Disruption of light-dark cycle of feeding and drinking behavior, and ambulatory activity induced by development of obesity in the Zucker rat.

To clarify the contribution of abnormalities and disruption of the light-dark cycle of feeding behavior during obesity progression in Zucker rats, feeding, drinking and ambulation were measured at four different stages of obesity. In the obese rats, the nocturnal pattern of feeding, drinking and ambulation shifted gradually into the light period with the progression of obesity. The lean rats however were unaffected. In the analysis of meal parameters, nocturnal dominance of meal size in the obese disappeared by 12 weeks of age and that of meal frequency was lost by 30 weeks of age. This disruption of the light-dark cycle in meal parameters appeared uneven at different stages indicating that synergistic impairment of meal size and meal frequency might contribute to the impairment of the nocturnal feeding pattern, which leads, in part, to the development of obesity.