Side display is a behavior in which one mouse is diagonally standing in front of another mouse, most often with intentions to fight. Side display is thought to be a threat-related or agonistic behavior.
The side display posture is commonly contrasted to the Upright behavior which is a stance the mouse takes when standing up on its hind legs, showing its ventral side. When doing the side display, by contrast, the mouse will orient itself towards the opponent in a broadside stance.
The side display is a behavior performed during agonistic encounters, and this is a threat behavior with aggressive intentions. The mouse approaches another mouse by taking a sideways stance, orienting its body diagonally.
Oftentimes, the side display will be observed in junction with intentions to bite and attack the other mouse.
The Many Terms Used in the Literature
When it comes to side display, there are many variations of the term used in literature. Below, the most commonly used phrases are mentioned.
In the past, side display was referred to as “offensive sidewards”, “defensive sideways”, “sideways posture.”
Currently, common terms for the side display include “sideways threat”, “lateral threatening”, “offensive side posture” and “lateral display.”
These terms are used interchangeably in scientific research. Sometimes, the side display posture is simply referred to as a “Threat” throughout an experiment, but the behavior will be clearly outlined and defined in the methodology section of the research paper as an operational term.
Habituation Reduces Side Display Threat
When mice are repeatedly exposed to the same intruder, instances of side display threat will decrease, a phenomenon known as habituation.
Behavioral Variants of the Side Display
Offensive Side Display
The side display can be divided into offensive and defensive categories. When a mouse is being offensive during an encounter, it will typically approach the other mouse, perform a sideways posture and attack or chase, depending on the behavior of the other mouse.
Defensive Side Display
In a defensive side display, the mouse will keep away from the other mouse before transitioning into flight mode.
Function of the Side Display
- As an aggressive display: The side display, also known as the lateral threat, shows as an aggressive stance in agonistic interactions which quickly transitions to other fighting behaviors. Therefore, side display is a useful stance in moments of aggressive encounters which may be crucial for survival and establishing dominance.
- As a defensive stance: Defensively, the side display may be observed prior to fleeing, serving as a segway behavior into the ultimate goal of avoiding a threat and self-preservation.
- For self-protection: Whether displayed offensively or defensively, the lateral threat posture serves the purpose of protecting the self in order to survive.
Application of the Behavior
The side display is most likely to be seen during an agonistic encounter with an opponent because it is an aggressive behavior.
- Territorial Claim: When mice are challenged by an intruder, they are likely to react aggressively and defend their territory with agonistic behaviors such as the side display posture.
- Isolation-Induced: Aggression and agonistic behaviors such as side display may be observed after a mouse has experienced prolonged bouts of isolation. This means of inducing aggression is commonly used in pharmaceutical studies.
- Pain-Induced: A mouse may exhibit side display when in pain. For example, it will display the behavior in a Passive/Avoidance Chamber with electric shock capabilities. Therefore, pain-induced methods are used to elicit aggression and increase the probability of observing aggressive behaviors such as side display in a laboratory setting.
Behavioral Tests for Assessing Side Display
- Standard Opponent Test: Here, two mice with different genetic backgrounds are placed together and observed for their agonistic behaviors. To study aggressive behaviors such as the side display, a mouse from an aggressive strain is placed with a mouse from a more passive strain and their behavioral profiles are noted.
- Resident-Intruder Test: In the Resident-Intruder Test, the side display behavior can easily be assessed and quantified. One mouse is the “resident” of the apparatus (due to prior acclimatization) and the other mouse is later introduced as the “intruder.” In this territorial encounter, aggressive behaviors are tallied up by the researchers who take into account side display as well as other aggressive behaviors.
- Social Interaction Test: During the social interaction test, two mice which are unfamiliar to each other are placed together in the same cage (neutral territory) for a limited amount of time (about 10 minutes) and the behaviors which they exhibit are observed, measured, and categorized. In this test, side display is measured as an aggressive behavior.
- Partition Test: This test is done using a Sociability Chamber. Mice are placed in two independent compartments separated by a middle partition composed of clear material. Therefore, the mice are visible to each other and can display aggressive behaviors such as the lateral threat without actually progressing to inflict damage.
Pharmaceutical Studies on the Side Display
D-Amphetamine and Phencyclidine Increase Sideways Threats
D-amphetamine administration at 0.3 or 1.0 mg/kg can increase the frequency in which mice display sideways threats. Phencyclidine (PCP) increases side display threat at doses of 0.1 and 0.3 mg/kg in mice. However, as PCP dose increases, side display frequency will proportionally decrease.
Crude Ginseng Saponins Decrease Sideways Posture in Mice
Side display frequency can be modulated by psychotropic supplements such as Panax ginseng. Crude ginseng saponins derived from the ginseng root at a concentration of 100 mg/kg, reduced the amount of side display to a frequency of almost 0 compared to the control’s 15 during the Resident-Intruder Test.
5-HT1B Receptor Agonist CP-94,253 Injections Reduce Sideways Threat
Side display reduces in a dose-dependent manner with injections of 5-HT1B receptor agonist CP-94,253 when injected into the ventral orbitofrontal cortex.
Apomorphine Attenuates Side Threats
Side display threats are reduced by apomorphine at dosages of 0.1 and 1.0 mg/kg doses. Notably, apomorphine’s effects vary widely based on what time point during the habituation process it is administered. Normally, mice are aggressive to an intruder mouse and, through gradual confrontations, the incidence of lateral threats will naturally decrease. If apomorphine is administered at the beginning of the habituation process, when the intruder mouse is first being introduced, the number of side display threats decreases significantly. However, if apomorphine is administered towards the end of the habituation process when aggression is naturally bound to decrease, side display will increase.
Aspartame and Sucrose Intake Increase Lateral Threat
Long-term intake of sucrose or aspartame is associated with increased aggression. Mice receiving 30% sucrose solution (S30) chronically will 100% of the time demonstrate the lateral threat, compared to 44% frequency in controls drinking water and a 78% likelihood in mice receiving aspartame chronically.
Strains Exhibiting the Side Display
Since the side display is a behavior expressed in an aggressive context or situation, aggressive mice will by nature have higher bouts of side display. But, even then, sub-strains are bound to show a variation in the likelihood of demonstrating the side display behavior. Take, for example, the BALB mouse strain, a commonly used mouse strain in behavioral research:
BALB Mice: BALB/cJ Versus BALB/cByJ Mice
BALB mice, depending on the substrain being studied, will have incredibly different side display frequencies. For example, in the Resident-Intruder test, following prolonged isolation in order to induce aggression, BALB/cJ mice are roughly 5 times more likely to demonstrate threatening side display than BALB/cByJ mice.
Dio3 -/- Male Mice Increased Levels Lateral Threat
The type 3 deiodinase (Dio3) is found in neurons and is responsible for protecting the brain from excessive thyroid hormone levels. Dio3 -/- mice are deficient in this factor and have been found to have high aggression levels and bouts of lateral threat posture which may occur as a result of an underlying abnormality in oxytocin and vasopressin systems (which are two neuropeptides which have been implicated in modulating aggression).
- Side display is a behavior in which one mouse is diagonally standing in front of another mouse.
- Other terms which refer to side display that appear frequently in the scientific literature are “defensive sideways,” “sideways posture,” “sideways threat,” “lateral threatening,” “offensive side posture,” and “lateral display.”
- Habituation decreases the likelihood of a mouse exhibiting the side display.
- Side display can be offensive or defensive, depending on which behaviors ensue next and which mouse is retreating from the other mouse. The offensive use of the behavior is more commonly studied.
- The side display has a protective function. The mouse can use it in an aggressive situation either offensively or defensively, in order to survive.
- Subjecting the mouse to pain or isolation increases the likelihood that this behavior will be displayed during an agonistic encounter.
- This behavior is commonly categorized as agonistic and can be observed during the Resident-Intruder Test, the Partition Test, the Standard Opponent Test, and the Social Interaction Test.
- Drugs such as sucrose, aspartame, serotonin agonists, and crude ginseng saponins all affect the frequency of this behavior in some way.
- Within a mouse strain, some sub-strains may be more likely to display the side display behavior. Such is the case with the BALB mouse strain where the BALB/cJ mice are roughly 5 times more likely to demonstrate threatening sideways posture than BALB/cByJ mice.
- Dio3 -/- mice are aggressive and display high levels of the side display due to underlying neurophysiological abnormalities in wiring (the brain’s connectivity and structure).
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