A variety of vertebrate and invertebrate animal species has been used in research in the lab. All the species used so far are listed here.

Posted values of body mass, body temperature, and circadian period are means only. Since some species exhibit more variability than others, the accuracy of the posted values is variable. Most values were measured in our lab, but some were obtained from the scientific literature. (Body temperature values for ectothermic animals are indicated as N/A, meaning "not applicable".)

Samples of data obtained from individuals of some of these species are available in the Data Repository section of this web site.

Links to abstracts or full-text articles describing the research that involved these animals in our lab can be found in the Research and Publications sections.

The Nile Grass Rat

As a diurnal rodent of small body size, good tempera- ment, and short breeding cycle, the Nile grass rat (Arvicanthis niloticus) is an attractive laboratory animal for biomedical research. Like the standard laboratory rat, it is relatively insensitive to variations in photoperiod and does not hibernate. Unlike the laboratory rat, it reaches asymptotic body mass early in life and does not exhibit marked sexual dimorphism.

The genus Arvicanthis, traditionally believed to contain five species including A. niloticus, belongs to the family Muridae, the large rodent family that includes the domestic mouse (Mus), the laboratory rat (Rattus), the hamster (Cricetus and Mesocricetus), and other rat-like rodents. The exact number of species within the genus Arvicanthis is still under debate.

The Nile grass rat, sometimes also called African grass rat, unstriped grass mouse, or Kuzu rat, is a chunky rodent with coarse, grayish brown fur. Adult head and body length is approximately 13 cm, tail length is 10 cm, and body weight in captivity is 120 g. Females are slightly (6 g) lighter than males. The species' natural geographic distribution is restricted to the northern half of Africa, particularly the Nile Delta of Egypt, and to the southwestern Arabian Peninsula, where it inhabits mostly grasslands and savannahs but also forests and scrubby thickets. Regular use of nests or burrows, particularly at night, has been observed both in the wild and under semi-natural laboratory conditions.

In temperament, the Nile grass rat is slightly more agitated than a laboratory rat but considerably more sedate than a squirrel. When group-housed from weaning, it can be easily handled as an adult. Single-housed individuals tend to become hostile towards conspecifics and aversive to human handling. In the wild, Nile grass rats form social groups with several adult males and females. Longevity has been reported to be as long as 6 years for healthy individuals, although in our colony most animals have not lived past 2 years of age.

Laboratory colonies of Nile grass rats in North America are descendant of 29 individuals trapped at the Masai Mara National Reserve in southwestern Kenya in 1993 by the research team headed by Professor Laura Smale at Michigan State University. The species breeds easily in captivity, particularly if provided with plenty of bedding and a small refuge (such as a hollow PVC pipe) in the cage. The ideal ambient temperature is 20-25 °C, and a short photoperiod (L11:D13) is recommended for proper gonadal function. Gestation lasts 23 days on average, and a new pregnancy can be initiated within a few hours of delivery of the previous litter if the male breeder is kept in the same cage as the female. Litter size varies from 5 to 9 pups. The pups are born with fur and can be weaned by 21 days of age. Infanticide and killing of the female by the male are occasionally observed, perhaps with a frequency higher than that encountered in the breeding of standard laboratory rats and mice, but they can be minimized by close monitoring of the breeding pairs.

Much of biomedical research is conducted with non-human animal subjects. Although a small fraction of this research is directed at improvements in veterinary care, the major goal is to improve human health. Experimentation with living organisms is performed in animals for the benefit of humankind.

The conduct of research with animals is strictly regulated in most of the world. In the United States, the use of animals in research is regulated by the Department of Agriculture (USDA) and, in all projects that receive federal funding, it must conform to detailed guidelines set out by the Public Health Service. Intentional infliction of pain is extremely rare and limited to research on the physiology of pain itself. Importantly, whether pain is expected or not, every research project must be pre-approved by an ethics committee. The task of the various Institutional Animal Care and Use Committees (IACUCs) is to decide, based on the scientific and ethical values of the community, whether the discomfort caused to the animals is justified by the expected benefits of the research project. Authorization to perform the project is denied if the justification is unsatisfactory.

Excellent guidelines for the humane use of animals in research are published by the Institute for Laboratory Animal Resources of the U.S. National Research Council: Guide for the Care and Use of Laboratory Animals, Eighth Edition (Washington, DC: National Academy Press, 2010). A copy can be purchased at www.nap.edu (ISBN: 978-0-309-15400-0).

Q: Specifically regarding circadian rhythms, Mr. Peter Freeman, a teacher at Diss High School (in England), asks whether what is learned about the suprachiasmatic nucleus (SCN) in golden hamsters is applicable to human beings.

A: The general anatomical and physiological features of hamsters and humans are similar, but, of course, not identical. Learning that the SCN is the master circadian pacemaker in hamsters does not guarantee that the SCN is the master circadian pacemaker in humans. However, studies have been conducted in many other species also. For instance, surgical destruction of the SCN has been shown to eliminate circadian rhythmicity in lizards, birds, hamsters, rats, mice, and other rodents. SCN lesion also eliminated daily rhythmicity of activity in rhesus monkeys and was associated with loss of rhythmicity in a woman with a gunshot wound in the brain. Rhythmic expression of circadian "clock genes" has been documented in living cells of insects, fishes, birds, rodents, ruminants, and humans. Thus, although the details of operation may differ between the hamster SCN and the human SCN, there is very strong evidence that the SCN is the master circadian pacemaker in hamsters and other mammals, including humans.