Cholinergic microstimulation of the peribrachial nucleus in the cat. I. Immediate and prolonged increases in ponto-geniculo-occipital waves.

The cholinergic agonist carbachol was injected into the pontine Pb area where PGO bursting cells have been recorded. When microinjections were localized to the ventrolateral aspect of the caudal Pb nucleus near aggregates of ChAT immunolabeled cholinergic neurons, carbachol produced an immediate onset of state-independent PGO waves in the ipsilateral LGB. These state-independent PGO waves persisted for 3-4 days. After the first 24 hrs PGO wave activity increasingly became associated with REM sleep and with REM transitional SP sleep as both of these PGO-related states increased in amount to 3-4 times baseline levels. The increase in amount of PGO-related states peaked on days 2-4 following one carbachol injection and persisted for 10-12 days. These results suggest a two stage process: stage one, PGO enhancement, is the direct consequence of the membrane activation of cholinoceptive PGO burst neurons by carbachol; stage two, REM enhancement, is the consequence of metabolic activation of endogenous cholinergic neurons. This experimental preparation is a useful model for the study of the electrophysiology and functional significance of PGO wave and REM sleep generation.     

Cholinergic mechanisms related to REM sleep. III. Tonic and phasic inhibition of monosynaptic reflexes induced by an anticholinesterase in the decerebrate cat

The depression of the postural activity induced by intravenous injection of eserine sulphate (0.1 mg/kg), an anticholinesterase, has been studied in precollicular decerebrate cats. The extensor and flexor monosynaptic reflexes elicited by single shock stimulation of the GS, P1-FDHL and DP nerves are tonically depressed during the episodes of postural atonia induced by the anticholinesterase. A further phasic depression of the monosynaptic reflexes occurs during the bursts of rapid eye movements (REM) typical of these episodes. These changes in spinal reflex activity closely resemble the tonic depression of the spinal reflexes described in the unrestrained cats during the desynchronized sleep as well as the phasic depression of the spinal reflexes characteristic of the hypnic bursts of REM. Results obtained after spinal cord section indicate that both the tonic and the phasic depression of the spinal reflexes induced by eserine are due to active inhibitory influences originating from supraspinal structures. A complete bilateral destruction of the vestibular nuclei or limited to the medial and descending vestibular nuclei abolishes not only the cholinergically induced bursts of REM, as reported in a previous paper, but also the related phasic depression of the monosynaptic reflexes. These findings can be related with previous observations showing that a bilateral lesion of the vestibular nuclei abolishes the REM bursts of desynchronized sleep, as well as the related phasic inhibition of the spinal reflexes. The tonic depression of the monosynaptic reflexes induced by the anticholinesterase, on the other hand, remains unmodified by this vestibular lesion. This depression, therefore, can be attributed to supraspinal descending inhibitory volleys originating from extravestibular structures.     

Minireview. Catecholamines and the sleep-wake cycle. II. REM sleep

The exact role of catecholamines (CA) on REM sleep is still controversial. Lesion studies suggest that norepinephrine plays a neuromodulatory role in REM sleep. Support for this view is provided by pharmacological studies in which noradrenergic neurons are activated or inhibited. Thus, disturbances in the dynamic balance between neurochemical systems may alter the conditions under which optimal REM sleep takes place. Discrete radiofrequency lesions to the pontine giganto-cellular tegmental field (which includes the nuclei reticularis pontis oralis and caudalis and where cholinergic and cholinoceptive neurons have been described), result in the elimination of REM sleep. Circumscribed, electrolytic lesions of the locus coeruleus (IC) area, which only minimally extend beyond it, eliminate atonia and reduce PGO activity in REM sleep. Selective destruction of the LC or ascending noradrenergic axons with 6-hydroxydopamine does not result in significant changes of tonic or phasic components of desynchronized sleep. These results indicate that noradrenergic neurons are not necessary for the initiation and maintenance of REM sleep. Most probably, many of the effects attributed to noradrenergic structures are due to destruction of non-noradrenergic neurons and fibers of passage in the lesioned area.Inhibition of CA synthesis with α-methyl-p-tyrosine has resulted in conflicting effects on REM sleep, which could be related to factors other than NE depletion. Systemic administration of dopamine-β-hydroxylase inhibitors (disulfiram, diethyldithiocarbamate, FLA-63, fusaric acid) produced consistent reductions of REM sleep. However, the simultaneous increase of 5-HT and DA levels complicates the interpretation of these results. Selective pharmacological stimulation of presynaptic α-adrenergic (α2) receptors with clonidine, xylazine or α-methyl-dopa decreases REM sleep. Specific blockade of α 2-receptors with yohimbine, piperoxane or tolazoline also reduces desynchronized sleep, but increases wakefulness. In contrast, drugs with similar affinity for pre and postsynaptic (α1) adrenoceptors (phentolamine) markedly increase REM sleep. Compounds Compounds with agonistic activity at postsynaptic α-adrenergic sites (methoxamine) consistently reduce REM sleep, while derivatives with inhibitory activity restricted to these receptors (thymoxamine, prazosin) produce REM sleep increments. Results from studies where propranolol and isoproterenol were administered to laboratory animals point to an involvement of β-adrenergic mechanisms in REM sleep modulation.Although there is no direct evidence to support a dopaminergic influence upon REM sleep executive mechanisms, indirect pharmacological data suggests a neuromodulatory role for dopaminergic neurons. Direct dopaminergic agonists and antagonists show biphasic effects on REM sleep. Low dosages of apomorphine increase, while large doses decrease, REM sleep. Opposite effects are observed after the dopaminergic antagonist pimozide. These dose-dependent effects seem to be related to the activation or blockade of different receptors.     

Asymmetry of the electroencephalographic manifestations of REM and slow-wave sleep in the cat

Studies were carried out on cats by bipolar electrodes implanted into symmetrical points of somatosensory cortical areas, caudate nuclei, hippocampus, lateral geniculate bodies, reticular formation of the midbrain after section of the half of midbrain tegmentum and commissural systems of the brain. Animals with sections usually have asymmetry of sleep EEG. The phenomenon is revealed of the coexistence of slow-wave and paradoxal sleep in different brain halves.     

Selective REM sleep deprivation during daytime. II. Muscle atonia in non-REM sleep

One of the hallmarks of rapid eye movement (REM) sleep is muscle atonia. Here we report extended epochs of muscle atonia in non-REM sleep (MAN). Their extent and time course was studied in a protocol that included a baseline night, a daytime sleep episode with or without selective REM sleep deprivation, and a recovery night. The distribution of the latency to the first occurrence of MAN was bimodal with a first mode shortly after sleep onset and a second mode 40 min later. Within a non-REM sleep episode, MAN showed a U-shaped distribution with the highest values before and after REM sleep. Whereas MAN was at a constant level over consecutive 2-h intervals of nighttime sleep, MAN showed high initial values when sleep began in the morning. Selective daytime REM sleep deprivation caused an initial enhancement of MAN during recovery sleep. It is concluded that episodes of MAN may represent an REM sleep equivalent and that it may be a marker of homeostatic and circadian REM sleep regulating processes. MAN episodes may contribute to the compensation of an REM sleep deficit.     

An ether stressor increases REM sleep in rats: possible role of prolactin

Sleep alterations after a 1-min exposure to ether vapor were studied in rats to determine if this stressor increases rapid eye-movement (REM) sleep as does an immobilization stressor. Ether exposure before light onset or dark onset was followed by significant increases in REM sleep starting approximately 3-4 h later and lasting for several hours. Non-REM (NREM) sleep and electroencephalographic slow-wave activity during NREM sleep were not altered. Exposure to ether vapor elicited prolactin (Prl) secretion. REM sleep was not promoted after ether exposure in hypophysectomized rats. If the hypophysectomy was partial and the rats secreted Prl after ether exposure, then increases in REM sleep were observed. Intracerebroventricular administration of an antiserum to Prl decreased spontaneous REM sleep and inhibited ether exposure-induced REM sleep. The results indicate that a brief exposure to ether vapor is followed by increases in REM sleep if the Prl response associated with stress is unimpaired. This suggests that Prl, which is a previously documented REM sleep-promoting hormone, may contribute to the stimulation of REM sleep after ether exposure.     

Exposure to dim artificial light at night increases REM sleep and awakenings in humans

Exposure to artificial light at night (ALAN) has become increasing common, especially in developed countries. We investigated the effect of dALAN exposure during sleep in healthy young male subjects. A total of 30 healthy young male volunteers from 21 to 29 years old were recruited for the study. They were randomly divided into two groups depending on light intensity (Group A: 5 lux and Group B: 10 lux). After a quality control process, 23 healthy subjects were included in the study (Group A: 11 subjects, Group B: 12 subjects). Subjects underwent an NPSG session with no light (Night 1) followed by an NPSG session randomly assigned to two different dim light conditions (5 or 10 lux, dom λ: 501.4 nm) for a whole night (Night 2). We found significant sleep structural differences between Nights 1 and 2, but no difference between Groups A and B. Exposure to dALAN during sleep was significantly associated with increased wake time after sleep onset (WASO; F = 7.273, p = 0.014), increased Stage N1 (F = 4.524, p = 0.045), decreased Stage N2 (F = 9.49, p = 0.006), increased Stage R (F = 6.698, p = 0.017) and non-significantly decreased REM density (F = 4.102, p = 0.056). We found that dALAN during sleep affects sleep structure. Exposure to dALAN during sleep increases the frequency of arousals, amount of shallow sleep and amount of REM sleep. This suggests adverse effects of dALAN during sleep on sleep quality and suggests the need to avoid exposure to dALAN during sleep.     

Cholinergic innervation of the gastric wall of the cat.

The inbuilt intrinsic cholinergic nervous apparatus of the gastric wall of the cat was studied by using two thiocholine methods for mapping the acetylcholinesterase-positive nerves and nerve cells. A rich distribution of acetylcholinesterase-positive nerves was observed in all layers of the gastric wall, except the superficial half of the lamina propria (with the epithelium), which was completely devoid of acetylcholinesterase activity, and the submucosa, in which a scarce distribution of large nerve fascicles and nerve trunks was observed. Acetylcholinesterase-positive ganglia were observed both in the subserous layer and in the myenteric plexus of Auerbach, whereas none were recognized in the submucous plexus of Meissner. This obviously fits well to the results of some electrophysiological experiments which indicate that the submucous plexus of Meissner includes an important intramural pathway from the extrinsic vagus nerves to the antrum region; so the submucous plexus of Meissner seems to be mainly involved in direct rapid conduction of nerve impulses without integrative activities, like a cable. Certain clear differences exist in the pattern of organization of the cholinergic intrinsic nervous apparatus within the different layers of the gastric wall in the fundic and pyloric regions. These differences seem to correspond quite logically to the different types of motor, secretory and neurohumoral activities of these main regions of the stomach. The activity of the non-specific cholinesterases was localized both in the neural elements and the smooth muscle, as well as in some epithelial cells.     

Effects of bromocriptine and alpha-flupenthixol on sleep in REM sleep deprived rats.

Administration of bromocriptine mesylate (5 mg/kg, i.p.), a dopamine receptor stimulant, to rats which were deprived of REM sleep for 24 hours resulted in a significant increase in wakefulness as well as significant reduction of REM sleep during the first 5 hours of EEG recording. These effects were completely abolished by pretreatment with α-flupenthixol (0.2 mg/kg, i.p.), a dopamine receptor blocker. The loss of REM sleep has not been regained during the next 25 hours of EEG recording suggesting that the stimulation of dopamine receptors reduced REM sleep without causing subsequent REM rebound. These data raise questions on the negative dopamine control of REM sleep and on the potential use of dopamine stimulants in clinical situations characterized by excessive REM or by REM sleep dysfunction (narcolepsy).     

Microinjection of the melanin-concentrating hormone into the lateral basal forebrain increases REM sleep and reduces wakefulness in the rat

AimsTo examine the effects of bilateral microinjection of melanin-concentrating hormone (MCH) 50 and 100 ng into the horizontal limb of the diagonal band of Broca (HDB) on sleep variables during the light phase of the light–dark cycle of the rat.Main methodsMale Wistar rats were implanted for chronic sleep recordings. In addition, a guide cannula was implanted above the right and left HDB. Following the microinjection of MCH or control solution the electroencephalogram and the electromyogram were recorded for 6 h. Data was collected and classified as either wakefulness (W), light sleep, slow wave sleep (SWS) or REM sleep (REMS). Latencies for SWS and REMS, as well as the number of REM periods and the mean duration of REM episodes were also determined.Key findingsMCH 50 and 100 ng significantly decreased W during the first 2-h of recording. Moreover, MCH 100 ng significantly reduced REMS latency and increased REMS time during the first 2-h block of the recording, due to an increase in the number of REM periods.SignificanceOur findings tend to suggest that the basal forebrain participates in the effects of MCH on W and REMS through the deactivation of cholinergic, glutamatergic and γ-aminobutyric acid (GABA)-ergic cells.     

Development of REM sleep drive and clinical implications.

Rapid eye movement (REM) sleep in the human declines from approximately 50% of total sleep time ( approximately 8 h) in the newborn to approximately 15% of total sleep time (approximately 1 h) in the adult, and this decrease takes place mainly between birth and the end of puberty. We hypothesize that without this developmental decrease in REM sleep drive, lifelong increases in REM sleep drive may ensue. In the rat, the developmental decrease in REM sleep occurs 10-30 days after birth, declining from >70% of total sleep time in the newborn to the adult level of approximately 15% of sleep time during this period. Rats at 12-21 days of age were anesthetized with ketamine and decapitated, and brain stem slices were cut for intracellular recordings. We found that excitatory responses of pedunculopontine nucleus (PPN) neurons to N-methyl-D-aspartic acid decrease, while responses to kainic acid increase, over this critical period. During this developmental period, inhibitory responses to serotonergic type 1 agonists increase but responses to serotonergic type 2 agonists do not change. The results suggest that as PPN neurons develop, they are increasingly activated by kainic acid and increasingly inhibited by serotonergic type 1 receptors. These processes may be related to the developmental decrease in REM sleep. Developmental disturbances in each of these systems could induce differential increases in REM sleep drive, accounting for the postpubertal onset of a number of different disorders manifesting increases in REM sleep drive. Examination of modulation by PPN projections to ascending and descending targets revealed the presence of common signals modulating ascending arousal-related functions and descending postural/locomotor-related functions.     

Role of dorsal raphe nucleus serotonin 5-HT1A receptor in the regulation of REM sleep

Cholinergic neurons in the laterodorsal (LDT) and the pedunculopontine (PPT) tegmental nuclei act to promote REM sleep (REMS). The predominantly glutamatergic neurons of the REMS-induction region of the medial pontine reticular formation are in turn activated by cholinergic cells, which results in the occurrence of tonic and phasic components of REMS. All these neurons are inhibited by serotonergic (5-HT), noradrenergic, and presumably histaminergic (H2 receptor) and dopaminergic (D2 and D3 receptor) cells. 5-Hydroxytryptamine-containing neurons in the dorsal raphe nucleus (DRN) virtually cease firing when an animal starts REMS, consequently decreasing the release of 5-HT during this state. The activation of GABA(A) receptors is apparently responsible for this phenomenon. Systemic administration of the selective 5-HT1A receptor agonist 8-OHDPAT induces dose-dependent effects; i.e. low doses increase slow wave sleep and reduce waking, whereas large doses increase waking and reduce slow wave sleep and REM sleep. Direct injection of 8-OHDPAT or flesinoxan, another 5-HT1A agonist into the DRN, or microdialysis perfusion of 8-OHDPAT into the DRN significantly increases REMS. On the other hand, infusion of 8-OHDPAT into the LDT selectively inhibits REMS, as does direct administration into the DRN of the 5-HT1A receptor antagonists pindolol or WAY 100635. Thus, presently available evidence indicates that selective activation of the somatodendritic 5-HT1A receptor in the DRN induces an increase of REMS. On the other hand, activation of the postsynaptic 5-HT1A receptor at the level of the PPT/LDT nuclei decreases REMS occurrence.     

CO2 dialysis in nucleus tractus solitarius region of rat increases ventilation in sleep and wakefulness.

To evaluate the function of widely distributed central chemoreceptors during sleep and wakefulness in the rat, we focally stimulate single chemoreceptor sites during naturally occurring sleep-wake cycles by microdialysis of artificial cerebrospinal fluid equilibrated with 25% CO2. In retrotrapezoid nucleus, this increased ventilation (tidal volume) by 24% only in wakefulness (Li A, Randall M, and Nattie E. J Appl Physiol 87: 910-919, 1999). In caudal medullary raphé, it increased ventilation (frequency) by 15-20% only in sleep (Nattie EE and Li A. J Appl Physiol 90: 1247-1257, 2001). Here, in nucleus tractus solitarius (NTS), focal acidification significantly increased ventilation by 11% in sleep and 7% in wakefulness rostrally (n = 5) and by 16% in sleep and 28% in wakefulness caudally (n = 5). The sleep-wake cycle was unaltered. Dialysis with 5% CO2 had no effect. Dialysis with 50% CO2 caudally did not further stimulate ventilation but did disrupt sleep. Central chemoreceptors in the NTS affect breathing in both sleep and wakefulness. The threshold for arousal in caudal NTS is greater than that for the stimulation of breathing.     

Selective brain cooling is impaired in REM sleep.

There are systemic and selective mechanisms for brain cooling in mammals. The difference between the temperatures of the vertebral and the carotid blood perfusing the brain is determined by selective heat loss and is, therefore, a quantitative indicator of the intensity of selective brain cooling. Across the wake-sleep cycle systemic and selective brain cooling are affected by state-dependent autonomic changes. In REM sleep selective brain cooling is impaired.     

Induction of wakefulness and inhibition of active (REM) sleep by GABAergic processes in the nucleus pontis oralis

The present study was undertaken to explore the role of brainstem GABAergic processes in the control of the behavioral states of sleep and wakefulness, and to compare the effects of GABAA agonists and antagonists with those of GABAB agonists and antagonists on these behavioral states. Accordingly, the following drugs were microinjected into the nucleus pontis oralis (NPO) in chronic, unanesthetized cats: muscimol (GABAA agonist), bicuculline (GABAA antagonist), baclofen (GABAB agonist) and phaclofen (GABAB antagonist). The percentage, latency, frequency and duration of each behavioral state were measured in order to quantify the effects of these microinjections on wakefulness and sleep. Microinjections of either muscimol or baclofen immediately induced wakefulness. There was a significant increase in the duration and the percentage of time spent in wakefulness as well as an increase in the latency to active (REM) sleep. These changes were accompanied by a decrease in the percentage of time spent in active and quiet sleep. In contrast, injections of bicuculline or phaclofen produced active sleep. The percentage of time spent in active sleep and the frequency of active sleep increased while the percentage of time spent in wakefulness and the latency to active sleep was significantly reduced. The effects of GABAA receptor agonists and antagonists on wakefulness and active sleep were comparable, but stronger than those of GABAB receptor agonists and antagonists. These data indicate that pontine GABAergic processes acting on both GABAA and GABAB receptors play a critical role in generating and maintaining wakefulness and in controlling the occurrence of state of active sleep.     

Potentiation of ketamine effects on the spiking activity in the lateral geniculate nucleus by rapid eye movement (REM) sleep deprivation.

In cats prepared for chronic recording of sleep, an investigation was made on the effects of an anaesthetic agent, ketamine [cl-581, 2-(O-chlorophenyl)-2-methylaminocyclohexamine HCl] and rapid eye movement (REM) sleep deprivation on spiking activity recorded from lateral geniculate (LGN) nucleus. In normal cats most of the LGN spikes occurring during sleep are found in REM sleep. Follwoing injection of 10 mg/kg of ketamine a substantial increase of slow wave sleep (SWS) spikes occurred. While selective REM sleep deprivation had the same effects, combined influences of ketamine and REM-sleep deprivation led to a marked potentiation of their individual effects probably by simultaneous stimulation of the neurone system which determines the endogenous electrical activity of LGN cells.