Prolonged enhancement of REM sleep produced by carbachol microinjection into the amygdala

Regulation of Dark Period Sleep by the Amygdala: A microinjection and optogenetics study

The central nucleus of the amygdala (CNA) projects to brainstem regions that generate and regulate rapid eye movement sleep (REM). We used optogenetics to assess the influence of CNA inputs into reticularis pontis oralis (RPO), pedunculopontine tegmentum (PPT) and nucleus subcoeruleus (SubC) on dark period sleep. We compared these results to effects of microinjections into CNA of the GABA_A agonist, muscimol (MUS, inhibition of cell bodies) and tetrodotoxin (TTX, inhibition of cell bodies and fibers of passage). For optogenetics, male Wistar rats received excitatory (AAV5-EF1a-DIO -hChR2(H134R)-EYFP) or inhibitory (AAV-EF1a-DIO-eNpHR3.0-EYFP; DIO-eNpHR3.0) opsins into CNA and AAV5-EF1a-mCherry-IRES-WGA-Cre into RPO, PPT, or SubC. This enabled only CNA neurons synaptically connected to each region to express opsin. Optic cannulae for light delivery into CNA and electrodes for determining sleep were implanted. Sleep was recorded with and without blue or amber light stimulation of CNA. Separate rats received MUS or TTX into CNA prior to recording sleep. Optogenetic activation of CNA neurons projecting to RPO enhanced REM and did not alter non-REM (NREM) whereas activation of CNA neurons projecting to PPT or SubC did not significantly affect sleep. Inhibition of CNA neurons projecting to any region did not significantly alter sleep. TTX inactivation of CNA decreased REM and increased NREM whereas muscimol inactivation did not significantly alter sleep. Thus, the amygdala can regulate decreases and increases in REM, and RPO is important for CNA promotion of REM. Fibers passing through CNA, likely from the basolateral nucleus of the amygdala, also play a role in regulating sleep.

Dopaminergic- and cholinergic-inputs from substantia nigra and pedunculo-pontine tegmentum, respectively, converge in amygdala to modulate rapid eye movement sleep in rats

Dreams appear intermittently during phasic rapid eye movement sleep (REMS). Although reasonable progress has been made about neuro-physio-pharmacological mechanism of appearance of REMS, appearance of dreams is a mystery. Isolated studies have reported that substantia nigra (SN) withdraws inhibition from pedunculo-pontine tegmentum (PPT) acetylcholine (ACh)-ergic REM-ON neurons to trigger REMS; some REM-ON neurons become phasically active during REMS; amygdala (Amyg), a limbic structure associated with emotions, may be related with dreaming like state; Amyg receives projections from both SN-Dopamine (DA)-ergic and PPT-ACh-ergic neurons. Collating these isolated findings, we proposed that on the background of REMS, SN-DA-ergic and PPT-ACh-ergic inputs phasically activate Amyg-neurons to manifest dreams. In the absence of better criteria, we recorded electrophysiological characteristics of REMS as the closest objective read-out for dreams in surgically prepared, chronic, freely moving rats. Microinjection of either DA-ergic or ACh-ergic agonist [Quinpirole (Qnp) or Carbachol (Carb)] bilaterally into Amyg increased, while antagonists [Haloperidol (Hal) or Scopolamine (Scop)] reduced REMS. Electrical stimulation of either bilateral SN or PPT increased REMS, which however, was prevented when stimulated in presence of Hal or Scop, respectively into the Amyg. These findings confirm and support our contention that SN-DA-ergic and PPT-ACh-ergic inputs integrate in Amyg for REMS regulation. Further, subject to confirmation in humans, we propose that on the background of REMS, some phasic PPT-ACh-ergic-REM-ON neurons intermittently trigger some neurons in Amyg, the area known to be associated with memory and emotions, causing intermittent appearance of REMS-associated dreams and in REMS behavior disorder.

Sleep, Narcolepsy, and Sodium Oxybate

Sodium oxybate (SO) has been in use for many decades to treat narcolepsy with cataplexy. It functions as a weak GABAB agonist but also as an energy source for the brain as a result of its metabolism to succinate and as a powerful antioxidant because of its capacity to induce the formation of NADPH. Its actions at thalamic GABAB receptors can induce slow-wave activity, while its actions at GABAB receptors on monoaminergic neurons can induce or delay REM sleep. By altering the balance between monoaminergic and cholinergic neuronal activity, SO uniquely can induce and prevent cataplexy. The formation of NADPH may enhance sleep’s restorative process by accelerating the removal of the reactive oxygen species (ROS), which accumulate during wakefulness. SO improves alertness in normal subjects and in patients with narcolepsy. SO may allay severe psychological stress - an inflammatory state triggered by increased levels of ROS and characterized by cholinergic supersensitivity and monoaminergic deficiency. SO may be able to eliminate the inflammatory state and correct the cholinergic/ monoaminergic imbalance.

Consolidative mechanisms of emotional processing in REM sleep and PTSD

Research suggests sleep plays a role in the consolidation of recently acquired memories for long-term storage. rapid eye movement (REM) sleep has been shown to play a complex role in emotional-memory processing, and may be involved in subsequent waking-day emotional reactivity and amygdala responsivity. Interaction of the hippocampus and basolateral amygdala with the medial-prefrontal cortex is associated with sleep-dependent learning and emotional memory processing. REM is also implicated in post-traumatic stress disorder (PTSD), which is characterized by sleep disturbance, heightened reactivity to fearful stimuli, and nightmares. Many suffers of PTSD also exhibit dampened medial-prefrontal cortex activity. However, the effects of PTSD-related brain changes on REM-dependent consolidation or the notion of 'over-consolidation' (strengthening of memory traces to such a degree that they become resistant to extinction) have been minimally explored. Here, we posit that (in addition to sleep architecture changes) the memory functions of REM must also be altered in PTSD. We propose a model of REM-dependent consolidation of learned fear in PTSD and examine how PTSD-related brain changes might interact with fear learning. We argue that reduced efficacy of inhibitory medial-prefrontal pathways may lead to maladaptive processing of traumatic memories in the early stages of consolidation after trauma.

GABA Cells in the Central Nucleus of the Amygdala Promote Cataplexy

Cataplexy is a hallmark of narcolepsy characterized by the sudden uncontrollable onset of muscle weakness or paralysis during wakefulness. It can occur spontaneously, but is typically triggered by positive emotions such as laughter. Although cataplexy was identified >130 years ago, its neural mechanism remains unclear. Here, we show that a newly identified GABA circuit within the central nucleus of the amygdala (CeA) promotes cataplexy. We used behavioral, electrophysiological, immunohistochemical, and chemogenetic strategies to target and manipulate CeA activity selectively in narcoleptic (orexin^-/-) mice to determine its functional role in controlling cataplexy. First, we show that chemogenetic activation of the entire CeA produces a marked increase in cataplexy attacks. Then, we show that GABA cells within the CeA are responsible for mediating this effect. To manipulate GABA cells specifically, we developed a new mouse line that enables genetic targeting of GABA cells in orexin^-/- mice. We found that chemogenetic activation of GABA CeA cells triggered a 253% increase in the number of cataplexy attacks without affecting their duration, suggesting that GABA cells play a functional role in initiating but not maintaining cataplexy. We show that GABA cell activation only promotes cataplexy attacks associated with emotionally rewarding stimuli, not those occurring spontaneously. However, we found that chemogenetic inhibition of GABA CeA cells does not prevent cataplexy, suggesting these cells are not required for initiating cataplexy attacks. Our results indicate that the CeA promotes cataplexy onset and that emotionally rewarding stimuli may trigger cataplexy by activating GABA cells in the CeA.SIGNIFICANCE STATEMENT Although cataplexy has been closely linked to positive emotions for >130 years, the neural circuitry that underlies this relationship is poorly understood. Recent work suggests that the amygdala, a brain area important for processing emotion, may be part of this circuit. This study provides the first functional evidence to implicate GABA cells in the amygdala as regulators of cataplexy triggered by positive emotions and identifies the amygdala as the brain region important more for gating the entrance into rather than the exit from cataplexy. We also generated a new mouse model for studying GABA neurons in narcoleptic mice, which could serve as a useful tool for studying the neurobiological underpinnings of narcolepsy.

The 'affect tagging and consolidation' (ATaC) model of depression vulnerability

Since the 1960's polysomnographic sleep research has demonstrated that depressive episodes are associated with REM sleep alterations. Some of these alterations, such as increased REM sleep density, have also been observed in first-degree relatives of patients and remitted patients, suggesting that they may be vulnerability markers of major depressive disorder (MDD), rather than mere epiphenomena of the disorder. Neuroimaging studies have revealed that depression is also associated with heightened amygdala reactivity to negative emotional stimuli, which may also be a vulnerability marker for MDD. Several models have been developed to explain the respective roles of REM sleep alterations and negatively-biased amygdala activity in the pathology of MDD, however the possible interaction between these two potential risk-factors remains uncharted. This paper reviews the roles of the amygdala and REM sleep in the encoding and consolidation of negative emotional memories, respectively. We present our 'affect tagging and consolidation' (ATaC) model, which argues that increased REM sleep density and negatively-biased amygdala activity are two separate, genetically influenced risk-factors for depression which interact to promote the development of negative memory bias - a well-known cognitive vulnerability marker for depression. Predictions of the ATaC model may motivate research aimed at improving our understanding of sleep dependent memory consolidation in depression aetiology.

Human amygdala activation during rapid eye movements of rapid eye movement sleep: an intracranial study

The amygdaloid complex plays a crucial role in processing emotional signals and in the formation of emotional memories. Neuroimaging studies have shown human amygdala activation during rapid eye movement sleep (REM). Stereotactically implanted electrodes for presurgical evaluation in epileptic patients provide a unique opportunity to directly record amygdala activity. The present study analysed amygdala activity associated with REM sleep eye movements on the millisecond scale. We propose that phasic activation associated with rapid eye movements may provide the amygdala with endogenous excitation during REM sleep. Standard polysomnography and stereo-electroencephalograph (SEEG) were recorded simultaneously during spontaneous sleep in the left amygdala of four patients. Time-frequency analysis and absolute power of gamma activity were obtained for 250 ms time windows preceding and following eye movement onset in REM sleep, and in spontaneous waking eye movements in the dark. Absolute power of the 44-48 Hz band increased significantly during the 250 ms time window after REM sleep rapid eye movements onset, but not during waking eye movements. Transient activation of the amygdala provides physiological support for the proposed participation of the amygdala in emotional expression, in the emotional content of dreams and for the reactivation and consolidation of emotional memories during REM sleep, as well as for next-day emotional regulation, and its possible role in the bidirectional interaction between REM sleep and such sleep disorders as nightmares, anxiety and post-traumatic sleep disorder. These results provide unique, direct evidence of increased activation of the human amygdala time-locked to REM sleep rapid eye movements.

REM Sleep at its Core - Circuits, Neurotransmitters, and Pathophysiology

Rapid eye movement (REM) sleep is generated and maintained by the interaction of a variety of neurotransmitter systems in the brainstem, forebrain, and hypothalamus. Within these circuits lies a core region that is active during REM sleep, known as the subcoeruleus nucleus (SubC) or sublaterodorsal nucleus. It is hypothesized that glutamatergic SubC neurons regulate REM sleep and its defining features such as muscle paralysis and cortical activation. REM sleep paralysis is initiated when glutamatergic SubC cells activate neurons in the ventral medial medulla, which causes release of GABA and glycine onto skeletal motoneurons. REM sleep timing is controlled by activity of GABAergic neurons in the ventrolateral periaqueductal gray and dorsal paragigantocellular reticular nucleus as well as melanin-concentrating hormone neurons in the hypothalamus and cholinergic cells in the laterodorsal and pedunculo-pontine tegmentum in the brainstem. Determining how these circuits interact with the SubC is important because breakdown in their communication is hypothesized to underlie narcolepsy/cataplexy and REM sleep behavior disorder (RBD). This review synthesizes our current understanding of mechanisms generating healthy REM sleep and how dysfunction of these circuits contributes to common REM sleep disorders such as cataplexy/narcolepsy and RBD.

Stress, arousal, and sleep

Stress is considered to be an important cause of disrupted sleep and insomnia. However, controlled and experimental studies in rodents indicate that effects of stress on sleep-wake regulation are complex and may strongly depend on the nature of the stressor. While most stressors are associated with at least a brief period of arousal and wakefulness, the subsequent amount and architecture of recovery sleep can vary dramatically across conditions even though classical markers of acute stress such as corticosterone are virtually the same. Sleep after stress appears to be highly influenced by situational variables including whether the stressor was controllable and/or predictable, whether the individual had the possibility to learn and adapt, and by the relative resilience and vulnerability of the individual experiencing stress. There are multiple brain regions and neurochemical systems linking stress and sleep, and the specific balance and interactions between these systems may ultimately determine the alterations in sleep-wake architecture. Factors that appear to play an important role in stress-induced wakefulness and sleep changes include various monominergic neurotransmitters, hypocretins, corticotropin releasing factor, and prolactin. In addition to the brain regions directly involved in stress responses such as the hypothalamus, the locus coeruleus, and the amygdala, differential effects of stressor controllability on behavior and sleep may be mediated by the medial prefrontal cortex. These various brain regions interact and influence each other and in turn affect the activity of sleep-wake controlling centers in the brain. Also, these regions likely play significant roles in memory processes and participate in the way stressful memories may affect arousal and sleep. Finally, stress-induced changes in sleep-architecture may affect sleep-related neuronal plasticity processes and thereby contribute to cognitive dysfunction and psychiatric disorders.

Altered sleep in Borderline Personality Disorder in relation to the core dimensions of psychopathology

The aim of the study was to review the literature regarding sleep disturbances in Borderline Personality Disorder (BPD) and to relate the reported sleep alterations to the underlying core dimensions of BPD pathology. We present a qualitative and theoretical review regarding the empirical studies that investigated objective and subjective sleep quality in BPD and in different psychiatric conditions showing high co-morbidity with this disorder. We show that disturbed sleep including sleep fragmentation, alterations in Slow Wave Sleep and REM sleep, and dysphoric dreaming are prevalent symptoms in BPD. We provide a framework relating the specific sleep alterations to the core dimensions of BPD pathology in order to clarify the inconsistencies of the different findings. The specific sleep disturbances in BPD seem to be related to different dimensions of psychopathological functioning and may have detrimental consequences on waking affect and cognition. Investigating disturbed sleep in BPD in relation to waking symptoms and underlying neural functioning would shed more light on the nature of this complex disorder. Moreover, a stronger emphasis on sleep disturbances would enrich the treatment protocols of BPD.

Effects of MPEP, a selective metabotropic glutamate mGlu5 ligand, on sleep and wakefulness in the rat

Metabotropic glutamate receptors (mGlu) have been implicated in the regulation of physiological and behavioral processes. Pharmacological evidence involves group I mGlu receptors in the regulation of emotional states and antagonism of these receptors has been proposed as a novel class of anxiolytic drugs having also antidepressant effects. Here, the effects of mGlu5 receptor selective modulation on sleep and wake states are explored. 32 male Wistar rats were implanted with electrodes for recording sleep and wake states. 2-Methyl-6-(phenylethynyl)pyridine hydrochloride (MPEP hydrochloride, 5, 10, and 20 mg/kg, i.p.), a potent, selective and systemically active mGlu5 receptor negative allosteric modulator, or vehicle was administered 1 h after the beginning of the light period. Sleep recordings were conducted for 3 h. MPEP (5, 10, and 20 mg/kg) significantly suppressed rapid eye movement (REM) sleep, decreasing the number of episodes and mean episode duration, and increased its latency. A reduction of light and deep slow wave sleep (SWS) latency was observed in the groups receiving 10 or 20 mg/kg, increasing latency to first wakefulness episode. 10 mg/kg of MPEP also increased non rapid eye movement sleep (NREM). The present results suggest that mGlu5 receptors might be involved in sleep regulation, more specifically in REM sleep, and drugs that block these receptors could potentially benefit the treatment of pathologies were REM sleep is enhanced.

Effects of microinjections of Group II metabotropic glutamate agents into the amygdala on sleep

Systemic administration of the Group II metabotropic glutamate (mGlu) receptor agonist, LY379268 (LY37), dose-dependently suppresses rapid eye movement sleep (REM) whereas systemic administration of the mGlu II receptor antagonist, LY341495 (LY34), increases arousal. Group II mGlu receptors are highly expressed in the amygdala, a brain region involved in the regulation of sleep and arousal. To determine whether the amygdala is involved in mediating the effects of Group II mGlu agents on sleep, we microinjected LY37 and LY34 into the basal amygdala (BA) and the central nucleus of the amygdala (CNA) and recorded sleep and wakefulness. Wistar rats were implanted with electrodes for recording sleep and with bilateral cannulae aimed into BA for drug administration. Different groups of rats received bilateral microinjections of LY37 into BA at two dosage ranges (3.2 mM, 5.3 mM or 10.7 mM or 0.1 nM, 2.0 nM or 10.0 nM) or one dosage range of LY34 (1.0 nM, 30.0 nM or 60.0 nM). Microinjections into CNA were conducted at one dosage range for LY37 (0.1 nM, 2.0 nM or 10.0 nM) and for LY34 (1.0 nM, 30.0 nM or 60.0 nM). All drugs or vehicle alone were administered in a counterbalanced order at 5-day intervals. Following microinjection, sleep was recorded for 20 h. Microinjection of LY37 into BA at both nM and mM concentrations significantly decreased REM without significantly altering NREM, total sleep or wakefulness. The high dosage of LY34 in BA significantly suppressed NREM and total sleep. Microinjections of LY37 or LY34 into CNA had no significant impact on sleep. We suggest that Group II mGlu receptors may influence specific cells in BA that control descending output (via the CNA or bed nucleus of the stria terminalis) that in turn regulates pontine REM generator regions.

Excitatory projections from the amygdala to neurons in the nucleus pontis oralis in the rat: an intracellular study

There is a consensus that active (REM) sleep (AS) is controlled by cholinergic projections from the laterodorsal and pedunculopontine tegmental nuclei (LDT/PPT) to neurons in the nucleus pontis oralis (NPO) that generate AS (i.e. AS-Generator neurons). The present study was designed to provide evidence that other projections to the NPO, such as those from the amygdala, are also capable of inducing AS. Accordingly, the responses of neurons, recorded intracellularly in the NPO, were examined following stimulation of the ipsilateral central nucleus of the amygdala (CNA) in urethane-anesthetized rats. Single pulse stimulation in the CNA produced an early, fast depolarizing potential (EPSP) in neurons within the NPO. The mean latency to the onset of these excitatory postsynaptic potentials (EPSPs) was 3.6±0.2 ms. A late, small-amplitude inhibitory synaptic potential (IPSP) was present following EPSPs in a portion of the NPO neurons. Following stimulation of the CNA with a train of 8-10 pulses, NPO neurons exhibited a sustained depolarization (5-10 mV) of their resting membrane potential. When single subthreshold intracellular depolarizing current pulses were delivered to NPO neurons, CNA-induced EPSPs were sufficient to promote the discharge of these cells. Stimulation of the CNA with a short train of stimuli induced potent temporal facilitation of EPSPs in NPO neurons. Two forms of synaptic plasticity were revealed by the patterns of response of NPO neurons following stimulation of the CNA: paired-pulse facilitation (PPF) and post-tetanic potentiation (PTP). Six of recorded NPO neurons were identified morphologically with neurobiotin. They were medium to large, multipolar cells with diameters >20 μM, which resemble AS-on cells in the NPO. The present results demonstrate that amygdalar projections are capable of exerting a powerful excitatory postsynaptic drive that activates NPO neurons. Therefore, we suggest that the amygdala is capable of inducing AS via direct projections to AS-Generator neurons in the NPO.

Effects of stressor predictability and controllability on sleep, temperature, and fear behavior in mice

STUDY OBJECTIVES

Predictability and controllability are important factors in the persisting effects of stress. We trained mice with signaled, escapable shock (SES) and with signaled, inescapable shock (SIS) to determine whether shock predictability can be a significant factor in the effects of stress on sleep.

DESIGN

Male BALB/cJ mice were implanted with transmitters for recording EEG, activity, and temperature via telemetry. After recovery from surgery, baseline sleep recordings were obtained for 2 days. The mice were then randomly assigned to SES (n = 9) and yoked SIS (n = 9) conditions. The mice were presented cues (90 dB, 2 kHz tones) that started 5.0 sec prior to and co-terminated with footshocks (0.5 mA; 5.0 sec maximum duration). SES mice always received shock but could terminate it by moving to the non-occupied chamber in a shuttlebox. SIS mice received identical tones and shocks, but could not alter shock duration. Twenty cue-shock pairings (1.0-min interstimulus intervals) were presented on 2 days (ST1 and ST2). Seven days after ST2, SES and SIS mice, in their home cages, were presented with cues identical to those presented during ST1 and ST2.

SETTING

NA.

PATIENTS OR PARTICIPANTS

NA.

INTERVENTIONS

NA.

MEASUREMENTS AND RESULTS

On each training and test day, EEG, activity and temperature were recorded for 20 hours. Freezing was scored in response to the cue alone. Compared to SIS mice, SES mice showed significantly increased REM after ST1 and ST2. Compared to SES mice, SIS mice showed significantly increased NREM after ST1 and ST2. Both groups showed reduced REM in response to cue presentation alone. Both groups showed similar stress-induced increases in temperature and freezing in response to the cue alone.

CONCLUSIONS

These findings indicate that predictability (modeled by signaled shock) can play a significant role in the effects of stress on sleep.

Projection neurons from the central nucleus of the amygdala to the nucleus pontis oralis

The present retrograde labeling study was designed to determine the presence and pattern of projections from individual subdivisions of the central nucleus of the amygdala (CNA) to the nucleus pontis oralis (NPO), which is a critical brainstem site involved in the generation and maintenance of active (REM) sleep. Projections from the CNA were labeled with the retrograde tracer cholera toxin B-subunit (CTB), which was injected, unilaterally, via microiontophoresis, into the NPO. Sections of the amygdala were immunostained in order to identify CTB-labeled CNA neurons and CNA neurons that contained CTB plus the vesicular glutamate transporter 2 (VGLUT2), which is a marker for glutamatergic neurons. Histological analyses revealed that retrogradely labeled neurons that project to the NPO were localized, ipsilaterally, within the medial, lateral, and capsular subdivisions of the CNA. In addition, a substantial proportion (24%) of all retrogradely labeled CNA neurons also exhibited VGLUT2 immunoreactivity. The present study demonstrates that glutamatergic neurons, which are present within various subdivisions of the CNA, project directly to the NPO. These data lend credence to the hypothesis that NPO neurons that are involved in the control of active sleep are activated by glutamatergic projections from the amygdala.

Conditional corticotropin-releasing hormone overexpression in the mouse forebrain enhances rapid eye movement sleep

Impaired sleep and enhanced stress hormone secretion are the hallmarks of stress-related disorders, including major depression. The central neuropeptide, corticotropin-releasing hormone (CRH), is a key hormone that regulates humoral and behavioral adaptation to stress. Its prolonged hypersecretion is believed to play a key role in the development and course of depressive symptoms, and is associated with sleep impairment. To investigate the specific effects of central CRH overexpression on sleep, we used conditional mouse mutants that overexpress CRH in the entire central nervous system (CRH-COE-Nes) or only in the forebrain, including limbic structures (CRH-COE-Cam). Compared with wild-type or control mice during baseline, both homozygous CRH-COE-Nes and -Cam mice showed constantly increased rapid eye movement (REM) sleep, whereas slightly suppressed non-REM sleep was detected only in CRH-COE-Nes mice during the light period. In response to 6-h sleep deprivation, elevated levels of REM sleep also became evident in heterozygous CRH-COE-Nes and -Cam mice during recovery, which was reversed by treatment with a CRH receptor type 1 (CRHR1) antagonist in heterozygous and homozygous CRH-COE-Nes mice. The peripheral stress hormone levels were not elevated at baseline, and even after sleep deprivation they were indistinguishable across genotypes. As the stress axis was not altered, sleep changes, in particular enhanced REM sleep, occurring in these models are most likely induced by the forebrain CRH through the activation of CRHR1. CRH hypersecretion in the forebrain seems to drive REM sleep, supporting the notion that enhanced REM sleep may serve as biomarker for clinical conditions associated with enhanced CRH secretion.

Differential effects of lorazepam on sleep and activity in C57BL/6J and BALB/cJ strain mice

Compared to C57BL/6 mice, BALB/c mice exhibit greater 'anxiousness' on behavioural tests of anxiety, and can show significantly longer sleep disruptions after exposure to anxiogenic situations. Relative to C57BL/6 mice, BALB/c mice also have reduced benzodiazepine (BZ) receptor densities in the brain and fivefold less BZ receptor density in the amygdala, a region important in anxiety and in the control of arousal. Lorazepam is a BZ receptor full agonist and has been used to treat both anxiety and insomnia. Differences between C57BL/6 and BALB/c mice raise the question of whether BZ agonists would impact sleep and activity differentially in the two strains. We examined the effects of two doses of lorazepam (0.5 and 1.5 mg kg(-1)) or saline alone (0.2 mL) on sleep and activity in C57BL/6 (n = 8) and BALB/c (n = 7) mice. Compared to saline, both doses of lorazepam significantly increased non-rapid eye movement (NREM) and reduced activity in both strains. In C57BL/6 mice, rapid eye movement (REM) was increased at both doses. In BALB/c mice, the 0.5 mg kg(-1) dose had no significant influence on REM, whereas REM was reduced significantly after the 1.5 mg kg(-1) dose. The results demonstrate significant differences between C57BL/6 and BALB/c mice in the effects of lorazepam on REM, whereas the effects on NREM and activity were similar. Strain differences in the number of BZ receptors in the amygdala, but not other brain regions, suggests possible site specificity in the effects of lorazepam on REM. These differences in BZ-binding sites in the amygdala could be a significant factor in differences in the sleep response between C57 and BALB/c mice.

GABAergic antagonism of the central nucleus of the amygdala attenuates reductions in rapid eye movement sleep after inescapable footshock stress

STUDY OBJECTIVES

Rapid eye movement sleep (REM) appears to be especially susceptible to the effects of stress; inescapable footshock stress (IS) can produce reductions in REM that can occur without recovery sleep. The amygdala has well-established roles in stress and emotion; the central nucleus of the amygdala (CNA) projects to REM regulatory regions in the brainstem and has been found to play a key role in the regulation of REM. The objective of this study was to determine whether the reduction in REM induced by IS could be regulated by CNA and brainstem regions.

DESIGN

The GABAergic agonist muscimol (MUS) and GABAergic antagonist bicuculline (BIC) were microinjected into CNA before IS, and sleep was recorded for 20 h. In a second experiment using the same manipulations, sleep was recorded for 2 h, after which the rats were killed to evaluate Fos expression (a marker of neuronal activity) in the locus coeruleus (LC), a brainstem REM regulatory region.

SETTING

NA.

PATIENTS OR PARTICIPANTS

The subjects were male, outbred Wistar rats.

INTERVENTIONS

The rats were surgically implanted with standard electrodes or with telemetry transmitters for determining arousal state.

MEASUREMENTS AND RESULTS

IS preceded by control or MUS microinjections selectively reduced REM and increased Fos expression in LC. By comparison, microinjection of BIC into CNA prior to IS attenuated both the reduction in REM and Fos expression in LC to levels seen in non-shocked controls.

CONCLUSIONS

The results suggest that the effects of IS on REM may involve local GABAergic inhibition in CNA and activation of LC.

Brain activity and temporal coupling related to eye movements during REM sleep: EEG and MEG results

EEG and MEG REM sleep gamma activity was studied immediately before rapid eye movement onset (PRE-EM), during REM sleep with eye movements away from eye movement onset -phasic-REM (Ph-REM)--and during REM sleep without eye movements, or tonic REM (T-REM). For this purpose, activity was segmented into three different time windows: of 62.5, 250 and 500 ms. Two strategies were used: one a statistical comparison of changes between T-REM, Ph-REM and PRE-EM; the other a descriptive approach using principal component analysis. Significant findings showed that both EEG and MEG gamma activity are higher directly before eye movement onset in PRE-EM periods and during Ph-REM than during T-REM; temporal coupling of electrical activity between the frontal and parietal regions is decreased, while temporal coupling between the right frontal and midline is increased. Just before eye movement onset, larger recording sites become related. For the first time, results showed a close temporal link between power and temporal coupling of fast oscillations andrapid eye movements in REM sleep, indicating increased activation, uncoupling between the left frontal executive areas and posterior sensory association regions and increased coupling between the right frontal attentional and midline alerting systems. Brain activity is reorganized by phasic events.

The role of active zone protein Rab3 interacting molecule 1 alpha in the regulation of norepinephrine release, response to novelty, and sleep

Sleep mechanisms and synaptic plasticity are thought to interact to regulate homeostasis and memory formation. However, the influences of molecules that mediate synaptic plasticity on sleep are not well understood. In this study we demonstrate that mice lacking Rab3 interacting molecule 1 alpha (RIM1 alpha) (Rim1 alpha KO), a protein of the synaptic active zone required for certain types of synaptic plasticity and learning, had 53+/-5% less baseline rapid eye movement (REM) sleep compared with their wild type littermates. Also, compared with wild type littermates, exposure of the mice to an open field or to a novel object induced more robust and longer lasting locomotion suggesting altered habituation. This difference in exploratory behavior correlated with genotype specific changes in REM and deregulated release of norepinephrine in the cortex and basal amygdala of the Rim1 alpha KO mice. Also, moderate sleep deprivation (4 h), a test of the homeostatic sleep response, induced REM sleep rebound with different time course in Rim1 alpha KO and their wild type littermates. As norepinephrine plays an important role in regulating arousal and REM sleep, our data suggest that noradrenergic deficiency in Rim1 alpha KO animals impacts exploratory behavior and sleep regulation and contributes to impairments in learning.

Mouse strain differences in the effects of corticotropin releasing hormone (CRH) on sleep and wakefulness

Corticotropin releasing hormone (CRH) plays a major role in central nervous system responses to stressors and has been implicated in stress-induced alterations in sleep. In the absence of stressors, CRH contributes to the regulation of spontaneous waking. We examined the effects of CRH and astressin (AST), a non-specific CRH antagonist, on wakefulness and sleep in two mouse strains with differential responsiveness to stress to determine whether CRH might also differentially affect undisturbed sleep and activity. Less reactive C57BL/6J (n=7) and high reactive BALB/cJ (n=7) male mice were implanted with a transmitter for determining sleep via telemetry and with a guide cannula aimed into a lateral ventricle. After recovery from surgery and habituation to handling, ICV microinjections of CRH (0.04, 0.2, and 0.4 microg), AST (0.1, 0.4, and 1.0 microg) or vehicle alone (pyrogen-free saline, 0.2 microl) were administered during the fourth hour after lights on and sleep was recorded for the subsequent 8 h. Comparisons of wakefulness and sleep were conducted across conditions and across strains. In C57BL/6J mice, REM was significantly decreased after microinjections of CRH (0.2 microg) and CRH (0.4 microg), and NREM and total sleep were decreased after microinjections of CRH (0.4 microg). CRH (0.04 microg) and AST did not significantly change wakefulness or sleep. In BALB/cJ mice, CRH (0.4 microg) increased wakefulness and decreased NREM, REM and total sleep. AST decreased active wakefulness and significantly increased REM at the low and high dosages. These findings demonstrate that CRH produces changes in arousal when given to otherwise undisturbed mice. Strain differences in the effects of CRH and AST may be linked to the relative responsiveness of C57BL/6J and BALB/cJ mice to stressors and to underlying differences in the CRH system.

Neuroimaging in sleep medicine

The development of neuroimaging techniques has made possible the characterization of cerebral function throughout the sleep-wake cycle in normal human subjects. Indeed, human brain activity during sleep is segregated within specific cortical and subcortical areas in relation to the sleep stage, sleep physiological events and previous waking activity. This approach has allowed sleep physiological theories developed from animal data to be confirmed, but has also introduced original concepts about the neurobiological mechanisms of sleep, dreams and memory in humans. In contrast, at present, few neuroimaging studies have been dedicated to human sleep disorders. The available work has brought interesting data that describe some aspects of the pathophysiology and neural consequences of disorders such as insomnia, sleep apnea and narcolepsy. However, the interpretation of many of these results is restricted by limited sample size and spatial/temporal resolution of the employed technique. The use of neuroimaging in sleep medicine is actually restrained by concerns resulting from the technical experimental settings and the characteristics of the diseases. Nevertheless, we predict that future studies, conducted with state of the art techniques on larger numbers of patients, will be able to address these issues and contribute significantly to the understanding of the neural basis of sleep pathologies. This may finally offer the opportunity to use neuroimaging, in addition to the clinical and electrophysiological assessments, as a helpful tool in the diagnosis, classification, treatment and monitoring of sleep disorders in humans.

Transient fear-induced alterations in evoked release of norepinephrine and GABA in amygdala slices

Presentation of a tonal cue that previously had been associated with a fearful experience (footshock) produces alterations in arousal and sleep that occur after the fearful cue is no longer presented. To begin investigating neurochemical mechanisms that may underlie the effects of fearful cue presentation, we measured release of [(3)H]-norepinephrine ([(3)H]-NE]) and [(14)C]-gamma-amino-butyric acid ([(14)C]-GABA) from brain regions known to regulate arousal states and REM sleep. Depolarization-evoked release of [(3)H]-NE from amygdalar slices of mice, which were trained to recognize a tone as a fearful cue, was suppressed at 2-3 h after exposure of animals to the fearful cue, but recovered after 4-5 h. Interestingly, depolarization-evoked release of [(14)C]-GABA was significantly increased in the amygdala, and also showed a tendency for enhancement in the hippocampus, NPO, and DRN at 2-3 h after cue presentation. The changes in [(14)C]-GABA release were also transient; 4-5 h after cue presentation no significant differences were detected between samples derived from experimental groups which experienced fearful or neutral cues. The similar time course of fearful cue-induced changes in neurotransmitter release and changes in arousal and REM sleep suggests that alterations in amygdalar neurotransmission may be involved in the changes in arousal and sleep that occur after fear.

Costly Signaling Theory of REM Sleep and Dreams

The function of REM sleep dreaming is still unknown. We situate our approach to understanding dream phenomenology and dream function within that part of evolutionary theory known as Costly Signaling Theory (CST). We contend that many of the signals produced by the dreaming brain can be and should be construed as “costly signals”—emotions or mental simulations that produce daytime behavioral dispositions that are costly to the dreamer. For example, often the dreamer will appear in the dream as handicapped in some way (i.e., no clothes, no ID, no money, is under attack, being chased etc.). The dreamer, during waking life, is then influenced by the carry-over effect of the unpleasant dream content. The informational and affective content of the dream creates a mental set in the dreamer that operates during the daytime to facilitate the signaling of a “handicapped” Self. The subtle signaling effect might be via display of the intense emotions or physical demeanor that had first appeared in the dream. When the dreamer shares his dream with others the dream has a more direct impact on waking life and social interactions. In effect, the dreamer uses his or her dreams to adopt a self-handicapping strategy when dealing with significant others. The increased use of costly signals (the self-handicapping strategy) during the daytime then facilitates some vital communicative goal of the dreamer.

A prominent role for amygdaloid complexes in the Variability in Heart Rate (VHR) during Rapid Eye Movement (REM) sleep relative to wakefulness

Rapid eye movement sleep (REMS) is associated with intense neuronal activity, rapid eye movements, muscular atonia and dreaming. Another important feature in REMS is the instability in autonomic, especially in cardiovascular regulation. The neural mechanisms underpinning the variability in heart rate (VHR) during REMS are not known in detail, especially in humans. During wakefulness, the right insula has frequently been reported as involved in cardiovascular regulation but this might not be the case during REMS. We aimed at characterizing the neural correlates of VHR during REMS as compared to wakefulness and to slow wave sleep (SWS), the other main component of human sleep, in normal young adults, based on the statistical analysis of a set of H(2)(15)O positron emission tomography (PET) sleep data acquired during SWS, REMS and wakefulness. The results showed that VHR correlated more tightly during REMS than during wakefulness with the rCBF in the right amygdaloid complex. Moreover, we assessed whether functional relationships between amygdala and any brain area changed depending the state of vigilance. Only the activity within in the insula was found to covary with the amygdala, significantly more tightly during wakefulness than during REMS in relation to the VHR. The functional connectivity between the amygdala and the insular cortex, two brain areas involved in cardiovascular regulation, differs significantly in REMS as compared to wakefulness. This suggests a functional reorganization of central cardiovascular regulation during REMS.

Effects of tetrodotoxin (TTX) inactivation of the central nucleus of the amygdala (CNA) on dark period sleep and activity

The amygdala has been implicated in emotional arousal and in the regulation of sleep. Previously, we demonstrated that tetrodotoxin (TTX), a sodium channel blocker that temporarily inactivates neurons and tracts, microinjected into the central nucleus of the amygdala (CNA) during the light period significantly reduced REM, shortened sleep latency, and increased EEG delta power in rats. TTX inactivation of CNA also reduced activity in the open field. These findings suggest that the amygdala modulates arousal in a variety of situations. To test the hypothesis that the amygdala may influence spontaneous arousal, we examined the effects of TTX inactivation of CNA on sleep and activity during the dark period when rats show higher arousal and less sleep. EEG and activity were recorded via telemetry in Wistar rats (n = 8). Bilateral microinjections of TTX (L: 2.5 ng/0.1; H: 5.0 ng/0.2 microl) or SAL (saline, 0.2 microl) were administered before lights off followed by recording throughout the 12-h dark period and following 12-h light period. Microinjections were given at 5-day intervals and were counterbalanced across condition. TTX significantly shortened sleep latency, increased NREM time, decreased REM time, and decreased activity. TTX increased NREM episode duration, whereas the number and duration of REM episodes were decreased. The present results indicate that TTX inactivation of CNA can increase NREM time when spontaneous arousal is high, suggesting a broad role for the amygdala in regulating arousal. The results suggest that understanding the ways in which the amygdala modulates arousal may provide insight into the mechanisms underlying altered sleep in mood and anxiety disorders.

Cholinergic regulation of the central nucleus of the amygdala in rats: Effects of local microinjections of cholinomimetics and cholinergic antagonists on arousal and sleep

The amygdala has emerged as an important forebrain modulator of arousal. Acetylcholine plays a role in the regulation of sleep and wakefulness, particularly rapid eye movement sleep (REM). The major cholinergic input to the amygdala comes from the basal forebrain, a region primarily linked to wakefulness. We examined sleep and the encephalogram for 8 h following bilateral microinjections into the central nucleus of the amygdala (CNA) of the cholinergic agonist, carbachol (CARB(L): 0.3 microg; CARB(H): 3.0 microg), the acetylcholinesterase inhibitor, neostigmine (NEO(L): 0.3 microg; NEO(H): 3.0 microg), the muscarinic antagonist, scopolamine (SCO(L): 0.3 microg; SCO(H): 1.0 microg), the nicotinic antagonist, mecamylamine (MEC(L): 0.3 microg; MEC(H): 1.0 microg) and saline (SAL, 0.2 microl) alone. Both doses of CARB and NEO significantly reduced REM, but did not significantly alter non-rapid eye movement sleep (NREM). Both doses of SCO significantly increased NREM, and SCO(H) also produced an initial increase in REM followed by a significant decrease. CARB(H) and NEO(H) decreased REM electroencephalogram (EEG) power in the 5.5-10 Hz band, and NEO(L) and NEO(H) decreased NREM EEG power in the 0.5-5.0 Hz band. CARB(L) decreased waking EEG power in the 0.5-5.0 Hz band, and NEO(H) decreased waking EEG power in the 5.0-10.0 Hz band. Both doses of SCO significantly increased waking EEG power in the 5.5-10.0 Hz band. Compared with SAL, MEC did not significantly alter sleep or EEG power. The reduction of REM by CARB and NEO and the alteration of sleep by SCO indicate that cholinergic regulation of the amygdala is involved in the control of arousal in rodents. In contrast, CARB microinjections into CNA increase REM in cats, though the reasons for the species difference are not known. The results are discussed in the context of anatomical inputs and species differences in the cholinergic regulation of CNA.

Two-way active avoidance training-specific increases in phosphorylated cAMP response element-binding protein in the dorsal hippocampus, amygdala, and hypothalamus

Previous studies have demonstrated that the activation of pontine-wave (P-wave) generating cells in the brainstem during post-training rapid eye movement (REM) sleep is critical for the consolidation of memory for two-way active avoidance (TWAA) learning in the rat. Here, using immunocytochemistry, we investigated the spatio-temporal distribution of CREB phosphorylation within different parts of the dorsal hippocampus, amygdala, and hypothalamus following a session of TWAA training in the rat. We show that the TWAA training trials increased phosphorylation of CREB (p-CREB) in the dorsal hippocampus, amygdala, amygdalo-hippocampal junction (AHi), and hypothalamus. However, the time intervals leading to training-induced p-CREB activity were different for different regions of the brain. In the dorsal hippocampus, p-CREB activity was maximal at 90 min and this activity disappeared by 180 min. In the AHi, activity of the p-CREB peaked by 180 min and disappeared by 360 min. In the amygdala, the p-CREB activity peaked at 180 min and still remained higher than the control at the 360 min interval. In the hypothalamus, at 90 min p-CREB activity was present only in the ventromedial hypothalamus; however, by 180 min this p-CREB activity was also present in the dorsal hypothalamus, perifornical area, and lateral hypothalamus. By 360 min, p-CREB activity disappeared from the hypothalamus. This TWAA training trials-induced spatiotemporal characteristic of CREB phosphorylation, for the first time, suggests that REM sleep P-wave generator activation-dependent memory processing involves different parts of the dorsal hippocampus, amygdala, and hypothalamus.

Fear-conditioned suppression of REM sleep: relationship to Fos expression patterns in limbic and brainstem regions in BALB/cJ mice

In fear conditioning, shock training (ST) and shock-associated fearful cues (FC) produce relatively selective decreases in rapid eye movement sleep (REM) in mice that vary with strain, and can last for an extended period. We examined sleep in BALB/cJ mice over 6 h after ST and FC, and in handling and tone control conditions. In separate groups of mice, we used immunohistochemical techniques to examine Fos expression in limbic and brainstem regions involved in fear conditioning and in the regulation of REM in 2-h intervals over this period. Significant reductions in REM were observed at 2 and 4 h after ST. Fos expression in the brainstem was significantly elevated at 2 h after ST in the laterodorsal and peduculopontine tegmentum, up to 4 h in the dorsal raphe nucleus (DRN) and up to 6 h in the locus coeruleus (LC). Significant elevations in Fos expression were observed in several regions of the amygdala up to 4 and 6 h after ST. Decreases in REM after FC were significant at 2 h. Increased Fos expression was observed in LC at 2 h and in DRN up to 6 h after FC. Increased Fos expression in the amygdala was observed in several regions of the amygdala at 2 h after FC, but not longer. Significant changes in Fos expression in the central nucleus of the amygdala were not observed at any time point examined or in any condition. The data are discussed with respect to the putative role of brainstem nuclei in regulating REM and the role of the amygdala in conditioned fear.

GABAergic regulation of the central nucleus of the amygdala: implications for sleep control

It is becoming established that the amygdala has a strong influence on arousal state, with most evidence indicating a role in the regulation of rapid eye movement sleep (REM). Electrically activating the central nucleus of the amygdala (CNA) can increase subsequent REM and enhance REM-related phenomena. However, drugs that may be inhibitory to CNA have been typically reported to reduce REM. This suggests that enhancing activity in CNA could promote REM, and that inhibiting activity in CNA could suppress REM. We reversibly inactivated CNA using the GABA(A) agonist, muscimol, or blocked GABAergic inhibition with the GABA(A) antagonist, bicuculline, and examined the effects on sleep and wakefulness. Rats (90-day-old male Sprague-Dawley) were implanted with electrodes for recording EEG and EMG. Cannulae were aimed into CNA for microinjecting muscimol (0.001, 0.3 and 1.0 microM/0.2 microl saline) or bicuculline (56 and 333 pM/0.2 microl saline). Each animal received bilateral microinjections of muscimol, bicuculine or saline alone followed by 6-h sleep recordings. Microinjections of low concentrations of muscimol into CNA produced relatively selective decreases in total REM and number of REM episodes that lasted up to 6 h. In contrast, microinjections of bicuculline into CNA produced significant increases in REM. There were no significant reductions in NREM or wakefulness. These findings demonstrate that inactivating CNA can produce a relatively selective suppression of REM. The possible role that spontaneous activity in CNA may play in REM initiation and/or maintenance is discussed.

Cataplexy-related neurons in the amygdala of the narcoleptic dog

The amygdala plays an important role in the interpretation of emotionally significant stimuli and has strong projections to brainstem regions regulating muscle tone and sleep. Cataplexy, a symptom of narcolepsy, is a loss of muscle tone usually triggered by sudden, strong emotions. Extracellular single-unit recordings were carried out in the amygdala of narcoleptic dogs to test the hypothesis that abnormal activity of a subpopulation of amygdala neurons is linked to cataplexy. Of the 218 cells recorded, 31 were sleep active, 78 were active in both waking and rapid-eye-movement sleep, 88 were maximally active during waking, and 21 were state independent. Two populations of cells showed a significant change in activity with cataplexy. A population of sleep active cells localized to central and basal nucleus increased discharges prior to and during cataplexy. A population of wake active cells localized to the cortical nucleus decreased activity prior to and during cataplexy. We hypothesize that these cell populations have a role in mediation or modulation of cataplexy through interactions with meso-pontine regions controlling atonia. The anticholinesterase physostigmine, at doses which increased cataplexy, did not alter the activity of the cataplexy-related cells or of other amygdala cells, suggesting that its effect on cataplexy is mediated 'downstream' of the amygdala. The alpha-1 blocker prazosin, at doses which increased cataplexy, increased discharge in a subgroup of the cataplexy active cells and in a number of other amygdala cells, indicating that prazosin may modulate cataplexy by its action on amygdala cells or their afferents.

Modulation of serotonergic projection from dorsal raphe nucleus to basolateral amygdala on sleep-waking cycle of rats

Putative serotonergic dorsal raphe nucleus (DRN) neurons display a dramatic role in the modulation of behavior. However, it is not clear how this modulation is mediated. The present study investigated the modulatory effects of serotonergic projection of the DRN to the basolateral amygdala (BLA) on the sleep-waking cycle using polysomnograph (PSG) in rats. DRN microinjection of kainic acid (KA) caused insomnia immediately. From the third day, however, slow wave sleep (SWS) and paradoxical sleep (PS) increased markedly. DRN microinjection of p-chlorophenylalanine (PCPA, once a day for 2 days), which inhibits the synthesis of serotonin (5-HT), led to similar effect to KA administration. The percent of sleep-wakefulness began to change on the third day after PCPA microinjection into the DRN, and the effect was most significant on the sixth day. The percent of sleep-wakefulness started to resume on the seventh day. SWS and PS were reduced after excitation of DRN neurons by microinjection of L-glutamate (L-Glu) into the DRN. Preapplication of the nonselective 5-HT receptor antagonist methysergide (MS) into bilateral BLA blocked the effect of DRN microinjection of L-Glu. Furthermore, bilateral BLA microinjection of 5-hydroxytryptophan (5-HTP), the precursor of 5-HT, on the sixth day after microinjection of PCPA into the DRN, could reverse the effect of PCPA microinjection. These results indicate that the modulation of the DRN on sleep is partially mediated by the serotonergic projection of the DRN to the BLA.

Chronic stimulation of the cat vagus nerve: effect on sleep and behavior

The effect of electrical vagus nerve stimulation (VNS) on sleep and behavior was analyzed in freely moving cats. Eight cats were prepared for 23-h sleep recordings. The left vagus nerve of four of them was stimulated during 1 min, five times at 1-h intervals, for 5 days. The VNS induces: ipsilateral myosis, blinking, licking, abdominal contractions, upward gaze, swallowing, and eventually yawning and compulsive eating, as well as an increase of ponto-geniculate-occipital (PGO) wave density and of the number of stages and total amount of rapid eye movement (REM) sleep. Besides, there was a sudden transition from waking stage to REM sleep. The present results suggest that VNS modifies sleep in the cat. This effect could be explained by an activation of the areas involved in the physiological mechanisms of sleep.

Emotional memory formation is enhanced across sleep intervals with high amounts of rapid eye movement sleep

Recent studies indicated a selective activation during rapid eye movement (REM) sleep of the amygdala known to play a decisive role in the processing of emotional stimuli. This study compared memory retention of emotional versus neutral text material over intervals covering either early sleep known to be dominated by nonREM slow wave sleep (SWS) or late sleep, in which REM sleep is dominant. Two groups of men were tested across 3-h periods of early and late sleep (sleep group) or corresponding retention intervals filled with wakefulness (wake group). Sleep was recorded polysomnographically. Cortisol concentrations in saliva were monitored at acquisition and retrieval testing. As expected, the amount of REM sleep was about three times greater during late than during early retention sleep, whereas a reversed pattern was observed for SWS distribution (P < 0.001). Sleep improved retention, compared with the effects of wake intervals (P < 0.02). However, this effect was substantial only in the late night (P < 0.005), during which retention was generally worse than during the early night (P < 0.02). Late sleep particularly enhanced memory for emotional texts. This effect was highly significant in comparison with memory for neutral texts (P < 0.01) and in comparison with memory after late and early wake intervals (P < 0.001). Cortisol concentration differed between early and late retention intervals but not between sleep and wake conditions. Results are consonant with a supportive function of REM sleep predominating late sleep for the formation of emotional memory in humans.

Multiple output pathways of the basal forebrain: organization, chemical heterogeneity, and roles in vigilance

Studies over the last decade have shown that the basal forebrain (BF) consists of more than its cholinergic neurons. The BF also contains non-cholinergic neurons, including gamma-aminobutyric acid-ergic neurons which co-distribute and co-project with the cholinergic neurons. Both types of neuron project, in variable proportions, to the cerebral cortex, hippocampus, thalamus, amygdala, and olfactory bulb, whereas descending projections to the posterior hypothalamus and brainstem nuclei are predominantly non-cholinergic. Some of the cholinergic and non-cholinergic projection neurons contain neuropeptides such as galanin, nitric oxide synthase, and possibly glutamate. To understand better the function of the BF, the organization of the multiple ascending and descending projections of BF neurons is reviewed along with their neurochemical heterogeneity, and possible functions of individual pathways are discussed. It is proposed that BF neurons belong to multiple systems with distinct cognitive, motivational, emotional, motor, and regulatory functions, and that through these pathways, the BF plays a role in controlling both cognitive and non-cognitive aspects of vigilance.

Effects of amygdala lesions on sleep in rhesus monkeys

The amygdala is important in processing emotion and in the acquisition and expression of fear and anxiety. It also appears to be involved in the regulation of sleep and wakefulness. The purpose of this study was to assess the effects of, fiber-sparing lesions of the amygdala on sleep in rhesus monkeys (Macaca mulatta). We recorded sleep from 18 age-matched male rhesus monkeys, 11 of which had previously received ibotenic acid lesions of the amygdala and seven of which were normal controls. Surface electrodes for sleep recording were attached and the subjects were seated in a restraint chair (to which they had been adapted) for the nocturnal sleep period. Despite adaptation, control animals had sleep patterns characterized by frequent arousals. Sleep was least disrupted in animals with large bilateral lesions of the amygdala. They had more sleep and a higher proportion of rapid-eye-movement (REM) sleep than did either animals with smaller lesions or control animals. Based on these results, it seems likely that, in the primate, the amygdala plays a role in sleep regulation and may be important in mediating the effects of emotions/stress on sleep. These findings may also be relevant to understanding sleep disturbances associated with psychopathology.

Functional neuroimaging of normal human sleep by positron emission tomography

Functional neuroimaging using positron emission tomography has recently yielded original data on the functional neuroanatomy of human sleep. This paper attempts to describe the possibilities and limitations of the technique and clarify its usefulness in sleep research. A short overview of the methods of acquisition and statistical analysis (statistical parametric mapping, SPM) is presented before the results of PET sleep studies are reviewed. The discussion attempts to integrate the functional neuroimaging data into the body of knowledge already acquired on sleep in animals and humans using various other techniques (intracellular recordings, in situ neurophysiology, lesional and pharmacological trials, scalp EEG recordings, behavioural or psychological description). The published PET data describe a very reproducible functional neuroanatomy in sleep. The core characteristics of this 'canonical' sleep may be summarized as follows. In slow-wave sleep, most deactivated areas are located in the dorsal pons and mesencephalon, cerebellum, thalami, basal ganglia, basal forebrain/hypothalamus, prefrontal cortex, anterior cingulate cortex, precuneus and in the mesial aspect of the temporal lobe. During rapid-eye movement sleep, significant activations were found in the pontine tegmentum, thalamic nuclei, limbic areas (amygdaloid complexes, hippocampal formation, anterior cingulate cortex) and in the posterior cortices (temporo-occipital areas). In contrast, the dorso-lateral prefrontal cortex, parietal cortex, as well as the posterior cingulate cortex and precuneus, were the least active brain regions. These preliminary studies open up a whole field in sleep research. More detailed explorations of sleep in humans are now accessible to experimental challenges using PET and other neuroimaging techniques. These new methods will contribute to a better understanding of sleep functions.

Differential c-fos expression in the rhinencephalon and striatum after enhanced sleep-wake states in the cat

In order to delimit the supra-brainstem structures that are activated during the sleep-waking cycle, we have examined c-fos immunoreactivity in four groups of polygraphically recorded cats killed after 3 h of prolonged waking (W), slow-wave sleep (SWS), or paradoxical sleep (PS), following microinjection of muscimol (a gamma-aminobutyric acid, GABA agonist) into the periaqueductal grey matter and adjacent areas [Sastre et al. (1996), Neuroscience, 74, 415-426]. Our results demonstrate that there was a direct relationship between a significant increase in c-fos labelling and the amount of PS in the laterodorsalis tegmenti in the pons, supramamillary nucleus, septum, hippocampus, gyrus cingulate, amygdala, stria terminalis and the accumbens nuclei. Moreover, in all these structures, the number of Fos-like immunoreactive neurons in the PS group was significantly higher (three to 30-fold) than in the SWS and W groups. We suggest that the dense expression of the immediate-early gene c-fos in the rhinencephalon and striatum may be considered as a tonic component of PS at the molecular level and that, during PS, the rhinencephalon and striatum are the main targets of an excitatory system originating in the pons.

Carbachol microinjection into the caudal peribrachial area induces long-term enhancement of PGO wave activity but not REM sleep

This study presents new findings of carbachol-induced long-term ponto-geniculo-occipital (PGO) enhancement lasting five days, but without REM sleep enhancement. A quantitative analysis of the number and types of bilateral PGO wave events during slow wave sleep with PGO activity (SP) and REM was performed in each of four cats over a period of six days following a single unilateral microinjection of carbachol nanospheres into the caudolateral peribrachial area. The results demonstrate increases in the summed total of all PGO wave events to continue for five days postcarbachol reaching a peak sixfold increase on day three in SP and REM. The tendency of PGO waves to occur in clusters of greater than three waves increased sevenfold on day three in SP and fourfold during REM. These findings indicate a dissociation of long-term PGO enhancement from long-term REM enhancement, and suggest that even a sixfold increase in PGO activity alone is not, in itself, sufficient to produce the cholinergic orchestration of REM sleep enhancement.

Neuronal degeneration in canine narcolepsy

Narcolepsy is a lifelong illness characterized by persistent sleepiness, hypnagogic hallucinations, and episodes of motor paralysis called cataplexy. We have tested the hypothesis that a transient neurodegenerative process is linked to symptom onset. Using the amino-cupric silver stain on brain sections from canine narcoleptics, we found elevated levels of axonal degeneration in the amygdala, basal forebrain (including the nucleus of the diagonal band, substantia innominata, and preoptic region), entopeduncular nucleus, and medial septal region. Reactive neuronal somata, an indicator of neuronal pathology, were found in the ventral amygdala. Axonal degeneration was maximal at 2-4 months of age. The number of reactive cells was maximal at 1 month of age. These degenerative changes precede or coincide with symptom onset. The forebrain degeneration that we have observed can explain the major symptoms of narcolepsy.

Sleep electroencephalographic response to muscarinic and serotonin1A receptor probes in patients with major depression and in normal controls

BACKGROUND

To test the hypothesis that depression is associated with an increased ratio of cholinergic to serotonergic neurotransmission, we compared the effects of pilocarpine, a muscarinic agonist, and ipsapirone, a serotonin (5-HT)1A agonist, on electroencephalographic (EEG) sleep in depressed and healthy subjects. We hypothesized, adopting the reciprocal interaction model, that the effects on REM sleep of these probes within the same individuals are negatively correlated and unmask neurobiological changes in depression.

METHODS

Polysomnographic recordings were obtained in 12 unmedicated patients with a current major depression and 12 normal controls. They received placebo, pilocarpine 25 mg, or ipsapirone 10 mg (orally, 15 min before bedtime, after premedication with the peripheral anticholinergic probanthine 30 mg, double blind, counterbalanced) on three occasions.

RESULTS

Pilocarpine shortened and ipsapirone prolonged REM latency equally in both groups. These effects were not correlated. Pilocarpine decreased slow-wave sleep and EEG delta power during the first nonREM episode more in controls than in patients, and enhanced EEG sigma power equally in both groups. Ipsapirone had no significant effects on EEG power.

CONCLUSION

These data do not support the postulate of muscarinic receptor up-regulation and 5-HT1A receptor down-regulation in depression. The significance of blunted delta power suppression in patients following pilocarpine warrants further investigations.