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We’ve been studying the body for most of human history, and yet we are still finding new organs (or parts of them - depending on your definition). Also, thanks to some marmosets, we know a little more about how anxiety and depression might work in your brain.

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Sources:
New glands
Valstar et al 2020 (https://www.sciencedirect.com/science/article/pii/S0167814020308094)
Asfhar-Oromieh et al 2015 (establishes technique can be used for PET and that it detects salivary glands) http://jnm.snmjournals.org/content/56/11/1697.full.pdf
Nulent et al 2018 (previous work done by the group that further confirms ability to see salivary glands in PET scans using PMSA) https://www.sciencedirect.com/science/article/abs/pii/S2212440318300476

Marmosets
Alexander et al 2020 (http://dx.doi.org/10.1038/s41467-020-19167-0)

Image Sources:
https://www.istockphoto.com/photo/common-marmoset-callithrix-jacchus-adults-standing-on-branch-gm1251686751-365372958
https://www.istockphoto.com/vector/adult-vector-illustration-of-common-marmosets-gm1272748274-374923006
https://www.istockphoto.com/photo/the-girl-clings-to-the-inflamed-salivary-gland-in-which-pain-concept-of-salivary-gm1221344075-357961764
https://www.istockphoto.com/vector/4-insert-the-swab-into-the-nostril-gm1279399379-378031381
https://www.istockphoto.com/photo/human-brain-with-colored-regions-gm184849805-18406670
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Go to Brilliant.org/SciShow to learn about their course Applied Probability. [♪intro]. There’s a common side effect for cancer patients who’ve gotten radiation therapy for cancers in their head or neck: chronic dry mouth or recurrent trouble swallowing after the procedure.  This is because the radiation necessary to kill the tumor can also end up damaging the salivary glands.  And having dry mouth all the time actually can really end up impacting a person’s quality of life.

But new research suggests a better way to prevent this, because scientists have found a whole new set of salivary glands... that we didn’t know about before. We’ve been looking at the human body for a long time now; we missed the glands! The key to how they were found involves a molecule called a tracer.

These are essentially molecules that can bind to other specific molecules in our bodies, and that we can track via scans. These are useful because they allow doctors to follow that molecule in the body. And that can help them map out the location of tumors derived from those tissues, where they start, and where they spread to.

Recently, scientists developed a tweak to a tracer that can bind to PSMA, which is a molecule found in a couple of different tissues, like the prostate and salivary glands.  This made the tracer much more powerful — so much so that they can show up in certain types of high-definition medical scans called PET scans. And this can help doctors see very precisely if prostate cancer has spread to different parts of the body.   Only, remember how we said that these tracers also bind to salivary glands? Well, because of that, in an earlier 2018 paper, a group of scientists in the Netherlands were interested in seeing if they could use this technique to precisely map out an individual person’s salivary glands.  Knowing precisely where each person’s salivary glands are located could be used to better individualize radiation therapy and prevent that chronic dry mouth.  The scientists saw the three major, known salivary glands light up when using this tracer, but they were surprised to see what looked like a fourth major set.  There had been hints in the past that there may be tissue there, but these looked like full blown glands.    To investigate this, in a paper published last month in the journal Radiotherapy and.

Oncology, the scientists got a hold of full-body PET scans of 100 cancer patients using this particular tracer. And they saw further evidence of a fourth set of salivary glands that had gone under the radar. Studying two donated cadavers confirmed it — they had found a wholly unknown set of salivary glands.    This new set is found draped around the auditory tube, which connects our ears to our throat.

If you’ve ever gotten a deep nasal swab — like they do for COVID-19 tests sometimes — these are near there. And since the technical term for this area is the torus tubarius, they’re calling these new glands the tubarial glands.    There’s a little ambiguity about whether these count as a new organ in and of themselves, or if we should group all the salivary glands into one big organ. But either way, it’s at least part of an organ that is totally new to us.   And because of this discovery, we can now be even more careful when aiming that radiation therapy, which should help improve the quality of care for cancer patients.

So this discovery is way more than just neat! Moving up from the salivary glands, we turn to an organ that’s also somewhat important: the brain. Our brains are subdivided into regions that seem to control different functions.

Over the years, we’ve come to recognize the broad strokes, but we’re still figuring out exactly how all of that works. Especially challenging are questions about things like anxiety or depression. If we can figure out how the different parts of the brain play a role in those disorders, we could figure out better ways to help people.

In new research this week from the University of Cambridge, scientists may have figured out another piece of the puzzle. In particular, it looks like over-activity in a specific part of the brain called the subgenual anterior cingulate cortex, or sgACC, may underlie key stress-related symptoms of depression and anxiety.   The researchers were doing experiments with common marmosets, a kind of small monkey.  They are good subjects for neuroscience studies since they’re primates, like humans, but also small and relatively easy to care for.  Previous work had suggested overactivity in the sgACC may be involved in anhedonia — a kind of inability to feel pleasure that’s a common part of depression.  This time around, the scientists wanted to know if the sgACC also played a role in how we perceive, deal with, and get over threatening circumstances. To test this out, the marmosets were divided into control and experimental groups, with the experimental group getting a drug that causes over-activation of the sgACC.  The scientists then put the marmosets through a number of tests to see how they’d react to threats, like a rubber snake.

Or a strange human coming into the room and making eye contact with them for two minutes. Which, I know, I would find threatening! Overall, they found that over-activation of the sgACC increased how worked up the marmosets got, and actually increased their heart rate as well.  This suggests over-activation in this particular brain region increased anxiety-like symptoms and made it harder for the marmosets to get over the initial threat.

The scientists think this may be related to anxiety disorders, especially ones characterized by “free-floating” anxiety without a clear cause. This is cool because it hints that studying this area more could help us better understand how depression and anxiety work. It certainly isn’t a solution yet, but it’s a clue that one day, we will be able to deal more effectively with these conditions.   This has been your weekly dose of science news -- but if you’re not through learning yet, you might enjoy a course from Brilliant.

Their course Applied Probability will help you understand how we deal with chance and randomness -- and give them an element of predictability. All of Brilliant’s interactive courses, from science to math to computer science to engineering, will help you sharpen your scientific thinking skills. And if you sign up at brilliant.org/scishow, you can even save 20% on an annual premium subscription if you’re one of the first 200 people in line.

Checking them out also supports SciShow, so thanks for that! [outro ♪].