Changes in the thermal characteristics of hypothalamic neurons during sleep and wakefulness

The characteristics of the mammalian thermoregulatory system are dependent upon arousal state. During NREM sleep thermoregulatory mechanisms are intact but body temperature is regulated at a lower level than during wakefulness. In REM sleep thermoregulatory effector mechanisms are inhibited and thermal homeostasis is severely disrupted. Thermosensitivity of neurons in the preoptic/anterior hypothalamus (POAH) was determined for behaving kangaroo rats (Dipodomys deserti) during electrophysiologically defined wakefulness, NREM sleep and REM sleep to elucidate possible neural mechanisms for previous findings of state-dependent changes in thermoregulation. Thirty cells were tested during at least two arousal states. During wakefulness, 70% of the recorded cells were sensitive to changes in local temperature, with the number of warm-sensitive (W) cells outnumbering cold-sensitive (C) cells by 1.6:1. In NREM sleep, 43% of the cells were thermally sensitive, with the ratio of W:C remaining the same as in wakefulness. In REM sleep only two cells were thermosensitive (both W). The decrease in neuronal thermosensitivity of POAH cells during REM sleep parallels findings of inhibition of thermoregulatory effector responses during REM, although further work is necessary to determine the source and nature of the inhibition.     

Glutamatergic Neurons in the Preoptic Hypothalamus Promote Wakefulness,Destabilize NREM Sleep,Suppress REM Sleep,and Regulate Cortical Dynamics

Clinical and experimental data from the last nine decades indicate that the preoptic area of the hypothalamus is a critical node in a brain network that controls sleep onset and homeostasis. By contrast, we recently reported that a group of glutamatergic neurons in the lateral and medial preoptic area increases wakefulness, challenging the long-standing notion in sleep neurobiology that the preoptic area is exclusively somnogenic. However, the precise role of these subcortical neurons in the control of behavioral state transitions and cortical dynamics remains unknown. Therefore, in this study, we used conditional expression of excitatory hM3Dq receptors in these preoptic glutamatergic (Vglut2⁺) neurons and show that their activation initiates wakefulness, decreases non-rapid eye movement (NREM) sleep, and causes a persistent suppression of rapid eye movement (REM) sleep. We also demonstrate, for the first time, that activation of these preoptic glutamatergic neurons causes a high degree of NREM sleep fragmentation, promotes state instability with frequent arousals from sleep, decreases body temperature, and shifts cortical dynamics (including oscillations, connectivity, and complexity) to a more wake-like state. We conclude that a subset of preoptic glutamatergic neurons can initiate, but not maintain, arousals from sleep, and their inactivation may be required for NREM stability and REM sleep generation. Further, these data provide novel empirical evidence supporting the hypothesis that the preoptic area causally contributes to the regulation of both sleep and wakefulness.SIGNIFICANCE STATEMENT Historically, the preoptic area of the hypothalamus has been considered a key site for sleep generation. However, emerging modeling and empirical data suggest that this region might play a dual role in sleep-wake control. We demonstrate that chemogenetic stimulation of preoptic glutamatergic neurons produces brief arousals that fragment sleep, persistently suppresses REM sleep, causes hypothermia, and shifts EEG patterns toward a “lighter” NREM sleep state. We propose that preoptic glutamatergic neurons can initiate, but not maintain, arousal from sleep and gate REM sleep generation, possibly to block REM-like intrusions during NREM-to-wake transitions. In contrast to the long-standing notion in sleep neurobiology that the preoptic area is exclusively somnogenic, we provide further evidence that preoptic neurons also generate wakefulness.     

Preoptic/anterior hypothalamic neurons: thermosensitivity in wakefulness and non rapid eye movement sleep

Thermosensitive neurons of the preoptic/anterior hypothalamic area (POAH) have been implicated in the regulation of both body temperature and non rapid eye movement (NREM) sleep. During NREM sleep, a majority of POAH warm-sensitive neurons (WSN) exhibit increased discharge compared to wakefulness. Cold-sensitive neurons (CSN) exhibit reduced discharge in NREM sleep compared to wakefulness. To further study the mechanism underlying these processes, the present study compared discharge rate and thermosensitivity (discharge rate change/°C) of WSNs and CSNs in NREM sleep and wakefulness in freely moving adult cats. The thermosensitivity of 24 WSNs and 31 CSNs from the medial POAH was determined from responses to local POAH warming and cooling. WSNs with increased discharge in NREM sleep exhibited increased thermosensitivity during NREM sleep compared to wakefulness. CSNs with decreased discharge during NREM sleep exhibited decreased thermosensitivity in NREM sleep. The change in thermosensitivity from wakefulness to NREM sleep was correlated with the change in discharge rate in WSNs but not in CSNs. In addition, 9 of 47 neurons that were thermo-insensitive during wakefulness became warm-sensitive during NREM sleep. Changes in POAH neuronal thermosensitivity could be a component of the mechanism for stabilization of state after state transition.     

Knockdown of orexin type 1 receptor in rat locus coeruleus increases REM sleep during the dark period

The locus coeruleus (LC) regulates sleep/wakefulness and is densely innervated by orexinergic neurons in the lateral hypothalamus. Here we used small interfering RNAs (siRNAs) to test the role of LC orexin type 1 receptor (OxR1) in sleep–wake control. In sleep studies, bilateral OxR1 siRNA injections led to an increase of time spent in rapid eye movement (REM) sleep, which was selective for the dark (active) period, peaked at approximately 30% of control during the second dark period after injection and then disappeared after 4 days. Cataplexy-like episodes were not observed. The percentage time spent in wakefulness and non-REM (NREM) sleep and the power spectral profile of NREM and REM sleep were unaffected. Control animals, injected with scrambled siRNA, had no sleep changes after injection. Quantification of the knockdown revealed that unilateral microinjection of siRNAs targeting OxR1 into the rat LC on two consecutive days induced a 45.5% reduction of OxR1 mRNA in the LC 2 days following the injections when compared with the contralateral side receiving injections of control (scrambled) siRNAs. This reduction disappeared 4 days after injection. Similarly, unilateral injection of OxR1 siRNA into the LC revealed a marked (33.5%) reduction of OxR1 staining 2 days following injections. In contrast, both the mRNA level and immunohistochemical staining for tyrosine hydroxylase were unaffected. The results indicate that a modest knockdown of OxR1 is sufficient to induce observable sleep changes. Moreover, orexin neurons, by acting on OxR1 in the LC, play a role in the diurnal gating of REM sleep.     

Inducible and neuronal nitric oxide synthases (NOS) have complementary roles in recovery sleep induction

Sleep homeostasis is the process by which recovery sleep is generated by prolonged wakefulness. The molecular mechanisms underlying this important phenomenon are poorly understood. We have previously shown that nitric oxide (NO) generation increases in the basal forebrain (BF) during sleep deprivation (SD). Moreover, both NO synthase (NOS) inhibition and a NO scavenger prevented recovery sleep induction, while administration of a NO donor during the spontaneous sleep-wake cycle increased sleep, indicating that NO is necessary and sufficient for the induction of recovery sleep. Next we wanted to know which NOS isoform is involved in the production of recovery sleep. Using in vivo microdialysis we infused specific inhibitors of NOS into the BF of rats during SD, and found that an inhibitor of inducible NOS (iNOS), 1400W, prevented non-rapid eye movement (NREM) recovery, while an inhibitor of neuronal NOS (nNOS), L-N-propyl-arginine, decreased REM recovery but did not affect NREM recovery. Using immunoblot analysis we found that iNOS was not expressed during the spontaneous sleep-wake cycle, but was induced by prolonged wakefulness (increased by 278%). A known iNOS inducer, lipopolysaccharide, evoked an increase in sleep that closely resembled recovery sleep, and its effects were abolished by 1400W. These results suggest that the elevation of NO produced by induction of iNOS in the BF during prolonged wakefulness is a specific mechanism for producing NREM recovery sleep and that the two NOS isoforms have a complementary role in NREM and REM recovery induction.     

Scalp recorded direct current brain potentials during human sleep

The direct current (DC) potential recorded from the scalp of awake humans has been considered a reflection of general changes in cortical excitability. This study examined DC potential shifts in humans during a night of continuous sleep. Standard polysomnographic recordings and skin temperature were measured simultaneously. Contrary to expectations, average DC potential level indicated higher negativity during nonrapid eye movement (NREM) sleep than REM sleep and wakefulness. Moreover, a dynamic regulation of the DC potential level was revealed in association with the NREM–REM sleep cycle comprising four successive phases: (i) a steep ‘NREM-transition-negative shift’ during the initial 10–15 min of the NREM sleep period; (ii) a more subtle ‘NREM-positive slope’ during the subsequent NREM sleep period; (iii) a steep ‘REM-transition-positive shift’ starting shortly prior to the REM sleep period, and (iv) a ‘REM-negative slope’, characterizing the remaining greater part of the REM sleep period. DC potential changes were only weakly related to changes in slow-wave activity (r² < 0.18). The NREM-negative slope and REM-positive slope could reflect, respectively, gradually increasing and decreasing cortical excitability resulting from widespread changes in the depolarization of apical dendrites. In contrast, the NREM-transition-negative shift and the REM-transition-positive shift may reflect the progression and retrogression, respectively, of a long-lasting hyperpolarization in deeply lying neurons.     

Participation of histaminergic H1 and noradrenergic alpha 1 receptors in orexin A-induced wakefulness in rats

The participation of histaminergic H(1) and noradrenergic alpha(1) receptors in orexin A-induced wakefulness was studied by examining the sleep-wakefulness cycle in rats. Intracerebroventricular infusion of orexin A (1 nmol) caused an increase in the wakefulness state, while non-rapid eye movement sleep (NREM sleep) and rapid eye movement sleep (REM sleep) states were decreased. Prazosin (150 nmol) showed no significant antagonistic effect on the orexin A-induced increase in the wakefulness state and decrease in NREM and REM sleep. On the contrary, pyrilamine (150 nmol) was effective in antagonizing orexin A-induced increase in wakefulness and decrease in NREM sleep. When prazosin (150 nmol) and pyrilamine (150 nmol) were simultaneously perfused into the lateral ventricle, an almost complete antagonistic effect was observed with the increase in the wakefulness state and decrease in NREM sleep. Orexin A (1 nmol) caused a significant decrease in the histamine contents of the cortex, hippocampus and hypothalamus, whereas noradrenaline contents were decreased only in the hypothalamus. From these results, we concluded that the arousal effect induced by orexin A occurs through histaminergic H(1) and noradrenergic alpha(1) receptors, although participation of the H(1) receptor was more important than the alpha(1) receptor.     

Automated determination of wakefulness and sleep in rats based on non-invasively acquired measures of movement and respiratory activity

The current standard for monitoring sleep in rats requires labor intensive surgical procedures and the implantation of chronic electrodes which have the potential to impact behavior and sleep. With the goal of developing a non-invasive method to determine sleep and wakefulness, we constructed a non-contact monitoring system to measure movement and respiratory activity using signals acquired with pulse Doppler radar and from digitized video analysis. A set of 23 frequency and time-domain features were derived from these signals and were calculated in 10 s epochs. Based on these features, a classification method for automated scoring of wakefulness, non-rapid eye movement sleep (NREM) and REM in rats was developed using a support vector machine (SVM). We then assessed the utility of the automated scoring system in discriminating wakefulness and sleep by comparing the results to standard scoring of wakefulness and sleep based on concurrently recorded EEG and EMG. Agreement between SVM automated scoring based on selected features and visual scores based on EEG and EMG were approximately 91% for wakefulness, 84% for NREM and 70% for REM. The results indicate that automated scoring based on non-invasively acquired movement and respiratory activity will be useful for studies requiring discrimination of wakefulness and sleep. However, additional information or signals will be needed to improve discrimination of NREM and REM episodes within sleep.     

Extracellular serotonin levels in the medullary reticular formation during normal sleep and after REM sleep deprivation

Rapid eye movement (REM) sleep is hypothesized to result from the activity of REM sleep-generating and REM sleep-inhibiting neurons. The serotoninergic (5-HT) neurons of the dorsal raphe nucleus (DRN) represents one such population of REM-sleep inhibiting neurons since they are silent during REM sleep. Consistent with the decrease in activity of 5-HT neurons, the brain extracellular levels of 5-HT are lower during REM sleep compared to wakefulness. It is not known whether serotonin release is also reduced as a consequence of REM sleep rebound. Using microdialysis sampling coupled to HPLC–ECD, we measured the extracellular levels of 5-HT and its metabolite (5-HIAA) in the medial medullary reticular formation (mMRF) of freely behaving rats during normal sleep, REM sleep deprivation as well as during REM sleep rebound. We found that the levels 5-HT and 5-HIAA were significantly decreased by REM sleep deprivation. The reduction of 5-HT release was maintained during REM sleep rebound but the extracellular level of its main metabolite was increased. In addition, even during REM sleep rebound, 5-HT release during sleep was low compared to wakefulness. Taken together these data support the permissive role of 5-HT neurotransmission for REM sleep expression.     

Effects of social stimuli on sleep in mice: non-rapid-eye-movement (NREM) sleep is promoted by aggressive interaction but not by sexual interaction

Sleep is generally considered to be a process of recovery from prior wakefulness. In addition to being affected by the duration of the waking period, sleep architecture and sleep EEG also depend on the quality of wakefulness. In the present experiment, we examined how sleep is affected by different social stimuli (social conflict and sexual interaction). Male C57BL/6J mice were placed in the cage of an aggressive dominant male or an estrous female for 1 h in the middle of the light phase. The conflict with an aggressive male had a pronounced NREM sleep-promoting effect. EEG slow wave activity, a measure of NREM sleep intensity, was increased for about 6 h and NREM sleep time was significantly increased for 12 h. REM sleep was strongly suppressed during the remainder of the light phase after the conflict, followed by a rebound later in the recovery phase. The sexual interaction, in contrast, had only mild effects. Both NREM sleep and REM sleep were somewhat suppressed shortly after the interaction. In a separate group of mice, blood samples were taken to measure prolactin and corticosterone. The results suggest that the temporary suppression of REM sleep following the social stimuli may be partly due to elevated corticosterone. The different effects of the social stimuli on NREM sleep are not easily explained by differences in the hormone responses. In conclusion, although both social conflict and sexual interaction induce a strong physiological activation, only social conflict has a strong stimulatory effect on NREM sleep mechanisms.     

Activation of visual cortex in REM sleep measured by 24-channel NIRS imaging.

To visualize dreaming brain functions we studied hemodynamic changes in the visual cortex during the transition from non-rapid eye movement (NREM) to rapid eye movement (REM) sleep, using a 24-channel Near-Infrared Spectroscopy (NIRS) imaging method. Results were compared to the activation in visual cortex by visual stimulation during wakefulness. Subjects were four healthy males between 25 and 49 years of age. Five all-night polysomnographic and NIRS recordings were made. Increases in the oxygenated hemoglobin concentration in visual cortex were observed from nine of 14 REM periods. The activated areas were broader during REM sleep than during visual stimulation. These findings suggest that activation of visual cortex in REM sleep might represent dream-related brain activity.     

Sleep-wakefulness effects after microinjections of hypocretin 1 (orexin A) in cholinoceptive areas of the cat oral pontine tegmentum

Hypocretinergic/orexinergic neurons, which are known to be implicated in narcolepsy, project to the pontine tegmentum areas involved in the control of rapid eye movement (REM) sleep. Here, we report the effects on sleep-wakefulness produced by low-volume microinjections of hypocretin (Hcrt)1 (20–30 nL, 100, 500 and 1000 μ m ) and carbachol (20–30 nL, 0.1  m ) delivered in two areas of the oral pontine tegmentum of free-moving cats with electrodes for chronic sleep recordings: in the dorsal oral pontine tegmentum (DOPT) and in the ventral part of the oral pontine reticular nucleus (vRPO). Carbachol in the DOPT produced dissociate polygraphic states, with some but not all REM sleep signs. In contrast, carbachol in the vRPO produced a shift with short latency from wakefulness (W) to REM sleep with all of its polygraphic and behavioral signs. Hcrt-1 in the DOPT increased W and decreased both slow-wave sleep (SWS) and REM sleep during the first 3 h post-drug. The same doses of Hcr-1 in the vRPO produced a significant suppression of REM sleep without a definitive trend for changes in the other states. Both groups showed significant decreases in the number of transitions from SWS to REM sleep. Thus, Hcrt-1 produced distinct effects in cholinoceptive areas of the oral pontine tegmentum; in the DOPT it promoted W, suppressed SWS and probably defacilitated REM sleep, and in the vRPO it directly inhibited REM sleep. Hypocretinergic/orexinergic signaling is lost in narcoleptics and this absence would mean that pontine defacilitation/inhibition of REM sleep would also be absent, explaining why these patients can fall directly into REM sleep from W.     

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.     

Role of polysialylated neural cell adhesion molecule in rapid eye movement sleep regulation in rats

Recent evidence suggests that synaptic plasticity occurs during homeostatic processes, including sleep–wakefulness regulation, although the underlying mechanisms are not well understood. Polysialylated neural cell adhesion molecule (PSA NCAM) is a transmembrane protein that has been implicated in various forms of plasticity. To investigate whether PSA NCAM is involved in the neuronal plasticity associated with spontaneous sleep–wakefulness regulation and sleep homeostasis, four studies were conducted using rats. First, we showed that PSA NCAM immunoreactivity is present in close proximity to key neurons in several nuclei of the sleep–wakefulness system, including the tuberomammillary hypothalamic nucleus, dorsal raphe nucleus, and locus coeruleus. Second, using western blot analysis and densitometric image analysis of immunoreactivity, we found that 6 h of sleep deprivation changed neither the levels nor the general location of PSA NCAM in the sleep–wakefulness system. Finally, we injected endoneuraminidase (Endo N) intracerebroventricularly to examine the effects of polysialic acid removal on sleep–wakefulness states and electroencephalogram (EEG) slow waves at both baseline and during recovery from 6 h of sleep deprivation. Endo N‐treated rats showed a small but significant decrease in baseline rapid eye movement (REM) sleep selectively in the late light phase, and a facilitated REM sleep rebound after sleep deprivation, as compared with saline‐injected controls. Non‐REM sleep and wakefulness were unaffected by Endo N. These results suggest that PSA NCAM is not particularly involved in the regulation of wakefulness or non‐REM sleep, but plays a role in the diurnal pattern of REM sleep as well as in some aspects of REM sleep homeostasis.     

Region-Specific and State-Dependent Astrocyte Ca2+ Dynamics during the Sleep-Wake Cycle in Mice

Neural activity is diverse, and varies depending on brain regions and sleep/wakefulness states. However, whether astrocyte activity differs between sleep/wakefulness states, and whether there are differences in astrocyte activity among brain regions remain poorly understood. Therefore, in this study, we recorded astrocyte intracellular calcium (Ca²⁺) concentrations of mice during sleep/wakefulness states in the cortex, hippocampus, hypothalamus, cerebellum, and pons using fiber photometry. For this purpose, male transgenic mice expressing the genetically encoded ratiometric Ca²⁺ sensor YCnano50 specifically in their astrocytes were used. We demonstrated that Ca²⁺ levels in astrocytes substantially decrease during rapid eye movement (REM) sleep, and increase after the onset of wakefulness. In contrast, differences in Ca²⁺ levels during non-REM (NREM) sleep were observed among the different brain regions, and no significant decrease was observed in the hypothalamus and pons. Further analyses focusing on the transition between sleep/wakefulness states and correlation analysis with the duration of REM sleep showed that Ca²⁺ dynamics differs among brain regions, suggesting the existence of several clusters, i.e., the first comprising the cortex and hippocampus, the second comprising the hypothalamus and pons, and the third comprising the cerebellum. Our study thus demonstrated that astrocyte Ca²⁺ levels change substantially according to sleep/wakefulness states. These changes were consistent in general unlike neural activity. However, we also clarified that Ca²⁺ dynamics varies depending on the brain region, implying that astrocytes may play various physiological roles in sleep.SIGNIFICANCE STATEMENT Sleep is an instinctive behavior of many organisms. In the previous five decades, the mechanism of the neural circuits controlling sleep/wakefulness states and the neural activities associated with sleep/wakefulness states in various brain regions have been elucidated. However, whether astrocytes, which are a type of glial cell, change their activity during different sleep/wakefulness states was poorly understood. Here, we demonstrated that dynamic changes in astrocyte Ca²⁺ concentrations occur in the cortex, hippocampus, hypothalamus, cerebellum, and pons of mice during natural sleep. Further analyses demonstrated that Ca²⁺ dynamics slightly differ among different brain regions, implying that the physiological roles of astrocytes in sleep/wakefulness might vary depending on the brain region.     

Dynamics of hippocampus and orbitofrontal cortex activity during arousing reactions from sleep: An intracranial electroencephalographic study

Sleep is punctuated by transient elevations of vigilance level called arousals or awakenings depending on their durations. Understanding the dynamics of brain activity modifications during these transitional phases could help to better understand the changes in cognitive functions according to vigilance states. In this study, we investigated the activity of memory‐related areas (hippocampus and orbitofrontal cortex) during short (3 s to 2 min) arousing reactions detected from thalamic activity, using intracranial recordings in four drug‐resistant epilepsy patients. The average power of the signal between 0.5 and 128 Hz was compared across four time windows: 10 s of preceding sleep, the first part and the end of the arousal/awakening, and 10 s of wakefulness. We observed that (a) in most frequency bands, the spectral power during hippocampal arousal/awakenings is intermediate between wakefulness and sleep whereas frontal cortex shows an early increase in low and fast activities during non‐rapid‐eye‐movement (NREM) sleep arousals/awakenings; (b) this pattern depends on the preceding sleep stage with fewer modifications for REM than for non‐REM sleep arousal/awakenings, potentially reflecting the EEG similarities between REM sleep and wakefulness; (c) a greater activation at the arousing reaction onset in the prefrontal cortex predicts longer arousals/awakenings. Our findings suggest that hippocampus and prefrontal arousals/awakenings are progressive phenomena modulated by sleep stage, and, in the neocortex, by the intensity of the early activation. This pattern of activity could underlie the link between sleep stage, arousal/awakening duration and restoration of memory abilities including dream recall.     

Complexity measures of the central respiratory networks during wakefulness and sleep

Since sleep is known to influence respiratory activity we studied whether the sleep state would affect the complexity value of the respiratory network output. Specifically, we tested the hypothesis that the complexity values of the diaphragm EMG (EMGdia) activity would be lower during REM compared to NREM. Furthermore, since REM is primarily generated by a homogeneous population of neurons in the medulla, the possibility that REM-related respiratory output would be less complex than that of the awake state was also considered. Additionally, in order to examine the influence of neuron vulnerabilities within the rostral ventral medulla (RVM) on the complexity of the respiratory network output, we inhibited respiratory neurons in the RVM by microdialysis of GABA(A) receptor agonist muscimol. Diaphragm EMG, nuchal EMG, EEG, EOG as well as other physiological signals (tracheal pressure, blood pressure and respiratory volume) were recorded from five unanesthetized chronically instrumented intact piglets (3-10 days old). Complexity of the diaphragm EMG (EMGdia) signal during wakefulness, NREM and REM was evaluated using the approximate entropy method (ApEn). ApEn values of the EMGdia during NREM and REM sleep were found significantly (p < 0.05 and p < 0.001, respectively) lower than those of awake EMGdia after muscimol inhibition. In the absence of muscimol, only the differences between REM and wakefulness ApEn values were found to be significantly different.     

Sleep during neuromuscular blockade in cats

The purpose of the experiment was to determine whether normal sleep patterns can occur during neuromuscular blockade. Electrographic variables for determining the states of sleep and wakefulness, the electrocorticogram, lateral geniculate nucleus potentials, and dorsal hippocampal potentials, were recorded before, during and after the administration of gallamine triethiodide to cats with chronically implanted electrodes. When respiratory muscles became paralyzed, artificial ventilation commenced through a chronic tracheal fistula. The electrographic wave forms of the states (wakefulness, NREM sleep and REM sleep) in paralyzed cats were indistinquishable by visual observation from those of freely moving animals. As compared to freely moving cats, paralyzed cats had more wakefulness at the expense of both states of sleep (about 33% NREM and 3% REM compared to 45% NREM and 15% REM respectively). REM sleep wasdemonstrated to occur, albeit increase across repeated session in the same cats nor was the distribution uneven within the average session. Large percentages of REM sleep with respect to total recording time were associated with large percentages of NREM sleep (correlation coefficient = 0.58). The sequence of sleep states was like that of freely behaving animals. The main conclusion is that this preparation, depsite low amounts of REM sleep, is useful in neural studies of sleep and wakefulness.     

Diurnal variations in REM and NREM sleep EEG power spectra in the rat

Diurnal variations were observed in the EEG power spectra of REM sleep and non-REM (NREM) sleep in the rat. Diurnal variations occured in peak EEG frequency and spectral power (0–27 Hz and 5–9 Hz bands) during REM sleep. During NREM sleep diurnal variations were observed in spectral power in the 0–27 Hz and 0–4 Hz bands. The significance of these findings is discussed in terms of correlative data involving diurnal variations in neurotransmitters and hormones, all of which have been implicated in the induction or maintenance of sleep states.     

Short-term effects of fluoxetine and trifluoromethylphenylpiperazine on electroencephalographic sleep in the rat

Fluoxetine and trifluoromethylphenylpiperazine (TFMPP) were studied for their short-term effects on electroencephalographic sleep in male rats. Following single injection, each drug produced a sizeable, dose-related suppression of rapid-eye-movement (REM) sleep that persisted for 4-5 h (fluoxetine, 0.625-5 mg/kg; TFMPP, 0.10-1.25 mg/kg). TFMPP also consistently increased non-REM (NREM) sleep during the second hour after drug injection, though this effect was not dose-related (it was seen at all doses tested). Fluoxetine produced small effects on NREM sleep that varied non-systematically with dose and time after drug injection. TFMPP, but not fluoxetine, also increased at all doses the number of delta waves per minute of NREM sleep in the second hour. A structural analog of TFMPP that is inactive at serotonin (5-HT) receptors [4-(m-trifluoromethylphenyl)piperadine; LY97117] was also tested, and found to be devoid of effects on NREM and REM sleep. Both fluoxetine (a 5-HT reuptake blocker) and TFMPP (a 5-HT agonist) enhance transmission across 5-HT synapses, though by different mechanisms. Because they have the common effect of suppressing REM sleep, and in a dose-related manner, the data support the notion that 5-HT neurons in the brain, when active, can suppress REM sleep.