Internal State-Dependent Modulation of Defensive Behavior in Mice

Subjects:

A total of 12 C57BL/6J mice (8–12 weeks old; 7 males and 5 females) were used. Mice were housed under standard laboratory conditions on a 12:12-hour light/dark cycle with ad libitum access to food and water. Subjects were assigned to two groups: Control (n = 6) or Trauma (n = 6). Prior to behavioral testing, mice were handled daily to reduce stress and ensure consistent behavioral performance.

Open Field Test:

Mice were placed in a square open-field arena and allowed to explore freely for 10 minutes. Total ambulation, number of entries into the center zone, and time spent thigmotactic were recorded. The OFT was conducted at baseline and again one week post-trauma to assess changes in anxiety-like behavior following fear conditioning.

Elevated Zero Maze:

Mice were placed on a circular elevated track consisting of two open and two enclosed quadrants for 5 minutes. Time spent in open areas, number of open-area entries, and latency to first open-area entry were recorded. The EZM was conducted at baseline and one week post-trauma to assess trait and post-trauma anxiety levels.

Fear Conditioning Model:

A 4-day paradigm was conducted across two distinct contexts. Context A was a clear, cylindrical plexiglass chamber with a smooth floor. Context B was a square enclosure with an electrical grid floor for foot shock delivery. On Day 1 (habituation), all mice were placed in Context A and received presentations of a serial compound stimulus (SCS) consisting of alternating tone and white noise pips with no shock. On Days 2–3 (conditioning), Trauma mice were placed in Context B and received 5 pairings of SCS followed by footshocks (0.3–0.9 mA, 1 sec); Control mice underwent identical handling in Context B without shock delivery. On Day 4 (recall), all mice were returned to Context B and presented with SCS only (5 trials) to assess fear memory retrieval.

Resident Intruder (RI) Test:

One week following fear conditioning, each subject mouse was tested in its home cage using the resident-intruder paradigm. A naive, weight-matched, same-sex intruder mouse was introduced into the resident's cage for 20 minutes. Sessions were video recorded and manually scored for aggressive behaviors including following, boxing, biting, pinning, and hostile digging, as well as social interaction time.