Noradrenaline inhibits preoptic sleep-active neurons through alpha 2-receptors in the rat

Homeostatic regulation of rapid eye movement sleep by the preoptic area of the hypothalamus

Rapid eye movement sleep (REMs) is characterized by activated electroencephalogram (EEG) and muscle atonia, accompanied by vivid dreams. REMs is homeostatically regulated, ensuring that any loss of REMs is compensated by a subsequent increase in its amount. However, the neural mechanisms underlying the homeostatic control of REMs are largely unknown. Here, we show that GABAergic neurons in the preoptic area of the hypothalamus projecting to the tuberomammillary nucleus (POAGAD2→TMN neurons) are crucial for the homeostatic regulation of REMs in mice. POAGAD2→TMN neurons are most active during REMs, and inhibiting them specifically decreases REMs. REMs restriction leads to an increased number and amplitude of calcium transients in POAGAD2→TMN neurons, reflecting the accumulation of REMs pressure. Inhibiting POAGAD2→TMN neurons during REMs restriction blocked the subsequent rebound of REMs. Our findings reveal a hypothalamic circuit whose activity mirrors the buildup of homeostatic REMs pressure during restriction and that is required for the ensuing rebound in REMs.

Homeostatic regulation of REM sleep by the preoptic area of the hypothalamus

Rapid-eye-movement sleep (REMs) is characterized by activated electroencephalogram (EEG) and muscle atonia, accompanied by vivid dreams. REMs is homeostatically regulated, ensuring that any loss of REMs is compensated by a subsequent increase in its amount. However, the neural mechanisms underlying the homeostatic control of REMs are largely unknown. Here, we show that GABAergic neurons in the preoptic area of the hypothalamus projecting to the tuberomammillary nucleus (POAGAD2→TMN neurons) are crucial for the homeostatic regulation of REMs. POAGAD2→TMN neurons are most active during REMs, and inhibiting them specifically decreases REMs. REMs restriction leads to an increased number and amplitude of calcium transients in POAGAD2→TMN neurons, reflecting the accumulation of REMs pressure. Inhibiting POAGAD2→TMN neurons during REMs restriction blocked the subsequent rebound of REMs. Our findings reveal a hypothalamic circuit whose activity mirrors the buildup of homeostatic REMs pressure during restriction and that is required for the ensuing rebound in REMs.

Adenosine A2A receptors and sleep

Adenosine, a known endogenous somnogen, induces sleep via A1 and A2A receptors. In this chapter, we review the current knowledge regarding the role of the adenosine A2A receptor and its agonists, antagonists, and allosteric modulators in sleep-wake regulation. Although many adenosine A2A receptor agonists, antagonists, and allosteric modulators have been identified, only a few have been tested to see if they can promote sleep or wakefulness. In addition, the growing popularity of natural sleep aids has led to an investigation of natural compounds that may improve sleep by activating the adenosine A2A receptor. Finally, we discuss the potential therapeutic advantage of allosteric modulators of adenosine A2A receptors over classic agonists and antagonists for treating sleep and neurologic disorders.

A comprehensive review and meta-analysis of neurological side effects related to second-generation antidepressants in individuals with major depressive disorder

Second-generation antidepressants (SGADs) often cause neurological side effects (SEs). This meta-analysis seeks to quantify the short-term rates of neurological SEs related to routinely used second-generation antidepressants used to treat major depressive disorder (MDD). A search of the PubMed, EMBASE,Cochrane Library databases and Web of Science was done to uncover double-blind, randomized, placebo-controlled studies evaluating the effectiveness of frequently used SGADs medicines in people with MDD. Qualifying studies were required to concentrate on the use of SGADs routinely used in MDD and to uncover data on treatment-emergent neurological SEs occurring within 12 weeks of therapy. Overall, 143 RCT studies containing 188 treatment arms were included in the meta-analyses. Most SGADs increased the risk of neurological SEs compared to placebo. The least tolerated antidepressants on the neurological tract were desvenlafaxine (OR=1.98; CI 0.85-4.65; p-value=0.12) and venlafaxine (OR=1.15; CI 0.96-1.38; p-value=0.13). Agomelatine, bupropion and vortioxetine exhibited reduced neurological SEs, showing diminished risk in insomnia (OR=0.56; CI 0.36-0.88; p-value=0.01), somnolence (OR=0.46; CI 0.27-0.79; p-value=0.01), vision blurred (OR=0.43; CI 0.19-0.96; p-value=0.04), respectively. Most SGADs did not or just marginally increased the risk of headache compared to placebo. In conclusion, frequently used SGADs demonstrated distinct patterns of neurological SEs, which physicians should consider when prescribing antidepressants to promote treatment adherence and favorable outcomes in patients with MDD.

Orexin neurons inhibit sleep to promote arousal

Humans and animals lacking orexin neurons exhibit daytime sleepiness, sleep attacks, and state instability. While the circuit basis by which orexin neurons contribute to consolidated wakefulness remains unclear, existing models posit that orexin neurons provide their wake-stabilizing influence by exerting excitatory tone on other brain arousal nodes. Here we show using in vivo optogenetics, in vitro optogenetic-based circuit mapping, and single-cell transcriptomics that orexin neurons also contribute to arousal maintenance through indirect inhibition of sleep-promoting neurons of the ventrolateral preoptic nucleus. Activation of this subcortical circuit rapidly drives wakefulness from sleep by differentially modulating the activity of ventrolateral preoptic neurons. We further identify and characterize a feedforward circuit through which orexin (and co-released glutamate) acts to indirectly target and inhibit sleep-promoting ventrolateral preoptic neurons to produce arousal. This revealed circuitry provides an alternate framework for understanding how orexin neurons contribute to the maintenance of consolidated wakefulness and stabilize behavioral state.

The Sleep-Promoting Ventrolateral Preoptic Nucleus: What Have We Learned over the Past 25 Years?

For over a century, the role of the preoptic hypothalamus and adjacent basal forebrain in sleep-wake regulation has been recognized. However, for years, the identity and location of sleep- and wake-promoting neurons in this region remained largely unresolved. Twenty-five years ago, Saper and colleagues uncovered a small collection of sleep-active neurons in the ventrolateral preoptic nucleus (VLPO) of the preoptic hypothalamus, and since this seminal discovery the VLPO has been intensively investigated by labs around the world, including our own. Herein, we first review the history of the preoptic area, with an emphasis on the VLPO in sleep-wake control. We then attempt to synthesize our current understanding of the circuit, cellular and synaptic bases by which the VLPO both regulates and is itself regulated, in order to exert a powerful control over behavioral state, as well as examining data suggesting an involvement of the VLPO in other physiological processes.

The NAergic locus coeruleus-ventrolateral preoptic area neural circuit mediates rapid arousal from sleep

The locus coeruleus (LC), which is located in the brain stem, plays an important role in promoting arousal. However, the neural circuitry underlying this function remains unclear. Using cortical electroencephalography combined with optrode recording, we found that LC noradrenergic (LC^NA) neurons exhibit high activity during wakefulness, while suppressing the activity of these neurons causes a reduction in wakefulness. Viral tracing showed that LC^NA neurons directly project to the ventrolateral preoptic area (VLPO) and that optogenetic activation of the noradrenergic (NAergic) LC-VLPO (NAergic^LC-VLPO) neural circuit promotes arousal. Optrode recordings in the VLPO revealed two functionally distinct neuronal populations that were stimulated in response to the optogenetic activation of LC^NA neurons. Consistently, we identified two types of VLPO neurons that exhibited different responses to NAergic projections from the LC mediated by discrete adrenergic receptors. Together, our results demonstrate that the NAergic^LC-VLPO neural circuit is a critical pathway for controlling wakefulness and that a synergistic effect is produced by inhibition of sleep-active neurons in the VLPO through α₂ receptors and activation of wake-active neurons in the VLPO through α₁ and β receptors.

Role of the Preoptic Area in Sleep and Thermoregulation

Sleep and body temperature are tightly interconnected in mammals: warming up our body helps to fall asleep and the body temperature in turn drops while falling asleep. The preoptic area of the hypothalamus (POA) serves as an essential brain region to coordinate sleep and body temperature. Understanding how these two behaviors are controlled within the POA requires the molecular identification of the involved circuits and mapping their local and brain-wide connectivity. Here, we review our current understanding of how sleep and body temperature are regulated with a focus on recently discovered sleep- and thermo-regulatory POA neurons. We further discuss unresolved key questions including the anatomical and functional overlap of sleep- and thermo-regulatory neurons, their pathways and the role of various signaling molecules. We suggest that analysis of genetically defined circuits will provide novel insights into the mechanisms underlying the coordinated regulation of sleep and body temperature in health and disease.

Dysfunction of the NAc-mPFC circuit in insomnia disorder

BACKGROUND

Insomnia disorder (ID) is a prevalent sleep disorder, which seriously affects people's daily life and was found to be associated with increased frequency of sleep stage shifts. Previous findings had revealed the critical role of the nucleus accumbens (NAc) in sleep-wake transition. However, the neuroimaging studies of the NAc in patients with ID have been rare. We hypothesized that structural and functional abnormalities of the NAc would be implicated in ID.

METHODS

Twenty-six ID patients and 36 matched healthy controls (HC) were included in the current study. The volumes and corresponding resting-state functional connectivity (RSFC) of the bilateral NAc were compared between the two groups. The abnormal RSFC in ID were then correlated with Pittsburgh Sleep Quality Index (PSQI).

RESULTS

Compared with HC, ID patients showed significantly increased volume of right NAc. Several brain regions showed increased RSFC with the NAc in ID patients, such as medial prefrontal cortex (mPFC), anterior cingulate cortex (ACC), caudate and putamen. Meanwhile, the occipital gyrus and temporal gyrus showed decreased RSFC with the NAc. Additionally, the increased RSFC strength between bilateral NAc and left mPFC was significant correlated with PSQI scores in ID patients.

CONCLUSION

Dysfunctions of the NAc-mPFC circuit were found in ID patients, which were associated with sleep quality measured by PSQI. The two patterns of increase and decrease of RSFC in ID patients observed in our study may reflect the state of hyperarousal and potential impairment of cognitive function in the patients, respectively. It is hoped that our study focusing on NAc-mPFC circuits could provide new insights for the neural mechanisms of ID and potential novel therapeutic targets for treatment of ID patients.

Molecular basis of atypicality of bupropion inferred from its receptor engagement in nervous system tissues

Despite decades of clinical use and research, the mechanism of action (MOA) of antidepressant medications remains poorly understood. Selective serotonin reuptake inhibitors (SSRIs) and serotonin-norepinephrine reuptake inhibitors (SNRIs) are the most commonly prescribed antidepressants-atypical antidepressants such as bupropion have also proven effective, while exhibiting a divergent clinical phenotype. The difference in phenotypic profiles presumably lies in the differences among the MOAs of SSRIs/SNRIs and bupropion. We integrated the ensemble of bupropion's affinities for all its receptors with the expression levels of those targets in nervous system tissues. This "combined target tissue" profile of bupropion was compared to those of duloxetine, fluoxetine, and venlafaxine to isolate the unique target tissue effects of bupropion. Our results suggest that the three monoamines-serotonin, norepinephrine, and dopamine-all contribute to the common antidepressant effects of SSRIs, SNRIs, and bupropion. At the same time, bupropion is unique in its action on 5-HT3AR in the dorsal root ganglion and nicotinic acetylcholine receptors in the pineal gland. These unique tissue-specific activities may explain unique therapeutic effects of bupropion, such as pain management and smoking cessation, and, given melatonin's association with nicotinic acetylcholine receptors and depression, highlight the underappreciated role of the melatonergic system in bupropion's MOA.

Insomnia and somnolence associated with second-generation antidepressants during the treatment of major depression: a meta-analysis

BACKGROUND

Sleep reduction or enhancement is frequently observed with second-generation antidepressant treatments, and they can be beneficial or harmful depending on the symptom profile of each subject. Nevertheless, relatively little attention has been given so far to rank those effects across compounds. The aim of this meta-analysis is to provide quantitative data about short-term rates of insomnia and somnolence associated with 14 second-generation antidepressants during the treatment of major depression.

METHODS

A literature search and a search of unpublished documents were performed. Eligible studies focusing on MD patients treated with second-generation antidepressants were entered in the analysis. Our primary outcome measures were insomnia and somnolence rates induced by antidepressants as compared with those associated with placebo. Sensitivity analyses were carried out as well.

RESULTS

Ten second-generation antidepressants showed higher rates of insomnia than placebo. The highest incidence was found for bupropion and desvenlafaxine. Agomelatine was the only antidepressant with a lower likelihood of inducing insomnia than placebo. Eleven antidepressants were associated with higher rates of somnolence than placebo. Fluvoxamine and mirtazapine showed the highest frequency of somnolence. Bupropion induced somnolence to a lower extent than placebo. Sensitivity analyses showed a degree of variation of those findings.

DISCUSSION

Antidepressants are associated with different insomnia and somnolence rates, mainly depending on their mechanisms of action. Despite some limitations, we underscore that the treatment-emergent insomnia and/or somnolence are frequent, and they could be used in clinical practice to face the specific needs of each patient.

α2-Adrenergic stimulation of the ventrolateral preoptic nucleus destabilizes the anesthetic state

The sleep-promoting ventrolateral preoptic nucleus (VLPO) shares reciprocal inhibitory inputs with wake-active neuronal nuclei, including the locus ceruleus. Electrophysiologically, sleep-promoting neurons in the VLPO are directly depolarized by the general anesthetic isoflurane and hyperpolarized by norepinephrine, a wake-promoting neurotransmitter. However, the integration of these competing influences on the VLPO, a sleep- and anesthetic-active structure, has yet to be evaluated in either brain slices in vitro or the intact organism. Single-cell multiplex RT-PCR conducted on both isoflurane-activated, putative sleep-promoting VLPO neurons and neighboring, state-indifferent VLPO neurons in mouse brain slices revealed widespread expression of α2A-, α2B- and α2C-adrenergic receptors in both populations. Indeed, both norepinephrine and the highly selective α2 agonist dexmedetomidine each reversed the VLPO depolarization induced by isoflurane in slices in vitro. When microinjected directly into the VLPO of a mouse lightly anesthetized with isoflurane, dexmedetomidine increased behavioral arousal and reduced the depressant effects of isoflurane on barrel cortex somatosensory-evoked potentials but failed to elicit spectral changes in spontaneous EEG. Based on these observations, we conclude that local modulation of α-adrenergic activity in the VLPO destabilizes, but does not fully antagonize, the anesthetic state, thus priming the brain for anesthetic emergence.

Wake-promoting actions of noradrenergic α1 - and β-receptors within the lateral hypothalamic area

Central norepinephrine exerts potent wake-promoting effects, in part through the actions of noradrenergic α1 - and β-receptors located in the medial septal and medial preoptic areas. The lateral hypothalamic area (LHA), including the lateral hypothalamus, perifornical area and adjacent dorsomedial hypothalamus, is implicated in the regulation of arousal and receives a substantial noradrenergic innervation. To date the functional significance of this innervation is unknown. The current studies examined the degree to which noradrenergic α1 - and β-receptor stimulation within the rat LHA modulates arousal. Specifically, these studies examined the wake-promoting effects of intra-tissue infusions (250 nL) of the α1 -receptor agonist phenylephrine (10, 20 and 40 nmol) and the β-receptor agonist isoproterenol (3, 10 and 30 nmol) in rats. Results show that stimulation of LHA α1 -receptors elicits robust and dose-dependent increases in waking. In contrast, β-receptor stimulation within the LHA had relatively modest arousal-promoting actions. Nonetheless, combined α1 - and β-receptor stimulation elicited additive wake-promoting effects. Arousal-promoting hypocretin/orexin (HCRT)-synthesising neurons are located within the LHA. Therefore, additional immunohistochemical studies examined whether α1 -receptor-dependent waking is associated with an activation of HCRT neurons as measured by Fos, the protein product of the immediate-early gene c-fos. Analyses indicate that although intra-LHA α1 -receptor agonist infusion elicited a robust increase in Fos immunoreactivity (ir) in this region, this treatment did not activate HCRT neurons as measured by Fos-ir. Collectively, these observations indicate that noradrenergic α1 -receptors within the LHA promote arousal via actions that are independent of HCRT neuronal activation.

Noradrenergic modulation of wakefulness/arousal

The locus coeruleus-noradrenergic system supplies norepinephrine throughout the central nervous system. State-dependent neuronal discharge activity of locus coeruleus noradrenergic neurons has long-suggested a role of this system in the induction of an alert waking state. Work over the past two decades provides unambiguous evidence that the locus coeruleus, and likely other noradrenergic nuclei, exert potent wake-promoting actions via an activation of noradrenergic β- and α₁-receptors located within multiple subcortical structures, including the general regions of the medial septal area, the medial preoptic area and, most recently, the lateral hypothalamus. Conversely, global blockade of β- and α₁-receptors or suppression of norepinephrine release results in profound sedation. The wake-promoting action of central noradrenergic neurotransmission has clinical implications for treatment of sleep/arousal disorders, such as insomnia and narcolepsy, and clinical conditions associated with excessive arousal, such as post-traumatic stress disorder.

Sleep-waking discharge profiles of median preoptic and surrounding neurons in mice

The median preoptic nucleus (MnPO), part of the anteroventral third ventricular region, plays a key role in body fluid homeostasis and cardiovascular regulation. Recently, a cluster of neurons showing sleep-related c-fos immunoreactivity was found in the rat MnPO, and a subsequent electrophysiological study found that nearly 76% of rat MnPO neurons exhibit increased discharge during sleep. In a recent single unit recording study in mice, we found that sleep-active neurons are not localized in any specific region of the preoptic/basal forebrain (POA/BFB). However, the discharge profiles of mouse MnPO neurons across wake-sleep states remained to be determined. In this study, we therefore examined whether the mouse MnPO contains a high proportion of sleep-active neurons and constitutes a distinct cluster of sleep-promoting neurons in the median preoptic region. We recorded a total of 234 single units in the MnPO, the laterally adjacent peri-MnPO, the dorsally adjacent medial septum (MS), and the ventrally adjacent periventricular (Pe)/medial preoptic (MPO) area (Pe/MPO). We found that the MnPO contained similar proportions of sleep-active (31.9%) and waking (W)-active (33.0%) neurons, together with many waking/paradoxical sleep (W/PS)-active neurons (23.4%), whereas the Pe/MPO and MS contained a high proportion of sleep-active neurons (66.0 and 62.9%, respectively), while the peri-MnPO contained a high proportion of W-active neurons (57.1%). In the MnPO, both W-active and W/PS-active neurons were distributed throughout the nucleus, whereas sleep-active neurons were mostly located on its border. Only slowly discharging (<5 Hz) slow-wave sleep (SWS)/PS-selective neurons were found in the MnPO. During the transition from W to SWS, all of these SWS/PS-selective neurons fired not before, but after, sleep onset, with a gradual increase in discharge rate. In addition to its well-known homeostatic and cardiovascular functions, the MnPO might modulate the sleep-waking cycle by playing different roles in sleep/wake state regulation.

Characterization and mapping of sleep-waking specific neurons in the basal forebrain and preoptic hypothalamus in mice

We recorded 872 single units across the complete sleep-waking cycle in the mouse preoptic area (POA) and basal forebrain (BFB), which are deeply involved in the regulation of sleep and wakefulness (W). Of these, 552 were sleep-active, 96 were waking-active, 106 were active during both waking and paradoxical sleep (PS), and the remaining 118 were state-indifferent. Among the 872, we distinguished slow-wave sleep (SWS)-specific, SWS/PS-specific, PS-specific, W-specific, and W/PS-specific neurons, the last group being further divided into specific tonic type I slow (TI-Ss) and specific tonic type I rapid (TI-Rs) both discharging specifically in association with cortical activation during both W and PS. Both the SWS/PS-specific and PS-specific neurons were distributed throughout a wide region of the POA and BFB, whereas the SWS-specific neurons were mainly located in the middle and ventral half of the POA and adjacent BFB, as were the W-specific and W/PS-specific neurons. At the transition from waking to sleep, the majority of SWS-specific and all SWS/PS-specific neurons fired after the onset of cortical synchronization (deactivation), whereas all W-specific and W/PS-specific neurons showed a significant decrease in firing rate >0.5 s before the onset. At the transition from SWS to W, the sleep-specific neurons showed a significant decrease in firing rate 0.1 s before the onset of cortical activation, while the W-specific and W/PS-specific neurons fired >0.5 s before the onset. TI-Ss neurons were characterized by a triphasic broad action potential, slow single isolated firing, and an antidromic response to cortical stimulation, whereas TI-Rs neurons were characterized by a narrow action potential and high frequency burst discharge in association with theta waves in PS. These data suggest that the forebrain sleep/waking switch is regulated by opposing activities of sleep-promoting (SWS-specific and SWS/PS-specific) and waking-promoting (W-specific and W/PS-specific) neurons, that the initiation of sleep is caused by decreased activity of the waking-promoting neurons (disfacilitation), and that the W/PS-specific neurons are deeply involved in the processes of cortical activation/deactivation.

An insight on the neuropharmacological activity of Telescopium telescopium--a mollusc from the Sunderban mangrove

The present study was carried out to evaluate the biological properties of the tissue extract of a marine snail Telescopium telescopium, collected from the coastal regions of West Bengal India. On extensive pharmacological screening, it was found that the biological extract of T. telescopium (TTE) produced significant central nervous system (CNS)-depressant activity as observed from the reduced spontaneous motility, potentiation of pentobarbitone induced sleeping time, hypothermia and respiratory depression with transient apnoea. The extract significantly decreased both residual curiosity and also muscle coordination. The fraction, obtained following saturation with 60-80% ammonium sulphate (80S), was also found to demonstrate predominant CNS-depressant activity. It was observed that both TTE and the 80S fraction significantly altered the brain noradrenaline and homovanillic acid levels without affecting the brain gamma amino butyric acid (GABA) concentration. Based on the present observations, it can be suggested that the CNS-depressant effects produced by TTE and 80S could be attributable to modified catecholamine metabolism in the brain.

Presence of alpha-1 norepinephrinergic and GABA-A receptors on medial preoptic hypothalamus thermosensitive neurons and their role in integrating brainstem ascending reticular activating system inputs in thermoregulation in rats

Thermal messages are relayed to the medial preoptic O-anterior hypothalamus (mPOAH) via the ascending reticular activating system (ARAS). According to previous findings that norepinephrine (NE)-ergic and GABA (gamma-amino butyric acid)-ergic inputs convey thermal information to the CNS, those neurotransmitters may be responsible for reciprocal correlation between body temperature and mPOAH warm-(WSNs) and cold-(CSNs) sensitive neuronal firing rates for thermoregulation. In this study on Wistar rats, we have characterized in vivo the role of alpha-1 NE-ergic and GABA-A receptors in the possible modulation of ARAS inputs to the thermosensitive neurons in the mPOAH. Nine WSNs, 7 CSNs and 19 thermo-insensitive neurons were recorded from mPOAH and effects of ARAS stimulation and iontophoretic application of prazosin as well as picrotoxin on those neurons were evaluated. The WSNs were excited by ARAS stimulation but inhibited by both prazosin and picrotoxin; whereas the CSNs were inhibited by ARAS stimulation and prazosin, but excited by picrotoxin. The NE excited the WSNs as well as the CSNs, while GABA had opposite effects on them, suggesting that NE and GABA interact in the mPOAH for thermoregulation. The findings unravel an intriguing possibility that in the mPOAH, GABA simultaneously acts on hetero-receptors located at pre-and post-synaptic sites, modulating the release of NE on the WSNs and CSNs for thermoregulation. Further, ARAS stimulation-induced similar excitatory and inhibitory responses of the WSNs and the CSNs support such converging inputs on these neurons for thermoregulation.

Delayed orexin signaling consolidates wakefulness and sleep: physiology and modeling

Orexin-producing neurons are clearly essential for the regulation of wakefulness and sleep because loss of these cells produces narcolepsy. However, little is understood about how these neurons dynamically interact with other wake- and sleep-regulatory nuclei to control behavioral states. Using survival analysis of wake bouts in wild-type and orexin knockout mice, we found that orexins are necessary for the maintenance of long bouts of wakefulness, but orexin deficiency has little impact on wake bouts <1 min. Since orexin neurons often begin firing several seconds before the onset of waking, this suggests a surprisingly delayed onset (>1 min) of functional effects. This delay has important implications for understanding the control of wakefulness and sleep because increasing evidence suggests that different mechanisms are involved in the production of brief and sustained wake bouts. We incorporated these findings into a mathematical model of the mouse sleep/wake network. Orexins excite monoaminergic neurons and we hypothesize that orexins increase the monoaminergic inhibition of sleep-promoting neurons in the ventrolateral preoptic nucleus. We modeled orexin effects as a time-dependent increase in the strength of inhibition from wake- to sleep-promoting populations and the resulting simulated behavior accurately reflects the fragmented sleep/wake behavior of narcolepsy and leads to several predictions. By integrating neurophysiology of the sleep/wake network with emergent properties of behavioral data, this model provides a novel framework for investigating network dynamics and mechanisms associated with normal and pathologic sleep/wake behavior.

Noradrenergic modulation of arousal

Through a highly divergent efferent projection system, the locus coeruleus-noradrenergic system supplies norepinephrine throughout the central nervous system. State-dependent neuronal discharge activity of locus coeruleus neurons has long-suggested a role of this system in the induction of an alert waking state. More recent work supports this hypothesis, demonstrating robust wake-promoting actions of the locus coeruleus-noradrenergic system. Norepinephrine enhances arousal, in part, via actions of beta- and alpha1-receptors located within multiple subcortical structures, including the general regions of the medial septal area and the medial preoptic areas. Recent anatomical studies suggest that arousal-enhancing actions of norepinephrine are not limited to the locus coeruleus system and likely include the A1 and A2 noradrenergic cell groups. Thus, noradrenergic modulation of arousal state involves multiple noradrenergic systems acting within multiple subcortical regions. Pharmacological studies indicate that the combined actions of these systems are necessary for the sustained maintenance of arousal levels associated with spontaneous waking. Enhanced arousal state is a prominent aspect of both stress and psychostimulant drug action and evidence indicates that noradrenergic systems likely play an important role in both stress-related and psychostimulant-induced arousal. These and other observations suggest that the dysregulation of noradrenergic neurotransmission could well contribute to the dysregulation of arousal associated with a variety of behavioral disorders including insomnia and stress-related disorders.

Adenosine inhibits basal forebrain cholinergic and noncholinergic neurons in vitro

Adenosine has been proposed as a homeostatic "sleep factor" that promotes the transition from waking to sleep by affecting several sleep-wake regulatory systems. In the basal forebrain, adenosine accumulates during wakefulness and, when locally applied, suppresses neuronal activity and promotes sleep. However, the neuronal phenotype mediating these effects is unknown. We used whole-cell patch-clamp recordings in in vitro rat brain slices to investigate the effect of adenosine on identified cholinergic and noncholinergic neurons of the magnocellular preoptic nucleus and substantia innominata. Adenosine (0.5-100 microM) reduced the magnocellular preoptic nucleus and substantia innominata cholinergic neuronal firing rate by activating an inwardly rectifying potassium current that reversed at -82 mV and was blocked by barium (100 microM). Application of the A1 receptor antagonist 8-cyclo-pentyl-theophylline (200 nM) blocked the effects of adenosine. Adenosine was also tested on two groups of electrophysiologically distinct noncholinergic magnocellular preoptic nucleus and substantia innominata neurons. In the first group adenosine, via activation of postsynaptic A1 receptors, reduced spontaneous firing via inhibition of the hyperpolarization-activated cation current. Blocking the H-current with ZD7288 (20 microM) abolished adenosine effects on these neurons. The second group was not affected by adenosine. These results demonstrate that, in the magnocellular preoptic nucleus and substantia innominata region of the basal forebrain, adenosine inhibits both cholinergic neurons and a subset of noncholinergic neurons. Both of these effects occur via postsynaptic A1 receptors, but are mediated downstream by two separate mechanisms.

Reduction of adrenergic neurotransmission with clonidine aggravates spike-wave seizures and alters activity in the cortex and the thalamus in WAG/Rij rats

The alpha-2 adrenoreceptor agonist clonidine in low dose inhibits the release of noradrenaline and aggravates absence seizures. The present study examines properties of two types of spike-wave discharges (SWD) in a genetic model of absence epilepsy, the WAG/Rij rats. After reduction of noradrenergic neurotransmission with clonidine (0.00625 mg/kg, i.p.), the electrical activity was recorded in the neocortex, the ventroposteromedial nucleus (VPM) and the reticular thalamic nucleus (RTN). Clonidine temporally reduced percentage of wakefulness but did not affect sleep. Clonidine decreased the spectral power of sleep EEG (mostly in the delta band), this effect was found in the cortex and in the VPM. Clonidine increased the incidence of SWD type I (generalized); the spectral power of SWD I was lower in the frontal cortex (mostly in 1-9 and 30-100 Hz) and in the VPM (1-5 Hz), but higher in the RTN (9-14 Hz). Local occipital SWD (type II) had a tendency to be less numerous after clonidine, they had a lower power in the 5-9 Hz band in the occipital cortex, in the VPM and in the RTN. It can be concluded that strengthening of 9-14 Hz activity in the RTN may underlie clonidine-induced aggravation of SWD I.

Gabaergic neurons with α2-adrenergic receptors in basal forebrain and preoptic area express c-Fos during sleep

The basal forebrain (BF) contains cholinergic neurons that stimulate cortical activation during waking. In addition, both the BF and adjacent preoptic area (POA) contain neurons that promote sleep. We examined c-Fos expression in cholinergic and GABAergic neurons in the BF and POA to determine whether they are differentially active following sleep deprivation versus recovery and whether the GABAergic neurons are active during sleep. Whereas the numbers of c-Fos+ cells and proportions of c-Fos+ cells that were cholinergic were decreased, the proportions that were GABAergic were increased following sleep recovery across BF and POA nuclei. Moreover, the sleep-active GABAergic neurons were immunostained for alpha2A-adrenergic receptors. We conclude that GABAergic neurons that commonly bear alpha2-adrenergic receptors comprise sleep-active cells of the BF and POA. These GABAergic cells would be inhibited by noradrenaline (NA) released from locus coeruleus neurons during waking; they would be disinhibited through diminished NA release during drowsiness and thus become active to promote sleep by inhibiting in turn wake-promoting neurons.

Alpha 2 adrenergic receptors on GABAergic, putative sleep-promoting basal forebrain neurons

The basal forebrain plays an important role in the modulation of cortical activity and sleep-wake states. Yet its role must be multivalent as lesions reportedly diminish cortical fast activity and also cortical slow activity along with slow wave sleep (SWS). Basal forebrain cholinergic vs. GABAergic cell groups could differentially influence these processes. By labelling recorded neurons with Neurobiotin (Nb) using the juxtacellular technique and identifying them by immunostaining, we previously found that whereas all cholinergic cells increased their firing, the majority of GABAergic neurons decreased their firing in association with evoked cortical activation in urethane-anaesthetized rats. Here, we examined the possibility that such GABAergic, cortical activation 'off' cells might bear alpha 2 adrenergic receptors (alpha2AR) through which noradrenaline (NA) could inhibit them during cortical activation. First using simple dual-immunostaining for glutamic acid decarboxylase (GAD) and the alpha2AAR, we found that the majority (approximately 60%) of GAD-immunopositive (GAD+) neurons through the magnocellular preoptic nucleus (MCPO) and substantia innominata (SI) were labelled for the alpha2AAR. Second, in urethane-anaesthetized rats, we examined whether Nb-labelled, GAD+ cortical activation 'off' neurons that discharged maximally in association with cortical slow wave activity, were immunopositive for alpha2AAR. We found that all the Nb+/GAD+'off' cells were labelled for the alpha2AAR. Such cells could be inhibited in association with cortical activation and waking when noradrenergic locus coeruleus (LC) neurons discharge and be disinhibited with cortical slow waves and SWS when these neurons become inactive. We thus propose that alpha2AR-bearing GABAergic basal forebrain neurons constitute sleep-active and sleep-promoting neurons.

Presence of alpha-1 adrenoreceptors on thermosensitive neurons in the medial preoptico-anterior hypothalamic area in rats

Earlier microinjection studies showed that norepinephrine in the medial preoptico-anterior hypothalamic area (mPOAH) regulates body temperature and the action is mediated through alpha-1 adrenoceptors. This study was conducted to confirm if the thermosensitive neurons in the mPOAH of rats possess alpha-1 adrenoceptors. First, the thermosensitivity of mPOAH neurons was tested and then the effects of microiontophoretic application of prazosin, alpha 1 adrenoceptor antagonist, on the firing rate of both the thermosensitive as well as the insensitive neurons were recorded. Prazosin significantly inhibited the firing rate of the thermosensitive neurons suggesting that most of the cold and warm sensitive neurons in the mPOAH possess alpha-1 adrenoceptors. These results at the single neuronal level confirm our earlier hypothesis that in the mPOAH, norepinephrine regulates body temperature by acting on alpha-1 adrenoceptors. The data also suggest that sensitivity of the mPOAH neurons to norepinephrine alter with changes in body temperature. The detailed physiological significance of the results with special reference to thermoregulation at the single neuronal level has been discussed.

An adenosine A2a agonist increases sleep and induces Fos in ventrolateral preoptic neurons

Considerable evidence indicates that adenosine may be an endogenous somnogen, yet the mechanism through which it promotes sleep is unknown. Adenosine may act via A1 receptors to promote sleep, but an A2a receptor antagonist can block the sleep induced by prostaglandin D(2). We previously reported that prostaglandin D(2) activates sleep-promoting neurons of the ventrolateral preoptic area, and we hypothesized that an A2a receptor agonist also should activate these neurons. Rats were instrumented for sleep recordings, and an injection cannula was placed in the subarachnoid space just anterior to the ventrolateral preoptic area. After an 8-10-day recovery period, the A2a receptor agonist CGS21680 (20 pmol/min) or saline was infused through the injection cannula, and the animals were killed 2 h later. The brains were stained using Fos immunohistochemistry, and the pattern of Fos expression was studied in the entire brain. CGS21680 increased non-rapid eye movement sleep and markedly increased the expression of Fos in the ventrolateral preoptic area and basal leptomeninges, but it reduced Fos expression in wake-active brain regions such as the tuberomammillary nucleus. CGS21680 also induced Fos in the shell and core of the nucleus accumbens and in the lateral subdivision of the central nucleus of the amygdala. To determine whether these effects may have been mediated through A1 receptors, an additional group of rats received subarachnoid infusion of the A1 receptor agonist N(6)-cyclopentyladenosine (2 pmol/min). In contrast to CGS21680, infusion of N(6)-cyclopentyladenosine into the subarachnoid space produced only a small decrease in rapid eye movement sleep, and the pattern of Fos expression induced by N(6)-cyclopentyladenosine was notable only for decreased Fos in regions near the infusion site. These findings suggest that an adenosine A2a receptor agonist may activate cells of the leptomeninges or nucleus accumbens that increase the activity of ventrolateral preoptic area neurons. These ventrolateral preoptic area neurons may then coordinate the inhibition of multiple wake-promoting regions, resulting in sleep.

Orexin-A regulates body temperature in coordination with arousal status

Orexins, hypothalamic neuropeptides, are involved in modulation of food intake and arousal status. To further examine their physiological roles in brain function, the effect of centrally administered orexin-A on body temperature was investigated in rats. Assessed by a telemetry sensor system implanted into the abdominal cavity, infusion of orexin-A into the third cerebroventricle (i3vt) increased body temperature in a dose-responsive manner. Expression of uncoupling protein 1 (UCP1) mRNA in brown adipose tissue (BAT), as a marker for peripheral thermogenesis, failed to increase after the infusion. Expression of UCP3 mRNA in skeletal muscle was up-regulated, whereas UCP2 in white adipose tissue was unchanged after the infusion. The resulting information indicates that orexin neurons regulate body temperature in coordination with arousal status independently of peripheral thermogenesis, which is regulated by BAT UCP1.

Discharge profiles of juxtacellularly labeled and immunohistochemically identified GABAergic basal forebrain neurons recorded in association with the electroencephalogram in anesthetized rats

The basal forebrain ostensibly plays a dual role in the modulation of cortical activation and behavioral state. It is essential for stimulating cortical activation in association with waking (and paradoxical sleep), yet also important for attenuating cortical activation and promoting slow wave sleep. Using juxtacellular recording and labeling of neurons with Neurobiotin followed by immunohistochemical staining for glutamic acid decarboxylase (GAD), we studied the discharge properties of identified GABAergic basal forebrain neurons in relation to electroencephalographic (EEG) activity in urethane-anesthetized rats to determine the part or parts that they may play in this dual role. The GABAergic neurons displayed distinct discharge profiles in relation to somatosensory stimulation-evoked cortical activation. Whereas a significant minority increased its average discharge rate, the majority decreased its average discharge rate in association with cortical activation. Moreover, subgroups displayed distinct discharge patterns related to different cortical activities, including very regular high-frequency tonic spiking within a gamma EEG frequency range and rhythmic cluster spiking within a theta-like frequency range during cortical activation. During irregular slow EEG activity in absence of stimulation, one subgroup displayed spike bursts correlated with cortical slow oscillations. As relatively large in size and also antidromically activated from the cortex, many GABAergic neurons recorded were considered to be cortically projecting and thus capable of directly modulating cortical activity. Subgroups of GABAergic basal forebrain neurons would thus have the capacity to promote cortical activation by modulating gamma or theta activity and others to attenuate cortical activation by modulating irregular slow oscillations that normally occur during slow wave sleep.

Identification of sleep-promoting neurons in vitro

The neurons responsible for the onset of sleep are thought to be located in the preoptic area and more specifically, in the ventrolateral preoptic nucleus (VLPO). Here we identify sleep-promoting neurons in vitro and show that they represent an homogeneous population of cells that must be inhibited by systems of arousal during the waking state. We find that two-thirds of the VLPO neurons are multipolar triangular cells that show a low-threshold spike. This proportion matches that of cells active during sleep in the same region. We then show, using single-cell reverse transcriptase followed by polymerase chain reaction, that these neurons probably contain gamma-aminobutyric acid (GABA). We also show that these neurons are inhibited by noradrenaline and acetylcholine, both of which are transmitters of wakefulness. As most of these cells are also inhibited by serotonin but unaffected by histamine, their overall inhibition by transmitters of wakefulness is in agreement with their relative inactivity during waking with respect to sleep. We propose that the reciprocal inhibitory interaction of such VLPO neurons with the noradrenergic, serotoninergic and cholinergic waking systems to which they project is a key factor for promoting sleep.

Region-dependent difference in the sleep-promoting potency of an adenosine A2A receptor agonist

The present study has demonstrated that the sleep-promoting potency of 2-[p-(2-carboxyethyl)phenethylamino]-5'-N-ethylcarboxamido adenosine (CGS21680), a selective agonist for the adenosine A2A receptor, varies depending on the location of the administration. CGS21680 was continuously administered to rats through a chronically implanted cannula for 6 h during their active phase. The tip of the cannula was located in the subarachnoid space or the brain ventricle neighbouring the established brain areas implicated in the regulation of sleep-wake phenomena, i.e. rostral basal forebrain, medial preoptic area, lateral preoptic area, posterior hypothalamus, and dorsal tegmentum of the pons and medulla. At an infusion rate of 2.0 pmol/min, the magnitude of increase in non-rapid eye movement sleep varied from 14 min (a 15% increase) to 96 min (a 103% increase), and those of rapid eye movement sleep varied from 6 min (a 40% increase) to 28 min (a 264% increase) from the respective baseline values. The largest increases in both types of sleep occurred when CGS21680 was administered to the subarachnoid space underlying the rostral basal forebrain. These findings were interpreted to mean that the major, if not the only, site responsible for the CGS21680-inducing sleep was located in or near the rostral basal forebrain. This interpretation was supported by the findings that the administration of CGS21680 to the rostral basal forebrain produced predominant expression of Fos within the shell of the nucleus accumbens and the medial portion of the olfactory tubercle, and that the microdialysis perfusion of CGS21680 into the shell of the nucleus accumbens also exhibited a sleep-promoting effect.

Adrenergic and cholinergic inputs in preoptic area of rats interact for sleep-wake thermoregulation

Isolated studies have shown that both norepinephrine and acetylcholine into the medial preoptico-anterior hypothalamic area tonically regulate sleep-wake and body temperature. A possible interaction between these neurotransmitters for the regulation of such functions has been investigated in this study. To study this interaction a combination of either prazosin and carbachol or, scopolamine and methoxamine was injected into the medial preoptico-anterior hypothalamic area and the effect on sleep, wake, and rectal temperature recorded simultaneously. The combination of chemicals were selected based on our previous studies where it was observed that each of the chemicals in a combination had opposite effects. It was observed that injection of the combination expressed a resultant summated effects of individual component chemicals when injected in isolation (observed in previous studies). Because effect of neither of the chemicals in the combination was dominant, the results suggest an interaction and integration of the adrenergic and cholinergic inputs in the medial preoptico-anterior hypothalamic area for the regulation of sleep-wakefulness and body temperature.

The role of alpha-2 receptors in the medial preoptic area in the regulation of sleep-wakefulness and body temperature

The study was conducted on 48 free-moving male rats to find out the role of the medial preoptic alpha2 receptors in the regulation of sleep and body temperature. Recording electrodes for assessment of sleep-wakefulness, and injector cannulae for injection of drugs in the medial preoptic area were chronically fixed on the skulls of the animals. The noradrenergic fibres projecting to the medial preoptic area were destroyed in 24 rats by administration of 6-hydroxydopamine at the ventral noradrenergic bundle. Though arousal was produced in normal rats by the injection of the alpha2 adrenergic agonist, clonidine, at the medial preoptic area, it induced sedation in rats with noradrenergic fibre lesion. Clonidine did not alter the rectal temperature in normal rats but it induced hypothermia in lesioned rats. Injection of alpha2 antagonist, yohimbine, at the medial preoptic area induced sleep in rats with intact noradrenergic fibres. However, the sleep inducing effect of this drug was very much attenuated in the lesioned animals. There was no significant change in body temperature, in both these groups of animals, after yohimbine administration. The study indicates the role of presynaptic alpha2 adrenergic receptors in arousal response and indirectly supports the contention that the alpha1 postsynaptic receptors at the medial preoptic area are involved in hypnogenesis. It also suggests that the thermal changes induced by adrenergic system are mediated through alpha1 postsynaptic receptors. But the thermal changes do not contribute towards the induced alterations in sleep-wakefulness. It is proposed that there should be separate sets of noradrenergic terminals for regulation of sleep and body temperature.

Food intake after adrenaline and noradrenaline injections into the hypothalamic paraventricular nucleus in pigeons

The effects of local injections of adrenaline (Adr, 6 nmol) or noradrenaline (Nor, 16 nmol) into the paraventricular nucleus (PVN) and into other anterior hypothalamic districts on feeding behavior were examined in satiated pigeons bearing a chronically implanted cannula. When infused into the PVN, both Adr and Nor reliably elicited feeding responses during the first hour after the injection. Feeding responses to Adr injections were significantly higher than those evoked by Nor. Other behavioral measurements (sleep, exploratory, and preening) were not affected by these treatments. Local pretreatment with phentolamine (20 nmol) but not with propranolol (20 nmol) abolished the feeding response induced by both Adr and Nor into the PVN. Lateral hypothalamic sites were also shown to respond to catecholamine injections with an increase in feeding, followed also by an increased sleep-like behavior duration. Together with other evidence, the present results indicate that adrenergically mediated circuits into the avian PVN play an important role in the mechanisms of food intake control, equivalent to that observed in mammalian species.

Mild electrical stimulation of pontine tegmentum around locus coeruleus reduces rapid eye movement sleep in rats

The norepinephrinergic neurons in the locus coeruleus (LC) cease firing during REM sleep (REMS) and increase firing during REMS deprivation. Most of the earlier studies used lesion and transection techniques which could not confirm the role of LC in REMS generation and/or its maintenance, if at all. Hence, in this study it was hypothesized that if the LC REM-off neurons must cease firing before the onset of REMS, its continuous activation should eliminate or at least reduce REMS. Electrophysiological parameters characterizing sleep-wakefulness-REMS were recorded in freely moving male albino rats. In an attempt not to allow the REM-off LC neurons to cease firing, low intensity (200 microA), low frequency (2 Hz) rectangular (300 microseconds) pulses were continuously delivered to the LC bilaterally through chronically implanted electrodes, and the effects on sleep-wakefulness-REMS were investigated. Although the stimulation did not affect sleep state of the animals, it reduced REMS significantly. The effect on REMS was similar to that of REMS deprivation. Total duration of REMS was significantly reduced during stimulation and showed a rebound increase during the post stimulation period. This reduction in REMS duration was primarily due to a significant reduction in the REMS frequency/h while the mean REMS duration/episode was not affected. Thus, the results of this study suggest that the stimulated area (LC) affects REMS, most likely by suppression of REMS generation process.

Prostaglandin D2 modulates sleep-related and noradrenaline-induced activity of preoptic and basal forebrain neurons in the rat

Prostaglandin D2 (PGD2) was applied by pressure through a multibarrel micropipette to sleep-related neurons in the preoptic and neighboring basal forebrain area in head-restrained unanesthetized rats. During wakefulness, PGD2 excited six of 13 sleep-active neurons, inhibited seven of 13 waking-active neurons, and did not affect the remaining neurons. During slow-wave sleep (SWS), however, PGD2 excited only three of 17 sleep-active neurons and inhibited two of 13 waking-active neurons. State-indifferent neurons, which lacked activity related to the sleep-waking state, were insensitive to PGD2 irrespective of wakefulness (n = 24) and SWS (n = 40). These results suggest that PGD2 promotes sleep by exciting sleep-active neurons and by inhibiting waking-active neurons. Furthermore, continuous administration of PGD2 attenuated activity changes associated with wakefulness of five sleep-active and three waking-active neurons tested. Because we had suggested the involvement of preoptic noradrenaline (NA) in arousal, we examined possible modulatory effects of PGD2 on NA-induced neuron responses. PGD2 attenuated NA-induced inhibitory responses in four of six sleep-active neurons and in one of 10 state-indifferent neurons. PGD2 also attenuated NA-induced excitation in four waking-active neurons tested. Accordingly, the modulatory action of PGD2 on sleep-related neurons is important in the mechanism of sleep.