Circadian Neuroendocrine-Immune Aspects of Feeding Behavior: Lessons from Calorie-Restricted or High-Fat-Fed Rats
The circadian clock is one of the most indispensable biological functions for living organisms that acts like a multifunctional timer to adjust the homeostatic system, including sleep and wakefulness, hormonal secretions, immune function, and various other bodily functions. In mammals, the circadian system is composed of many individual, tissue-specific cellular clocks. To generate coherent physiological and behavioral responses, the phases of this multitude of cellular clocks are orchestrated by a master circadian pacemaker residing in the suprachiasmatic nuclei of the hypothalamus. At a molecular level, circadian clocks are based on clock genes, some of which encode proteins able to feedback and inhibit their own transcription. These cellular oscillators consist of interlocked transcriptional and posttranslational feedback loops that involve a small number of core clock genes (about 12 genes identified currently). Virtually all neuroendocrine and immunological variables investigated in animals and humans display biological periodicity. Circadian rhythmicity is revealed for every hormone in circulation as well as for circulating immune cells, lymphocyte metabolism and transformability, cytokines, receptors, and adhesion molecules. This review discusses the circadian disruption of hormone release and immune-related mechanisms by calorie restriction and a high fat diet in rats. In every case the experimental manipulation used has perturbed the temporal organization by affecting the shape and amplitude of a rhythm or by modifying the intrinsic oscillatory mechanism itself.
KeywordsLuteinizing Hormone Calorie Restriction Circadian Clock Clock Gene Plasma ACTH
Monocyte chemoattractant protein-1
Plasminogen activator inhibitor-1
Tumor necrosis factor-α
Work in authors’ laboratories was supported in part by DGES, Spain, Agencia Nacional de Promoción Científica y Tecnológica, Argentina, the University of Buenos Aires and CONICET, Argentina.
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