One mouse will pin another mouse by grabbing the recipient mouse’s flank and then holding the recipient mouse down, in order to limit its range of movement.
Pinning is a behavior with multiple interpretations, depending on the context in which it was observed.
When pinning is observed between two mice which are interacting positively together, pinning is a social behavior. In this context, the pin is commonly observed in junction with Allogrooming which is a bonding behavior. Pinning is a socially acceptable behavior observed when two young rodents are playing with each other. Therefore, pinning is a behavior that is used to measure social development behaviors in mice.
Pinning is more likely to be aggressive in an interaction between two adult mice and may be followed by bouts of barbering. The mouse that is performing the pin is typically the dominant mouse. Therefore, it is common to also classify pinning as an agonistic behavior.
Function of the Pinning Behavior
- For affiliation: Pinning establishes bonds between young mice during playtime and is important for normal development and the creation of social relationships, contributing to the overall success of survival to the mouse.
- For agonistic encounters: Pinning is an agonistic behavior in which one mouse immobilizes another mouse in order to attack or barber the subdominant mouse, thus serving to establish social hierarchy and aid in survival.
- For nurturing the young: When a mother pins her pup, it is to ensure that the pup gets properly fed. Thus, the pup has higher chances of living and developing healthily.
- For healthy development: Pinning, when observed in the context of social play, serves the function of fostering proper, healthy development. Social play (and, by extension, pinning) is associated with the development of cognitive competence and mental flexibility. Such development is crucial for proper functioning, autonomous behaviors, and, ultimately, survival.
Application of Behavior
- In young pups socially bonding: Pups that are socially bonding will demonstrate pinning during play-fighting sessions.
- In adult mice during aggressive interactions: Older mice are more likely to display pinning in an aggressive manner, using it to segway into other agonistic behaviors, such as barbering.
- During the pre-weaning period: A mother will pin her pup in order to gain control and assist them in feeding.
Behavioral Tests for Assessing Pinning in Mice
- Social Interaction Test: Pinning behavior, in its playful form, can be observed while two mice are interacting together in a neutral chamber. The interaction is allowed to span for an allotted period of time, such as 30 minutes, and it captures by video recording. Then, the researcher will tally up the frequencies of the behaviors.
- The Resident-Intruder Test: In its aggressive context, pinning is commonly observed in the Resident-Intruder Test. In this test, two mice are placed in a small tube and the more dominant mouse will gain control, pinning down the other mouse.
- The Open Field: Sometimes, in behavioral research, mice will be placed together in an Open Field together and their behavior, such as the number of pins they perform, will be counted.
When collecting data, some researchers will classify pinning as a social behavior or aggressive behavior. A third possibility is to count pinning in both social and aggressive categories. This is done when multiple behaviors are counted under each category and the sum score is used to determine whether social or aggressive behaviors collectively are more frequent.
DEHP Reduces or Increases Social Play and Pinning Behavior
Pinning and social behaviors are affected by D1-(2-ethylhexyl) phthalate (DEHP), a plasticizer used in polyvinyl chloride (PVC) plastics which has been shown to be an environmental disrupter of the endocrine system.
In pubertal mice, DEHP exposure is associated with a significant decrease in the amount of pinning behaviors in females (about 25% frequency at dosage levels 1 and 50 mg/kg/d). By contrast, males receiving 50 mg/kg/d of DEHP exposure had an increased frequency of play and pinning behaviors by about 76%. In adults, DEHP reduces social and pinning behaviors in males and females at 200 mg/kg/d.
Abnormalities in the Pinning Behavior
Lack of Neuregulin-1 Gene
The neuregulin-1 (NRG1) is a possible candidate gene for schizophrenia and has a functional role in social and cognitive processes. Mice that have had the NRG1 gene knocked out will show a higher frequency of pinning and aggressive behaviors than control wild-type mice.
Pten Haploinsufficient Mice
Phosphatase and tensin homolog (Pten) mutations are associated with autism spectrum disorder (ASD). Pten haploinsufficient mice modeling ASD have been found to have less aggressive behaviors such as pinning and more repetitive behaviors than controls.
- Pinning is performed by grabbing the recipient mouse’s flank and then holding the recipient mouse down, in order to limit its range of movement.
- Pinning can be playful or agonistic, depending on the context and the behaviors which proceed.
- Survival and appropriate healthy development are associated with pinning.
- Pinning can be observed by placing two mice in an Open Field, as well as during the Resident-Intruder Task.
- The Social Interaction Test combined with video recording is an observational method for tallying the total frequency of pinnings within an allotted period of time.
- Abnormalities in pinning can be observed in mice with genetic mutations. Mice that lack the neuregulin-1 gene demonstrate pinning frequently and are aggressive. While mice that have a Pten mutation do not pin often when compared to controls.
Thus, pinning is a complex behavior which can either be playful or aggressive, depending on the context and the behaviors which follow immediately. Typically, in young or adolescent mice, pinning is performed during playtime. In older mice, where reproduction and dominance are of greater value, pinning is more likely to be performed in an aggressive manner. Pinning can also be observed when mothers are trying to control their offspring during the pre-weaning period.
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- Curley, James P., et al. “The meaning of weaning: influence of the weaning period on behavioral development in mice.” Developmental neuroscience 31.4 (2009): 318-331.
- Wang, Ran, et al. “Effects of early pubertal exposure to di-(2-ethylhexyl) phthalate on social behavior of mice.” Hormones and behavior 80 (2016): 117-124.
- O’Tuathaigh, C. M. P., et al. “Phenotypic characterization of spatial cognition and social behavior in mice with ‘knockout’ of the schizophrenia risk gene neuregulin 1.” Neuroscience 1 47.1 (2007): 18-27.
- Clipperton‐Allen, A. E., and D. T. Page. “Decreased aggression and increased repetitive behavior in Pten haploinsufficient mice.” Genes, Brain and Behavior 14.2 (2015): 145-157.
- O’Tuathaigh, C. M. P., et al. “Phenotypic characterization of spatial cognition and social behavior in mice with ‘knockout’ of the schizophrenia risk gene neuregulin 1.” Neuroscience 147.1 (2007): 18-27.