This week a new source of cells to repair damaged hearts as well as a way to tailor make hearing aids according to an individual's needs. Plus, new insight into how nicotine causes weight loss and more evidence for the theory that life originated from outer space.
In this episode
00:17 - More evidence that life's building blocks came from space
More evidence that life's building blocks came from space
Regular listeners may remember that back in March we covered a story in which US researchers discovered that the simple molecules needed to make amino acids - the building blocks of proteins -
may have hitched a ride to earth on meteorites. Now researchers working on fragments of a large meteorite that exploded over Lake Tagish in Canada back in the year 2000 have found more
evidence that the molecules of life may have come from space.
Led by Canadian researcher Dr Chris Herd, and publishing their results in the journal Science this week, the team think that some of the smallest molecules needed to build proteins formed out in space, in the swirling mess of forming planets and stars more than 4 billion years ago.
But that's not all - the new results suggest that some of this material got swept up into large asteroids, and modified through chemical reactions with water inside the asteroids, to create more complex chemicals. Then chunks of the asteroids broke off and went shooting through space, depositing these vital chemicals on earth - and probably many other planets too.
研究人员进行了详细的分析our pieces from the meteorite that had fallen in different places on the lake. They found evidence of many organic chemicals that are needed to make the building blocks of life, including simple amino acids, which are needed to build proteins.
Their results suggest that organic chemicals in the asteroid formed when dust mixed with ice out in deep space, then got heated up by radioactivity. This melted some of the ice, making liquid water that seeped through the asteroid, causing reactions that produced the chemicals needed to kickstart life when they fell to earth.
The team's results suggest that the levels of organic chemicals may vary widely even within the same meteorite. And from what we know about biochemical reactions, it's likely that there's a pretty small range of concentrations at which these chemicals can kick off the processes leading to the development of more complex molecules, and ultimately living organisms.
So while it's looking more likely that the ingredients for life may have been delivered from space, we also need to look at many more different samples from meteorites, to see what kinds of amounts of these chemicals are actually being dropped on the planet, and whether they would be the right amount to get life going.
Unlike most other meteorites that hit the planet, this one hit a sub-zero temperature frozen lake. Local people carefully gathered meteorite samples and kept them frozen, helping to reduce the chances of contamination. The scientists think that the samples from Tagish Lake are the cleanest ones we've got - almost as good as going up into space and sampling asteroids directly. But plans are also underway to send spacecraft up to sample material from asteroids, so hopefully there will be more answers coming our way soon.
03:52 - How nicotine causes weight loss
How nicotine causes weight loss
Why ex-smokers commonly complain about gaining weight when they
quit, and why active smokers are usually thinner on average, has been cracked by scientists in the US.
Nicotine has always been regarded as the prime suspect, because experimental animals lose weight when given the drug, but no one has ever worked out why.
Now, writing in Science, Yale scientist Yann Mineur and his colleagues have tracked the smoking gun to a region of the brain's hypothalamus concerned with appetite.
In this area, the team have found, are nerve cells activated by nicotine that make a chemical called proopiomelanocortin (POMC). When this substance is released from these cells into an adjacent, appetite-related region of the brain known as the paraventricular nucleus, it has an anorexic effect.
The team made the discovery in experimental mice by using drugs to selectively activate or block certain subclasses of the chemical docking stations, called acetyl choline receptors, that nicotine binds to in the brain.
One drug tested, cytisine, closely mimicked nicotine's appetite-blocking action. It binds selectively to acetyl choline alpha3-beta4 receptors, so the team used a modified virus to deactivate just these receptors in the hypothalami of one group of mice.
These treated animals ceased to lose weight when the nicotine-mimicking drug was subsequently given. Using a separate batch of animals, the team then made electrical recordings from nerve cells when nicotine was added, which revealed that the drug was triggering bursts of activity in nerve cells that produce POMC, suggesting that this might be the anti-appetite signal.
Consistent with this theory, mice from which POMC has been "knocked out" genetically do not show any nicotine-induced changes in appetite. And when the team used a modified virus in another group of mice to deactivate a gene called melanocortin 4R (Mc4R), which encodes the receptor for POMC, the food intake amongst these animals was also unaffected by nicotine.
Together these findings show that nicotine triggers a specific subset of POMC-producing nerve cells in the brain's hypothalamus. Acting via the melanocortin (Mc4R) receptor in the adjacent paraventricular nucleus, this damps down sensations of hunger and contributes to reduced calorie intake.
根据Mineur和他的同事们,molecular clockwork of this pathway could be useful in producing new drugs designed to prevent weight-gain following smoking cessation, and also to tackle obesity and its related metabolic disorders.
13:07 - Better Hearing for Dummies
Better Hearing for Dummies
Professor Ray Meddis, University of Essex
Jane - Hearing aids work on the general principle that if you are finding it hard to hear something you simply turn the volume up. Fine if you are talking to one person in a quiet room, but if you are in a noisy environment then everything is amplified. Now unique computer modelling techniques, combined with new ways of carrying out hearing tests, are revolutionising the way that hearing loss and impairment is diagnosed and treated. Professor Ray Meddis is leading the work at the University of Essex.
Ray - Hearing consists of a number of stages between the sound arriving at the ear and then the signal going up to the brain. The computer model tries to represent each one of these stages separately. The test that we use involved two measurements, one concerns tuning and the other one concerns compression. Tuning refers to the situation where you can hear one sound and tune out background sounds. It's a bit like a radio where you can tune into one radio station, but you don't want interference from another station. Now with normal hearing this tuning takes place naturally so one of our tests focuses on that particular problem. Compression is concerned with how intrusive other sounds are when they become louder. So normally we can tune out another sound if it is quiet, but as it increases in intensity then we have more difficulty in tuning it out. A person with hearing loss often has a particular difficulty in tuning out irrelevant sounds and so our compression measure is particularly concerned with increasing the intensity of the sound and then noticing how that comes to make it difficult to listen to a particular vocal sound.
Jane - Strange as it may seem, it was the art of dressmaking that inspired Ray and his team to take this tailor-made approach to the diagnosis and treatment of hearing impairment.
Ray - When generating a computer model for a patient with hearing loss, we always start off with a normal model and we try and make a single adjustment which refers to the particular pathology which we feel is causing the problem for that particular patient. When you have a dress made the tailor measures your body size then changes the shape of the dummy to represent your body size and then cuts and sews the clothing so that it fits the dummy. The reasonable expectation is that when the customer comes back the clothing will fit the customer perfectly. Now we believed that we could do the same thing with hearing impairment. We already have a model of normal hearing, so by making certain adjustments we could make the dummy simulate impaired hearing and the idea was we could then use that dummy to fit the hearing aid and we would adjust the hearing aid so that we got the best possible output from the impaired hearing dummy. Our hope is that we will be able to use the hearing dummy to make these adjustments before the hearing aid is supplied to the patient. In other words the hearing aid should be fitted to the dummy just like a dress would be fitted to a tailors dummy and then when the patient comes back, ideally, the aid should be perfectly suited to their particular needs.
Jane - Supported by the Engineering and Physical Sciences Research Council, this cutting-edge work has also led to a prototype design for a new type of hearing aid.
Ray - Because our primary interest was in developing computer models we came to realise that hearing aids respond differently to sounds compared to a normal hearing individual. So it seemed to us that we could build a hearing aid that simulated normal human hearing so it compressed the sound in the same way, tuned the sound in the same way and dealt with variations in level in the same way. We have designed a new type of hearing aid which uses something called instantaneous compression. Currently in hearing aids sound is compressed, but it takes a little while for the compressor to respond to the sound levels and this gives rise to some complications. But by simulating normal human hearing we've been able to produce instantaneous compression without the distortion which everybody used to believe was an unavoidable accompaniment of instantaneous compression.
Jane - So a number of aspects of this research are cutting-edge.
Ray - The research is a world first in a number of respects. First of all this will be the first model to represent a number of different kinds of hearing impairment. It is also the first attempt anybody has made to go through the complete cycle that is measuring the hearing loss, designing the hearing dummy, adjusting the hearing aid using the hearing dummy and then modifying the hearing aid to suit the patient.
简-新方法简化了complicated laboratory testing process, significantly cutting down on the time it takes and the number of trials involved, along with the level of expertise required. Within four years we could see this system of testing in widespread use, along with the new type of hearing aid.
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