Of mice and medicine: In defence of animal experiments

A sad-eyed, mournful-mouthed beagle stares out from a poster on a bus shelter by the front door of the Ear Institute of University College London. Below the melancholy dog blares the legend 'Boycott Vivisection'. It is clearly intended to be a reprimand to the scientists passing through the door into one of the world's leading research centres on hearing and deafness. Not that there are any experiments on dogs going on in the Institute, but then facts are not always the first currency when it comes to the emotive subject of experiments on animals.

The number of research procedures on animals carried out in the UK rose by 3 per cent last year. The figure has risen steadily over the past decade to just over 3.7 million in 2010. 'Procedures' is the term used by the Home Office, which is looking at ways to meet a commitment in the Government's coalition agreement to reduce the use of animals in scientific research. And it is a significant word, for behind it lies a major shift in animal experimentation.

The headline figure disguises considerable changes. Experiments on many of the kind of animals which most inspire protest among animal rights activists were down: dogs by 2 per cent, rabbits by 10 per cent and cats by 32 per cent. Even the eponymous guinea pigs were down 29 per cent. There was also a fall of 11 per cent in the number of animals used in toxicity trials, as thanks to rule changes one test can now be used to satisfy several requirements.

Where there was an increase was in mice and fish – the latter up a whopping 23 per cent. What that reveals is a switch to animals whose genes can be easily modified. An extraordinary 44 per cent of those 'procedures' turn out not to be what most members of the public imagine as an 'animal experiment' but merely the act of breeding transgenic creatures, mostly done by allowing mice to do what male and female mice do naturally anyway. But the nature of the experiments has undergone a notable change.

For decades now, the terms of the debate on this subject have been set by the emotive, sentimental or absolutist intolerance of animal rights activists. We rarely hear the other side of the story, from the scientists who have for years kept themselves in the shadows, for fear of attacks from animal rights extremists, the most violent of whom are now in jail.

Inside the Ear Institute, research is being done by Professor David McAlpine and his colleagues into the problem of tinnitus – that odd buzzing sound in the ears which afflicts most of us when we leave a noisy rock concert. For more than five million people in the UK, however, that noise never goes away.

"People with tinnitus hear a constant noise in their ears, a buzzing, beeping or whining. It can get very distressing," says a senior researcher, Dr Roland Schaette. "Around 10 per cent of the population are chronic sufferers. And for 1 to 2 per cent, their quality of life is badly affected. They lose silence. Some can't relax or sleep. Social isolation and depression can follow. It can drive some people to suicide."

Dr Schaette uses mice in his research, to fill the gap between theoretical models and his experiments on human subjects. "We do behavioural training with the mice," he explains. "Obviously you can't ask them what they are experiencing so you have to train them to behave. We play a loud noise, and they jump. Next we play a low noise before the loud one and they learn not to jump when the big noise comes. Then you induce tinnitus in them and play a low constant noise at the same pitch as the first low noise. Mice with tinnitus don't hear [this] so they jump when the big noise comes; mice without, don't."

What happens then is that Dr Schaette and his research assistant use electro-physiological recording techniques to see how nerve activities are affected. "We place a tiny wire into the brain of a mouse that has been sedated with anaesthetic, and given a pain killer," he says. "Then we can record the reaction of a tiny area of the brain, even down to a single neurone, to see how nerve activities are affected, how it alters and what mechanisms alter it." At the end of the experiment the scientists increase the sedative to a fatal dose so that the mouse dies.

So couldn't they achieve the same ends without using an animal? "There are lots of ways of finding things out," interjects Prof McAlpine. "For some tasks you can use a dish of cells. For others you can used brain imaging like magneto-encephalography", which maps activity by the brain's natural electrical currents by recording the magnetic fields they generate.

"But that is a very limited technique. It is great for telling how the human brain lights up when the body is doing particular activities. But it won't tell you how neural pathways change in tinnitus. You can't tell without an animal model to investigate the neurones. There are more synapses – connections between neurones in the brain – than there are stars in the universe. We can look at which connections grow when a mouse learns a task."

But it is not research like this which accounts for the rise in animal experiments. Across the river at King's College London, in the school of biomedical sciences, research is being done manipulating mice genes in a search for a cure for Parkinson's Disease, the progressive disorder that causes problems with movement, including tremor and muscle rigidity.

This debilitating disease is caused by the death of nerve cells in the brain. It gets worse as more nerve cells die. Doctors don't know why. But through experiments on animals they have discovered drugs which dramatically alleviate the terrible shaking which characterises the disease. The problem is these only work for five years. So further experiments are underway as Roger Morris, Professor of Molecular Neurobiology and Head of the School of Biomedical Sciences at King's College explains.

"The primary cause of Parkinson's is the death of neurons that deliver an essential chemical called dopamine to the forebrain," he says. "The primary treatment is to provide a substitute chemical, L-DOPA. But in the healthy brain, dopamine is released only in very specific regions. L-DOPA, however, penetrates the whole brain, in a way that the body is not used to. Abnormal changes start to happen, resulting in continuous uncontrolled limb and body movements."

Scientists at King's – which has 22,000 experimental animals, 21,000 of them mice – have, over the past couple of decades, used marmosets – small, primitive New World monkeys – to discover the dose of L-DOPA which brings the fewest unwanted side effects. Work with such non-human primates is not quite so controversial as experiments with African monkeys. But this is the kind of work which most incenses animal rights activists.

Professor Morris is unapologetic. "There is a lot you can do without animals. Most scientists who use animals do so as part of a whole portfolio of techniques, which will include work with isolated molecules and genes, building up to whole cells growing on plastic dishes in tissue culture to study the more complex integration of cells to work together as a single tissue," he says. Some 90 per cent of his staff's work is done with individual molecules and cells in culture.

"At all these stages, extensive use is made of computational modelling, and analyses of databases, to bring together all the information available on how the particular aspect we work on functions in a living body," he continues. "And there are now non-invasive brain imaging techniques that tell us a lot. But real diseases are diseases of the whole body, and can only be studied in the whole body."

Dopamine deficiency is a key component of Parkinson's but the underlying cause is a complex set of interactions triggered by inflammation in the autoimmune system. "So we need to understand the interaction between two complex bodily systems – the brain, and the immune system – to understand this multi-tissue, multi-step disease. The body's controls on how those two systems interact are lost the moment both are cultured in a plastic dish. We need to look at living brain."

britain has the strictest rules in the world on such experiments, a House of Lords select committee has found. The Animals (Scientific Procedures) Act 1986 says they can only be performed where there is a clear potential benefit to either people, animals or the environment, and when there is no means of obtaining these benefits without using animals. The act also builds in a cost-benefit analysis which insists, in a very English test of reasonableness, that the good to humans must clearly outweigh the harm to animals.

Experiments must use the minimum number of animals, involve animals with the lowest degree of sensitivity, and cause the least suffering consistent with arriving at a clear scientific conclusion. Institutions, projects and scientists need three sets of licences. Home Office inspectors visit their labs around 12 times a year.

Evidence of proportionality is not hard to find. More than 120,000 people suffer from Parkinson's today in the UK. That seems a grievous problem set against the discomfort of a relatively small colony of marmosets – numbering just a few hundred over the past decade – whose suffering has dramatically improved the treatment of the disease. Moreover, when Parkinson's is induced in marmosets the disease does not progress as it does in human beings "and the animals live into old age, housed in pairs throughout their lives in an enriched environment," Prof Morris says.

All this is a big change from the bad old days. "I was appalled at some of what was allowed when I started my PhD in the United States in 1972," he recalls. "The kind of science done in living experiments with animals has completely changed." Thirty years ago a lot of experiments were with cats and dogs or primates.

Today there are more experiments recorded, but the animals used are mostly mice and fish and the procedures are considerably less severe. Before 1984, scientists could do anything with an animal that the Home Office had not specifically disallowed. Today the default is reversed; nothing is allowed that has not been specifically sanctioned.

In the old days the first line of experiment was often with the living animal, and the tests used were not very sophisticated. Now, before they get to an animal, scientists have refined the question they want to ask by extensive work with cells and computer modelling.

Previously, scientists had to breed a large number of animals just to get the type they needed – mice of the same age with the same parents. Now, thanks to genetic modification, they can generate precisely the number and kind they need for a particular experiment.

"We increase the number of animals used," says Professor Dominic Wells, of the neuromuscular disease group at the Royal Veterinary College, "but we decrease the overall severity of what we're doing." The technology allows a gene to be deleted so that an adult mouse appears to be normal until asked to remember something, which it cannot then do.

A scientist working elsewhere on spinal cord injuries, who asked to remain unnamed for fear of animal rights reprisals, elaborated on this. He is working on trying to stimulate the human body to regenerate nerves in the spinal cords of the 400,000 people in Europe who are paralysed after back or neck injuries from car accidents, violent falls or sports injuries.

"Human suffering is far more protracted and severe than anything we would allow in animals," he told me. "Procedures are done to reduce discomfort to a minimum. Our work is about understanding the early stages of the development of diseases, before irreversible brain damage has commenced, and understanding the subsequent disease mechanism so we can prevent it at an early stage. So we don't need to take animals to extremes. We can study the effects of that in humans."

What that means in practice is that, in his case, rats are partially paralysed – in one paw or to impair the tail. "You wouldn't enter a rat with a partial lesion of its spinal cord in a rat race," he told me, "but it can get around the cage well enough. What we are studying is mechanisms, so a 10 per cent paralysis will suffice to study what prevents a paraplegic human from recovering – and being condemned to 30 years in a wheelchair." Researchers have already discovered an enzyme which allows previously disabled rats to walk again almost normally.

There are both scientific and moral reasons that impel scientists to choose the simplest animal system that will give them the result they seek. "We do have a moral perspective about an animal's suffering," says David McAlpine. "There is a hierarchy. I'm unashamedly modernist about that. You take the animal that's the lowest in the hierarchy that will answer your question."

So basic studies on cell-division could be done to Nobel Prize level, as they were by Sir Paul Nurse, studying something as primitive as yeast, Prof Morris says. "It's very fast, very simple and you get clear answers quickly. But as you ask more detailed or complicated questions you need to go up the chain – to fish, mice, rats, bigger mammals and sometimes primates."

Prof McAlpine concurs. "Fruit flies go deaf for the same reasons you and I do," he says. "So you can do some basic work with them and do it much more quickly because they have simpler nervous systems. A mouse has a different hearing range from a human – it hears much higher sounds – but mice are close enough to us for use to study the range of hearing loss problems we have. For some things people use guinea pigs because they have a very similar hearing range to humans; you can do a cochlear implant in a guinea pig but not in mouse.

Despite the focus on dogs, cats and monkeys in the campaign posters of animal rights activists, those creatures were used in less than half of 1 per cent of all procedures in last year's official figures. A report by Professor Sir Patrick Bateson, president of the Zoological Society, in July found that 91 per cent of research on non-human primates between 1997 and 2007 was of high quality and scientifically and ethically justified. It is being conducted by 72 researchers working mainly on Alzheimer's and Parkinson's. Some animals were used in more than one procedure since the experiments had only minimal effect on the animals. Since then, The National Centre for the Replacement, Refinement and Reduction of Animals in Research has been brought into tighten up conditions to avoid even that 9 per cent failure rate. They vet each application for experiments involving primates.

But monkeys are not the area of innovative work in animal research. Fish are. Or to be more precise, zebrafish. In the Randall Division of Cell and Molecular Biophysics at King's College in London, Dr Claudia Linker is at her computer looking at a video made through a microscope of a small tear made in the tail of a zebrafish.

Zebrafish are those tiny, iridescent, black-striped creatures, originally natives of the Ganges River in India but popular now in Britain's home aquariums. But they are perfect creatures for the study of the early development of embryos. Not only do they grow up and reproduce in just three months, going through the same development stages as a human embryo, but their tiny eggs have clear shells that develop rapidly into translucent embryos so they can be studied using just an optical microscope.

They are easy to keep in a laboratory, lay around 200 eggs at a time which can be harvested without the need to kill the mother (as happens with lab mice). They develop from egg to fish within 18 hours. Scientists can not only look at a fish's heart beating under a microscope, they can mark individual cells with a fluorescent marker gene which they transfer from jellyfish. They can use different coloured markers for different cells and watch different cells participating in the embryo's development and multi-tag all the tissues. And their genes can be modified more easily than those of mice.

Dr Linker is enthralled by what she can see. The movement of blood cells towards the wound is clearly evident. "Can you see them moving?" she asks and shows me different examples of migratory cells. "My work is to find out how cells know when to start migrating, where to go, what to do when they arrive at their destination. I am not working on curing a particular disease but on understanding how the basic mechanism directing cell migration works. Once we understand it we might learn how to intervene to promote cells to do what we want, for example, stop the migration of cancer cells. It's very exciting, but it is open-ended."

Down the corridor, her colleague Professor Simon Hughes is doing something similar on skeletal muscle development. "We need to understand what is the signal mechanism within an embryo that says make a muscle here, a heart there, a liver over there – and you can't find that out from a test-tube."

Research on zebrafish published earlier in the year found that the fish are able to repair muscle within their hearts. "That's not something that happens in us, or mice. By experimenting with that it may well be possible to gain some insight that will enable human hearts to be regenerated," says Prof Hughes, who once researched with mice but switched to zebrafish. He is attempting to lay the groundwork for treatments for muscular dystrophy.

Wandering through a laboratory like this can be an exciting journey. By the stairs I meet Dr QueeLim Ch'ng who decided to study C elegans, a little worm almost too small to see with the naked eye, and discovered proteins which turn out to be involved in premature ageing, and which in man are critically involved in Alzheimer's.

Another King's scientist has discovered that coral produces a chemical which enables it to adapt to living in UV light – and that fish which eat the coral transfer that chemical to their eyes, so they don't get UV damage from light. The next step will be to see how the chemical moves from the fish's digestive system into its eyes by implanting the chemical in mice; the hope is that the research will lead to a treatment to prevent macular degeneration, which causes blindness in humans.

In another lab, a PhD student has identified the world's first therapy to partially reverse arm disabilities in strokes – and he did it by injecting a human molecule which naturally occurs in muscle into the upper arm muscles of rats. It even works 24 hours after a stroke.

Several of the range of drugs which have changed the lives of people with Aids have been based on animal experiments studying the mechanism of which cells it infects, how it gets into those cells, why it binds to particular receptors, and which drugs block that interaction. "Now," says Professor Morris, "we are working on something similar with Alzheimer's, trying to make a mouse model by altering three mouse genes to reproduce in mice some of the behaviour found in people with Alzheimer's."

For a nation of pet-lovers, we Britons take a surprisingly pragmatic attitude to all this. Most of us are aware of the ambiguity of our relationship with animals. Over 90 per cent of the population eats meat. As we are happy to breed animals for food, so we are content, too, to see them bred for experiments which improve human health. Polls consistently show that 60 per cent of the population are happy for any experiments to be done on animals. The proportion of Brits who accept animal experiments, subject to the kind of conditions now in place, is over 90 per cent. When you spend a little time with the scientists involved, you understand why.