title: Rhythms of mammalian body temperature can sustain peripheral circadian clocks.
abstract: BACKGROUND
  Low-amplitude temperature oscillations can entrain the phase of circadian rhythms in several unicellular and multicellular organisms, including Neurospora and Drosophila. Because mammalian body temperature is subject to circadian variations of 1 degrees C-4 degrees C, we wished to determine whether these temperature cycles could serve as a Zeitgeber for circadian gene expression in peripheral cell types.
  
  
  RESULTS
  In RAT1 fibroblasts cultured in vitro, circadian gene expression could be established by a square wave temperature rhythm with a (Delta)T of 4 degrees C (12 hr 37 degrees C/12 hr 33 degrees C). To examine whether natural body temperature rhythms can also affect circadian gene expression, we first measured core body temperature cycles in the peritoneal cavities of mice by radiotelemetry. We then reproduced these rhythms with high precision in the liquid medium of cultured fibroblasts for several days by means of a homemade computer-driven incubator. While these "in vivo" temperature rhythms were incapable of establishing circadian gene expression de novo, they could maintain previously induced rhythms for multiple days; by contrast, the rhythms of control cells kept at constant temperature rapidly dampened. Moreover, circadian oscillations of environmental temperature could reentrain circadian clocks in the livers of mice, probably via the changes they imposed upon both body temperature and feeding behavior. Interestingly, these changes in ambient temperature did not affect the phase of the central circadian pacemaker in the suprachiasmatic nucleus (SCN) of the hypothalamus.
  
  
  CONCLUSIONS
  We postulate that both endogenous and environmental temperature cycles can participate in the synchronization of peripheral clocks in mammals.
authors.affiliation: Department of Molecular Biology, University of Geneva, Sciences II, 30, Quai Ernest Ansermet, CH-1211 Geneva, Switzerland.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Brown
authors.forename: Gottlieb
authors.initials: G
authors.lastname: Zumbrunn
authors.forename: Fabienne
authors.initials: F
authors.lastname: Fleury-Olela
authors.forename: Nicolas
authors.initials: N
authors.lastname: Preitner
authors.forename: Ueli
authors.initials: U
authors.lastname: Schibler
mesh_terms: D000818:Animals; D001831:Body Temperature / Q000235:genetics / Q000502:physiology*; D002460:Cell Line; D002940:Circadian Rhythm / Q000235:genetics / Q000502:physiology*; D004268:DNA-Binding Proteins; D005347:Fibroblasts / Q000502:physiology; D015870:Gene Expression; D008099:Liver / Q000502:physiology; D051379:Mice; D008807:Mice, Inbred BALB C; D008954:Models, Biological; D051381:Rats; D013493:Suprachiasmatic Nucleus / Q000502:physiology; D014157:Transcription Factors / Q000235:genetics
chemical_list: C485975:DBP protein, rat; D004268:DNA-Binding Proteins; C498260:Dbp protein, mouse; D014157:Transcription Factors