For decades, lab rats and mice have been used to make great scientific and medical advances , from cancer drugs and HIV antiretrovirals to the yearly flu vaccine. Lab mice—most often of the species Mus musculus, or house mouse—are biomedical swiss army knives, with genomes that are easily manipulated for genetic studies.
The physiology of the human body, however, is more closely mimicked in Rattus norvegicus , or the Norway rat , and its various strains. Rats are also easily trainable and perfectly suited for psychological experiments, especially considering their neural networks so closely resemble our own.
In the s and '60s, for example, researchers studying the biological underpinnings of curiosity noted that lab rats, devoid of any other stimulus or task, prefer to explore the unknown parts of a maze. Rats are also much larger than mice and have thicker tails and blunter snouts. But it's the characteristics shared by mice and rats that make them both scourges of the city and the perfect scientific guinea pigs, so to speak.
As a result, rodents have all but taken over our labs, making up nearly 95 percent of all laboratory animals. Over the past four decades, the number of studies using mice and rats more than quadrupled, while the number of published papers about dogs, cats and rabbits has remained fairly constant. By , mice alone were responsible for three times as many research papers as zebra fish, fruit flies and roundworms combined.
Studies with rodents address everything from neurology and psychology to drugs and disease. Researchers have implanted electronics into mice brains to control their movements , repeatedly tested the addictive properties of cocaine on mice , administered electric shocks to rodents as a negative stimulus , implanted human brains in mice skulls , and sent mice and rats scurrying through endless labyrinths of tests.
For all that lab mice and rats have helped humans accomplish, the day-to-day experience of the animals takes place largely out of the public eye. But the life of lab rodents may be key to understanding and improving their role in the course of scientific discovery. Scientists must complete animal handling and ethical training before they are permitted to work with laboratory animals, though the rules vary depending on where the experiment takes place.
While Canadian and European scientists are overseen by a national governing body, the rules in the United States vary by institution with some overall guidance from the National Institute of Health. The U. Animal Welfare Act , which protects most animals used for research, excludes mice and rats.
Most universities offer a training course on how to handle the animals in a way to best reduce stress and suffering. The best practices have been updated over the years to reflect a changing understanding of the rodents and their needs.
After a study published in Nature showed that handling lab rats by the tail causes more anxiety than guiding the animals through a tunnel or lifting them with cupped hands, labs around the world abandoned the previously common technique.
Scientists who want to experiment with rodents are required to fill out a detailed application explaining why the work requires animal subjects. Mice and rats are also relatively inexpensive and can be bought in large quantities from commercial producers that breed rodents specifically for research.
The rodents are also generally mild-tempered and docile, making them easy for researchers to handle, although some types of mice and rats can be more difficult to restrain than others. Most of the mice and rats used in medical trials are inbred so that, other than sex differences, they are almost identical genetically.
This helps make the results of medical trials more uniform, according to the National Human Genome Research Institute. As a minimum requirement, mice used in experiments must be of the same purebred species. Another reason rodents are used as models in medical testing is that their genetic, biological and behavior characteristics closely resemble those of humans, and many symptoms of human conditions can be replicated in mice and rats.
Estimates suggest that for the year , there were just short of , opiate and crack cocaine users in England alone. Using rats, researchers showed that addiction manifests itself differently in different individuals and that, for some, compulsive cocaine-seeking behaviour continues despite adverse circumstances. Drug addiction had largely been regarded as the end point of a progressive loss of control over drug seeking resulting from a failure of part of the brain — the prefrontal cortex — that deals with decision making.
However, our researchers were able to show that long term exposure to drugs also alters an area of the brain called the basolateral amygdala, which is associated with the link between a stimulus and an emotion. In fact, using their rat model, our researchers have now identified a completely new path in the brain that links impulses with habits. This brain circuit links the basolateral amygdala indirectly with the dorsolateral striatum, which is the neural locus of habits.
See also: Highway to addiction: how drugs and alcohol can hijack your brain. Atherosclerosis is a severe disease of the arteries, responsible for heart attack and stroke. The disease is initiated by accumulation of fatty deposits in the artery wall. In , Cambridge scientists were involved in research that identified the mechanism behind hardening of the arteries, and, using rats, found a generic medication normally used to treat acne could be an effective treatment for the condition.
See also: Cause of hardening of the arteries - and potential treatment - identified. Our Horizons email lets you know when the latest issue of the University of Cambridge's research magazine is available for you to read online. Enter your email address below, confirm you are happy to receive emails from us and select 'Subscribe' to sign up. I wish to receive an email when a new edition of the University's Horizons research magazine is published.
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