The Long Evans rat is an outbred stock of the common Norway rat used extensively in scientific research. It is easily identified by its characteristic white body and a pigmented “hood,” typically black or brown, that covers its head and extends down its back. First developed over a century ago, this strain has become a standard model in many laboratories globally. Its unique combination of physical traits and behavioral characteristics makes it particularly suitable for specific fields of biomedical investigation.
Origin and Distinguishing Features
The Long Evans rat was first developed in 1915 by Drs. Joseph Long and Herbert Evans at the University of California, Berkeley. They created the strain by crossbreeding female albino rats from the Wistar Institute with a wild gray male Norway rat (Rattus norvegicus). The goal was to produce a hardier and more vigorous animal for research purposes.
The most prominent feature of the Long Evans rat is its coat coloration. The classic presentation is a pigmented hood, either black or brown, that covers the head and shoulders, often accompanied by a stripe running down the spine. The rest of the body is typically white. Unlike albino strains such as the Wistar or Sprague Dawley, Long Evans rats have pigmented eyes, which grants them normal vision.
This strain is maintained as an outbred stock, meaning its breeding is managed to maximize genetic variation, similar to a natural population. This genetic diversity is a useful characteristic for studies where results need to be applicable to a general population rather than a highly specific genetic line. This contrasts with inbred strains, where animals are as genetically identical as possible.
Primary Uses in Scientific Research
The Long Evans rat is a preferred model in behavioral science, where researchers study processes like learning, memory, and cognition. Studies have shown that Long Evans rats often learn operant tasks, which involve performing an action to receive a reward, more quickly than some albino strains. Their inquisitive nature makes them well-suited for navigating mazes and other tests designed to assess cognitive function and memory. This makes them a frequent choice for modeling neuropsychiatric and neurodegenerative disorders.
Another significant area of use is in addiction research, particularly studies focused on alcohol consumption. Compared to other rat strains, Long Evans rats voluntarily consume higher amounts of alcohol, which allows researchers to study its behavioral and biological effects more effectively. Their robust physiology also makes them a general-purpose model for toxicology and studies of maternal behavior.
Temperament and Comparison to Other Strains
The temperament of the Long Evans rat is often described as inquisitive and active. While generally considered docile enough for handling, some research suggests they can be more aggressive and reactive to stress than other common laboratory strains. This increased activity and engagement with their environment contributes to their strong performance in behavioral and cognitive tasks. These same traits of intelligence and curiosity also make them popular as pets.
When compared to other widely used outbred stocks like the Sprague Dawley and Wistar rats, several key differences emerge. Behaviorally, Long Evans rats are often more active and may learn certain tasks faster, whereas Sprague Dawley rats are noted for their calmness and ease of handling, making them a frequent choice for surgical and nutritional studies. Physiologically, different strains have varying predispositions to health issues. For example, Sprague Dawley rats are known to have a higher incidence of pituitary tumors, while Long Evans rats are considered relatively resistant to spontaneous tumor development.