Measuring Circadian and Acute Light Responses in Mice using Wheel Running Activity

Summary

This article will review methods that can be used to determine circadian function and light responsiveness in mice.

Abstract

Circadian rhythms are physiological functions that cycle over a period of approximately 24 hours (circadian- circa: approximate and diem: day)^{1, 2}. They are responsible for timing our sleep/wake cycles and hormone secretion. Since this timing is not precisely 24-hours, it is synchronized to the solar day by light input. This is accomplished via photic input from the retina to the suprachiasmatic nucleus (SCN) which serves as the master pacemaker synchronizing peripheral clocks in other regions of the brain and peripheral tissues to the environmental light dark cycle^3-7. The alignment of rhythms to this environmental light dark cycle organizes particular physiological events to the correct temporal niche, which is crucial for survival⁸. For example, mice sleep during the day and are active at night. This ability to consolidate activity to either the light or dark portion of the day is referred to as circadian photoentrainment and requires light input to the circadian clock⁹. Activity of mice at night is robust particularly in the presence of a running wheel. Measuring this behavior is a minimally invasive method that can be used to evaluate the functionality of the circadian system as well as light input to this system. Methods that will covered here are used to examine the circadian clock, light input to this system, as well as the direct influence of light on wheel running behavior.

Protocol

1. Equipment Setup

1. Preparation of animal groups is very important when setting up any behavioral experiment. For wheel running activity, all mice need to be male, age matched, and if possible from sibling matings. Ideally younger mice, approximately 3 months old, are used for wheel running activity.
2. Prior to placing any animals on wheels, the room needs to be completely setup. This includes preparing each cage with 1 wheel, 1 wheel revolution probe, a small amount of mouse bedding in the bottom of each cage and ample food and water for 2 weeks.
3. Room lighting is highly important, when setting up wheel running cages it is i....

Discussion

Circadian rhythms have been measured and recorded in various organisms throughout history. While we have specifically described the method for recording activity rhythms in mice, this technique can be easily modified to measure rhythms in other rodents such as hamsters and rats, which are often used in circadian studies. However, the freerunning period and time to re-entrain in other organisms will vary. For instance, the freerunning period of a hamster in constant darkness is 24.0 hours, while in mice it is less than 24.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
11.5 cm running wheels	Mini Mitter
Vital View Software for Data Acquisition	Mini Mitter
Clock lab for data analysis	Actimetrics