Two-Way Choice Test for Social Odors in Mice

Abstract

This exercise and the next both deal with scent communication in mice. We practice two techniques frequently used in the Animal Behavior laboratory: In this first experiment, we test a mammal’s response to conspecific odors in a two-way choice apparatus, also called a Y- or T-maze, an often used bioassay device. [In the following experiment (Chap. 21), we observe and quantify scent marking behavior in response to two different stimuli in an “open field.”]

House mice (Mus musculus or M. domesticus) provide a good model of scent marking in mammals in general. They live in demes, large groups of related individuals. As in many other social mammals, mice mark their territories and home ranges with urine. Both sexes excrete in their urine signaling and priming pheromones that carry a great variety of information. To test what kinds of olfactory signals mice of certain age, sex, and status categories are able to discriminate, we can employ a two-way choice test. In the following, we survey some of the olfactory signals that play important roles in the life of a house mouse.

Urine marks signal individuals’ group sex, maturity, group membership, and dominance in an area. In addition, mouse urine also contains important chemical signals that regulate sexual behavior. Some of these signals strongly depend on genetic dispositions. For instance, the Major Histocompatibility Complex codes for signals that affect mate choice: mice choose mates with nonparental urine odors (Yamazaki and Beauchamp 2007). Further, urinary odors vary with hormonal status. Even intrauterine hormonal stimulation of mouse embryos, such as by neighboring male sibling embryos, can androgenize females and change their urinary odors in turn (Vom Saal and Bronson 1980; Vom Saal 1989; Drickamer 2001a, b; Ryan and Vondanbergh 2002).