Effects of beta-blockade on atrial and atrioventricular nodal refractoriness, and atrial fibrillatory rate during atrial fibrillation in pigs.

Despite their widespread use in atrial fibrillation, the effects of beta-adrenoceptor blockers on atrial and atrioventricular (AV) nodal refractoriness, and atrial fibrillatory rate during atrial fibrillation have been incompletely characterised. In particular, it is unknown whether additional sodium channel (class I) blocking effects play a role. Effects of bisoprolol (no class I effect) and metoprolol (mild class I effect) were therefore compared in 12 open-chest pigs.

An on-line automated sleep-wake classification system for laboratory animals.

A computerized sleep-wake classification program is presented that is capable of classifying sleep-wake states on-line in four animals simultaneously. Every 10 s the classification algorithm assigns sleep-wake states on the basis of the power spectrum of an EEG signal and the standard deviation of an EMG signal. The system was developed specifically for long-term circadian rhythm experiments and can run uninterrupted for an unlimited period of time.

The effect of old age on the free-running period of circadian rhythms in rat.

The free-running period is regarded to be an exclusive feature of the endogenous circadian clock. Changes during aging in the free-running period may therefore reflect age-related changes in the internal organization of this clock. However, the literature on alterations in the free-running period in aging is not unequivocal.

Effects of a novel melatonin analog on circadian rhythms of body temperature and activity in young, middle-aged, and old rats.

Circadian rhythms of body temperature and activity were recorded in young, middle-aged, and old rats. A new melatonin analog, S20242, was administered daily around the onset of darkness for a 2-week period. Compared to the young animals, there was a significant age-related reduction in the amplitude and stability of body temperature and activity in both the middle-aged and old rats.

Effect of light intensity on diurnal sleep-wake distribution in young and old rats.

During the aging process, the amplitude of the circadian rhythms of many physiological variables is reduced. It has been hypothesized that increasing light intensity during the light phase of the light-dark cycle might result in a reduction of age-related changes in the circadian rhythms. Indeed, in the present sleep-wake study in young and old rats it was found that (a) various parameters, such as the light-dark differences and total amounts of each behavioral state responded positively to changes in environmental light intensity (i.