Effects of two body weight reduction regimens on schedule dependent and schedule induced behavior

Fifteen male hooded rats were divided into three equal groups on the basis of body weights. One group was allowed to eat ad lib and constituted the Control Group. The second group of animals was reduced over 7 days and adjusted to 80 percent of the body weight of the animals in the Control Group for a 23 day period and constituted the Adjusted Group. Animals in the third group were reduced to 80 percent of their own predeprivation body weight over 7 days and were maintained at this constant level for a 23 day period and constituted the Constant Group. The two experimental groups were then allowed to feed ad lib for the remainder of the experiment. Both the Adjusted and the Constant Groups were tested throughout restricted and ad lib eating periods on a FI 1 min food reinforcement generator schedule. Schedule dependent lever pressing, schedule induced licking and drinking, food intake and body weights were recorded for the duration of the experiment. Results demonstrate that schedule induced licking and drinking and schedule dependent lever pressing increased in the Constant Group at reduced body weight. Animals in the Adjusted Group did not change significantly on these measures during the same periods. When animals were returned to ad lib feeding conditions, the Constant Group initially increased body weight at a faster rate, ate significantly more, and exhibited significantly increased schedule induced licking and drinking. These initial differences disappeared later during the same period. The two experimental groups did not attain the expected body weight of the normal Control Group during 78 days of ad lib eating. Apparently, when animals are initially deprived rapidly and maintained at relatively constant body weight reduction, a prolonged body weight deficit occurs even though these same animals eat normal amounts of food.