Recording and Analysis of Circadian Rhythms in Running-wheel Activity in Rodents

Summary

Circadian rhythms in voluntary wheel-running activity in mammals are tightly coupled to the molecular oscillations of a master clock in the brain. As such, these daily rhythms in behavior can be used to study the influence of genetic, pharmacological, and environmental factors on the functioning of this circadian clock.

Abstract

When rodents have free access to a running wheel in their home cage, voluntary use of this wheel will depend on the time of day^1-5. Nocturnal rodents, including rats, hamsters, and mice, are active during the night and relatively inactive during the day. Many other behavioral and physiological measures also exhibit daily rhythms, but in rodents, running-wheel activity serves as a particularly reliable and convenient measure of the output of the master circadian clock, the suprachiasmatic nucleus (SCN) of the hypothalamus. In general, through a process called entrainment, the daily pattern of running-wheel activity will naturally align with the environmental light-dark cycle (LD cycle; e.g. 12 hr-light:12 hr-dark). However circadian rhythms are endogenously generated patterns in behavior that exhibit a ~24 hr period, and persist in constant darkness. Thus, in the absence of an LD cycle, the recording and analysis of running-wheel activity can be used to determine the subjective time-of-day. Because these rhythms are directed by the circadian clock the subjective time-of-day is referred to as the circadian time (CT). In contrast, when an LD cycle is present, the time-of-day that is determined by the environmental LD cycle is called the zeitgeber time (ZT).

Although circadian rhythms in running-wheel activity are typically linked to the SCN clock^6-8, circadian oscillators in many other regions of the brain and body^9-14 could also be involved in the regulation of daily activity rhythms. For instance, daily rhythms in food-anticipatory activity do not require the SCN^15,16 and instead, are correlated with changes in the activity of extra-SCN oscillators^17-20. Thus, running-wheel activity recordings can provide important behavioral information not only about the output of the master SCN clock, but also on the activity of extra-SCN oscillators. Below we describe the equipment and methods used to record, analyze and display circadian locomotor activity rhythms in laboratory rodents.

Protocol

1. Animal Housing

1. Cage: In order to record the running-wheel activity of an individual rodent, each cage should house a single rodent and running-wheel. Because running wheels can be considered a form of enrichment, all rodents in any study should have similar access to a running wheel.
2. Bedding changes: Animal handling as well as changes in cages or bedding can all have non-photic effects on circadian rhythms^21-23, so, cages with mesh-flooring are ideal because they minimize contact with the animal. Notwithstanding the availability of such a tray-system, bedding changes should be avoided during crit....

Results

1. Computer programs: Specialized computer programs are typically used in the generation of actograms and the calculation of circadian period. These programs include, but are not limited to, Actiview (Minimitter, Bend, OR) and Circadia.
2. Actograms: Actograms provide a graphic illustration of the daily patterns of running-wheel activity. There are single-plotted (x-axis = 24 hr) and double-plotted (x-axis = 48 hr) actograms. Both methods plot sequential days from top to bottom, but double-plott.......

Discussion

Monitoring daily activity rhythms using running wheels is the most commonly used and reliable method for assessing the output of the master circadian clock in nocturnal rodents. Wheel-running activity, however, is only one of many aspects of behavior and physiology that can be monitored continuously. Although the vast majority of running-wheel activity occurs during the night, over 30% of the total wakefulness occurs during the daytime^25,26. Other endpoints can be used to assess circadian rhythms, including ge.......

Materials

List of materials used in this article

Name	Company	Catalog Number	Comments
Vitalview Card & Software	Mini Mitter	#855-0030-00	(Bend, OR, USA)
DP24 Dataport	Mini Mitter	#840-0024-00	(Bend, OR, USA)
QA4-Module	Mini Mitter	#130-0050-00	(Bend, OR, USA)
Magnetic Switch	Mini Mitter	#130-0015-00	(Bend, OR, USA)
C-50 Cable assembly	Mini Mitter	#060-0045-10	(Bend, OR, USA)
Rat running wheel assembly	Mini Mitter	#640-0700-00	(Bend, OR, USA)
Cage and tray support	Mini Mitter	#640-0400-00	(Bend, OR, USA)
Useable cut away cage	Mini Mitter	#664-2154-00	(Bend, OR, USA)
Grid floor for cage	Mini Mitter	#676-2154-00	(Bend, OR, USA)
Waste tray	Mini Mitter	#684-2154-00	(Bend, OR, USA)
Lamp housing	Microlites Scientific	#R-101	(Toronto, ON, Canada)
4W Fluorescent lamps	Microlites Scientific	#F4T5/CW	(Toronto, ON, Canada)
Isolation chambers	Custom built		28"H x 20"W x 28"D ½" Black Melamine.