Substituted Azabicyclo[2.2.1]heptanes as Selective Orexin-1 Antagonists: Discovery of JNJ-54717793

The orexin system consists of two neuropeptides (orexin-A and orexin-B) that exert their mode of action on two receptors (orexin-1 and orexin-2). While the role of the orexin-2 receptor is established as an important modulator of sleep wake states, the role of the orexin-1 receptor is believed to play a role in addiction, panic, or anxiety. In this manuscript, we describe the optimization of a nonselective substituted azabicyclo[2.2.1]heptane dual orexin receptor antagonist (DORA) into orally bioavailable, brain penetrating, selective orexin-1 receptor (OX1R) antagonists. This resulted in the discovery of our first candidate for clinical development, JNJ-54717793.

Translational evaluation of novel selective orexin-1 receptor antagonist JNJ-61393215 in an experimental model for panic in rodents and humans

Orexin neurons originating in the perifornical and lateral hypothalamic area project to anxiety- and panic-associated neural circuitry, and are highly reactive to anxiogenic stimuli. Preclinical evidence suggests that the orexin system, and particularly the orexin-1 receptor (OX1R), may be involved in the pathophysiology of panic and anxiety. Selective OX1R antagonists thus may constitute a potential new treatment strategy for panic- and anxiety-related disorders. Here, we characterized a novel selective OX1R antagonist, JNJ-61393215, and determined its affinity and potency for human and rat OX1R in vitro. We also evaluated the safety, pharmacokinetic, and pharmacodynamic properties of JNJ-61393215 in first-in-human single- and multiple-ascending dose studies conducted. Finally, the potential anxiolytic effects of JNJ-61393215 were evaluated both in rats and in healthy men using 35% CO₂ inhalation challenge to induce panic symptoms. In the rat CO₂ model of panic anxiety, JNJ-61393215 demonstrated dose-dependent attenuation of CO₂-induced panic-like behavior without altering baseline locomotor or autonomic activity, and had minimal effect on spontaneous sleep. In phase-1 human studies, JNJ-61393215 at 90 mg demonstrated significant reduction (P < 0.02) in CO₂-induced fear and anxiety symptoms that were comparable to those obtained using alprazolam. The most frequently reported adverse events were somnolence and headache, and all events were mild in severity. These results support the safety, tolerability, and anxiolytic effects of JNJ-61393215, and validate CO₂ exposure as a translational cross-species experimental model to evaluate the therapeutic potential of novel anxiolytic drugs.

Putative role of GPR139 on sleep modulation using pharmacological and genetic rodent models

GPR139 is a G-protein coupled receptor expressed in circumventricular regions of the habenula and septum. Amino acids L-tryptophan and L-phenylalanine have been shown to activate GPR139 at physiologically relevant concentrations. The aim of the present study was to investigate the role of GPR139 on sleep modulation using pharmacological and genetic (GPR139 knockout mice, KO) rodent models. To evaluate the effects of GPR139 pharmacological activation on sleep, rats were orally dosed with the selective GPR139 agonist JNJ-63533054 (3-30 mg/kg). When acutely administered at the beginning of the light phase, the GPR139 agonist dose-dependently reduced non-rapid eye movement (NREM) latency and increased NREM sleep duration without altering rapid eye movement (REM) sleep. This effect progressively dissipated upon 7-day repeated dosing, suggesting functional desensitization. Under baseline conditions, GPR139 KO mice spent less time in REM sleep compared to their wild type littermates during the dark phase, whereas NREM sleep was not altered. Under conditions of pharmacologically enhanced monoamine endogenous tone, GPR139 KO mice showed a blunted response to citalopram or fluoxetine induced REM sleep suppression and an attenuated response to the wake promoting effect of amphetamine. These findings indicate an emerging role of GPR139 in the modulation of sleep states.

Pharmacologic Characterization of JNJ-42226314, [1-(4-Fluorophenyl)indol-5-yl]-[3-[4-(thiazole-2-carbonyl)piperazin-1-yl]azetidin-1-yl]methanone, a Reversible, Selective, and Potent Monoacylglycerol Lipase Inhibitor

The serine hydrolase monoacylglycerol lipase (MAGL) is the rate-limiting enzyme responsible for the degradation of the endocannabinoid 2-arachidonoylglycerol (2-AG) into arachidonic acid and glycerol. Inhibition of 2-AG degradation leads to elevation of 2-AG, the most abundant endogenous agonist of the cannabinoid receptors (CBs) CB1 and CB2. Activation of these receptors has demonstrated beneficial effects on mood, appetite, pain, and inflammation. Therefore, MAGL inhibitors have the potential to produce therapeutic effects in a vast array of complex human diseases. The present report describes the pharmacologic characterization of [1-(4-fluorophenyl)indol-5-yl]-[3-[4-(thiazole-2-carbonyl)piperazin-1-yl]azetidin-1-yl]methanone (JNJ-42226314), a reversible and highly selective MAGL inhibitor. JNJ-42226314 inhibits MAGL in a competitive mode with respect to the 2-AG substrate. In rodent brain, the compound time- and dose-dependently bound to MAGL, indirectly led to CB1 occupancy by raising 2-AG levels, and raised norepinephrine levels in cortex. In vivo, the compound exhibited antinociceptive efficacy in both the rat complete Freund's adjuvant-induced radiant heat hypersensitivity and chronic constriction injury-induced cold hypersensitivity models of inflammatory and neuropathic pain, respectively. Though 30 mg/kg induced hippocampal synaptic depression, altered sleep onset, and decreased electroencephalogram gamma power, 3 mg/kg still provided approximately 80% enzyme occupancy, significantly increased 2-AG and norepinephrine levels, and produced neuropathic antinociception without synaptic depression or decreased gamma power. Thus, it is anticipated that the profile exhibited by this compound will allow for precise modulation of 2-AG levels in vivo, supporting potential therapeutic application in several central nervous system disorders. SIGNIFICANCE STATEMENT: Potentiation of endocannabinoid signaling activity via inhibition of the serine hydrolase monoacylglycerol lipase (MAGL) is an appealing strategy in the development of treatments for several disorders, including ones related to mood, pain, and inflammation. [1-(4-Fluorophenyl)indol-5-yl]-[3-[4-(thiazole-2-carbonyl)piperazin-1-yl]azetidin-1-yl]methanone is presented in this report to be a novel, potent, selective, and reversible noncovalent MAGL inhibitor that demonstrates dose-dependent enhancement of the major endocannabinoid 2-arachidonoylglycerol as well as efficacy in models of neuropathic and inflammatory pain.

Evaluation of JNJ-54717793 a Novel Brain Penetrant Selective Orexin 1 Receptor Antagonist in Two Rat Models of Panic Attack Provocation

Orexin neurons originating in the perifornical and lateral hypothalamic area are highly reactive to anxiogenic stimuli and have strong projections to anxiety and panic-associated circuitry. Recent studies support a role for the orexin system and in particular the orexin 1 receptor (OX1R) in coordinating an integrative stress response. However, no selective OX1R antagonist has been systematically tested in two preclinical models of using panicogenic stimuli that induce panic attack in the majority of people with panic disorder, namely an acute hypercapnia-panic provocation model and a model involving chronic inhibition of GABA synthesis in the perifornical hypothalamic area followed by intravenous sodium lactate infusion. Here we report on a novel brain penetrant, selective and high affinity OX1R antagonist JNJ-54717793 (1S,2R,4R)-7-([(3-fluoro-2-pyrimidin-2-ylphenyl)carbonyl]-N-[5-(trifluoromethyl)pyrazin-2-yl]-7-azabicyclo[2.2.1]heptan-2-amine). JNJ-54717793 is a high affinity/potent OX1R antagonist and has an excellent selectivity profile including 50 fold versus the OX2R. Ex vivo receptor binding studies demonstrated that after oral administration JNJ-54717793 crossed the blood brain barrier and occupied OX1Rs in the rat brain. While JNJ-54717793 had minimal effect on spontaneous sleep in rats and in wild-type mice, its administration in OX2R knockout mice, selectively promoted rapid eye movement sleep, demonstrating target engagement and specific OX1R blockade. JNJ-54717793 attenuated CO2 and sodium lactate induced panic-like behaviors and cardiovascular responses without altering baseline locomotor or autonomic activity. These data confirm that selective OX1R antagonism may represent a novel approach of treating anxiety disorders, with no apparent sedative effects.

Selective Inhibition of Orexin-2 Receptors Prevents Stress-Induced ACTH Release in Mice

Orexins peptides exert a prominent role in arousal-related processes including stress responding, by activating orexin-1 (OX1R) and orexin-2 (OX2R) receptors located widely throughout the brain. Stress or orexin administration stimulates hyperarousal, adrenocorticotropic hormone (ACTH) and corticosterone release, and selective OX1R blockade can attenuate several stress-induced behavioral and cardiovascular responses but not the hypothalamic-pituitary-adrenal (HPA) axis activation. As opposed to OX1R, OX2R are preferentially expressed in the paraventricular hypothalamic nucleus which is involved in the HPA axis regulation. In the present study, we investigated the effects of a psychological stress elicited by cage exchange (CE) on ACTH release in two murine models (genetic and pharmacological) of selective OX2R inhibition. CE-induced stress produced a significant increase in ACTH serum levels. Mice lacking the OX2R exhibited a blunted stress response. Stress-induced ACTH release was absent in mice pre-treated with the selective OX2R antagonist JNJ-42847922 (30 mg/kg po), whereas pre-treatment with the dual OX1/2R antagonist SB-649868 (30 mg/kg po) only partially attenuated the increase of ACTH. To assess whether the intrinsic and distinct sleep-promoting properties of each antagonist could account for the differential stress response, a separate group of mice implanted with electrodes for standard sleep recording were orally dosed with JNJ-42847922 or SB-649868 during the light phase. While both compounds reduced the latency to non-rapid eye movement (NREM) sleep without affecting its duration, a prevalent REM-sleep promoting effect was observed only in mice treated with the dual OX1/2R antagonist. These data indicate that in a psychological stress model, genetic or pharmacological inhibition of OX2R markedly attenuated stress-induced ACTH secretion, as a separately mediated effect from the NREM sleep induction of OX2R antagonism.

Direct Imaging of Hippocampal Epileptiform Calcium Motifs Following Kainic Acid Administration in Freely Behaving Mice

Prolonged exposure to abnormally high calcium concentrations is thought to be a core mechanism underlying hippocampal damage in epileptic patients; however, no prior study has characterized calcium activity during seizures in the live, intact hippocampus. We have directly investigated this possibility by combining whole-brain electroencephalographic (EEG) measurements with microendoscopic calcium imaging of pyramidal cells in the CA1 hippocampal region of freely behaving mice treated with the pro-convulsant kainic acid (KA). We observed that KA administration led to systematic patterns of epileptiform calcium activity: a series of large-scale, intensifying flashes of increased calcium fluorescence concurrent with a cluster of low-amplitude EEG waveforms. This was accompanied by a steady increase in cellular calcium levels (>5 fold increase relative to the baseline), followed by an intense spreading calcium wave characterized by a 218% increase in global mean intensity of calcium fluorescence (n = 8, range [114–349%], p < 10⁻⁴; t-test). The wave had no consistent EEG phenotype and occurred before the onset of motor convulsions. Similar changes in calcium activity were also observed in animals treated with 2 different proconvulsant agents, N-methyl-D-aspartate (NMDA) and pentylenetetrazol (PTZ), suggesting the measured changes in calcium dynamics are a signature of seizure activity rather than a KA-specific pathology. Additionally, despite reducing the behavioral severity of KA-induced seizures, the anticonvulsant drug valproate (VA, 300 mg/kg) did not modify the observed abnormalities in calcium dynamics. These results confirm the presence of pathological calcium activity preceding convulsive motor seizures and support calcium as a candidate signaling molecule in a pathway connecting seizures to subsequent cellular damage. Integrating in vivo calcium imaging with traditional assessment of seizures could potentially increase translatability of pharmacological intervention, leading to novel drug screening paradigms and therapeutics designed to target and abolish abnormal patterns of both electrical and calcium excitation.

GPR139, an Orphan Receptor Highly Enriched in the Habenula and Septum, Is Activated by the Essential Amino Acids L-Tryptophan and L-Phenylalanine

GPR139 is an orphan G-protein-coupled receptor expressed in the central nervous system. To identify its physiologic ligand, we measured GPR139 receptor activity from recombinant cells after treatment with amino acids, orphan ligands, serum, and tissue extracts. GPR139 activity was measured using guanosine 5'-O-(3-[(35)S]thio)-triphosphate binding, calcium mobilization, and extracellular signal-regulated kinases phosphorylation assays. Amino acids L-tryptophan (L-Trp) and L-phenylalanine (L-Phe) activated GPR139, with EC50 values in the 30- to 300-μM range, consistent with the physiologic concentrations of L-Trp and L-Phe in tissues. Chromatography of rat brain, rat serum, and human serum extracts revealed two peaks of GPR139 activity, which corresponded to the elution peaks of L-Trp and L-Phe. With the purpose of identifying novel tools to study GPR139 function, a high-throughput screening campaign led to the identification of a selective small-molecule agonist [JNJ-63533054, (S)-3-chloro-N-(2-oxo-2-((1-phenylethyl)amino)ethyl) benzamide]. The tritium-labeled JNJ-63533054 bound to cell membranes expressing GPR139 and could be specifically displaced by L-Trp and L-Phe. Sequence alignment revealed that GPR139 is highly conserved across species, and RNA sequencing studies of rat and human tissues indicated its exclusive expression in the brain and pituitary gland. Immunohistochemical analysis showed specific expression of the receptor in circumventricular regions of the habenula and septum in mice. Together, these findings suggest that L-Trp and L-Phe are candidate physiologic ligands for GPR139, and we hypothesize that this receptor may act as a sensor to detect dynamic changes of L-Trp and L-Phe in the brain.

Characterization of JNJ-42847922, a Selective Orexin-2 Receptor Antagonist, as a Clinical Candidate for the Treatment of Insomnia

Dual orexin receptor antagonists have been shown to promote sleep in various species, including humans. Emerging research indicates that selective orexin-2 receptor (OX2R) antagonists may offer specificity and a more adequate sleep profile by preserving normal sleep architecture. Here, we characterized JNJ-42847922 ([5-(4,6-dimethyl-pyrimidin-2-yl)-hexahydro-pyrrolo[3,4-c]pyrrol-2-yl]-(2-fluoro-6-[1,2,3]triazol-2-yl-phenyl)-methanone), a high-affinity/potent OX2R antagonist. JNJ-42847922 had an approximate 2-log selectivity ratio versus the human orexin-1 receptor. Ex vivo receptor binding studies demonstrated that JNJ-42847922 quickly occupied OX2R binding sites in the rat brain after oral administration and rapidly cleared from the brain. In rats, single oral administration of JNJ-42847922 (3-30 mg/kg) during the light phase dose dependently reduced the latency to non-rapid eye movement (NREM) sleep and prolonged NREM sleep time in the first 2 hours, whereas REM sleep was minimally affected. The reduced sleep onset and increased sleep duration were maintained upon 7-day repeated dosing (30 mg/kg) with JNJ-42847922, then all sleep parameters returned to baseline levels following discontinuation. Although the compound promoted sleep in wild-type mice, it had no effect in OX2R knockout mice, consistent with a specific OX2R-mediated sleep response. JNJ-42847922 did not increase dopamine release in rat nucleus accumbens or produce place preference in mice after subchronic conditioning, indicating that the compound lacks intrinsic motivational properties in contrast to zolpidem. In a single ascending dose study conducted in healthy subjects, JNJ-42847922 increased somnolence and displayed a favorable pharmacokinetic and safety profile for a sedative/hypnotic, thus emerging as a promising candidate for further clinical development for the treatment of insomnia.

Novel benzamide-based histamine h3 receptor antagonists: the identification of two candidates for clinical development

The preclinical characterization of novel phenyl(piperazin-1-yl)methanones that are histamine H3 receptor antagonists is described. The compounds described are high affinity histamine H3 antagonists. Optimization of the physical properties of these histamine H3 antagonists led to the discovery of several promising lead compounds, and extensive preclinical profiling aided in the identification of compounds with optimal duration of action for wake promoting activity. This led to the discovery of two development candidates for Phase I and Phase II clinical trials.

Selective pharmacological blockade of the 5-HT7 receptor attenuates light and 8-OH-DPAT induced phase shifts of mouse circadian wheel running activity

Recent reports have illustrated a reciprocal relationship between circadian rhythm disruption and mood disorders. The 5-HT7 receptor may provide a crucial link between the two sides of this equation since the receptor plays a critical role in sleep, depression, and circadian rhythm regulation. To further define the role of the 5-HT7 receptor as a potential pharmacotherapy to correct circadian rhythm disruptions, the current study utilized the selective 5-HT7 antagonist JNJ-18038683 (10 mg/kg) in three different circadian paradigms. While JNJ-18038683 was ineffective at phase shifting the onset of wheel running activity in mice when administered at different circadian time (CT) points across the circadian cycle, pretreatment with JNJ-18038683 blocked non-photic phase advance (CT6) induced by the 5-HT1A/7 receptor agonist 8-OH-DPAT (3 mg/kg). Since light induced phase shifts in mammals are partially mediated via the modulation of the serotonergic system, we determined if JNJ-18038683 altered phase shifts induced by a light pulse at times known to phase delay (CT15) or advance (CT22) wheel running activity in free running mice. Light exposure resulted in a robust shift in the onset of activity in vehicle treated animals at both times tested. Administration of JNJ-18038683 significantly attenuated the light induced phase delay and completely blocked the phase advance. The current study demonstrates that pharmacological blockade of the 5-HT7 receptor by JNJ-18038683 blunts both non-photic and photic phase shifts of circadian wheel running activity in mice. These findings highlight the importance of the 5-HT7 receptor in modulating circadian rhythms. Due to the opposite modulating effects of light resetting between diurnal and nocturnal species, pharmacotherapy targeting the 5-HT7 receptor in conjunction with bright light therapy may prove therapeutically beneficial by correcting the desynchronization of internal rhythms observed in depressed individuals.

A selective orexin-1 receptor antagonist attenuates stress-induced hyperarousal without hypnotic effects

Orexins (OXs) are peptides produced by perifornical (PeF) and lateral hypothalamic neurons that exert a prominent role in arousal-related processes, including stress. A critical role for the orexin-1 receptor (OX1R) in complex emotional behavior is emerging, such as overactivation of the OX1R pathway being associated with panic or anxiety states. Here we characterize a brain-penetrant, selective, and high-affinity OX1R antagonist, compound 56 [N-({3-[(3-ethoxy-6-methylpyridin-2-yl)carbonyl]-3-azabicyclo[4.1.0]hept-4-yl}methyl)-5-(trifluoromethyl)pyrimidin-2-amine]. Ex vivo receptor binding studies demonstrated that, after subcutaneous administration, compound 56 crossed the blood-brain barrier and occupied OX1Rs in the rat brain at lower doses than standard OX1R antagonists GSK-1059865 [5-bromo-N-({1-[(3-fluoro-2-methoxyphenyl)carbonyl]-5-methylpiperidin-2-yl}methyl)pyridin-2-amine], SB-334867 [1-(2-methyl-1,3-benzoxazol-6-yl)-3-(1,5-naphthyridin-4-yl)urea], and SB-408124 [1-(6,8-difluoro-2-methylquinolin-4-yl)-3-[4-(dimethylamino)phenyl]urea]. Although compound 56 did not alter spontaneous sleep in rats and in wild-type mice, its administration in orexin-2 receptor knockout mice selectively promoted rapid eye movement sleep, demonstrating target engagement and specific OX1R blockade. In a rat model of psychological stress induced by cage exchange, the OX1R antagonist prevented the prolongation of sleep onset without affecting sleep duration. In a rat model of panic vulnerability (involving disinhibition of the PeF OX region) to threatening internal state changes (i.e., intravenous sodium lactate infusion), compound 56 attenuated sodium lactate-induced panic-like behaviors and cardiovascular responses without altering baseline locomotor or autonomic activity. In conclusion, OX1R antagonism represents a novel therapeutic strategy for the treatment of various psychiatric disorders associated with stress or hyperarousal states.

Zolpidem reduces hippocampal neuronal activity in freely behaving mice: a large scale calcium imaging study with miniaturized fluorescence microscope

Therapeutic drugs for cognitive and psychiatric disorders are often characterized by their molecular mechanism of action. Here we demonstrate a new approach to elucidate drug action on large-scale neuronal activity by tracking somatic calcium dynamics in hundreds of CA1 hippocampal neurons of pharmacologically manipulated behaving mice. We used an adeno-associated viral vector to express the calcium sensor GCaMP3 in CA1 pyramidal cells under control of the CaMKII promoter and a miniaturized microscope to observe cellular dynamics. We visualized these dynamics with and without a systemic administration of Zolpidem, a GABAA agonist that is the most commonly prescribed drug for the treatment of insomnia in the United States. Despite growing concerns about the potential adverse effects of Zolpidem on memory and cognition, it remained unclear whether Zolpidem alters neuronal activity in the hippocampus, a brain area critical for cognition and memory. Zolpidem, when delivered at a dose known to induce and prolong sleep, strongly suppressed CA1 calcium signaling. The rate of calcium transients after Zolpidem administration was significantly lower compared to vehicle treatment. To factor out the contribution of changes in locomotor or physiological conditions following Zolpidem treatment, we compared the cellular activity across comparable epochs matched by locomotor and physiological assessments. This analysis revealed significantly depressive effects of Zolpidem regardless of the animal's state. Individual hippocampal CA1 pyramidal cells differed in their responses to Zolpidem with the majority (∼ 65%) significantly decreasing the rate of calcium transients, and a small subset (3%) showing an unexpected and significant increase. By linking molecular mechanisms with the dynamics of neural circuitry and behavioral states, this approach has the potential to contribute substantially to the development of new therapeutics for the treatment of CNS disorders.

Pharmacological or genetic orexin1 receptor inhibition attenuates MK-801 induced glutamate release in mouse cortex

The orexin/hypocretin neuropeptides are produced by a cluster of neurons within the lateral posterior hypothalamus and participate in neuronal regulation by activating their receptors (OX1 and OX2 receptors). The orexin system projects widely through the brain and functions as an interface between multiple regulatory systems including wakefulness, energy balance, stress, reward, and emotion. Recent studies have demonstrated that orexins and glutamate interact at the synaptic level and that orexins facilitate glutamate actions. We tested the hypothesis that orexins modulate glutamate signaling via OX1 receptors by monitoring levels of glutamate in frontal cortex of freely moving mice using enzyme coated biosensors under inhibited OX1 receptor conditions. MK-801, an NMDA receptor antagonist, was administered subcutaneously (0.178 mg/kg) to indirectly disinhibit pyramidal neurons and therefore increase cortical glutamate release. In wild-type mice, pretreatment with the OX1 receptor antagonist GSK-1059865 (10 mg/kg S.C.) which had no effect by itself, significantly attenuated the cortical glutamate release elicited by MK-801. OX1 receptor knockout mice had a blunted glutamate release response to MK-801 and exhibited about half of the glutamate release observed in wild-type mice in agreement with the data obtained with transient blockade of OX1 receptors. These results indicate that pharmacological (transient) or genetic (permanent) inhibition of the OX1 receptor similarly interfere with glutamatergic function in the cortex. Selectively targeting the OX1 receptor with an antagonist may normalize hyperglutamatergic states and thus may represent a novel therapeutic strategy for the treatment of various psychiatric disorders associated with hyperactive states.

Orexin-1 receptor blockade dysregulates REM sleep in the presence of orexin-2 receptor antagonism

In accordance with the prominent role of orexins in the maintenance of wakefulness via activation of orexin-1 (OX1R) and orexin-2 (OX2R) receptors, various dual OX1/2R antagonists have been shown to promote sleep in animals and humans. While selective blockade of OX2R seems to be sufficient to initiate and prolong sleep, the beneficial effect of additional inhibition of OX1R remains controversial. The relative contribution of OX1R and OX2R to the sleep effects induced by a dual OX1/2R antagonist was further investigated in the rat, and specifically on rapid eye movement (REM) sleep since a deficiency of the orexin system is associated with narcolepsy/cataplexy based on clinical and pre-clinical data. As expected, the dual OX1/2R antagonist SB-649868 was effective in promoting non-REM (NREM) and REM sleep following oral dosing (10 and 30 mg/kg) at the onset of the dark phase. However, a disruption of REM sleep was evidenced by a more pronounced reduction in the onset of REM as compared to NREM sleep, a marked enhancement of the REM/total sleep ratio, and the occurrence of a few episodes of direct wake to REM sleep transitions (REM intrusion). When administered subcutaneously, the OX2R antagonist JNJ-10397049 (10 mg/kg) increased NREM duration whereas the OX1R antagonist GSK-1059865 (10 mg/kg) did not alter sleep. REM sleep was not affected either by OX2R or OX1R blockade alone, but administration of the OX1R antagonist in combination with the OX2R antagonist induced a significant reduction in REM sleep latency and an increase in REM sleep duration at the expense of the time spent in NREM sleep. These results indicate that additional blockade of OX1R to OX2R antagonism elicits a dysregulation of REM sleep by shifting the balance in favor of REM sleep at the expense of NREM sleep that may increase the risk of adverse events. Translation of this hypothesis remains to be tested in the clinic.

Translational evaluation of JNJ-18038683, a 5-hydroxytryptamine type 7 receptor antagonist, on rapid eye movement sleep and in major depressive disorder

In rodents 5-hydroxytryptamine type 7 (5-HT(7)) receptor blockade has been shown to be effective in models of depression and to increase the latency to rapid eye movement (REM) sleep and decrease REM duration. In the clinic, the REM sleep reduction observed with many antidepressants may serve as a biomarker. We report here the preclinical and clinical evaluation of a 5-HT(7) receptor antagonist, (3-(4-chlorophenyl)-1,4,5,6,7,8-hexahydro-1-(phenylmethyl)pyrazolo[3,4-d]azepine 2-hydroxy-1,2,3-propanetricarboxylate) (JNJ-18038683). In rodents, JNJ-18038683 increased the latency to REM sleep and decreased REM duration, and this effect was maintained after repeated administration for 7 days. The compound was effective in the mouse tail suspension test. JNJ-18038683 enhanced serotonin transmission, antidepressant-like behavior, and REM sleep suppression induced by citalopram in rodents. In healthy human volunteers JNJ-18038683 prolonged REM latency and reduced REM sleep duration, demonstrating that the effect of 5-HT(7) blockade on REM sleep translated from rodents to humans. Like in rats, JNJ-18038683 enhanced REM sleep suppression induced by citalopram in humans, although a drug-drug interaction could not be ruled out. In a double-blind, active, and placebo-controlled clinical trial in 225 patients suffering from major depressive disorder, neither treatment with pharmacologically active doses of JNJ-18038683 or escitalopram separated from placebo, indicating a failed study lacking assay sensitivity. Post hoc analyses using an enrichment window strategy, where all the efficacy data from sites with an implausible high placebo response [placebo group Montgomery-Åsberg Depression Rating Scale (MADRS) < = 12] and from sites with no placebo response (MADRS > = 28) are removed, there was a clinically meaningful difference between JNJ-18038683 and placebo. Further clinical studies are required to characterize the potential antidepressant efficacy of JNJ-18038683.

JNJ-39220675, a novel selective histamine H3 receptor antagonist, reduces the abuse-related effects of alcohol in rats

RATIONALE

A few recent studies suggest that brain histamine levels and signaling via H(3) receptors play an important role in modulation of alcohol stimulation and reward in rodents.

OBJECTIVE

The present study characterized the effects of a novel, selective, and brain penetrant H(3) receptor antagonist (JNJ-39220675) on the reinforcing effects of alcohol in rats.

METHODS

The effect of JNJ-39220675 on alcohol intake and alcohol relapse-like behavior was evaluated in selectively bred alcohol-preferring (P) rats using the standard two-bottle choice method. The compound was also tested on operant alcohol self administration in non-dependent rats and on alcohol-induced ataxia using the rotarod apparatus. In addition, alcohol-induced dopamine release in the nucleus accumbens was tested in freely moving rats.

RESULTS

Subcutaneous administration of the selective H(3) receptor antagonist dose-dependently reduced both alcohol intake and preference in alcohol-preferring rats. JNJ-39220675 also reduced alcohol preference in the same strain of rats following a 3-day alcohol deprivation. The compound significantly and dose-dependently reduced alcohol self-administration without changing saccharin self-administration in alcohol non-dependent rats. Furthermore, the compound did not change the ataxic effects of alcohol, alcohol elimination rate, nor alcohol-induced dopamine release in nucleus accumbens.

CONCLUSIONS

These results indicate that blockade of H(3) receptor should be considered as a new attractive mechanism for the treatment of alcoholism.

Diamine-based human histamine H3 receptor antagonists: (4-aminobutyn-1-yl)benzylamines

A series of (4-aminobutyn-1-yl)benzylamines were prepared and the SAR around three key areas: (1) the amine attached to the butynyl linker (R(3)R(4)N-); (2) the benzylamine moiety (R(1)R(2)N-); and (3) the point of attachment of the benzylamine group (R(1)R(2)N- in the ortho, meta, or para positions) was examined. One compound, 4-[3-(4-piperidin-1-yl-but-1-ynyl)-benzyl]-morpholine (9s) was chosen for further profiling and found to be a selective histamine H(3) antagonist with desirable drug-like properties. Ex vivo receptor occupancy studies established that 9s does occupy H(3) binding sites in the brain of rats after oral administration. Subcutaneous doses of 9s (10mg/kg) given during the natural sleep phase demonstrated robust wake-promoting effects.

Blockade of orexin-1 receptors attenuates orexin-2 receptor antagonism-induced sleep promotion in the rat

Orexins are peptides produced by lateral hypothalamic neurons that exert a prominent role in the maintenance of wakefulness by activating orexin-1 (OX1R) and orexin-2 (OX2R) receptor located in wake-active structures. Pharmacological blockade of both receptors by the dual OX1/2R antagonist (2R)-2-[(1S)-6,7-dimethoxy-1-{2-[4-(trifluoromethyl)phenyl]ethyl}-3,4-dihydroisoquinolin-2(1H)-yl]-N-methyl-2-phenylethanamide (almorexant) has been shown to promote sleep in animals and humans during their active period. However, the selective distribution of OX1R and OX2R in distinct neuronal circuits may result in a differential impact of these receptors in sleep-wake modulation. The respective role of OX1R and OX2R on sleep in correlation with monoamine release was evaluated in rats treated with selective antagonists alone or in combination. When administered in either phase of the light/dark cycle, the OX2R antagonist 1-(2,4-dibromophenyl)-3-[(4S,5S)-2,2-dimethyl-4-phenyl-1,3-dioxan-5-yl]urea (JNJ-10397049) decreased the latency for persistent sleep and increased nonrapid eye movement and rapid eye movement sleep time. Almorexant produced less hypnotic activity, whereas the OX1R antagonist 1-(6,8-difluoro-2-methylquinolin-4-yl)-3-[4-(dimethylamino)phenyl]urea (SB-408124) had no effect. Microdialysis studies showed that either OX2R or OX1/2R antagonism decreased extracellular histamine concentration in the lateral hypothalamus, whereas both OX1R and OX1/2R antagonists increased dopamine release in the prefrontal cortex. Finally, coadministration of the OX1R with the OX2R antagonist greatly attenuated the sleep-promoting effects of the OX2R antagonist. These results indicate that blockade of OX2R is sufficient to initiate and prolong sleep, consistent with the hypothesis of a deactivation of the histaminergic system. In addition, it is suggested that simultaneous inhibition of OX1R attenuates the sleep-promoting effects mediated by selective OX2R blockade, possibly correlated with dopaminergic neurotransmission.

Pharmacological characterization of JNJ-28583867, a histamine H3 receptor antagonist and serotonin reuptake inhibitor

Wake-promoting agents such as modafinil are used in the clinic as adjuncts to antidepressant therapy in order to alleviate lethargy. The wake-promoting action of histamine H(3) receptor antagonists has been evidenced in numerous animal studies. They may therefore be a viable strategy for use as an antidepressant therapy in conjunction with selective serotonin reuptake inhibitors. JNJ-28583867 (2-Methyl-4-(4-methylsulfanyl-phenyl)-7-(3-morpholin-4-yl-propoxy)-1,2,3,4-tetrahydro-isoquinoline) is a selective and potent histamine H(3) receptor antagonist (K(i)=10.6 nM) and inhibitor of the serotonin transporter (SERT) (K(i)=3.7 nM), with 30-fold selectivity for SERT over the dopamine and norepinephrine transporters. After subcutaneous administration, JNJ-28583867 occupied both the histamine H(3) receptor and the SERT in rat brain at low doses (<1 mg/kg). JNJ-28583867 blocked imetit-induced drinking (3-10 mg/kg i.p.), confirming in vivo functional activity at the histamine H(3) receptor and also significantly increased cortical extracellular levels of serotonin at doses of 0.3 mg/kg (s.c.) and higher. Smaller increases in cortical extracellular levels of norepinephrine and dopamine were also observed. JNJ-28583867 (3-30 mg/kg p.o.) showed antidepressant-like activity in the mouse tail suspension test. JNJ-28583867 (1-3 mg/kg s.c.) caused a dose-dependent increase in the time spent awake mirrored by a decrease in NREM. Concomitantly, JNJ-28583867 produced a potent suppression of REM sleep from the dose of 1 mg/kg onwards. JNJ-28583867 has good oral bioavailability in the rat (32%), a half-life of 6.9 h and a C(max) of 260 ng/ml after 10 mg/kg p.o. In summary, JNJ-28583867 is a combined histamine H(3) receptor antagonist-SERT inhibitor with in vivo efficacy in biochemical and behavioral models of depression and wakefulness.

Histamine H3 receptor antagonists: From target identification to drug leads

The successful cloning and functional expression of the histamine H(3) receptor in the late 1990 s has greatly facilitated our efforts to identify small molecule, non-imidazole based compounds to permit the evaluation of H(3) antagonists in models of CNS disorders. High-throughput screening identified several series of lead compounds, including a series of imidazopyridines, which led to JNJ-6379490, a compound with high affinity for the human H(3) receptor. Analysis of structural features common to several series of non-imidazole H(3) receptor ligands resulted in a pharmacophore model. This model led to the design of JNJ-5207852, a diamine-based H(3) antagonist with good in vitro and in vivo efficacy but with an undesirable long half-life. However, further modifications of the template provided an understanding of the effect of structural modifications on pharmacokinetic properties, ultimately affording several additional series of compounds including JNJ-10181457, a compound with an improved pharmacokinetic profile. These compounds allowed in vivo pharmacological evaluation to show that H(3) antagonists promote wakefulness, but unlike modafinil and classical psychostimultants, they do not increase locomotor activity or produce any alteration of the EEG power spectral activity in rats. H(3) antagonists also increase extracellular acetylcholine and norepinephrine but not dopamine in rat frontal cortex and show efficacy in various models of learning-memory deficit. In addition, cFos immunoreactivity studies show H(3) antagonists activate neuronal cells in restricted rat brain regions in contrast to widespread activation after modafinil or amphetamine treatment. Therefore, H(3) antagonists are promising clinical candidates for the treatment of excessive day time sleepiness and/or cognitive disorders.

Selective blockade of 5-hydroxytryptamine (5-HT)7 receptors enhances 5-HT transmission, antidepressant-like behavior, and rapid eye movement sleep suppression induced by citalopram in rodents

Evidence has accumulated supporting a role for 5-hydroxytryptamine (5-HT)7 receptors in circadian rhythms, sleep, and mood disorders, presumably as a consequence of the modulation of 5-HT-mediated neuronal activity. We hypothesized that a selective 5-HT7 receptor antagonist, (2R)-1-[(3-hydroxyphenyl)sulfonyl]-2-[2-(4-methyl-1-piperidinyl)ethyl]-pyrrolidine (SB-269970), should increase activity of 5-HT neurons and potentiate the effect of selective serotonin reuptake inhibitors (citalopram). In rats, administration of 3 mg/kg s.c. citalopram alone increased the extracellular concentration of 5-HT. This effect of citalopram on extracellular 5-HT concentration was significantly enhanced by an ineffective dose of SB-269970. Combining this dose of SB-269970 with a low dose of citalopram also resulted in a significant increase in extracellular concentration of 5-HT, suggesting a potentiation of neurochemical effects. In mice, citalopram and SB-269970 dose-dependently decreased immobility time in the tail suspension test. The dose-effect curve of citalopram was shifted leftward by coadministration of an effective dose of SB-269970. Furthermore, combining ineffective doses of citalopram and SB-269970 also resulted in a significant decrease of immobility time in the tail suspension test, suggesting potentiation of antidepressant-like effects. In rats, SB-269970 potentiated the increase of rapid eye movement (REM) latency and the REM sleep decrease induced by citalopram. SB-269970 also reversed the increase in sleep fragmentation induced by citalopram. Rat plasma and brain concentrations of citalopram were not affected by coadministration of SB-269970, arguing for a pharmacodynamic rather than a pharmacokinetic mechanism. Overall, these results indicate that selective blockade of 5-HT7 receptors may enhance the antidepressant efficacy of citalopram and may provide a novel therapy to alleviate sleep disturbances associated with depression.

Diurnal Sex Differences in the Sleep-Wake Cycle of Mice are Dependent on Gonadal Function

STUDY OBJECTIVES

Sex is an important determinant of the pathophysiology of several disorders that influence and/or impair sleep-wake regulation. To date, few studies have examined either the role of sex or the gonadal hormones on sleep and wakefulness. The difficulty in performing well-controlled clinical experiments on sex and sleep underscores the need for effective animal models to investigate the influence of the gonadal hormones on sleep-wake states. This study describes the influence of sex on sleep and wakefulness in mice, the primary mammalian genetic model for sleep analysis, and tests the hypothesis that gonadal function drives sex differences in sleep-wake states.

DESIGN

Electroencephalogram/electromyogram sleep-wake patterns were recorded in intact and gonadectomized male and female C57BL/6J mice maintained on a 14-hour light:10-hour dark schedule. Following a 24-hour baseline recording, mice were sleep deprived during the light phase by gentle handling and given a 10-hour recovery opportunity during the immediate dark phase.

MEASUREMENTS AND RESULTS

Intact female mice spent more time awake than intact males during 24 hours of baseline recording at the expense of non-rapid eye movement (NREM) sleep. Though the recovery response of NREM sleep was similar between males and females, when examined in reference to baseline levels, females exhibited a more robust recovery response. Gonadectomy in males and females reduced or eliminated the majority of sex differences in sleep architecture and homeostasis.

CONCLUSIONS

These data demonstrate that the gonadal hormones influence the amount, distribution, and intensity of sleep but do not account for all sex differences in the sleep-wake cycle.

Altered sleep regulation in leptin-deficient mice

Recent epidemiological, clinical, and experimental studies have demonstrated important links between sleep duration and architecture, circadian rhythms, and metabolism, although the genetic pathways that interconnect these processes are not well understood. Leptin is a circulating hormone and major adiposity signal involved in long-term energy homeostasis. In this study, we tested the hypothesis that leptin deficiency leads to impairments in sleep-wake regulation. Male ob/ob mice, a genetic model of leptin deficiency, had significantly disrupted sleep architecture with an elevated number of arousals from sleep [wild-type (WT) mice, 108.2 ± 7.2 vs. ob/ob mice, 148.4 ± 4.5, P < 0.001] and increased stage shifts (WT, 519.1 ± 25.2 vs. ob/ob, 748.0 ± 38.8, P < 0.001) compared with WT mice. Ob/ob mice also had more frequent, but shorter-lasting sleep bouts compared with WT mice, indicating impaired sleep consolidation. Interestingly, ob/ob mice showed changes in sleep time, with increased amounts of 24-h non-rapid eye movement (NREM) sleep (WT, 601.5 ± 10.8 vs. ob/ob, 669.2 ± 13.4 min, P < 0.001). Ob/ob mice had overall lower body temperature (WT, 35.1 ± 0.2 vs. ob/ob, 33.4 ± 0.2°C, P < 0.001) and locomotor activity counts (WT, 25125 ± 2137 vs. ob/ob, 5219 ± 1759, P < 0.001). Ob/ob mice displayed an attenuated diurnal rhythm of sleep-wake stages, NREM delta power, and locomotor activity. Following sleep deprivation, ob/ob mice had smaller amounts of NREM and REM recovery sleep, both in terms of the magnitude and the duration of the recovery response. In combination, these results indicate that leptin deficiency disrupts the regulation of sleep architecture and diurnal rhythmicity.

Deletion of the mammalian circadian clock gene BMAL1/Mop3 alters baseline sleep architecture and the response to sleep deprivation

STUDY OBJECTIVES

The finding that deletion or mutation of core circadian clock genes in both mice and flies induce unexpected alterations in sleep amount, sleep architecture and the recovery response to sleep deprivation, has led to new insights into functions of the circadian system that extend beyond its role as a regulator of the timing of the sleep-wake cycle. A key transcription factor in the transcriptional/translational feedback loop of mammalian circadian genes is BMAL1/Mop3, a heterodimeric partner to CLOCK. It was previously shown that mice deficient in the BMAL1/Mop3 gene become immediately arrhythmic in constant darkness and have reduced locomotor activity levels under entrained and constant conditions. In this study, we tested the hypothesis that the mammalian BMAL1/Mop3 gene would have regulatory effects on sleep-wake patterns.

DESIGN

In mice with targeted deletion of the BMAL1/Mop3 gene, EEG/EMG sleep-wake patterns were recorded under entrained and free-running conditions as well as following acute (6-hrs) sleep deprivation.

MEASUREMENTS AND RESULTS

Mice homozygous for the BMAL1/Mop3 deletion showed an attenuated rhythm of sleep and wakefulness distribution across the 24-hr period. In addition, these mice showed increases in total sleep time, sleep fragmentation and EEG delta power under baseline conditions, and an attenuated compensatory response to acute sleep deprivation.

CONCLUSIONS

These new data strengthen the hypothesis that molecular components of the circadian system play a central role in the generation of sleep and wakefulness beyond just the timing of these behavioral vigilance states.

Acute wake-promoting actions of JNJ-5207852, a novel, diamine-based H3 antagonist

1 1-[4-(3-piperidin-1-yl-propoxy)-benzyl]-piperidine (JNJ-5207852) is a novel, non-imidazole histamine H3 receptor antagonist, with high affinity at the rat (pKi=8.9) and human (pKi=9.24) H3 receptor. JNJ-5207852 is selective for the H3 receptor, with negligible binding to other receptors, transporters and ion channels at 1 microm. 2 JNJ-5207852 readily penetrates the brain tissue after subcutaneous (s.c.) administration, as determined by ex vivo autoradiography (ED50 of 0.13 mg kg(-1) in mice). In vitro autoradiography with 3H-JNJ-5207852 in mouse brain slices shows a binding pattern identical to that of 3H-R-alpha-methylhistamine, with high specific binding in the cortex, striatum and hypothalamus. No specific binding of 3H-JNJ-5207852 was observed in brains of H3 receptor knockout mice. 3 In mice and rats, JNJ-5207852 (1-10 mg kg(-1) s.c.) increases time spent awake and decreases REM sleep and slow-wave sleep, but fails to have an effect on wakefulness or sleep in H3 receptor knockout mice. No rebound hypersomnolence, as measured by slow-wave delta power, is observed. The wake-promoting effects of this H3 receptor antagonist are not associated with hypermotility. 4 A 4-week daily treatment of mice with JNJ-5207852 (10 mg kg(-1) i.p.) did not lead to a change in body weight, possibly due to the compound being a neutral antagonist at the H3 receptor. 5 JNJ-5207852 is extensively absorbed after oral administration and reaches high brain levels. 6 The data indicate that JNJ-5207852 is a novel, potent and selective H3 antagonist with good in vitro and in vivo efficacy, and confirm the wake-promoting effects of H3 receptor antagonists.

Behavioral characterization of mice lacking histamine H(3) receptors

Brain histamine H(3) receptors are predominantly presynaptic and serve an important autoregulatory function for the release of histamine and other neurotransmitters. They have been implicated in a variety of brain functions, including arousal, locomotor activity, thermoregulation, food intake, and memory. The recent cloning of the H(3) receptor in our laboratory has made it possible to create a transgenic line of mice devoid of H(3) receptors. This paper provides the first description of the H(3) receptor-deficient mouse (H(3)(-/-)), including molecular and pharmacologic verification of the receptor deletion as well as phenotypic screens. The H(3)(-/-) mice showed a decrease in overall locomotion, wheel-running behavior, and body temperature during the dark phase but maintained normal circadian rhythmicity. H(3)(-/-) mice were insensitive to the wake-promoting effects of the H(3) receptor antagonist thioperamide. We also observed a slightly decreased stereotypic response to the dopamine releaser, methamphetamine, and an insensitivity to the amnesic effects of the cholinergic receptor antagonist, scopolamine. These data indicate that the H(3) receptor-deficient mouse represents a valuable model for studying histaminergic regulation of a variety of behaviors and neurotransmitter systems, including dopamine and acetylcholine.

Role of serotonin in sleep mechanisms

Since near the time of its discovery over 40 years ago, the serotonergic system has been implicated in the regulation of the sleep-wake cycle. While early studies indicate that serotonin (5-HT) was associated with the initiation and maintenance of sleep, later studies indicate that serotonergic neurons also play a role in inhibiting sleep. As reviewed in this paper, the complex effects of 5-HT in the regulation of sleep is due in part to the fact that 5-HT can act at different areas of the brain that have been associated with the control of sleep and wake. In addition, the recent discovery of multiple 5-HT receptors through the mammalian brain led to the finding that different 5-HT receptors are selectively involved in the regulation of the different sleep states.

Current understanding of the circadian clock and the clinical implications for neurological disorders

The changes in behavior that occur on a 24-hour basis to match the 24-hour changes in the physical environment due to the rotation of the earth on its axis are a hallmark of life on the planet Earth. The nervous system of both lower and higher organisms has evolved over millions of years to meet the demands of the dramatic changes in the physical environment that occur in relation to the changes in the light-dark cycle, optimizing the survival and reproductive success of the organism. During the past 50 years, it has been clearly established that the 24-hour nature of life was not simply a response to the 24-hour changes in the physical environment imposed by celestial mechanics, but instead was due to an internal time-keeping system in the brain. Many neurological disorders are associated with abnormal 24-hour rhythms, including the sleep-wake cycle. The recent discovery of the molecular basis of the neural clock in animals offers neurologists new avenues for studying the pathophysiology of neurological disorders.

Similar genetic mechanisms may underlie sleep-wake states in neonatal and adult rats

Genetic differences in the characteristics of sleep-wake states in adult animals offer a potential window for examining how the neonatal and adult behavioural states are related to one another. Our recent finding that adult Wistar-Kyoto (WKY) rats show pronounced genetic differences in sleep-wake patterns relative to the Wistar (WIS) control strain led us to investigate the relationship between these behavioural states in neonates and adults in a longitudinal study in these two strains of rats. Similar pronounced differences in the sleep-wake states were observed between WKY and WIS rats in neonatal and in adult animals. At both ages, WKY rats spent more time in activesleep (AS) and rapid eye movement sleep (REMS) and less time in quiet sleep (QS) and non-REM sleep (NREMS) than WIS rats, and the sleep-wake states were more fragmented in neonatal and adult WKY rats. While it is not known how neonatal AS and QS are physiologically related to adult REMS and NREMS, respectively, the finding of similar differences in the amounts of sleep-wake states in neonatal and adult WKY and WIS rats argues strongly that at some level they are controlled by similar genetic as well as cellular/physiological mechanisms.

The selective neurokinin 1 receptor antagonist R116301 modulates photic responses of the hamster circadian system

The recent development of selective NK(1) receptor antagonists that are active in vivo provides an important research tool to examine the role of substance P in the regulation of circadian rhythmicity. First, we tested whether R116301 [(2R-trans)-4-[1-[3,5-bis(trifluoromethyl)benzoyl]-2-(phenylmethyl)-4-piperidinyl]-N-(2,6-dimethylphenyl)-1-acetamide (S) hydroxybutanedioate], a new selective NK(1) antagonist, alters the phase-shifting effects of light. Hamsters housed in constant darkness were injected with different doses of R116301, just before being exposed to a light pulse during the subjective night. The results were compared with those obtained with the NK(1) antagonist L-760,735 [2-(R)-(1-(R)-3,5-bis(trifluoromethyl)phenyl)ethoxy)-4-(5-(dimethylaminomethyl)-1,2,3-trioazol-4-yl)methyl-3-(5)-phenyl)morpholine]. Second, the effects of the NK(1) antagonists R116301 or L-760,735 injected immediately after exposure to a light pulse were similarly determined. Third, we investigated whether R116301 or L-760,735 injected during the mid-subjective day or the late subjective night can phase-shift the circadian rhythm of locomotor activity in hamsters housed in constant light. Both compounds reduced, by more than 30%, the phase-advancing effects of a light pulse in hamsters otherwise maintained in constant darkness, only when the drugs were administered before the light pulse. Under constant light conditions, both NK(1) receptor antagonists induced significant phase-advances when injected during the subjective day, but not during the subjective night. The present results indicate that tachykinergic neurotransmission modulates the photic responses of the circadian system upstream of phase resetting mechanisms and suggest that an inhibition of the NK(1) receptor signals "darkness" to the circadian clock.

Sleep in the Wistar-Kyoto rat, a putative genetic animal model for depression

The Wistar-Kyoto (WKY) rat exhibits several behavioral and hormonal abnormalities often associated with depression. One of the hallmarks of depression consists of alterations in the sleep-wake cycle, particularly in rapid eye movement (REM) sleep. If the WKY rat is indeed an animal model for depression, we hypothesized that it should also show sleep abnormalities relative to the control strain, the Wistar (WIS) rat Under baseline conditions, WKY rats showed a 50% increase in total REM sleep time during the 12 h light phase and an increase in sleep fragmentation during both the light and dark phase. The WKY rats also exhibited lower EEG power densities over the entire frequency range (0.2-25.0 Hz) during REM sleep. After a 6 h sleep deprivation, the REM sleep rebound was more pronounced during the dark but not the light phase in the WKY rats. Since the WKY rat represents a genetic model for depression with altered EEG sleep patterns, this strain may be particularly useful for investigating the relationship between depression and sleep abnormalities.

High corticosterone levels in prenatally stressed rats predict persistent paradoxical sleep alterations

Prenatal stress predisposes rats to long-lasting disturbances that persist throughout adulthood (e.g., high anxiety, dysfunction of the hypothalamo-pituitary-adrenal axis, and abnormal circadian timing). These disturbances parallel to a large extent those found in depressed patients, in which hypercortisolemia and sleep alterations may be related to stress-inducing events. We studied sleep-wake parameters in control and prenatally stressed adult rats (3-4 months old) and examined possible relationships with their corticosterone levels (determined at 2 months of age). Under baseline conditions, prenatally stressed rats showed increased amounts of paradoxical sleep, positively correlated to plasma corticosterone levels. Other changes include increased sleep fragmentation, total light slow-wave sleep time, and a slight decrease in the percentage of deep slow-wave sleep relative to total sleep time. During recovery sleep from acute restraint stress, all sleep changes persisted and were correlated with stress-induced corticosterone secretion. High corticosterone levels under baseline conditions as well as an acute stress challenge may thus predict long-term sleep-wake alterations in rats. Taken together with other behavioral and hormonal abnormalities in prenatally stressed animals, the pronounced changes in sleep-wake parameters that are similar to those found in depressed patients suggest that prenatal stress may be a useful animal model of depression.

Survey on the pharmacodynamics of the new antipsychotic risperidone

This review reports on the pharmacodynamics of the new antipsychotic risperidone. The primary action of risperidone is serotonin 5-HT2 receptor blockade as shown by displacement of radioligand binding (Ki: 0.16 nM), activity on isolated tissues (EC50: 0.5 nM), and antagonism of peripherally (ED50: 0.0011 mg/kg) and centrally (ED50: 0.014 mg/kg) acting 5-HT2 receptor agonists in rats. Risperidone is at least as potent as the specific 5-HT2 receptor antagonist ritanserin in these tests. Risperidone is also a potent dopamine D2 receptor antagonist as indicated by displacement of radioligand binding (Ki: 1.4 nM), activity in isolated striatal slices (IC50: 0.89 nM), and antagonism of peripherally (ED50: 0.0057 mg/kg in dogs) and centrally acting D2 receptor agonists (ED50: 0.056-0.15 mg/kg in rats). Risperidone shows all effects common to D2 antagonists, including enhancement of prolactin release. However, some central effects such as catalepsy and blockade of motor activity occur at high doses only. Risperidone is 4-10 times less potent than haloperidol as a central D2 antagonist in rats and it differs from haloperidol by the following characteristics: predominant 5-HT2 antagonism; LSD antagonism; effects on sleep; smooth dose-response curves for D2 antagonism; synergism of combined 5-HT2/D2 antagonism; pronounced effects on amphetamine-induced oxygen consumption; increased social interaction; and pronounced effects on dopamine (DA) turnover. Risperidone displays similar activity at pre- and postsynaptic D2 receptors and at D2 receptors from various rat brain regions. The binding affinity for D4 and D3 receptors is 5 and 9 times weaker, respectively, than for D2 receptors; interaction with D1 receptors occurs only at very high concentrations. The pharmacological profile of risperidone includes interaction with histamine H1 and alpha-adrenergic receptors but the compound is devoid of significant interaction with cholinergic and a variety of other types of receptors. Risperidone has excellent oral activity, a rapid onset, and a 24-h duration of action. Its major metabolite, 9-hydroxyrisperidone, closely mimics risperidone in pharmacodynamics. Risperidone can be characterized as a potent D2 antagonist with predominant 5HT2 antagonistic activity and optimal pharmacokinetic properties.

Functional activity of 5-HT2 receptors in the modulation of the sleep/wakefulness states

In the light of recent pharmacological investigations using agonists and antagonists that have potent actions on 5-hydroxytryptamine-2 (5-HT2) receptors, the possible functional role of 5-HT2 receptors in the modulation of the sleep/wakefulness states was examined. Data obtained from animals and from clinical studies suggest that serotonin may exert an inhibitory control on deep slow-wave sleep (SWS) through 5-HT2 receptors. In further investigations, the existence of a diurnal variation in the functional activity of 5-HT2 receptors, that depends on the day/night cycle and/or the melatonin rhythm, was revealed. Questions remain with regard to the physiological significance, of the 5-HT2 receptor-mediated deep SWS regulation, the anatomical site(s) of 5-HT2 receptors involved in this regulation and the mechanism underlying diurnal fluctuations in the functional activity of 5-HT2 receptors.

Effects of ritanserin and chlordiazepoxide on sleep-wakefulness alterations in rats following chronic cocaine treatment

The effects of ritanserin, a 5-hydroxytryptamine-2 (5-HT2) receptor antagonist, and chlordiazepoxide, a benzodiazepine agonist, on sleep-wakefulness disturbances in rats after acute administration of cocaine and after discontinuation of chronic cocaine treatment were examined. Intraperitoneal (IP) injection of chlordiazepoxide (10 mg/kg) but not ritanserin (0.63 mg/kg) prevented the increase of wakefulness (W) and the reduction of light slow wave sleep (SWS1) and deep slow wave sleep (SWS2) induced by an acute injection of cocaine (20 mg/kg IP). Daily injection of cocaine (20 mg/kg for 5 days, then 30 mg/kg for 5 days IP) at the onset of the light phase elicited an increase of W and a concomitant decrease of SWS1, SWS2 and paradoxical sleep (PS) in the light phase, followed by a rebound in SWS2 and PS in the subsequent dark phase. Following cocaine discontinuation, the circadian distribution of sleep-wakefulness states remained disturbed in saline-treated rats for at least 5 days. Both ritanserin (0.63 mg/kg IP/day) and chlordiazepoxide (10 mg/kg IP/day) reduced the alteration in the distribution of W and SWS2 throughout the light-dark cycle from the first day of administration on, but failed to prevent PS alterations. The mechanisms by which both compounds exert their effect are probably quite different. For chlordiazepoxide sedative and sleep-inducing properties probably play a major role. In contrast, for ritanserin SWS2-increasing properties and its ability to reverse preference for drugs of abuse without inducing aversion might be key factors.

Sleep-wakefulness patterns in the helpless rat

Sleep-wakefulness patterns were analyzed during a 15-day period in the rat, in relation to induction of helplessness. After a session of inescapable electric footshocks, rats did exhibit escape deficits in avoidance conditioning as classically described, and their spontaneous sleep-wakefulness patterns were not different from those of controls. However, reduced PS latency and increased PS amounts were observed in the helpless group after shuttle-box sessions, especially during the initial period after the induction of helplessness. Such modifications of PS latency and PS amounts are evocative of the sleep impairments classically observed in endogenous depression.

Differential effects of the new antipsychotic risperidone on sleep and wakefulness in the rat

The effects of risperidone, a new antipsychotic with potent 5-hydroxytryptamine2 (5-HT2) and dopamine-D2 (DA-D2) antagonistic properties, were studied on sleep-wakefulness patterns in rats. Administration of low doses (0.01-0.16 mg/kg i.p.) resulted in a significant increase of deep slow wave sleep (SWS2) and a decrease of wakefulness (W) and light slow wave sleep (SWS1). High doses (0.63-2.5 mg/kg) produced opposite effects. Paradoxical sleep (PS) was significantly reduced over the dose range tested. The increase of SWS2 after low doses of risperidone could be related to a predominant and potent 5-HT2 receptor blocking activity.

The light-dark cycle modulates the effects of ritanserin on sleep-wakefulness patterns in the rat

The 5-HT2 receptor antagonist ritanserin (0.63 mg/kg IP) produced differential effects on sleep-wakefulness patterns in rats when administered during the light or dark period: an increase in the duration of deep slow wave sleep at the expense of light slow wave sleep, paradoxical sleep and wakefulness when injected during the light period, and no major sleep alteration when given at dark onset. Since circadian variations in serotonin receptor density might modulate the sleep response, we examined the effects of ritanserin on sleep in rats exposed to continuous light for 10 days, and whether 5-HT2 receptors were affected in separate groups of rats exposed to similar conditions. No significant changes in the KD- and Bmax -values of various receptors were found. However, ritanserin produced greater effects in continuous light conditions than when given during the light period in the 12-hr light-dark condition. This suggests a possible role of 5-HT2 receptors in the organization of sleep when the environmental photoperiod is disturbed.

Melatonin modulates the sensitivity of 5-hydroxytryptamine-2 receptor-mediated sleep-wakefulness regulation in the rat

The interaction between melatonin and two 5-hydroxytryptamine (5-HT2) compounds was studied on sleep patterns in rats. Administration of the 5-HT2 receptor antagonist ritanserin (0.63 mg/kg, i.p.) resulted in a significant increase of deep slow wave sleep (SWS2) and a decrease of paradoxical sleep (PS). The 5-HT2 receptor agonist DOM (1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane) (0.63 mg/kg, i.p.) produced a significant reduction of both SWS2 and PS. Melatonin (1 mg/kg, i.p.) alone did not alter sleep but counteracted the sleep effects induced by ritanserin as well as DOM. It is proposed that melatonin modulates the sensitivity of 5-HT2 receptor-mediated sleep response probably by an indirect route.

Functional role of 5-HT2 receptors in the regulation of sleep and wakefulness in the rat

Recently developed agents specifically acting on different 5-hydroxytryptamine (5-HT) receptor populations were used to analyze the functional role of 5-HT2 receptor subtypes in the sleep-wakefulness cycle of the rat. The 5-HT2 receptor antagonist ritanserin injected intraperitoneally (IP) (0.04-2.5 mg/kg) induced an increase in deep slow wave sleep (SWS2) duration at the expense of wakefulness (W), light slow wave sleep (SWS1) and paradoxical sleep (PS). The stimulation of 5-HT2 receptors by 1-(2,5-dimethoxy-4-methylphenyl)-2-aminopropane (DOM) produced a dose-related increase in W and a dose-dependent decrease in both SWS2 and PS. Pretreatment with ritanserin (0.16-2.5 mg/kg) or with cinanserin (2.5-5 mg/kg), another 5-HT2 receptor antagonist, dose-dependently reversed the W enhancement and the SWS2 deficit produced by DOM, but not the PS deficit. Sleep-wakefulness alterations (increase in W and SWS1 combined with a suppression of SWS2 and PS) observed after IP injection of two putative 5-HT1 receptor agonists, 8-hydroxy-2-(di-n-propylamino) tetralin (8-OH-DPAT) (2.5 mg/kg) and 5-methoxy-3-(1,2,3,6-tetrahydro-4-pyridinyl)-1H-indole (RU 24969) (0.63 mg/kg), were not modified by ritanserin pretreatment (0.16-2.5 mg/kg). These results further support the hypothesis that the serotonergic system plays an active role in the regulation of the sleep-wakefulness cycle in the rat and that 5-HT2 receptors are involved in this action. In addition, it is suggested that 5-HT1 receptor subtypes are unlikely to interact with 5-HT2 receptors in the sleep-wakefulness modulation mediated through 5-HT2 receptors.

Time course of night sleep EEG in the first year of life: a description based on automatic analysis

The aim of this study is to describe the time course of night sleep in the first year of life. Forty-eight infants aged between 1 and 54 weeks were polygraphically recorded for 1 night. The central occipital EEG derivation was processed with a lab computer in order to obtain every 30 sec an EEG parameter value. The parameter is based on the joint frequency-amplitude distribution of the EEG and displays fluctuations between 2 extreme levels, high voltage low frequency (HVLF) and low voltage high frequency (LVHF). The range of the fluctuations between HVLF and LVHF increases from the period of 1-6 weeks to the period of 7-14 weeks. A further increase of the parameter range occurs after 24 weeks, which remains restricted to the first half of the night. The recurrence time of LVHF and HVLF episodes (possibly corresponding to quiet sleep paradoxical sleep cycles) is about 56 min and does not change with age in the first year of life.