Olfactory Behavioral Testing in the Adult Mouse

Summary

Fundamental, yet unique properties of the rodent olfactory system have led to its increasing study among biologists. A relatively simple assessment of its function is then also needed. Here we describe sensitive tests for the characterization of mouse olfactory sensitivity and preference.

Abstract

The rodent olfactory system is of increasing interest to scientists, studied, in part, in systems biology because of its stereotyped, yet accessible circuitry. In addition, this area's unique ability to generate new neurons throughout an organism's lifetime makes it an attractive system for developmental and regenerative biologists alike. Such interest necessitates a means for a quick, yet reliable assessment of olfactory function. Many tests of olfactory ability are complex, variable or not specifically designed for mice. Also, some tests are sensitive to memory deficits as well as defects in olfactory abilities, confounding obtained results.

Here, we describe a simple battery of tests designed to identify defects in olfactory sensitivity and preference. First, an initial general health assessment allows for the identification of animals suitable for further testing. Second, mice are exposed to various dilutions of scents to ascertain whether there is a threshold difference. Third, mice are presented with various scents, both attractive and aversive, that allow for the assessment of olfactory preference. These simple studies should make the initial characterization of olfactory behavior accessible for labs of varied resources and expertise.

Protocol

General Health Exam

A more comprehensive treatment of general health exams can be found in Jacqueline Crawley’s excellent behavioral phenotyping resource, What’s Wrong with my Mouse? ¹. We first use a modified observational test battery to assess the general health of the subject. The battery includes items from Samuel Irwin’s comprehensive assessment protocol² to quickly identify those subjects that will be unsuitable for further testing. In brief, the modified battery identifies animals that are physically abnormal (eg. severely under- or over-weight, poorly groomed, dyspneic) or that exhibit abnormal postu....

Discussion

The aforementioned tests allow for the quick and reliable assessment of basic olfactory function. It is not to be overlooked, however, that this reliability requires the proper selection and preparation of subjects for testing. Animals that are ill or otherwise incapacitated are often inconsistent test subjects. Also, habituation of the test subjects is key. We have found that the use of multiple cages during the habituation process allows the animals to become comfortable with experimenter handling and changing surr.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
2-Methylbutyric acid	Reagent	Sigma-Aldrich	W269506	Concentrations Used:9.16 x 10-1 – 10-8 M (in H20)
Pure Vanilla Extract	Reagent	McCormick & Co.	n/a	Concentrations Used:10-1 – 10-5 dilution (in H20)
Peanut Butter (Skippy, Extra Crunchy)	Reagent	Unilever	n/a	Concentrations Used:10% (w/v), in mineral oil
Cinnamon Extract	Reagent	McCormick & Co.	n/a	Concentrations Used:10-1 – 10-5 dilution (in H20)
Mineral Oil, light	Reagent	Fisher Scientific	O121-1	Concentrations Used:N/A