Deep Slow Wave Sleep Research Articles

Functional activity of 5-HT2 receptors in the modulation of the sleep/wakefulness states.

In the light of recent pharmacological investigations using agonists and antagonists that have potent actions on 5-hydroxytryptamine-2 (5-HT2) receptors, the possible functional role of 5-HT2 receptors in the modulation of the sleep/wakefulness states was examined. Data obtained from animals and from clinical studies suggest that serotonin may exert an inhibitory control on deep slow-wave sleep (SWS) through 5-HT2 receptors. In further investigations, the existence of a diurnal variation in the functional activity of 5-HT2 receptors, that depends on the day/night cycle and/or the melatonin rhythm, was revealed. Questions remain with regard to the physiological significance, of the 5-HT2 receptor-mediated deep SWS regulation, the anatomical site(s) of 5-HT2 receptors involved in this regulation and the mechanism underlying diurnal fluctuations in the functional activity of 5-HT2 receptors.

The 5-HT 1A antagonist (−)-alprenolol fails to modify sleep or zimeldine-induced sleep-waking effects in rats

Sleep and waking in rats were studied for 8 h following administration of a selective 5-hydroxytryptamine (5-HT) reuptake inhibitor (zimeldine), a putative 5-HT 1A antagonist {L(−)-alprenolol hydrogene tartrate monohydrate [(−)-alprenolol]} and a combination of (−)-alprenolol and zimeldine. Consistent with earlier findings, zimeldine gave a biphasic effect on sleep and waking. Waking was increased during the first 3 h, followed by a small decrease. Deep slow-wave sleep (SWS-2) showed the opposite trend. An initial decrease in SWS-2 was followed by an increase after around 3 h. Rapid eye movement sleep was markedly suppressed and latencies to sleep increased after zimeldine. (−)-Alprenolol had no effects on the different sleep and waking stages or latencies to sleep. The 5-HT 1A antagonist also failed to modify the effects of zimeldine administration. The behavioral syndrome induced by a selective 5-HT 1A agonist [8-hydroxy-2-(di- n-propyl-amino)-tetralin (8-OH-DPAT)] was clearly antagonized by administration of (−)-alprenolol, indicating that (−)-alprenolol was an efficient 5-HT 1A blocker. The data indicate that the sleep-waking effects of zimeldine cannot easily be explained by stimulation of 5-HT 1A receptors.

Effects of ethanol injection to the preoptic area on sleep and temperature in rats

Bilateral microinjection of ethanol to the preoptic area of rats causes a dose-dependent hypnotic effect at doses that do not affect brain temperature. Rats were polygraphically recorded for 6 h, and brain temperature was recorded every 10 min for 3 h. Administration of 0.047 μmol ethanol increased total sleep during the 3–6 h interval, while 0.24 and 0.47 μmol ethanol increased deep slow-wave sleep (SWS 2) and total sleep during the 3–6- and 0–6-h intervals. The 0.24-μmol ethanol microinjections also increased REM sleep for the 0–6-h interval. No changes in sleep latencies were observed.

Spike-wave discharges and sleep-wake states in rats with absence epilepsy

The occurrence of spike-wave discharges was studied in relation to the daily fluctuations of vigilance level in rats. Eight rats of the WAG/Rij strain, an animal model for idiopathic generalized epilepsy of the absence type, which were equipped with cortical EEG and nuchal EMG electrodes, served as subjects. It was found that spike-wave discharges predominantly occur during light slow wave sleep and passive wakefulness. REM sleep, active wakefulness, and deep slow wave sleep are less susceptible to the occurrence of spikewave discharges. Finally, spike-wave discharges tend to prevail in transitional states. A crucial role for the degree of stability of the level of vigilance in the genesis of absence seizures is suggested.

Role of adenosine in sleep and temperature regulation in the preoptic area of rats

We have examined the effects on sleep and brain temperature of bilateral microinjections of adenosine and adenosine analogs to the preoptic area (PO) of rats. Administration of adenosine (12.5 nmoles), a nonselective adenosine A1/A2 receptor agonist NECA (N-ethyl-carboxamido-adenosine, 1.0 nmole), and the selective adenosine A1 receptor agonist CPA (cyclopentyladenosine, 0.25, 0.5 nmoles) increased total sleep primarily through an enhancement in deep slow-wave sleep (SWS 2), while adenosine also increased REM sleep. Administration of 12.5 nmoles adenosine and 0.25 nmoles CPA did not affect brain temperature, while 1.0 nmole NECA and 0.5 nmoles CPA caused a transient and prolonged hypothermia, respectively. Administration of the selective adenosine A2 receptor agonist CV-1808 (2-phenylaminoadenosine, 5, 10 nmoles) had no effect on sleep or brain temperature. The present results demonstrate a site for the central hypnotic action of adenosine, and a functional role for adenosine A1 receptors in the hypothalamus.

Absence epilepsy and the level of vigilance in rats of the WAG/Rij strain

In man, a relationship exists between sleep-wake states and absence epilepsy. During wakefulness, spike-wave discharges predominantly occur when the level of vigilance is not high, while during sleep they have a preference to occur during slow-wave sleep. During this latter type of sleep, spike-wave discharges prevail in periods where slow-wave sleep is light. In a series of experiments, the WAG/Rij rat model for absence epilepsy was characterized with respect to the relationships between the level of vigilance, sleep-wake states and the occurrence of spike-wave discharges. In the first experiment, continuous recordings were made for a period of 48 h and a clear circadian rhythm was established for the number of spike-wave discharges. A maximum appeared during the middle of the dark period of the rat, whereas a minimum was detected directly after the onset of the light period, the time period during which deep slow-wave sleep predominates. The relationship of spike-wave discharges with states of vigilance was elaborated in a second study. Spike-wave discharges were mainly found during light slow-wave sleep, during passive wakefulness and in transition phases from sleep to wakefulness. During REM sleep no spike-wave discharges were found. In the last three experiments, the level of alertness was enhanced by various procedures as photostimulation, a learning task and deprivation of REM sleep. In all cases, an increase of alertness decreased the amount of epilepsy.(ABSTRACT TRUNCATED AT 250 WORDS)

Exposure to heat restores sleep in cats with preoptic/anterior hypothalamic cell loss

Evidence suggests that thermosensitive neurons of the preoptic/anterior hypothalamus (POAH) influence sleep- and arousal-regulating mechanisms. We examined the effeccts of POAH cell loss, produced by microinjection of neurotoxin ( N-methyl- dl-aspartic acid ), on sleep and thermoregulation in cats. Cats with bilateral POAH cell loss did not defend their body temperatures in the heat as effectively as normals, and did not initiate panting until brain temperatures rose to abnormally high levels. During 14 h polygraphic recordings of sleep-waking state conducted at an ambient temperature ( T a ) of 23°C, POAH-damaged cats exhibited reduced sleep. Amounts of deep slow-wave sleep (SWS2) were significantly less than prelesion values through 7 weeks postlesion; significant REM sleep deficits persisted for 5 weeks. However, these sleep disturbances were dramatically attenuated when cats were exposed to high T a S . During 6 h recordings at T a S of 13, 23, or 33 °C, total sleep time was greatest at 33 °C at both 2 and 4 weeks postlesion. At 4 weeks, amounts of SWS2 at 33 °C were similar to maximal prelesion values. Increased sleep at 33 °C was associated with elevated brain temperatures. The finding that, after POAH damage, abnormally high brain temperatures were required to elicit both panting and normal amounts of SWS suggests that impaired hypothalamic sensitivity to heat was responsible for both deficits. These results support the hypothesis that thermosensitive neurons participate in the tonic regulation of sleep and arousal.

Effects of zimeldine, a selective 5-HT reuptake inhibitor, combined with ritanserin, a selective 5-HT 2 antagonist, on waking and sleep stages in rats

Sleep and waking in rats were studied 8 h following administration of a selective 5-hydroxytryptamine (5-HT) reuptake inhibitor (zimeldine), a selective 5-HT 2 antagonist (ritanserin) and a combination of ritanserin and zimeldine. Consistent with earlier findings, zimeldine gave a biphasic effect on sleep and waking. Waking was increased the first 3 h, followed by an increase in deep slow wave sleep (SWS-2), maximal in hours 4 and 5. Ritanserin gave an increase in SWS-2 that was spread out over the recording period. Ritanserin + zimeldine also gave a biphasic effect as zimeldine did, and the initial increase in waking and the following increase in SWS-2 tended to be stronger. Thus, ritanserin did not block the initial waking effect seen after zimeldine administration, indicating that this waking effect was not due to 5-HT 2 stimulation. The increase in SWS-2 seemed to reflect an addition of the increases following the zimeldine and ritanserin alone conditions. This suggests that the increase in SWS-2 seen after 5-HT reuptake inhibition and 5-HT 2 blockade are independent phenomena. Zimeldine alone, ritanserin alone and the combination all gave a clear reduction of rapid eye movement sleep.

Involvement of histaminergic neurons in arousal mechanisms demonstrated with H 3-receptor ligands in the cat

The effects of histamine H 3-receptor ligands on sleep-waking parameters were studied in freely moving cats. Oral administration of (R)α-methylhistamine (αMHA), a H 3-agonist, caused a significant increase in deep slow wave sleep while that of thioperamide, a H 3-antagonist, enhanced wakefulness in a marked and dose-dependent manner. The arousal effects of thioperamide were prevented by pretreatment with αMHA or mepyramine, a H 1-receptor antagonist. The findings support the hypothesis that the histaminergic neurons are critically involved in arousal mechanisms and suggest that H 3-receptors play an active part in these mechanisms by regulating histamine transmission.

Effect of quinolinic acid on wakefulness and sleep in the rabbit

Quinolinic acid (QUIN), an endogenous neuroactive metabolite of tryptophan, administered i.c.v. in doses of 45, 90, 180, and 270 nmol in rabbits, demonstrated an excitatory action on the sleep-wake cycle and behaviour. Doses of 90 and 180 nmol completely abolished the paradoxical sleep phase and induced a 5-fold decrease in the duration of deep slow wave sleep (dSWS) in the first hour of the experiment. Light slow wave sleep (1SWS) duration was not altered. Sniffing behaviour was markedly activated by 180 nmol of QUIN. A dose of 270 nmol completely blocked sleep, diminished the restoration of sleep, induced panic behaviour and, in some animals, induced generalized tonic seizures. Data suggest an excitatory action of QUIN on NMDA receptors involved in the regulation of the sleep-wake cycle in the rabbit.

Differential effects of the new antipsychotic risperidone on sleep and wakefulness in the rat

The effects of risperidone, a new antipsychotic with potent 5-hydroxytryptamine 2 (5-HT 2) and dopamine-D 2 (DA-D 2) antagonistic properties, were studied on sleep-wakefulness patterns in rats. Administration of low doses (0.01–0.16 mg/kg i.p.) resulted in a significant increase of deep slow wave sleep (SWS2) and a decrease of wakefulness (W) and light slow wave sleep (SWSl). High doses (0.63–2.5 mg/kg) produced opposite effects. Paradoxical sleep (PS) was significantly reduced over the dose range tested. The increase of SWS2 after low doses of risperidone could be related to a predominant and potent 5-HT 2 receptor blocking activity.

The light-dark cycle modulates the effects of ritanserin on sleep-wakefulness patterns in the rat

The 5-HT2 receptor antagonist ritanserin (0.63 mg/kg IP) produced differential effects on sleep-wakefulness patterns in rats when administered during the light or dark period: an increase in the duration of deep slow wave sleep at the expense of light slow wave sleep, paradoxical sleep and wakefulness when injected during the light period, and no major sleep alteration when given at dark onset. Since circadian variations in serotonin receptor density might modulate the sleep response, we examined the effects of ritanserin on sleep in rats exposed to continuous light for 10 days, and whether 5-HT2 receptors were affected in separate groups of rats exposed to similar conditions. No significant changes in the KD- and Bmax -values of various receptors were found. However, ritanserin produced greater effects in continuous light conditions than when given during the light period in the 12-hr light-dark condition. This suggests a possible role of 5-HT2 receptors in the organization of sleep when the environmental photoperiod is disturbed.

Melatonin modulates the sensitivity of 5-hydroxytryptamine-2 receptor-mediated sleep—wakefulness regulation in the rat

The interaction between melatonin and two 5-hydroxytryptamine (5-HT 2) compounds was studied on sleep patterns in rats. Administration of the 5-HT 2 receptor antagonist ritanserin (0.63 mg/kg, i.p.) resulted in a significant increase of deep slow wave sleep (SWS2) and a decrease of paradoxical sleep (PS). The 5-HT 2 receptor agonist DOM (1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane) (0.63 mg/kg, i.p.) produced a significant reduction of both SWS2 and PS. Melatonin (1 mg/kg, i.p.) alone did not alter sleep but counteracted the sleep effects induced by ritanserin as well as DOM. It is proposed that melatonin modulates the sensitivity of 5-HT 2 receptor-mediated sleep response probably by an indirect route.

Functional role of 5-HT2 receptors in the regulation of sleep and wakefulness in the rat

Recently developed agents specifically acting on different 5-hydroxytryptamine (5-HT) receptor populations were used to analyze the functional role of 5-HT2 receptor subtypes in the sleep-wakefulness cycle of the rat. The 5-HT2 receptor antagonist ritanserin injected intraperitoneally (IP) (0.04-2.5 mg/kg) induced an increase in deep slow wave sleep (SWS2) duration at the expense of wakefulness (W), light slow wave sleep (SWS1) and paradoxical sleep (PS). The stimulation of 5-HT2 receptors by 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) produced a dose-related increase in W and a dose-dependent decrease in both SWS2 and PS. Pretreatment with ritanserin (0.16-2.5 mg/kg) or with cinanserin (2.5-5 mg/kg), another 5-HT2 receptor antagonist, dose-dependently reversed the W enhancement and the SWS2 deficit produced by DOM, but not the PS deficit. Sleep-wakefulness alterations (increase in W and SWS1 combined with a suppression of SWS2 and PS) observed after IP injection of two putative 5-HT1 receptor agonists, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (2.5 mg/kg) and 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969) (0.63 mg/kg), were not modified by ritanserin pretreatment (0.16-2.5 mg/kg). These results further support the hypothesis that the serotonergic system plays an active role in the regulation of the sleep-wakefulness cycle in the rat and that 5-HT2 receptors are involved in this action. In addition, it is suggested that 5-HT1 receptor subtypes are unlikely to interact with 5-HT2 receptors in the sleep-wakefulness modulation mediated through 5-HT2 receptors.

A critical role of the posterior hypothalamus in the mechanisms of wakefulness determined by microinjection of muscimol in freely moving cats

In order to determine critical sites within the hypothalamus responsible for the induction and maintenance of wakefulness (W), we performed microinjections of muscimol, a potent γ-aminobutyric acid (GABA) agonist, in various lateral hypothalamic regions of freely moving cats. We found that bilateral injections of a small amount of muscimol (0.1–1.0 μg/0.5 μl) in the preoptic and anterior hypothalamus and rostral mesencephalic tegmentum resulted in increased vigilance and insomnia. In contrast, microinjections of muscimol in the middle and anterior parts of the posterior hypothalamus induced long-lasting behavioral and electroencephalographic signs of sleep with short latency. The hypersomnia was characterized by a significant increase in both light and deep slow wave sleep (SWS), and a nearly complete suppression of paradoxical sleep (PS). Animals with muscimol microinjections in the ventrolateral part of the posterior hypothalamus, however, exhibited increased SWS followed by a significant increase in PS. When injected into the posterior hypothalamus of insomniac cats pretreated with p-chlorophenylalanine (PCPA), muscimol induced not only SWS but also PS with short latency. The present data thus support the hypotheses that the posterior hypothalamus plays a critical role in the mechanisms of W and that sleep might result from functional blockade of the hypothalamic waking center.

Long-lasting insomnia induced by preoptic neuron lesions and its transient reversal by muscimol injection into the posterior hypothalamus in the cat

In order to analyse the role of the anterior hypothalamus in the regulation of the sleep-waking cycle we made bilateral neuronal lesions at different levels of the anterior hypothalamus in cats, by means of microinjections of a cell-specific neurotoxin: ibotenic acid. These lesions resulted in severe insomnia in eight cats. This insomnia was characterized by a large decrease or even disappearance of paradoxical sleep and deep slow wave sleep and, to a lesser extent, by a decrease of light slow wave sleep, for 2–3 weeks. In the other five animals, we observed a large reduction of deep slow wave sleep (0–40% of control level), but a less intensive decrease of time spent in paradoxical sleep (50–75% of control level) and no marked effect on light slow wave sleep. During the first 3–6 postoperative days we also noticed hyperthermia in all cats; thereafter, the animals presented only a slight increase in brain temperature which did not appear to trigger the sleep impairment. Histological analysis of the different lesions revealed that the insomnia could be attributed to neuronal cell body destruction in the mediobasal part of the anterior hypothalamus covering: the medial preoptic area and a narrow portion of the lateral preoptic area as well as a restricted part of the anterior hypothalamic nucleus. In order to investigate the putative role of the posterior hypothalamic structures in the mechanism of insomnia after lesion of the mediobasal preoptic area neurons we injected an agonist of GABA into the ventrolateral part of the posterior hypothalamus to locally depress the neuronal activity. The bilateral intracerebral microinjection of muscimol (0.5–5 μg) induced a transient intensive hypersomnia (slow wave sleep and paradoxical sleep). These findings indicate that neuronal cell loss in the mediobasal preoptic area induced a long lasting insomnia. Thus, it may be hypothesized that the integrity of this structure is necessary for sleep appearance. Finally, our data are in keeping with an intrahypothalamic regulation of the sleep-waking cycle.

Animal models of chronic anxiety and “fearlessness”

Three behavioral animal models have been described, a feline and a rodent model of chronic anxiety, and a rodent model of “fearless” behavior. The models have been obtained by pre- or perinatal exposure to diazepam (DZ) or RO 15–1788 which produced enduring postnatal deficits or enrichment, respectively, of brain benzodiazepine (BDZ) receptors. The receptor-deficient one-year-old cat progenies showed hyperarousal, unabated restless behavior, delayed acquisition of instrumentally conditioned behavior, bizarre escape responses and absence or reduced alpha-like EEG activity. The receptor-deficient rat progencies, studied at the age of 5–6 months, showed a reduction of time spent in deep slow wave sleep, and inability to habituate to novel environment, such as the radial arm maze. In the maze, the behavior of these progenies was characterized by delayed and incomplete exploratory activity often terminated by sudden escape, numerous fecal deposits and significantly more frequent than normal errors of “working memory.” On the other hand, in all aspects, the receptor-enriched progenies were superior to the control animals as well as to the receptor-deficient group, particularly when the animals were challenged by novel and “intimidating” visual and/or auditory stimuli. In addition, 12 out of 51 receptor-deficient rats reared for 18 months developed mammary fibroadenomas, while no such tumors were found in the group of 44 vehicle-exposed control animals. Increased density and affinity of BDZ brain recepotrs was also observed after adult rats were treated with RO 15–1788 administered water for 7 or 14 days.

Relationship between sleep-wakefulness cycle and regional cerebral blood flow in kainic acid-induced epileptic focus in hippocampus.

Concurrent monitorings of polygraph and continuous measurements of rCBF of the epileptic focus were made in the nonanesthetized chronic cats. The influences of the sleep-wakefulness cycle on IIDs and rCBF of the epileptic focus of the hippocampus were analyzed. 1) IIDs increased remarkably during LSW and DSW but not as much as during DSW-P. 2) The rCBF decreased gradually during LSW and DSW. But the rCBF during DSW-P increased slightly as compared to that of DSW. 3) The frequencies of IIDs increased in association with hypoperfusion of the epileptic focus. 4) The spiking rate of the hippocampal focus decreased with the appearance of PGO during the deep slow wave sleep stages.

Evidence for histaminergic arousal mechanisms in the hypothalamus of cat

Polygraphic 23-hr recordings were carried out in 25 adult cats in order to examine the effects of both systemic and local injections of various histaminergic and antihistaminergic drugs on sleep-waking cycles. α-Fluroromethylhistidine (α-FMH), a specific inhibitor of histidine decarboxylase, when injected intraperitoneally at a dose of 20 mg/kg, induced a significant increase in deep slow wave sleep (S2) and a decrease in wakefulness (W), without modifying light slow wave sleep (S1) and paradoxical sleep (PS). Intraperitoneal injections of mepyramine (1 mg and 5 mg/kg), a well-known histamine H 1-receptor antagonist, increased deep slow wave sleep and decreased wakefulness, as well as paradoxical sleep. Bilateral injections of α-FMH (50 μg/l μl) into the ventrolateral posterior hypothalamus, where histamine immunoreactive neurones have been recently identified, resulted in a significant decrease in wakefulness and increase in deep slow wave sleep. Similarly, injections of mepyramine (120 μg/1 μl) in the same structures caused a significant decrease in wakefulness and an increase in deep slow wave and paradoxical sleep as well. In contrast, local injections of SKF-91488 (50 μg/l μl), a specific inhibitor of histamine- N-methyltransferase, led to a significant increase in wakefulness and decrease in both slow wave sleep (SWS) and paradoxical sleep. Injections of histamine, at doses of 5, 30 and 60 μg/1 μl, also increased wakefulness and decreased slow wave sleep dose dependently, while these effects were completely blocked by pretreatment with mepyramine. The results suggest that histaminergic systems in the hypothalamus play an important role in arousal mechanisms and their actions are mediated through H 1-receptors.

Differential effects of persistent nociceptive stimulation on sleep stages

The purpose of this work was to investigate the sequence of modifications of sleep and pain parameters in a condition of persistent nociceptive stimulation. In freely moving cats carrying implanted electrodes, continuous polygraphic and behavioral recordings were collected 24 h a day for several consecutive days before and after treatment. Injection of formalin (2 ml, 37%) elicited continuous wakefulness (1–6 h) associated with behavioral manifestations of pain. This insomnia was followed by the delayed appearance of LS (light, slow wave sleep) DS (deep slow wave sleep) and REM (rapid eye movement sleep). On days 1 and 2 after injection, pain manifestations displayed a gradual decrease, while total sleep time (LS + DS + REM) slowly returned to normal levels. On day 1, the amount of LS was not modified, but DS and REM were greatly decreased. For 12 h after the first REM episode, REM was decreased while DS was already at the basal levels. Formalin elicited a long-lasting increase in EMG activity of the tibialis anterior muscle which was suppressed during REM and returned to higher levels afterwards. Prolonged wakefulness and delay in sleep stage appearance were also recorded when a 24-h sleep deprivation preceded formalin injection. In this condition, LS, DS and REM amount were at basal levels from their first reappearance, and a rebound in total sleep time and DS occurred on day 2 after the injection. After injection of smaller doses of formalin (0.5 ml, 8%), the amount of LS, DS and REM was at control levels since day 1. The results suggest that (1) the amount of sleep depends on sleep debt and on the level of pain intensity and (2) sleep stages are differentially sensitive to persistent pain.