The History of the Lab Rat

In my reporting for Discover, I regularly see studies that rely on laboratory rats to answer a variety of questions. One study, for example, considered whether garlic had protective properties against toxins. Another studied rats' hunger and impulse control. And in a study that no one in my family wanted to hear about at dinner time, researchers measured brain activity in decapitated rats.

For me, these stories prompted a new question — why do rats show up so much in research? Why are they running through mazes, pushing levers to receive treats or being placed into rat-sized guillotines?

The history of the lab rat dates back centuries, and the sequencing of the rat genome in the early 2000s means rat research is providing more insight than ever. 

Long before researchers were getting young male rats drunk to measure the impact of substance abuse on developing brains, scientists were experimenting with rats and nutrition. Prior to 1850, European scientists used Rattus norvegicus (aka Norway/street rat) in nutrition experiments. In 1856, one of the first published rat experiments described the effect of an adrenalectomy in albino rats. It was in the 1890s that the first known rat research came to the U.S. with neuroanatomical studies at the University of Chicago.

More than a century later, scientists formed the Rat Genome Database in 1999, allowing them to share information and contribute to the rat genome sequencing. Because rat and human genomes have similarities, the project has enabled studies of genetically-based diseases.

Rats and mice are now used in 90 to 95 percent of research involving mammals. A 2021 study in Scientific Reports looked at 16 major research institutions in the U.S. and found that 99.3 percent of mammals used in laboratory experiments were mice and rats.

Rat research now informs studies related to Alzheimer's disease, arthritis, cancer research, cardiovascular disease, diabetes, spinal cord injury, cardiovascular disease and substance abuse (hence the aforementioned drunk teen rats). 

Rats are the most common rodent used in research, and there are a variety of reasons why.

In terms of behavior, rats are desirable research subjects because they are social creatures. They are also curious and can be trained to perform repetitive tasks. They also aren't fussy eaters and have a varied diet.

Rats age quickly and reach sexual maturity after only a few months. Rats typically mate once they are 100 to 120 days old, and female rats reach menopause around 450 to 540 days old. The rodents' rapid aging is helpful to scientists studying the aging process in humans. However, scientists still disagree on how rat age correlates to human age. 

But there are similarities between rats and humans that are more straightforward. Rats can be used to study almost every organ system in humans. There are also strong structural similarities between rat and human brains, which enables neuroscientists to use rats to learn more about human brain functions.

In rat brains, for example, almost a third of the sensorimotor cortex is designated for processing information sensed by the rat's whiskers. Likewise, the human cortex uses nearly 40 percent to process visual information. 

The need for laboratory rats has increased in the past 60 years and will likely continue to grow. In 1966, the Animal Welfare Act created stipulations for using large mammals such as monkeys or dogs in research. The law was a response to pet owners whose animals had been stolen and sold to laboratories. It regulated how cats, dogs, guinea pigs, hamsters, nonhuman primates and rabbits were sold, transported and handled.

In time, the law evolved to include all warm-blooded animals, with the exception of mice, rats and birds. Because the law specifically does not include rats, government officials do not inspect laboratories that use and house rats. Without government oversight, it's difficult to determine how many rats are in the U.S. labs. One study estimated as many as 115 million rats are being used for research.

A 2023 Congressional Report noted that animal advocates would like to see more oversight and transparency regarding the use of rats, mice and birds in scientific experiments. Until then, it should be noted that the above studies that involved getting rats drunk, poisoning them or decapitating them occurred outside the U.S. in laboratories in Iran, Italy, New Zealand and Pakistan.