Daily rhythm of locomotor activity is abolished during rapid eye movement sleep deprivation in the rat

Circadian rhythms and depression: human psychopathology and animal models

Most organisms (including humans) developed daily rhythms in almost every aspect of their body. It is not surprising that rhythms are also related to affect in health and disease. In the present review we present data that demonstrate the evidence for significant interactions between circadian rhythms and affect from both human studies and animal models research. A number of lines of evidence obtained from human and from animal models research clearly demonstrate relationships between depression and circadian rhythms including (1) daily patterns of depression; (2) seasonal affective disorder; (3) connections between circadian clock genes and depression; (4) relationship between sleep disorders and depression; (5) the antidepressant effect of sleep deprivation; (6) the antidepressant effect of bright light exposure; and (7) the effects of antidepressant drugs on sleep and circadian rhythms. The integration of data suggests that the relationships between the circadian system and depression are well established but the underlying biology of the interactions is far from being understood. We suggest that an important factor hindering research into the underlying mechanisms is the lack of good animal models and we propose that additional efforts in that area should be made. One step in that direction could be the attempt to develop models utilizing diurnal animals which might have a better homology to humans with regard to their circadian rhythms. This article is part of a Special Issue entitled 'Anxiety and Depression'.

Environmental lighting has a selective influence on ethanol intake in rats

The effect of lighting condition on levels of absolute ethanol intake were systematically examined in the present study. Wistar rats were exposed to one of three lighting conditions: constant light, constant dark, and a standard 12/12 light/dark cycle. The animals were acclimatized to lighting conditions for 2 weeks prior to ethanol (EtOH) acquisition with water and food available ad lib. EtOH was then presented in increasing concentrations from 2% (v/v; 95% with tap water) to 10% on alternate days in free choice with water. Immediately following the acquisition phase, a maintenance period was initiated that began with everyday presentations of 10% EtOH solution in free choice with water. After 10 days, lighting conditions for the constant light and dark groups were switched to normal lighting (12/12 light/ dark). EtOH and water intake were recorded for an additional 10 days. Rats exposed to constant light during EtOH acquisition and maintenance consumed less EtOH during the maintenance period than rats exposed to normal lighting conditions. When lighting conditions were switched to a normal cycle, water consumption increased significantly but EtOH intake did not change. Rats living in constant dark during EtOH acquisition and maintenance consumed less EtOH during the acquisition period when compared with rats living in normal lighting conditions. Unlike animals trained under constant lighting, switching to normal lighting conditions had no effect on EtOH or water intake. There were no differences in water consumption levels among the groups during acquisition and maintenance, suggesting a specificity of the effects of lighting condition on EtOH intake. The present study, therefore, has attempted to show that an environmental variable such as lighting may exert a selective influence on EtOH self-selection in rats.

Magnetic fields mimic the behavioral effects of REM sleep deprivation in humans

The discovery of rapid eye movement (REM) sleep by Aserinsky and Kleitman in 1953 initiated the impetus for sleep research and specifically the investigations of the effects of REM sleep deprivation (RSD) on animal and human behavior. The behavioral effects of RSD include the enhancement of motivational and "drive"-related behaviors. In laboratory animals, RSD has been reported to increase appetite, sexual behavior, aggressiveness, and locomotor activity. Moreover, RSD reportedly improves mood in patients with endogenous depression and heightens appetite and sexual interest in normal subjects. Since "drive"-related behaviors are thought to involve activation of limbic dopaminergic reward sites, RSD may enhance motivational behaviors through an action on limbic dopaminergic functions. In the present communication, we present two patients (one with multiple sclerosis and the other with Parkinson's disease) in whom treatment with magnetic fields produced behavioral effects which paralleled those observed in REM-sleep-deprived animals and humans. We propose, therefore, that the behavioral and mental effects of treatment with magnetic fields may be mediated via RSD and, by inference, involve activation of limbic dopaminergic reward sites.

Continuous recording of locomotor activity in groups of rats: postweaning maturation

A method was developed for continuous recording of locomotor activity in ten groups of rats housed in standard plastic cages under controlled lighting conditions. An inexpensive pressure transducer detected movements in the cage, and a light resistor monitored the lighting. The output voltages from the sensors were digitized, integrated for 5 s, and stored for off-line analysis. The data from separate cages were averaged for the detection of statistical differences between the experimental groups. The method was applied to study maturational changes after weaning. Wistar rats were recorded from 21 to 62 days of age under 12/12 h light/dark cycle. The cumulative activity distributions of the pups of 4 and 5 weeks of age differed significantly from those of 7-9 weeks, or older. Differences between the rats aged 8 or 9 weeks and the older adults were less consistent, but still detectable. The cumulative activity distributions of the males and females did not differ significantly from each other.

Facilitation of shuttle-box avoidance by the platform method: temporal effects

Two experiments were carried out in order to 1) replicate a previous finding according to which the treatment on large platforms (commonly used as control for the stress induced by smaller paradoxical sleep deprivation platforms) can facilitate the acquisition and long-term retention (LTR) of a distributed shuttle-box avoidance in rats, and 2) further examine the temporal conditions in which that facilitation can be observed. The results showed that an immediate posttraining treatment lasting 6 hours induced a significant improvement of acquisition both when applied in the light (8 a.m.) and in the dark cycle (8 p.m.), while the LTR (10 and 31 days) seemed to be better preserved when the treatment was applied during the dark cycle. A shorter treatment (3 h) had no effect upon shuttle-box avoidance, regardless of whether it was applied in the dark or in the light cycle and whether it was immediate or delayed for 3 h. In summary, under certain temporal conditions, a posttraining immediate treatment on large platforms can facilitate the acquisition and/or the LTR of shuttle-box avoidance. Stress hormones and/or the enhancement of CNS arousal are suggested to be some of the mechanisms operating in this facilitatory effect.

Effects of partial food restriction on nocturnal meal size and feeding speed are counteracted by concurrent REM sleep deprivation in the rat

Effects of rapid eye movement (REM) sleep deprivation on meal size and feeding speed were investigated by means of the cuff pedestal technique in 9 male rats exposed to partial food restriction. Reduction of available food by 50% alone, when accomplished by providing the pellets at the beginning of each dark period, during 7 consecutive days, induced a quite linear increase both in the meal size and feeding speed. When the same feeding schedule was repeated in combination with REM sleep deprivation, the meal size remained smaller and the feeding time was prolonged (during the first 3-4 days) when compared to those during food restriction alone, although losses of body weight were almost doubled. These findings are in agreement with the effects of REM sleep deprivation on the meal pattern in rats on ad libitum diet and provide further support for the suggestion of the importance of REM sleep in the generation of the light/dark rhythm of feeding in the rat.

Decision-making to initiate voluntary movements in the rat is altered during deprivation of rapid eye movement sleep

Eight male rats were deprived of rapid eye movement (REM) sleep for 6 days by means of a cuff pedestal which makes it possible to use the animal as its own control. In order to obtain access to food, the rat had to jump from its pedestal to a strip of wire mesh suspended from the ceiling of the deprivation chamber. The number as well as duration of hangings on the wire mesh was continuously recorded. An initial increase in jumping frequency was associated with decreased duration of hangings. This initial effect was totally reversed from the fourth day of deprivation onwards. It is suggested that the threshold in decision making to initiate voluntary movement is altered during the course of REM sleep deprivation.

Effects of rapid eye movement sleep deprivation on regional brain metabolism as measured by 2-[14C]deoxyglucose autoradiography

Regional brain metabolic activity of six male Sprague-Dawley rats was investigated with 2-[14C]deoxyglucose autoradiography. Regional brain metabolic activity was determined bilaterally for 60 brain structures, using laser densitometry. After 5 days of uninterrupted rapid eye movement sleep deprivation, increased metabolic activity was found in the lateral habenula, the caudal and middle parts of the limbic system, and in the corpus callosum.

Circadian rhythms of water and alcohol intake: effect of REM-sleep deprivation and lesion of the suprachiasmatic nucleus

The recently discovered increase in alcohol drinking produced by a 7 day period of rapid eye movement (REM)-sleep deprivation with a modified flowerpot technique and the subsequent decrease during REM-rebound were now examined through continual monitoring of drinking with a computer attached to drinkometers. REM-sleep deprivation abolished the circadian rhythms of both alcohol and water intake. The circadian rhythm of water drinking returned during the first post-deprivation day but alcohol drinking was almost eliminated during the first 18 hr and there was no circadian rhythm to the alcohol drinking on the following 3 days. In an additional study, the circadian rhythms of both water and alcohol intake were abolished by electrolytic lesioning of the suprachiasmatic nuclei. The lesion did not, however, alter the mean level of alcohol drinking. Thus the abolition of circadian rhythms is not sufficient for increasing alcohol consumption and the increase produced during REM-sleep deprivation appears to be mediated by other mechanisms.

The consolidation hypothesis for REM sleep function: stress and other confounding factors--a review

One commonly held hypothesis about the function of REM sleep (RS) concerns the consolidation of plastic processes, particularly those relating to learning and memory. The majority of the experimental data apparently supporting this hypothesis come from RS deprivation (RSD) studies. However, this review points out that: (i) there are several shortcomings with the methodology of animal RSD investigations, (ii) RSD seems to produce arousal and stereotyped behaviour which may interfere with learning etc., and consequently give artificial support to the hypothesis. The review then examines evidence outside the field of RSD, relating to the hypothesis, which seems further to confound or contradict it. Whilst the hypothesis is not rejected, these problems need to be addressed further by its supporters.

Loss of eye movements abolishes light entrainment of circadian mesolimbic catecholamine excitability: a function for REM?

Light entrainment of the circadian rhythm of mesolimbic dopamine excitability, measured by the amphetamine-induced locomotor response, and the circadian feeding rhythm was abolished following section of the extraocular muscles of the rat. Endogenous (free-running) circadian rhythms were preserved. The results are consistent with electrophysiologic evidence that the rapid eye movements during paradoxical sleep transmit light-modulated electrical potentials to regions of the brain that influence circadian rhythms and dopamine release.