Active BehaviorMaintenance BehaviorMouse Ethogram

Nesting Behaviors

By August 1, 2019 August 3rd, 2019 No Comments

Definition

Nesting behaviors refer to a mouse creating or building a nest for itself or its offspring. 

Overview/Description 

Nesting behaviors occur when a mouse is building its shelter. There are two types of nesting-behaviors known to date: maternal nesting and non-maternal (or thermoregulatory) nesting

In the case of non-maternal nesting, a mouse builds a nest for general use. Non-maternal nesting (referred to as ‘nesting’ in this article) is crucial for survival and is a core mouse behavior. By building a nest, a mouse accomplishes many things which ensure its survival including shelter from the environment which includes predators and possible adverse weather conditions. 

Nesting behaviors are crucial for a mouse’s survival. They are the behaviors that collectively enable the mouse to create a nest and shelter. Therefore, nesting behaviors are also maintenance behaviors. Since a mouse performs nesting behaviors during the awake-phase of the day, they are further classified as an active behavior characterized by the general presence of motion and locomotion. 

Related Behaviors

Nesting behaviors are a complex set of behaviors that are made possible by a subset of other aligned behaviors. Comprising nesting behaviors are the following behaviors:

  • Digging. When digging, a mouse is using its fore- and hind-limbs to displace materials. Digging is an essential behavior for nesting and is also often observed when a mouse is burrowing. 
  • Shoveling. Shoveling differs from digging in that the mouse does not use its forelimbs as it does when digging. Instead, when shoveling, the mouse uses its head and snout to move the bedding.  
  • Push-digging. Push-digging is performed in order to move adjacent materials away from the nest instead of towards it. So, a mouse will push-dig any material to the sides of the cage or somewhere away from the nest’s location. Push-digging may be observed in combination with forward movement or locomotion.  
  • Carrying. A mouse will carry materials to the nest location, in order to be able to use those materials to build the nest. This is an important behavior since it is implicated in the actual supply of materials that are necessary for composing a nest. 
  • Fraying. When a  mouse is ripping apart material into smaller pieces by bitting or gnawing at the material, it is known as fraying. The resulting torn materials are then used as pieces while nesting and constructing a nest. This resourceful behavior is useful because it demonstrates that a mouse can manipulate materials in order to form shelter and meet one of its basic needs. 
  • Sorting. Sorting is a deliberate action where a mouse is organizing its nesting material. When sorting, the mouse will place the material is specific locations. For example, a mouse may organize bedding material in order based on size, aligning bedding pieces from small to large. 
  • Pulling-in. When pulling-in, a mouse is pulling nesting material toward the nest. The mouse remains in the nest and does not move away from the nest in order to bring in material.
  • Fluffing. Fluffing is a means of enlarging the nest while the mouse is located inside the nest. When a mouse is fluffing, the nest will almost seem like it’s jumping or moving.

Function of Nesting Behaviors

Non-Maternal Nesting Functions

Nesting serves many functions since nests: 

  • Provide shelter.  Nests protect mice from adverse weather conditions and thus prolong their survival time by shielding them from the rain or wind, ultimately reducing their risk of becoming ill. 
  • Offer heat conservation. Since mice are sensitive to cold conditions, nests provide a means of heat conservation. Therefore, nests inadvertently reduce the stress that derives as a result of cold exposure. In laboratories, mice that are housed at standard laboratory temperatures (20 to 26°C) have increased tumor growth as well as reduced adaptive immunity when compared to mice that are housed in more thermoneutral conditions (about 30°C). 
  • Preserve the mice’s energy. If a mouse is cold, then its energy is used for keeping the organism and body warm. Thus, energy is used for the purposes of staying warm instead of for other homeostatic functions, such as restoration. Therefore, nests are a means for mice to stay warm and preserve their energy for being used in other bodily functions. 
  • Are protective. Nests, due to their shape and form, keep mice unseen and hidden from competitors and predators. If potential predators cannot see mice, this reduces their chances of detection and thus increases their chances of survival.  
  • May be a physiological need. In experimental studies, mice show a strong drive to collect and gather material. Even if the temperature is high enough and the mice may not need to insulate, they will still gather materials and create a nest. 
  • Facilitate homeostatic goals. Since nesting is so important to mice, it may be understood as a means of maintaining homeostasis which is for obvious reasons crucial for survival. 
  • Reduce exposure to stressors. In general, nests are able to shield mice from stressors, enabling them to maintain low-stress levels and rest adequately, ultimately helping them to survive for a longer. 

Maternal Nesting Functions

  • Provide a safe, nurturing environment. By providing a safe, nurturing environment the litter size increases, as mentioned above, pups are able to survive. A safe, nurturing environment offers the pups all the resources they need in order to survive through infancy and grow up into mature mice. 
  • For thermoregulation. Since pups do not have the ability to thermoregulate, they must depend on body heat from their parents and littermates or, alternatively,  insulation from the nest, in order to stay warm. Therefore, nests are a mechanism for warming newborns since they are unable to warm themselves.
  • Position appropriately the pups in order to suckle. A successfully built nest enables the mother to position the pups in such a way that they can ultimately have an easier time suckling. This is an advantage because the nurtured pups are more likely to survive and reach maturity. 
  • To minimize the risk of separation. Since newborn pups cannot see or navigate, the maternal nest is a way to enclose them within a safe environment and minimize their risk of getting separated from the group. This ultimately increases their chances of survival and developing normally. 
  • Support adequate development. Since maternal nests are a means of providing warmth and shelter, they are a crucial component when it comes to ensuring the pup’s development and, ultimately, survival. 

Application of Nesting Behaviors

Non-maternal Nesting Applications

Since nesting is such a vital part of mouse behavior due to its importance for survival, it will be observed under laboratory conditions. However, certain conditions are known to be able to elicit nesting, including: 

  • Cold conditions. Cold conditions and temperatures trigger nesting because nesting is a means for the mouse to keep warm. 
  • Access to materials. When materials are present, a mouse is very likely to use them for the purposes of creating a nest. 

Maternal Nesting Applications

Since maternal nesting is specific to newborn pups and the reproductive period, it can be observed when an expecting mother is about to deliver newborns. Therefore, the applications of maternal nesting are limited to:

  • After mating. Mice will use more nesting material, in order to build nests, if they have recently mated. Mice are expected to use high amounts of nesting material all the way through parturition, indicating that they are spending more time and focus on nesting. Then, about 10 days after parturition, the amount of nesting materials that they use significantly drops.  
  • When the mouse is pregnant or lactating.  A mouse that is pregnant or lactating will demonstrate nesting behavior. Mice that have abnormalities or diseases will nest at lower rates and form less complex nests. More on this in the later sections on Mouse Strains and Abnormalities. 
  • A mouse being in the presence of an infant. If an adult mouse is in the presence of a newborn pup, then its maternal nesting instinct is likely to be triggered. It is possible for mice to begin building nests for newborn pups that are not in their own genetic pool.

Research Techniques Used for Studying Nesting Behaviors

  • Genetic studies. Genetic studies can be used for the purposes of studying nesting behaviors in mice. Researchers can learn more about the relationship between genetics and nesting behaviors through the use of genetic manipulation and genetically modified mice. Well-designed genetic studies are able to reach the conclusion of how genetics are influential on nesting behaviors which may ultimately lead to insights of how to improve any related abnormalities. 
  • Pharmaceutical studies. Pharmaceutical studies are also a means of studying nesting behaviors. By giving mice a supplement of drugs or medicine, researchers are able to identify and study how nesting behaviors are affected by certain classes of drugs. Pharmaceutical studies are often combined with genetic studies, which offer genetic disease models, in order to study the impact of drugs on nesting behaviors.
  • Behavioral studies. In behavioral studies, researchers subject mice to behavioral tests which are carefully selected based on their validity of studying the desired behavior. Behavioral studies are often combined with elements of genetic and pharmaceutical studies, in order to assess specifically how genetics and drugs affect nesting behaviors. 

Behavioral Tests for Assessing Nesting Behaviors

Assessing Non-Maternal Nesting

Nest building performance can be used to monitor impairments (or progress) in a mouse’s behavior by means of quantifying and measuring the nest and the behaviors involved. 

Typically, scores with several grade levels may be used which will categorize the nest depending on whether a nest exists to whether the nest has high walls that surround the mouse. Some researchers will measure the nest’s height and calculate the percentage of used or unused nesting material. To learn more, check out our article on non-maternal nesting.

Assessing Maternal Behaviors

Nest building performance can be used to monitor impairments (or progress) in a mouse’s behavior by means of quantifying and measuring the nest and the behaviors involved. 

Typically, scores with several grade levels may be used which will categorize the nest depending on whether a nest exists to whether the nest has high walls that surround the mouse. Some researchers will measure the nest’s height and calculate the percentage of used or unused nesting material. 

Maternal nesting can be assessed throughout a mouse’s reproductive life. Typically, maternal nests will be assessed across many stages. In experimental studies, researchers will use nulligravid, primigravid, and lactating females and compare them to virgin females in order to establish maternal nesting patterns across time. To learn more, check out our article on maternal nesting.

Pharmaceutical Studies on the Behavior

Non-Maternal Nesting and Pharmaceutical Studies

  • Xamoterol improves nest building in down syndrome mice. A norepinephrine precursor, L-threo-3,4-dihydroxyphenylserine (xamoterol), improves nest building in Ts65Dn mice which model Down syndrome. Xamoterol, a partial agonist for the β1-adrenergic receptor, improves Ts65Dn mice’s nest performance by increasing the amount of material they used to form the nest and improving the nests’ form. 
  • Alzheimer’s mice’s nesting is improved by bexarotene. Alzheimer’s mice typically have problems in their nest-building abilities. One drug that reverses this inability is bexarotene. Bexarotene, also referred to as ‘Targretin,’ is a retinoid X receptor (RXR) agonist that can move across the blood-brain barrier and has been approved by the U.S. Food and Drug Administration. RXR agonists may be able to clear β-amyloid (Aβ) build up within the brain which is typical in Alzheimer’s disease. When Alzheimer’s Tg2576 mice are given bexarotene, their nest construction is significantly improved just after 3 days of treatment, receiving bexarotene at 100 mg/kg/day. 
  • Donepezil increases nesting behavior in autistic mice. Typically, ASD mice have very low scores in the nesting test, building poorer nests than control mice. Donepezil is an acetylcholinesterase inhibitor and therefore prevents the breakdown of acetylcholine, a neurotransmitter that is already low in patients with autism spectrum disorder (ASD). When autistic mice, induced with ASD via the well-validated method of valproic acid injection, are given a donepezil dose of 0.3 mg/kg daily and subchronically, nesting abilities are improved. ASD mice receiving donepezil roughly averaged a nesting score of 5 (the highest possible) while non-treated ASD mice received a score of 3.5, significantly lower than the treated ASD mice’s score. 

Maternal Nesting and Pharmaceutical Studies

  • Progesterone increases nest weight. Progesterone is a sex hormone. Administering progesterone subcutaneously through hormone-dipped pellets to mice will lead to a subsequent increase in maternal nest weight and a higher percentage of built maternal nests. In fact, giving progesterone to ovariectomized mice also induces maternal nesting. Also, giving progesterone to non-pregnant mice will lead to the elicitation of maternal behaviors such as maternal nesting.  
  • Estrogen dose suppresses nest building. Estrogen, also referred to as oestrogen, is a main female sex hormone. In mice, using the same method as described above, in the ‘Progesterone Increases Nest Weight’ bullet point, through subcutaneously administered pellets, estrogen is associated with suppressed maternal nest building. 
  • Testosterone propionate reduces maternal nest building. Testosterone propionate is a manufactured medication, designed originally with treating conditions associated with low testosterone levels. In mice, testosterone propionate reduces maternal behaviors, including nesting. Mice that are given testosterone propionate will have lower nest building scores since they create nests that are not as intricate as typical brood nests. 
  • Lipopolysaccharide injections decrease maternal nesting. Sickness is associated with altered behavior. Lipopolysaccharides are able to induce behavioral symptoms that are similar to sickness, leading to decreased levels of locomotion, a reduction in social activities, and even anorexia. This is because lipopolysaccharides are a bacterial fragment that can induce sickness by mimicking cytokines’ molecular structure when injected to mice in a controlled setting. Maternal mice that are injected with lipopolysaccharides will demonstrate lower nesting scores than saline-injected mice under a 22°C setting. However, under colder temperatures, maternal mice injected with lipopolysaccharides will build nests that are not significantly different than controls’, implying that sickness modulates behavior under particular circumstances. 
  • Chlorpyrifos injections postpone nest building instinct. Organophosphates (OPs) are an important group of pesticides for which strong human epidemiological evidence has been gathered against demonstrating that it can cause damage to the nervous system due to acute intoxication. Chlorpyrifos is a particular type of OP pesticide. Chlorpyrifos (CPF) is one of the top-selling insecticides, the most commonly used OP in the USA for the purposes of pest control. Yes, the Environmental Protection Agency has banned its residential use due to potential safety issues of childhood exposure. Newborn pups that have been given injections with CPF affect maternal care. Pups that have been injected with CPF influence maternal care and are associated with postponed nest building. This demonstrates the complexity of maternal nesting by demonstrating that the pups themselves can influence maternal nesting behaviors.

Mouse Strains and Nesting Behaviors

Non-Nesting Across Mouse Strains

  • C57BL/6 mice. C57BL/6 mice are used as comparator or control mice in behavioral studies because these mice are considered to have normal nesting habits. The majority of C57BL/6 mice are expected to score 4-5 on nest construction using the 5-point scale system described previously. A hippocampus lesion, which will be mentioned again later under the “Abnormalities” section, alters nesting behaviors. C57BL/6 mice that have had a hippocampus lesion will have a median score of 1-2 on nest construction, also on a 5-point scale system, and are highly unlikely to exceed having a score of 3. 
  • Tg2576 mice. Tg2576 mice are transgenic mouse models of Alzheimer’s disease. These mice have the human mutation of the amyloid-β precursor protein (APP) overexpressed. These mice, when supplied paper towels to their home cages, fail to construct nests. This inability is further modulated by increasing age, an effect that is not present in their wild-type counterparts. Even when Tg2576 mice are subjected to a colder than normal environment, they do not begin to nest. 
  • 3xTg-AD mice. 3xTg-AD mice have triple mutations in the APP, PS1 and Mapt genes and represent rarer forms of Alzheimer’s disease. 3xTg-AD mice have Aβ plaques and neurofibrillary tangles which are similar to those in human patients who have Alzheimer’s disease. 3xTg-AD mice do not display any differences from non-transgenic controls when it comes to nest building, although they do perform worse than the non-transgenic controls in other behavioral tests, such as Passive/Avoidance and the T-Maze Reversal tests. 
  • Ts65Dn mice. Ts65Dn mice are predominantly used for modeling Down syndrome and display cognitive deficits similar to those found in humans with Down syndrome, such as impairments in contextual learning. Ts65Dn mice are genetically manipulated to have Down syndrome and are trisomic for a fragment of the mouse chromosome 16 which extends from Mrpl39 to Znf295. These mice are also noted to have advanced degeneration of locus coeruleus neurons. Ts65Dn mice have poorly formed nests and are likely to use only a small quantity of any nesting material provided. 
  • PLCβ1-/- mice. Schizophrenic patients have been found to have lower levels of phospholipids in their brains. Phospholipase C (PLC) β1 is specifically expressed in the amygdala, hippocampus, olfactory bulb, and cerebral cortex and schizophrenics have been found to have possible shortages of PLCβ1. PLCβ1-/- knockout mice lack PLCβ1, an enzyme associated with G-protein coupled receptors that perform hydrolyzation which eventually leads to the formation of secondary messengers. Perhaps due to these molecular changes, PLCβ1 knockout mice have compromised nesting abilities. PLCβ1 mice do not initiate nesting as quickly as normal, healthy mice and they are not as responsive to the presence of nesting materials as healthy mice are.
  • MECP2308/Y mice. Rett syndrome, a type of mental retardation observed predominantly in females, can be modeled in mice that have the methyl-CpG binding protein 2 (MECP2) gene mutated. MECP2 mice are used to model Rett syndrome. This is an X-linked disorder caused by a faultiness of the MECP2 gene. These mice show large impairments in nest building and cannot build nests in the way that normal, healthy mice can. 

Maternal Nesting Across Mouse Strains 

Maternal nesting varies across mouse strains. Since mice differ by genetics, the variability in maternal nesting can be assessed and analyzed in such a way that it can be partly explained by genetics. Below are several mouse strains and their expected type of maternal nesting:

  • Ephrin-A5-/- mice. Throughout the central nervous system’s neural circuits ephrin ligands and Eph families of tyrosine kinase receptors can be found. The Eph families of tyrosine kinase receptors along with the ephrin ligands are involved in regulating animal behavior. Ephrin-A5 is a particular kind of ligand (one of the eight identified ligands for the Eph receptors) which has been found to be expressed in brain regions that are associated with maternal behaviors, such as the preoptic area and the hypothalamus. Ephrin-A5 transcripts can also be detected in the suprachiasmatic nucleus, the arcuate nucleus, and the paraventricular nucleus. Ephrin-A5-/- mice which have the ephrin-A5 genetically knocked out display poorer maternal nesting quality when compared to normal wild-type mice. While pregnant wild-type mice are expected to tear up about 90% of the nesting material and already create a nest by the 6-hour mark of being presented with the nesting material, Ephrin-A5-/- mice leave the nesting material intact, indicating minimal maternal nesting by contrast.   
  • TPH2-/- mice. Tryptophan hydroxylase-2 (TPH2) is known to catalyze the first and rate-limiting step of serotonin biosynthesis. Mice that have TPH2 mutated (TPH2-/-) show different maternal nesting patterns than TPH2+/+ mice do (mice which still have the gene fully intact). TPH2-/- mothers that have the TPH2 gene mutated have a litter with low survival rates and high incidences of cannibalism. When compared to TPH2+/+ mice, TPH-/- mice have nests that are poorly constructed, less well-defined and not as tightly gathered. By genetically depleting the brain of serotonin due to TPH2 mutation, subsequent effects on maternal nesting can be noted. 
  • PET-1-/- Mice. PET-1 is a transcription factor that belongs to the ETS family and is exclusively expressed in brain cells which are a part of the serotonin system. Mice that lack the gene for PET-1 (PET-1-/-) and thus cannot produce this transcription factor show compromised maternal behaviors including poorer nesting skills. One study, by Lerch-Haner et al. established that only 47.6% of PET-1-.- mice will complete their nests compared to 86.5% of PET-1+/+ control mice who complete theirs. Also, only 13.5% of controls will have an incomplete nest while 42.9% of PET-1 deficient mice will have an incomplete nest. Furthermore, almost 10% of PET-1-.- mice will not build a nest at all, an observation that did not occur at all within the controls since they all managed to build at least some portion of a maternal nest.
  • 129Sv mice. 129Sv female mice are quick to start nest building and will begin to nest-build at a sooner point in time than other mouse strains such as C57BL/6J. However, when considering nest building as a part of all of the homecage behaviors that a female mouse exhibits, nest building takes a smaller fraction of this strain’s time, indicating that this behavior does not occur frequently in female 129Sv mice. 
  • Vitamin D receptor knockout mice. Vitamin D has several key functions within the brain and depends on the vitamin D receptor (VDR) in order to get them done. In humans, there is increasing evidence that links mutations in the VDR with psychiatric conditions. Mice that have had VDR knocked out show many abnormal behaviors, like barbering, and also compromised maternal nest-building abilities. VDR knockout mice are more likely to build a cup-shaped nest (which has a completeness score of about 3 out of 5) while wild-type mice, by comparison, are more likely to create a hooded nest (about a 4 out of 5).

Abnormalities of Nesting Behaviors

Non-Nesting Abnormalities

  • Hippocampus lesion. Mice with a complete hippocampal lesion have inhibited, disrupted nesting habits. Lesions to the ventral or dorsal hippocampus do not have such effects, suggesting that these regions are sub-threshold but play an additive role in nesting behaviors.
  • Pain and sickness. Mice that are sick are reported to have minimal (if any) nesting behavior. Also, mice that are experiencing pain have altered nesting behavior, but this returns to normal levels when the pain has passed.
  • Autism spectrum disorder. Autism spectrum disorder has been associated with abnormal abilities of nesting behaviors. Mice that have autism spectrum disorders are not able to build nests that are quality compared to normal or healthy mice, implying that autism is associated with poorer nesting abilities. 
  • Rett syndrome. Rett syndrome is an abnormality that affects nesting behaviors. Prior to its genetic discovery, it was often classified as a type of autism spectrum disorder. In mice, Rett syndrome is associated with poorer nesting outcomes. 
  • Schizophrenia. Schizophrenia is another abnormality in mice that is associated with poorer nesting outcomes. Mice that model schizophrenia do not build nests of good quality, demonstrating that schizophrenia compromises nest-building abilities. 
  • Down syndrome. Down syndrome is associated with poorer nest building and thus is a nesting abnormality. Mice that model Down syndrome will not have properly formed, complex nests. 
  • Alzheimer’s disease. Alzheimer’s disease is an abnormality that affects normal cognitive processing in mice. Typically, mice are not able to build nests that are of comparable quality to chosen controls’ nests. However, there are some transgenic mouse models of Alzheimer’s disease, such as the 3xTg-AD mice, which build nests that are not significantly different than controls’. 

Maternal Nesting Abnormalities

  • Bulbectomization. Olfactory bulb removal through surgical means, also known as bulbectomization, results in an abnormality wherein a pregnant mouse no longer has its olfactory bulb, the part of the brain which receives neural inputs regarding odors as sensed by cells located in the nasal cavity, in place. Bulbectomization inhibits nest building in pregnant mice (and also in virgin mice), suggesting that the olfactory bulb is involved indirectly in both thermoregulatory and maternal nesting.  
  • Fatty-acid deficiency. N-3 fatty acid-deficient pregnant mice have lower nest scores than control mice that have an adequate fatty-acid deficient diet. Furthermore, after delivery, about 40% of n-3 fatty acid dams may be expected to attack or neglect their newborns by not nursing them. The deficient dams will have lower levels of brain docosahexaenoic acid (DHA) levels than the dams that follow an adequate diet. 
  • Vitamin D receptor deficiency. A deficiency in vitamin D receptors can influence maternal behavior. Vitamin D, in itself, is a steroid hormone that has multiple important roles in the brain and is mediated by the vitamin D receptors. Without the receptors, maternal nesting becomes compromised and many other abnormalities in maternal behavior occur such as pup neglect and cannibalism. 
  • Abnormalities of the Serotonergic System. Serotonin is a hormone and neurotransmitter with various roles in the brain. However, its function on maternal nesting is still not fully understood. Mice that have a mutation in the serotonergic system, such as TPH2-/- mice of PET-1-/- mice, have been shown to have abnormally low scores of maternal nesting which negatively affects pup survival.

Disease Models of Nesting Behaviors

Non-Maternal Nesting Disease Models

  • Rett Syndrome in MECP2308/Y mice. The gene encoding methyl-CpG binding protein 2 (MeCP2) is linked as the leading cause of mental retardation with autistic features in females. This is an X-linked disorder caused by faultiness of the MECP2 gene. Interestingly, ten-week-old MECP2308/Y mice do not have abnormal anxiety responses, locomotion deficits, or issues with grooming and ataxia. However, these mice do display impairments in nest building and utilization. 
  • PLCβ1-/- mice modeling schizophrenia rarely nest. Nesting is very rarely observed in mice which lack the phospholipase C β1 gene (PLCβ1-/-), a particular mouse strain used to model schizophrenia since they also demonstrate deficiencies in this gene. One experiment showed that PLCβ1-/- mice are much less responsive towards building a nest out of provided cage materials when compared to wild-type mice. When given materials, all wild-type mice featured in the experiment built their nests within the hour, a stark contrast to the tested PLCβ1-/- mice out of which not one mouse built a nest. 
  • Transgenic mouse models of Alzheimer’s disease. In most, but not all, transgenic mouse models of Alzheimer’s disease, deficits pertaining to nesting can be observed. While some mice, such as 3xTg-AD mutant mice do not have nesting affected due to their disease, other mice modeling Alzheimer’s disease, such as Tg2576 mice, do. These mice either have decreased nest quality or prolongation of latency before initiating nest building. Such observations indicate that deficient nesting patterns may be a characteristic of Alzheimer’s disease mouse models but continue to display variability across transgenic mouse models.
  • Down syndrome. The most common cause of mental retardation in children is Down syndrome. Down syndrome and is characterized by deficits in memory, as well as contextual learning. As mentioned previously, in mice, Down syndrome alters nesting behavior and significantly compromises the quality of the nest. Down syndrome is predominantly modeled using Ts65Dn mice. These mice are also noted to have advanced degeneration of locus coeruleus neurons. Although the locus coeruleus has not been established to serve a role in contextual discrimination, it is required for contextual learning and deficits in its neuronal population have been correlated with neurodegenerative diseases.
  • Autism spectrum disorder. Mice that model autism spectrum disorder have their nesting abilities compromised. Mice that have been induced with autism spectrum disorder using the well-validated method of valproic acid injection will show deteriorated nesting abilities.

Maternal Nesting Disease Models

  • Limited nesting/bedding. Limited nesting or the bedding-maternal procedure is a disease model mimicking the early life stress paradigm. A mother is deprived of available nesting materials, thus cannot make a well-formed nest. This, in turn, creates stress on the pups since they do not have a warm, tight nest to grow up in. By modeling stress, researchers can measure how nesting influences upcoming generations of newborns given environmental shortcomings by decreasing the quality of maternal nesting through environmental manipulation. 
  • Postpartum depression.
    • Induction through an n-3 fatty acid-deficient diet. Pregnant mice that are fed on an n-3 fatty acid-deficient diet have poorer nest building abilities than pregnant mice following an n-3 fatty acid-adequate diet. Furthermore, about 40% of dams that are on this type of diet are expected to neglect their pups by not nursing them or to attack their newborn pups. Female mice on an adequate diet, have higher levels of brain docosahexaenoic acid than deficient mice. This suggests that such a diet deficient in n-3 fatty acids can be used to induce postpartum disorder in mice and that dietary n-3 fatty acid intake is associated with normal maternal behavior and the prevention of postpartum depression. 
    • Induction through chronic social defeat. Chronic stress is a known predictor of depressive disorders. Social stress is a particular form of stress that is common in both humans and mice. The majority of mouse models of depression were initially developed for male mice and may not be applicable to postpartum female mice. In order to induce postpartum depression, lactating female dams are exposed daily to a novel male intruder. Subsequently, overall maternal care is reduced which includes nesting and bouts of self-grooming significantly increase in comparison to controls. 

Summary

  • Nesting behaviors refer to a mouse creating or building a nest for itself or its offspring. 
  • Nesting behaviors refer to any point that a mouse is building its shelter. There are two types of nesting-behaviors known to date: maternal nesting and non-maternal, or thermoregulatory, nesting. 
  • Behaviors that are related to nesting and are important for executing nesting include: digging, shoveling, push-digging, carrying, fraying, sorting, pulling-in, and fluffing.
  • Non-maternal nesting has many functions. A mouse needs to be able to nest in order to: provide shelter, have heat conservation, preserve energy, be protected, fulfill a physiological need, and facilitate homeostatic goals. 
  • Maternal nesting has many functions and is crucial for: providing a safe and nurturing environment to newborns, providing thermoregulation,  positioning the pups appropriately in order to be able to suckle, minimizing the risk of separation, supporting adequate development. 
  • Non-maternal nesting can be observed under the following conditions: cold environment and access to materials.
  • Maternal nesting can be observed under the following conditions: after mating, when a mouse is pregnant or lactating, or in the presence of an infant. 
  • In order to study nesting behaviors, researchers use genetic, pharmaceutical, and behavioral studies, or some combination of them. 
  • Some notable pharmaceutical behaviors have established that
    • For non-maternal nesting:
      • Xamoterol improves nest building in down syndrome mice.
      • Alzheimer’s mice’s nesting is improved by bexarotene.
      • Donepezil increases nesting behavior in autistic mice. 
    • For maternal nesting
      • Progesterone increases nest weight.
      • An estrogen dose suppresses ne st building.
      • Testosterone propionate reduces maternal nest building.
      • Lipopolysaccharide injections decrease maternal nesting.
      • Chlorpyrifos injections postpone nest building instinct.
  • Across mouse strains, nesting varies. For example: 
    • For non-maternal nesting:
      • C57BL/6 mice are used as comparator or control mice in behavioral studies because these mice are considered to have normal nesting habits.
      • Tg2576 mice are transgenic mouse models of Alzheimer’s disease and when supplied paper towels to their home cages, fail to construct nests. 
      • 3xTg-AD mice also model Alzheimer’s disease but do not display any differences from non-transgenic controls when it comes to nest building
      • Ts65Dn mice model Down syndrome and have poorly formed nests and are likely to use only a small quantity of any nesting material provided. 
      • PLCβ1 mice model schizophrenia and do not initiate nesting as quickly as normal, healthy mice and they are not as responsive to the presence of nesting materials as healthy mice are.
      • MECP2308/Y mice model Rett syndrome and also demonstrate impaired nest building skills.
    • For maternal nesting:
      • Ephrin-A5-/- mice display poorer maternal nesting quality when compared to normal wild-type mice.
      • TPH2-/- mothers that have the TPH2 gene mutated have a litter with low survival rates and high incidences of cannibalism. When compared to TPH2+/+ mice, TPH-/- mice have nests that are poorly constructed, less well-defined and not as tightly gathered.
      • Mice that lack the gene for PET-1 show compromised maternal behaviors including poorer nesting skills.
      • Maternal nest building takes a smaller fraction of 129Sv mouse’s overall cage time, indicating that this behavior does not occur as frequently as expected when the mouse is pregnant. 
      • Mice that have had VDR knocked out show many abnormal behaviors, like barbering, and also compromised maternal nest-building abilities.
  • Abnormalities are known to affect nesting behaviors. For example,
    • for thermoregulatory nesting:
      • Mice with a complete hippocampal lesion have inhibited, disrupted nesting habits. 
      • Mice that are sick are reported to have minimal (if any) nesting behavior.
      • Autism spectrum disorder has been associated with abnormal abilities of nesting behaviors. 
      • Rett syndrome is an abnormality that affects nesting behaviors negatively.
      • Down syndrome is associated with poorer nest building and thus is a nesting abnormality. 
      • Usually, Alzheimer’s disease is an abnormality that affects normal cognitive processing in mice.
    • for maternal nesting:
      • Bulbectomization inhibits nest building in pregnant mice.
      • N-3 fatty acid-deficient pregnant mice have lower nest scores than control mice that have an adequate fatty-acid deficient diet.
      • Without vitamin D receptors, maternal nesting becomes compromised and many other abnormalities in maternal behavior occur such as pup neglect and cannibalism. 
      • Mice that have a mutation in the serotonergic system, such as TPH2-/- mice of PET-1-/- mice, have been shown to have abnormally low scores of maternal nesting which negatively affects pup survival.
  • Disease models can be used to model abnormalities or diseases of nesting in mice. 
    • For thermoregulatory nesting:
      • Rett Syndrome is modeled using MECP2308/Y mice
      • Schizophrenia is modeled using PLCβ1-/- mice.
      • Alzheimer’s disease can be modeled in many different ways, such as by using 3xTg-AD mutant mice or Tg2576 mice.
      • Down syndrome is predominantly modeled using Ts65Dn mice.
      • Autism spectrum disorder is another disease model with compromised nesting abilities, especially when modeled using valproic acid injections.
    • For maternal nesting:
      • Limited nesting/bedding is a disease model mimicking the early life stress paradigm, thereby decreasing the quality of maternal nesting through environmental manipulation. 
      • Postpartum depression is another disease model that affects maternal nesting. It is modeled either through limiting the female mouse to an n-3 fatty acid-deficient diet or exposing her to chronic social defeat. 

References

  1. http://mousebehavior.org/nesting-behavior/ 
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