The Best of the Naked Scientists 2

US scientists have unlocked the secret of how the nervous system senses low temperatures, discovering in the process why sucking a mint makes your mouth feel cold.

Writing in Nature, David Julius, from the University of California San Francisco, found that mice lacking a gene called TRPM8 ceased to react to low temperatures. When offered a choice of a warm or cold surface, the TRPM8-deficient mice would spend significantly longer sitting in the cold than normal control animals. 

The missing gene encodes a pore which sits in the membrane of a specific class of cold-sensitive nerve fibres. When the nerve is cooled down the pore changes shape, triggering the production of excitatory nerve impulses that are relayed to the brain. The pore is also activated by menthol, which provokes the pore to change shape at much higher temperatures than it would normally, explaining why sucking a mint makes your breath feel cold against the back of your mouth.

But "Polos" making your mouth cold isn't the "hole" story because the mice weren't entirely cold-insensitive. Taking the temperature down below 10 degrees C resulted in an increase in nerve activity again, suggesting that there might be a further "extreme cold" receptor waiting to be discovered, or that at these low temperatures the physical damage done to tissue is enough to trigger other pain pathways. 

Either way, researchers hope that by understanding the workings of these sensory nerve pathways they will be able to design better drugs to block pain syndromes including those triggered by exposure to the cold.

If you drink milk that isn't skimmed, it's got lots and lots of fat in it. Having lots of fat isn't good for you because of the calories, but also because it furs up your blood vessels. Milk is also very rich in calcium which, in people who are prone to stones, can deposit in the kidney and cause kidney stones. And the other side effect of milk that not many people know, is if you have irritation to the stomach lining and you're at risk of getting stomach ulcers, calcium is used as a co-signal by the wall of the stomach to produce acid. If you have calcium levels in the blood going up, you make more acid. Some people think when they have a dodgy stomach that drinking milk will settle it. When you first do that your stomach feels happier because you've given the acid something to eat other than the wall of your stomach. But then the calcium is absorbed and goes into the blood stream and increases the amount of acid your stomach makes, causing a vicious cycle.

Chris - I'm very pleased to welcome Nicky Clayton from Cambridge University. Now Nicky you work on scrub jays, I understand that's a kind of bird, but perhaps you could kick off by telling us first of all what actually is a scrub jay and why would you want to work on it?

Nicky - Well, I work on a number of birds which are part of the crow family. This includes ravens and magpies and jays, and the ones that I work on are jays, rooks and jackdaws.

Chris - But why are you particularly interested in this family of animals?

Nicky - Well, these birds are particularly clever. We think of them as the feathered Einsteins or the feathered apes of the bird world. They have huge brains for their body size and there are all kinds of examples of just how clever they are.

Chris - One of the things you did recently was to see how good they were at planning for a rainy day, so tell us about that.

Nicky - Well, these birds hide food for the future. We call this caching behaviour, from the French word to hide. What we were interested in was the extent to which they could plan, because obviously other animals hide food, like squirrels, and many animals hibernate or migrate which means they have a forward looking behaviour. But there is a difference between a simple forward looking behaviour that might be triggered by a seasonal cue which will be entirely inborn and actually planning which would require some sort of thinking or forethought.

Chris - So how do you know they're actually doing that?

Nicky - So what we did was we asked whether they could plan for tomorrow's breakfast, and this is an experiment that was actually done by two of my Ph.D. students. It was led by Caroline Raby with help from Dean Alexis, and a member of my department Tony Dickinson, so credit must go to them as well as to me. What we did was to ask whether they could plan for tomorrow's breakfast, so we taught them that there were a suite of room that they could visit during the day.

Chris - Like a bird motel or something?

Nicky - That's right, a bird motel with a suite of three rooms and in the evening they went to sleep in the dark just as all birds do and when they woke up in the morning, they found themselves in one of two motel rooms. On some days they found themselves in motel room 1, they woke up hungry and breakfast was served, so no problem. On other days however, they found themselves in motel room 2, which was unlucky because when they woke up hungry as usual, there was no breakfast. But then all of a sudden, we gave them an unexpected test, which was to give them the opportunity to hide food as well as eat it in the evening and all the birds put the vast majority of the food, in motel room 2, where breakfast wasn't served.

Chris - So they knew that they had been hungry there in the past so they were relying on this past experience to plan for tomorrow because they may be in motel room 2 and have no food.

Nicky - Exactly, but they hadn't been trained to hide food in either of these rooms, and they used their past experience about which rooms served breakfast in the morning and which didn't to solve a potential problem. They didn't know where they'd be in the morning, so just in case, they'd put the food in the room where breakfast isn't served.

Chris - Why do they have this trait, you can see why we might do that because we are a bit more complex than they are, but what benefit does it serve this family of birds to have this ability?

Nicky - Well, that's a very interesting question from a number of levels; my husband, Dr. Nathan Emery and I have suggested that intelligence has evolved independently in two very different groups of animals: Apes, which obviously includes us, and members of the crow family. We think that this is because in the wild they have similar problems to solve, and they evolved around the same time as apes (around 5 million years ago), they are also highly social. One of the major theories formulated by Nicholas Humphrey is that the reason why we and other apes are so intelligent is because we live complex social lives. This is not just about living in a big group, but having to keep track of who does what to you and being able to network and do politics. The argument is that, those are exactly the type of problems that the members of the crow family solve.

Chris - I saw this piece in the Daily Telegraph this week, it says: "A quick smoke is good for the wings. Birds are picking up discarded cigarette butts and using their smoke to fumigate their wings of parasites, experts have suggested. Rooks have been spotted swooping onto the tracks at Exeter St. David's railway station in Devon and then placing their wings over the smoke to collect the fumes. One commuter said: I noticed the rooks because they are not usually found in towns. They were generally flapping about when a chap flicked a cigarette butt onto the track. It was still alight, and one of the rooks swooped down, picked the butt up with its beak and they flew around and landed on the platform dancing around with a cigarette butt in its beak. It looked quite comical, but then it dropped the butt onto the platform, placed its wings over it, collecting the smoke. It seemed as though it was using it to get rid of something, like an ant or a parasite or something." And then they got a quote from someone at the RCPB who said they've never heard about it but perhaps they'd learn to use the cigarette smoke to kill off parasites.

Nicky - How very clever, I've got to go and see them. I've never seen that but of course rooks are renowned for doing a number of very innovative and seemingly clever things. One of the most famous examples is that a couple of years ago they won the award for BBC's cleverest animal. This was rooks on one of the M4 motorway service stations, and what the birds were doing was finding a very innovative way of getting food that was at the bottom of the rubbish bins on the service station. So two birds would sit in tandem on the opposite ends of the rubbish bin, and slowly pull up the bin-liner under their feet. They would do it in tandem so that all the food would go to the middle where it's within beak's reach and then one bird would start tossing the food over the side while the other bird popped down onto the pavement to guard the food so it couldn't be stolen by others.

Chris - And because no one has ever shown them how to do that, they've had to work that out for themselves and then teach each other, so one has had to look at what the other one is doing to work out how to do it?

Nicky - Well I guess the million dollar question is whether each individual bird works it out for themselves and it just so happens that lots of them do it, or whether they are actually learning from one another. That's very interesting and it's one of the kinds of experiments that we are starting to do at Cambridge University; to look at whether the rooks will learn from one another and whether you could actually get mini cultures depending of which individual bird is learning to do things in a particular way.

Kat - I think one of the most fascinating things that have come out of bird research recently is that they use tools, because you can associate humans or Chimps with using tools, but birds have beaks so why do they need to use tools? So tell us a bit about tool usage in birds.

Nicky - Well, your beak can only go so far, just in the same way that if there is a small hole, you can't get your hand in there, it may also be that the hole is sufficiently small or deep that the food is out of beak's reach and that's when you'd need a tool. There are a number of species of birds that use tools, but the most remarkable thing is that one member of the crow family, the New Caledonia crow actually makes tools. So this sort of puts in on par with chimpanzees; they don't just use tools, they actually manufacture them, and they make different types of tools for different purposes.

Chris - Is there any clue given to us if you look at the animal's brains as to why these birds have these spectacular abilities compared with other animal that don't perform like this?

Nicky - Well if you look at the relative brain size, then obviously we have the biggest relative brain, but if you look at the next ones down it's the dolphins, but it's also the apes within the mammals and in the birds there are two groups, the crows and the parrots. If you look at where the enlargement is in the brain, just as in apes the enlargement is in the neocortex the same is true for the crows, the enlargement is in the avian neocortical area. So the same part of the brain is enlarged.

Chris - Thanks Nicky. That's Nicky Clayton from Cambridge University who works on Scrub jays and trying to use them to get insight into how they plan for the future and perhaps how our brains work too.

It was a great pleasure to introduce to the show from the British Antarctic Survey, one of the team who first discovered the hole in the ozone layer in the mid 1980's: Jonathan Shankin.Chris -   What is the ozone layer, and where is it?Jonathan -   The ozone layer is high up in the atmosphere, from about 10 to maybe 30 kilometres.  If you brought all the ozone in that layer down to the surface, you would have just 3 mm of pure ozone gas, but that 3mm is spread through maybe 20km of atmosphere, so even in the ozone layer there's not much ozone.Chris -   So it's very thin, isn't it?Jonathan -   It is very thin, and the worry that we have for the Antarctic is that during the Antarctic spring we have a hole in the ozone layer.Chris -   How did you actually discover that the hole was there, what were you actually doing that enabled you to make that finding?Jonathan -   We were actually making routine measurements of ozone.  They started in the international geophysical year 1957-58 and we've been making them ever since.  Really, the work was looking not to show that there's anything wrong with the ozone layer, we were trying to show that it was okay, that spray cans weren't destroying it, Concorde wasn't destroying it.  We spotted that, during the Antarctic spring, ozone levels were dropping.  We followed that up and found that it was a systematic change; it was different each year, getting lower and lower.  That was published in Nature, the Americans went back to their satellite data and said, "Oh, whoops, you're right, we missed it."Chris - Why spring? What's the significance of the season?Jonathan -   The significance of spring is really why it's over Antarctica.  It's to do with the temperature high in the atmosphere.  Once you get up to 14-20km, temperatures get to below -80 Celsius.  At that sort of temperature, you get clouds forming in the ozone layer.  Chemical reactions can occur on the surface of those clouds that convert the chlorine and bromine from halons into an active form, chlorine monoxide or bromine monoxide, and then when the sun returns in the arctic spring you get very efficient catalytic cycles that convert ozone back into oxygen.  A molecule of oxygen has two atoms of oxygen, ozone has three atoms, and we get about 1% per day being converted back into oxygen.Chris -   So what's the significance of the spray cans, what do they contribute, and also why just Antarctica, why not the North pole?Jonathan -   The spray cans used to be powered by chlorofluorocarbons (CFCs) as a propellant, it was also found in upholstery foams, in plastic cartons and a whole host of exciting uses.  They were mostly released in the northern hemisphere, but the process of diffusion means they get well mixed throughout the atmosphere.  Roughly speaking, the concentration of CFCs at the South pole and the North pole are exactly the same, but what is different is the temperature.  Over the Antarctic, every winter it's cold enough to form these stratospheric clouds high up in the atmosphere, but for the Arctic, it's only exceptionally cold winters due to the circulation of the atmosphere that enables these clouds to form.  By and large, the Northern Hemisphere circulation is more complex, the atmosphere is better mixed and it's about 10 degrees warmer, so these clouds are quite rare.  But they have been seen over Cambridge.Chris -   So why doesn't the ozone from elsewhere in the atmosphere just flow in to Antarctica and replace the deficit, filling the hole?Jonathan -   Essentially it can't.  During the Antarctic winter you get very strong circumpolar circulation - called a polar vortex.  That effectively acts as a barrier, it stops the air mixing from out of the Antarctic into the Antarctic.  So what happens is during the spring you get a build up of ozone rich air around the Antarctic, in the middle you get very low levels of ozone, and that's the ozone hole.Kat -   I would just like to backtrack a bit and ask why is the ozone layer so important, does it really matter if it's vanished?  Can't we just take the ozone from down at street level and shove it back up there?Jonathan -   It does matter if it disappears, what happens is that more ultra-violet (UV) light from the sun can get through to the surface when there's less ozone.  This UV light can trigger skin cancers, cataracts and genetic damage in micro-organisms.  So it's not very good for us to have too much UV.  For example when we have the ozone hole in the Antarctic, you can get burned in 5 minutes if you don't put on factor 30 sun block.Kat -   Wow.  How is it actually linked in to global warming, which is something that we're becoming increasingly aware of?Jonathan -   It's quite a complex thing.  The ozone hole is actually completely separate in many ways from global warming, but global warming actually makes the ozone hole worse.  That's because greenhouse gases act like a blanket, and though the surface of the Earth is heating up, the ozone layer is actually getting colder.  The fact that it's getting colder means that more of those clouds can form, then more ozone destruction means it gets colder still, and it's a positive feedback cycle.Chris -   Have the mechanisms we've put in place to try to limit the use of the agents, the CFCs that we think are responsible, actually worked?  Is the hole shrinking?Jonathan -   There's a big international treaty called the Montreal protocol, and all bar one of the worlds countries have signed up to the basic thing, so that's really good news.  The amounts of these ozone-damaging things in the atmosphere are actually going down, so were definitely getting there with this one.  But it is a symptom and not a thing in itself, and unless we tackle at a basic level what's causing many of these environmental problems, things can only get worse.Chris -   Just to crystallise this in people's minds; how big is that hole over Antarctica?Jonathan -   The Antarctic is 50 times the size of the UK, the ozone hole is bigger than that.  Not by much but it gives you an idea.Chris -   So at least fifty times the size of out own nation, it's quite a sobering thought.Jonathan -   It is, and something we created entirely off our own bat.Chris -   In actually quite a short space of time.Jonathan -   In as little as 10 years.  It shows you how fragile our atmosphere is, and how much care we need to take in case something similar happens in the future.

[We put this question to David Thomas, author of 'Surviving Antarctica']Because your eyeball is contained within your head, and your head is kept at body temperature, it never gets cold enough to freeze. The eyeballs in a dead body would indeed freeze, but while you're alive and radiating heat it can't. Even tears wont freeze immediately, as they are very salty, and salt reduces the freezing point.