Behavioral Research Report

Resident-intruder Paradigm

I was tasked with researching the Resident-Intruder Paradigm so here we go!

The Resident-Intruder Paradigm is used to test or categorize both offensive and defensive behavior specifically in rats. It is often used for acute and chronic social stress experiments. Usually, male rats are used because they are territorial and often exhibit offensive behavior (resident) when another rat (intruder) is introduced to the cage. Offensive behavior can be defined as, "initiative of the offender and a range of introductory, often threatening, behavioral displays before attempting to reach the back and neck as non-vulnerable targets for the consummatory aggressive attack bites" (Koolhaas 2013). Likewise, the new rat entering the cage will often display defensive behavior. Defensive behavior can be described as any aggressive behavior in response to another individual's attack. Due to territoriality, the resident will attack unfamiliar males intruding in its home cage. Therefore, researchers can study aggressive behavior using the "resident" as the experimental group. To determine the nature or context of the aggression, they can change the type of "intruder" they are using such, as using females, or anesthetized males, or by changing their environment. In retaliation of the resident's aggression or attack, the intruder rat may display defensive behaviors which can be observed and categorized by researchers as well. In this case, the "intruder" is now the experimental group. 

The Procedure is as follows:

1. Cage must be sizeable to ensure complete expression of aggression- floor space should be at least 1/2 square meters.

2. House a male rat with a female for a least a week before the experiment (to increase territoriality).

3. Remove the female companion from the cage at least one hour before the test begins. BUT...

4. Do not clean the bedding of the cage during that initial week or before later testing, since territoriality is strongly based on the presence of olfactory cues. These cues are important for the resident in establishing its territory and for the intruder to know that it is in the home cage of the resident. 

5. Introduce intruder- intruder should be an unaggressive strain of rat/be smaller than the resident. The resident should NOT have had any previous interaction with the resident. 

6. Make sure to record the test! A test duration of 10 min is usually sufficient for the expression of the full offensive behavioral repertoire. For standardization, one may consider recording for ten minutes after the first attack.

7.  Once the test is completed, remove the intruder and add the female companion back in. 

Note: It is best to test only during the dark phase; the rats' main activity phase

Data Collection:

Determine the duration and frequency of either the behavioral patterns you have created or the ones already identified. Categorize these behaviors as aggressive, defensive or indifferent.

 Examples of behaviors:

1. Attack latency: the time between the introduction of the intruder and the first clinch attack

2. Move towards

3. Social exploration

4. Ano-genital sniffing

5. Rearing

6. Lateral threat

7. Upright posture

8. Clinch attack

9. Keep down

10. Chase

11. Non-social explore

12. Rest or inactivity

13. Submission latency

14. Submissive posture

15. Move away

16. Flight

17. Defensive upright posture

18. Freeze

19. Non-social explore

My Thoughts:

 Although this is an effective tactic for categorizing aggressive and defensive behavior, this can be potentially dangerous to both the resident and the intruder. Care needs to be taken to ensure the safety of the rats. 

Article: Article: Koolhaas, J. M., Coppens, C. M., de Boer, S. F., Buwalda, B., Meerlo, P., Timmermans, P. J. A. The Resident-intruder Paradigm: A Standardized Test for Aggression, Violence and Social Stress. <em>J. Vis. Exp.</em> (77), e4367, doi:10.3791/4367 (2013).