Factors influencing the hunger and thirst motivated behavior of hypothalamic hyperphagic rats

Abstract

Female rats with lesions in the area of the ventromedial hypothalamus were hyperphagic but performed significantly worse than controls on high fixed ratio schedules for both food and water reinforcements. Preoperative training of the experimental task eliminated these performance deficits but identical deprivation in terms of preoperative body weight did not. Identical deprivation had no effect on either the pretrained or nonpretrained lesioned groups using water reinforcement, and only a moderate effect with nonpretrained animals for food reinforcement. Preoperative training, on the other hand, greatly facilitated the hunger and thirst motivated behavior of obese as well as deprived lesioned rats. Pretraining was most effective when postoperative testing at the highest ratio of reinforcement was not preceded by a period of ad lib feeding or the reintroduction of lower ratios. Rather than hypothesizing a reduction in motivation, the performance deficits of nonpretrained lesioned animals are attributed primarily to a lesion induced hyperreactivity to long periods of nonreinforcement.