Intensity and precision of circadian wheel running in three outbred rat strains

The laboratory rat is widely used in many areas of neurobiologic and behavioral research. However, studies of circadian activity rhythms have usually employed other rodent species whose activity patterns are more amenable to measurement in the circadian paradigm. Nevertheless, the rat may be the optimal choice in certain investigations of circadian function because of the wealth of data on the neuroanatomy and neuropharmacology of this species. This study was undertaken to determine whether choice of rat strain could affect the quality of measured circadian activity data. Intensity of wheel running (wheel revolutions per day), precision of onset, and longevity of consistently interpretable running records were assessed in three common outbred rat stains, Long-Evans, Wistar, and Sprague-Dawley. Long-Evans rats showed greater intensity of wheel running while entrained and at four and eight weeks of free running in constant darkness. There was no difference in precision of running onset among the three strains. Thus, use of the Long-Evans strain, with its greater intensity of wheel running and similar precision of activity onset, may confer advantages in studies involving measurement of circadian activity rhythms in the rat.