Resident-Intruder Aggression Test
Overview
The resident-intruder aggression test is the gold standard paradigm for quantifying offensive aggression in rodents, exploiting the territorial behavior that male mice exhibit when a conspecific is introduced into their established home cage. The resident mouse is individually housed for 1 to 3 weeks prior to testing to establish territorial ownership, during which bedding is left unchanged to build olfactory territorial markers. The intruder is a group-housed, weight-matched, unfamiliar male of a less aggressive strain (such as BALB/c or A/J when testing C57BL/6 residents), which is introduced into the resident home cage for a 10-minute encounter. This design capitalizes on the well-characterized offensive aggression circuitry involving the ventromedial hypothalamus ventrolateral subdivision, medial amygdala, and lateral septum.
Trained observers or automated behavioral classifiers score a hierarchy of agonistic behaviors including attack latency (time to first offensive action), number and duration of attack bouts, bite frequency, lateral threat postures, tail-rattling displays, pursuit episodes, and clinch fighting. The attack latency is the most widely reported metric, with values below 60 seconds considered highly aggressive and values exceeding 300 seconds indicating low aggression or social submission. Defensive behaviors of the intruder (upright posture, flight, freezing) are scored simultaneously to confirm that agonistic interactions are occurring and to assess intruder welfare for humane endpoint application.
ConductMaze supports the resident-intruder paradigm through dual-animal tracking in the home cage environment using overhead or angled video with identity-maintained tracking via size-differential or coat-color discrimination algorithms. The system automatically detects close-proximity interaction bouts, flags putative attack events based on rapid approach velocity and sustained body contact, and generates frame-by-frame ethograms that can be verified against manual scoring. Automated bite detection uses body-contour deformation analysis when animals are in sustained ventral contact, and cumulative aggression scores are computed per session with configurable severity thresholds.
Trial Flow
Isolation Period
Individually house resident male for 7-21 days with unchanged bedding to establish territory
Intruder Selection
Select weight-matched, group-housed intruder male of less aggressive strain; mark for identification
Intruder Introduction
Place intruder into far corner of resident home cage; start recording and timer simultaneously
Behavioral Observation
Monitor continuous agonistic interactions for 10-minute session duration
Attack Classification
Classify each agonistic bout as attack, lateral threat, tail rattle, pursuit, or clinch
Welfare Check
Apply humane endpoint criteria: terminate if intruder sustains visible wounds or prolonged pinning exceeds 30 seconds
Behavior Scoring
Compute attack latency, bout frequency, cumulative attack duration, bite count, and aggression composite score
Session End
Remove intruder; inspect both animals for injuries; return intruder to group housing
Parameters
| Parameter | Type | Default | Description |
|---|---|---|---|
| Session Duration | duration | 600 | Maximum encounter duration in seconds (standard 10 min) |
| Isolation Period | integer | 14 | Days of individual housing for the resident prior to testing |
| Resident Strain | enum | C57BL/6J | Strain of the resident mouse |
| Intruder Strain | enum | BALB/cJ | Strain of the intruder mouse (typically less aggressive) |
| Weight Match Tolerance | float | 2.0 | Maximum body weight difference between resident and intruder in grams |
| Humane Endpoint Threshold | seconds | 30 | Maximum sustained pinning duration before session termination in seconds |
| Light Phase | enum | dark | Testing during dark (active) or light (inactive) phase of the cycle |
| Illumination | integer | 5 | Red-light illumination level in lux for dark-phase testing |
| Attack Proximity Threshold | distance | 2.0 | Maximum inter-animal distance for close-contact bout detection in centimeters |
Metrics
| Metric | Unit | Description |
|---|---|---|
| Attack Latency | seconds | Time from intruder introduction to first offensive attack bout |
| Attack Bouts | count | Total number of discrete attack episodes during the session |
| Total Attack Duration | seconds | Cumulative time spent in offensive attack behavior |
| Bite Count | count | Number of discrete biting events identified during attacks |
| Pursuit Duration | seconds | Cumulative time the resident actively chases the intruder |
| Lateral Threat Displays | count | Number of broadside threat postures with arched back and piloerection |
| Tail Rattles | count | Number of rapid tail-vibration displays preceding or during attacks |
| Aggression Composite Score | score | Weighted composite of attack frequency, duration, and bite count (0-100 scale) |
Sample Data
| Subject | Treatment | Attack Latency (s) | Attack Bouts | Bite Count | Pursuit (s) | Aggression Score |
|---|
Representative data for illustration purposes. Actual values will vary by species, strain, and experimental conditions.
Applications
- 1Anti-aggressive drug screening — dose-response evaluation of serotonergic, GABAergic, and vasopressinergic compounds
- 2Hormonal regulation of aggression — assessing testosterone, estrogen, and corticosterone manipulations on offensive behavior
- 3Neuropsychiatric modeling — studying aggression phenotypes in models of intermittent explosive disorder and conduct disorder
- 4Social defeat stress — using the resident-intruder paradigm to generate chronic social defeat for depression models
- 5Genetic aggression phenotyping — characterizing aggression in MAOA-knockout, 5-HT1B-knockout, and other transgenic lines
Related Protocols
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