Simple and Computer-assisted Olfactory Testing for Mice

Summary

We present a simple and unbiased olfactory test in mice. With this protocol olfactory discrimination, preference, avoidance and sensitivity to a novel odor as compared to water can be assessed in single behavioral sessions. This method is indicated for a single experimenter and analysis is based on computer-assisted video processing.

Abstract

Olfaction is highly conserved among species and is required for reproduction and survival.

In humans, olfaction is also one of the senses that is affected with aging and is a strong predictor of neurodegenerative diseases. Thus, olfaction testing is used as a non-invasive diagnostic method to detect neurological deficits early on. In order to understand the mechanisms underlying olfactory network susceptibility, olfactory research in rodents has gained momentum in the past decade.

Here, we present a very simple, time efficient and reproducible olfactory testing method of innate odor perception and sensitivity in mice without the need of any prior food or water restriction. The tests are performed in a familiar environment to the mice, require only the scents and a 2 min session of odorant exposure. The analysis is performed, post-hoc, using computer-assisted commands on ImageJ and can be, therefore, carried out from start to end by one researcher.

This protocol does not require any special hardware or setup and is indicated for any laboratory interested in testing olfactory perception and sensitivity.

Introduction

Olfaction is one of the most developed and important sensory functions in mammals. Any impairment in olfactory activity may affect food intake, social behavior and, in the worst case scenario, even survival. In humans, olfactory deterioration is age dependent¹ and is considered a strong predictor of neurological disorders^2–6. The olfactory identification test developed by the University of Pennsylvania currently represents one of the most used, non-invasive and quantifiable, diagnostic tests which can assess early neurological deficits⁷ and predict with high probability the progression of dementia^8,9

Protocol

All the animal procedures are in accordance with the EU Directive 2010/63/EU on the protection of animals used for scientific purposes and are approved by the local Animal Care Committee (Canton of Fribourg, Switzerland).

1. Animal Preparation

1. Experimental animals
   1. Perform experiments on adult male wild type and transgenic mice (C57BL/6 background) of 3-5 months of age. The three groups of mice correspond to wild type littermate controls (group A, Jagged1 flox/flox¹⁹) and two conditional KO mouse lines (group B, Jagged1ncKO and C, Jagged1gcKO).
   2. House mice under standard laboratory conditions in a....

Results

The perception test measures the attraction to peanut butter and avoidance to 2-MB acid. Three groups of mice are tested and the time spent in the “odor perimeter” are quantified as compared to water. In the preference test, the control group A displays significant preference to the odor as compared to water (t₈ = 2.52, p <0.05). On the other hand, group B does not show any significant attraction to peanut butter and spends more time with water (t₆ = 3.22, p <0.05). Thus, it behaves differentl.......

Discussion

The tests proposed in this protocol allow to evaluate different aspects of innate olfactory behavior in mice: perception to odors, discrimination between odors versus water and sensitivity to odors. This protocol can be applied to any odor according to the preference and avoidance scale previously shown¹⁵. Since the protocol is based on exploratory activity it is important that mice do not display any motor impairment or anxiety which may affect their movement and interfere with olfactory exploration. The test.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Mouse cage	Italplast (Italy)	1144B	36 cm length x 20.5 cm width x 13.5 cm height
Chipped wood bedding	Abedd (Austria)	LTE E-001	3 cm high
Peanut butter	Migros (Switzerland)	NA	1:10
2-Methylbutyric	Sigma Aldrich (Switzerland)	W269514	Pure
Female urine from fertile females of same mouse strain	NA	NA	Dilution series
Camera	Olympus (US)	Camedia C-8080	MOV files
Quicktime for Java (Windows)	Apple (USA)	NA	video plugin for visualizing MOV files
ImageJ for Windows	NIH (USA)	NA	Video Processing/Analysis