Feeding behavior and entrainment limits in the circadian system of the rat

Abstract

The entrainment limits of the circadian rhythms of feeding activity were studied in Wistar rats exposed to gradually increasing and decreasing or to static light-dark cycles. In the former, the entrainment limits of feeding behavior were 22 h 10 min and 26 h 40 min. In the latter, the upper limit was higher, because rats under zeitgeber period ( t) length = 27 h ( t27) and t28 met the criteria of entrainment. The lower limit, on the other hand, was not modified because none of the t22 animals showed entrained rhythms and one-half of the t23 rats exhibited two components in their circadian feeding rhythms, one with a period of 23 h and the other free running. This 23-h component reflected not only the masking effect of light-dark cycles but also seemed a true light-entrained component. In well-synchronized animals, food intake seemed to depend more on the number of cycles that the animal experienced than on actual time lived; however, other feeding parameters, such as meal frequency and feeding duration, remained constant when expressed per 24 h, irrespective of the t cycle. These results concerning feeding duration, meal frequency, and food intake revealed that the homeostatic and circadian controls interacted to a degree that depended on the type of variable considered. In conclusion, the entrainment limits appeared much more imprecise than they were previously thought to be, because the circadian system can only be partially synchronized near its entrainment limits. The hypothesis that the rat’s circadian system is composed of multiple oscillators with different intrinsic frequencies and varying capacities for light synchronization would explain the partial desynchronization observed near the entrainment limits.

Activity rhythm of golden hamster (Mesocricetus auratus) can be entrained to a 19-h light-dark cycle

“…Values are means Ϯ SE of the different variables described in MATERIALS AND METHODS. values that were close to 25.5 and 22 h, respectively. Moreover, it has been reported in rats that the upper entrainment limit of feeding activity rhythm occurs at 28 h if the animals are exposed directly to T cycles from T24, and only at 26 h 44 min with a 10 min/day increase in T cycle from T24 to T30 (36). These studies suggest that pacemaker function is differentially affected depending on previous environmental history or on the time required to adapt to changing conditions.…”

Circadian rhythm of plasma sodium is disrupted in spontaneously hypertensive rats fed a high-NaCl diet

“…Arterial pressure displays a circadian rhythm that is entrained to the light-dark cycle, resulting in the highest arterial pressures during the night when the activity of rats is the greatest and the lowest arterial pressures during the daytime when rats typically sleep (6,8). Ingestive behavior follows a similar pattern, i.e., rats primarily consume food during the nighttime (30). Therefore, the present study tests the hypothesis that plasma sodium concentration displays a 24-h rhythm parallel to the MAP rhythm and may contribute to changes in MAP observed throughout the 24-h cycle.…”

Theoretical and conceptual issues in time–place discrimination

“…Third, anticipation of meals by a circadian system is thought to operate within a limited range of circadian entrainment. The limited range of entrainment has been estimated to be between 22 and 31 h (Stephan, 1981) and between 22.2 and 28.0 h (Madrid et al. , 1998).…”