PubMed1987
The effect of reducing the dietary protein content at different stages of development was investigated. A group of control rats was fed a diet with 25% protein throughout the entire study. Four other groups were fed only 6% protein in a diet isocaloric with the control diet. In an "intrauterine"-deprivation (prenatal) group, the feeding of the low protein diet was limited to the span from mating to delivery. In a "postnatal"-deprivation (lactation) group, the reduced protein diet was limited to the 25 days allowed for lactation. In a "perinatal"-deprivation group, the low-protein diet was fed during both the pregnancy and the 25 days after birth. Protein deprivation in a "preperinatal" group started 1 month before mating and continued throughout gestation and lactation to day 25 after birth. Except for the perinatal group, consisting of two animals, other groups consisted each of three or four rats. Behavioral variables--activity, rest, eating, drinking, exploring, grooming, curling up, and lying down--were studied in rats from each group at 90 days of age for 3 days at consecutive near-12-min intervals for observation spans of 1 min. Two animals subjected to bilateral suprachiasmatic lesions, subsequently validated histologically, and two sham-operated controls were also investigated. Both the population-mean and the single cosinor methods were used for data analysis in conjunction with linear least-squares spectra. Cosinor methods allow the rejection of the zero-amplitude assumption on a group basis for the intact controls (P = 0.007), the intrauterine malnutrition group (P = 0.034), the lactation group (P = 0.059), the preperinatal group (P = 0.055), and on an individualized basis for the two animals constituting the perinatal group (P = 0.007 and 0.002). These results by population-mean cosinor are complemented by the single cosinor demonstration of rhythms for most animals and variables investigated. The results demonstrate, on an individualized basis, the persistence of circadian rhythms under differently timed conditions of protein malnutrition. The data on the behavior of rats with bilateral lesions of the suprachiasmatic nuclei show a circadian to ultradian variance transposition. In most behaviors, there are prominent ultradian rhythms, which, however, require study over longer spans with dense observations on additional animals.