Omission of the habituation procedure in the acquisition of a working memory task - evidence from Balb/c, C57/BL6J, and CD-1 mice.

Training animals in spatial mazes have always been preceded by prior habituation to the test apparatus and testing conditions with the main goal to reduce fear and anxiety from exposure to the unfamiliar maze environment. This approach makes assumptions about the baseline level of emotionality in animals without actual objective measurements. It also ignores that genetic factors and experimental manipulations can reduce or prolong fear and anxiety from novelty, hence affecting the acquisition of a memory task. In the present study, C57, CD-1 and Balb/c mice were introduced to a working memory task in a radial-arm maze without habituation. Fear-induced anxiety from exposure to the novelty in this maze is demonstrated by a very low number of arm entries. Animals have to climb onto a bridge in order to reach an arm of the maze. In the first session block, Bab/c mice made very few arm entries and made more arm repeats than CD-1 and C57 mice, and CD-1 made few arm entries and made more arm repeats than C57/BL6J mice. In the second session block, all three strains of mice did make 8 arm entries. Balb/c mice seem to perform better than C57 and CD-1 mice as shown by a low number of arm repeats in the second session block, a high number of correct choices before first errors in the third session block, and low number of errors and sessions to criterion. In the present case, a high baseline level of emotionality did not prevent Balb/c mice to perform better than C57 and CD-1 mice.