Measuring Behavior 2005: Jacquot and Little

Of the object recognition in mice and the importance of the object characteristics

C. Jacquot and H.J. Little

DDepartment of Basic Medical Sciences: Pharmacology, St George’s Hospital Medical School, University of London, London, UK

The Object Recognition test is a behavioral test widely used to assess memory in rodents. It is based on the tendency of rodents to explore novel objects. It is divided in 3 parts:

Habituation to the arena.
A sample phase where the experimental animal is placed in an arena with 2 identical objects.
After a certain delay, the choice phase, where the animal is exposed to one of the objects used during the acquisition phase plus a novel one.

A normal animal would spend more time during the choice phase exploring the novel object than the familiar one. An absence of any difference in the exploration of the 2 objects during the choice phase is interpreted as a memory deficit.

During the use of this test, we realised that slight changes to the methodology could make considerable differences to the results and, consequently, could lead to misinterpretation. In order to provide a reliable test and to decrease the variability we observed in our results, we asked the following questions:

Is the exploration time greater with small or large objects?
How does the shape of an object influence the exploration?
Do the presence of an object during the habituation to the arena or handling the animals before the test increase the overall exploration of the objects?

The importance of these parameters is difficult to assess when reading the literature. Our results highlighted that adding an object during the habituation phase will increase the exploration of the objects. The object choice is another important factor in the methodology of this test: animals will longer explore larger objects rather than smaller ones and complex shape objects are more ‘attractive’ to mice, which could represent a bias in the results. This presentation provides information on the importance of these parameters that will aid test design and reliability for use in mice.

Paper presented at Measuring Behavior 2005 , 5^th International Conference on Methods and Techniques in Behavioral Research, 30 August - 2 September 2005, Wageningen, The Netherlands.