Question

magine a parabiosis experiment in which the circulatory system of an ob/ob mouse is joined with a mouse having damage to its ventromedial hypothalamus (VMH). We expect:

Group of answer choices

The ob/ob mouse will lose weight; the VMH-lesion mouse will continue to get fatter

The ob/ob mouse will lose weight; the VMH-lesion mouse will also lose weight

The ob/ob mouse will continue to get fatter; the VMH-lesion mouse will also continue to get fatter

The ob/ob mouse will continue to get fatter; the VMH-lesion mouse will lose weight

Answer 1

The ob/ob mice have mutation in leptin gene and hence, will be obese. Leptin is a satiety hormone that leads to decreased in appetite. Thus, lack of leptin in ob/ob mice will lead to increase in hunger and hence, obesity. In the VMH lesion mouse, there is decreased expression of leptin receptor on the Ventromedial Hypothalamus. However, there is increased production of leptin in these mice.

In parabiosis experiments, the circulatory system of the ob/ob mice is joined to the circulatory system of the VMH lesion mice. Thus, leptin from the VMH lesion mice will enter the circulation of ob/ob mice and will bind to leptin receptors. This will cause increased signaling, leading to loss of appetite. Thus, the ob/ob mice will start losing fat and will become leaner. The VMH lesion mice however, do not obtain any leptin from ob/ob mice. As VMH lesion mice lack leptin receptors, they will show no effects of leptin. Hence, they will continue to be obese and will grow fatter. VMH lesion mice will not lose any weight.

Right choice: The ob/ob mouse will lose weight; the VMH-lesion mouse will continue to get fatter.