Research News......
Study Reveals Racial Differences in Blood Pressure Regulation in
Healthy, Young Women.
Our bodies must make a number of adjustments to stay upright as we change position from seating or lying to the upright posture. As we stand up, the blood in our vasculature is subject to the laws of gravity, and thus is drawn towards our feet. However, if blood volume were not maintained at the level of the heart and brain, we soon would feel dizzy and become unconscious. These cardiovascular responses are similar to those astronauts experience after hypogravity exposure. In order to combat these symptoms, our bodies have developed a complex but beautifully orchestrated system to maintain blood pressure so we can continue to function upright. The extent to which an individual can maintain blood pressure at normal levels during posture changes or hypogravitational exposure is termed “orthostatic tolerance”.
However, as with all physiological systems, not all people are as adept at regulating blood pressure under these conditions; women more frequently suffer from orthostatic intolerance, meaning that they are at greater risk for losing consciousness or experiencing dizziness in response to postural or gravitational challenges. A recent study published in the journal Hypertension by Kumba Hinds, MPH and Dr. Nina Stachenfeld at the John B. Pierce Laboratory, is the first to directly assess racial differences in orthostatic tolerance in women. They chose to examine racial differences because of the well-known differences in blood pressure regulation between black and white men and women, differences that are apparent even in young, healthy people. In order to study this question, young black and white women underwent maximal “lower body negative pressure” testing. A technique used by NASA to test orthostatic tolerance in astronauts, lower body negative pressure simulates standing and gradually pulls blood to the lower extremities. The pressure is maintained until the participant indicates feelings of dizziness. The greater the level of lower body negative pressure a person can withstand, the greater their orthostatic tolerance.
A key finding was that black women were able to tolerate a much greater orthostatic challenge than white women. In fact, as a group, orthostatic tolerance was more than two times that of the white women, and was similar to that typically found in men, suggesting that sex differences in orthostatic tolerance do not extend to black women. Dr. Stachenfeld suggests that while “this improved orthostatic tolerance is an advantage for young black women during posture changes, we need to explore the mechanisms that contribute to the difference in blood pressure regulation in these young women. Some of the possible mechanisms, such as cardiovascular stiffness and poor endothelial function, increase the risks for hypertension later in life.” NIHMSID #20349
Narayanan Receives Donald B. Lindsley Prize
Researcher recognized for outstanding thesis in behavioral neuroscience
The Society for Neuroscience (SfN) has awarded the Donald B. Lindsley Prize to Nandakumar Narayanan, MD, PhD, and Kay M. Tye, PhD, and during Neuroscience 2009, SfN’s annual meeting and the world’s largest source of emerging news on brain science and health. Supported by The Grass Foundation, the prize, which includes $2,500, recognizes an outstanding PhD thesis in the area of general behavioral neuroscience. The award was established in 1979 in honor of Donald B. Lindsley, PhD, a pioneer in the field of behavioral neuroscience.
Narayanan completed his thesis research in Mark Laubach’s laboratory at the John B. Pierce Laboratory and was a student in the Medical Scientist Training Program and Interdepartmental Neuroscience Program at Yale University. He is currently undergoing residency training in neurology at Yale.
Narayanan’s thesis studied the role of medial prefrontal cortex in executive control. His thesis work described how the dorsomedial prefrontal cortex suppresses inappropriate actions. He discovered that neurons in rodent prefrontal cortex fire persistently when rats must wait for a stimulus before making a movement and that these cells control the level of “delay activity” in the motor cortex. These findings suggest that inappropriate actions occur when the prefrontal cortex fails to achieve control over the motor system. He also discovered that neurons in the medial prefrontal cortex track successes and failures from one trial to the next and that rats exhibit brain potentials that are similar to those found in human beings when mistakes are made. His thesis research, so far, has led to six journal articles (Neuron, Journal of Neuroscience, Journal of Neurophysiology) and was supported by grants from the Tourette Syndrome Association and National Science Foundation to Mark Laubach.
These three papers are the core findings from the thesis:
http://spikelab.jbpierce.org/Publications/Narayanan-Laubach-Neuron-2006.pdf
http://spikelab.jbpierce.org/Publications/Narayanan-JNP-2008.pdf
http://spikelab.jbpierce.org/Publications/Narayanan-JNP-2009.pdf
Researchers discover evidence of a sweet taste receptor in the brain
When blood glucose levels fall to dangerously low levels, the brain initiates protective physiological responses that work to restore glucose to normal levels. These responses are primarily mediated by specialized brain cells, called “glucosensing” neurons, which react to fluctuations in extracellular glucose. However, the mechanism by which these cells sense glucose remains controversial. On one hand, intracellular metabolism of glucose might operate as a glucose sensor in neurons in much the same way that insulin-releasing cells of the pancreas react to changes in blood glucose levels. On the other hand, other evidence shows that brain cells can perform their glucosensing functions independently of intracellular metabolism, which implies the neurons may be able to detect glucose levels directly via a membrane receptor.
Dr. Ivan de Araujo and colleagues at the John B. Pierce Laboratory investigated the possibility that the receptor might be the well-known sweet taste receptor, a membrane-bound protein exquisitely sensitive to changes in glucose concentration. The researchers found that sweet-like receptors are indeed present in the brain, particularly in the hypothalamus, the central controller of body metabolism. Importantly, Dr. de Araujo found that the transcription levels of the sweet receptor gene were significantly higher during hypoglycemia, and that this effect could be reversed by exposing hypothalamic cells to an artificial sweetener. These findings raise the remarkable possibility that hypothalamic nuclei can “taste” the chemical composition of the blood and cerebral spinal fluid, thereby allowing the brain to fine-tune physiological responses according to the nutritional state of the organism. (See the Neurobiology of Feeding Laboratory)
Reduced brain response to milkshake predicts weight gain, according to a study published in the October 17th issue of the journal Science.
In a unique collaboration between clinical psychologists led by Eric Stice at the Oregon Research Institute and the University of Texas and sensory neuroscientist Dana Small at The John B. Pierce Laboratory and Yale University, young women sipped a tasty milkshake while having their brain scanned with functional magnetic resonance imaging. “The goal of the study was to identify brain regions that respond differently to food in overweight and obese girls compared to their lean peers and then to determine if these abnormal responses predict weight gain” says Small. The team found a very consistent decreased response in overweight and obese girls in a region of the brain called the striatum, which is known to contain dopamine and encode reward. This decrease was amplified in subjects who possessed a genetic variation associated with reduced dopamine and predicted weight gain in this group of girls. According to Small, “the finding either suggests that overweight and obese girls eat more to achieve the same brain response, or that the brain has adapted or down-regulated in response to overeating.” The finding is important because it suggests that individual differences in the neurophysiology of food reward may put some at risk for overeating in the current environment, which is rich in palatable and energy dense foods. For more information go to the lab of Affective Sensory Neuroscience.
