Mice (Laboratory) - Pathology
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Anatomic features
The laboratory mouse has several unique characteristics, and there are vast differences in normal anatomy, physiology, and behaviour among different strains of mice, many of which represent abnormalities arising from homozygosity of recessive or mutant traits in inbred mice.
The dental formula is 2(I 1/1, M 3/3) = 16. The incisors are open-rooted and grow continuously.
The stomach is divided into a proximal nonglandular portion and a distal glandular portion.
The left lung consists of one lobe, while the right lung consists of four lobes.
Mice have 3 pectoral and 2 inguinal pairs of mammary glands, with mammary tissue enveloping much of the subcutis, including the neck. Mammary tissue can be found immediately adjacent to to salivary glands.
The mouse has the narrowest thermoneutral zone of any mammal thus far measured. A mouse responds to decreases in ambient temperature by nonshivering thermogenesis, and to increases in ambient temperature by decreasing metabolic rate and increasing vascularization of the ears. Nonshivering thermogenesis can produce a threefold increase in basal metabolic rate, and for the most part occurs in brown fat. The highest concentration of brown fat is found in the subcutaneous tissues between the scapulae.
The brain and spinal cord are larger in mature male mice compared to females.
The zona reticularis of the adrenal cortex is not discernible from the zona fasciculata. A unique feature of the mouse adrenal is the X zone of the cortex, which surrounds the medulla. The X zone is composed of basophilic cells but when males reach sexual maturity and females undergo their first pregnancy, the X zone disappears.
Melanosis occurs in several organs, including the anteroventral meninges of the olfactory bulbs, optic nerves, parathyroid glands, heart valves, and spleens of melanotic mouse strains, such as B6 mice.
Strain Information
Most laboratory mice have contributions from both Mus musculus musculus and Mus musculus domesticus. There is evidence that smaller contributions also may have come from Mus musculus molossinus and Mus musculus castaneus. Therefore, they should not be referred to by species name, but rather as laboratory mice or by use of a specific strain or stock name. (In addition, some recently developed laboratory mouse strains are derived wholly from other Mus species or other subspecies, such as M. spretus). The laboratory mouse genome, including its retroelements, is a mosaic and an artificial creation, and there is no true "wildtype" laboratory mouse. There are over 450 inbred strains that have arisen during the last century but the great majority of biomedical resaerch, including genomic research, is based on a relatively few mouse strains, including C57BL/6, BALB/c, C3H/He, 129, FVB, and outbred Swiss stocks.
Genetically Engineered Mice
References
- Percy, D.H., and Barthold, S.W. (2007) Pathology of laboratory rodents and rabbits. Blackwell Publishing. pp. 3-123.