Behavioral profile of wild mice in the elevated plus-maze test for anxiety

Systematic observations of the defensive behavior of wild rodents have grea tly informed the experimental study of anxiety and its neural substrates in laboratory animals. However, as the former work has been almost exclusivel y carried out in rats, few data are available concerning the reactivity of wild mice to standardized tests of anxiety-related behavior. In the present experiments, we employed ethological measures to examine the behavioral re sponses of a wild-derived population of house mice (Mus musculus) in the el evated plus-maze. Ln direct comparisons with laboratory Swiss mice, male wi ld mice exhibited substantially elevated levels of exploratory activities a nd an overall "preference" for the open arms of the plus-maze. On re-exposu re to the plus-maze, male wild mice showed further increases in open arm ex ploration, while Swiss mice showed a marked shift to the enclosed parts of the plus-maze. Tested over a single session, female wild mice also exhibite d a profile of high open arm exploration, but showed levels of exploratory behaviors and locomotor activity similar to female Swiss counterparts. Whil e exploratory patterns in wild mice show similarities to profiles seen in c ertain laboratory strains (e.g., BALB/c), wild mice displayed a number of a dditional behaviors that are unprecedented in plus-maze studies with labora tory mice. These included actual and attempted jumps from the maze, spontan eous freezing, and exploration of the upper ledges of the closed arms. Thus , while in conventional terms the behavior of wild mice was consistent with one of low anxiety-like behavior, the presence of these unique elements in stead indicates a profile more accurately characterized by high reactivity and escape motivation. We discuss how the use of an ethological approach to measuring plus-maze behavior can support accurate interpretation of other exceptional profiles in this test, such as those possibly arising from phen otyping of transgenic and gene knockout mice. (C) 2000 Elsevier Science Inc . All rights reserved.