Sleep and serotonin in two strains of Mus musculus

Ultradian rhythms in young and adult mice: further support for the basic rest-activity cycle

Basic Rest-Activity Cycle (BRAC) rhythmicity has been shown in many parameters in animals as well as in humans. A similarity between the periods of BRAC and REM/NREM cycles has been frequently reported. However, this does not necessarily prove the idea that BRAC is a diurnal extension of the REM/NREM cycle. A concurrent variation of the BRAC and REM/NREM cycles during ontogenetic development would confirm the link between these rhythms. For this purpose, we investigated the existence of a BRAC periodicity in young (23 days of life) and adult (90 days of life) mice, in comparison with the REM/NREM species-specific cycle. Reaction times of the avoidance response to a visual warning stimulus that preceded an electric shock were measured by a computer-controlled shuttle-box. Results revealed the existence of an evident ultradian rhythm in all subjects confirming previous reports of a 20-min BRAC in avoidance behavior of adult mice. Furthermore, young mice showed a shorter periodicity of about 9 min, which is analogous to their 10-min REM/NREM cycle. These results seem to confirm the hypothesis of a strong relationship between BRAC and REM/NREM sleep cycle.

Sleep and sleep regulation in normal and prion protein-deficient mice

Mice are the preferred mammalian species for genetic investigations of the role of proteins. The normal function of the prion protein (PrP) is unknown, although it plays a major role in the prion diseases, including fatal familial insomnia. We investigated its role in sleep and sleep regulation by comparing baseline recordings and the effects of sleep deprivation in PrP knockout mice (129/SV) and wild-type controls (129/SV x C57BL/6), which are the mice used for most gene targeting experiments and whose behavior is not well characterized. Although no difference was evident in the amount of vigilance states, the null mice exhibited a larger degree of sleep fragmentation than the wild-type with almost double the amount of short waking episodes. As in other rodents, cortical temperature closely reflected the time course of waking. The increase of slow-wave activity (SWA; mean EEG power density in the 0.25-4.0 Hz range) at waking to nonrapid eye movement (NREM) sleep transitions was faster and reached a lower level in the null mice than in the wild-type. The contribution of the lower frequencies (0.25-5.0 Hz) to the spectrum was smaller than in other rodents in all three vigilance states, and the distinction between NREM sleep and REM sleep was most marked in the theta band. After the sleep deprivation, SWA was increased, but the changes in EEG power density and SWA were more prominent and lasted longer in the PrP-null mice. Our results suggest that PrP plays a role in promoting sleep continuity.

Ultradian rhythms in avoidance behavior of DBA mice

This study investigates ultradian rhythm in avoidance behavior of mice, which may constitute a basic rest activity cycle (BRAC). Reaction times (RTs) of an avoidance response to a visual warning stimulus that preceded an electric shock were measured by the use of a computer-controlled shuttle box. The male naive DBA mice were brought to a criterion of 98% correct responses in numerous training sessions. For each subject, all the temporal sequences of the RTs in the trials following achievement of the criterion were examined with discrete Fourier transform. Periodograms were obtained from three sessions for each of the two animals in the first experiment and from 15 subjects in the second experiment. Analysis of the periodograms reveals a stable rhythm in avoidance behavior of mice, with a period of about 14 min. The presence of these periodicities could show the existence, also in small rodents, of a BRAC rhythm.

An overview of neurobiological comparisons in mouse strains

A literature review of research dealing with mouse strain comparisons along neurobiological parameters is presented in tabular form which provides a rank-ordering of strains and estimates of percentage differences in individual parameters. Drawing from 86 references, three tables deal respectively, with comparisons of neurochemical, neuroanatomical, and neuropsychophysiological parameters.

Wheel running sleep in two strains of mice: plasticity and rigidity in the expression of circadian rhythmicity

The effects of 12--12 h, 6--6 h, 3--3 h and 1--1 h light--dark (L-D) cycles and of constant light (L--L) on wheel-running activity and electrograhically defined sleep were studied in two strains of mice, C57BL/6 and SEC/1Re. Wheel-running activity was inhibited by light and enhanced by darkness; however, in the C57 strain the L-D-induced changes were less pronounced and superimposed to a clear circadian rhythm. Under the L-L schedule clear patterns of daily rhythmicity were evident in the C57 strain but not in the SEC strain. Sleep was enhanced by light and inhibited by darkness. The L-D-induced changes of sleep were superimposed on the circadian rhythm in both strains; however, in the C57 strain these changes were larger in the circadian phase in which the animals were active. Under the L-L-schedule the C57 strain was characterized by more clear-cut patterns of daily rhythmicity than SEC mice. These phenomena are discussed in terms of plasticity of free-running rhythms of sleep and activity and of the genetic factors involved in the expression of circadian rhythmicity.

Sleep and activity rhythms in mice: a description of circadian patterns and unexpected disruptions in sleep

Studies on daily and circadian rhythms in wheel running and electrographically defined wakefulness, NREM sleep, and REM sleep in M. musculus were done to gather data on the temporal distribution of activity and sleep. Generally, peaks in NREM and sleep tended to coincide and to alternate with the coincident peaks of wakefulness and wheel running. However, during the active phase of the circadian wheel running cycle some NREM and REM sleep did occur; conversely, during its rest phase, wakefulness was often present. The most striking finding was that in mice with clearly entrained or free-running activity onsets, the circadian peak-through patterns in wakefulness, NREM, and REM sleep were not always distinct--they could be damped and/or polyphasic. Several explanations of these phenomena are considered.