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Scientists Pinpoint Brain Cells That Signal When To Stop Eating

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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."

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New Patient Test Could Suggest Whether Therapy or Meds Will Work Better for Anxiety
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Like many psychological disorders, there's no one-size-fits-all treatment for patients with anxiety. Some might benefit from taking antidepressants, which boost mood-affecting brain chemicals called neurotransmitters. Others might respond better to therapy, and particularly a form called cognitive behavioral therapy, or CBT.

Figuring out which form of treatment works best often requires months of trial and error. But experts may have developed a quick clinical test to expedite this process, suggests a new study published in the journal Neuropsychopharmacology.

Researchers at the University of Illinois at Chicago have noted that patients with higher levels of anxiety exhibit more electrical activity in their brains when they make a mistake. They call this phenomenon error-related negativity, or ERN, and measure it using electroencephalography (EEG), a test that records the brain's electric signals.

“People with anxiety disorders tend to show an exaggerated neural response to their own mistakes,” the paper’s lead author, UIC psychiatrist Stephanie Gorka, said in a news release. “This is a biological internal alarm that tells you that you've made a mistake and that you should modify your behavior to prevent making the same mistake again. It is useful in helping people adapt, but for those with anxiety, this alarm is much, much louder.”

Gorka and her colleagues wanted to know whether individual differences in ERN could predict treatment outcomes, so they recruited 60 adult volunteers with various types of anxiety disorders. Also involved was a control group of 26 participants with no history of psychological disorders.

Psychiatrists gauged subjects’ baseline ERN levels by having them wear an EEG cap while performing tricky computer tasks. Ultimately, they all made mistakes thanks to the game's challenging nature. Then, randomized subjects with anxiety disorders were instructed to take an SSRI antidepressant every day for three months, or receive weekly cognitive behavioral therapy for the same duration. (Cognitive behavioral therapy is a type of evidence-based talk therapy that forces patients to challenge maladaptive thoughts and develop coping mechanisms to modify their emotions and behavior.)

After three months, the study's patients took the same computer test while wearing EEG caps. Researchers found that those who'd exhibited higher ERN levels at the study's beginning had reduced anxiety levels if they'd been treated with CBT compared to those treated with medication. This might be because the structured form of therapy is all about changing behavior: Those with enhanced ERN might be more receptive to CBT than other patients, as they're already preoccupied with the way they act.

EEG equipment sounds high-tech, but it's relatively cheap and easy to access. Thanks to its availability, UIC psychiatrists think their anxiety test could easily be used in doctors’ offices to measure ERN before determining a course of treatment.

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A Pitless Avocado Wants to Keep You Safe From the Dreaded 'Avocado Hand'
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The humble avocado is a deceptively dangerous fruit. Some emergency room doctors have recently reported an uptick in a certain kind of injury—“avocado hand,” a knife injury caused by clumsily trying to get the pit out of an avocado with a knife. There are ways to safely pit an avocado (including the ones likely taught in your local knife skills class, or simply using a spoon), but there’s also another option. You could just buy one that doesn’t have a pit at all, as The Telegraph reports.

British retailer Marks & Spencer has started selling cocktail avocados, a skinny, almost zucchini-like type of avocado that doesn’t have a seed inside. Grown in Spain, they’re hard to find in stores (Marks & Spencer seems to be the only place in the UK to have them), and are only available during the month of December.

The avocados aren’t genetically modified, according to The Independent. They grow naturally from an unpollinated avocado blossom, and their growth is stunted by the lack of seed. Though you may not be able to find them in your local grocery, these “avocaditos” can grow wherever regular-sized Fuerte avocados grow, including Mexico and California, and some specialty producers already sell them in the U.S. Despite the elongated shape, they taste pretty much like any other avocado. But you don’t really need a knife to eat them, since the skin is edible, too.

If you insist on taking your life in your hand and pitting your own full-sized avocado, click here to let us guide you through the process. No one wants to go to the ER over a salad topping, no matter how delicious. Safety first!

[h/t The Telegraph]

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