INTRODUCTION: Motivational experiments allow for assessing the inner drive of the subject to carry out a particular task. For this purpose the Skinner box is widely used. It allows the animal to acquire a conditional response, which can be used to measure the level of motivation. Adipose tissue is involved in maintaining body energy status. It secrets hormone leptin, which signals the brain about current fat storage. Thus, low level of plasma leptin elicits hunger and other responses of the organism related e.g. fertility. AIM(S): In the study we sought to establish a link between plasma leptin level and the level of motivation demonstrated by the animal. METHOD(S): Mice were trained in Skinner box to successfully acquire a conditional response. In addition all animals were calorie restricted (CR) prior to training, to improve performance. Afterwards mice were divided into 3 groups: group fasted for 6 h, group fasted for 24 h and group with CR. Last group of 6 was used as a control, where animals were fed ad libitum. Test was performed on all mice, in which overall lever press was counted during 20 minutes in the Skinner box. Second panel of animals was used to measure the actual plasma leptin level. Animals were sacrificed, blood plasma collected and leptin measurement was carried out using ELISA method. RESULTS: The highest level of motivation was observed in CR only group. Similar result was observed in a group that was fasted for 24 h. Surprisingly the group fasted for 6h only did not show significant differences from control animals. Motivation and plasma leptin level are negatively correlated in our study, with CR animals showing the lowest concentration of hormone. CONCLUSIONS: We demonstrated that calorie restriction is the most crucial factor in controlling motivation level of the animal, compared to short lasting starvation periods. This might be explained by strongly decreasing level of leptin hormone in the animal, when CR is introduced.
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