Early nutrition and the activity and feeding of rats in an artificial environment.

Male hooded rats were divided into 3 equal groups: (1) controls were given a complete diet ad libitum at all times; (2) for 8 weeks from the age of 28 days, undernourished (UN) rats received the complete diet in restricted amounts; (3) low protein (LP) rats received a low-protein, high-carbohydrate diet for the same period. From 12 weeks all rats were given the complete diet ad libitum, until tested at 35 weeks. Each rat was then put alone, for 12 days, in a residential “plus-maze” with a central nest box and 4 arms radiating from it; food was supplied at the end of one arm, water in the nest box. On Days 4 to 9 each rat had access to the arms for only 1 hr daily. Entries into the arms, and duration of stay, were recorded automatically. All arms were regularly visited by rats of all classes, even when access was only for 1 hr. Visits per day to the 3 nonfood arms combined were usually higher than visits to the food arm, but duration of stay in the food arm was higher than the total duration in the other 3 arms. LP rats made most visits to the arms and were especially active after the 6 days of restriction; but they were less adaptable than the control and UN rats in adjusting food intake during the period of restricted access. In contrast, the UN rats spent most time in the arms.