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Archive for July 2007

I Am Fed Up With You…. Obesity Is ‘Socially Contagious’

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Science Daily Are your friends making you fat? Or keeping you slender? According to new research from Harvard and the University of California, San Diego, the short answer on both counts is “yes.”

A social network map of 2,200 people, the largest group of connected individuals in the Framingham Heart Study, in the year 2000. Each circle represents one person, and the size of each circle is proportional to that person’s body-mass index (BMI). Yellow circles indicate people who are considered medically obese and green circles indicate people who are not obese. Lines indicate family and friendship ties. (Credit: Figure courtesy of James Fowler, UC San Diego)

Appearing in the July 26 issue of the New England Journal of Medicine, a study coauthored by Nicholas Christakis of Harvard Medical School and James Fowler of UC San Diego suggests that obesity is “socially contagious,” spreading from person to person in a social network.

The study — the first to examine this phenomenon — finds that if one person becomes obese, those closely connected to them have a greater chance of becoming obese themselves. Surprisingly, the greatest effect is seen not among people sharing the same genes or the same household but among friends.

If a person you consider a friend becomes obese, the researchers found, your own chances of becoming obese go up 57 percent. Among mutual friends, the effect is even stronger, with chances increasing 171 percent.

Christakis and Fowler also looked at the influence of siblings, spouses and neighbors. Among siblings, if one becomes obese, the likelihood for the other to become obese increases 40 percent; among spouses, 37 percent. There was no effect among neighbors, unless they were also friends.

The researchers analyzed data over a period of 32 years for 12,067 adults, who underwent repeated medical assessments as part of the Framingham Heart Study. They were able to map a densely interconnected social network of the study’s subjects by using the tracking sheets (which had previously been archived in a basement) that recorded not only the subjects’ family members but also unrelated friends who could be expected to find them in a few years.

The network map took two years to assemble and includes information on the participants’ body-mass index. Among the first things the researchers noticed was that, consistent with other studies finding an obesity epidemic in the U.S., the whole network grew heavier over time.

Also immediately apparent were distinct clusters of thin and heavy individuals. Statistical analysis revealed that this clustering could not be attributed solely to the selective formation of ties among people of comparable weights.

“It’s not that obese or non-obese people simply find other similar people to hang out with,” said Christakis, a physician and a professor in Harvard Medical School’s department of health care policy. “Rather, there is a direct, causal relationship.”

Further analysis also suggested that people’s influence on each other’s obesity status could not be put down just to similarities in lifestyle and environment, to, for example, people eating the same foods together or engaging in the same physical activities. Not only do siblings and spouses have less influence than friends, but also geography doesn’t play a role. The striking impact of friends seems to be independent of whether or not the friends live in the same region.

“When we looked at the effect of distance, we found that your friend who’s 500 miles away has just as much impact on your obesity as [one] next door,” said Fowler, an associate professor of political science at UC San Diego and an expert in social networks.

In part because the study also identifies a larger effect among people of the same sex, the researchers believe that people affect not only each other’s behaviors but also, more subtly, norms.

“What appears to be happening is that a person becoming obese most likely causes a change of norms about what counts as an appropriate body size. People come to think that it is okay to be bigger since those around them are bigger, and this sensibility spreads,” said Christakis.

“This is about people’s ideas about their bodies and their health,” Fowler said. “Consciously or unconsciously, people look to others when they are deciding how much to eat, how much to exercise and how much weight is too much.”

“Social effects, I think, are much stronger than people before realized. There’s been an intensive effort to find genes that are responsible for obesity and physical processes that are responsible for obesity and what our paper suggests is that you really should spend time looking at the social side of life as well,” said Fowler.

The policy implications of the study, the researchers say, are profound. The social-network effects extend three degrees of separation — to your friends’ friends’ friends — so any public-health intervention aimed at reducing obesity should consider this in its cost-benefit analysis.

“When we help one person lose weight, we’re not just helping one person, we’re helping many,” Fowler said. “And that needs to be taken into account by policy analysts and also by politicians who are trying to decide what the best measures are for making society healthier.”

“It’s important to remember,” Fowler said, “that we’ve not only shown that obesity is contagious but that thinness is contagious.”

N Engl J Med. 2007 Jul 26;357(4):370-379. Epub 2007 Jul 25.

The Spread of Obesity in a Large Social Network over 32 Years.

Christakis NA, Fowler JH.

From the Department of Health Care Policy, Harvard Medical School, Boston (N.A.C.); the Department of Medicine, Mt. Auburn Hospital, Cambridge, MA (N.A.C.); the Department of Sociology, Harvard University, Cambridge, MA (N.A.C.); and the Department of Political Science, University of California, San Diego, San Diego (J.H.F.).

BACKGROUND: The prevalence of obesity has increased substantially over the past 30 years. We performed a quantitative analysis of the nature and extent of the person-to-person spread of obesity as a possible factor contributing to the obesity epidemic. METHODS: We evaluated a densely interconnected social network of 12,067 people assessed repeatedly from 1971 to 2003 as part of the Framingham Heart Study. The body-mass index was available for all subjects. We used longitudinal statistical models to examine whether weight gain in one person was associated with weight gain in his or her friends, siblings, spouse, and neighbors. RESULTS: Discernible clusters of obese persons (body-mass index [the weight in kilograms divided by the square of the height in meters], >/=30) were present in the network at all time points, and the clusters extended to three degrees of separation. These clusters did not appear to be solely attributable to the selective formation of social ties among obese persons. A person’s chances of becoming obese increased by 57% (95% confidence interval [CI], 6 to 123) if he or she had a friend who became obese in a given interval. Among pairs of adult siblings, if one sibling became obese, the chance that the other would become obese increased by 40% (95% CI, 21 to 60). If one spouse became obese, the likelihood that the other spouse would become obese increased by 37% (95% CI, 7 to 73). These effects were not seen among neighbors in the immediate geographic location. Persons of the same sex had relatively greater influence on each other than those of the opposite sex. The spread of smoking cessation did not account for the spread of obesity in the network. CONCLUSIONS: Network phenomena appear to be relevant to the biologic and behavioral trait of obesity, and obesity appears to spread through social ties. These findings have implications for clinical and public health interventions. Copyright 2007 Massachusetts Medical Society.

PMID: 17652652 [PubMed – as supplied by publisher]

Written by huehueteotl

July 27, 2007 at 1:15 pm

Chinese sage may provide alcoholism cure

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The active ingredient in Chinese medicinal sage could help alcoholics beat their addiction, Italian researchers said.

The National Research Council’s institute in Cagliari says the herb, Salvia Miltiorrhiza, has been used for centuries in China to treat blood diseases, heart disorders and insomnia, ANSA said Thursday.

Researcher Giancarlo Colombo said Chinese sage reduced alcohol consumption in mice and eliminated a “customary spike in drinking seen when mice go back on the bottle after being on the wagon for a while,” ANSA said.

Scientists said the herb may help turn alcoholics into moderate drinkers.

“It’s been working brilliantly in mice and we’re about to start on our human guinea pigs, once we’re sure it’s entirely safe,” Colombo said.

Alcohol Clin Exp Res. 2006 May;30(5):754-62.

Identification of miltirone as active ingredient of Salvia miltiorrhiza responsible for the reducing effect of root extracts on alcohol intake in rats.

Colombo G, Serra S, Vacca G, Orrù A, Maccioni P, Morazzoni P, Bombardelli E, Riva A, Gessa GL, Carai MA.

C.N.R. Institute of Neuroscience, Cagliari, Italy.

BACKGROUND: Previous work found that extracts from the roots of Salvia miltiorrhiza, a Chinese medicinal herb, reduced alcohol intake in selectively bred Sardinian alcohol-preferring (sP) rats. The present study was designed to evaluate whether miltirone, one of the possible active constituents of S. miltiorrhiza, might be responsible for the reducing effect of the extracts on alcohol intake. METHODS: An initial experiment assessed the effect of 100 mg/kg (intragastric, i.g.) of 4 extracts of S. miltiorrhiza, differing in miltirone content (0, 2, 3, and 7%, respectively), on alcohol intake in alcohol-experienced sP rats exposed to the 2-bottle “alcohol (10%, volume in volume) versus water” choice regimen. Subsequently, the effect of pure miltirone (2.5-10 mg/kg, i.g., i.e., a dose range comparable to its content in the effective doses of the active extracts) on acquisition and maintenance of alcohol-drinking behavior was evaluated in alcohol-naive and alcohol-experienced sP rats exposed to the 2-bottle choice regimen. The effect of miltirone (10 mg/kg, i.g.) on blood alcohol levels was assessed after the i.g. and intraperitoneal (i.p.) administration of alcohol. Finally, the effect of miltirone (30-100 mg/kg, i.g.) on the severity of alcohol withdrawal syndrome was evaluated in Wistar rats made physically dependent on alcohol by the repeated administration of intoxicating doses of alcohol. RESULTS: The reducing effect of 4 different extracts of S. miltiorrhiza on alcohol intake was positively and significantly correlated with their miltirone content. Pure miltirone reduced alcohol intake in alcohol-experienced rats and delayed acquisition of alcohol-drinking behavior in alcohol-naive rats. Similar to S. miltiorrhiza extracts, miltirone markedly reduced blood alcohol levels when alcohol was administered i.g. but not i.p., suggesting that miltirone hampered alcohol absorption from the gastrointestinal system. Finally, miltirone failed to affect the severity of alcohol withdrawal syndrome in alcohol-dependent rats. CONCLUSIONS: The results of the present study suggest that miltirone is the likely active constituent of S. miltiorrhiza responsible for the reducing effect of its extracts on alcohol intake in different experimental models of excessive alcohol consumption.

PMID: 16634843 [PubMed – indexed for MEDLINE]

Written by huehueteotl

July 27, 2007 at 1:11 pm

Mobius Strip: ‘Endless Ribbon’ Mystery Solved

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Dr Eugene Starostin and Dr Gert van der Heijden (both from UCL Civil & Environmental Engineering) recently published the solution to a 75-year-old mystery.

A Möbius strip made with a piece of paper and tape. (Credit: David Benbennick / Courtesy of Wikimedia Commons)

The two academics have discovered how to predict the shape of a Möbius strip, the ‘endless ribbon’ which is obtained by taking a rectangular strip of paper, twisting one end through 180 degrees, and then joining the ends.

The shape takes its name from August Möbius, the German mathematician who presented his discovery of a 3D-shape with only one ‘side’ to the Academy of Sciences in Paris in 1858. The shape was rediscovered by artists and famously depicted by Escher.

The first papers that attempted to work out how to predict the 3D shape of an inextensible Möbius strip were published in 1930, but the problem has remained unresolved until now.

Dr Starostin and Dr van der Heijden realised that the shape can be described by a set of 20-year-old equations that have only been published online. Their letter to ‘Nature Materials’ demonstrates that these differential equations govern the shapes of elastic strips when they are at rest, and enable researchers to calculate their geometry.

Möbius strips are not merely mathematical abstractions. Conveyor belts, recording tapes and rollercoasters are all manufactured in this shape, and chemists have now grown single crystals in the form of a Möbius strip.

The academics believe their methods can be used to model ‘crumpled’ shapes that are not based on rectangular strips, such as screwed-up paper, the drape of fabrics and leaves.

“This is the first non-trivial application of this mathematical theory,” said Dr Starostin. “It could prove to be useful to other research communities, such as mechanics and physics.”

Nat Mater. 2007 Jul 15; [Epub ahead of print]

The shape of a Möbius strip.

Starostin EL, van der Heijden GH.

The Möbius strip, obtained by taking a rectangular strip of plastic or paper, twisting one end through 180( composite function), and then joining the ends, is the canonical example of a one-sided surface. Finding its characteristic developable shape has been an open problem ever since its first formulation in refs 1,2. Here we use the invariant variational bicomplex formalism to derive the first equilibrium equations for a wide developable strip undergoing large deformations, thereby giving the first non-trivial demonstration of the potential of this approach. We then formulate the boundary-value problem for the Möbius strip and solve it numerically. Solutions for increasing width show the formation of creases bounding nearly flat triangular regions, a feature also familiar from fabric draping and paper crumpling. This could give new insight into energy localization phenomena in unstretchable sheets, which might help to predict points of onset of tearing. It could also aid our understanding of the relationship between geometry and physical properties of nano- and microscopic Möbius strip structures.

PMID: 17632519 [PubMed – as supplied by publisher]

Written by huehueteotl

July 27, 2007 at 9:01 am

Hearing Colors And Seeing Sounds

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How Real Is Synesthesia?

In the psychological phenomenon known as “synesthesia,” individuals’ sensory systems are a bit more intertwined than usual. Some people, for example, report seeing colors when musical notes are played.

In the study, participants had to name the color of the font that a color word is printed in. For example, if the word “blue” was printed in red ink, the participant would say “red” — a moderately difficult task that requires some mental gymnastics. (Credit: ScienceDaily)

One of the most common forms is grapheme-color synesthesia, in which letters or numbers (collectively called “graphemes”) are highlighted with particular colors. Although synesthesia has been well documented, it is unknown whether these experiences, reported as vivid and realistic, are actually being perceived or if they are a byproduct of some other psychological mechanism such as memory.

New research published in the June issue of Psychological Science, a journal of the Association for Psychological Science, sheds some light on the veracity of these perceptions.

Danko Nikolic, a researcher from the Max Planck Institute for Brain Research in Frankfurt, Germany, and his colleagues relied on a variation of a classic psychological method known as the Stroop task to test this. In this task, participants must name the color of the font that a color word is printed in. For example, if the word “blue” was printed in red ink, the participant would say “red” — a moderately difficult task that requires some mental gymnastics.

To understand Nikolic’s version of the experiment, a rudimentary understanding of color perception is required: When anyone views a particular color, specific neurons in the visual cortex area of our brain are activated. These specific neurons will deactivate, however, if a color from the opposite end of the spectrum is presented. So, any neuron activated when the color blue is present will deactivate when it’s exact opposite, yellow, comes into the visual field.

Using this logic, Nikolic presented grapheme-color synesthetes with their five most color eliciting letters or numbers. The color of the letter or number was either the same as its common association (congruent), different but not completely opposite of the color association (incongruent independent), or on the opposite end of the spectrum from the associated color (opponent incongruent). The researchers then measured how long it took the participants to name the color of the grapheme.

As expected, opponent incongruent colors made it quite difficult for individuals with grapheme-color synesthesia to respond quickly. It took participants much longer to name opponent incongruent colors than independent incongruent colors. Congruent colors — colors that matched the association — actually facilitated the process of naming the colors.

In a separate experiment, the researchers found that this color-opponency system did not work for memories. They presented the same participants with pictures of objects that a color is commonly associated with (a lemon, for example). But like the previous experiment, the objects were in unexpected colors. Reaction times in this experiment were significantly less impeded by the color change and did not differ from reaction times of control subjects who were not synesthetes. Coupled with the results from the first experiment, these findings suggest that synesthetic colors are perceived in a realistic way, just as synesthetes report.

Psychol Sci. 2007 Jun;18(6):481-6.

Color opponency in synaesthetic experiences.

Nikolić D, Lichti P, Singer W.

Department of Neurophysiology, Max-Planck Institute for Brain Research, Frankfurt am Main, Germany.

Grapheme-color synaesthesia is a rare condition in which perception of a letter or a digit is associated with concurrent perception of a color. Synaesthetes report that these color experiences are vivid and realistic. We used a Stroop task to show that synaesthetically induced color, like real color, is processed in color-opponent channels (red-green or blue-yellow). Synaesthetic color produced maximal interference with the perception and naming of the real color of a grapheme if the real color was opponent to the synaesthetic color. Interference was reduced considerably if the synaesthetic and real colors engaged different color channels (e.g., synaesthetic blue and real red). No dependence on color opponency was found for semantic conflicts between shape and color (e.g., a blue lemon). Thus, the neural representation of synaesthetic colors closely resembles that of real colors. This suggests involvement of early stages of visual processing in color synaesthesia and explains the vivid and realistic nature of synaesthetic experiences.

PMID: 17576258 [PubMed – in process]

Written by huehueteotl

July 27, 2007 at 8:55 am

Posted in Psychology

Neurons For Numerosity: Parietal Neurons ‘Sum Up’ Individual Items In A Group

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As any child knows, to answer the question “how many,” one must start by adding up individual objects in a group. This cognitive ability is shared by animals as diverse as humans and birds.

Neurons in the lateral intraparietal area of the monkey brain have been shown to integrate information about space and time. A new study asks whether they also “add up” numerical quantity. (Credit: Article authors and PLoS Biology)

Surprisingly, the exact brain mechanisms responsible for this process remained unknown until now. In from the University of Illinois at Chicago now report novel evidence for the existence of “accumulator neurons,” which respond to increasing numbers of items in a display with progressively increasing activity, in the parietal cortex of monkeys.

The authors focused on the parietal cortex based on evidence that damage to this brain region disrupts basic mathematical skills, and is activated during functional imaging studies when people perform basic computations. To understand how parietal cortex contributes to numerical behavior, the authors studied the activity of neurons in the lateral intraparietal area in monkeys while they looked at arrays of dots on a computer screen.

Parietal neurons responded with progressively increasing activity as the total number of elements in the display was varied across a wide range of values (2-32). These neurons resemble “accumulator neurons” that have been suggested to serve the first stage in counting.

This information could be used by other neurons that respond best for a particular cardinal number, such as “4,” as have been reported in prior studies. These findings support computer models that separate the processes of summing and numerical identification, and may also explain the fact that parietal cortex damage causes both numerical and spatial confusion.

Neurons in the lateral intraparietal area in monkeys respond in a graded fashion to the number of items in a visual array during a delayed saccade task, suggesting that the neurons “sum up” individual elements to represent accumulated magnitude.

Citation: Roitman JD, Brannon EM, Platt ML (2007) Monotonic Coding of Numerosity in Macaque Lateral Intraparietal Area. PLoS Biol 5(8): e208 doi:10.1371/journal.pbio.0050208

Monotonic Coding of Numerosity in Macaque Lateral Intraparietal Area

Jamie D. Roitman1¤*, Elizabeth M. Brannon2,3, Michael L. Platt1,3

1 Department of Neurobiology, Duke University, Durham, North Carolina, United States of America, 2 Department of Psychology and Neuroscience, Duke University, Durham, North Carolina, United States of America, 3 Center for Cognitive Neuroscience, Duke University, Durham, North Carolina, United States of America

As any child knows, the first step in counting is summing up individual elements, yet the brain mechanisms responsible for this process remain obscure. Here we show, for the first time, that a population of neurons in the lateral intraparietal area of monkeys encodes the total number of elements within their classical receptive fields in a graded fashion, across a wide range of numerical values (2–32). Moreover, modulation of neuronal activity by visual quantity developed rapidly, within 100 ms of stimulus onset, and was independent of attention, reward expectations, or stimulus attributes such as size, density, or color. The responses of these neurons resemble the outputs of “accumulator neurons” postulated in computational models of number processing. Numerical accumulator neurons may provide inputs to neurons encoding specific cardinal values, such as “4,” that have been described in previous work. Our findings may explain the frequent association of visuospatial and numerical deficits following damage to parietal cortex in humans.

Written by huehueteotl

July 26, 2007 at 3:12 pm

New Method To Combat HIV

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Researchers at the University of Minnesota’s Center for Drug Design have developed a new method to combat HIV/AIDS, potentially replacing the traditional cocktail drug approach.

The new approach — proven accurate in lab tests — merges the features of two antiviral agents into one drug, achieving the same effect as when two or more drugs are taken separately. The cocktail approach most commonly prescribed to HIV-infected patients is expensive and high in toxicity because many drugs are taken at one time.

The researchers named the new concept Portmanteau Inhibitors, and the results were published in a July 4 issue of the Journal of Medicinal Chemistry. The principal researcher is Robert Vince, Ph.D., director of the center and a professor of medicinal chemistry in the College of Pharmacy.

“It’s one drug that does the same thing as two independent drugs would do,” Vince said. “It’s a new approach in HIV/AIDS treatment.”

Besides remedying cost and toxicity problems, a Portmanteau Inhibitor is less likely to develop resistance from the virus because of its multifaceted approach. Most importantly, research found that the separate components of the drug did not interfere with each other while attacking HIV.

“One drug is not durable. It develops resistance very quickly,” said Zhenqiang Wang, Ph.D., a researcher in the Center for Drug Design, and co-investigator of the research. “This makes it much more difficult for resistance to develop.”

The next step will be more research and testing to see how the drug reacts once distributed in the body. But, preliminary research and confirmation of the new concept shows promise because the quality of life for AIDS patients hinges on low costing medication and minimal side effects, Wang said.

“It’s huge,” he said. “This concept could lead to a replacement for the cocktail treatment.”

J Med Chem. 2007 Jul 26;50(15):3416-9. Epub 2007 Jul 4.

Rationally Designed Dual Inhibitors of HIV Reverse Transcriptase and Integrase.

Wang Z, Bennett EM, Wilson DJ, Salomon C, Vince R.

Center for Drug Design, Academic Health Center, University of Minnesota, 308 Harvard Street SE, Minneapolis, Minnesota 55455.

Bifunctional inhibitors were designed and synthesized based on 1-[(2-hydroxyethoxy)methyl]-6-(phenylthio)thymine (HEPT)a1 non-nucleoside reverse transcriptase (RT) inhibitors and diketoacid (DKA) integrase (IN) inhibitors. Biochemical studies revealed activity against RT and IN at low nanomolar and low micromolar concentrations, respectively. Exceptionally low IC50 values from a cell-based assay were achieved along with remarkably high therapeutic indices. Compound 7 was identified as the best compound of the series (IC50: 24 nM against RT, 4.4 muM against IN, and 10 nM against HIV-1).

PMID: 17608468 [PubMed – in process]

Written by huehueteotl

July 26, 2007 at 3:03 pm

Posted in HIV, what I read

Sleep-Wake Controls Identified, Involved in Coma And Anesthesia Too

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How do we wake up? How do we shift from restful sleep to dreaming? Researchers at the University of Arkansas for Medical Sciences (UAMS) have discovered a new brain mechanism that just might explain how we do that. This new mechanism also may help us understand how certain anesthetics put us to sleep and how certain stimulants wake us up

Edgar Garcia-Rill, Ph.D., a professor of neurobiology and developmental sciences in the UAMS College of Medicine and director of the Center for Translational Neuroscience

In their first published study on this topic, researchers in the UAMS Center for Translational Neuroscience found that some neurons in the reticular activating system, a region of the brain that controls sleep-wake states, are electrically coupled.

“By finding drugs for increasing the electrical coupling of these cells, we create a stronger pathway for potential sleep-wake control,” said study author Edgar Garcia-Rill, Ph.D., a professor of neurobiology and developmental sciences in the UAMS College of Medicine and director of the Center for Translational Neuroscience.

“The possible clinical applications range from the ability to wake people up from anesthesia more rapidly, to stimulating someone in a comatose state to awaken if there are enough of these cells left alive to couple them,” Garcia-Rill said.

The study, “Evidence for Electrical Coupling in the SubCoeruleus (SubC) Nucleus,” documenting this cellular new mechanism, was published in the April issue of the Journal of Neurophysiology. In June, the research team presented additional findings at the annual meeting of the Associated for Professional Sleep Societies in Minneapolis.

The researchers found that neurons in the SubCoeruleus nucleus, a part of the brain believed to control the phase of deep sleep known as rapid-eye-movement (REM) sleep, joined in a way that allowed them to transmit electrical activity across the cells. The activity occurred spontaneously or could be induced by chemical agents that induce REM sleep.

The research article was accompanied by an editorial that called the finding “seminal” in the field of sleep-wake research. The editorial was written by peers Matthew Ennis of the Department of Anatomy and Neurobiology at the University of Tennessee Health Center in Memphis and Subimal Datta of the Department of Psychiatry and Behavioral Neuroscience at the Boston University School of Medicine.

“The findings of [the researchers] provide novel and exciting avenues for understanding sleep-wake control as well as for the treatment of sleep and arousal disorders,” wrote Ennis and Datta in the editorial.

Lead author of the study was David S. Heister, a graduate student pursuing a combined medical and doctoral degree in the Department of Neurobiology and Developmental Sciences of the UAMS Graduate School and UAMS College of Medicine.

Joining Heister and Garcia-Rill are Abdallah Hayar, Ph.D., and Amanda Charlesworth, Ph.D., UAMS faculty members in the Department of Neurobiology and Developmental Sciences and researchers in the Center for Translational Neuroscience; Charlotte Yates, Ph.D., from the Department of Physical Therapy at the University of Central Arkansas; and former UAMS faculty member Yi-Hong Zhou, Ph.D., of the University of California-Irvine.

The researchers pointed to earlier work with animal models showing that stimulation of a specific region of the brain, the reticular activating system, produced electrical activity similar to that seen during waking and REM sleep. In studying the SubCoeruleus region of the brain, the researchers detected the presence of electrical coupling of cells, a mechanism that may help the brain switch between the sleep and waking states. The presence of electrical coupling between these cells offers a potential pathway for substances that could better regulate the sleep-wake control, Garcia-Rill said.

The electroencephalogram, or EEG, of the waking brain shows fast rhythms of 10-60 cycles per second, while the sleeping brain cycles at frequencies below 10 per second. Electrical coupling would allow many cells to fire together, generating a rhythm that is transmitted to other parts of the brain to induce changes in sleep-wake states. In collaboration with the chemical transmitters that control the firing rates in individual cells, the two mechanisms could generate any of the frequencies seen in the EEG. Some anesthetics are known to block gap junctions, the channels by which electrical coupling takes place, while some stimulants increase electrical coupling.

J Neurophysiol. 2007 Apr;97(4):3142-7. Epub 2007 Jan 10.

Evidence for Electrical Coupling in the SubCoeruleus (SubC) Nucleus.
Heister DS, Hayar A, Charlesworth A, Yates C, Zhou YH, Garcia-Rill E.

Center for Translational Neuroscience, Dept. of Neurobiology and Developmental Sciences, University of Arkansas for Medical Sciences, 4301 W. Markham St., Slot 847, Little Rock, AR 72205, USA.

SubCoeruleus (SubC) neurons, which are thought to modulate rapid-eye-movement (REM) sleep, were recorded in brain stem slices from 7- to 20-day rats and found to manifest spikelets, indicative of electrical coupling. Spikelets occurred spontaneously or could be induced by superfusion of the cholinergic agonist carbachol. Whole cell recordings revealed that carbachol induced membrane oscillations and spikelets in the theta frequency range in SubC neurons in the presence of fast synaptic blockers. Electrical coupling in neurons is mediated by the gap junction protein connexin 36 (Cx 36). We found that Cx 36 gene expression and protein in the mesopontine tegmentum decreased during development. Cx 36 protein levels specifically in the SubC decreased in concert with the developmental decrease in REM sleep. The presence of electrical coupling in the SubC introduces a novel potential mechanism of action for the regulation of sleep-wake states.

PMID: 17215497 [PubMed – indexed for MEDLINE]

Written by huehueteotl

July 26, 2007 at 3:00 pm