Effects of muscimol and flurazepam on the sleep EEG in the rat

Gamma-aminobutyric acid (GABA) receptor mediates suanzaorentang, a traditional Chinese herb remedy, -induced sleep alteration

The sedative-hypnotic medications, including benzodiazepines and non-benzodiazepines, are the most common treatments for insomnia. However, concerns regarding patterns of inappropriate use, dependence and adverse effects have led to caution in prescribing those sedative-hypnotic medications. On the other hand, a traditional Chinese herb remedy, suanzaorentang, has been efficiently and widely used in clinic for insomnia relief without severe side effects in Asia. Although suanzaorentang has been reported to improve sleep disruption in insomniac patients, its mechanism is still unclear. The present study was designed to elucidate the effects of oral administration of suanzaorentang on physiological sleep-wake architectures and its underlying mechanism in rats. We found that oral administration of suanzaorentang at the beginning of the dark onset dose-dependently increased non-rapid eye movement sleep (NREMS) during the dark period, but had no significant effect on rapid eye movement sleep (REMS). Our results also indicated that intracerebroventricular (ICV) administration of gamma-aminobutyric acid (GABA) receptor type A antagonist, bicuculline, significantly blocked suanzaorentang-induced enhancement in NREMS during the dark period, but GABA(B) receptor antagonist, 2-hydroxysaclofen had no effect. These results implicated that this traditional Chinese herb remedy, suanzaorentang increases spontaneous sleep activity and its effects may be mediated through the GABA(A) receptors, but not GABA(B) receptors.

The GABAA receptor agonist THIP alters the EEG in waking and sleep of mice

THIP is a GABA(A) agonist with hypnotic properties consisting in reducing sleep latency and prolonging and consolidating sleep. THIP has been reported to increase EEG slow-wave activity (SWA; EEG power in the 0.75-4 Hz band) in non-REM (NREM) sleep in both rats and humans. We investigated the effects of THIP on sleep in C57BL/6 mice. EEG recordings were performed after 2, 4 and 6 mg/kg THIP and saline control. The results were compared with analyses of recordings obtained after 6 h of sleep deprivation (SD) in the same strain of mice. The two higher doses of THIP induced an abnormal EEG pattern both in waking and NREM sleep. The EEG was characterized by sporadic asymmetric high-voltage potentials recurring at a low-frequency (<1 Hz) on the background of a low-amplitude EEG pattern. In contrast, after SD the typical regular synchronous high amplitude delta waves predominated. THIP at 4 and 6 mg/kg led to a prominent enhancement of spectral power in the low-frequency range of the waking and sleep EEG which was much higher than the increase attained after 6 h SD. This effect was particularly prominent in the waking EEG. In NREM sleep the increase of spectral power after THIP reflected the frequency of recurrence of the high-voltage potentials, and was restricted to a narrower frequency band than after SD. The EEG changes after 2mg/kg differed little from saline control. Sleep latency was not affected by the two lower doses of THIP, and was prolonged after 6 mg/kg. REM sleep was suppressed after the two higher doses. In contrast to previous results reported in other species, THIP did not have a hypnotic action in mice. The changes induced by THIP in the waking and sleep EEG differed from those caused by enhanced physiological sleep pressure encountered after SD. Considering the abnormal EEG pattern and the similarity of the spectral changes in the sleep and waking EEG, THIP does not seem to exert a specific effect on mechanisms involved in sleep regulation.

H3 agonist immepip markedly reduces cortical histamine release, but only weakly promotes sleep in the rat

Presynaptic H3 receptors exert negative control on brain histamine synthesis and release and may thereby play a key role in the control of the sleep/wake cycle. This suggests that pharmacological stimulation by H3 receptor agonists may potentially decrease wakefulness and induce sleep. This study reports the effect of a potent and selective H3 agonist, immepip, on EEG assessed sleep/wake phases in Sprague-Dawley rats at doses that significantly modulate brain histamine release. Immepip injected intraperitoneally (i.p.) at 5 or 10 mg kg(-1) induced a sustained decrease in cortical histamine efflux as measured by in vivo microdialysis. In a separate experiment, rats were prepared for EEG/EMG recording and evaluated during the dark phase of their light/dark cycle. The results showed that the same i.p. doses of 5 and 10 mg kg(-1) of immepip was devoid of any significant impact on the sleep/wake phases (active awake, drowsiness and slow wave sleep), except for a slight, albeit significant, decrease in sleep onset latency. These results reveal that a marked H3 receptor agonist-mediated reduction in cortical histamine release is not corroborated by a significant sleep promoting effect and therefore question the hypnotic potential of H3 agonists.

GABA mechanisms and sleep

GABA is the main inhibitory neurotransmitter of the CNS. It is well established that activation of GABA(A) receptors favors sleep. Three generations of hypnotics are based on these GABA(A) receptor-mediated inhibitory processes. The first and second generation of hypnotics (barbiturates and benzodiazepines respectively) decrease waking, increase slow-wave sleep and enhance the intermediate stage situated between slow-wave sleep and paradoxical sleep, at the expense of this last sleep stage. The third generation of hypnotics (imidazopyridines and cyclopyrrolones) act similarly on waking and slow-wave sleep but the slight decrease of paradoxical sleep during the first hours does not result from an increase of the intermediate stage. It has been shown that GABA(B) receptor antagonists increase brain-activated behavioral states (waking and paradoxical sleep: dreaming stage). Recently, a specific GABA(C) receptor antagonist was synthesized and found by i.c.v. infusion to increase waking at the expense of slow-wave sleep and paradoxical sleep. Since the sensitivity of GABA(C) receptors for GABA is higher than that of GABA(A) and GABA(B) receptors, GABA(C) receptor agonists and antagonists, when available for clinical practice, could open up a new era for therapy of troubles such as insomnia, epilepsy and narcolepsy. They could possibly act at lower doses, with fewer side effects than currently used drugs. This paper reviews the influence of different kinds of molecules that affect sleep and waking by acting on GABA receptors.

Effect of oleamide on sleep and its relationship to blood pressure, body temperature, and locomotor activity in rats

Oleamide (cis-9,10-octadecenoamide) is a brain lipid that has recently been isolated from the cerebral fluid of sleep-deprived cats. Intracerebroventricular and intraperitoneal administration of oleamide induces sleep in rats. However, it is unclear whether oleamide's hypnogenic effects are mediated, in part, by its actions on blood pressure and core body temperature. Here we show that systemic administration of oleamide (10 and 20 mg/kg) in rats increased slow-wave sleep 2, without affecting blood pressure and heart rate. In addition, oleamide decreased body temperature and locomotor activity in a dose-dependent manner. These latter effects were not correlated in time with the observed increases in slow-wave sleep. These data suggest that the hypnogenic effects of oleamide are not related to changes in blood pressure, heart rate, or body temperature.

Infusion of neurosteroids into the rat nucleus basalis affects paradoxical sleep in accordance with their memory modulating properties

The neurosteroids pregnenolone sulfate and allopregnanolone affect memory processes in an opposite manner, pregnenolone sulfate acts as a potent memory-enhancer whereas allopregnanolone impairs memory performance. The mechanisms underlying these memory modulating properties have yet to be elucidated. We have previously reported that infusions of either neurosteroid into the nucleus basalis magnocellularis, one of the main forebrain cholinergic nuclei, differentially affect spatial memory in rats. The relationships between memory performance and paradoxical sleep are well documented, therefore we investigated whether neurosteroids infused into the nucleus basalis magnocellularis affected the sleep-wakefulness cycle in rats, measured by electroencephalographic recordings. Results show that pregnenolone sulfate (5 ng) increased by 12%, whereas allopregnanolone (2 ng) decreased by 24%, the duration of paradoxical sleep in the 24 h interval following injection compared to control recordings. Pregnenolone sulfate inhibits GABA(A) receptors whereas allopregnanolone stimulates them. Since cholinergic neurons of the nucleus basalis magnocellularis are GABA-modulated, it may be postulated that these neurosteroids modify paradoxical sleep by acting on the cholinergic transmission. This may account, at least in part, for the memory modulating properties of these compounds.

Effects of muscimol or homotaurine on sleep-wake states in alcohol-dependent rats during withdrawal

Sleep-wake states were studied following withdrawal in 36 adult male wistar alcohol-dependent rats, after chronic administration of ethanol (10 g/kg/24 h) for 13 days. In the light phase of the withdrawal day, 12 alcohol-dependent rats received muscimol (0.25 mg/kg), 12 received homotaurine (140 mg/kg), and 12 received 0.9% physiological saline (10 ml/kg). The results have been compared with a control group of 36 rats that received water during the treatment phase of the experiment, and the 14th day received intraperitoneal muscimol or homotaurine. Muscimol significantly improves the alterations of sleep-wake states in alcohol-withdrawn rats, decreasing the percentage of active wakefulness and increasing the percentage of REMS, but without any action on the latency of appearance of REMS, which remains shortened. The effects of homotaurine are less important on the wakefulness, but it also increases the percentage of REMS without influencing its latency of appearance. The influence of these GABA(A) agonists is not identical during the whole period of survey in the light phase, as there are important differences in the temporal sequences for each of them. We conclude that the stimulation of GABA(A) receptors, of which the activity is decreased during alcohol withdrawal, significantly improves the disturbances in the sleep-wake states in the alcohol-dependent rats, in a time-related manner, and there are significant pharmacodynamic differences between muscimol and homotaurine.

Effect of the GABA uptake inhibitor tiagabine on sleep and EEG power spectra in the rat

1. The sleep profiles induced by agonists and agonistic modulators of gamma-aminobutyric acidA (GABA[A]) receptors differ markedly. With regard to GABA(A) agonists, the effects may be due to the fact that these agents are poor substrates for uptake and are therefore likely to activate GABA(A) receptors tonically. To investigate this possibility, we assessed the sleep effects of two doses (2 and 10 mg kg[-1]) of the GABA re-uptake inhibitor tiagabine, administered intraperitoneally at light onset in 8 rats. Electroencephalogram (EEG) and electromyogram were recorded during the first 8 h after the injection. 2. Compared with vehicle, tiagabine had minimal effects on the temporal pattern of non-rapid eye movement sleep (non-REMS) and on the total time spent therein. However, tiagabine dose-dependently elevated EEG activity during non-REMs, most prominently in the lower frequencies (1-8 Hz) and least pronounced in the frequencies between 11 and 16 Hz. During the first 2 h after the injection, 10 mg kg(-1) tiagabine elicited repetitive episodes of hypersynchronous EEG waves during wakefulness and slightly suppressed REMS. Except for these effects, tiagabine hardly influenced the time spent in and EEG activity during wakefulness and REMS. 3. The effects of tiagabine on state-specific EEG activity were qualitatively very similar to those elicited by GABA(A) agonists. These findings support the hypothesis that the influence of GABA(A) agonists on EEG signals may be caused by tonic stimulation of GABA(A) receptors.

Muscimol and midazolam do not potentiate each other's effects on sleep EEG in the rat

The interaction of a gamma-aminobutyric acid-A (GABAA) receptor agonist and a benzodiazepine-type modulator of GABAA receptors on sleep was investigated. Low doses of muscimol (0.3 mg/kg) and the benzodiazepine midazolam (1.5 mg/kg) were administered alone and in combination, in random order, to eight rats. All injections were given intraperitoneally at light onset. Electroencephalogram (EEG) and electromyogram were recorded during the first 6 h post injection. Compared with vehicle, muscimol hardly affected the time spent in non-rapid eye movement sleep (non-REMS) and REMS, but significantly enhanced EEG activity in the frequency range between 2 and 6 Hz during non-REMS. Midazolam significantly increased the time spent in non-REMS, reduced EEG activity at frequencies < 12 Hz, and elevated EEG activity in most higher frequencies during this state. The combined administration of muscimol and midazolam affected non-REMS-specific EEG activity in an unexpected fashion: the effects were intermediate between those of muscimol and midazolam. These results indicate that muscimol and midazolam have dissimilar effects on EEG within non-REMS and demonstrate that midazolam does not augment but attenuates the muscimol-induced changes in sleep EEG. Our data are at variance with established mechanisms, according to which agonistic modulators would have similar effects and should potentiate the effects of GABAA agonists. The present data suggest that application of agonists and agonistic modulators of GABAA receptors causes differential net effects on sleep parameters.

Effects of the GABAB antagonist CGP 35348 on sleep-wake states, behaviour, and spike-wave discharges in old rats

The GABAB antagonist CGP 35348 was intraperitoneally given in doses of 100, 300, and 900 mg/kg to old rats. These rats were earlier chronically provided with EEG and EMG electrodes. Sleep recordings based on visual inspection of EEG and EMG recordings were made for 3 h post injection, and spontaneous behaviour in the recording cage was additionally observed. With 100 and 300 mg/kg, the drug produced an increase in the duration of REM sleep compared to the saline-injected control group. The REM sleep latency was correspondingly reduced. Non-REM sleep and total sleep duration increased and an s-shaped dose-response relationship was found. Explorative behaviour was diminished after injections with 100 and 300 mg/kg CGP 35348. The number and duration of spike-wave discharges were reduced after all doses of CGP 35348 and during all 3 recording hours. The latter outcomes confirm the strong suppressive action of this drug on spike-wave discharges; these effects have also been reported in models of absence epilepsy. The hypnotic properties and especially the increase in REM sleep after the administration of CGP 35348 deserve attention considering the paucity of drugs which facilitate REM sleep. The discovery of drugs promoting REM sleep might have theoretical as well as clinical consequences.

Pregnenolone enhances EEG delta activity during non-rapid eye movement sleep in the rat, in contrast to midazolam

Several endogenous steroids exert their neuroactivity through non-genomic effects and act as potent GABAA receptor-agonists or-antagonists. To examine the influence of the main precursor of these steroids on sleep-wake behaviour, pregnenolone (400 micrograms) was dissolved in oil and administrated s.c. to 8 rats at the beginning of the light period. For comparison, the benzodiazepine midazolam was also injected (3 mg/kg). The effects on the amounts of the vigilance states and on the EEG signals within each state were investigated during 24 hours. Compared to control vehicle, pregnenolone did not significantly affect the duration of the vigilance states. However, delta activity (0.5-4 Hz) within non-rapid eye movement sleep (nonREMS) was enhanced throughout the recording period. Midazolam increased nonREMS, decreased wakefulness and, transiently, also suppressed rapid eye movement sleep (REMS). Spectral analysis of the EEG within nonREMS showed a long lasting reduction in delta and theta activity (4-9 Hz) and a shorter lasting enhancement in the higher frequencies (10-25 Hz). EEG activity within REMS and wakefulness was elevated in the higher frequencies (> or = 10 Hz) during the the first half of the recording period. We conclude that in the rat, the effects of midazolam on EEG activity closely resemble those of benzodiazepines in other mammalian species. The influence of pregnenolone on EEG delta activity within nonREMS indicates that pregnenolone acts as an inverse GABAA-benzodiazepine agonist.

CSF levels of diazepam-binding inhibitor correlate with REM latency in schizophrenia, a pilot study

CSF diazepam-binding inhibitor-like immunoreactivity (DBI-LI) and polysomnography were studied in 28 drug-free male schizophrenic (DSM-III-R) patients. They underwent a three-night polysomnography evaluation and a lumbar puncture. CSF DBI-LI correlated positively with REM latency, the REM latency/2d nonREM period ratio and stage-4% sleep, and negatively with stage-1% sleep. CSF DBI-LI did not correlate significantly with duration of sleep or sleep latency. CSF DBI-LI during haloperidol treatment did not correlate significantly with sleep EEG measures. The results of this first study of the relationship between endogenous DBI and sleep in humans suggest that physiological effects of DBI other than interactions with the BZD/GABAA receptor complex may explain its positive effects on sleep. However, the absence of similar sleep data in normal subjects precludes us from establishing a specific relationship between DBI and sleep in schizophrenia.

Do benzodiazepines induce sleep by a GABAergic mechanism?

In order to further characterize the possible role of GABA function in the sleep-inducing properties of benzodiazepines (BZs), we have administered the GABA agonist muscimol (0.05 and 0.1 mg/kg) and the GABA antagonist bicuculline (1.25 and 2.5 mg/kg) IP, alone and in combination with triazolam (0.8 mg/kg). There was no evidence of interaction of these compounds with triazolam vis a vis sleep. These data are consistent with an earlier report indicating a lack of interaction of muscimol with flurazepam, and suggest that non-GABAergic mechanisms may be involved in the hypnotic properties of benzodiazepines.

Effect of chlorpromazine and haloperidol on negative contrast

Rats shifted from 32 to 4% sucrose consume substantially less of the 4% solution than animals that have not had prior experience with the 32% sucrose. This negative contrast effect was not substantially influenced by chlorpromazine (1, 3, and 5 mg/kg) or haloperidol (0.1, 0.5, and 1.0 mg/kg). Haloperidol decreased overall lick frequency, but this decrease occurred proportionately in shifted and unshifted rats, leaving contrast intact. The benzodiazepine flurazepam (5, 10, and 20 mg/kg), included as a positive control, reduced contrast at the two highest doses. The results suggest that neuroleptics do not disrupt consummatory contrast and that dopaminergic antagonists may not influence reward relativity.