” schedule and thus was uncoupled from the SCN. Since feeding schedules are a strong entraining signal for metabolism and behavior, we explored whether the changed feeding patterns such as developed by working rats could have promoted the internal desynchrony. Food restricted to the dark phase (the normal activity phase) reverted all metabolic disturbances to the normal range and prevented body weight increase, demonstrating the important contribution of feeding habits to prevent internal desynchrony and obesity in the night worker. Conclusion: Feeding schedules are relevant to prevent internal desynchrony in the night worker and may explain metabolic disturbances arising from disturbed feeding patterns. Support: CONACyT 79797, 82462 and PAPIIT-UNAM IN-203907 Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil