A nucleoside-nucleotide mixture may reduce memory deterioration in old senescence-accelerated mice

We investigated the effects of a mixture of dietary nucleosides and nucleotides (NS + NT) on memory in 1- and 7-mo-old senescence-accelerated mice (SAM). Memory retention was studied with passive avoidance (step-through) and active avoidance (shuttle) tests. For 14 wk, mice in the control groups were fed a 20 g of casein/100 g diet, whereas the NS + NT groups were fed this diet supplemented with a 0.5 g of NS + NT mixture/100 g. All mice were killed at wk 14, and we studied the brain histopathology. Lipofuscin, monovacuoles and multiple vacuoles of various brain regions were measured. Body weight, food intake and ambulatory activity did not differ between the control and NS + NT groups. In old mice, the time of passive avoidance was significantly higher in the NS + NT group than in the control group at d 1 and 7 (P < 0.05). However, such an effect of NS + NT was not observed in young mice. In the active avoidance test, the incidence of successful avoidance in old mice was higher in the NS + NT group than in the control group at d 1 and 2 (P < 0.05). The percentages of specific brain cells containing lipofuscin were lower in NS + NT groups than in the control groups in both young and old mice (P < 0.05). The number of monovacuoles and multiple vacuoles in specific brain regions tended to be lower (P = 0.1-0.25) in NS + NT than in control groups, with significant differences in the microvacuoles of the middle cortex of young mice and in the multiple vacuoles in the hind cortex of old mice (P < 0.05). These results suggest that increased dietary NS + NT may be associated with decreases in the age-induced deterioration of brain morphology and certain memory tasks.