leptin in brain affects body energy balance

[Guest guest]

Fat hormone leptin affects a specific type of target neurons in the

brain

Thursday, 24-Jun-2004 News-Medical.Net

Nina Balthasar and her colleagues have presented direct evidence that

the fat hormone leptin affects a specific type of target neurons in the

brain -- a prime link in the brain's regulation of the body's energy

balance.

Leptin is known to be produced by the body's fat tissues and to signal

brain cells to reduce appetite and food intake and increase energy

expenditures. Although researchers had produced indirect evidence that

leptin affects the activity of particular neurons called POMC neurons in

the brain, there had been no direct evidence of such an effect. The POMC

neurons are found in the brain's hypothalamus, believed to be an

important region for regulating the body's energy balance.

To directly demonstrate such an effect of leptin, Balthasar and her

colleagues constructed a mutant mouse in which they could selectively

knock out the receptors for leptin on the surface of POMC neurons. When

they tested the effect of eliminating the receptors, they found that the

mice had significantly increased body weight, due to an increase in fat

mass.

Surprisingly, however, the researchers found that the mice gained less

weight than would be expected if POMC neurons were the only targets of

leptin. The researchers theorize that the reduction of POMC neuron

activity due to lack of leptin signaling triggers compensatory

mechanisms that reduce the impact on the animals' weight and energy

metabolism. The researchers theorized that leptin might act to inhibit

other neurons that, in turn, normally inhibit POMC neurons, thereby

enhancing POMC activity.

http://www.cell.com/