Does Scheduled Glucose Induce Anticipatory Activity in Rats?

*Corresponding author e-mail: brenotercio@yahoo.com.br Introduction: Food-entrained rhythms have been identified in several species. However, the entrainment mechanisms underlying the expression of these rhythms are not completely described. It has been reported that glucose phase-shifts the food-entrainable oscillator in rats. We aimed to test whether scheduled glucose ingestion is sufficient to induce anticipatory activity, studying the expression of the motor activity rhythm in rats. Methods: Male and female Wistar rats (n = 10) were used. They were entrained to a 12h:12h LD cycle with ad-lib food for 3 days. Food was withheld on day 3 at ZT 12. From the 4th to 13th day the animals received glucose solution (50 %) in plastic flasks (20 mL/ day/animal) between ZT 06-09, and then meal (glucose solution) was ommited for two days. The motor activity was monitored by infrared motion sensors positioned 15 cm above the cage lids connected to a personal computer where data were collected each 5 min using Aschoff softwere (E. T. Santos, A. Maitelli, J. F. Araujo, Universidade Federal do Rio Grande do Norte, 2000). Motor activity data were normalized by the daily mean. Rhythms analyses, which included actogram, periodogram, waveform and cosinor, were performed on El Temps software (A. Díez-Noguera, Universitat de Barcelona, 1999). Results: The rats anticipated mealtime. Locomotion between ZT 04-06 averaged over days 1-2, over the last two days (12-13) of restricted glucose and on meal omission 2 were statistically different (ANOVA for repeated measures, F (2,18) = 12,440, P 0.94). The motor activity rhythm of six animals seemed to fully entrain to mealtime. Averaged acrophase over days 1-2 and 12-13 occurred 16.97 ± 0.42 h and 8.84 ± 0.47 h after lights-on, respectively, and 9.66 ± 0.67 h on meal omission 2. ANOVA revealed significant difference between these days (F (2, 18) = 95.84, P 0.42). Conclusion: Daily glucose ingestion induces anticipatory activity in rats and possibly also entrains the circadian pacemaker in the suprachiasmatic nucleus of the hypothalamus. Support: CNPq, FAPERN. Publication History Article published online: 16 June 2026 © 2009. Brazilian Sleep Academy. This is an open access article published by Thieme under the terms of the Creative Commons Attribution-NonDerivative-NonCommercial License, permitting copying and reproduction so long as the original work is given appropriate credit. Contents may not be used for commercial purposes, or adapted, remixed, transformed or built upon. (https://creativecommons.org/licenses/by-nc-nd/4.0/) Thieme Revinter Publicações Ltda. Rua Rego Freitas, 175, loja 1, República, São Paulo, SP, CEP 01220-010, Brazil