Interleukin-6 levels fluctuate with the light-dark cycle in the brain and peripheral tissues in rats

Zhiwei Guan, Alexandros N. Vgontzas, Takenori Omori, Xuwen Peng, Edward O. Bixler, Jidong Fang

Research output: Contribution to journalArticle

36 Scopus citations

Abstract

Interleukin-6 (IL-6) has been implicated in excessive daytime sleepiness (EDS) in humans, and exogenous IL-6 also induces sleep alterations both in humans and rats. The IL-6 levels in human blood vary with the light-dark cycle with IL-6 levels being high during the dark period and low during the light period, whereas in the pituitary of rats the IL-6 levels are elevated during the light period compared to the dark period. However, it is unknown whether IL-6 in the brain is affected by the light-dark cycle. We hypothesized that IL-6 levels in the brain are regulated by the light-dark cycles and are elevated during the period that is predominantly occupied by sleep. To test this hypothesis, we measured IL-6 levels in the brain, blood, and adipose tissue of rats across light-dark cycle every 4 h. IL-6 levels were significantly higher during the light period than during the dark period in the cortex, hippocampus and hypothalamus. In the brainstem, IL-6 levels did not significantly vary across the light-dark cycles. IL-6 levels in the blood and adipose tissues were also significantly higher during the light period than during the dark period. IL-6 levels were positively correlated between the blood and adipose tissue, between hypothalamus and blood, and between the hypothalamus and hippocampus. These observations suggest that IL-6 levels vary across the light-dark cycle among different tissues and that IL-6 levels are elevated both centrally and peripherally during the period predominantly occupied by sleep but decreased during the period that primarily consists of wakefulness.

Original languageEnglish (US)
Pages (from-to)526-529
Number of pages4
JournalBrain, Behavior, and Immunity
Volume19
Issue number6
DOIs
StatePublished - Nov 1 2005

All Science Journal Classification (ASJC) codes

  • Immunology
  • Endocrine and Autonomic Systems
  • Behavioral Neuroscience

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