Circadian mechanisms of food anticipatory rhythms in rats fed once or twice daily: clock gene and endocrine correlates

PLoS One. 2014 Dec 11;9(12):e112451. doi: 10.1371/journal.pone.0112451. eCollection 2014.


Circadian clocks in many brain regions and peripheral tissues are entrained by the daily rhythm of food intake. Clocks in one or more of these locations generate a daily rhythm of locomotor activity that anticipates a regular mealtime. Rats and mice can also anticipate two daily meals. Whether this involves 1 or 2 circadian clocks is unknown. To gain insight into how the circadian system adjusts to 2 daily mealtimes, male rats in a 12∶12 light-dark cycle were fed a 2 h meal either 4 h after lights-on or 4 h after lights-off, or a 1 h meal at both times. After 30 days, brain, blood, adrenal and stomach tissue were collected at 6 time points. Multiple clock genes from adrenals and stomachs were assayed by RT-PCR. Blood was assayed for corticosterone and ghrelin. Bmal1 expression was quantified in 14 brain regions by in situ hybridization. Clock gene rhythms in adrenal and stomach from day-fed rats oscillated in antiphase with the rhythms in night-fed rats, and at an intermediate phase in rats fed twice daily. Corticosterone and ghrelin in 1-meal rats peaked at or prior to the expected mealtime. In 2-meal rats, corticosterone peaked only prior the nighttime meal, while ghrelin peaked prior to the daytime meal and then remained elevated. The olfactory bulb, nucleus accumbens, dorsal striatum, cerebellum and arcuate nucleus exhibited significant daily rhythms of Bmal1 in the night-fed groups that were approximately in antiphase in the day-fed groups, and at intermediate levels (arrhythmic) in rats anticipating 2 daily meals. The dissociations between anticipatory activity and the peripheral clocks and hormones in rats anticipating 2 daily meals argue against a role for these signals in the timing of behavioral rhythms. The absence of rhythmicity at the tissue level in brain regions from rats anticipating 2 daily meals support behavioral evidence that circadian clock cells in these tissues may reorganize into two populations coupled to different meals.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • ARNTL Transcription Factors / metabolism
  • Adrenal Glands / metabolism
  • Animals
  • Anticipation, Psychological*
  • Brain / metabolism
  • Brain / physiology
  • Circadian Clocks / genetics*
  • Corticosterone / blood
  • Food*
  • Gastric Mucosa / metabolism
  • Ghrelin / blood
  • Hormones / metabolism*
  • Male
  • Mice
  • Motor Activity
  • Period Circadian Proteins / metabolism
  • Rats
  • Rats, Sprague-Dawley


  • ARNTL Transcription Factors
  • Ghrelin
  • Hormones
  • Per1 protein, rat
  • Per2 protein, rat
  • Period Circadian Proteins
  • Corticosterone

Grant support

DFP was supported by an NSERC Postgraduate Scholarship ( MM and MP were supported by NSERC Undergraduate Summer Research Awards ( AA was supported by NSERC Canada operating grant RGPIN341538 ( HI was supported by NSF IOS-1145796 ( REM was supported by NSERC Canada operating grant RGPIN155172 ( The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.