Differential effects of sodium butyrate and physostigmine upon the activities of para-sleep in acute brain stem preparations

Neural Control of REM Sleep and Motor Atonia: Current Perspectives

PURPOSE OF REVIEW

Since the formal discovery of rapid eye movement (REM) sleep in 1953, we have gained a vast amount of knowledge regarding the specific populations of neurons, their connections, and synaptic mechanisms regulating this stage of sleep and its accompanying features. This article discusses REM sleep circuits and their dysfunction, specifically emphasizing recent studies using conditional genetic tools.

RECENT FINDINGS

Sublaterodorsal nucleus (SLD) in the dorsolateral pons, especially the glutamatergic subpopulation in this region (SLDGlut), are shown to be indispensable for REM sleep. These neurons appear to be single REM generators in the rodent brain and may initiate and orchestrate all REM sleep events, including cortical and hippocampal activation and muscle atonia through distinct pathways. However, several cell groups in the brainstem and hypothalamus may influence SLDGlut neuron activity, thereby modulating REM sleep timing, amounts, and architecture. Damage to SLDGlut neurons or their projections involved in muscle atonia leads to REM behavior disorder, whereas the abnormal activation of this pathway during wakefulness may underlie cataplexy in narcolepsy. Despite some opposing views, it has become evident that SLDGlut neurons are the sole generators of REM sleep and its associated characteristics. Further research should prioritize a deeper understanding of their cellular, synaptic, and molecular properties, as well as the mechanisms that trigger their activation during cataplexy and make them susceptible in RBD.

Activation of inactivation process initiates rapid eye movement sleep

Interactions among REM-ON and REM-OFF neurons form the basic scaffold for rapid eye movement sleep (REMS) regulation; however, precise mechanism of their activation and cessation, respectively, was unclear. Locus coeruleus (LC) noradrenalin (NA)-ergic neurons are REM-OFF type and receive GABA-ergic inputs among others. GABA acts postsynaptically on the NA-ergic REM-OFF neurons in the LC and presynaptically on the latter's projection terminals and modulates NA-release on the REM-ON neurons. Normally during wakefulness and non-REMS continuous release of NA from the REM-OFF neurons, which however, is reduced during the latter phase, inhibits the REM-ON neurons and prevents REMS. At this stage GABA from substantia nigra pars reticulate acting presynaptically on NA-ergic terminals on REM-ON neurons withdraws NA-release causing the REM-ON neurons to escape inhibition and being active, may be even momentarily. A working-model showing neurochemical-map explaining activation of inactivation process, showing contribution of GABA-ergic presynaptic inhibition in withdrawing NA-release and dis-inhibition induced activation of REM-ON neurons, which in turn activates other GABA-ergic neurons and shutting-off REM-OFF neurons for the initiation of REMS-generation has been explained. Our model satisfactorily explains yet unexplained puzzles (i) why normally REMS does not appear during waking, rather, appears following non-REMS; (ii) why cessation of LC-NA-ergic-REM-OFF neurons is essential for REMS-generation; (iii) factor(s) which does not allow cessation of REM-OFF neurons causes REMS-loss; (iv) the association of changes in levels of GABA and NA in the brain during REMS and its deprivation and associated symptoms; v) why often dreams are associated with REMS.

Neurobiological mechanisms for the regulation of mammalian sleep-wake behavior: reinterpretation of historical evidence and inclusion of contemporary cellular and molecular evidence

At its most basic level, the function of mammalian sleep can be described as a restorative process of the brain and body; recently, however, progressive research has revealed a host of vital functions to which sleep is essential. Although many excellent reviews on sleep behavior have been published, none have incorporated contemporary studies examining the molecular mechanisms that govern the various stages of sleep. Utilizing a holistic approach, this review is focused on the basic mechanisms involved in the transition from wakefulness, initiation of sleep and the subsequent generation of slow-wave sleep and rapid eye movement (REM) sleep. Additionally, using recent molecular studies and experimental evidence that provides a direct link to sleep as a behavior, we have developed a new model, the cellular-molecular-network model, explaining the mechanisms responsible for regulating REM sleep. By analyzing the fundamental neurobiological mechanisms responsible for the generation and maintenance of sleep-wake behavior in mammals, we intend to provide a broader understanding of our present knowledge in the field of sleep research.

Role of norepinephrine in the regulation of rapid eye movement sleep

Sleep and wakefulness are instinctive behaviours that are present across the animal species. Rapid eye movement (REM) sleep is a unique biological phenomenon expressed during sleep. It evolved about 300 million years ago and is noticed in the more evolved animal species. Although it has been objectively identified in its present characteristic form about half a century ago, the mechanics of how REM is generated, and what happens upon its loss are not known. Nevertheless, extensive research has shown that norepinephrine plays a crucial role in its regulation. The present knowledge that has been reviewed in this manuscript suggests that neurons in the brain stem are responsible for controlling this state and presence of excess norepinephrine in the brain does not allow its generation. Furthermore, REM sleep loss increases levels of norepinephrine in the brain that affects several factors including an increase in Na-K ATPase activity. It has been argued that such increased norepinephrine is ultimately responsible for REM sleep deprivation, associated disturbances in at least some of the physiological conditions leading to alteration in behavioural expression and settling into pathological conditions.

Sleep-waking cycle in chronic rat preparations with brain stem transected at the caudopontine level

The brain stem of rats was transected at the middle of the nucleus reticularis pontis caudalis. The preparations were maintained 2-9 days, and their EEG activity and behavior were studied. Maintained EEG activity and EEG arousal to visual and olfactory stimuli indicated the presence of sleep-waking cycle. Three stages were identified. Two of them corresponded to waking with hippocampal theta rhythm and to slow wave sleep in intact rats. The third stage (absent in intact rats) was characterized by slow waves and spindles of low amplitude in the cortex and low frequency theta rhythm, and it was considered as "drowsiness." Waking without theta rhythm, paradoxical sleep, and its forerunner intermediate stage were never found. Paroxystic-like EEG episodes were frequently observed. Thus, although present, the sleep-waking cycle is severely impaired in the caudopontine rats. The impairment is similar to that found previously in rats transected at the intercollicular or pretrigeminal level. The preparations were able to crawl abortively and to swallow liquid. Their respiratory rhythm was normal, but the heart rate increased. Thus, the caudal part of the preparations showed remarkable ability in controlling motor and vegetative functions.

Sleep patterning and behaviour in cats with pontine lesions creating REM without atonia

Lesions of the dorsal pontine tegmentum release muscle tone and motor behaviour, much of it similar to orienting during wakefulness, into rapid eye movement sleep (REM), a state normally characterized by paralysis. Sleep after pontine lesions may be altered, with more REM-A episodes of shorter duration compared to normal REM. We examined behaviour, ponto-geniculo-occipital (PGO) waves (which may be central markers of orienting) and sleep in lesioned cats: (i) to characterize the relationship of PGO waves to behaviour in REM-A; (ii) to determine whether post-lesion changes in the timing and duration of REM-A episodes were due to activity-related awakenings: and (iii) to determine whether alterations in sleep changed the circadian sleep/wake cycle in cats. Behavioural release in REM-A was generally related to episode length, but episode length was not necessarily shorter than normal REM in cats capable of full locomotion in REM-A. PGO wave frequency was reduced overall during REM-A, but was higher during REM-A with behaviour than during quiet REM-A without overt behaviour. Pontine lesions did not significantly alter the circadian sleep/wake cycle: REM-A had approximately the same Light/Dark distribution as normal REM. Differences in the patterning of normal REM and REM-A within sleep involve more than mere movement-induced awakenings. Brainstem lesions that eliminate the atonia of REM may damage neural circuitry involved in REM initiation and maintenance; this circuitry is separate from circadian control mechanisms.

Carbachol microinjections in the mediodorsal pontine tegmentum are unable to induce paradoxical sleep after caudal pontine and prebulbar transections in the cat

In 7 cats, total transections of the brainstem at the caudal pontine or the prebulbar level led to preparations which presented neither behavioral nor electrophysiological signs of paradoxical sleep (PS) throughout their survival periods (17-30 days). Carbachol microinjections in the mediodorsal pontine tegmentum (MDPT), which induced PS in the intact cat, were no longer able to induce it in the transected animals. Rapid eye movement (REM) and pontogeniculo-occipital (PGO)-like bursts were evoked by carbachol microinjections in the pontine magnocellular tegmental field (FTM) of cats transected at the prebulbar level, as in the intact cat. Only REM bursts were obtained by the same injections in caudal pontine transected cats. It is concluded that (1) the pons is insufficient to generate PS; (2) complex reciprocal interactions with the medulla are necessary for the generation of this state of sleep; and (3) the production of long REM and PGO bursts is controlled by the caudal pontine tegmentum.

Responses of locus coeruleus neurons to labyrinth and neck stimulation

The electrical activity of a large population of locus coeruleus (LC)-complex neurons, some of which were antidromically activated by stimulation of the spinal cord at T12-L1, was recorded in precollicular decerebrate cats during labyrinth and neck stimulation. Some of these neurons showed physiological characteristics attributed to norepinephrine (NE)-containing LC neurons, i.e., (i) a slow and regular resting discharge; (ii) a typical biphasic response to compression of the paws consisting of short impulse bursts followed by a silent period, which was attributed to recurrent and/or lateral inhibition of the corresponding neurons; and (iii) a suppression of the resting discharge during episodes of postural atonia, associated with rapid eye movements (REM), induced by systemic injection of an anticholinesterase, a finding which closely resembled that occurring in intact animals during desynchronized sleep. Among the neurons tested, 80 of 141 (i.e., 56.7%) responded to the labyrinth input elicited by sinusoidal tilt about the longitudinal axis of the whole animal at the standard parameters of 0.15 Hz, +/- 10 degrees, and 73 of 99 (i.e., 73.7%) responded to the neck input elicited by rotation of the body about the longitudinal axis at the same parameters, while maintaining the head stationary. A periodic modulation of firing rate of the units was observed during the sinusoidal stimuli. In particular, most of the LC-complex units were maximally excited during side-up tilt of the animal and side-down neck rotation, the response peak occurring with an average phase lead of about +17.9 degrees and +34.2 degrees with respect to the extreme animal and neck displacements, respectively. Similar results were also obtained from the antidromically identified coeruleospinal (CS) neurons. The degree of convergence and the modalities of interaction of vestibular and neck inputs on LC-complex neurons were also investigated. In addition to the results described above, the LC-complex neurons were also tested to changing parameters of stimulation. In particular, both static and dynamic components of single unit responses were elicited by increasing frequencies of animal tilt and neck rotation. Moreover, the relative stability of the phase angle of the responses evaluated with respect to the animal position in most of the units tested at increasing frequencies of tilt allowed the conclusion to attribute these responses to the properties of macular ultricular receptors. This conclusion is supported by the results of experiments showing that LC-complex neurons displayed steady changes in their discharge rate during static tilt of the animal.(ABSTRACT TRUNCATED AT 400 WORDS)

Cholinergic brainstem sites for gain control of vestibulospinal reflexes in cats

Decerebrate cats were injected with carbachol into the locus coeruleus (LC) or with carbachol or bethanechol into the dorsal pontine reticular formation (pRF) of one side; recordings were made of the tonic contraction of forelimb extensor muscles of both sides and of their responses to sinusoidal roll tilt of the animal. Both drugs had similar effects when injected into the pRF: a decrease in the tonic contraction of limb extensors and a greatly enhanced amplitude and gain with slightly decreased phase lead in the responses to animal tilt of the forelimb extensor, triceps brachii, ipsilateral to the side of injection. Injected into the LC, carbachol produced a response opposite to the above: it increased the tonic contraction of limb extensors ipsilateral to the side of injection, but decreased the amplitude and gain of the EMG responses of limb extensor muscles to labyrinth stimulation induced by sinusoidal tilt. These findings did not depend on changes in posture since they were still observed when postural EMG activity was maintained constant by appropriate changes in static stretch of the muscle. Moreover, the magnitude of the effects increased in a dose-dependent manner. Results suggest that cholinergic activation of dorsal pRF neurons through muscarinic receptors increases the background discharge of medullary inhibitory reticulospinal (RS) system neurons, thus increasing their modulatory influence. Further, it is postulated that cholinergic activation of LC neurons would cause them to inhibit this tonic facilitatory drive by the pRF. Common to both sites of carbachol injection is the increase in phase lag of the EMG response of limb extensors to animal tilt.(ABSTRACT TRUNCATED AT 250 WORDS)

Behavioral states in the chronic medullary and midpontine cat

Behavioral state organization was studied in the caudal portion of chronically maintained cats with transections at the ponto-medullary junction or midpontine level. The cats spent most of their time in a 'quiescent state.' This state was periodically interrupted by 'phasic activations.' During quiescence, ECG and reticular unit activity rates were low and regular. EMG levels resembled those seen during non-REM sleep in intact cats. During phasic activations, unit activity in the nucleus gigantocellularis and neck EMG activity increased to levels seen in the intact cat during active waking. Gross postural changes, vestibular slow phase head nystagmus and head shake reflexes could be observed at these times. No periods of neck muscle atonia were observed in either state. No periods of brain-stem controlled rapid eye movements (REMs) occurred. Unit activity patterns similar to those seen in the intact cat during REM sleep were never observed. Physostigmine administration did not produce REM sleep signs, but rather, triggered an aroused state. Phasic activations occurred in a regular ultradian rhythm, with a period similar to that seen in the REM sleep cycle. We conclude that the chronic medullary cat retains primitive aroused and quiescent states, but does not have any of the local signs of REM sleep. However, the medulla does have the capability of generating ultradian rhythmicities which may contribute to the control of the basic rest activity cycle and the REM, non-REM sleep cycle.

REM sleep signs rostral to chronic transections at the pontomedullary junction

The brainstems of 3 cats were transected at the ponto-medullary junction and the cats maintained in stable condition for periods of from 16 to 31 days. After transection, all of these cats had periods in which forebrain sensorimotor cortex, olfactory bulb, hippocampus, eye movement and lateral geniculate recordings exhibited the pattern of activity seen only in REM sleep in the intact cat. We conclude that medullary regions are not required to generate these signs of REM sleep. The pons is necessary for REM sleep and is sufficient to produce REM sleep signs in rostral as well as caudal brain regions. However, the medulla may contribute to regulation of the duration and periodicity of REM sleep.