The laboratory rat (Rattus norvegicus) is descended from the Norway rat, and likely accompanied settlers to the New World in the hulls of ships. While its distribution is worldwide, they originated in Asia. Rats have been used for research since the 1800s. Albino rats were used for physiological studies as early as 1828, and the oldest inbred strain dates from 1856.[1]
While not covered by the Animal Welfare Act, rats used in federally funded projects are covered by Public Health Service Policy, administered by the Office of Laboratory Animal Welfare (OLAW) and the ILAR Guide for the Care and Use of Laboratory Animals.
Rats are used as research models for nutrition, toxicology and teratology, as well as specific conditions including arthritis, gerontology and asthma, to name a few. Rats have been the animal of choice for the study of hypertension, first as a surgically induced model, and later as a specially bred strain, the SHR/N rat, developed in Japan in 1963[2]. It is also being explored as a model for childhood ADHD. Other strains have been developed for specific conditions including the Brattleboro rat as a diabetes model and Zucker rats for obesity. Rat strains continue to be developed, and transgenic rats are also available.
The most commonly used inbred strain is the Fischer 344[3], an old inbred strain. The Fischer rat is a general purpose model and an animal of choice for cancer and toxicology[4]. The most common albino outbred strains are the Sprague Dawley rat, and the Wistar rat, developed at the Wistar Institute in Philadelphia. In addition to the "laboratory rat”, there is the roof rat (Rattus rattus), the cotton rat and the kangaroo rat; some of these rats are only distantly related.[5]
Rats are social animals and live in colonies with well defined territories that they mark with urine and glandular secretions. Rats can be aggressive, and social conflicts are most common at feeding sites, prime nesting sites, and territorial boundaries. Young are communally raised and females share nursing duties.[6]. They are nocturnal and are born naked and hairless (altricial). Rats are typically housed in shoebox caging with solid floors. Since the animals are burrowers by nature, bedding allows the animals to practice normal behaviors. Other enrichments for rats include tunnels, tubes and levels to increase the complexity of the cages and chew toys.
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[6] Harkness, J., et al., Harkness and Wagner’s The Biology and Medicine of Rabbits and Rodents, Fifth Ed., Hoboken:Wiley-Blackwell, 2010, p.97