The temporal organization of behavioral patterns and metabolic activit
y was assessed in chronic low protein malnourished rats and their nutr
itional controls at 60 days of age. Spontaneous activity was video-rec
orded during 3 days for 10 min every hour and the frequency of explora
tion, grooming and ingestive behaviors was obtained, their basal metab
olic rate was measured during 5 min every hour for one 24 h cycle. Rat
s: of both nutritional groups showed a clear diurnal rhythmicity in al
l behavioral patterns, characterized by an increase of activity during
the dark phase and a decrease during the light phase. Effects of maln
utrition 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 accord
ing to autocorrelation and cosinor analysis. In both groups, the metab
olic rate showed a bimodal diurnal rhythm, which fitted significantly
to a 12 h period model and was not affected in malnourished rats. Thes
e data provide evidence that the circadian system is highly resistant
to malnutrition. In malnourished rats rhythmicity of ingestive behavio
r was specifically affected, probably because the relation between met
abolic processes and ingestive behaviors may be enhanced as a compensa
tory mechanism aimed to counteract the deficient diet composition.