title: Circadian clocks for all meal-times: anticipation of 2 daily meals in rats.
abstract: Anticipation of a daily meal in rats has been conceptualized as a rest-activity rhythm driven by a food-entrained circadian oscillator separate from the pacemaker generating light-dark (LD) entrained rhythms. Rats can also anticipate two daily mealtimes, but whether this involves independently entrained oscillators, one 'continuously consulted' clock, cue-dependent non-circadian interval timing or a combination of processes, is unclear. Rats received two daily meals, beginning 3-h (meal 1) and 13-h (meal 2) after lights-on (LD 14:10). Anticipatory wheel running began 68±8 min prior to meal 1 and 101±9 min prior to meal 2 but neither the duration nor the variability of anticipation bout lengths exhibited the scalar property, a hallmark of interval timing. Meal omission tests in LD and constant dark (DD) did not alter the timing of either bout of anticipation, and anticipation of meal 2 was not altered by a 3-h advance of meal 1. Food anticipatory running in this 2-meal protocol thus does not exhibit properties of interval timing despite the availability of external time cues in LD. Across all days, the two bouts of anticipation were uncorrelated, a result more consistent with two independently entrained oscillators than a single consulted clock. Similar results were obtained for meals scheduled 3-h and 10-h after lights-on, and for a food-bin measure of anticipation. Most rats that showed weak or no anticipation to one or both meals exhibited elevated activity at mealtime during 1 or 2 day food deprivation tests in DD, suggesting covert operation of circadian timing in the absence of anticipatory behavior. A control experiment confirmed that daytime feeding did not shift LD-entrained rhythms, ruling out displaced nocturnal activity as an explanation for daytime activity. The results favor a multiple oscillator basis for 2-meal anticipatory rhythms and provide no evidence for involvement of cue-dependent interval timing.
authors.affiliation: Department of Psychology, Simon Fraser University, Burnaby, Canada. mistlber@sfu.ca
authors.forename: Ralph E
authors.initials: RE
authors.lastname: Mistlberger
authors.forename: Brianne A
authors.initials: BA
authors.lastname: Kent
authors.forename: Sofina
authors.initials: S
authors.lastname: Chan
authors.forename: Danica F
authors.initials: DF
authors.lastname: Patton
authors.forename: Alexander
authors.initials: A
authors.lastname: Weinberg
authors.forename: Maksim
authors.initials: M
authors.lastname: Parfyonov
mesh_terms: D000818:Animals; D059031:Anticipation, Psychological; D002940:Circadian Rhythm / Q000502:physiology*; D004435:Eating / Q000502:physiology*; D005247:Feeding Behavior / Q000502:physiology*; D005508:Food Deprivation; D008297:Male; D009043:Motor Activity / Q000502:physiology*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors