Vector diagram of laboratory mouse (black and white)

The laboratory mouse or lab mouse is a small

mammal Mammals () are a group of vertebrate animals constituting the class Mammalia (), characterized by the presence of mammary glands which in females produce milk for feeding (nursing) their young, a neocortex (a region of the brain), fur ...

of the order

Rodent Rodents (from Latin , 'to gnaw') are mammals of the order Rodentia (), which are characterized by a single pair of continuously growing incisors in each of the upper and lower jaws. About 40% of all mammal species are rodents. They are n ...

ia which is bred and used for

scientific research The scientific method is an empirical method for acquiring knowledge that has characterized the development of science since at least the 17th century (with notable practitioners in previous centuries; see the article history of scientific m ...

or feeders for certain pets. Laboratory

mice A mouse ( : mice) is a small rodent. Characteristically, mice are known to have a pointed snout, small rounded ears, a body-length scaly tail, and a high breeding rate. The best known mouse species is the common house mouse (''Mus musculus'' ...

are usually of the species ''

Mus musculus Mus or MUS may refer to: Abbreviations * MUS, the NATO country code for Mauritius * MUS, the IATA airport code for Minami Torishima Airport * MUS, abbreviation for the Centre for Modern Urban Studies on Campus The Hague, Leiden University, Net ...

''. They are the most commonly used mammalian research model and are used for research in

genetics Genetics is the study of genes, genetic variation, and heredity in organisms.Hartl D, Jones E (2005) It is an important branch in biology because heredity is vital to organisms' evolution. Gregor Mendel, a Moravian Augustinian friar work ...

physiology Physiology (; ) is the scientific study of functions and mechanisms in a living system. As a sub-discipline of biology, physiology focuses on how organisms, organ systems, individual organs, cells, and biomolecules carry out the chemic ...

psychology Psychology is the science, scientific study of mind and behavior. Psychology includes the study of consciousness, conscious and Unconscious mind, unconscious phenomena, including feelings and thoughts. It is an academic discipline of immens ...

medicine Medicine is the science and practice of caring for a patient, managing the diagnosis, prognosis, prevention, treatment, palliation of their injury or disease, and promoting their health. Medicine encompasses a variety of health care pr ...

and other

scientific Science is a systematic endeavor that builds and organizes knowledge in the form of testable explanations and predictions about the universe. Science may be as old as the human species, and some of the earliest archeological evidence for ...

disciplines. Mice belong to the

Euarchontoglires Euarchontoglires (synonymous with Supraprimates) is a clade and a superorder of mammals, the living members of which belong to one of the five following groups: rodents, lagomorphs, treeshrews, colugos, and primates. Evolutionary affinities wi ...

clade, which includes humans. This close relationship, the associated high homology with humans, their ease of maintenance and handling, and their high reproduction rate, make mice particularly suitable models for human-oriented research. The laboratory mouse genome has been sequenced and many mouse genes have human homologues. Other mouse species sometimes used in laboratory research include two American species, the white-footed mouse (''Peromyscus leucopus'') and the North American deer mouse ('' Peromyscus maniculatus'').

History as a biological model

Mice have been used in biomedical research since the 17th Century (from May 30, 1678) when

William Harvey William Harvey (1 April 1578 – 3 June 1657) was an English physician who made influential contributions in anatomy and physiology. He was the first known physician to describe completely, and in detail, the systemic circulation and propert ...

used them for his studies on reproduction and blood circulation and

Robert Hooke Robert Hooke FRS (; 18 July 16353 March 1703) was an English polymath active as a scientist, natural philosopher and architect, who is credited to be one of two scientists to discover microorganisms in 1665 using a compound microscope that ...

used them to investigate the biological consequences of an increase in air pressure. During the 18th century

Joseph Priestley Joseph Priestley (; 24 March 1733 – 6 February 1804) was an English chemist, natural philosopher, separatist theologian, grammarian, multi-subject educator, and liberal political theorist. He published over 150 works, and conducted ...

and

Antoine Lavoisier Antoine-Laurent de Lavoisier ( , ; ; 26 August 17438 May 1794),
CNRS (

respiration. In the 19th century

Gregor Mendel Gregor Johann Mendel, OSA (; cs, Řehoř Jan Mendel; 20 July 1822 – 6 January 1884) was a biologist, meteorologist, mathematician, Augustinian friar and abbot of St. Thomas' Abbey in Brünn (''Brno''), Margraviate of Moravia. Mendel was ...

carried out his early investigations of inheritance on mouse coat color but was asked by his superior to stop breeding in his cell "smelly creatures that, in addition, copulated and had sex". He then switched his investigations to peas but, as his observations were published in a somewhat obscure botanical journal, they were virtually ignored for over 35 years until they were rediscovered in the early 20th century. In 1902

Lucien Cuénot Lucien Claude Marie Julien Cuénot (; 21 October 1866 – 7 January 1951) was a French biologist. In the first half of the 20th century, Mendelism was not a popular subject among French biologists. Cuénot defied popular opinion and shirked the “ ...

published the results of his experiments using mice which showed that Mendel's laws of inheritance were also valid for animals — results that were soon confirmed and extended to other species. In the early part of the 20th century,

Harvard Harvard University is a private Ivy League research university in Cambridge, Massachusetts. Founded in 1636 as Harvard College and named for its first benefactor, the Puritan clergyman John Harvard, it is the oldest institution of higher le ...

undergraduate

Clarence Cook Little Clarence Cook Little (October 6, 1888 – December 22, 1971) was an American genetics, cancer, and tobacco researcher and academic administrator, as well as a eugenicist. Early life C. C. Little was born in Brookline, Massachusetts and atte ...

was conducting studies on mouse genetics in the laboratory of

William Ernest Castle William Ernest Castle (October 25, 1867 – June 3, 1962) was an early American geneticist. Early years William Ernest Castle was born on a farm in Ohio and took an early interest in natural history. He graduated in 1889 from Denison University ...

. Little and Castle collaborated closely with

Abbie Lathrop Abbie E. C. Lathrop (1868 – 1918) was a rodent fancier who bred fancy mice and inbred strains for animal models, particularly for research on development and hereditary properties of cancer. Biography Lathrop was born in 1868 in Illinois to scho ...

who was a breeder of fancy mice and rats which she marketed to rodent hobbyists and keepers of exotic pets, and later began selling in large numbers to scientific researchers. Together they generated the DBA (Dilute, Brown and non-Agouti) inbred mouse strain and initiated the systematic generation of inbred strains. The mouse has since been used extensively as a

model organism A model organism (often shortened to model) is a non-human species that is extensively studied to understand particular biological phenomena, with the expectation that discoveries made in the model organism will provide insight into the workin ...

and is associated with many important biological discoveries of the 20th and 21st Centuries. The

Jackson Laboratory The Jackson Laboratory (often abbreviated as JAX) is an independent, non-profit biomedical research institution which was founded by a eugenicist. It employs more than 3,000 employees in Bar Harbor, Maine; Sacramento, California; Farmington, ...

Bar Harbor, Maine Bar Harbor is a resort town on Mount Desert Island in Hancock County, Maine, United States. As of the 2020 census, its population is 5,089. During the summer and fall seasons, it is a popular tourist destination and, until a catastrophic fire ...

is currently one of the world's largest suppliers of laboratory mice, at around 3 million mice a year. The laboratory is also the world's source for more than 8,000 strains of genetically defined mice and is home of the Mouse Genome Informatics database.

Reproduction

Breeding onset occurs at about 50 days of age in both females and males, although females may have their first

estrus The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous ...

at 25–40 days. Mice are polyestrous and breed year round; ovulation is spontaneous. The duration of the

estrous cycle The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestro ...

is 4–5 days and lasts about 12 hours, occurring in the evening. Vaginal smears are useful in timed matings to determine the stage of the estrous cycle. Mating can be confirmed by the presence of a copulatory plug in the vagina up to 24 hours post-copulation. The presence of sperm on a vaginal smear is also a reliable indicator of mating. The average gestation period is 20 days. A fertile

postpartum estrus The estrous cycle (, originally ) is the set of recurring physiological changes that are induced by reproductive hormones in most mammalian therian females. Estrous cycles start after sexual maturity in females and are interrupted by anestrous p ...

occurs 14–24 hours following parturition, and simultaneous lactation and gestation prolongs gestation by 3–10 days owing to delayed implantation. The average

litter Litter consists of waste products that have been discarded incorrectly, without consent, at an unsuitable location. Litter can also be used as a verb; to litter means to drop and leave objects, often man-made, such as aluminum cans, paper cups ...

size is 10–12 during optimum production, but is highly strain-dependent. As a general rule, inbred mice tend to have longer gestation periods and smaller litters than outbred and hybrid mice. The young are called pups and weigh at birth, are hairless, and have closed eyelids and ears. Pups are weaned at 3 weeks of age when they weigh about . If the female does not mate during the postpartum estrus, she resumes cycling 2–5 days post-weaning. Newborn males are distinguished from newborn females by noting the greater

anogenital distance Anogenital distance (AGD) is the distance from the midpoint of the anus to the genitalia, the underside of the vagina, the clitoris or the scrotum. It is considered medically significant for a number of reasons, in both humans and other animals ...

and larger genital papilla in the male. This is best accomplished by lifting the tails of littermates and comparing perinea.

Genetics and strains

Mice are mammals of the

clade A clade (), also known as a monophyletic group or natural group, is a group of organisms that are monophyletic – that is, composed of a common ancestor and all its lineal descendants – on a phylogenetic tree. Rather than the English ter ...

(a group consisting of an ancestor and all its descendants)

, which means they are amongst the closest non-

primate Primates are a diverse order of mammals. They are divided into the strepsirrhines, which include the lemurs, galagos, and lorisids, and the haplorhines, which include the tarsiers and the simians ( monkeys and apes, the latter includin ...

relatives of humans along with

lagomorphs The lagomorphs are the members of the taxonomic order Lagomorpha, of which there are two living families: the Leporidae (hares and rabbits) and the Ochotonidae (pikas). The name of the order is derived from the Ancient Greek ''lagos'' (λαγ� ...

treeshrew The treeshrews (or tree shrews or banxrings) are small mammals native to the tropical forests of South and Southeast Asia. They make up the entire order Scandentia, which split into two families: the Tupaiidae (19 species, "ordinary" treeshre ...

s, and flying lemurs. Laboratory mice are the same species as the

house mouse The house mouse (''Mus musculus'') is a small mammal of the order Rodentia, characteristically having a pointed snout, large rounded ears, and a long and almost hairless tail. It is one of the most abundant species of the genus ''Mus''. Although ...

; however, they are often very different in

behaviour Behavior (American English) or behaviour (British English) is the range of actions and mannerisms made by individuals, organisms, systems or artificial entities in some environment. These systems can include other systems or organisms as wel ...

and

. There are hundreds of established inbred, outbred, and

transgenic A transgene is a gene that has been transferred naturally, or by any of a number of genetic engineering techniques, from one organism to another. The introduction of a transgene, in a process known as transgenesis, has the potential to change the ...

strains. A '' strain'', in reference to rodents, is a group in which all members are as nearly as possible genetically identical. In laboratory mice, this is accomplished through

inbreeding Inbreeding is the production of offspring from the mating or breeding of individuals or organisms that are closely related genetically. By analogy, the term is used in human reproduction, but more commonly refers to the genetic disorders a ...

. By having this type of population, it is possible to conduct experiments on the roles of genes, or conduct experiments that exclude genetic variation as a factor. In contrast, outbred populations are used when identical

genotype The genotype of an organism is its complete set of genetic material. Genotype can also be used to refer to the alleles or variants an individual carries in a particular gene or genetic location. The number of alleles an individual can have in a ...

s are unnecessary or a population with genetic variation is required, and are usually referred to as ''stocks'' rather than ''strains''. Over 400 standardized, inbred strains have been developed. Most laboratory mice are hybrids of different subspecies, most commonly of ''Mus musculus domesticus'' and ''Mus musculus musculus''. Laboratory mice can have a variety of coat colours, including agouti, black and

albino Albinism is the congenital absence of melanin in an animal or plant resulting in white hair, feathers, scales and skin and pink or blue eyes. Individuals with the condition are referred to as albino. Varied use and interpretation of the term ...

. Many (but not all) laboratory strains are inbred. The different strains are identified with specific letter-digit combinations; for example

C57BL/6 C57BL/6, often referred to as "C57 black 6", "C57" or "black 6", is a common inbred strain of laboratory mouse. It is the most widely used "genetic background" for genetically modified mice for use as models of human disease. They are the most wid ...

and

BALB/c BALB/c is an albino, laboratory-bred strain of the house mouse from which a number of common substrains are derived. Now over 200 generations from New York in 1920, BALB/c mice are distributed globally, and are among the most widely used inbred ...

. The first such inbred strains were produced in 1909 by

, who was influential in promoting the mouse as a laboratory organism. In 2011, an estimated 83% of laboratory rodents supplied in the U.S. were C57BL/6 laboratory mice.

Genome

Sequencing of the laboratory mouse

genome In the fields of molecular biology and genetics, a genome is all the genetic information of an organism. It consists of nucleotide sequences of DNA (or RNA in RNA viruses). The nuclear genome includes protein-coding genes and non-coding ...

was completed in late 2002 using the C57BL/6 strain. This was only the second mammalian genome to be sequenced after humans. The

haploid Ploidy () is the number of complete sets of chromosomes in a cell, and hence the number of possible alleles for autosomal and pseudoautosomal genes. Sets of chromosomes refer to the number of maternal and paternal chromosome copies, respective ...

genome is about three billion

base pair A base pair (bp) is a fundamental unit of double-stranded nucleic acids consisting of two nucleobases bound to each other by hydrogen bonds. They form the building blocks of the DNA double helix and contribute to the folded structure of both D ...

s long (3,000 Mb distributed over 19 autosomal chromosomes plus 1 respectively 2 sex chromosomes), therefore equal to the size of the human genome. Estimating the number of genes contained in the mouse genome is difficult, in part because the definition of a

gene In biology, the word gene (from , ; "...Wilhelm Johannsen coined the word gene to describe the Mendelian units of heredity..." meaning ''generation'' or ''birth'' or ''gender'') can have several different meanings. The Mendelian gene is a b ...

is still being debated and extended. The current count of primary coding genes in the laboratory mouse is 23,139. compared to an estimated 20,774 in humans.

Mutant and transgenic strains

Various

mutant In biology, and especially in genetics, a mutant is an organism or a new genetic character arising or resulting from an instance of mutation, which is generally an alteration of the DNA sequence of the genome or chromosome of an organism. It ...

strains of mice have been created by a number of methods. A small selection from the many available strains includes - * Mice resulting from ordinary

breeding Breeding is sexual reproduction that produces offspring, usually animals or plants. It can only occur between a male and a female animal or plant. Breeding may refer to: * Animal husbandry, through selected specimens such as dogs, horses, and r ...

and

: ** Non-obese diabetic (NOD) mice, which develop

diabetes mellitus type 1 Type 1 diabetes (T1D), formerly known as juvenile diabetes, is an autoimmune disease that originates when cells that make insulin (beta cells) are destroyed by the immune system. Insulin is a hormone required for the cells to use blood sugar for ...

. ** Murphy Roths large (MRL) mice, with unusual regenerative capacities ** Japanese waltzing mice, which walk in a circular pattern due to a mutation adversely affecting their inner ears **

Immunodeficient Immunodeficiency, also known as immunocompromisation, is a state in which the immune system's ability to fight infectious diseases and cancer is compromised or entirely absent. Most cases are acquired ("secondary") due to extrinsic factors that a ...

nude mice A nude mouse is a laboratory mouse from a strain with a genetic mutation that causes a deteriorated or absent thymus, resulting in an inhibited immune system due to a greatly reduced number of T cells. The phenotype (main outward appearance) of ...

, lacking hair and a

thymus The thymus is a specialized primary lymphoid organ of the immune system. Within the thymus, thymus cell lymphocytes or '' T cells'' mature. T cells are critical to the adaptive immune system, where the body adapts to specific foreign invaders ...

: these mice do not produce

T lymphocyte A T cell is a type of lymphocyte. T cells are one of the important white blood cells of the immune system and play a central role in the adaptive immune response. T cells can be distinguished from other lymphocytes by the presence of a T-cell re ...

s; therefore, they do not mount cellular immune responses. They are used for research in

immunology Immunology is a branch of medicineImmunology for Medical Students, Roderick Nairn, Matthew Helbert, Mosby, 2007 and biology that covers the medical study of immune systems in humans, animals, plants and sapient species. In such we can see ther ...

and transplantation. **

Severe combined immunodeficiency Severe combined immunodeficiency (SCID), also known as Swiss-type agammaglobulinemia, is a rare genetic disorder characterized by the disturbed development of functional T cells and B cells caused by numerous genetic mutations that result in diffe ...

(SCID) mice, with an almost completely defective

immune system The immune system is a network of biological processes that protects an organism from diseases. It detects and responds to a wide variety of pathogens, from viruses to parasitic worms, as well as cancer cells and objects such as wood splinte ...

** FVB mice, whose large litter sizes and large oocyte pronuclei expedite use in genetic research ** , which fail to recruit nutrient copper into milk causing pup death. It is caused by an

autosomal An autosome is any chromosome that is not a sex chromosome. The members of an autosome pair in a diploid cell have the same morphology, unlike those in allosomal (sex chromosome) pairs, which may have different structures. The DNA in autosom ...

recessive In genetics, dominance is the phenomenon of one variant ( allele) of a gene on a chromosome masking or overriding the effect of a different variant of the same gene on the other copy of the chromosome. The first variant is termed dominant an ...

mutation '' tx'' which arose in an inbred. Theophilos et al. 1996 found this to be genetic and localized to chromosome 8, near the

centromere The centromere links a pair of sister chromatids together during cell division. This constricted region of chromosome connects the sister chromatids, creating a short arm (p) and a long arm (q) on the chromatids. During mitosis, spindle fibers ...

. * Transgenic mice, with foreign genes inserted into their genome: ** Abnormally large mice, with an inserted rat

growth hormone Growth hormone (GH) or somatotropin, also known as human growth hormone (hGH or HGH) in its human form, is a peptide hormone that stimulates growth, cell reproduction, and cell regeneration in humans and other animals. It is thus important in ...

gene ** Oncomice, with an activated

oncogene An oncogene is a gene that has the potential to cause cancer. In tumor cells, these genes are often mutated, or expressed at high levels.

, so as to significantly increase the incidence of

cancer Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...

Doogie mice In neuroscience, long-term potentiation (LTP) is a persistent strengthening of synapses based on recent patterns of activity. These are patterns of synaptic activity that produce a long-lasting increase in signal transmission between two neurons ...

, with enhanced

NMDA receptor The ''N''-methyl-D-aspartate receptor (also known as the NMDA receptor or NMDAR), is a glutamate receptor and ion channel found in neurons. The NMDA receptor is one of three types of ionotropic glutamate receptors, the other two being AMPA and ...

function, resulting in improved memory and learning *

Knockout mice A knockout mouse, or knock-out mouse, is a genetically modified mouse (''Mus musculus'') in which researchers have inactivated, or "knocked out", an existing gene by replacing it or disrupting it with an artificial piece of DNA. They are importan ...

, where a specific gene was made inoperable by a technique known as

gene knockout A gene knockout (abbreviation: KO) is a genetic technique in which one of an organism's genes is made inoperative ("knocked out" of the organism). However, KO can also refer to the gene that is knocked out or the organism that carries the gene kno ...

: the purpose is to study the function of the gene's product or to simulate a human disease ** Fat mice, prone to obesity due to a carboxypeptidase E deficiency ** Strong muscular mice, with a disabled

myostatin Myostatin (also known as growth differentiation factor 8, abbreviated GDF8) is a protein that in humans is encoded by the ''MSTN'' gene. Myostatin is a myokine that is produced and released by myocytes and acts on muscle cells to inhibit muscle ...

gene, nicknamed "mighty mice". Since 1998, it has been possible to clone mice from cells derived from adult animals.

Appearance and behaviour

Laboratory mice have retained many of the physical and behavioural characteristics of house mice; however, due to many generations of artificial selection, some of these characteristics now vary markedly. Due to the large number of strains of laboratory mice, it is impractical to comprehensively describe the appearance and behaviour of all of them; however, they are described below for two of the most commonly used strains.

C57BL/6

C57BL/6 mice have a dark brown, nearly black coat. They are more sensitive to noise and odours and are more likely to bite than the more docile laboratory strains such as

. Group-housed C57BL/6 mice (and other strains) display barbering behaviour, in which the dominant mouse in a cage selectively removes hair from its subordinate cage mates. Mice that have been barbered extensively can have large bald patches on their bodies, commonly around the head, snout, and shoulders, although barbering may appear anywhere on the body. Both hair and vibrissae may be removed. Barbering is more frequently seen in female mice; male mice are more likely to display dominance through fighting. C57BL/6 has several unusual characteristics which make it useful for some research studies but inappropriate for others: It is unusually sensitive to pain and to cold, and

analgesic An analgesic drug, also called simply an analgesic (American English), analgaesic (British English), pain reliever, or painkiller, is any member of the group of drugs used to achieve relief from pain (that is, analgesia or pain management). It ...

medications are less effective in this strain. Unlike most laboratory mouse strains, the C57BL/6 drinks

alcoholic beverage An alcoholic beverage (also called an alcoholic drink, adult beverage, or a drink) is a drink that contains ethanol, a type of Alcohol (chemistry), alcohol that acts Alcohol (drug), as a drug and is produced by Ethanol fermentation, fermentat ...

s voluntarily. It is more susceptible than average to morphine addiction,

atherosclerosis Atherosclerosis is a pattern of the disease arteriosclerosis in which the wall of the artery develops abnormalities, called lesions. These lesions may lead to narrowing due to the buildup of atheromatous plaque. At onset there are usually no s ...

, and age-related

hearing loss Hearing loss is a partial or total inability to hear. Hearing loss may be present at birth or acquired at any time afterwards. Hearing loss may occur in one or both ears. In children, hearing problems can affect the ability to acquire spoken l ...

. When compared directly to BALB/c mice, C57BL/6 mice also express both a robust response to social rewards and empathy.

BALB/c

BALB/c is an

laboratory-bred strain from which a number of common substrains are derived. With over 200 generations bred since 1920, BALB/c mice are distributed globally and are among the most widely used inbred strains used in animal experimentation. BALB/c are noted for displaying high levels of anxiety and for being relatively resistant to diet-induced

, making them a useful model for cardiovascular research. Male BALB/c mice are aggressive and will fight other males if housed together. However, the BALB/Lac substrain is much more docile. Most BALB/c mice substrains have a long reproductive life-span. There are noted differences between different BALB/c substrains, though these are thought to be due to

mutation In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, m ...

rather than genetic contamination. The BALB/cWt is unusual in that 3% of progeny display true

hermaphroditism In reproductive biology, a hermaphrodite () is an organism that has both kinds of reproductive organs and can produce both gametes associated with male and female sexes. Many taxonomic groups of animals (mostly invertebrates) do not have s ...

Husbandry

Handling

Traditionally, laboratory mice have been picked up by the base of the tail. However, recent research has shown that this type of handling increases anxiety and aversive behaviour. Instead, handling mice using a tunnel or cupped hands is advocated. In behavioural tests, tail-handled mice show less willingness to explore and to investigate test stimuli, as opposed to tunnel-handled mice which readily explore and show robust responses to test stimuli.

Nutrition

In nature, mice are usually

herbivore A herbivore is an animal anatomically and physiologically adapted to eating plant material, for example foliage or marine algae, for the main component of its diet. As a result of their plant diet, herbivorous animals typically have mouthpar ...

s, consuming a wide range of fruit or grain.Mouse: Northwestern University Ecodome Information Page
/ref> However, in laboratory studies it is usually necessary to avoid biological variation and to achieve this, laboratory mice are almost always fed only commercial pelleted mouse feed. Food intake is approximately per of body weight per day; water intake is approximately per 100 g of body weight per day.

Injection procedures

Routes of administration A route of administration in pharmacology and toxicology is the way by which a medication, drug, fluid, poison, or other substance is taken into the body. Routes of administration are generally classified by the location at which the substance i ...

of injections in laboratory mice are mainly subcutaneous,

intraperitoneal The peritoneum is the serous membrane forming the lining of the abdominal cavity or coelom in amniotes and some invertebrates, such as annelids. It covers most of the intra-abdominal (or coelomic) organs, and is composed of a layer of mesothel ...

and

intravenous Intravenous therapy (abbreviated as IV therapy) is a medical technique that administers fluids, medications and nutrients directly into a person's vein. The intravenous route of administration is commonly used for rehydration or to provide nutrie ...

Intramuscular administration Intramuscular injection, often abbreviated IM, is the injection of a substance into a muscle. In medicine, it is one of several methods for parenteral administration of medications. Intramuscular injection may be preferred because muscles have ...

is not recommended due to small muscle mass. Intracerebral administration is also possible. Each route has a recommended injection site, approximate needle gauge and recommended maximum injected volume at a single time at one site, as given in the table below: To facilitate intravenous injection into the tail, laboratory mice can be carefully warmed under heat lamps to vasodilate the vessels.

Anaesthesia

A common regimen for

general anesthesia General anaesthesia (UK) or general anesthesia (US) is a medically induced loss of consciousness that renders the patient unarousable even with painful stimuli. This effect is achieved by administering either intravenous or inhalational general ...

for the house mouse is

ketamine Ketamine is a dissociative anesthetic used medically for induction and maintenance of anesthesia. It is also used as a recreational drug. It is one of the safest anesthetics, as, in contrast with opiates, ether, and propofol, it suppress ...

(in the dose of 100 mg per kg body weight) plus

xylazine Xylazine is a pharmaceutical drug used for sedation, anesthesia, muscle relaxation, and analgesia in animals such as horses, cattle, and other non-human mammals. Veterinarians also use xylazine as an emetic, especially in cats. It is an anal ...

(in the dose of 5–10 mg per kg), injected by the intraperitoneal route.Guidelines for Systemic Anesthetics (Mouse)
From Duke University and Medical Center – Animal Care & Use Program. Retrieved April 2011 It has a duration of effect of about 30 minutes.

Euthanasia

Approved procedures for

euthanasia Euthanasia (from el, εὐθανασία 'good death': εὖ, ''eu'' 'well, good' + θάνατος, ''thanatos'' 'death') is the practice of intentionally ending life to eliminate pain and suffering. Different countries have different eut ...

of laboratory mice include compressed gas, injectable

barbiturate Barbiturates are a class of depressant drugs that are chemically derived from barbituric acid. They are effective when used medically as anxiolytics, hypnotics, and anticonvulsants, but have physical and psychological addiction potential a ...

anesthetics An anesthetic (American English) or anaesthetic (British English; see spelling differences) is a drug used to induce anesthesia ⁠— ⁠in other words, to result in a temporary loss of sensation or awareness. They may be divided into two ...

, inhalable anesthetics, such as Halothane, and physical methods, such as cervical dislocation and decapitation. In 2013, the

American Veterinary Medical Association The American Veterinary Medical Association (AVMA), founded in 1863, is a not-for-profit association representing more than 99,500 veterinarians in the US. The AVMA provides information resources, continuing education opportunities, publicati ...

issued new guidelines for induction, stating that a flow rate of 10% to 30% volume/min is optimal for euthanasing laboratory mice.2013 AVMA Guidelines for the Euthanasia of Animals
/ref>

Pathogen susceptibility

A recent study detected a murine astrovirus in laboratory mice held at more than half of the US and Japanese institutes investigated. Murine astrovirus was found in nine mice strains, including NSG, NOD-SCID, NSG-3GS, C57BL6-''Timp-3^−/−'', uPA-NOG, B6J, ICR, Bash2, and

BALB/C BALB/c is an albino, laboratory-bred strain of the house mouse from which a number of common substrains are derived. Now over 200 generations from New York in 1920, BALB/c mice are distributed globally, and are among the most widely used inbred ...

, with various degrees of prevalence. The pathogenicity of the murine astrovirus was not known.

Legislation in research

United Kingdom

In the U.K., as with all other vertebrates and some invertebrates, any scientific procedure which is likely to cause "pain, suffering, distress or lasting harm" is regulated by the Home Office under the

Animals (Scientific Procedures) Act 1986 The Animals (Scientific Procedures) Act 1986, sometimes referred to as ASPA, is an Act of Parliament, Act of the Parliament of the United Kingdom (1986 c. 14) passed in 1986, which regulates the use of animals used for research in the UK. The Act ...

. U.K. regulations are considered amongst the most comprehensive and rigorous in the world. Detailed data on the use of laboratory mice (and other species) in research in the U.K. are published each year. In the U.K. in 2013, there were a total of 3,077,115 regulated procedures on mice in scientific procedure establishments, licensed under the Act.

United States

In the U.S., laboratory mice are not regulated under the Animal Welfare Act administered by the

USDA The United States Department of Agriculture (USDA) is the federal executive department responsible for developing and executing federal laws related to farming, forestry, rural economic development, and food. It aims to meet the needs of comme ...

APHIS ''Aphis'' is a genus of insects in the family Aphididae containing at least 600 species of aphids. It includes many notorious agricultural pests, such as the soybean aphid '' Aphis glycines''. Many species of ''Aphis'', such as '' A. coreopsidis ...

. However, the

Public Health Service Act The Public Health Service Act is a United States federal law enacted in 1944. The full act is codified in Title 42 of the United States Code (The Public Health and Welfare), Chapter 6A ( Public Health Service). Contents The act clearly establ ...

(PHS) as administered by the

National Institutes of Health The National Institutes of Health, commonly referred to as NIH (with each letter pronounced individually), is the primary agency of the United States government responsible for biomedical and public health research. It was founded in the lat ...

does offer a standard for their care and use. Compliance with the PHS is required for a research project to receive federal funding. PHS policy is administered by the Office of Laboratory Animal Welfare. Many academic research institutes seek accreditation voluntarily, often through the

Association for Assessment and Accreditation of Laboratory Animal Care The Association for Assessment and Accreditation of Laboratory Animal Care International, or AAALAC, is a private, nonprofit organization that promotes the humane treatment of animals in science through voluntary accreditation and assessment progr ...

, which maintains the standards of care found within ''The Guide for the Care and Use of Laboratory Animals'' and the PHS policy. This accreditation is, however, not a prerequisite for federal funding, unlike the actual compliance.

Limitations

While mice are by far the most widely used animals in biomedical research, recent studies have highlighted their limitations. For example, the utility of rodents in testing for

sepsis Sepsis, formerly known as septicemia (septicaemia in British English) or blood poisoning, is a life-threatening condition that arises when the body's response to infection causes injury to its own tissues and organs. This initial stage is follo ...

burn A burn is an injury to skin, or other tissues, caused by heat, cold, electricity, chemicals, friction, or ultraviolet radiation (like sunburn). Most burns are due to heat from hot liquids (called scalding), solids, or fire. Burns occur ma ...

inflammation Inflammation (from la, inflammatio) is part of the complex biological response of body tissues to harmful stimuli, such as pathogens, damaged cells, or irritants, and is a protective response involving immune cells, blood vessels, and molec ...

stroke A stroke is a disease, medical condition in which poor cerebral circulation, blood flow to the brain causes cell death. There are two main types of stroke: brain ischemia, ischemic, due to lack of blood flow, and intracranial hemorrhage, hemorr ...

ALS Amyotrophic lateral sclerosis (ALS), also known as motor neuron disease (MND) or Lou Gehrig's disease, is a neurodegenerative disease that results in the progressive loss of motor neurons that control voluntary muscles. ALS is the most comm ...

Alzheimer's disease Alzheimer's disease (AD) is a neurodegenerative disease that usually starts slowly and progressively worsens. It is the cause of 60–70% of cases of dementia. The most common early symptom is difficulty in remembering recent events. As ...

diabetes Diabetes, also known as diabetes mellitus, is a group of metabolic disorders characterized by a high blood sugar level ( hyperglycemia) over a prolonged period of time. Symptoms often include frequent urination, increased thirst and increased ...

multiple sclerosis Multiple (cerebral) sclerosis (MS), also known as encephalomyelitis disseminata or disseminated sclerosis, is the most common demyelinating disease, in which the insulating covers of nerve cells in the brain and spinal cord are damaged. This ...

Parkinson's disease Parkinson's disease (PD), or simply Parkinson's, is a long-term degenerative disorder of the central nervous system that mainly affects the motor system. The symptoms usually emerge slowly, and as the disease worsens, non-motor symptoms beco ...

, and other illnesses has been called into question by a number of researchers. Regarding experiments on mice, some researchers have complained that "years and billions of dollars have been wasted following false leads" as a result of a preoccupation with the use of these animals in studies. Mice differ from humans in several immune properties: mice are more resistant to some

toxins A toxin is a naturally occurring organic poison produced by metabolic activities of living cells or organisms. Toxins occur especially as a protein or conjugated protein. The term toxin was first used by organic chemist Ludwig Brieger (1849� ...

than humans; have a lower total

neutrophil Neutrophils (also known as neutrocytes or heterophils) are the most abundant type of granulocytes and make up 40% to 70% of all white blood cells in humans. They form an essential part of the innate immune system, with their functions varying ...

fraction in the

blood Blood is a body fluid in the circulatory system of humans and other vertebrates that delivers necessary substances such as nutrients and oxygen to the cells, and transports metabolic waste products away from those same cells. Blood in the cir ...

, a lower

enzymatic capacity, lower activity of the

complement system The complement system, also known as complement cascade, is a part of the immune system that enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and ...

, and a different set of

pentraxins Pentraxins (PTX), also known as pentaxins, are an evolutionary conserved family of proteins characterised by containing a pentraxin protein domain. Proteins of the pentraxin family are involved in acute immunological responses. They are a clas ...

involved in the inflammatory process; and lack genes for important components of the immune system, such as IL-8, IL-37,

TLR10 Toll-like receptor 10 is a protein that in humans is encoded by the ''TLR10'' gene. TLR10 has also been designated as CD290 ( cluster of differentiation 290). TLR10 has not been extensively studied because it is a pseudogene in mice, though all ot ...

, ICAM-3, etc. Laboratory mice reared in specific-pathogen-free (SPF) conditions usually have a rather immature immune system with a deficit of memory T cells. These mice may have limited diversity of the

microbiota Microbiota are the range of microorganisms that may be commensal, symbiotic, or pathogenic found in and on all multicellular organisms, including plants. Microbiota include bacteria, archaea, protists, fungi, and viruses, and have been found ...

, which directly affects the immune system and the development of pathological conditions. Moreover, persistent virus infections (for example, herpesviruses) are activated in humans, but not in SPF mice with septic complications and may change the resistance to bacterial

coinfections Coinfection is the simultaneous infection of a host by multiple pathogen species. In virology, coinfection includes simultaneous infection of a single cell by two or more virus particles. An example is the coinfection of liver cells with hepatiti ...

. "Dirty" mice are possibly better suitable for mimicking human pathologies. In addition, inbred mouse strains are used in the overwhelming majority of studies, while the

human population Humans (''Homo sapiens'') are the most abundant and widespread species of primate, characterized by bipedalism and exceptional cognitive skills due to a large and complex brain. This has enabled the development of advanced tools, culture, ...

is heterogeneous, pointing to the importance of studies in interstrain hybrid, outbred, and nonlinear mice. An article in '' The Scientist'' notes, "The difficulties associated with using animal models for human disease result from the metabolic, anatomic, and cellular differences between humans and other creatures, but the problems go even deeper than that" including issues with the design and execution of the tests themselves. In addition, the caging of laboratory animals may render them irrelevant models of human health because these animals lack day-to-day variations in experiences, agency, and challenges that they can overcome. The impoverished environments inside small mouse cages can have deleterious influences on biomedical results, especially with respect to studies of mental health and of systems that depend upon healthy psychological states. For example, researchers have found that many mice in laboratories are obese from excess food and minimal exercise, which alters their physiology and drug metabolism. Many laboratory animals, including mice, are chronically stressed, which can also negatively affect research outcomes and the ability to accurately extrapolate findings to humans. Researchers have also noted that many studies involving mice are poorly designed, leading to questionable findings. Some studies suggests that inadequate published data in animal testing may result in irreproducible research, with missing details about how experiments are done are omitted from published papers or differences in testing that may introduce bias. Examples of hidden bias include a 2014 study from

McGill University McGill University (french: link=no, Université McGill) is an English-language public research university located in Montreal, Quebec, Canada. Founded in 1821 by royal charter granted by King George IV,Frost, Stanley Brice. ''McGill Univer ...

which suggests that mice handled by men rather than women showed higher stress levels. Another study in 2016 suggested that gut

microbiome A microbiome () is the community of microorganisms that can usually be found living together in any given habitat. It was defined more precisely in 1988 by Whipps ''et al.'' as "a characteristic microbial community occupying a reasonably wel ...

s in mice may have an impact upon scientific research.

Market size

The worldwide market for gene-altered mice is predicted to grow to $1.59 billion by 2022, growing at a rate of 7.5 percent per year.

References

External links

Taxonomy * http://www.findmice.org/ Genetics
Ensembl Mus musculus genome browser
from the

Ensembl Ensembl genome database project is a scientific project at the European Bioinformatics Institute, which provides a centralized resource for geneticists, molecular biologists and other researchers studying the genomes of our own species and other v ...

Project
Vega Mus musculus genome browser
includes NOD mouse sequence and annotation Media
Pictures, movies and applets showing the anatomy of ''Mus musculus''
from www.digimorph.org

Study of male mouse "song" with mouse song recording (MP3), by Washington University Medical School *
Arkive
Photographs.Short text.
High-Resolution Brain Maps and Brain Atlases of ''Mus musculus''
Further reading

from the Louisiana Veterinary Medical Association
Nature Mouse Special 2002

by David G. Besselsen {{Authority control Cosmopolitan mammals House mouse Old World rats and mice Cruelty to animals Animal models