Allo in Greek means “other”. Allogrooming is a behavior which refers to one mouse grooming another mouse. Allogrooming has wide applications and is both a grooming behavior and an affiliative behavior. Sometimes, allogrooming can be referred to as “social grooming” since it is an affiliative behavior which occurs during social interactions.
Allogrooming, sometimes also written as ‘allo-grooming’ with a hyphen, is also classified as a maintenance behavior. Allogrooming means that one mouse is grooming or cleaning another mouse. In some instances, allogrooming can also be an investigative behavior wherein the mouse is getting to know and familiarize itself with the other mouse.
In allogrooming, the actor mouse will stabilize itself while grooming the recipient mouse by using its forepaws. When allogrooming, the actor mouse will lick the recipient mouse’s fur. It is also typical for the actor mouse to utilize its teeth to carefully nibble and clean the recipient mouse’s hair. The teeth are placed close to the recipient mouse’s body (at the base of the hair) and then the teeth are moved or pulled outwards, performing a combing-like motion.
In some cases, barbering (the plucking of a mouse’s whiskers) may be observed during bouts of allogrooming.
Behavioral Variants of Allogrooming
In general, allogrooming is a casual and positive behavior. However, vigorous instances of allogrooming do exist. A researcher can distinguish between cases of vigorous and normal allogrooming by observing the behavior of the recipient mouse. When allogrooming is vigorous, the recipient mouse will be still and very rigid. During casual or normal allogrooming, the recipient mouse is relaxed and doing other things in the cage, such as shuffling the cage material. The relationship between aggression and vigorous allogrooming is a current research topic that is receiving attention from researchers interested in behavioral studies.
Function of Allogrooming
Allogrooming is a social interaction between two mice that is frequently observed when mice are active and awake. Since allogrooming is a key social and grooming behavior, it has many important functions which serve to benefit the mouse’s health and chances of survival. The following are considered to be the functions of allogrooming:
- To attend to the offspring’s hygiene. Mothers that allogroom their pups are essentially providing a layer of defense for their offspring. Since saliva has antibacterial properties, mothers who allogroom their pups provide an adaptive value which increases survival by protecting their pups against pathogens. Since pups do not have a fully developed immune system, a mother’s saliva (which contains antimicrobial properties) acts as a shield of immunity.
- To control for louse populations around the head. Mice cannot groom the backs of their necks, so this area may be susceptible to lice if not cleaned by other mice via allogrooming. Therefore, allogrooming helps inhibit the rise of louse populations within a mouse colony.
- To promote group cohesiveness. Through allogrooming, a group’s cohesiveness is reinforced. When mice are allogrooming one another, a sense of affiliation is instilled and the mice become more and more familiar with one another. This is important because unfamiliarity (such as perceiving other mice as strangers or intruders) is unhealthy since it can persistently raise stress levels which in turn will affect a mouse’s well-being and ability to survive. Group cohesiveness, on the other hand, provides the mice a good environment to live in.
- To strengthen existing bonds. By allogrooming, existing bonds are strengthened. This is somewhat related to the previous point but is more specific. While group cohesiveness is generally promoting the well-being of the entire group, strengthening existing bonds can refer to the relationship between specific mice belonging to the group.
- To identify potential sexual partners. When male and female mice are allogrooming, the interaction can serve as a possible future sexual partnership between the two mice. This is evolutionarily useful because, in the first instance, group cohesion is strengthened and if the mice mate, then the herd expands.
Application of the Behavior
Allogrooming can be observed in a variety of contexts, such as:
- Within the presence of another mouse. Since allogrooming is essentially a social interaction between mice, it will probably be observed whenever two mice are in near vicinity to each other and are friendly towards each other (instead of agonistic).
- During huddling. When mice are sharing their living space with other mice and are huddling together (lying in close proximity to one another) bouts of allogrooming are likely to be observed.
- During play soliciting. Allogrooming may occur naturally as a result of play soliciting behaviors. For example, if a mouse pushes itself (with its snout or whole body) under its partner’s body, allogrooming may be elicited and performed by the partner.
- During maternal grooming. When a mother is tending to her young, instances of allogrooming are bound to occur.
Since allogrooming is a behavior commonly observed in mice during their times of interaction, several research techniques have been developed in order to study it, including:
- Behavioral studies. Allogrooming can be observed during behavioral studies. Behavioral studies use apparatuses and mazes in order to elicit or create an opportune environment for a behavior such as allogrooming to occur.
- Pharmaceutical studies. Through pharmaceutical studies, where a certain drug, supplement, or chemical agent is administered to mice, allogrooming can be studied by comparing how mice behavior varies according to the experimental treatment and dosage.
- Genetic studies. Allogrooming is also targetable through genetic studies. By altering certain genes, observable changes occur in behavior.
Behavioral Tests for Assessing Allogrooming
In order to measure allogrooming and study it, scientists will usually introduce two mice to each other by placing them in close proximity. The following behavioral tests can be used to study allogrooming:
- The Social Interaction Test. In this test, one mouse is an inhabitant and a new, unknown mouse is introduced. Based on the interaction between the two mice, social behaviors like allogrooming are observed, measured, and quantified. Allogrooming is measured as a social interaction because it requires one mouse to groom or clean another mouse.
- The Visible Burrow System. This test uses a cage designed to mimic mice’s natural environment. It’s arrangement has an open area linked side panels which resemble runnels, thus creating an environment optimal for a wide range of behaviors to occur. Before an experiment begins, mice are individually labeled or marked with hair dye and introduced to the setting at the beginning of their dark cycle. A video recording system is used to capture the mice’s behaviors over a long period of time. Some experiments which use the visible burrow system can last for weeks.
- Video Analysis. Video analysis is used in studying the different types of grooming behaviors. By capturing video footage of the mouse, specific details can be focused on which otherwise may have gone unnoticed during real-time observation. Video analysis offers the researcher control over the video, thus enabling detailed behavioral recording.
Defining Allogrooming in Behavioral Studies
Allogrooming is a frequently measured behavior in animal research. Typically, research papers will specifically outline what they consider to be “allogrooming,” in order to define the behavior’s parameters before measuring it. A study may define allogrooming as all the lickings which one mouse will give to another (thus, measuring all of the expressions of groom and head groom in total) while excluding instances of aggressive grooming.
Pharmaceutical Studies on Allogrooming
Pharmaceutical studies enable scientists to study allogrooming and how it is affected as a result of administration of certain drugs or substances.
Sodium Valproate Decreases Allogrooming
A commonly used mouse model of autism in behavioral research makes use of sodium valproate (VPA) injections. Children that have had in utero exposure to VPA develop fetal valproate syndrome which is a syndrome that shares symptoms with autism, including: language and communication deficits, stereotypic behavior, delays in development, and hyperexcitability. In fact, just a single dose of 400 mg/kg VPA on postnatal day 14 (which is equivalent to the the human third trimester) is enough to induce an autism model in BALB/c mice. Since autism is associated with social deficits, affiliative behaviors are affected and in mice that’s observed as a reduction in allogrooming behaviors. Mice induced with autism via VPA injections have decreased allogrooming and anogenital sniffing, both of which are affiliative forms of interaction.
XAV939 Injection Decreases Allogrooming in Mice
XAV939 is a small compound that can be administered to developing embryonic mice via in utero injections. XAV939 affects mouse development, including the way that the neocortex forms, which, in turn, later affects observable behaviors such as self-grooming. Mice that receive XAV939 injections in utero have increased levels of the Axin protein in radial glia cells. Such high levels of Axin affect cellular processes and ultimately lead to heightened intermediate progenitors and thus excess levels of pyramidal neurons within the neocortex. Therefore, overproduction of pyramidal neurons in the neocortex as caused by XAV939 injections leads to a neocortical malfunction (due to malformation) which further affects observable behavior.
Experimental mice injected with XAV939 display behavioral deficits resembling those found in autism, such as decreased social behaviors and increased repetitive behaviors. Mice receiving this injection spend significantly less time allogrooming and more time self-grooming. The low instances of allogrooming due to the XAV939 injection demonstrates how malformation in high-order brain regions such as the neocortex can cause an imbalance in excitatory and inhibitory brain systems.
Oxytocin Antagonist May Increase Vigorous Allogrooming
Oxytocin is a neuropeptide that is mostly produced by the supraoptic and paraventricular nuclei found in the hypothalamus. These neurons project to many different areas of the brain and secrete oxytocin. Research using mice has established that higher levels of oxytocin (achieved as a result of oxytocin administration) elicits more self-grooming behaviors in mice, but it is also possible that blocking or antagonizing central oxytocin pathways may lead to an increase in vigorous allogrooming, according to a 2015 behavioral study published by Arakawa et al. in the academic research journal Physiology and Behavior.
Allogrooming Decreased by L-DOPA after Social Defeat Experience
L-DOPA is an amino acid that is naturally produced in the body,a known precursor to catecholamine neurotransmitter such as epinephrine (adrenaline), norepinephrine, and dopamine. L-DOPA can also be manufactured and sold as a drug in controlled dosages and used for medical or experimental purposes.
In animal research, L-DOPA has been demonstrated to affect allogrooming behavior. Mice that have experienced social defeat and have been given L-DOPA will show decreased levels of allogrooming. On the other hand, mice that do not experience social defeat but are given L-DOPA will have the same levels of allogrooming behavior as control mice, thus remaining unaffected. This interaction demonstrates the complex interrelationships between drugs and behaviors and how one environment or setting can decrease allogrooming.
Mouse Strains Exhibiting Allogrooming
BTBR Mice Have Low Allogrooming Levels
BTBR T+tf/J (BTBR) mice demonstrate low levels of allogrooming which is in line with their general low-sociability behavioral phenotype. BTBR mice are an inbred mouse strain which are commonly used in behavioral studies for the purposes of modeling the diagnostic symptoms associated with autism. While BTBR mice have low levels of allogrooming and other social interaction behaviors such as social approach, they do not exhibit deficits in motor abilities nor high levels of anxiety-like behavior, meaning that their deficits are mainly specific to social disturbances.
R1117X Mutant Mice
The SHANK3 gene is implicated in having many different functions in the brain due to its structure complexity and thus is an important gene for optimum performance. SHANK3 abnormalities have also been identified in patients with autism spectrum disorder. Additionally, a mutation in SHANK3 where in an arginine is changed to a stop-codon (R1117X) has been associated with schizophrenic patients. This demonstrates the phenomenon of how mutations in the same gene can be associated with different disorders. Mice with a R1117X mutation in the SHANK3 gene demonstrate increased levels of allogrooming behavior and have synaptic defects in the brain’s prefrontal cortex.
NF-κB p50-Deficient Mice
The nuclear factor (NF)-κB is a transcription factor that is crucial for cell survival and for regulating inflammatory immune responses. It has been demonstrated to be active in neurons. Mice with NF-κB, lacking the subunit p50, perform poorly in cognitive tasks and also show less instances of allogrooming when compared to wild-type mice.
C57B1/6J, BALB/CJ, and NIH Subordinate Mice Allogroom
Across all three strains, allogrooming is much more frequent amongst subordinate mice (subordinate to subordinate) than any other combination (dominant to subordinate or subordinate to dominant). Furthermore, BALB/CJ and NIH mice have more allogrooming behaviors (performed between same-strain mice) than the C57B1/6J mice do.
In genetics research, the homeobox transcription factory (EN2) has been shown in human studies to be correlated with autism spectrum disorder (ASD) susceptibility. So, researchers are using EN2 -/- mice which lack EN2, in order to model ASD. These mice are genetically modified to lack EN2 and subsequently show lower instances of allogrooming than normal, wild-type mice.
Autism Spectrum Disorders
Since allogrooming is essentially a social behavior, and it is defined as the grooming interaction between two mice, when autism spectrum disorders (ASDs) are induced in mice, they usually affect social behaviors like allogrooming. For example, one mouse model of ASDs where in mice are manipulated into having an overproduction of upper-layer neurons via XAV939 injections will have increased levels of self-grooming but decreased allogrooming. Also, genetic models of ASDs such as BTBR mice have lowered levels of allogrooming than control mice.
Allogrooming in Disease Models
Genetic ASD Mouse Models:
In order to model ASD, genetic mouse models can be used. The following mouse strains model ASD and have altered allogrooming patterns compared to wild-type or comparator mice.
EN2 -/- Mice Model ASD and Have Altered Allorooming Behaviors
In genetics research, the homeobox transcription factory (EN2) has been shown in human studies to be correlated with autism spectrum disorder (ASD) susceptibility. So, researchers are using EN2 -/- mice which lack EN2, in order to model ASD. One study showed that EN2 -/- mice had less instances of allogrooming when compared with the control group. Since allogrooming is a social behavior, this finding was interpreted to parallel the social deficits observed in humans with ASD. On a side note, the researchers also found that the ASD mice had difficulty in memory tasks, as shown from the data acquired by means of using the Morris Water Maze and the increased latency times in each test trial, possibly implying a relationship between grooming, sociability, and memory abilities.
BTBR Mice Model ASD and Have Altered Allogrooming Behaviors
BTBR mice demonstrate low levels of allogrooming which is in line with their general low-sociability behavioral phenotype. BTBR mice are an inbred mouse strain which are commonly used in behavioral studies for the purposes of modeling the diagnostic symptoms associated with autism.
R1117X Mutant Mice Model ASD and Have Altered Allogrooming Behaviors
The SHANK3 gene is implicated in having many different functions in the brain due to its structure complexity and thus is an important gene for optimum performance. SHANK3 abnormalities have also been identified in patients with autism spectrum disorder.
Chemically Induced ASD Mouse Models:
XAV939 Injections Lead to ASD Mouse Model Induction
As mentioned previously, under the ‘Pharmaceutical’ section, XAV939 injections will have increased levels of self-grooming but decreased allogrooming.
Valproic Acid Leads to ASD Mouse Model Induction
The mechanisms and relationship between valproic acid and ASD induction was explained under the ‘Pharmaceutical’ section. But, valproic acid is another method for inducing ASD in mice.
- When one mouse cleans or grooms another mouse, it is known as allogrooming.
- Allogrooming is an affiliative behavior, creating bonds or reinforcing social structures.
- Allogrooming can be observed through the social interaction test or through group-housing conditions.
- When allogrooming is vigorous, the recipient mouse will be still and very rigid.
- The following are the functions of allogrooming behavior in mice: to attend to the offspring’s hygiene, to control for louse populations around the head, to promote group cohesiveness, to strengthen existing bonds, and to identify potential sexual partners.
- Allogrooming can be observed under the following conditions: within the presence of another mouse, during huddling, during play soliciting, during and maternal grooming.
- Allogrooming can be studied using behavioral studies, pharmaceutical studies, genetic studies, or some combination of them.
- These behavioral tests are used in order to assess allogrooming in mice: the social interaction test, the visible burrow system, and video analysis.
- Pharmaceutical studies have established that:
- Sodium valproate decreases allogrooming
- XAV939 injections decrease allogrooming
- Oxytocin antagonist may increase vigorous allogrooming
- Allogrooming can be decreased by L-DOPA after the mouse has also experienced social defeat
- Allogrooming will vary from mouse strain to mouse strain. For example:
- BTBR mice have low allogrooming levels
- R1117X mutant mice have increased levels of allogrooming behavior
- NF-κB p50-deficient mice have fewer instances of allogrooming than wild-type mice
- C57B1/6J, BALB/CJ, and NIH subordinate mice have a tendency to allogroom due to hierarchical structures
- EN2-/- mice have lower allogrooming instances.
- Disease models are bound to show different allogrooming behaviors than controls, especially disease models like EN2 -/- mice that reflect diseases like ASD which is associated with social abnormalities.
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