Z.J.M. Van Hulzen

Paradoxical sleep deprivation and locomotor activity in rats

Abstract Wistar rats were tested for activity immediately following 72 hrs of paradoxical sleep (PS) deprivation. Activity was assessed by scoring barrier crossings and rearings in an observation box for a period of 45 min. PS deprivation was established by means of the watertank technique, employing the classical platform situation in one group and the multiple platform situation in another group of rats. The latter condition was developed to remove movement restriction, a potentially confounding variable, from the platform situation. During the first 15 min-period of the activity test, both deprivation groups exhibited a significant increase in the number of crossings and a decrease in the number of rearings, as compared to nondeprivation control groups. The classical platform group showed significantly fewer crossings and fewer rearings than the multiple platform group, which was probably due to higher stressfulness of the first condition.

Photically evoked potentials in the visual cortex following paradoxical sleep deprivation in rats

Immediately following 72 hr of paradoxical sleep (PS) deprivation, the P3-N3 amplitude of the photically evoked response in the visual cortex was measured in waking rats. PS deprivation was achieved instrumentally by one of three different techniques: the classical platform, the multiple platform, or the pendulum technique. For each of the techniques a control condition was run additionally. The PS deprivation effect consisted of a decrement in the P3-N3 amplitude, which was interpreted as indicating an increase in tonic arousal having a depressing influence on cortical excitability. Concomitantly, a relatively large technique effect occurred, in which the difference between the two platform techniques on the one hand, and the pendulum technique on the other, was most apparent. The same factors did not influence behavioural activity taking place during the presentation of photic stimulation, but did during the preceding 5 min adaptation period. Although the present findings are in contrast with previous reports in animals, they may not be inconsistent with the basic idea of the neural excitability hypothesis of PS.

Effects of paradoxical sleep deprivation on two-way avoidance acquisition

Immediately following 72 hrs of paradoxical sleep (PS) deprivation, Wistar rats were given a shuttle-box avoidance task consisting of 50 trials. At an interval of 6 days retention was assessed through a reacquisition session of 20 trials. In a first experiment, the pendulum technique was employed for PS deprivation and its effects were compared with those produced by the conventional watertank technique. The first technique consists of arousing animals from sleep before PS can arise, by swinging their cages in a way that produces postural imbalance at regular intervals. A moving pendulum just not causing imbalance in the animals served as control for this technique. As control for the watertank technique the large platform was chosen. Shuttle-box avoidance was greatly impaired during the second half of the acquisition session in both platform conditions as compared to both pendulum conditions. A relatively small deficit was found toward the end of the session in both PS deprivation conditions as compared to both control conditions. No differences in avoidance were established during retention testing, suggesting that performance rather than learning deficits occurred during acquisition. In a second experiment, the multiple platform was used for PS deprivation. This modified version of the watertank technique also disrupted performance during shuttle-box avoidance acquisition. However, this effect appeared to be less pronounced than the effect found in the classical platform condition of Experiment 1. It is concluded that the performance deficit induced by both the classical and the multiple platform condition was mainly due to nonspecific effects.

Selective deprivation of paradoxical sleep and consolidation of shuttle-box avoidance.

Investigated whether paradoxical sleep is implicated in the storage of information acquired during shuttle-box avoidance. Wistar rats were given 5 brief training sessions distributed over the light period of the diurnal cycle. During the intervals between sessions the animals were selectively deprived of paradoxical sleep by awakening them every time they showed this type of sleep. The onset of paradoxical sleep was identified when hippocampal theta rhythm occurred during behavioural sleep. Yoked control animals got the same treatment irrespective of their sleep-waking behaviour, whereas free sleep rats were allowed to sleep undisturbed. In spite of large differences in the amount of paradoxical sleep during the intersession intervals no differences in learning performances were found among the groups. A tendency toward more intertrial crossings was noted in the paradoxical sleep deprived group at the end of training. It is concluded that storage of information acquired during distributed shuttle-box avoidance is not dependent on the presence of paradoxical sleep immediately following learning. Some possibilities are considered that paradoxical sleep may still be involved in memory storage processes.

Paradoxical sleep in the dark period of the rat: a dissociation between electrophysiological and behavioral characteristics

Paradoxical sleep (PS) occurring in the dark period of the illumination cycle is studied in adult, male, Wistar rats. In contrast to the light period, behaviorally the rats give the impression of being awake at the onset of PS. This is caused by the fact that PS in the dark starts from a short-lasting state characterized by dissociating criteria: behavioral characteristics such as open eyes and body posture phenomena indicating quiet wakefulness along with full-blown hippocampal EEG waves implying slow wave sleep (SWS). These behavioral characteristics continue at the onset of PS, suggesting that PS in the dark differs from that in the light period. The intrinsic characteristics of PS, as the hippocampal theta rhythm, the suppression of the neck muscle EMG and the phasic activities, however, indicate that PS is the same phenomenon in both illumination periods. The implication of this finding with respect to the triggering of PS and its relationship with SWS is discussed.

Paradoxical Sleep Deprivation in Animal Studies: Some Methodological Considerations

Publisher Summary Deprivation of paradoxical sleep (PS) is used extensively in animals as a method for investigating the possible role of PS in behavioral processes. Two hypotheses, based mainly on this approach, have received much attention in the current literature. The information processing hypothesis of PS relates PS to learning and memory processes; whereas, the neural excitability hypothesis assigns PS a more general role of reducing brain excitability. Several lines of evidence are in agreement with the idea that PS is a state conducive to information processing. Unfortunately, research devoted to delineating more precisely the role of PS in learning and memory processes has provided inconsistent results. The reasons responsible for the discrepancies between studies may be at least partly methodological.

Spatial memory processing during hippocampal long-term potentiation in rats

It was investigated in rats whether hippocampal long-term potentiation (LTP) influences working and/or reference memory processing in the radial maze. After preliminary training to an intermediate level of performance, experimental subjects received a series of high-frequency trains of electrical pulses applied to the right perforant path. Two control groups were adopted in order to control for possible effects of stimulation plus operation, and operation alone, respectively. Twenty-four hours after the experimental treatment, animals were administered one trial of radial maze training. This sequence of hippocampal stimulation and radial maze training was replicated 15 times. After a retention interval of 2 months, one radial maze trial was presented on each of 3 consecutive days. The analysis of field potential data showed that periodic LTP stimulation produced a state of hippocampal LTP confined to the initial portion of the acquisition phase. Evaluation of radial maze data revealed a marginal improvement of working memory performance in the experimental group during the rising phase of hippocampal LTP.