Is Crawling babies Overrated?
Posted: Monday, July 29, 2002
In a Study of the Brain, Special Nerves Registered the Emotional Context of a Pleasurable Touch
By Shankar Vedantam, Washington Post, July 29, 2002
Neuroscientists have discovered what romantics have always known: The touch of a lover's hand is special.
Scientists announced a study today that shows humans have a special set of nerves for feeling pleasure at a mother's caress or a lover's embrace.
These nerves are sensitive to the soft touch of fingers gliding over a forearm or a parent's soothing hand, but not to rough touches, jabs or pinches. Scientists speculate that the nerves might be designed to guide humans toward tenderness and nurturing -- a theory bolstered by the fact that the nerves are wired to the same brain areas activated by romantic love and sexual arousal.
Although these special nerves, which have thin fibers and send relatively slow signals to the brain, had been identified in animals and humans, their role had been unclear.
Scientists had wondered about their purpose, especially because they do not work as efficiently as thick nerve fibers, which are also found in skin.
The research, published in the current issue of Nature Neuroscience, indicates that while the thick fibers rapidly shoot electrical signals to the somatosensory cortex of the brain and convey information about contact and pressure, the thin, slow fibers connect to the insular cortex and convey the emotional context of the touching. Both sets of fibers fire together, and the brain combines information about physical contact with information about emotional context, melding them into the richness of physical experience.
A crucial reason nature might have endowed people with two different sets of nerves is that the slow fibers function from the earliest hours of life, perhaps even in the womb, while the fast fibers develop slowly after birth.
Newborn infants might be able to feel the love in a parent's touch before they can feel the touch itself.
Referring to studies showing that babies need physical contact and nurturing, the group of scientists wrote, "The profound importance of such a system for human well-being has long been suggested, at least since the classical study of baby monkeys who show affection for a surrogate mother in response to tactile comfort."
The nerve system continues to function throughout life, underscoring the importance of such comfort. While the thicker nerve fibers that communicate contact information are more densely packed into areas such as the palm, the thinner nerves are found on hairy areas of the skin such as the forearm.
"Their functional role is below the level of consciousness and has to do with the emotional aspects of touch -- like the pleasure of touch," lead scientist Hakan Olausson, a neurophysiologist at the Sahlgrenska University Hospital in Goteborg, Sweden, said in a telephone interview. "The fast fibers indicate when we are touched and how strong the touch is. [The slow fibers] signal the fine aspects of touch."
Evidence about the functioning of the slow-fiber nerve system was difficult to obtain because gentle touches also trigger the parallel nerve system.
Researchers knew how to trigger only the thin nerve system in animals, but that didn't reveal much about pleasure: "The cat cannot say, 'It's good and this is what I feel,' " said Yves Lamarre, a professor of neurophysiology at the University of Montreal and one of the authors of the research. "To study these fibers in humans was theoretically impossible. If you stimulate the skin, you stimulate the large fibers that provide most of the sensation you feel. It would mask the small fibers."
Olausson, Lamarre and a team of scientists from Sweden and Canada based their report on studies of an unusual patient -- a 54-year-old woman from Montreal, referred to as G.L., who suffered from a disease that destroyed the nerve system that responds to the rougher touches. Since she was 31, G.L. has reported being unable to feel touch below the level of her nose.
While G.L. said her abilities to perceive temperature, pain and itching were intact, researchers found that she could feel only a dull burning sensation when pinched or when exposed to cold. She could not feel a vibrating sensation at all.
"Not only is this patient lacking skin sensation, she lacks information about movement," Lamarre said. "When she closes her eyes, she has no idea where she is in space. She moves but doesn't know she is moving. When she wakes up in the night, she doesn't know if she has blankets on her."
Olausson and Lamarre realized that the patient might be able to tell them about the working of the thin nerve system. Tests showed that nerve system had not been affected by her disorder.
In an experiment where G.L. could not see what the scientists were doing, they ran a soft watercolor brush up her forearm. When G.L. concentrated, she reported feeling a faint and diffuse sensation.
"Without knowing what kind of stimulus we delivered, she reported the [touch] was clearly pleasant, with no sensation of pain, temperature, itch or tickle," the researchers wrote. The researchers compared G.L.'s response with 24 neurologically intact individuals. They found that G.L. found the movement of the brush to be as pleasant as normal volunteers did.
Interestingly, G.L. could not tell the direction in which the brush was moving -- information presumably relayed by the thick nerve fibers -- meaning that when people with uncompromised nervous systems perceive pressure, temperature and pleasure, different nerves might be involved for different sensations.
After conducting sophisticated brain scans of the volunteers, Olausson and Lamarre found that the thin nerve system was hooked into the front parts of the insular cortex, the same area that was activated, "intriguingly, during visually evoked romantic love and sexual arousal."
These nerves, the researchers concluded, "are an important component in the construction of the sense of self."
Olausson said areas such as the palm might have fewer thin nerves and more thick nerves because the primary role of the palm is to pick up information about objects.
That said, there were still aspects of pleasure and emotion that could be transmitted through the thick fibers in the palm. Healthy volunteers in the experiment were divided about whether a caress on the palm was pleasurable.
"The next step is to examine patients who have no [slow] fibers -- patients with just the fast fibers," Olausson said. "If the hypothesis is correct, they should lack the emotional sense of touch, the sense of emotional well-being."
© 2002 The Washington Post Company
Send page by E-Mail Dwarf Galaxies Give Universe A Breath Of Fresh Oxygen
Posted: Friday, July 26, 2002
Source: NASA/Marshall Space Flight Center (http://www.msfc.nasa.gov/)
Astronomers have discovered that a nearby dwarf galaxy is spewing oxygen and other "heavy" elements into intergalactic space. This observation from NASA's Chandra X-ray Observatory supports the idea that dwarf galaxies may be responsible for most of the heavy elements between the galaxies.
Despite comprising only a very small fraction of the mass of the universe, so-called heavy elements - everything other than hydrogen and helium -- are essential for the formation of planets and can greatly influence astronomical phenomena, including the rate at which galaxies form.
A team led by Crystal Martin of the University of California, Santa Barbara, observed the dwarf galaxy NGC 1569 using Chandra. As reported in an article to be published in The Astrophysical Journal, they found that huge quantities of oxygen and other heavy elements are escaping from the galaxy in bubbles of multimillion-degree gases that are thousands of light years in diameter.
"Dwarf galaxies are much smaller than ordinary galaxies like our Milky Way and much more common," said Martin. "Because of their small mass, they have relatively low gravity and matter can escape more easily from dwarfs than from normal galaxies. This makes them very important in understanding how the universe was seeded with various elements."
Scientists have speculated that heavy elements escaping from dwarf galaxies in the early universe could play a dominant role in enriching the intergalactic gas from which other galaxies form. Enriched gas cools more quickly, so the rate and manner of formation of new galaxies in the early universe would have been strongly affected by this process.
"With Chandra it was possible to test these ideas," said Henry Kobulnicky of the University of Wisconsin, Madison, a member of the research team. "We could trace the distribution of oxygen and other elements in the galaxy and determine how much of this matter is escaping from the galaxy."
NGC 1569 is a good case study because it is only about 7 million light years from Earth, and for the last 10 million to 20 million years it has been undergoing a burst of star formation and supernova explosions, perhaps triggered by a collision with a massive gas cloud. The supernovae eject oxygen and other heavy elements at high velocity into the gas in the galaxy, heating it to millions of degrees. Hot gas boils off the gaseous disk of the galaxy and expands outward at speeds of hundreds of thousands of miles per hour.
The team found large hot bubbles extending above and below a disk of gas along the equator of the galaxy. The measured concentration of oxygen, neon, magnesium, and silicon showed that the elements from thousands of supernovas are evaporating out of the galaxy, carrying much of the surrounding gas with them. The astronomers estimate the bubbles are carrying away an amount of oxygen equivalent to that found in about 3 million suns.
In addition to Martin and Kobulnicky, Timothy Heckman of John Hopkins University in Baltimore, was part of the team that observed NGC 1569 for 27.4 hours using the Advanced CCD Imaging Spectrometer (ACIS) on April 11, 2001. ACIS was built for NASA by Penn State, University Park, and the Massachusetts Institute of Technology, Cambridge, Mass. NASA's Marshall Space Flight Center, Huntsville, Ala., manages the Chandra program for the Office of Space Science, Washington. TRW, Inc., Redondo Beach, Calif., is the prime contractor for the spacecraft. The Smithsonian's Chandra X-ray Center controls science and flight operations from Cambridge.
Images associated with this release are available on the World Wide Web at:
Send page by E-Mail Brain Imaging Reveal Biological Basis For Human Cooperation
Posted: Thursday, July 18, 2002
Source: Emory University Health Sciences Center (http://www.emory.edu/)
Functional MRI scans have revealed a "biologically embedded" basis for altruistic behavior, with several characteristic regions of the brain being activated when players of a game called "Prisoner's Dilemma" decide to trust each other and cooperate, rather than betray each other for immediate gain, say researchers from Emory University. They report on their study in the July 18 issue of the journal Neuron, published by Cell Press.
For many years, evolutionary biologists, behaviorists, economists and political scientists have attempted to understand why cooperation exists between human beings, even though that cooperation may not result in a direct or immediate reward. This unselfish behavior called "altruism" is almost uniquely a human trait.
Up until now, almost all brain imaging experiments that have studied the social brain have done so by exposing subjects to static 2-D images inside the scanner. "This study represents an attempt to learn about the social brain by scanning people as they are engaged in a true social interaction," said James K. Rilling, Ph.D., principal investigator in the Emory study, who is currently serving a postdoctoral fellowship at Princeton University. In the Fall of 2003, Dr. Rilling will return to Emory as a faculty member with a joint appointment in the Center for Behavioral Neuroscience (CBN) at Emory University School of Medicine and the Emory University Department of Anthroplogy.
In two separate experiments, the researchers used fMRI to scan the brains of 36 women while they played the "Prisoner's Dilemma Game," a decades-old model for cooperation based on reciprocal altruism. Two players independently chose to either cooperate with each other or not (defect), and each was awarded a sum of money that depended upon the interaction of both players' choices in that round.
In the first experiment, 19 subjects were scanned in four game sessions designed to observe neural function during cooperation and non-cooperation during both human interactions (social) and interactions with a computer (non-social). The results of the first experiment revealed different patterns of neural activation depending on whether the playing partner was identified as a human or a computer. In the second experiment, 17 subjects were scanned during three game sessions, focusing specifically on human interaction.
Mutual cooperation was the most common outcome in games played with presumed human partners in both experiments, even though a player was maximally rewarded for defecting when the other player cooperated. During the mutually cooperative social interactions, activation was noted in those areas of the brain that are linked to reward processing: the nucleus accumbens, the caudate nucleus, ventromedial frontal/orbitofrontal cortex and rostral anterior cingulate cortex.
"Our study shows, for the first time, that social cooperation is intrinsically rewarding to the human brain, even in the face of pressures to the contrary, " said Gregory S. Berns, M.D., Ph.D., co-investigator and associate professor of psychiatry in the Emory University School of Medicine Department of Psychiatry and Behavioral Sciences and member of the CBN. "It suggests that the altruistic drive to cooperate is biologically embedded-- either genetically programmed or acquired through socialization during childhood and adolescence."
"Reciprocal altruism activates a reward circuit, and this activation may often be sufficiently reinforcing to override subsequent temptations to accept but not reciprocate altruism. This may be what motivates us to persist with cooperative social interactions and reap the benefits of sustained mutual cooperation," said Dr. Rilling.
"The combination of game behavior and functional brain imaging also provides a unique paradigm to explore the neural basis of social behavioral disorders such as autism, drug addiction and sociopathy, that are characterized by deficits in social reciprocity, impulse regulation, or social reward processing," adds Clint Kilts, Ph.D., co-investigator and associate professor of psychiatry at Emory. "It defines the most complex form of the human genesis of a social bond. It may help us define why wars are fought and loves are lost."
The study was sponsored by the Markey Center for Neurological Sciences Fellowship, National Institute on Drug Abuse (NIDA), National Institutes of Mental Health (NIMH) and National Alliance for Research on Schizophrenia and Depression (NARSAD). Other Emory researchers involved in the study were David A. Gutman, Thorsten R. Zeh, and Giuseppe Pagnoni, Ph.D.
Send page by E-Mail Genetic Studies Shed Light On The Malaria Parasite
Posted: Thursday, July 18, 2002
Source: NIH/National Institute Of Allergy And Infectious Diseases (http://www.niaid.nih.gov/)
Researchers at the National Institutes of Health (NIH) report mining the genome of the malaria parasite has uncovered new data showing the parasite is genetically more diverse and much older -- at least 100,000 years old -- than some scientists have thought. The new information suggests creating vaccines to control the deadly disease poses a greater challenge than some may have imagined.
In a second paper, the NIH-led group also found that parasites resistant to chloroquine, a former mainstay antimalaria drug, arose in several geographic locations and rapidly spread across continents. This finding upends the long-held notion of some scientists that chloroquine resistance developed independently in only two areas in the mid-20th century and slowly spread to other countries from those sites. The new information implies that resistance to chloroquine and other antimalaria drugs can arise and spread more pervasively than previously thought and argues for careful drug-use monitoring programs.
The new reports appear in back-to-back papers published in the July 18 issue of Nature.
Plasmodium falciparum, the parasite responsible for most deadly cases of malaria, thrives in the tropics and infects about 300 million people annually. One to 2 million people, mostly infants and children, die of the disease each year. The number of cases of malaria worldwide is increasing, mainly because of the evolution of drug-resistant parasites.
Debate regarding the genetic diversity and origin of the parasite has been ongoing since the late 1990s. It was then that a group of evolutionary biologists first proposed a "Malaria Eve" hypothesis to explain the origin of the parasite. By examining 10 genes of the malaria parasite, these scientists proposed that the bug is relatively young -- 3,000 to 5,000 years old -- and genetically similar from place to place, and as such, should not be too difficult to control.
To explore the question in more detail, Xin-zhuan Su, Ph.D., and Jianbing Mu, Ph.D., of the National Institute of Allergy and Infectious Diseases (NIAID), Wen-Hgsiung Li, Ph.D., of the University of Chicago, and their colleagues at the NIH National Center for Biotechnology Information (NCBI) looked for genetic differences among geographically distinct parasites. The five P. falciparum parasites they chose each hailed from a different geographical region: Southeast Asia, Africa, South America, Central America and Papua New Guinea. The researchers compared the same 204 genes in chromosome 3 of each of these parasites to see if they could detect any nucleotide differences. This painstaking process revealed great diversity in the five genomes. Based on these differences, the scientists estimate the earliest common parasite ancestor must be 100,000 to 180,000 years old, a timeframe coincident with human population expansion out of Africa. "We speculate," says Dr. Su, "that when the human population grew, the malaria parasite grew with it."
In the second study, Dr. Su, John Wootton, Ph.D., of NCBI, and their colleagues set out to obtain a detailed picture of the origin and spread of chloroquine-resistant P. falciparum. Dr. Su's group looked for genetic diversity in 87 parasites isolated from patients worldwide. For each isolate, the researchers typed 342 DNA markers over the entire parasite genome, including the gene linked to chloroquine resistance, and thereby revealed a "genetic fingerprint." This is the first time DNA fingerprinting of the entire genome has been done for a complex parasite, notes Dr. Su. As such, the data is more reliable and powerful than previous research findings to answer evolutionary questions.
Dr. Wootton then used computations based on population genetic theory and computer simulations to expose the recent evolutionary history hidden in segments of the parasite genomes. "This showed very clearly that a large segment of a parasite chromosome had hitchhiked along with the key chloroquine resistance gene," says Dr. Wootton. "This is a hallmark, we think, of how chloroquine has exerted strong Darwinian selection and profoundly influenced recent P. falciparum evolution." This analysis revealed at least four independent chloroquine resistance founder events: one in Southeast Asia in the late 1950s, which later spread throughout most of Asia and Africa; at least two in South America; and one in Papua New Guinea.
"This study changes our thinking about chloroquine resistance," says Dr. Su. "First, it has happened more frequently than we thought. Second, we now know that the African parasite that developed resistance in the late 1970s did not arise independently but came from Southeast Asia." It took only 10 to 15 years for these resistant parasites to spread throughout Africa. "This means that when a drug- or vaccine-resistant parasite arises, it will not take long for this resistance to spread to other continents, reflecting human travel, particularly by air, and the high transmission rate via mosquitoes in Africa."
Their genome-wide picture also shows how genetic recombination -- shuffling of DNA from two parent parasites -- has occurred rapidly and generated enormous genetic diversity. "This could enable the parasite to evolve resistance to multiple drugs and vaccines in the future," says Dr. Su.
NIAID is a component of the National Institutes of Health (NIH). NIAID supports basic and applied research to prevent, diagnose, and treat infectious and immune-mediated illnesses, including HIV/AIDS and other sexually transmitted diseases, illness from potential agents of bioterrorism, tuberculosis, malaria, autoimmune disorders, asthma and allergies.
NCBI is a component of the NIH National Library of Medicine. NCBI creates public databases, conducts research in computational biology, develops software tools for analyzing genome data, and disseminates biomedical information.
J Mu et al. Chromosome-wide SNPs reveal an ancient origin for Plasmodium falciparum. Nature 418:323-326 (2002).
J Wootton et al. Genetic diversity and chloroquine selective sweeps in Plasmodium falciparum. Nature 418:320-323 (2002).
Press releases, fact sheets and other NIAID-related materials are available on the NIAID Web site at http://www.niaid.nih.gov.
The National Institute of Allergy and Infectious Diseases is a component of the National Institutes of Health, U.S. Department of Health and Human Services
Send page by E-Mail Scientists identify the spark of life
Posted: Thursday, July 18, 2002
By Mark Henderson, Science Correspondent, www.timesonline.co.uk
BRITISH scientists have discovered the gene that provides the spark of life, when an egg is fertilised by a sperm, in research that promises dramatic advances in fertility treatment and stem cell experiments.
A ten-year study has revealed that the gene in sperm triggers the crucial process by which an egg starts dividing to form an embryo, solving a mystery that has confounded medical science for two centuries.
The breakthrough, by researchers at the University of Wales College of Medicine in Cardiff and University College, London, paves the way for improved therapy for infertile couples and treatments that use cloned stem cells to tackle Alzheimer’s, Parkinson’s and diabetes.
Scientists believe it will eventually allow them to fertilise eggs using sperm that have previously been considered useless, and to transform success rates in therapeutic cloning.
It has long been known that fertilisation is followed by a surge of calcium but the molecules that start this process have remained elusive.
“We’re thrilled to be at the forefront of such an exciting discovery,” Professor Tony Lai, head of the Cardiff team, said. “The potential benefits to medicine are immense.”
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Send page by E-Mail The Sun: A Great Ball Of Iron?
Posted: Wednesday, July 17, 2002
Source: University Of Missouri-Rolla (http://www.umr.edu)
For years, scientists have assumed that the sun is an enormous mass of hydrogen. But in a paper presented before the American Astronomical Society, Dr. Oliver Manuel, a professor of nuclear chemistry at UMR, says iron, not hydrogen, is the sun's most abundant element.
Manuel claims that hydrogen fusion creates some of the sun's heat, as hydrogen -- the lightest of all elements -- moves to the sun's surface. But most of the heat comes from the core of an exploded supernova that continues to generate energy within the iron-rich interior of the sun, Manuel says.
"We think that the solar system came from a single star, and the sun formed on a collapsed supernova core," Manuel says. "The inner planets are made mostly of matter produced in the inner part of that star, and the outer planets of material form the outer layers of that star."
Manuel's theory that the solar system was born catastrophically out of a supernova goes against the widely-held belief among astrophysicists that the sun and planets were formed 4.5 billion years ago in a relatively ambiguous cloud of interstellar dust. Iron and the heavy element known as xenon are at the center of Manuel's efforts to change the way people think about the solar system's origins.
Born of a supernova
Manuel believes a supernova rocked our area of the Milky Way galaxy some five billion years ago, giving birth to all the heavenly bodies that populate the solar system. Analyses of meteorites reveal that all primordial helium is accompanied by "strange xenon," he says, adding that both helium and strange xenon came from the outer layer of the supernova that created the solar system. Helium and strange xenon are also seen together in Jupiter.
Manuel has spent the better part of his 40-year scientific career trying to convince others of his hypothesis. Back in 1975, Manuel and another UMR researcher, Dr. Dwarka Das Sabu, first proposed that the solar system formed from the debris of a spinning star that exploded as a supernova. They based their claim on studies of meteorites and moon samples which showed traces of strange xenon.
Data from NASA's Galileo probe of Jupiter's helium-rich atmosphere in 1996 reveals traces of strange xenon gases -- solid evidence against the conventional model of the solar system's creation, Manuel says.
Editor's Note: The original news release can be found at http://web.umr.edu/~newsinfo/ironsun.html
Send page by E-Mail Discovery May Unlock Secrets To Start Of Life On Earth
Posted: Friday, July 5, 2002
Source: Saint Louis University (http://www.slu.edu/)
Saint Louis University Geologist's Discovery May Unlock Secrets To Start Of Life On Earth
ST. LOUIS -- A Saint Louis University geologist has unearthed further evidence in his mounting case that shifting of the continents -- and perhaps life on Earth -- began much earlier than many scientists believe.
Tim Kusky, a professor of Earth and atmospheric sciences, has discovered the world's first large intact pieces of oceanic mantle from the planet's earliest period, the Archean. The nearly mile-long section of rock, which is billions of years old, may hold clues as to when life developed on the planet. The major finding was reported Monday in the July issue of GSA-Today -- the premier journal of the Geological Society of America.
Working with colleagues from Peking University, Kusky uncovered the rare find at a site near the Great Wall where last year the team discovered the planet's oldest complete section of oceanic crust. Reported in Science, their work recently was heralded by the Chinese government as one of the most significant scientific findings of 2001.
This latest discovery may prove even more remarkable. For years, scientists have longed to find large pieces of the planet's deep interiors. But until now, they've had to rely on only tiny fragments to study. Formed tens of kilometers below the ancient sea floor, this new discovery's massive mantle rocks are preserved in a highly faulted belt 100 kilometers long.
Unlike the sea floor samples Kusky found last year, the mantle rocks preserve 2.5 billion-year-old minerals that hold clues to the origin of plate tectonics. The minerals, including an unusual type of chromite deposit only known from deep ocean floor rocks appear to have been deformed at extremely high temperatures before they were completely crystallized by volcanic magma.
This shows that the mantle rocks were flowing away from the ridges on the oceanic floor, evidence that the continents began shifting more than 500 million years earlier than now widely believed.
Because the discovery shows that the plates were moving in that early period, these findings could have a more far-reaching effect on theories related to the development of life on the planet. Just when single-celled organisms evolved into more complex organisms has been contested for years. Because hot volcanic vents on the sea floor may have provided the nutrients and temperatures needed for life to flourish, Kusky said it's possible that life developed and diversified around these vents as the plates started stirring.
Kusky and Peking University's J.H. Li have initiated a series of studies on the section of ancient mantle and it's minerals aimed at understanding the conditions of the Earth 2.5 billion years ago. Their work is being funded by U.S. National Science Foundation, the Chinese National Natural Science Foundation, Saint Louis University and Peking University. The Chinese government also has dedicated a natural geologic park at the site of the discovery.
Saint Louis University is a leading Catholic, Jesuit, research institution ranked among the top 50 national, doctoral universities as a best value by U.S. News & World Report. Founded in 1818, the University strives to foster the intellectual and spiritual growth of its more than 11,000 students through a broad array of undergraduate, graduate and professional degree programs on campuses in St. Louis and Madrid, Spain.
Send page by E-Mail Third and Smallest Skull Of "First Eurasians"
Posted: Friday, July 5, 2002
Source: American Association For The Advancement Of Science (http://www.aaas.org/)
Large Brains Not Required? Third And Smallest Skull Of "First Eurasians" Reported In Science
The skull and jawbone of a small, lightly-built individual, discovered at an archeological site in Dmanisi, Georgia, may call into question the prevailing idea that larger brain size was behind the migration of human ancestors out of Africa. An international research team describes their find in the journal Science, published by the American Association for the Advancement of Science.
The scientists found a petite new individual, with a small brain, thin brow ridge, short nose, and huge canine teeth, according to co-author David Lordkipanidze of the Georgian Academy of Sciences, in Tbilisi. This was the third specimen found at the site. By comparison, the other two skulls had room for substantially larger brains.
All three specimens are approximately 1.75 million years old, making them the largest collection of individuals from any one site older than around 800,000 years. Lordkipanidze and his colleagues have tentatively concluded that the three belong to the same species, Homo erectus, thought to be the first hominid species to leave Africa. The Dmanisi fossils most closely resemble the African version of Homo erectus, called Homo ergaster.
"We have now a very rich collection, of three skulls and three jawbones, which gives us a chance to study very properly this question [of how to classify the early hominids,] said Lordkipanidze. "These questions are often based on isolated finds, but here we have the chance to study a population."
The brain of the new Dmanisi specimen was probably around 600 cubic centimeters, while modern human brains are at least twice that much, according to Lordkipanidze. The other two specimen's brains were approximately 800 cubic centimeters.
Scientists have proposed that the evolution of larger brains was directly related to our ancestors' migration out of Africa. According to this scenario, increased intelligence enabled these early humans to adapt to new environments.
The new skull's small brain size "suggests that enlargement of the brain was not the only reason to leave Africa. My feeling is there should be a combination of reasons, not just one reason, that forced people out of Africa," Lordkipanidze said.
The new fossils also offer a rare glimpse into the diversity of a primitive human species. While we take it for granted that modern humans come in all shapes and sizes, scientists know little about individual variation among our ancestors.
"We are seeing a difference mainly in size, not morphology," said Lordkipanidze. "For now, my hypothesis is that we are seeing variability within the population."
Until the discoveries at Dmanisi (Leo Gabunia and colleagues reported the first two in the 12 May 2000 issue of Science), researchers generally believed that the first human species to leave Africa departed only one million years ago, and that they had large brains and relatively advanced stone tools.
The tools found at Dmanisi are of the primitive "pebble-chopper" variety, similar to the Oldowan tools of East Africa.
The skull and jawbone are unusually well-preserved, in part because a solid limestone layer overhead protected them against the usual compaction that occurs over time in sedimentary rocks. Along with the hominid fossils, the Science authors found remains of ancient species of rhinoceros, deer, wolf, horse, and saber-toothed cat.
The other authors of the paper are Abesalom Vekua, Givi Maisuradze, Alexander Mouskhelishvili, Medea Nioradze, and Merab Tvalchrelidze, at the Georgian Academy of Sciences, in Tbilisi, Georgia; G. Philip Rightmire, at Binghamton University, in Binghamton, New York, United States; Jordi Agusti, at the Institut de Paleontologia M. Crusafont, in Sabadell, Spain; Reid Ferring, at U. of North Texas, in Denton, Texas, United States; Marcia Ponce de Leon and Christoph Zollikofer, at U. Zürich-Irchel, in Zürich, Switzerland, Martha Tappen, at U. Minnesota, in Minneapolis, Minnesota, United States.
This research was funded by the Georgian Academy of Sciences, the National Geographic Society, The Leakey Foundation, the Fulbright Foundation, the Spanish Ministry of Science, Generalitat de Catalunya, the University of Zurich, the Eckler Fund of Binghamton University, the American School of Prehistoric Research, and the Peabody Museum of Harvard University.
Send page by E-Mail Decision Making At The Cellular Level
Posted: Monday, July 1, 2002
Source: Johns Hopkins Medical Institutions (http://www.hopkinsmedicine.org)
It’s a wonder cells make it through the day with the barrage of cues and messages they receive and transmit to direct the most basic and necessary functions of life. Such cell communication, or signal transduction, was at least thought to be an "automatic" cascade of biochemical events. Now, however, a study reported in a recent issue of Nature by Johns Hopkins and Harvard scientists has found that even before a message makes it through the outer cell membrane to the inner nucleus, the cell is busy activating a molecular switch to guide how the message will be delivered in the first place.
"Our results add a layer of complexity to understanding how messages are communicated by cells," says Mark Donowitz, M.D., professor of medicine at Hopkins and a co-author of the study in the June 20 issue. "But by the same token, the new layer offers an exciting new aspect of cellular circuitry that could lead to potential therapies for many serious disorders," he says.
"This extra step in cell signaling actually lets the cell figure out how it’s going to communicate what it needs to," says Donowitz. "Without this switchboard system, the cell would go crazy and overload because every stimulus that passed by would be forwarded to its interior."
The two most common cellular signals are calcium and cyclic adenosine monophosphate, or cAMP. They are sometimes known as "second messengers" because they intercept messages from receptors on the cell surface and relay them to proteins within the cell, altering their shape and thus their behavior and that of the cell at large.
Donowitz and colleagues showed that a cell decides which signal to use, calcium or cAMP, by the presence or absence of a specific protein called sodium/hydrogen exchanger regulatory factor 2, or NHERF2. Specifically, their experiments tested how the receptor for parathyroid hormone, and for parathyroid hormone-related protein (also a hormone), on the cell surface signals the interior of the cell to perform specific functions. They found that the signal includes more than just the receptor and the proteins that latch onto it, but requires an additional class of proteins (of which NHERF2 is a member) called PDZ proteins that determine whether to send the signal via calcium or through cAMP. If NHERF2 is present along with the parathyroid hormone receptor, then the signal is sent via calcium. If there is no NHERF2, then cAMP is responsible for delivering the message.
The cell’s decision to use calcium or cAMP is important because each generates different responses from its target proteins, says Donowitz. For example, a signal relayed by cAMP might induce a kidney cell to release water or a bone cell to break down into its constituent minerals. Likewise, signals relayed by calcium could lead to the aggregation of blood platelets, which cause clots, or to the release of histamine, a major component of the allergic response.
"These results show that at the very earliest stage of cell signaling, called receptor binding, there is a switch that determines what kind of signal will be used," says Donowitz. "To understand cell signaling, you really have to know the whole system."
The receptor for parathyroid hormone, for example, is crucial for signaling and proper functioning of the parathyroid glands, intestinal cells and kidney cells. Parathyroid hormone and parathyroid hormone-related protein are vital to the normal functioning of the body. Disruptions in the regulation or amount of these substances can lead to serious ailments, including kidney stones, convulsions, decalcification of bones or "rubber bones," and can interfere with the normal growth of bones and cartilage. Common diseases that are caused in part by faulty signaling in cells include cancer, diabetes and disorders of the immune system.
Other authors of the study are C. Chris Yun of Hopkins, Matthew J. Mahon (lead author) and Gino V. Segre (senior author), both of Massachusetts General Hospital and Harvard Medical School.
M.J. Mahon, et al. Nature (2002) Na+/H+ exchanger regulatory factor 2 directs parathyroid hormone 1 receptor signalling. Vol. 417:858-861.
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Editor's Note: The original news release can be found at http://www.hopkinsmedicine.org/press/2002/June/020625.htm
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