Scientists Pinpoint Brain Cells That Signal When To Stop Eating


Nature employs a lot of checks and balances to keep life running smoothly. For example: When an animal’s stomach is full, its brain tells it to stop eating (although you might not be able to tell from watching your dog at dinnertime). Scientists say they’ve found the exact group of brain cells responsible for that “stop eating!” message—and what happens when those cells are damaged. Their report was published in the journal Science.

Many call obesity an epidemic. But what we often overlook are the myriad factors that can lead to a person becoming and staying overweight or obese. It’s not a matter of simply deciding to eat less; genetics, gut bacteria, hormones, socioeconomic status, chemical exposure, and, now, this little bundle of brain cells, have all been implicated.

The discovery of the brain’s satiety (or fullness) center was a happy accident. A team of researchers were studying the enzymes that boost or weaken synapses, the connections between brain cells. They focused their attention on an enzyme called OGT, which is known to affect how the body uses sugar and insulin.

To find out the relationship between OGT and synapses, the researchers switched off the OGT-encoding genes in a group of adult laboratory mice. Another group of mice went about their genetic business as usual. All the mice were allowed to eat as much as they wanted.

Before the researchers even began their tests, the OGT-deficient mice had doubled in weight. As the study continued, those mice continued to expand to twice their size every three weeks. And it wasn’t muscle they were gaining; it was fat, all over their bodies.

Image Credit: Johns Hopkins Medicine

The scientists began monitoring how often and how much the mice were eating. Both groups ate about 18 meals a day, but the mice in the experimental group lingered over their food and ate more calories at every meal than their control-group counterparts. The researchers then cut the chubby mice off, limiting their diet to reasonable portions. In the absence of extra calories, the mice stopped gaining weight, which suggests that the problem lay in their satiety signaling.

"These mice don't understand that they've had enough food, so they keep eating," co-author Olof Lagerlöf said in a press statement.

The thing is, the hippocampus and cortex—the areas deprived of OGT in the experimental group—aren’t generally associated with eating. So the researchers wondered if changes had occurred elsewhere in the rodents’ brains. The researchers euthanized the mice, removed their brains, and looked at thin slices of brain tissue under a high-powered microscope. They were looking for a region with a notable absence of OGT, and they found it, in a little bundle of nerve cells called the paraventricular nucleus (PVN).

Unlike the hippocampus and cortex, the PVN is known for affecting appetite and eating. But like any part of the brain, the PVN needs healthy synapses in order to do its job, and the researchers found that synapses in the fat rodents’ PVNs were in bad shape. The OGT-deficient mice had three times fewer PVN synapses than the control group.

"That result suggests that, in these cells, OGT helps maintain synapses," co-author Richard Huganir said. "The number of synapses on these cells was so low that they probably aren't receiving enough input to fire. In turn, that suggests that these cells are responsible for sending the message to stop eating."

The researchers confirmed their theory, so they tried boosting the synapses instead of wearing them down. Sure enough, mice with strong PVN synapses decreased their food intake by 25 percent.

"There are still many things about this system that we don't know," Lagerlöf said, "but we think that glucose works with OGT in these cells to control 'portion size' for the mice. We believe we have found a new receiver of information that directly affects brain activity and feeding behavior, and if our findings bear out in other animals, including people, they may advance the search for drugs or other means of controlling appetites."

'Lime Disease' Could Give You a Nasty Rash This Summer

A cold Corona or virgin margarita is best enjoyed by the pool, but watch where you’re squeezing those limes. As Slate illustrates in a new video, there’s a lesser-known “lime disease,” and it can give you a nasty skin rash if you’re not careful.

When lime juice comes into contact with your skin and is then exposed to UV rays, it can cause a chemical reaction that results in phytophotodermatitis. It looks a little like a poison ivy reaction or sun poisoning, and some of the symptoms include redness, blistering, and inflammation. It’s the same reaction caused by a corrosive sap on the giant hogweed, an invasive weed that’s spreading throughout the U.S.

"Lime disease" may sound random, but it’s a lot more common than you might think. Dermatologist Barry D. Goldman tells Slate he sees cases of the skin condition almost daily in the summer. Some people have even reported receiving second-degree burns as a result of the citric acid from lime juice. According to the Mayo Clinic, the chemical that causes phytophotodermatitis can also be found in wild parsnip, wild dill, wild parsley, buttercups, and other citrus fruits.

To play it safe, keep your limes confined to the great indoors or wash your hands with soap after handling the fruit. You can learn more about phytophotodermatitis by checking out Slate’s video below.

[h/t Slate]

Lia Is a Disposable Pregnancy Test You Can Flush Down the Toilet

It’s a common Hollywood plot point: A character spots a discarded pregnancy test in a bathroom trash can. Surprise! Someone’s pregnancy is revealed, though they weren’t yet ready to tell anyone (and perhaps never planned on telling them at all). Lia is a new type of disposable pregnancy test designed to be flushed down the toilet to make sure no one ever experiences that kind of privacy violation, according to Glamour.

Lia hasn’t hit the market yet, but when it does, it will be the first major redesign of the home pregnancy test in decades. The first at-home pregnancy test in the U.S. debuted in 1977, and while it took two hours to show a result, it gave women the option to learn their pregnancy status with relative accuracy (it was 97 percent accurate for positive results, but only 80 percent accurate for negative results) for the first time without going to the doctor. In 1988, Unilever came out with the first wand-style pregnancy test—the plastic kind you pee on to reveal the blue stripe indicators. Since then, not much has changed about the basic design of the at-home pregnancy test except the graphics that companies use to convey the test’s results. (The science undergirding the tests has advanced over the years, though.)

Unlike the plastic sticks, Lia is disposable and can be flushed down the toilet or composted. With the shape reminiscent of a sanitary pad, it works similar to the traditional pee-stick test: You urinate on it, then wait for the stripes to appear. While it’s water-resistant enough to withstand the two minutes of pee-soaking required to get a result, the test strip is made of the type of plant fibers that go into toilet paper and will eventually disintegrate in water. It can also be composted: In one experiment, it took 10 weeks to completely degrade in soil.

A diagram of Lia's features

Like other pregnancy tests available at the drug store, Lia’s results are based on the concentration of human chorionic gonadotropin (a pregnancy hormone) in your pee. It’s FDA approved, and the company reports that it’s more than 99 percent accurate, comparable to other tests on the market.

No matter what the circumstances surrounding a pregnancy are, most people don’t want to share the fact that they could be pregnant with everyone they might share a bathroom with—most people wait several months into their pregnancy to announce the news—and even if they want to tell the world immediately, they probably don’t want to do so via trash can. Lia’s paper design makes it easy to dispose of the test without worrying about who might stumble upon your wastebasket. It’s also more sustainable and won’t clog up landfills like plastic tests. While people don’t use as many pregnancy tests as, say, plastic straws, the over-the-counter plastic pregnancy test market is still a huge one, and a contributor to environmental pollution. As a bonus, the lack of plastic makes Lia cheaper to produce, too.

Lia will eventually be available in stores and online. It’s scheduled to be released sometime in 2018.

[h/t Glamour]


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