SOFT-DIET FEEDING DURING DEVELOPMENT ENHANCES LATER LEARNING-ABILITIES IN FEMALE RATS

We investigated whether a decrease in masticatory work affected not on ly jaw bone growth but also radial eight-arm maze learning, and whethe r there was a sexual difference in this effect, if any. Male and femal e rats, weaned at 3 weeks of age, were fed either pelleted or powdered chow until 16 weeks of age and learning experiments were conducted at 10-13 weeks of age. Almost all of the five dimensions of the jaw bone s were greater in rats fed pelleted chow than in rats fed powdered cho w in both sexes. The number of correct choices in the last five trials was significantly greater in female, but not in male, rats fed powder ed chow, and the number of trials to attain at least seven correct cho ices in the first eight choices in five consecutive trials was greater in female rats fed pelleted chow than in female rats fed powdered cho w and in male rats fed either powdered or pelleted chow. These results suggest that 1) a decrease in masticatory work due to soft-diet feedi ng during development enhances later learning ability preferentially i n female rats, and 2) the reported sexual inferiority of female rats i n learning and memory functions is due to hard-diet feeding as the sta ndard laboratory condition.