DIFFERENTIAL CIRCADIAN EATING PATTERNS IN 2 PSYCHOGENETICALLY SELECTED STRAINS OF RATS FED LOW-FAT, MEDIUM-FAT, AND HIGH-FAT DIETS

Spontaneous eating patterns in male, inbred Roman high-and low-avoidan ce rats (RHA/Verh, RLA/Verh) were continuously recorded while animals were successively offered three isocaloric (approximate to 16.5-kJ/g) diets: a low-fat, high-carbohydrate diet (LF; 3.3% fat), a medium-fat diet (MF; 18% fat), and a high-fat diet (HF; 40% fat), the latter bein g followed once again by the LF diet. Under the conditions of this exp eriment, overall 24-h food intake did not differ significantly between RHA/Verh and RLA/Verh rats, but was significantly higher for both rat strains on the MF and HF diets than on the LF diet. Despite the simil ar 24h-food intake, RHA/Verh rats ate transiently less than RLA/Verh r ats during the third quarter of the dark phase under all dietary condi tions. These differences were due to the RHA/Verh rats' longer interme al intervals (with all diets) and smaller meals (with the MF and HF di ets) and were compensated for during the last 3 h of the dark phase. O n the LF diet, dark-phase meal frequency was higher and both nocturnal meal size and mean eating rate within meals were lower in RLA/Verh ra ts than in RHA/Verh rats. With the MF and HF diets, mean nocturnal mea l size and meal duration were higher and mean eating rate was lower in RLA/Verh rats than in RHA/Verh rats. For both strains, nocturnal meal size was significantly higher with the MF and HF diets than with the LF diet, and nocturnal meal frequency was lower with the HF diet than with the other two diets. Although body weights were similar at the st art of the study, RLA/Verh rats gained significantly more weight than did RHA/Verh rats by the end. As has often been the case with other as pects of behavior studied, differences in neuromodulatory systems (e.g ., serotoninergic and dopaminergic) between RHA/Verh and RLA/Verh rats may directly or indirectly contribute to the subtle differences in ea ting patterns observed here.