Wahlsten2 project protocol

Wildness in 21 inbred strains of mice assessed through a rating scale   (2003)

Wahlsten D, Crabbe JC, Metten P
With: Bryden C, Moisan B, Cooper SF, Schlumbohm J, Yu C-H

Rating scales for wildness and ease of handling and its application to 21 inbred strains are published in Wahlsten et al., 2003. The behavior tests that were performed are summarized in Table 1. The wildness rating scales are summarized in Table 2.

This study was conducted on the same set of mice that were tested for several behavioral parameters and examined for brain defects (Wahlsten1).

Virtually every procedure or test requires capture of the mouse, brief holding, then recapture for return to its cage. For example, one trial in the water maze requires capture of the mouse, picking it up and placing in the water, then capture and picking up for return to the cage at the end of the trial. Thus, one trial involves two episodes of capture and two of holding.

Ratings were developed (see Table 2) for these situations when handling mice:

    1. Capture - when the mouse is grabbed by the tail and picked up; this applies equally to use of a human hand and forceps

    2. Hold - when the mouse is lifted from the substrate and placed in a new location while holding it by the tail; occurs when changing cages, marking the tail, weighing, and testing in many kinds of apparatus; also while holding for injection with a hypodermic needle.

Wildness was rated only once per trial for capture and once per trial for handling. By convention, the worst behavior score on the trial was assigned. For example, if the mouse is easy to capture and handle at the start of the trial but then it jumps onto the floor and runs around the room during recapture, the capture score for that trial would be 6 (the worst score; see Table 2). Injection with a needle usually involves one capture, then one handling, followed by return to the cage, but a mouse may escape during the handling while being injected. If its capture rating is 2 on initial capture but then it escapes during injection and runs around the table, the capture score for that trial would be 4 (see Table 2). For a session involving more than one trial of a single kind, the worst score attained on all trials was assigned (See Table 1 for number of trials per test).

Table 1. Behavioral tests used for rating wildness

1open field112
2elevated plus maze212
4rotorod2411during saline injection (i.p.)
5rotorod343+373 trials before and 3 trials after saline
6rotorod4511during ethanol injection (i.p.)
7rotorod553+373 trials before and 3 trials after ethanol
8water escape1836pretraining
9water escape2948
10water escape31048
11water escape41148
12water escape51248
14weighing21512after free feeding over weekend
15weighing31612after 24 h food deprivation

Table 2. Rating scales for mouse wildness

Each scale yields a single integer rating. The scale is ordinal; differences between adjacent values may not be of equal size throughout the range.

Capture - from the home cage, the testing cage, or a test apparatus

Score  Behavior       Frequency  Comments
-----  ------------   ---------  ------------------------------
  0    Minimal        4766      
       resistance to
  1    Evades touch   542       Must complete at least one
       by running               circuit of cage, going end to
       around cage              end twice or following along the
                                full perimeter
  2    Jumps onto     191       While being pursued; does not
       wall of cage             apply to cagemates awaiting
                                their turn; mouse is often
                                captured by the tail, once on
                                the wall
  3    Jumps out of   60        Either large jump from cage
       cage                     floor or short hop down from
       completely               wall; often is captured after
       onto table               landing on table
  4    Runs from      36        With or without experimenter in
       vicinity of              pursuit
  5    Jumps off      48        Usually while being pursued, but
       table or                 could happen with one large jump
       apparatus                from the cage floor; often
       onto floor               captured soon after landing
  6    Runs around    107       Need not complete a full
       room                     circuit; anything requiring
                                active pursuit to recapture

Holding - when being picked up and then placed on a different substrate or held for injection
Score  Behavior       Frequency  Comments
-----  ----------    ----------  ----------------------------
  0    Minor          4527      
  1    Squeaks or     777       Must be clearly audible
  2    Vigorous       341       May attempt to pull away or
       struggle or              climb up tail; can occur without
       twisting/shak            any squeak being heard
  3    Attempts to    51        Jaws open near hand or forceps
  4    Bites          52        Teeth make contact with glove or
       experimenter             skin or forceps; need not
                                penetrate or draw blood
Notes: Frequencies are based on 392 mice from 21 inbred strains on 15 tests (Table 1). Some mice did not complete all 15 tests but no trial was terminated because of excess wildness.

Investigator Notes

We have found that it is too time consuming and distracting to rate wildness on every trial during a session, so we made note of mice that performed badly on several trials. If, however, one does a study mainly aimed at rating wildness, then a separate rating could be made for each trial.

It is common practice in many tests to first capture and then hold the mouse by the tail, so one may add the two scales. In this application, a score of 0 will certainly indicate a docile or placid animal and a 10 will denote one that escaped capture and ran around the room, then bit the experimenter when it was finally captured. A score of 5, on the other hand, could arise from extreme difficulties with either capture or handling, or from mild difficulties with both. Consequently, if a total score is calculated, it is important to record Capture and Hold separately, too.