Diurnal Behavioral and Metabolic Patterns in Chronic Malnourished Rats

Abstract

The temporal organization of behavioral patterns and metabolic activity was assessed in chronic low protein malnourished rats and their nutritional controls at 60 days of age. Spontaneous activity was video-recorded during 3 days for 10 min every hour and the frequency of exploration, grooming and ingestive behaviors was obtained, their basal metabolic rate was measured during 5 min every hour for one 24 h cycle. Rats of both nutritional groups showed a clear diurnal rhythmicity in all behavioral patterns, characterized by an increase of activity during the dark phase and a decrease during the light phase. Effects of malnutrition were selective and produced mainly a general decrease of the mean value and amplitude of the rhythm of ingestive behavior, as well as a bimodal pattern and rhythmic components of 12, 24 and 30 h according to autocorrelation and cosinor analysis. In both groups, the metabolic rate showed a bimodal diurnal rhythm, which fitted significantly to a 12 h period model and was not affected in malnourished rats. These data provide evidence that the circadian system is highly resistant to malnutrition. In malnourished rats rhythmicity of ingestive behavior was specifically affected, probably because the relation between metabolic processes and ingestive behaviors may be enhanced as a compensatory mechanism aimed to counteract the deficient diet composition.