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Aguilar-Roblero, R; Salazar-Juarez, A; Parra, L; Escobar, C (2003)

RESTRICTED FEEDING SCHEDULES MODULATE FREE-RUNNING DRINKING ACTIVITY IN MALNOURISHED RATS

BIOL RHYTHM RES 34(5):459-473
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Low protein malnourished rats held in 12:12 light-dark conditions exhibit two bouts of drinking activity, which resemble a "splitting" pattern. These findings have suggested a weak coupling force between the light-(LEO) and the food-entrainable oscillators (FEO). Food restriction to a few hours daily exerts a strong entraining influence on FEO and allows to uncouple both oscillators. To further understand the coupling relation between LEO and FEO, we evaluated the influence of restricted feeding schedules (RFS) on the circadian rhythm of drinking behavior in malnourished rats and their controls. Adult rats were entrained to RFS with a low protein or a regular chow diet in a counterbalanced design. All groups developed drinking anticipatory activity (FAA) to meal time, with similar intensity and onset time. RFS produced lengthening in the period of LEO's free-running rhythm and this effect was significant in MAL rats. Behavioral patterns in control as well as malnourished rats entrained with regular chow indicated independence between LEO and FEO. In contrast, 60% of MAL rats entrained with the low protein diet exhibited phase control by meal time on LEO's free-running. Present data indicate that low protein diets may induce enhanced potency of food as an entraining signal and produce a change in the coupling force between both oscillators, promoting that LEO couples to the FEO. In such conditions FEO seems to override the influence of LEO on the temporal organization of behavior and imposes its phase on the free-running component.