Risky Brain Response
Authors: Claire Murphy, Andrew Bender
Alzheimer's disease (AD) is the most common cause of dementia in those over 65. A growing public health concern, it has devastating effects on memory, even the sense of self, and causes financial and personal hardships for families who give care. Although having a risk factor does not definitively predict that a given person will get Alzheimer's disease, it does increase the chances of developing AD and thus, people at high risk of AD may have changes in performance or biological changes that may signal the beginning of AD. We have studied people with the Apoe e4 risk factor for AD to look for changes in the way the brain responds when it is trying to remember an odor. The study found that the brain response pattern, measured with EEG when they are performing the odor memory task is different in older adults who do and do not have the Apoe risk factor. Early identification of those at risk for developing AD will allow for early intervention as more powerful drugs become available for treating AD, so the ability to see changes in the brain's response in those at risk is a very encouraging sign.
Contact: Claire Murphy, Ph.D. San Diego State University and the University of California, San Diego; phone: 619 594-4559; FAX 619 594-3773; email: mailto:mcmurphy@sciences.sdsu.edu
Brain Automatically Adjusts
Authors: Jennifer Beshel, Leslie M. Kay
Tests on rats carried out at the University of Chicago show that their brains adjust when distinguishing between similar smells by increasing cell cooperation in their olfactory bulbs, the portion of the brain regulating transmission of information from the nose.
Previous studies in other animals have looked at how artificially increasing or decreasing cell cooperation affects smell, but this is the first study to examine the ways that mammals themselves respond to challenges of distinguishing smells by studying activity in the olfactory bulb while varying the discrimination difficulty.
For the experiment, researchers implanted electrodes into the olfactory bulbs of rats and tested them as they distinguished between smells that were similar or that were quite different. Activated olfactory bulb regions overlap when smells are similar but are distinct when the smells are different.
When the smells were similar, researchers found that cooperative activity in the olfactory bulb increased dramatically, showing that the olfactory bulb was working hard and using a unique strategy to distinguish smells. Distinguishing distinct smells produced little increase in cooperative activity.
The research suggests that the olfactory bulb in humans may respond in the same way, since the human olfactory brain is nearly the same as rats’.
Contact: Jennifer Beshel, Dept. of Psychology, The University of Chicago, Chicago, IL; phone: 773-551-1961; FAX; 773-702-6898; email: beshel@uchicago.edu
Pleasant and Unpleasant Odor
Authors: Hadas Lapid, David Harel, Noam Sobel
Mix yellow and cyan paint, and you get green. But what happens when you mix different odors? There is some understanding of what happens to odor intensity when you mix odors of different intensities, but only poor understanding of what happens to odor pleasantness when you mix odors of different pleasantnesses. To address this, human subjects rated the pleasantness of different odor mixtures. At first, we were surprised to find that a small addition of a pleasant odor to an unpleasant odor was more influential than a similarly small addition of an unpleasant odor to a pleasant odor. Further examination, however, revealed that this impression was probably dominated by changes in the overall quantity of the unpleasant odor. For example, when you mix 25% pleasant odor with 75% unpleasant odor, it becomes much less unpleasant than 100% unpleasant odor. This change, however, may be due more to the 25% reduction in unpleasant odor than to the addition of 25% pleasant odor. In this study we aim to elucidate the rules underlying this interaction such that we will be able to predict the pleasantness of odor mixtures based on the pleasantness of their components.
Contact: Hadas Lapid, Dept. of CS and Applied Math, The Weizmann Institute of Science, Israel; phone: +972-8-9346255; FAX: +972-8-9344131; email: hadas.lapid@weizmann.ac.il
Smelly Environments
Authors: Christiane Linster, Nathalie Mandairon, Emily Wyatt, Leslie M. Kay
Many brain systems improve when animals are exposed to complex (enriched) environments. The smell system shows strong enrichment effects and is one of the few places in mammalian brains where new nerve cells grow throughout life.
Previous studies showed that exposure to a smell for one hour per day for less than two weeks increases survival of newborn nerve cells (granule cells) in rats’ olfactory bulbs, the portion of the brain regulating transmission of information from the nose. This made them better at distinguishing odors, but it was unclear how this improves smell ability. This study shows FOR THE FIRST TIME that the number and distribution of olfactory bulb granule cells responding to odors increases, producing more cooperation among olfactory bulb cells.
One experiment showed that daily odor exposure increased the number of granule cells responding to odors. A computer model then predicted that increasing the granule cell response strength increases cell cooperation during smelling. In a second experiment, the researchers implanted electrodes into rats’ olfactory bulbs and tested them as they smelled odors. Cooperative activity in the olfactory bulb increased only in rats that had received odor enrichment. Since the human olfactory system is nearly identical to rats’, these data predict that people may also benefit from smelly environments.
Contact: Christiane Linster, Dept. of Neurobiology & Behavior, Cornell University, Ithaca, NY; email: CL243@cornell.edu
Dousing the Flame
Authors: R. Kyle Palmer, Daniel Long, Heather Devantier, Raymond Salemme, Robert Bryant
“Give me your spiciest wings.” A short time later, you find yourself regretting your choice of appetizers. Ice-water doesn’t help, because the fire in your mouth isn’t coming from heat. The uncomfortable feeling is actually a taste response to a chemical called capsaicin found in chili peppers. Capsaicin, and perhaps some pharmaceuticals, activates a receptor in your tongue called TRPV1 to create a spicy hot taste sensation. Scientists from Redpoint Bio, studying the taste responses of mice, have found a way to control that spicy heat at will. Mice also have TRPV1 receptors in their tongues, and even thirsty mice normally will not drink solutions of capsaicin. The scientists found that mice vigorously lapped up even highly concentrated capsaicin solutions if they also contained a small amount of a chemical specifically designed to block the activity of TRPV1. These TRPV1 antagonists, in other words, completely abolished the aversive taste of capsaicin. This is the first time that antagonists of receptors in the tongue have been demonstrated to block an unpalatable aversive taste. TRPV1 antagonists could be useful for adjusting the taste of spicy foods, but also might be used to attenuate the unpalatable tastes of some orally administered medicines.
Coffee or Candy?
Authors: Riccardo Accolla, Brice Bathellier, Carl C. H. Petersen, Alan Carleton
Our brain seems to represent the enormous amount of information coming from the outside world in a remarkable, ordered, way. Visual, auditory, olfactory and somatosensory cortices are thus mapped according to specific properties of the stimulus (color/orientation, frequency, odor quality, touched body area). The organizing principles of the gustatory cortex, however, are still unclear: is there no form of spatial arrangement as suggested by neurons often responding to many taste modalities? If so, how and where does the discrimination of different tastes take place? To investigate the functional architecture of the gustatory cortex we used an in vivo imaging technique that allows mapping the activity of a large cortical region with a good spatial resolution. We found that four of the primary taste modalities (sweet, bitter, salty and sour) are represented by distinctive spatial patterns, but that no region was specific to a single modality. In addition, the gustatory cortex seems to process in different spatial way pleasant and unpleasant stimuli. We therefore propose that these specific cortical patterns can be used to discriminate among various tastants. Eventually, the spatial maps could constitute a good reference to address the question on how sensory experience and eating disorders could affect brain perception.
Contact: Riccardo Accolla Flavour Perception Group and Laboratory of Sensory Processing, Brain Mind Institute, Ecole Polytechnique Fédérale de Lausanne, Lausanne (EPFL), CH-1015, Switzerland; phone: +41216931674 ; FAX : +41216931650 ; email : riccardo.accolla@epfl.ch
Different People
Authors: Alexey N. Pronin, Hong Xu, Huixian Tang, Lan Zhang, Qing Li and Xiaodong Li
Compared to many other aspects of human biology, the molecular basics of taste are not very well understood. Only recently a group of genes (termed hT2Rs) encoding receptors that recognize bitter molecules was identified in humans. Many of these genes exist as several different variants; however, the impact of this variation is not clear. Four years ago it was shown that variation in one of the bitter receptor genes determines whether or not people taste bitterness of a chemical called PTC. To this day that was the only example how variation in one gene can affect human taste. We identified specific variants of two other bitter receptor genes. Using an assay we developed, we demonstrated that different variants of these genes respond differently to several bitter molecules. Importantly, we showed that people who have different variants of the same genes have very different sensitivities to the bitterness of these molecules. This includes whether they sense the bitter aftertaste of a common low-calorie sweetener, saccharin (Sweet’N Low). Our findings thus reveal new examples of variations in human bitter taste and provide an explanation for them. Better understanding of human taste should lead to better tasting food products.
Contact: Alexey N. Pronin, Senomyx, Inc., 4767 Nexus Centre Drive, San Diego, CA; phone: 858-646-8346; FAX; 858-404-0752; email: alexey.pronin@senomyx.com
Mom’s Smell
Authors: Robyn Hudson, Estrella Chévez, Ivette Caldelas, Hans Distel
Daily (circadian) rhythms in physiology, mood and behavior are a well-known feature of everyday life. They help keep bodily functions in sync with each other and with the external world. The clearest environmental cue governing such rhythms is the regular change from night to day. But might not animals use other information to organize their daily lives? This is a keenly researched topic, including among biologists interested in the adaptive strategies of infant mammals, many of which are born blind and cannot use the light/dark cycle. How do they manage? Almost certainly using cues provided by the mother. Newborn mammals are born suckers and sniffers, with baby rabbits a good example. Like other mammalian young they use odor cues on the mother’s ventrum to locate nipples and suckle. When we hand-raised young rabbits and simultaneously presented them at feeding time with a chemically identified maternal pheromonal cue, this synchronized their daily rhythm in body temperature and behavioral activity and they throve. Littermates that were hand-raised without the odor cue did not show such rhythmicity and failed to thrive. Thus, in rabbits, a maternal odor contributes to pups’ survival by synchronizing their daily physiological and behavioral rhythms; in other mammals also?
Contact: Robyn Hudson, Instituto de Investigaciones Biomédicas, Universidad Nacional Autónoma de México, 04510, Mexico; phone +0052 55 5622 3828; Fax: +0052 55 5550 0044: email: rhudson@biomedicas.unam.mx
Nose Tells Time
Authors: Nathaniel N. Urban, Vikrant Kapoor
The richness of many smells such as that of a good red wine seems to develop slowly over some seconds. Animal studies have lent some support to the notion that odor-evoked neural activity evolves slowly, and in many cases this evolution is coordinated by the sniff cycle. By visualizing the activity of neurons from the mouse olfactory bulb we have observed highly reliable and odor-specific regulation of the timing of neural activity. Specifically, we observe that the activity of a single neuron for less than a millisecond can trigger a cascade of activity across a network of connected neurons that lasts more than a second. Moreover, we observe that new populations of neurons are activated specifically by repeated stimulation at intervals similar to the sniff cycle, suggesting that this neuronal network is tuned to the frequencies at which active sampling of odor stimuli occurs.
Contact: Nathaniel N. Urban,
Carnegie Mellon University, Pittsburgh, PA 15213; phone: 412-268-5122; FAX: 412-268-8423; email: nurban@cmu.edu
GABA
Authors: Yumi Nakamura, Yuchio Yanagawa, Kunihiko Obata, Masahito Watanabe, Hiroshi Ueno
Conventional wisdom says that there are four taste sensations, sweet, salty, sour and bitter. However, there is also a fifth taste sensation, umami, which was first identified in 1908 and has recently been scientifically recognized. A known umami component is glutamate, an amino acid found abundantly in food, particularly in protein-containing foods such as meat, seafood and cheese. Glutamate is a substrate for glutamate decarboxylase (GAD) which produces GABA, a major inhibitory neurotransmitter in the central nervous system. We have located GAD in taste buds and have found that when glutamate enters into taste buds, GABA is produced. GABA has its own receptor, a sort of chemical switch that may transmit various signals, including the salty taste sensation to the brain.
Salt has been used to enhance the taste of umami as well as the sweet taste while cooking. Although chefs and homemakers have learned this from experience, scientifically the relationship between umami and salt had not been clearly understood. Our experiments suggest the possibility that GAD functions as a taste modulator by producing GABA which may alter the sensation of saltiness via the GABA receptor. Because GABA is a neurotransmitter and acts as a transducer in the taste signaling pathway, it may be possible to manipulate the taste signals to by-pass the taste receptors located on the surface of tongue cells. The taste signals could then be controlled by directly controlling the transmission of the signals to the brain. In other words, the taste sensations can be controlled by activating GAD. Umami, the taste sensation, may turn out to be not only “full flavored” as translated from Japanese, but also lead us to further deciphering the mystery of the taste signaling pathways.
Contact: Yumi Nakamura, Laboratory of Applied Microbiology and Biochemistry, Nara Women’s University, Nara, Japan; phone: +81-742-20-3493; FAX: +81-742-20-3448; email: day.nakamura@cc.nara-wu.ac.jp
