Effects of clozapine-N-oxide and compound 21 on sleep in laboratory mice

Chemogenetic inhibition of corticotropin releasing hormone neurons in the paraventricular nucleus attenuates traumatic stress-induced deficit of NREM sleep, but not REM sleep in mice

Present study was aimed to elucidate the role of corticotropin releasing hormone (CRH) neurons located in the paraventricular nucleus of the hypothalamus (PVN) in the mechanisms of stress-induced insomnia. Experiments were done in the rodent model of traumatic stress, mice exposure to the predator (rat) odor. Sleep changes associated with this model of stress were first assessed in adult male C57BL/6J wild-type mice (n = 12). The effect of chemogenetic silencing of CRH neurons within the PVN on traumatic stress-induced insomnia was examined in adult male CRH-ires-Cre mice using designer receptors exclusively activated by designer drugs (DREADD) technology. Animals received bilateral injections of inhibitory DREADD vector AAV-hSyn-DIO-hM4Di-mCherry (n = 10) or control AAV-hSyn-DIO-mCherry virus (n = 10) into the PVN during surgery. The DREADD was activated by intraperitoneal injection of clozapine-N-oxide (CNO) prior to the induction of traumatic stress. The exposure of mice to rat odor induced strong long-lasting suppression of both non-rapid eye movement (NREM) and rapid eye movement (REM) sleep stages in both experiments. Selective suppression of CRH neurons within the PVN alleviated acute insomnia by significantly increasing the time spent in NREM sleep but it did not counteract the stress-induced deficit in REM sleep. These findings suggest a specific role for CRH-secreting neurons within the PVN in the suppression of NREM sleep during acute insomnia caused by predator odor stress, whereas REM sleep suppression is controlled by a different mechanism.

Rest, Repair, Repeat: The Complex Relationship of Autophagy and Sleep

Autophagy and sleep are two evolutionary conserved mechanisms across the animal kingdom. Autophagy is a pathway for the degradation of cytoplasmic material in the lysosome, playing important roles in the homeostasis and health of the organism. On the other hand, sleep is a homeostatically regulated state with numerous presumed essential roles, including the restoration of tissue and physiological functions, such as brain waste clearance via the activation of the glymphatic systems. Given that sleep and autophagy are crucial processes tightly linked to homeostasis and maintenance of good health, understanding how they interact is of great interest, especially as sleep quality decreases in our modern 24-hour societies. Autophagy represents a promising target for therapeutic interventions in this context. Here, we review the contrasted and complementary roles of autophagy and sleep in maintaining homeostasis. Specifically, we focus on recent evidence suggesting that sleep impairment may increase autophagy, while autophagosome levels may modulate the amount of sleep. We discuss outstanding questions at the intersection of these two fields, highlighting methodological shortcomings in the current literature. Overcoming these limitations will be instrumental to design new experiments with the aim of answering one of the greatest mysteries of our time - why do we sleep?

SEX-DEPENDENT MODULATION OF BEHAVIORAL ALLOCATION VIA VENTRAL TEGMENTAL AREA-NUCLEUS ACCUMBENS SHELL CIRCUITRY

Diagnostic criteria for substance use disorder, cocaine type (i.e., cocaine use disorder), outlined in the 5 th edition of the Diagnostic and Statistical Manual, imply that the disorder arises, at least in part, from the maladaptive allocation of behavior to drug use. To date, however, the neural circuits involved in the allocation of behavior have not been systematically evaluated. Herein, a chemogenetics approach (i.e., designer receptors exclusively activated by designer drugs (DREADDs)) was utilized in combination with a concurrent choice self-administration experimental paradigm to evaluate the role of the mesolimbic neurocircuit in the allocation of behavior. Pharmacological activation of hM3D(G q ) DREADDs in neurons projecting from the ventral tegmental area (VTA) to the nucleus accumbens (AcbSh) induced a sex-dependent shift in the allocation of behavior in rodents transduced with DREADDs. Specifically, male DREADDs animals exhibited a robust increase in responding for a natural (i.e., sucrose) reward following pharmacological activation of the VTA-AcbSh circuit; female DREADDs rodents, in sharp contrast, displayed a prominent decrease in drug-reinforced (i.e., cocaine) responding. The sequential activation of hM3D(G q ) and KORD DREADDs within the same neuronal population validated the role of the VTA-AcbSh circuit in reinforced responding for concurrently available natural and drug rewards. Collectively, the VTA-AcbSh circuit is fundamentally involved in behavioral allocation affording a key target for the development of novel pharmacotherapies.

Chronic chemogenetic slow-wave-sleep enhancement in mice

While epidemiological associations and brief studies of sleep effects in human disease have been conducted, rigorous long-term studies of sleep manipulations and in animal models are needed to establish causation and to understand mechanisms. We have previously developed a mouse model of acute slow-wave-sleep (SWS) enhancement using chemogenetic activation of parafacial zone GABAergic neurons (PZGABA) in the parvicellular reticular formation of the pontine brainstem. However, it was unknown if SWS could be enhanced chronically in this model. In the present study, mice expressing the chemogenetic receptor hM3Dq in PZGABA were administered daily with one of three chemogenetic ligands, clozapine N-oxide (CNO), deschloroclozapine (DCZ) and compound 21 (C21), and sleep-wake phenotypes were analyzed using electroencephalogram (EEG) and electromyogram (EMG). We found that SWS time is increased for three hours, and at the same magnitude for at least six months. This phenotype is associated with an increase of slow wave activity (SWA) of similar magnitude throughout the 6-month dosing period. Interestingly, at the end of the 6-month dosing period, SWA remains increased for at least a week. This study validates a mouse model of chronic SWS enhancement that will allow mechanistic investigations into how SWS promotes physiological function and prevents diseases. The approach of a rotating schedule of three chemogenetic ligands may be broadly applicable in chemogenetic studies that require chronic administration.

Mesolimbic dopamine neurons drive infradian rhythms in sleep-wake and heightened activity state

Infradian mood and sleep-wake rhythms with periods of 48 hours and beyond have been observed in patients with bipolar disorder (BD), which even persist in the absence of exogenous timing cues, indicating an endogenous origin. Here, we show that mice exposed to methamphetamine in drinking water develop infradian locomotor rhythms with periods of 48 hours and beyond which extend to sleep length and manic state-associated behaviors in support of a model for cycling in BD. The cycling capacity is abrogated upon genetic disruption of dopamine (DA) production in DA neurons of the ventral tegmental area (VTA) or ablation of nucleus accumbens projecting DA neurons. Furthermore, chemogenetic activation of VTADA neurons including those that project to the nucleus accumbens led to locomotor period lengthening in circadian clock-deficient mice, which was counteracted by antipsychotic treatment. Together, our findings argue that BD cycling relies on infradian rhythm generation that depends on mesolimbic DA neurons.

Chemogenetic activation of astrocytes modulates sleep-wakefulness states in a brain region-dependent manner

Study Objectives

Astrocytes change their intracellular calcium (Ca2+) concentration during sleep/wakefulness states in mice. Furthermore, the Ca2+ dynamics in astrocytes vary depending on the brain region. However, it remains unclear whether alterations in astrocyte activity can affect sleep-wake states and cortical oscillations in a brain region-dependent manner.

Methods

Astrocyte activity was artificially manipulated in mice using chemogenetics. Astrocytes in the hippocampus and pons, which are 2 brain regions previously classified into different clusters based on their Ca2+ dynamics during sleep-wakefulness, were focused on to compare whether there are differences in the effects of astrocytes from different brain regions.

Results

The chemogenetic activation of astrocytes in the hippocampus significantly decreased the total time of wakefulness and increased the total time of sleep. This had little effect on cortical oscillations in all sleep-wakefulness states. On the other hand, the activation of astrocytes in the pons substantially suppressed rapid eye movement (REM) sleep in association with a decreased number of REM episodes, indicating strong inhibition of REM onset. Regarding cortical oscillations, the delta wave component during non-REM sleep was significantly enhanced.

Conclusions

These results suggest that astrocytes modulate sleep-wakefulness states and cortical oscillations. Furthermore, the role of astrocytes in sleep-wakefulness states appears to vary among brain regions.

Glial cells undergo rapid changes following acute chemogenetic manipulation of cortical layer 5 projection neurons

Bidirectional communication between neurons and glial cells is crucial to establishing and maintaining normal brain function. Some of these interactions are activity-dependent, yet it remains largely unexplored how acute changes in neuronal activity affect glial-to-neuron and neuron-to-glial dynamics. Here, we use excitatory and inhibitory designer receptors exclusively activated by designer drugs (DREADD) to study the effects of acute chemogenetic manipulations of a subpopulation of layer 5 cortical projection and dentate gyrus neurons in adult (Rbp4Cre) mouse brains. We show that acute chemogenetic neuronal activation reduces synaptic density, and increases microglia and astrocyte reactivity, but does not affect parvalbumin (PV+) neurons, only perineuronal nets (PNN). Conversely, acute silencing increases synaptic density and decreases glial reactivity. We show fast glial response upon clozapine-N-oxide (CNO) administration in cortical and subcortical regions. Together, our work provides evidence of fast, activity-dependent, bidirectional interactions between neurons and glial cells.

Ventral subiculum promotes wakefulness through several pathways in male mice

The ventral subiculum (vSUB), the major output structure of the hippocampal formation, regulates motivation, stress integration, and anxiety-like behaviors that rely on heightened arousal. However, the roles and underlying neural circuits of the vSUB in wakefulness are poorly known. Using in vivo fiber photometry and multichannel electrophysiological recordings in mice, we found that the vSUB glutamatergic neurons exhibited high activities during wakefulness. Moreover, activation of vSUB glutamatergic neurons caused an increase in wakefulness and anxiety-like behaviors and induced a rapid transition from sleep to wakefulness. In addition, optogenetic stimulation of vSUB glutamatergic terminals and retrograde-targeted chemogenetic activation of vSUB glutamatergic neurons revealed that vSUB promoted arousal by innervating the lateral hypothalamus (LH), nucleus accumbens (NAc) shell, and prefrontal cortex (PFC). Nevertheless, local microinjection of dopamine D1 or D2/D3 receptor antagonist blocked the wake-promoting effect induced by chemogenetic activation of vSUB pathways. Finally, chemogenetic inhibition of vSUB glutamatergic neurons decreased arousal. Altogether, our findings reveal a prominent contribution of vSUB glutamatergic neurons to the control of wakefulness through several pathways.

Chemogenetic Seizure Control: Keeping the Horses in the BARN(I)

Acetylcholine Receptor Based Chemogenetics Engineered for Neuronal Inhibition and Seizure Control Assessed in Mice Nguyen QA, Klein PM, Xie C, Benthall KN, Iafrati J, Homidan J, Bendor JT, Dudok B, Farrell JS, Gschwind T, Porter CL, Keravala A, Dodson GS, Soltesz I. Nat Commun . 2024;15(1):601. doi:10.1038/s41467-024-44853-8 Epilepsy is a prevalent disorder involving neuronal network hyperexcitability, yet existing therapeutic strategies often fail to provide optimal patient outcomes. Chemogenetic approaches, where exogenous receptors are expressed in defined brain areas and specifically activated by selective agonists, are appealing methods to constrain overactive neuronal activity. We developed BARNI (Bradanicline- and Acetylcholine-activated Receptor for Neuronal Inhibition), an engineered channel comprised of the α7 nicotinic acetylcholine receptor ligand-binding domain coupled to an α1 glycine receptor anion pore domain. Here we demonstrate that BARNI activation by the clinical stage α7 nicotinic acetylcholine receptor-selective agonist bradanicline effectively suppressed targeted neuronal activity, and controlled both acute and chronic seizures in male mice. Our results provide evidence for the use of an inhibitory acetylcholine-based engineered channel activatable by both exogenous and endogenous agonists as a potential therapeutic approach to treating epilepsy.

Neocortical long-range inhibition promotes cortical synchrony and sleep

Behavioral states such as sleep and wake are highly correlated with specific patterns of rhythmic activity in the cortex. During low arousal states such as slow wave sleep, the cortex is synchronized and dominated by low frequency rhythms coordinated across multiple regions. Although recent evidence suggests that GABAergic inhibitory neurons are key players in cortical state modulation, the in vivo circuit mechanisms coordinating synchronized activity among local and distant neocortical networks are not well understood. Here, we show that somatostatin and chondrolectin co-expressing cells (Sst-Chodl cells), a sparse and unique class of neocortical inhibitory neurons, are selectively active during low arousal states and are largely silent during periods of high arousal. In contrast to other neocortical inhibitory neurons, we show these neurons have long-range axons that project across neocortical areas. Activation of Sst-Chodl cells is sufficient to promote synchronized cortical states characteristic of low arousal, with increased spike co-firing and low frequency brain rhythms, and to alter behavioral states by promoting sleep. Contrary to the prevailing belief that sleep is exclusively driven by subcortical mechanisms, our findings reveal that these long-range inhibitory neurons not only track changes in behavioral state but are sufficient to induce both sleep-like cortical states and sleep behavior, establishing a crucial circuit component in regulating behavioral states.

The neural basis of resting-state fMRI functional connectivity in fronto-limbic circuits revealed by chemogenetic manipulation

Measures of fMRI resting-state functional connectivity (rs-FC) are an essential tool for basic and clinical investigations of fronto-limbic circuits. Understanding the relationship between rs-FC and the underlying patterns of neural activity in these circuits is therefore vital. Here we introduced inhibitory designer receptors exclusively activated by designer drugs (DREADDs) into the amygdala of two male macaques. We evaluated the causal effect of activating the DREADD receptors on rs-FC and neural activity within circuits connecting amygdala and frontal cortex. Activating the inhibitory DREADD increased rs-FC between amygdala and ventrolateral prefrontal cortex. Neurophysiological recordings revealed that the DREADD-induced increase in fMRI rs-FC was associated with increased local field potential coherency in the alpha band (6.5-14.5 Hz) between amygdala and ventrolateral prefrontal cortex. Thus, our multi-modal approach reveals the specific signature of neuronal activity that underlies rs-FC in fronto-limbic circuits.

Neuronal PAS domain 1 identifies a major subpopulation of wakefulness-promoting GABAergic neurons in the basal forebrain

Here, we describe a group of basal forebrain (BF) neurons expressing neuronal Per-Arnt-Sim (PAS) domain 1 (Npas1), a developmental transcription factor linked to neuropsychiatric disorders. Immunohistochemical staining in Npas1-cre-2A-TdTomato mice revealed BF Npas1+ neurons are distinct from well-studied parvalbumin or cholinergic neurons. Npas1 staining in GAD67-GFP knock-in mice confirmed that the vast majority of Npas1+ neurons are GABAergic, with minimal colocalization with glutamatergic neurons in vGlut1-cre-tdTomato or vGlut2-cre-tdTomato mice. The density of Npas1+ neurons was high, five to six times that of neighboring cholinergic, parvalbumin, or glutamatergic neurons. Anterograde tracing identified prominent projections of BF Npas1+ neurons to brain regions involved in sleep-wake control, motivated behaviors, and olfaction such as the lateral hypothalamus, lateral habenula, nucleus accumbens shell, ventral tegmental area, and olfactory bulb. Chemogenetic activation of BF Npas1+ neurons in the light period increased the amount of wakefulness and the latency to sleep for 2 to 3 h, due to an increase in long wake bouts and short NREM sleep bouts. NREM slow-wave and sigma power, as well as sleep spindle density, amplitude, and duration, were reduced, reminiscent of findings in several neuropsychiatric disorders. Together with previous findings implicating BF Npas1+ neurons in stress responsiveness, the anatomical projections of BF Npas1+ neurons and the effect of activating them suggest a possible role for BF Npas1+ neurons in motivationally driven wakefulness and stress-induced insomnia. Identification of this major subpopulation of BF GABAergic neurons will facilitate studies of their role in sleep disorders, dementia, and other neuropsychiatric conditions involving BF.

Clozapine N-oxide, compound 21, and JHU37160 do not influence effortful reward-seeking behavior in mice

RATIONALE

Clozapine N-oxide (CNO) has been developed as a ligand to selectively activate designer receptors exclusively activated by designer drugs (DREADDs). However, previous studies have revealed that peripherally injected CNO is reverse-metabolized into clozapine, which, in addition to activating DREADDs, acts as an antagonist at various neurotransmitter receptors, suggesting potential off-target effects of CNO on animal physiology and behaviors. Recently, second-generation DREADD agonists compound 21 (C21) and JHU37160 (J60) have been developed, but their off-target effects are not fully understood.

OBJECTIVES

The present studies assessed the effect of novel DREADD ligands on reward-seeking behavior.

METHODS

We first tested the possible effect of acute i.p. injection of low-to-moderate (0.1, 0.3, 1, 3 mg/kg) of CNO, C21, and J60 on motivated reward-seeking behavior in wild-type mice. We then examined whether a high dose (10 mg/kg) of these drugs might be able to alter responding.

RESULTS

Low-to-moderate doses of all drugs and a high dose of CNO or C21 did not alter operant lick responding for a reward under a progressive ratio schedule of reinforcement, in which the number of operant lick responses to obtain a reward increases after each reward collection. However, high-dose J60 resulted in a total lack of responding that was later observed in an open field arena to be due to a sedative effect.

CONCLUSIONS

This study provides definitive evidence that commonly used doses of CNO, C21, and J60 have negligible off-target effects on motivated reward-seeking but urges caution when using high doses of J60 due to sedative effects.

Deschloroclozapine exhibits an exquisite agonistic effect at lower concentration compared to clozapine-N-oxide in hM3Dq expressing chemogenetically modified rats

Introduction

Within the realm of chemogenetics, a particular form of agonists targeting designer receptors exclusively activated by designer drugs (DREADDs) has emerged. Deschloroclozapine (DCZ), a recently introduced DREADDs agonist, demonstrates remarkable potency in activating targeted neurons at a lower dosage compared to clozapine-N-oxide (CNO).

Methods

We conducted a comparative analysis of the effects of subcutaneously administered CNO (1 mg/kg) and DCZ (0.1 mg/kg) in our transgenic rats expressing hM3Dq and mCherry exclusively in oxytocin (OXT) neurons.

Results and Discussion

Notably, DCZ exhibited a swift and robust elevation of serum OXT, surpassing the effects of CNO, with a significant increase in the area under the curve (AUC) up to 3 hours post-administration. Comprehensive assessment of brain neuronal activity, using Fos as an indicator, revealed comparable effects between CNO and DCZ. Additionally, in a neuropathic pain model, both CNO and DCZ increased the mechanical nociceptive and thermal thresholds; however, the DCZ-treated group exhibited a significantly accelerated onset of the effects, aligning harmoniously with the observed alterations in serum OXT concentration following DCZ administration. These findings emphasize the remarkable efficacy of DCZ in rats, suggesting its equivalent or potentially superior performance to CNO at considerably lower dosages, thus positioning it as a promising contender among DREADDs agonists.

Neuronal PAS domain 1 identifies a major subpopulation of wakefulness-promoting GABAergic neurons in basal forebrain

Here we describe a novel group of basal forebrain (BF) neurons expressing neuronal PAS domain 1 (Npas1), a developmental transcription factor linked to neuropsychiatric disorders. Immunohistochemical staining in Npas1-cre-2A-TdTomato mice revealed BF Npas1 + neurons are distinct from well-studied parvalbumin or cholinergic neurons. Npas1 staining in GAD67-GFP knock-in mice confirmed that the vast majority of Npas1 + neurons are GABAergic, with minimal colocalization with glutamatergic neurons in vGlut1-cre-tdTomato or vGlut2-cre-tdTomato mice. The density of Npas1 + neurons was high, 5-6 times that of neighboring cholinergic, parvalbumin or glutamatergic neurons. Anterograde tracing identified prominent projections of BF Npas1 + neurons to brain regions involved in sleep-wake control, motivated behaviors and olfaction such as the lateral hypothalamus, lateral habenula, nucleus accumbens shell, ventral tegmental area and olfactory bulb. Chemogenetic activation of BF Npas1 + neurons in the light (inactive) period increased the amount of wakefulness and the latency to sleep for 2-3 hr, due to an increase in long wake bouts and short NREM sleep bouts. Non-REM slow-wave (0-1.5 Hz) and sigma (9-15 Hz) power, as well as sleep spindle density, amplitude and duration, were reduced, reminiscent of findings in several neuropsychiatric disorders. Together with previous findings implicating BF Npas1 + neurons in stress responsiveness, the anatomical projections of BF Npas1 + neurons and the effect of activating them suggest a possible role for BF Npas1 + neurons in motivationally-driven wakefulness and stress-induced insomnia. Identification of this major subpopulation of BF GABAergic neurons will facilitate studies of their role in sleep disorders, dementia and other neuropsychiatric conditions involving BF.

SIGNIFICANCE STATEMENT

We characterize a group of basal forebrain (BF) neurons in the mouse expressing neuronal PAS domain 1 (Npas1), a developmental transcription factor linked to neuropsychiatric disorders. BF Npas1 + neurons are a major subset of GABAergic neurons distinct and more numerous than cholinergic, parvalbumin or glutamate neurons. BF Npas1 + neurons target brain areas involved in arousal, motivation and olfaction. Activation of BF Npas1 + neurons in the light (inactive) period increased wakefulness and the latency to sleep due to increased long wake bouts. Non-REM sleep slow waves and spindles were reduced reminiscent of findings in several neuropsychiatric disorders. Identification of this major subpopulation of BF GABAergic wake-promoting neurons will allow studies of their role in insomnia, dementia and other conditions involving BF.

Advanced neurobiological tools to interrogate metabolism

Engineered neurobiological tools for the manipulation of cellular activity, such as chemogenetics and optogenetics, have become a cornerstone of modern neuroscience research. These tools are invaluable for the interrogation of the central control of metabolism as they provide a direct means to establish a causal relationship between brain activity and biological processes at the cellular, tissue and organismal levels. The utility of these methods has grown substantially due to advances in cellular-targeting strategies, alongside improvements in the resolution and potency of such tools. Furthermore, the potential to recapitulate endogenous cellular signalling has been enriched by insights into the molecular signatures and activity dynamics of discrete brain cell types. However, each modulatory tool has a specific set of advantages and limitations; therefore, tool selection and suitability are of paramount importance to optimally interrogate the cellular and circuit-based underpinnings of metabolic outcomes within the organism. Here, we describe the key principles and uses of engineered neurobiological tools. We also highlight inspiring applications and outline critical considerations to be made when using these tools within the field of metabolism research. We contend that the appropriate application of these biotechnological advances will enable the delineation of the central circuitry regulating systemic metabolism with unprecedented potential.

Prefrontal Cortical Regulation of REM Sleep

Rapid-eye-movement (REM) sleep is accompanied by intense cortical activity, underlying its wake-like electroencephalogram (EEG). The neural activity inducing REM sleep is thought to originate from subcortical circuits in brainstem and hypothalamus. However, whether cortical neurons can also trigger REM sleep has remained unknown. Here, we show in mice that the medial prefrontal cortex (mPFC) strongly promotes REM sleep. Bidirectional optogenetic manipulations demonstrate that excitatory mPFC neurons promote REM sleep through their projections to the lateral hypothalamus (LH) and regulate phasic events, reflected in accelerated EEG theta oscillations and increased eye-movement density during REM sleep. Calcium imaging reveals that the majority of LH-projecting mPFC neurons are maximally activated during REM sleep and a subpopulation is recruited during phasic theta accelerations. Our results delineate a cortico-hypothalamic circuit for the top-down control of REM sleep and identify a critical role of the mPFC in regulating phasic events during REM sleep.

Somatostatin neurons in prefrontal cortex initiate sleep-preparatory behavior and sleep via the preoptic and lateral hypothalamus

The prefrontal cortex (PFC) enables mammals to respond to situations, including internal states, with appropriate actions. One such internal state could be 'tiredness'. Here, using activity tagging in the mouse PFC, we identified particularly excitable, fast-spiking, somatostatin-expressing, γ-aminobutyric acid (GABA) (PFCSst-GABA) cells that responded to sleep deprivation. These cells projected to the lateral preoptic (LPO) hypothalamus and the lateral hypothalamus (LH). Stimulating PFCSst-GABA terminals in the LPO hypothalamus caused sleep-preparatory behavior (nesting, elevated theta power and elevated temperature), and stimulating PFCSst-GABA terminals in the LH mimicked recovery sleep (non-rapid eye-movement sleep with higher delta power and lower body temperature). PFCSst-GABA terminals had enhanced activity during nesting and sleep, inducing inhibitory postsynaptic currents on diverse cells in the LPO hypothalamus and the LH. The PFC also might feature in deciding sleep location in the absence of excessive fatigue. These findings suggest that the PFC instructs the hypothalamus to ensure that optimal sleep takes place in a suitable place.

Prefrontal cortical regulation of REM sleep

Rapid eye movement (REM) sleep is accompanied by intense cortical activity, underlying its wake-like electroencephalogram. The neural activity inducing REM sleep is thought to originate from subcortical circuits in brainstem and hypothalamus. However, whether cortical neurons can also trigger REM sleep has remained unknown. Here we show in mice that the medial prefrontal cortex (mPFC) strongly promotes REM sleep. Bidirectional optogenetic manipulations demonstrate that excitatory mPFC neurons promote REM sleep through their projections to the lateral hypothalamus and regulate phasic events, reflected in accelerated electroencephalogram theta oscillations and increased eye movement density during REM sleep. Calcium imaging reveals that the majority of lateral hypothalamus-projecting mPFC neurons are maximally activated during REM sleep and a subpopulation is recruited during phasic theta accelerations. Our results delineate a cortico-hypothalamic circuit for the top-down control of REM sleep and identify a critical role of the mPFC in regulating phasic events during REM sleep.

Parvalbumin neurons in the anterior nucleus of thalamus control absence seizures

OBJECTIVE

Anterior nucleus of thalamus (ANT) has been widely accepted as a potential therapeutic target for drug-resistant epilepsy. Although increased volume of the ANT was also reported in patients with absence epilepsy, the relationship between the ANT and absence epilepsy has been barely illustrated.

METHODS

Using chemogenetics, we evaluated the effect of ANT parvalbumin (PV) neurons on pentylenetetrazole (PTZ)-induced absence seizures in mice.

RESULTS

We found that intraperitoneal injection of PTZ (30 mg/kg) can stably induce absence-like seizures characterized by bilaterally synchronous spike-wave discharges (SWDs). Selective activation of PV neurons in the ANT by chemogenetics could aggravate the severity of absence seizures, whereas selective inhibition of that cannot reverse this condition and even promote absence seizures as well. Moreover, chemogenetic inhibition of ANT PV neurons without administration of PTZ was also sufficient to generate SWDs. Analysis of background EEG showed that chemogenetic activation or inhibition of ANT PV neurons could both significantly increase the EEG power of delta oscillation in the frontal cortex, which might mediate the pro-seizure effect of ANT PV neurons.

SIGNIFICANCE

Our findings indicated that either activation or inhibition of ANT PV neurons might disturb the intrinsic delta rhythms in the cortex and worsen absence seizures, which highlighted the importance of maintaining the activity of ANT PV neurons in absence seizure.

Activation of Basal Forebrain Astrocytes Induces Wakefulness without Compensatory Changes in Sleep Drive

Mammalian sleep is regulated by a homeostatic process that increases sleep drive and intensity as a function of prior wake time. Sleep homeostasis has traditionally been thought to be a product of neurons, but recent findings demonstrate that this process is also modulated by glial astrocytes. The precise role of astrocytes in the accumulation and discharge of sleep drive is unknown. We investigated this question by selectively activating basal forebrain (BF) astrocytes using designer receptors exclusively activated by designer drugs (DREADDs) in male and female mice. DREADD activation of the Gq-protein-coupled pathway in BF astrocytes produced long and continuous periods of wakefulness that paradoxically did not cause the expected homeostatic response to sleep loss (e.g., increases in sleep time or intensity). Further investigations showed that this was not because of indirect effects of the ligand that activated DREADDs. These findings suggest that the need for sleep is not only driven by wakefulness per se, but also by specific neuronal-glial circuits that are differentially activated in wakefulness.SIGNIFICANCE STATEMENT Sleep drive is controlled by a homeostatic process that increases sleep duration and intensity based on prior time spent awake. Non-neuronal brain cells (e.g., glial astrocytes) influence this homeostatic process, but their precise role is unclear. We used a genetic technique to activate astrocytes in the basal forebrain (BF) of mice, a brain region important for sleep and wake expression and sleep homeostasis. Astroglial activation induced prolonged wakefulness without the expected homeostatic increase in sleep drive (i.e., sleep duration and intensity). These findings indicate that our need to sleep is also driven by non-neuronal cells, and not only by time spent awake.

A medullary hub for controlling REM sleep and pontine waves

Rapid-eye-movement (REM) sleep is a distinct behavioral state associated with vivid dreaming and memory processing. Phasic bursts of electrical activity, measurable as spike-like pontine (P)-waves, are a hallmark of REM sleep implicated in memory consolidation. However, the brainstem circuits regulating P-waves, and their interactions with circuits generating REM sleep, remain largely unknown. Here, we show that an excitatory population of dorsomedial medulla (dmM) neurons expressing corticotropin-releasing-hormone (CRH) regulates both REM sleep and P-waves in mice. Calcium imaging showed that dmM CRH neurons are selectively activated during REM sleep and recruited during P-waves, and opto- and chemogenetic experiments revealed that this population promotes REM sleep. Chemogenetic manipulation also induced prolonged changes in P-wave frequency, while brief optogenetic activation reliably triggered P-waves along with transiently accelerated theta oscillations in the electroencephalogram (EEG). Together, these findings anatomically and functionally delineate a common medullary hub for the regulation of both REM sleep and P-waves.

Up-regulation of LCN2 in the anterior cingulate cortex contributes to neural injury-induced chronic pain

Chronic pain caused by disease or injury affects more than 30% of the general population. The molecular and cellular mechanisms underpinning the development of chronic pain remain unclear, resulting in scant effective treatments. Here, we combined electrophysiological recording, in vivo two-photon (2P) calcium imaging, fiber photometry, Western blotting, and chemogenetic methods to define a role for the secreted pro-inflammatory factor, Lipocalin-2 (LCN2), in chronic pain development in mice with spared nerve injury (SNI). We found that LCN2 expression was upregulated in the anterior cingulate cortex (ACC) at 14 days after SNI, resulting in hyperactivity of ACC glutamatergic neurons (ACC^Glu) and pain sensitization. By contrast, suppressing LCN2 protein levels in the ACC with viral constructs or exogenous application of neutralizing antibodies leads to significant attenuation of chronic pain by preventing ACC^Glu neuronal hyperactivity in SNI 2W mice. In addition, administering purified recombinant LCN2 protein in the ACC could induce pain sensitization by inducing ACC^Glu neuronal hyperactivity in naïve mice. This study provides a mechanism by which LCN2-mediated hyperactivity of ACC^Glu neurons contributes to pain sensitization, and reveals a new potential target for treating chronic pain.

The role of orexin neuron activity in sleep/wakefulness regulation

Orexin (also known as hypocretin) is a neuropeptide exclusively synthesized in the neurons of the lateral hypothalamus (LH). Initially orexin was thought to be involved in the regulation of feeding behavior. However, it is now known to also be a critical regulator of sleep/wakefulness, especially the maintenance of wakefulness. Although the somas of orexin neurons are exclusively located in the LH, these neurons send axons throughout the brain and spinal cord. Orexin neurons integrate inputs from various brain regions and project to neurons that are involved in the regulation of sleep/wakefulness. Orexin knockout mice have a fragmentation of sleep/wakefulness and cataplexy-like behavior arrest, which is similar to the sleep disorder narcolepsy. Recent progress with manipulation of neural activity of targeted neurons, using experimental tools such as optogenetics and chemogenetics, has emphasized the role of orexin neuron activity on the regulation of sleep/wakefulness. Recording of orexin neuron activity in vivo using electrophysiological and gene-encoded calcium indicator proteins revealed that these cells have specific activity patterns across sleep/wakefulness state changes. Here, we also discuss not only the role of the orexin peptide, but also the role of other co-transmitters that are synthesized and released from orexin neurons and involved in sleep/wakefulness regulation.