In the rat the exposure to an ambient temperature (Ta) of −10 °C induces an almost total REM sleep deprivation that results in a proportional rebound in the following recovery at normal laboratory Ta ...when the exposure lasts for 24 h, but in a rebound much lower than expected when the exposure lasts 48 h. The possibility that this may be related to plastic changes in the nervous structures involved in the control of thermoregulation and REM sleep has been investigated by measuring changes in the concentration of adenosine 3′:5′-cyclic monophosphate (cAMP) and
d-myo-inositol 1,4,5-trisphosphate (IP
3) in the preoptic-anterior hypothalamic area (PO-AH), the ventromedial hypothalamic nucleus (VMH) and, as a control, the cerebral cortex (CC). Second messenger concentration was determined in animals either stimulated by being exposed to hypoxia, a depolarizing condition that induces maximal second messenger accumulation or unstimulated, at the end of a 24-h and a 48-h exposure to −10 °C and also between 4 h 15 min and 4 h 30 min into recovery (early recovery). At the end of both exposure conditions, cAMP concentration significantly decreased in PO-AH-VMH, but did not change in CC, whilst changes in IP
3 concentration were similar in all these regions. The low cAMP concentration in PO-AH-VMH was concomitant with a significantly low accumulation in hypoxia. The normal capacity of cAMP accumulation was only restored in the early recovery following 24 h of exposure, but not following 48 h of exposure, suggesting that this may be a biochemical equivalent of the REM sleep inhibition observed during 48 h of exposure and which is carried over to the recovery.
The occurrence of REM sleep in the rat appears to be under the control of either sleep related processes and homeostatic regulation of physiological variables. With respect to this, it has been ...observed that in this species REM sleep may occur in the form of two types of episodes, Single and Sequential episodes, which are supposed to play a different functional role. Since it is possible to distinguish Single and Sequential REM sleep episodes also in human beings, the aim of this pilot study was to asses whether a sleep deprivation may differently affect these two types of REM episodes. The sleep deprivation was induced in young human subjects by a progressive restriction of sleep within the same night period. Seventy-two PSG tracing belonging to six subjects have been analyzed. The results show that sleep deprivation does not significantly affect the relative occurrence of Single and Sequential REM sleep episodes, suggesting that in human beings these two types of REM episodes might not have a different functional role.
The occurrence of REM sleep episodes, separated by intervals >3 min (single episodes) and ≤3 min (sequential episodes), was determined in the rat during the recovery (ambient temperature (Ta) 23°C, L ...period of the LD 12 h:12 h-cycle), which followed the exposure to low Ta (0 and −10°C) during the D period of the previous LD-cycle, either in normal light (DL) or in continuous darkness (DD). Both exposures were characterized by an almost complete disappearance of REM sleep, whilst the recoveries showed an increase in the amount of REM sleep in the form of sequential episodes, which in DD was particularly prominent and concomitant with a decrease in the amount of REM sleep in the form of single episodes. The initial 2 h-rate of REM sleep occurrence was lower following the exposure to Ta −10°C, than to Ta 0°C. In DD, such an effect was due to the large reduction in the occurrence of sequential REM sleep episodes. A functional correlate of this finding is that the accumulation capacity of a second messenger (cAMP) was found to be lower at the end of the exposure to Ta −10°C, with respect to both the control (Ta 23°C) and the end of exposure to Ta 0°C, in the preoptic–anterior hypothalamus, but not in the cerebral cortex.
This study was carried out in order to further test the hypothesis that the occurrence of REM sleep in the rat in the form of episodes separated by long intervals (
single REM sleep episodes) and by ...short intervals (
sequential REM sleep episodes) is differently influenced by changes in both sleep and ambient related processes. Rats were studied during the exposure to Ta −10°C for 24 or 48 h and during a 12 h recovery period at laboratory Ta (23°C) following either the first or the second 24 h of cold exposure. The exposure to such a low Ta induced an almost complete abolition of REM sleep which was followed, during recovery, by a marked REM sleep rebound. However, in spite of the larger REM sleep deprivation, the REM sleep rebound was weaker following the 48 h-exposure than that following the exposure for 24 h. The increase in the amount of REM sleep during the recovery period was due to an increase in the amount of that occurring in the form of sequential episodes, whilst that in the form of single episodes did not change with respect to control levels. However, the occurrence of REM sleep in the form of sequential episodes was partially impaired during the REM sleep rebound observed in the recovery period following the 48 h-exposure. These results would suggest that the homeostatic regulation of physiological variables may conflict with that of REM sleep occurrence and that the degree of such a contrast is indicated, at low Ta, by the amount of REM sleep in the form of single episodes and, during the following recovery, by the amount of REM sleep in the form of sequential episodes.
The effects of the rhythmical delivery of an auditory stimulus (1000 Hz, from 50 to 100 dB, 20 ms, every 20 s) on the pattern of rapid eye movement (REM) sleep occurrence was studied in the rat. The ...stimulation was simultaneously carried out on pairs of rats over 5 consecutive days (10-h recording sessions), during which a tone of increasing intensity (50, 63, 75, 88, 100 dB) was used. In each experimental session, auditory stimulation was triggered by the REM sleep occurrence of one rat (REMS-selective stimulation) whilst the other rat simultaneously received the same stimuli, but during any stage of the wake–sleep cycle (REMS-unselective stimulation). The results showed that the total amount of REM sleep in the 10-h recording session was increased over the 5 days of stimulation in the REMS-unselective group. This effect was due to an increase in the mean duration of REM sleep episodes. However, no significant changes were observed in animals under REMS-selective stimulation, nor in a third group of animals in which the spontaneous evolution of REM sleep occurrence (REMS-spontaneous) was studied. Since 86% of the stimuli under the REMS-unselective auditory stimulation fell outside REM sleep, the result would suggest that REM sleep occurrence is affected when the stimuli are delivered during a time period (i.e. during wakefulness or non-REM sleep) in which it is well known that physiological regulations are fully operant.
From a physiological viewpoint, REM sleep (REMS) is a period during which homeostatic physiological regulations are impaired. In the rat, REMS occurs in two forms respectively characterized by ...episodes separated by long intervals (single REMS episodes) and by episodes which have short intervals and occur in sequences (REMS clusters). Since the partition of REMS in the form of either single or clustered episodes may reveal how the REMS drive and body homeostatic processes interact in the control of REMS occurrence, we have used this approach to clarify the effects of the rhythmical delivery of an auditory stimulus (1000 Hz, 63 or 88 dB, 50 ms, every 20 s), which has been previously observed by different authors to enhance REMS in the absence of a previous sleep deprivation. Stimuli were delivered to pairs of animals and triggered by the occurrence of REMS in one rat (REMS-selective stimulation), whilst the other animal received the same stimulus irrespectively of the stage of the wake-sleep cycle (REMS-unselective stimulation). The results showed that the REMS-selective stimulation did not change the overall amount of REMS, since an increase in the occurrence of REMS clusters was concomitant with a decrease in the occurrence of single REMS episodes. In contrast, under the REMS-unselective stimulation, the total amount of REMS was increased during the second day of stimulation through an increase in the duration of both types of REMS episodes. Since during the REMS-unselective stimulation 87% of the stimuli fell outside REMS (i.e., during the REMS interval), the results show that the occurrence of REMS is more consistently affected when the stimuli are delivered in a period during which homeostatic physiological regulations are fully operant.
