Re: How Exercise Fuels the Brain

[Guest guest]

From the NYTimes

Ralph Giarnella MD

Southington Ct. USA 

FEBRUARY 22, 2012, 12:01 AM

How Exercise Fuels the Brain

http://well.blogs.nytimes.com/2012/02/22/how-exercise-fuels-the-brain/

By GRETCHEN REYNOLDS

Stapleton/ReutersDoes exercise keep your brain running?

Moving the body demands a lot from the brain. Exercise activates countless

neurons, which generate, receive and interpret repeated, rapid-fire messages

from the nervous system, coordinating muscle contractions, vision, balance,

organ function and all of the complex interactions of bodily systems that allow

you to take one step, then another.

This increase in brain activity naturally increases the brain’s need for

nutrients, but until recently, scientists hadn’t fully understood how neurons

fuel themselves during exercise. Now a series of animal studies from Japan

suggest that the exercising brain has unique methods of keeping itself fueled.

What’s more, the finely honed energy balance that occurs in the brain appears

to have implications not only for how well the brain functions during exercise,

but also for how well our thinking and memory work the rest of the time.

For many years, scientists had believed that the brain, which is a very hungry

organ, subsisted only on glucose, or blood sugar, which it absorbed from the

passing bloodstream. But about 10 years ago, some neuroscientists found that

specialized cells in the brain, known as astrocytes, that act as support cells

for neurons actually contained small stores of glycogen, or stored

carbohydrates. And glycogen, as it turns out, is critical for the health of

cells throughout the brain.

In petri dishes, when neurons, which do not have energy stores of their own, are

starved of blood sugar, their neighboring astrocytes undergo a complex

physiological process that results in those cells’ stores of glycogen being

broken down into a form easily burned by neurons. This substance is released

into the space between the cells and the neurons swallow it, maintaining their

energy levels.

But while scientists knew that the brain had and could access these energy

stores, they had been unable to study when the brain’s stored energy was being

used in actual live conditions, outside of petri dishes, because brain glycogen

is metabolized or burned away very rapidly after death; it’s gone before it

can be measured.

That’s where the Japanese researchers came in. They had developed a new method

of using high-powered microwave irradiation to instantly freeze glycogen levels

at death, so that the scientists could accurately assess just how much brain

glycogen remained in the astrocytes or had recently been used.

In the first of their new experiments, published last year in The Journal of

Physiology, scientists at the Laboratory of Biochemistry and Neuroscience at the

University of Tsukuba gathered two groups of adult male rats and had one group

start a treadmill running program, while the other group sat for the same period

of time each day on unmoving treadmills. The researchers’ aim was to determine

how much the level of brain glycogen changed during and after exercise.

Using their glycogen detection method, they discovered that prolonged exercise

significantly lowered the brain’s stores of energy, and that the losses were

especially noticeable in certain areas of the brain, like the frontal cortex and

the hippocampus, that are involved in thinking and memory, as well as in the

mechanics of moving.

The findings of their subsequent follow-up experiment, however, were even more

intriguing and consequential. In that study, which appears in this month’s

issue of The Journal of Physiology, the researchers studied animals after a

single bout of exercise and also after four weeks of regular, moderate-intensity

running.

After the single session on the treadmill, the animals were allowed to rest and

feed, and then their brain glycogen levels were studied. The food, it appeared,

had gone directly to their heads; their brain levels of glycogen not only had

been restored to what they had been before the workout, but had soared past that

point, increasing by as much as a 60 percent in the frontal cortex and

hippocampus and slightly less in other parts of the brain. The astrocytes had

“overcompensated,†resulting in a kind of brain carbo-loading.

The levels, however, had dropped back to normal within about 24 hours.

That was not the case, though, if the animals continued to exercise. In those

rats that ran for four weeks, the “supercompensation†became the new normal,

with their baseline levels of glycogen showing substantial increases compared

with the sedentary animals. The increases were especially notable in, again,

those portions of the brain critical to learning and memory formation — the

cortex and the hippocampus.

Which is why the findings are potentially so meaningful – and not just for

rats.

While a brain with more fuel reserves is potentially a brain that can sustain

and direct movement longer, it also “may be a key mechanism underlying

exercise-enhanced cognitive function,†says Hideaki Soya, a professor of

exercise biochemistry at the University of Tsukuba and senior author of the

studies, since supercompensation occurs most strikingly in the parts of the

brain that allow us better to think and to remember. As a result, Dr. Soya says,

“it is tempting to suggest that increased storage and utility of brain

glycogen in the cortex and hippocampus might be involved in the developmentâ€

of a better, sharper brain.

Given the limits of current technologies, brain glycogen metabolism cannot be

studied in people. But even so, the studies’ findings make D.I.Y. brain-fuel

supercompensation efforts seem like an attractive possibility. And, according to

unpublished data from Dr. Soya’s lab, the process may even be easy.

He and his colleagues have found that “glycogen supercompensation in some

brain loci†is “enhanced in rats receiving carbohydrates immediately after

exhaustive exercise.†So for people, that might mean that after a run or other

exercise that is prolonged or strenuous enough to leave you tired, a bottle of

chocolate milk or a banana might be just the thing your brain is needing.

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