How Do Frogs Survive the Cold? By Freezing


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They aren’t moving. They’re not responding to touch or light. Their hearts aren’t beating. They’re no longer breathing. Their skin is ice-cold and hard to the touch. By that description, you probably don’t think I’m describing living things. However, there are some animals that survive like this because of a process called freeze tolerance.

Unlike mammals, whose bodies are always working to maintain a constant temperature, cold-blooded animals (ectotherms) are at the mercy of their environment. As a result, when the temperature plummets, they have to come up with a physiological means to survive the bitter cold winters.

Bugs and amphibians are the freeze-tolerant animals researchers study most often. Among amphibians, a few select frogs show a clear freeze-tolerance response. Large amounts of their bodily fluid freeze into ice particles to help them make it through the winter.

The physiological changes that prepare freeze-tolerant animals for cold weather begin as the temperature drops, but they don’t happen overnight. These animals distribute substances called cryoprotectants, which allow them to get colder than freezing while shielding them against dehydration and other cell changes that can occur when ice forms. Once frozen, the animals can withstand temperatures ranging from 32 to -22 degrees F, depending on the species. Freeze tolerance can last from weeks to months. Cycling through this process is a must for any frog that wants to see the next summer.

However, thawing may be just as important as freezing. Freeze-tolerant animals likely go through several freeze-thaw cycles, during which the distribution of cryoprotectants and tolerance to the cold increases. This suggests that the cryoprotective process isn’t finished after the first freeze and is a cumulative process as the winter grows colder. When spring arrives and the weather returns to consistently above-freezing temperatures, the animals thaw, their hearts start beating again and they continue on without negative effects.

Scientists want to learn more about freeze tolerance from the animals that do it so well. In case you missed it, humans can’t freeze and thaw themselves. By studying the physiological changes in freeze-tolerant species, researchers can apply this work to mammals, such as by storing organs for later use and keeping cell lines healthy while in storage. Studying an “ideal” organism that has overcome a functional problem allows scientists to better understand those problems in mammals. Therefore, comparative physiologists continue to research the unique traits of various organisms to understand how evolution has already handled these challenges.

Brian StogsdillBrian Stogsdill is a graduate student at Wright State University, in Dayton, Ohio, currently finishing his doctorate in biomedical science. Stogsdill researches freeze tolerance and aquaglyceroporins (a family of proteins that conduct water). 

The Fat-blocking Powers of Fiber

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An estimated 610,000 people in the U.S. die from heart disease each year. One common cause of heart disease is the narrowing of blood vessels due to the buildup of fatty deposits (plaque). Many factors—including eating a lot of fatty foods—can lead to plaque buildup in blood vessels.

Your liver processes excess fat by packaging it into cholesterol droplets known as low-density lipoproteins (LDLs). LDLs travel throughout the body in the blood. Often, the droplets get stuck to the blood vessel walls, where they accumulate. The buildup of plaque eventually blocks blood flow, most often in the blood vessels that supply blood to your heart. However, eating fiber can help prevent the early stages of heart disease and plaque buildup.

Fiber is a plant’s supply of stored energy, but your gut can’t digest it. During a meal, your small intestine breaks down the food you eat and absorbs nutrients. Fiber resembles a mesh-like structure. Indigestible fiber acts like a large net—think of a butterfly net—to block places where fat can be absorbed. A meal high in dietary fiber blocks some of the absorption of fats, stopping fats from moving outside the gut into the bloodstream.

When there is less fat absorbed from your gut, your liver does not have to package it into LDL droplets, which lowers LDL levels in the blood. In addition, when your liver needs fat to make hormones and bile, it can produce another kind of cholesterol called high-density lipoproteins (HDL). HDL can remove some of the plaque in blood vessels and send it back to the liver. HDL is known as “good cholesterol” for this reason. Consuming meals high in fiber can help HDL with this process.

Recent studies have shown that eating fiber-rich brown rice or taking more than 5 grams of fiber supplements daily can improve some measures of cardiovascular function in adults. Leafy or green vegetables such as spinach, lettuce and broccoli are also good sources of fiber. So make a salad or try adding greens to an entree or a smoothie—I promise you can’t even taste blended spinach in a fiber-packed smoothie. There are plenty of options to fiber up your diet and keep your heart healthy.

Gabrielle RoweGabrielle Rowe is a PhD candidate in the physiology program at the University of Louisville. She is interested in studying small heart vessel function, stem cells and aging.

Spotlight On: Preeclampsia

Pregnant woman holding hands over belly on black background

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Lady Sybil Crawley—the feisty youngest sister of a wealthy British family on the PBS television series “Downton Abbey”—made her way into viewers’ hearts. Devotees of the show were shocked when, in a surprise twist, she died soon after giving birth. Lady Sybil died from high blood pressure during pregnancy (preeclampsia) that developed into a more serious condition called eclampsia in which high blood pressure causes potentially fatal seizures.

Unfortunately, this type of tragedy is not a distant memory from the early 1900s when “Downton Abbey” was set. Preeclampsia still causes too many deaths—or near deaths—in the U.S. each year. However, when diagnosed properly, preeclampsia is manageable.

Preeclampsia develops in about 5–8 percent of all pregnancies. Symptoms include headaches, nausea, vomiting, and excessive swelling of the feet, hands and face.

There are also invisible symptoms, such as damage to internal organs like the liver and kidneys. Preeclampsia occurs when a woman’s blood pressure rises too high (140/90 mmHg or above) during mid- to late-pregnancy (more than 20 weeks of gestation). The increased blood pressure limits the amount of blood that the baby receives and can slow down fetal growth. Babies born to women with preeclampsia are frequently smaller and weigh less than those born to women with normal blood pressure. Preeclampsia is often connected with other health conditions such as obesity, diabetes, kidney disease and a history of high blood pressure.

A woman’s age, race and where she lives can also increase the likelihood of developing preeclampsia. Women over age 40, black women and women from the southern U.S. also have an increased risk of developing high blood pressure during pregnancy. The reasons why Southern women have greater risk are not clear, but it may be linked to the prevalence of obesity and diabetes, especially in the Deep South.

It is important for expectant women and their families to know the symptoms of preeclampsia, talk openly with their doctors about their potential risks and speak up when something doesn’t feel right. May is Preeclampsia Awareness Month. Talk to the pregnant women in your life and learn about preeclampsia together.

Jessica Taylor, PhDJessica C. Taylor, PhD, is the Senior Manager of Higher Education Programs at the American Physiological Society. She is a cardiovascular physiologist, the mother of one and hails from Mississippi.

Photoblog: Experimental Biology 2018

Ever wonder what happens at a scientific meeting? They’re a great place for scientists to get new ideas and collaborate with their colleagues on important advancements in scientific research and discovery. But it’s not all work. These meetings also give researchers the chance to catch up with friends and former co-workers and to socialize with new colleagues.

 I Spy Physiology volunteer blog editor Audrey Vasauskas was among the more than 11,000 attendees at the APS annual meeting at Experimental Biology (EB) in April. She photoblogged her experience during her time in San Diego. Check out what the meeting looked like to her.

The Research

“I submitted two abstracts to the meeting this year, one on my bench research in pulmonary arterial hypertension and one on an outreach educational program for high school students that I co-directed.  I was very excited that the EB organizers added a separate section for science outreach so that I could share what we are doing within our community. It took place during the opening reception, which brought in many people to view the posters and chat.  It was nice to have so many people come by to share ideas and suggestions on my research, for both the pulmonary hypertension and the outreach projects.  I’ve gotten some of the best suggestions for future work through speaking with poster attendees!  I have also been able to set up some great collaborations.”


The Collaboration

“The EB meeting is an excellent opportunity to meet people interested in the same field of research and make important connections for collaborations and idea sharing. For example, I was able to connect with a faculty member also studying pulmonary hypertension for insight and a possible collaboration. It is also a great time to catch up with colleagues who I don’t normally get the luxury to speak with in-person! I spent time with my former postdoctoral mentor. It was great to see her and hear about her graduate students’ research during the Respiration Section Trainee Highlights Breakfast.”


The Fun

“EB is so much fun! I love learning about areas outside of my research as well as getting up-to-date in my field. However, my favorite part is connecting with old friends who come together for this special event. Whether at formal section dinners or impromptu meetings, it’s the people who make EB great! I loved the APS Connect Zone, where we could relax, play games and talk. Lunches on-site and nearby were also fantastic. Of course, going to a meeting far from home also calls for exploration. Getting out in San Diego was a blast! My friends and I rode the water taxi to Coronado Island to see the Pacific Ocean and walk around. It was a great afternoon.”


The Food

“Yummmmmm … so much food, so little time.”


Wrapping Up and Looking Forward

“I look forward to attending the EB meeting every year, and it never disappoints! I am able to present my research, meet new people and see old friends. The meeting stimulates new scientific ideas and collaborations in a fun, collegial way. Every year after the EB meeting, I feel renewed in my love for science and exploration and grateful to have had an opportunity to travel, explore and contribute to the scientific community through my participation!”

-Audrey Vasauskas

Did You Know?: A Muscle May Increase Pneumonia in Older People

Old man in white is coughing. Symptoms and disease.

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By the year 2030, an estimated 70 million people in the U.S.—about 20 percent of the total population—will be older than 65. Going forward, this number is only expected to rise due to a combination of declining birth rates and increased life expectancy.

A well-known witticism is “Age is an issue of mind over matter. If you don’t mind, it doesn’t matter.” But as we get older, we face an increase in a variety of life-threatening diseases and illnesses, so we should mind the matter of aging.

One of the leading causes of death in older adults is pneumonia, an infection of the lungs. A major risk factor for pneumonia in older people is not being able to effectively clear their airways due to muscle weakness. Common causes of weakened respiratory muscles are age, spinal cord injury, muscular dystrophies and Lou Gehrig’s disease (ALS).

The diaphragm is a thin muscle that separates your chest cavity from your abdomen. It is the primary muscle for breathing and is very important in airway clearance (i.e., coughing and sneezing). Specialized nerve cells called phrenic motor neurons control the diaphragm muscle. There are different types of phrenic motor neurons. Smaller ones activate smaller muscle fibers and are responsible for low-force, repetitive tasks such as breathing. Larger motor neurons activate larger muscle fibers and control higher force jobs such as clearing the airway. Our lab has found that just like other muscles, the diaphragm gets weaker and smaller with age (sarcopenia). We have also shown that we lose some phrenic motor neurons, especially the large ones, as we get older. This loss of nerve cells causes the diaphragm muscle to have trouble generating the force needed to clear the airways.

For the most part, older people can breathe fine, but they may have trouble coughing and sneezing effectively. Not being able to clear mucus and bacteria from their airways may increase their risk for respiratory infections. Understanding the causes of age-related degeneration of the diaphragm muscle will lay the groundwork for effective therapies and improve the healthy lifespan of our aging population.

Obaid Khurram 2Obaid Khurram, PhD, recently graduated from the Mayo Clinic Graduate School of Biomedical Sciences. Obaid studied motor control of the diaphragm muscle, particularly in cases of motor neuron loss. He will continue studying motor control of skeletal muscles during his postdoctoral training at Northwestern University.


The Heart Adapts to the Sex of Heart Transplant Recipients


Peter Kerkhof, PhD, presents his poster, “Sex-Specific Aspects in Cardiac Transplantation Evaluated by Left Ventricular Size in Male and Female Recipients” at Experimental Biology 2018. Credit: Nathalie Fuentes

Whether you are male or female can play a role in your health when it comes to how well you recover and thrive after an organ transplant. Because donated organs are in high demand, the sex of the donor is not taken into consideration when assessing compatibility. However, men and women who receive donated organs can respond differently after transplantation, including in cases when the immune system rejects the transplanted organ. For some people, organ rejection may be influenced by the sex of the donor.

The influence of biological sex on transplant outcome has not been thoroughly studied—even as more than 3,000 people in the U.S. are waiting for a heart transplant on any given day. Peter Kerkhof, PhD, and colleagues at VU University Medical Center in the Netherlands evaluated current knowledge about the impact of biological sex differences in heart transplantation and explored why there is a discrepancy between rejection rates for male and female recipients. Kerkhof presented his team’s research at Experimental Biology 2018.

The researchers analyzed computer tomography scans of 94 patients who had a heart transplant. Forty percent of the transplanted hearts were from male donors, and 60 percent were from females. The research team discovered that the left ventricle—which supplies most of the heart’s pumping power and is essential for normal function—in transplanted hearts is able to adapt to the new body in size and pumping power, even if the recipient was of the opposite sex.

The researchers saw evidence of this adaptation in the ejection fraction of the heart recipients. Ejection fraction compares the amount of blood in the heart to the amount of blood pumped out and was found to be smaller in all female recipients, even those with male donor organs. The smaller ejection fraction in women is similar to what occurs in healthy women when compared to men. Now more research is needed to learn about the mechanisms responsible for sex-specific adaptation in heart transplant recipients.


Nathalie Fuentes OrtizNathalie Fuentes is a PhD candidate in the biomedical sciences program at Penn State College of Medicine. Her studies in Dr. Patricia Silveyra’s lab include the development of sex-specific therapies to treat lung diseases, sex differences in asthma-related lung inflammation triggered by ground-level ozone and the role of male and female sex hormones in lung disease. Nathalie is originally from Caguas, Puerto Rico.

Nathalie served as a meeting blogger for Experimental Biology 2018.


Herbal Tea: Healthier Hot or Cold?

herbal tea

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Tea—the most widely consumed beverage in the world next to water—can be found in almost 80 percent of U.S. households. In 2017, people in the U.S. consumed over 84 billion servings of tea—that’s more than 3.8 billion gallons! Tea is versatile: served hot or iced, anytime, anywhere and for any occasion.

Herbal tea is gaining popularity among consumers. It is made by boiling herbs or dissolved plant compounds in water to extract the active herbal ingredients. Herbal tea infusions are believed to fight off heart attacks, cancer and other diseases. However, whether it’s healthier to drink herbal tea hot or cold is unclear.

Claire Maufrais, PhD, and colleagues from the University of Fribourg in Switzerland studied volunteers who drank unsweetened, caffeinated herbal tea (yerba mate) either cold or hot. Yerba mate is a plant native to the South American rainforests. Some research suggests that yerba mate may improve blood sugar and cholesterol levels. It is also sometimes used as a natural remedy for chronic fatigue, headaches and depression.

The researchers monitored the volunteers’ heart rate, blood flow, blood pressure, amount of oxygen their bodies used, and how much fat was broken down to release energy (fat oxidation) for 90 minutes after each drink was consumed. They found that drinking the tea at cold temperatures boosted a metabolic process in which the body burns calories to produce heat. Compared to hot tea, cold tea also increased fat oxidation without causing stress to the volunteers’ cardiovascular systems. Maufrais’ next goal is to evaluate if cold herbal tea could be effective for weight control.

Read the full study about herbal tea by the University of Fribourg’s research team in Frontiers in Physiology.

Nathalie Fuentes OrtizNathalie Fuentes is a PhD candidate in the biomedical sciences program at Penn State College of Medicine. Her studies in Dr. Patricia Silveyra’s lab include the development of sex-specific therapies to treat lung diseases, sex differences in asthma-related lung inflammation triggered by ground-level ozone and the role of male and female sex hormones in lung disease. Nathalie is originally from Caguas, Puerto Rico.

Nathalie served as a meeting blogger for Experimental Biology 2018.

Do Caffeine and Menstrual Cycles Affect Athletic Performance?

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Mara Rutherford presents her poster, “Effects of Caffeine and Menstrual Phase on Performance of Female Athletes during Heat Stress,” at Experimental Biology 2018. Credit: Nathalie Fuentes

Menstruation and its effect on athletic performance is not often discussed in athletics, even though most female athletes deal with it in their daily lives. However, more researchers have begun to look at this subject, and some are observing how other factors, such as caffeine consumption, could influence a female’s performance during sports.

A recent survey found that 61 percent of women are self-proclaimed coffee addicts. Previous research has shown that that caffeine stimulates the central nervous system to enhance endurance performance. In addition, many female athletes use birth control pills (oral contraceptives) to regulate their menstrual cycle; these pills may also enhance the effects of caffeine.

Maura M. Rutherford, a student in the department of human kinetics at Saint Francis Xavier University in Canada, and other scientists studied the potential impact of caffeine and hormonal changes across the menstrual cycle on women’s athletic performance. Six recreationally active women who were taking oral contraceptives volunteered for this study. They took a caffeine supplement and then ran 5 kilometers (3.1 miles) at different stages of their menstrual cycle. The investigators found that caffeine supplementation improved the athletes’ performance in the early follicular phase, when the follicles that will eventually release an egg during ovulation start to develop. However, caffeine did not improve the running time in the mid-follicular phase (i.e., ovulation) of the menstrual cycle. These results could be due to a sudden increase in fatigue that was observed in this phase.

Nathalie Fuentes OrtizNathalie Fuentes is a PhD candidate in the biomedical sciences program at Penn State College of Medicine. Her studies in Dr. Patricia Silveyra’s lab include the development of sex-specific therapies to treat lung diseases, sex differences in asthma-related lung inflammation triggered by ground-level ozone and the role of male and female sex hormones in lung disease. Nathalie is originally from Caguas, Puerto Rico.

Nathalie served as a meeting blogger for Experimental Biology 2018.

Can Altitude Affect Blood Flow and Your DNA?

An estimated 400 million people—myself included—live at elevations higher than 1,500 meters above sea level. The beautiful scenery, rugged mountains and clean air are part of the appeal to many of us. But interesting changes in the body seem to occur as a response to living at high altitude. Scientists from all over the world are working hard to understand these changes and how and why they happen.

At increasing altitudes, air pressure in the atmosphere (atmospheric pressure) decreases. Atmospheric pressure helps us get air into our lungs and blood. As the air pressure decreases, we inhale less oxygen with each breath, throwing off our normal breathing patterns,which means we don’t get enough oxygen to use for energy. As a result, the blood flow to the brain increases. This is called hypoxia. Carbon dioxide in the blood also decreases (hypocapnia), which causes decreased blood flow in the brain. Two researchers presented posters at the Experimental Biology 2018 meeting in San Diego that explore the role of genetics, cerebral blood flow and altitude on our bodies.

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Hailey Lafave presents her poster, “Tracking cerebral blood flow regulation during incremental ascent to altitude: Effect of superimposed hypoxia and hypocapnia” at Experimental Biology 2018. Credit: Nathalie Fuentes

Hailey C. Lafave, of Mount Royal University in Alberta, Canada, studied hikers who trekked 4,370 meters above sea level over seven days in the Nepal Himalayas. The hikers’ vital signs were measured at 1,400 meters on day 1; 3,440 meters on day 3; and 4,370 meters on day 7. The study found that the hikers’ blood oxygen levels and blood pressure decreased at higher altitudes. Blood flow increased on the seventh day of hiking (at an elevation of 4,370 meters), but not at lower elevations (3,440 meters) on the third day. This novel finding could be used as a metric to detect hypocapnia on cerebral blood flow regulation at altitude.

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Elijah Lawrence’s poster, “Genetic missense variants at the EGLN1 locus associated with high-altitude adaptation in Tibetans are rare in Andeans” at Experimental Biology 2018. Credit: Nathalie Fuentes

Elijah S. Lawrence, of the University of California, San Diego, collaborated with researchers at the Universidad Peruana Cayetano Heredia in Peru to study why people who live at high altitude full-time experience hypoxia. The results demonstrate one of the most rapid evolution observations in humans. Lawrence found differences in the DNA of people living in high versus low altitudes. Genetic variations associated with hypoxia may be why some populations living at high altitude are particularly adapted to their environment and suffer from less severe hypoxia-induced complications.

As we continue to learn how hypoxia and hypocapnia affect the body and how we genetically adapt to our environment, remember to breathe slowly and deeply when you’re at high altitude to decrease your heart rate. This will help your body take in the oxygen it needs.

Nathalie Fuentes OrtizNathalie Fuentes is a PhD candidate in the biomedical sciences program at Penn State College of Medicine. Her studies in Dr. Patricia Silveyra’s lab include the development of sex-specific therapies to treat lung diseases, sex differences in asthma-related lung inflammation triggered by ground-level ozone and the role of male and female sex hormones in lung disease. Nathalie is originally from Caguas, Puerto Rico.

Nathalie served as a meeting blogger for Experimental Biology 2018.

How, What and When to Eat: Scientists Weigh In at Experimental Biology 2018

Each year, scientists who study physiology and other biomedical research fields—including anatomy, biochemistry, pathology and pharmacology—gather at the Experimental Biology (EB) meeting. Scientific meetings such as EB provide a platform to present and learn about new and cutting-edge research and form collaborations with colleagues that can lead to advances in science and medicine. This year’s EB meeting in San Diego featured studies ranging in topics from nutrition and exercise to mental well-being and women’s health. Read on for more about how the food we eat—and when we eat it—affects the body.

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You may already know that probiotics—live bacteria found in yogurt and nutritional supplements—are good for digestive health. Now researchers from Auburn University in Alabama have found that drinking kefir, a fermented milk-based beverage, may help lower blood pressure. Their study suggests that probiotic-rich kefir restores balance to bacteria in the intestines and an enzyme in the brain that controls nervous system function. It seems the gut and brain are working together to regulate blood pressure.

Diner: Artificial Sweetener Caddy

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Have you replaced the sugar in your morning coffee with a no-calorie artificial sweetener? This approach may help you cut calories, but according to researchers from the Medical College of Wisconsin, it may not reduce your risk of obesity or diabetes. Their data suggest that zero-calorie sweeteners change how the body processes fat and gets energy. Moderation with any type of sweetener, artificial or natural, seems to be the key.

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Breakfast skippers: New research from the Mayo Clinic suggests that passing on breakfast may be a cause of weight gain. Adult volunteers were found to gain less weight when they ate breakfast at least five days a week when compared to those who broke their fast later in the day. The results appear to confirm what your mother always told you: “Breakfast is the most important meal of the day.”

If you’re considering becoming pregnant, make sure your prenatal multivitamin includes zinc. Researchers at Pennsylvania State University found zinc is crucial for the health of a woman’s eggs. Zinc deficiency seemed to impair the development of eggs very early on, months before they are ready for release (ovulation) and fertilization. Zinc-deficient eggs were smaller and had problems with cell division, which can prevent fertilization from occurring.

Alternate-day fasting is a weight loss method that’s recently become more popular—but does it work? A research team from Kent State University in Ohio found that obesity-prone mice lost more weight when their calories were restricted every other day than lean mice did. This was the case even though the mice burned the same amount of calories on fasting and non-fasting days. The results suggest that alternate-day fasting may be effective in some people, but not as much in others.

Interested in learning about more research presented at the meeting? Read Meditation, Stress and Mental Fatigue: Research from Experimental Biology 2018.

Erica Roth