Fat Hormone Can Rewire Brain, U.S. Studies Show

Fat Hormone Can Rewire Brain, U.S. Studies Show
Thu Apr 1, 5:59 PM ET

By Maggie Fox, Health and Science Correspondent

WASHINGTON (Reuters) - Leptin, a hormone that affects weight and appetite,
apparently helps wire the brain in ways that might set an animal on a
lifetime path to slenderness or obesity, two teams of U.S. researchers said
on Thursday.

The studies, published in Friday's issue of the journal Science, may take
doctors a step closer to understanding whether leptin could be manipulated
to help overweight people lose weight and keep it off.


The findings might also help explain why the food a person eats when very
young, or even what a mother eats while pregnant, affects weight, heart
disease and other aspects of metabolism later in life.


And they help shed light on why it is so hard for many people to lose weight
and keep it off.


In one study, a team at the Howard Hughes Medical Institute and Rockefeller
University and at Yale University, found that leptin affects both the
physical structure and the function of neural circuits in the brain.


"This is a very dynamic effect that's quite dramatic and somewhat
surprising. In response to leptin, the cells create new connections," said
Rockefeller's Dr. Jeffrey Friedman.


"The malleability of these feeding circuits by leptin suggest the
possibility that the brain's wiring may be different in lean versus obese
individuals," Friedman added in a statement.


The researchers worked with specially bred mice, but when it comes to basic
biology, mice are very similar to humans.


When it was discovered in 1994, leptin thrilled scientists because it seemed
so basic to obesity and appetite. Overweight rodents fed leptin lost weight
and studies quickly showed that some overweight people had unusually low
levels of the hormone.


But leptin's effect was not so straightforward in humans, and it became
clear that simply injecting obese people with it was not going to make them
lose weight.


In a second study, scientists at Oregon Health & Science University found
exposure to leptin early in life affected brain structures involved in
weight regulation.


Also working with mice, Richard Simerly and colleagues tracked development
of neurons in a part of the brain called the arcuate nucleus of the
hypothalamus.


Brain circuits there were less developed in mice genetically engineered to
make no leptin compared to normal mice. Injecting baby mice with leptin
restored normal brain structure, they found.


"We're excited about this finding because it shows how exposure to leptin
can directly affect development of brain structures involved in regulating
body weight," Simerly said in a statement.


"Our findings suggest a link between the developmental actions of leptin and
early onset obesity," he added.


"We were shocked by how clear the result was. Leptin plays an important role
in brain development, by acting specifically on the clusters of brain cells
that regulate food intake."


The findings may help explain how some people seem to have a body weight
"set point" -- "until now a nebulous concept in search of a mechanism," said
Joel Elmquist and Jeffrey Flier of Harvard Medical School (news - web sites)
and Beth Israel Deaconess Medical Center in Boston.

The findings support "the concept that under- and over-nutrition during
critical periods of hypothalamic (brain) development may induce long-lasting
and potentially irreversible effects into adulthood," they wrote in a
commentary in Science.
--
Ken

"They want the federal government controlling Social Security like it's some
kind of federal program."

-Bushism's, 2000