Variation in nocturnality and circadian activity rhythms between photoresponsive F344 and nonphotoresponsive Sprague Dawley rats

Abstract

Background: Variation in circadian rhythms and nocturnality may, hypothetically, be related to or independent of genetic variation in photoperiodic mediation of seasonal changes in physiology and behavior. We hypothesized that strain variation in photoperiodism between photoperiodic F344 rats and nonphotoperiodic Harlan Sprague Dawley (HSD) rats might be caused by underlying variation in clock function. We predicted that HSD rats would have more activity during the day or subjective day, longer free-running rhythms, poor entrainment to short day length, and shorter duration of activity, traits that have been associated with nonphotoperiodism in other laboratory rodent species, relative to F344 rats. An alternative hypothesis, that differences are due to variation in melatonin secretion or responses to melatonin, predicts either no such differences or inconsistent combinations of differences.

Photoperiodic Effects on Seasonal Physiology, Reproductive Status and Hypothalamic Gene Expression in Young Male F344 Rats

“…F344 rats are increasingly used as a model for studying photoresponsiveness ( 17 , 23 – 25 ), although more information is required on the consequences of photoperiodic history and the responses of this strain to changing photoperiod to be able to compare the results with those obtained from other well-studied photoperiodic species. We aimed to design the present study to reflect the experimental design of a typical photoperiodic study (i.e.…”

“…validated qPCR primers as used in the present study) than other photoperiodic species, the use of rats simplifies both the experimental design and the laboratory work. In addition, one strong advantage to using F344 rats as an experimental model of photoperiodism is that they provide a good system for comparing the results with nonseasonal rodents, as seen in recent studies on the hypothalamic-pituitary-adrenal axis ( 24 ) and circadian rhythms ( 23 ), as well as on food selection and the mechanisms underlying energy metabolism ( 45 ).…”

Orexin Neurons Are Necessary for the Circadian Control of REM Sleep

“…Thus to measure the amplitudes of circadian rhythms of sleep/ wakefulness, we used the circadian index (CI) and the nocturnality ratio. 30,31 The CIs of Wake, NREM sleep, REM sleep, LMA and T b were calculated from the following formula: CI = (mean night -mean day )/mean 24hr , where mean day is the average over the subjective day, mean night is the average over the subjective night, and mean 24hr is the average over the entire day. 12,13 CIs are plotted as positive values in which low values indicate little circadian variation.…”