Hypocretin (orexin): role in normal behavior and neuropathology

A comparative study of hypothalamic involvement in patients with myelin oligodendrocyte glycoprotein antibody-associated disease, neuromyelitis optica spectrum disorder, and multiple sclerosis

BACKGROUND AND PURPOSE

We aimed to characterize hypothalamic involvement in myelin oligodendrocyte glycoprotein antibody-associated disease (MOGAD) and compare it with neuromyelitis optica spectrum disorder (NMOSD) and multiple sclerosis (MS).

METHODS

A retrospective study was performed to identify hypothalamic lesions in patients diagnosed with MOGAD, NMOSD, or MS from January 2013 to May 2020. The demographic, clinical, and radiological features were recorded. Hypothalamic dysfunction and prognosis were assessed through physical examination, biochemical testing, sleep monitoring, and magnetic resonance imaging.

RESULTS

Hypothalamic lesions were observed in seven of 96 patients (7.3%) with MOGAD, 34 of 536 (6.3%) with NMOSD, and 16 of 356 (4.5%) with MS (p = 0.407). The time from disease onset to development of hypothalamic lesions was shortest in MOGAD (12 months). The frequency of bilateral hypothalamic lesions was the lowest in MOGAD (p = 0.008). The rate of hypothalamic dysfunction in MOGAD was 28.6%, which was lower than that in NMOSD (70.6%) but greater than that in MS patients (18.8%; p = 0.095 and p = 0.349, respectively). Hypothalamic dysfunction in MOGAD manifests as hypothalamic-pituitary-adrenal axis dysfunction and hypersomnia. The proportion of complete regression of hypothalamic lesions in MOGAD (100%) was much greater than that in NMOSD (41.7%) and MS patients (18.2%; p = 0.007 and p = 0.001, respectively). An improvement in hypothalamic dysfunction was observed in all MOGAD patients after immunotherapy.

CONCLUSIONS

MOGAD patients have a relatively high incidence of asymptomatic hypothalamic lesions. The overall prognosis of patients with hypothalamic involvement is good in MOGAD, as the lesions completely resolve, and dysfunction improves after immunotherapy.

Optics-free Spatial Genomics for Mapping Mouse Brain Aging

Spatial transcriptomics has revolutionized our understanding of cellular network dynamics in aging and disease by enabling the mapping of molecular and cellular organization across various anatomical locations. Despite these advances, current methods face significant challenges in throughput and cost, limiting their utility for comprehensive studies. To address these limitations, we introduce IRISeq (Imaging Reconstruction using Indexed Sequencing), a optics-free spatial transcriptomics platform that eliminates the need for predefined capture arrays or extensive imaging, allowing for the rapid and cost-effective processing of multiple tissue sections simultaneously. Its capacity to reconstruct images based solely on sequencing local DNA interactions allows for profiling of tissues without size constraints and across varied resolutions. Applying IRISeq, we examined gene expression and cellular dynamics in thirty brain regions of both adult and aged mice, uncovering region-specific changes in gene expression associated with aging. Further cell type-centric analysis further identified age-related cell subtypes and intricate changes in cell interactions that are distinct to certain spatial niches, emphasizing the unique aspects of aging in different brain regions. The affordability and simplicity of IRISeq position it as a versatile tool for mapping region-specific gene expression and cellular interactions across various biological systems.

Orexin receptors in paraventricular nucleus influence sexual behavior via regulating the sympathetic outflow in males

BACKGROUND

Orexins are hypothalamic neuropeptides associated with various neurophysiological activities such as sleep, arousal, and reward. However, there are few studies investigating the relationships between orexin receptors in the paraventricular nucleus and sexual behaviors.

OBJECTIVES

To explore the roles of orexin receptors in the paraventricular nucleus on sexual behaviors and uncover its potential mechanisms in males.

MATERIALS AND METHODS

Orexin A, orexin 1 receptor antagonist SB334867, and orexin 2 receptor antagonist TCS-OX2-29 were microinjected into the paraventricular nucleus to investigate the effects of orexin receptors on copulatory behavior testing of C57BL/6 mice. To explore if ejaculation could activate orexin 1 receptor-expressing neurons in the paraventricular nucleus, fluorescence immunohistochemical double staining was utilized. The levels of serum norepinephrine were measured and the lumbar sympathetic nerve activity was recorded to reflect the sympathetic nervous system activity. Moreover, the bulbospongiosus muscle-electromyogram was recorded and analyzed. To test whether perifornical/lateral hypothalamic area orexinergic neurons directly projected to the paraventricular nucleus, virus retrograde tracing technology was utilized.

RESULTS

Orexin A significantly enhanced sexual performance by shortening the intromission and ejaculation latencies, and increasing the mount and intromission frequencies, while the opposite outcomes appeared with SB334867. However, TCS-OX2-29 had no significant effects on sexual behaviors. Moreover, orexin A increased lumbar sympathetic nerve activity and the levels of serum norepinephrine, while SB334867 decreased lumbar sympathetic nerve activity and norepinephrine, which caused a significant decrease in sympathetic nervous system outflow. Meanwhile, a robust increase in the bulbospongiosus muscle-electromyogram activity was identified after microinjecting orexin A. Furthermore, cFos immunopositive cells were increased and double stained with orexin 1 receptor-expressing neurons in the mating group. Additionally, the retrograde tracing results demonstrated that orexinergic neurons in the perifornical/lateral hypothalamic area directly projected to the paraventricular nucleus.

CONCLUSIONS

Orexin 1 receptor in the paraventricular nucleus could influence the ejaculatory reflex via mediating the sympathetic nervous system activity, which might be of great importance in the treatment of premature ejaculation in the future.

Sleep and Chronobiology as a Key to Understand Cluster Headache

The cluster headache is a primary headache characterized by attacks of unilateral pain associated with ipsilateral cranial autonomic features. These attacks recur in clusters during the years alternating with periods of complete remission, and their onset is often during the night. This annual and nocturnal periodicity hides a strong and mysterious link among CH, sleep, chronobiology and circadian rhythm. Behind this relationship, there may be the influence of genetic components or of anatomical structures such as the hypothalamus, which are both involved in regulating the biological clock and contributing even to the periodicity of cluster headaches. The bidirectional relationship manifests itself also with the presence of sleep disturbances in patients affected by cluster headaches. What if the key to studying the physiopathology of such disease could rely on the mechanisms of chronobiology? The purpose of this review is to analyze this link in order to interpret the pathophysiology of cluster headaches and the possible therapeutic implications.

Sleep in Disorders of Consciousness: A Brief Overview on a Still under Investigated Issue

Consciousness is a multifaceted concept, involving both wakefulness, i.e., a condition of being alert that is regulated by the brainstem, and awareness, a subjective experience of any thoughts or perception or emotion. Recently, the European Academy of Neurology has published international guidelines for a better diagnosis of coma and other disorders of consciousness (DOC) through the investigation of sleep patterns, such as slow-wave and REM, and the study of the EEG using machine learning methods and artificial intelligence. The management of sleep disorders in DOC patients is an increasingly hot topic and deserves careful diagnosis, to allow for the most accurate prognosis and the best medical treatment possible. The aim of this review was to investigate the anatomo-physiological basis of the sleep/wake cycle, as well as the main sleep patterns and sleep disorders in patients with DOC. We found that the sleep characteristics in DOC patients are still controversial. DOC patients often present a theta/delta pattern, while epileptiform activity, as well as other sleep elements, have been reported as correlating with outcomes in patients with coma and DOC. The absence of spindles, as well as REM and K-complexes of NREM sleep, have been used as poor predictors for early awakening in DOC patients, especially in UWS patients. Therefore, sleep could be considered a marker of DOC recovery, and effective treatments for sleep disorders may either indirectly or directly favor recovery of consciousness.

Narcolepsy-A Neuropathological Obscure Sleep Disorder: A Narrative Review of Current Literature

Narcolepsy is a chronic, long-term neurological disorder characterized by a decreased ability to regulate sleep-wake cycles. Some clinical symptoms enter into differential diagnosis with other neurological diseases. Excessive daytime sleepiness and brief involuntary sleep episodes are the main clinical symptoms. The majority of people with narcolepsy experience cataplexy, which is a loss of muscle tone. Many people experience neurological complications such as sleep cycle disruption, hallucinations or sleep paralysis. Because of the associated neurological conditions, the exact pathophysiology of narcolepsy is unknown. The differential diagnosis is essential because relatively clinical symptoms of narcolepsy are easy to diagnose when all symptoms are present, but it becomes much more complicated when sleep attacks are isolated and cataplexy is episodic or absent. Treatment is tailored to the patient's symptoms and clinical diagnosis. To facilitate the diagnosis and treatment of sleep disorders and to better understand the neuropathological mechanisms of this sleep disorder, this review summarizes current knowledge on narcolepsy, in particular, genetic and non-genetic associations of narcolepsy, the pathophysiology up to the inflammatory response, the neuromorphological hallmarks of narcolepsy, and possible links with other diseases, such as diabetes, ischemic stroke and Alzheimer's disease. This review also reports all of the most recent updated research and therapeutic advances in narcolepsy. There have been significant advances in highlighting the pathogenesis of narcolepsy, with substantial evidence for an autoimmune response against hypocretin neurons; however, there are some gaps that need to be filled. To treat narcolepsy, more research should be focused on identifying molecular targets and novel autoantigens. In addition to therapeutic advances, standardized criteria for narcolepsy and diagnostic measures are widely accepted, but they may be reviewed and updated in the future with comprehension. Tailored treatment to the patient's symptoms and clinical diagnosis and future treatment modalities with hypocretin agonists, GABA agonists, histamine receptor antagonists and immunomodulatory drugs should be aimed at addressing the underlying cause of narcolepsy.

Effects of selective orexin receptor-2 and cannabinoid receptor-1 antagonists on the response of medial prefrontal cortex neurons to tramadol

Tramadol is widely used to control pain in various diseases, but the relevant mechanisms are less known despite the severe risks of abuse. The medial prefrontal cortex (mPFC) is one of the critical centers of the reward system. Studies have shown that orexins and endocannabinoids are likely to play an important role in addiction. In this study, the effect of orexin receptor-2 (OX2R) and endocannabinoid receptor-1 (CB1R) blockade on the neuronal activity of mPFC was investigated in response to tramadol in male rats. Tramadol was injected intraperitoneally, and its effects on the firing of mPFC pyramidal neurons were investigated using in vivo extracellular single-unit recording. Tramadol affected the pyramidal neuronal activity of the mPFC. AM251 (18 nmol/4 μl), as a selective CB1R antagonist, and TCS-OX2-29 (50 nmol/4 μl), as a selective OX2R antagonist, individually or simultaneously were microinjected into the lateral ventricle of the brain (intracerebroventricular, ICV). The results showed that the ratio of neurons with the excitatory/inhibitory or no responses was significantly changed by tramadol (p < .05). These changes were prevented by blockade of CB1Rs alone or blockade of OX2Rs and CB1Rs simultaneously (p < .05). However, blockade of these receptors in the vehicle group had no significant effect on neuronal activity. The findings of this study indicate the potential role of orexin and endocannabinoid systems in mediating the effects of tramadol in mPFC and the possible interaction between the two systems via OX2 and CB1 receptors. However, further studies are needed to identify these effects by examining intracellular signaling.

Interactions between Sleep and Emotions in Humans and Animal Models

Recently, increased interest and efforts were observed in describing the possible interaction between sleep and emotions. Human and animal model studies addressed the implication of both sleep patterns and emotional processing in neurophysiology and neuropathology in suggesting a bidirectional interaction intimately modulated by complex mechanisms and factors. In this context, we aimed to discuss recent evidence and possible mechanisms implicated in this interaction, as provided by both human and animal models in studies. In addition, considering the affective component of brain physiological patterns, we aimed to find reasonable evidence in describing the two-way association between comorbid sleep impairments and psychiatric disorders. The main scientific literature databases (PubMed/Medline, Web of Science) were screened with keyword combinations for relevant content taking into consideration only English written papers and the inclusion and exclusion criteria, according to PRISMA guidelines. We found that a strong modulatory interaction between sleep processes and emotional states resides on the activity of several key brain structures, such as the amygdala, prefrontal cortex, hippocampus, and brainstem nuclei. In addition, evidence suggested that physiologically and behaviorally related mechanisms of sleep are intimately interacting with emotional perception and processing which could advise the key role of sleep in the unconscious character of emotional processes. However, further studies are needed to explain and correlate the functional analysis with causative and protective factors of sleep impairments and negative emotional modulation on neurophysiologic processing, mental health, and clinical contexts.

Circadian Clocks, Sleep, and Metabolism

A molecular circadian clock exists not only in the brain, but also in most cells of the body. Research over the past two decades has demonstrated that it directs daily rhythmicity of nearly every aspect of metabolism. It also consolidates sleep-wake behavior each day into an activity/feeding period and a sleep/fasting period. Otherwise, sleep-wake states are mostly controlled by hypothalamic and thalamic regulatory circuits in the brain that direct overall brain state. Recent evidence suggests that hypothalamic control of appetite and metabolism may be concomitant with sleep-wake regulation, and even share the same control centers. Thus, circadian control of metabolic pathways might be overlaid by sleep-wake control of the same pathways, providing a flexible and redundant system to modify metabolism according to both activity and environment.

Pleasure, addiction, and hypocretin (orexin)

The hypocretins/orexins were discovered in 1998. Within 2 years, this led to the discovery of the cause of human narcolepsy, a 90% loss of hypothalamic neurons containing these peptides. Further work demonstrated that these neurons were not simply linked to waking. Rather these neurons were active during pleasurable behaviors in waking and were silenced by aversive stimulation. This was seen in wild-type mice, rats, cats, and dogs. It was also evident in humans, with increased Hcrt release during pleasurable activities and decreased release, to the levels seen in sleep, during pain. We found that human heroin addicts have, on average, an increase of 54% in the number of detectable Hcrt neurons compared to "control" human brains and that these Hcrt neurons are substantially smaller than those in control brains. We found that in mice, chronic morphine administration induced the same changes in Hcrt neuron number and size. Our studies in the mouse allowed us to determine the specificity, dose response relations, time course of the change in the number of Hcrt neurons, and that the increased number of Hcrt neurons after opiates was not due to neurogenesis. Furthermore, we found that it took a month or longer for these anatomical changes in the mouse brain to return to baseline. Human narcoleptics, despite their prescribed use of several commonly addictive drugs, do not show significant evidence of dose escalation or substance use disorder. Similarly, mice in which the peptide has been eliminated are resistant to addiction. These findings are consistent with the concept that an increased number of Hcrt neurons may underlie and maintain opioid or cocaine use disorders.

Calorie restriction improves aging-induced impairment of cognitive function in relation to deregulation of corticosterone status and brain regional GABA system

Aging is known to affect adversely the corticosterone status and the brain function including cognition. Calorie restricted (CR) diet has been found to improve brain aging. The objective of the present investigation is to study the effect of short-term CR diet without any food deprivation on aging-induced impairment of cognitive function in relation to the corticosterone status and the brain regional GABA system. The result showed that aging-induced deregulation of the brain regional GABA system, increase in plasma and adrenal corticosterone levels and cognitive impairment were attenuated with short-term CR diet supplementation for consecutive 1 and 2 months to the aged (18 and 24 months) rats. But in young rats (4 months) consumption of the same CR diet under similar conditions reversibly affected those above-mentioned parameters. These results, thus suggest that (a) aging down-regulates brain regional GABA system with an up-regulation of corticosterone status and impairment of cognitive function, (b) CR diet consumption improves this aging-induced deregulation of brain regional GABA system, corticosterone status, and cognitive function, (c) these attenuating effects of CR diet are greater with a longer period of consumption but (d) CR diet consumption is harmful to young rats as observed in those parameters.

Orexinergic modulation of serotonin neurons in the dorsal raphe of a diurnal rodent, Arvicanthis niloticus

The hypothalamic neuropeptide, orexin (or hypocretin), is implicated in numerous physiology and behavioral functions, including affective states such as depression and anxiety. The underlying mechanisms and neural circuits through which orexin modulates affective responses remain unclear. The objective of the present study was to test the hypothesis that the serotonin (5-HT) system of the dorsal raphe nucleus (DRN) is a downstream target through which orexin potentially manifests its role in affective states. Using a diurnal rodent, the Nile grass rat (Arvicanthis niloticus), we first characterized the expression of the orexin receptors OX1R and OX2R in the DRN using in situ hybridization. The results revealed distinct distributions of OX1R and OX2R mRNAs, with OX1R predominantly expressed in the dorsal and lateral wings of the DRN that are involved in affective processes, while OX2R was mostly found in the ventral DRN that is more involved in sensory-motor function. We next examined how the orexin-OX1R pathway regulates 5-HT in the DRN and some of its projection sites using a selective OX1R antagonist SB-334867 (10 mg/kg, i.p.). A single injection of SB-334867 decreased 5-HT-ir fibers within the anterior cingulate cortex (aCgC); five once-daily administrations of SB-334867 decreased 5-HT-ir not only in the aCgC but also in the DRN, oval bed nucleus of the stria terminalis (ovBNST), nucleus accumbens shell (NAcSh), and periaqueductal gray (PAG). HPLC analysis revealed that five once-daily administrations of SB-334867 did not affect 5-HT turnover to any of the five sites, although it increased the levels of both 5-HT and 5-HIAA in the NAcSh. These results together suggest that orexinergic modulation of DRN 5-HT neurons via OX1Rs may be one pathway through which orexin regulates mood and anxiety, as well as perhaps other neurobiological processes.

Transcriptional changes in the hypothalamus, pituitary, and mammary gland underlying decreased lactation performance in mice under heat stress

Because of climate change, heat stress (HS) causes more and more impacts on dairy animals to decrease lactation performance. The neuroendocrine system is key in regulating systemic physiological processes and milk synthesis. However, the hypothalamic-pituitary axis response to HS is still unclear. In this study, a group of lactating mice underwent a daily 2-h heat treatment (36°C) for 14 d to explore possible cross-talk between the hypothalamic-pituitary axis and mammary gland under HS. Transcriptome analyses by multitissue RNA-Seq indicated the possible mechanisms of reduced lactation performance in animals under HS. In the hypothalamus, the cAMP signaling pathway was activated to resist neuronal death, and the expression of downstream genes was increased to promote cell survival under HS. Reduced food intake might be caused by down-regulated appetite-related peptide, whereas up-regulated neuropeptide Y acted to attenuate reduced food intake. In pituitary, energy stress from lower food intake might result in reduced secretion of prolactin and growth hormone. Under HS, the mammary gland may undergo hypoxic stress, causing mammary epithelial cell apoptosis. Together, these data showed systemic changes in tissues to accommodate the effects of HS on lactation.-Han, J., Shao, J., Chen, Q., Sun, H., Guan, L., Li, Y., Liu, J., Liu, H. Transcriptional changes in the hypothalamus, pituitary, and mammary gland underlying decreased lactation performance in mice under heat stress.

The neuronal network of laughing in young patients with untreated narcolepsy

OBJECTIVE

To investigate the neuronal correlates of spontaneous laughter in drug-naive pediatric patients with narcolepsy type I (NT1) compared to healthy controls by means of blood oxygen level-dependent (BOLD) MRI.

METHODS

Twenty-one children/adolescents with recent onset of NT1 and 21 age- and sex-matched healthy controls were studied with fMRI while viewing funny videos using a naturalistic paradigm. Whole-brain hemodynamic correlates of spontaneous laughter were investigated in each group and compared by use of appropriate second-level general linear model analyses. If recorded, cataplexy events were treated as the effect of no interest at the single-participant level. Correlations analyses between these contrasts and behavioral findings were performed.

RESULTS

Emotion-induced laughter occurred in 16 patients (294 events) and 21 controls (357 events). In controls, laughter-related BOLD increases involved a widespread cortical and subcortical network including the bilateral motor and premotor areas, cingulated cortex, insula, and amygdala. In NT1, laughter induced BOLD signal increments in the motor cortex, right thalamus, and left subthalamic nucleus/zona incerta (STN/ZI). STN/ZI and thalamic changes were significantly higher during fMRI sessions with laughter without cataplexy compared to sessions in which laughter was associated with cataplexy.

CONCLUSION

Laughter expression in individuals with NT1 involves different brain circuits compared to controls by means of overactivation of cortical and subcortical regions belonging to the volitional control of laughter. The activation of the STN/ZI region observed predominantly in patients with NT1 during laugh episodes without cataplexy suggests that the ZI could act to prevent cataplexy.

Hypocretin receptor 1 involvement in cocaine-associated behavior: Therapeutic potential and novel mechanistic insights

Since its discovery in 1998, the hypocretin/orexin system has been identified as a critical modulator of behavior. Through interactions with dopamine neurons of the ventral tegmental area, this system is poised to regulate motivation for drug rewards by impacting dopamine neurotransmission in target structures including the nucleus accumbens. Across numerous experiments, we and others have identified a critical influence of hypocretin receptor 1 in mediating the behavioral and physiological effects of cocaine which positions this receptor as a potential target for the treatment of cocaine addiction. Here we discuss evidence for hypocretin receptor 1 involvement in driving cocaine-associated behavior and how hypocretin receptor 1 in the ventral tegmental area are critical for supporting dopamine neuron activity and dopamine neurotransmission. We then present new data supporting the novel hypothesis that in addition to exerting acute actions on dopamine systems, pharmacological hypocretin manipulations also produce lasting adaptations to dopamine terminals that impact sensitivity to cocaine, and ultimately, future behavior.

Advances in pediatrics in 2017: current practices and challenges in allergy, endocrinology, gastroenterology, genetics, immunology, infectious diseases, neonatology, nephrology, neurology, pulmonology from the perspective of Italian Journal of Pediatrics

This review provides an overview of a remarkable number of significant studies in pediatrics that have been published over the past year in the Italian Journal of Pediatrics. We have selected information from papers presented in the Journal that deal with allergy, endocrinology, gastroenterology, genetics, immunology, infectious diseases, neonatology, nephrology, neurology, pulmonology. The relevant epidemiologic findings, and developments in prevention, diagnosis and treatment of the last year have been discussed and placed in context. We think that advances achieved in 2017 will help readers to make the future of patients better.

The hypocretin/orexin system as a target for excessive motivation in alcohol use disorders

The hypocretin/orexin (ORX) system has been repeatedly demonstrated to regulate motivation for drugs of abuse, including alcohol. In particular, ORX seems to be critically involved in highly motivated behaviors, as is observed in high-seeking individuals in a population, in the seeking of highly palatable substances, and in models of dependence. It seems logical that this system could be considered as a potential target for treatment for addiction, particularly alcohol addiction, as ORX pharmacological manipulations significantly reduce drinking. However, the ORX system also plays a role in a wide range of other behaviors, emotions, and physiological functions and is disrupted in a number of non-dependence-associated disorders. It is therefore important to consider how the ORX system might be optimally targeted for potential treatment for alcohol use disorders either in combination with or separate from its role in other functions or diseases. This review will focus on the role of ORX in alcohol-associated behaviors and whether and how this system could be targeted to treat alcohol use disorders while avoiding impacts on other ORX-relevant functions. A brief overview of the ORX system will be followed by a discussion of some of the factors that makes it particularly intriguing as a target for alcohol addiction treatment, a consideration of some potential challenges associated with targeting this system and, finally, some future directions to optimize new treatments.

Redox Mechanisms in Migraine: Novel Therapeutics and Dietary Interventions

SIGNIFICANCE

Migraine represents the third most prevalent and the seventh most disabling human disorder. Approximately 30% of migraine patients experience transient, fully reversible, focal neurological symptoms (aura) preceding the attack. Recent Advances: Awareness of the hypothesis that migraine actually embodies a spectrum of illnesses-ranging from episodic to chronic forms-is progressively increasing and poses novel challenges for clarifying the underlying pathophysiological mechanisms of migraine as well as for the development of novel therapeutic interventions. Several theories have evolved to the current concept that a combination of genetic, epigenetic, and environmental factors may play a role in migraine pathogenesis, although their relative importance is still being debated.

CRITICAL ISSUES

One critical issue that deserves a particular attention is the role of oxidative stress in migraine. Indeed, potentially harmful oxidative events occur during the migraine attack and long-lasting or frequent migraine episodes may increase brain exposure to oxidative events that can lead to chronic transformation. Moreover, a wide variety of dietary, environmental, physiological, behavioral, and pharmacological migraine triggers may act through oxidative stress, with clear implications for migraine treatment and prophylaxis. Interestingly, almost all current prophylactic migraine agents exert antioxidant effects.

FUTURE DIRECTIONS

Increasing awareness of the role of oxidative stress and/or decreased antioxidant defenses in migraine pathogenesis and progression to a chronic condition lays the foundations for the design of novel prophylactic approaches, which, by reducing brain oxidative phenomena, could favorably modify the clinical course of migraine. Antioxid. Redox Signal. 28, 1144-1183.

Changes in the Cholinergic, Catecholaminergic, Orexinergic and Serotonergic Structures Forming Part of the Sleep Systems of Adult Mice Exposed to Intrauterine Alcohol

We examined the effect of chronic prenatal alcohol exposure on certain neuronal systems involved with the sleep-wake cycle of C57BL/6J mice exposed to prenatal alcohol once they had reached 56 days post-natal. Pregnant mice were exposed to alcohol, through oral gavage, on gestational days 7–16, with recorded blood alcohol concentration (BAC)s averaging 1.84 mg/ml (chronic alcohol group, CA). Two control groups, an oral gavage sucrose control group (chronic alcohol control group, CAc) and a non-treated control group (NTc), were also examined. At 56 days post-natal, the pups from each group were sacrificed and the whole brain sectioned in a coronal plane and immunolabeled for cholineacetyltransferase (ChAT), tyrosine hydroxylase (TH), serotonin (5HT) and orexin-A (OxA) which labels cholinergic, catecholaminergic, serotonergic and orexinergic structures respectively. The overall nuclear organization and neuronal morphology were identical in all three groups studied, and resemble that previously reported for laboratory rodents. Quantification of the estimated numbers of ChAT immunopositive (+) neurons of the pons, the TH+ neurons of the pons and the OxA+ neurons of the hypothalamus showed no statistically significant difference between the three experimental groups. The stereologically estimated areas and volumes of OxA+ neurons in the CA group were statistically significantly larger than the groups not exposed to prenatal alcohol, but the ChAT+ neurons in the CA group were statistically significantly smaller. The density of orexinergic boutons in the anterior cingulate cortex was lower in the CA group than the other groups. No statistically significant difference was found in the area and volume of TH+ neurons between the three experimental groups. These differences are discussed in relation to the sleep disorders recorded in children with fetal alcohol spectrum disorder (FASD).

Reversible inactivation of the lateral hypothalamus reversed high reward choices in cost-benefit decision-making in rats

The Lateral hypothalamus (LH) is an important component of the networks underlying the control of feeding and other motivated behaviors. Cost-benefit decision-making is mediated largely by the prefrontal cortex (PFC) which strongly innervates the LH. Therefore, in the current study, we conducted a series of experiments to elucidate the role of the perifornical area of the lateral hypothalamus (PeF-LH) in effort and/or delay-based decision-making. We trained different groups of rats in a delay-based and/or an effort-based form of cost-benefit T-maze decision- making task in which they could either choose to pay the cost to obtain a high reward in one arm or could obtain a low reward in the other arm with no cost. During test days, the rats received local injections of either vehicle or lidocaine4% (0.5 μl/side), in the PeF-LH. In an effort-based decision task, PeF-LH inactivation led to decrease in high reward choice. Similarly, in a delay-based decision task animals' preference changed to a low but immediately available reward. This was not caused by a spatial memory or motor deficit. PeF-LH inactivation modified decision behavior. The results imply that PeF-LH is important for allowing the animal to pay a cost to acquire greater rewards.

The link between obesity and migraine in childhood: a systematic review

Obesity and headache are two highly prevalent diseases both in adults and children and they are associated with a strong personal and social impact. Many studies suggest that obesity is comorbid with headache in general, and migraine in particular and obesity seems to be a risk factor for migraine progression and for migraine frequency both in adults and in children. Research shows that there are multiple areas of overlap between migraine pathophysiology and the central and peripheral pathways regulating feeding: inflammatory mediators such as the calcitonin gene-related protein (CGRP), neurotransmitters such as serotonin, peptides such as orexin and adipocytokines such as adiponectin (ADP) and leptin could explain the common pathogenesis. In this paper we discussed the association between obesity and migraine through the analysis of the most recent studies in children and we reviewed data from literature in order to assess the association between obesity and headache and to clarify the possible common pathogenic mechanisms.

Individual differences in orexin-I receptor modulation of motivation for the opioid remifentanil

Orexin-1 receptors (Ox1Rs) have been implicated in the motivation for drugs of abuse. Here, we utilized a within-session behavioral-economics threshold procedure to screen for individual differences in economic demand for the ultra-short-acting opioid remifentanil and to test whether antagonism of Ox1Rs reduces remifentanil demand. The behavioral-economics procedure revealed robust individual differences in free consumption of remifentanil (Q₀ parameter; hedonic set point). Rats with low baseline Q₀ (low takers) displayed high demand elasticity (α parameter; reduced responding as drug price increased indicating low motivation for drug), whereas subjects with a higher Q₀ (high takers) exhibit low demand elasticity (low α) by continuing to self-administer remifentanil despite increased cost (reflecting higher motivation for drug). In a punished responding paradigm utilizing footshock, subjects that were classified as high takers at baseline withstood twice as much shock as low takers to continue self-administering remifentanil. Interestingly, Ox1R antagonism with SB-334867 reduced Q₀ and increased α in low takers but not in high takers. Similarly, the Ox1R antagonist attenuated cue-induced, but not drug-induced, reinstatement of remifentanil seeking in low takers but had no significant effect on reinstatement of drug seeking in high takers. Together, these data reveal a novel role of orexins in demand for remifentanil: Ox1Rs modulate demand in low takers but not in individuals that exhibit addictive-like behaviors (high takers). Finally, the behavioral assays in this study can serve as a novel laboratory model for studying individual differences in opioid use disorders.

Identifying a gene expression signature of cluster headache in blood

Cluster headache is a relatively rare headache disorder, typically characterized by multiple daily, short-lasting attacks of excruciating, unilateral (peri-)orbital or temporal pain associated with autonomic symptoms and restlessness. To better understand the pathophysiology of cluster headache, we used RNA sequencing to identify differentially expressed genes and pathways in whole blood of patients with episodic (n = 19) or chronic (n = 20) cluster headache in comparison with headache-free controls (n = 20). Gene expression data were analysed by gene and by module of co-expressed genes with particular attention to previously implicated disease pathways including hypocretin dysregulation. Only moderate gene expression differences were identified and no associations were found with previously reported pathogenic mechanisms. At the level of functional gene sets, associations were observed for genes involved in several brain-related mechanisms such as GABA receptor function and voltage-gated channels. In addition, genes and modules of co-expressed genes showed a role for intracellular signalling cascades, mitochondria and inflammation. Although larger study samples may be required to identify the full range of involved pathways, these results indicate a role for mitochondria, intracellular signalling and inflammation in cluster headache.

Sleep and Neurodegeneration: A Critical Appraisal

Sleep abnormalities are clearly recognized as a distinct clinical symptom of concern in neurodegenerative disorders. Appropriate management of sleep-related symptoms has a positive impact on quality of life in patients with neurodegenerative disorders. This review provides an overview of mechanisms that are currently being considered that tie sleep with neurodegeneration. It appraises the literature regarding specific sleep changes seen in common neurodegenerative diseases, with a focus on Alzheimer disease and synucleinopathies (ie, Parkinson disease, dementia with Lewy bodies, multiple system atrophy), that have been better studied. Sleep changes may also serve as markers to identify patients in the preclinical stage of some neurodegenerative disorders. A hypothetical model is postulated founded on the conjecture that specific sleep abnormalities, when noted to increase in severity beyond that expected for age, could be a surrogate marker reflecting pathophysiological processes related to neurodegenerative disorders. This provides a clinical strategy for screening patients in the preclinical stages of neurodegenerative disorders to enable therapeutic trials to establish the efficacy of neuroprotective agents to prevent or delay the development of symptoms and functional decline. It is unclear if sleep disturbance directly impacts neurodegenerative processes or is a secondary outcome of neurodegeneration; this is an active area of research. The clinical importance of recognizing and managing sleep changes in neurodegenerative disorders is beyond doubt.

Hubs and spokes of the lateral hypothalamus: cell types, circuits and behaviour

The hypothalamus is among the most phylogenetically conserved regions in the vertebrate brain, reflecting its critical role in maintaining physiological and behavioural homeostasis. By integrating signals arising from both the brain and periphery, it governs a litany of behaviourally important functions essential for survival. In particular, the lateral hypothalamic area (LHA) is central to the orchestration of sleep-wake states, feeding, energy balance and motivated behaviour. Underlying these diverse functions is a heterogeneous assembly of cell populations typically defined by neurochemical markers, such as the well-described neuropeptides hypocretin/orexin and melanin-concentrating hormone. However, anatomical and functional evidence suggests a rich diversity of other cell populations with complex neurochemical profiles that include neuropeptides, receptors and components of fast neurotransmission. Collectively, the LHA acts as a hub for the integration of diverse central and peripheral signals and, through complex local and long-range output circuits, coordinates adaptive behavioural responses to the environment. Despite tremendous progress in our understanding of the LHA, defining the identity of functionally discrete LHA cell types, and their roles in driving complex behaviour, remain significant challenges in the field. In this review, we discuss advances in our understanding of the neurochemical and cellular heterogeneity of LHA neurons and the recent application of powerful new techniques, such as opto- and chemogenetics, in defining the role of LHA circuits in feeding, reward, arousal and stress. From pioneering work to recent developments, we review how the interrogation of LHA cells and circuits is contributing to a mechanistic understanding of how the LHA coordinates complex behaviour.

Metabolic signals in sleep regulation: recent insights

Sleep and energy balance are essential for health. The two processes act in concert to regulate central and peripheral homeostasis. During sleep, energy is conserved due to suspended activity, movement, and sensory responses, and is redirected to restore and replenish proteins and their assemblies into cellular structures. During wakefulness, various energy-demanding activities lead to hunger. Thus, hunger promotes arousal, and subsequent feeding, followed by satiety that promotes sleep via changes in neuroendocrine or neuropeptide signals. These signals overlap with circuits of sleep-wakefulness, feeding, and energy expenditure. Here, we will briefly review the literature that describes the interplay between the circadian system, sleep-wake, and feeding-fasting cycles that are needed to maintain energy balance and a healthy metabolic profile. In doing so, we describe the neuroendocrine, hormonal/peptide signals that integrate sleep and feeding behavior with energy metabolism.

Circadian Clocks as Modulators of Metabolic Comorbidity in Psychiatric Disorders

Psychiatric disorders such as schizophrenia, bipolar disorder, and major depressive disorder are often accompanied by metabolic dysfunction symptoms, including obesity and diabetes. Since the circadian system controls important brain systems that regulate affective, cognitive, and metabolic functions, and neuropsychiatric and metabolic diseases are often correlated with disturbances of circadian rhythms, we hypothesize that dysregulation of circadian clocks plays a central role in metabolic comorbidity in psychiatric disorders. In this review paper, we highlight the role of circadian clocks in glucocorticoid, dopamine, and orexin/melanin-concentrating hormone systems and describe how a dysfunction of these clocks may contribute to the simultaneous development of psychiatric and metabolic symptoms.

Neurobiology and sleep disorders in cluster headache

Cluster headache is characterized by unilateral attacks of severe pain accompanied by cranial autonomic features. Apart from these there are also sleep-related complaints and strong chronobiological features. The interaction between sleep and headache is complex at any level and evidence suggests that it may be of critical importance in our understanding of primary headache disorders. In cluster headache several interactions between sleep and the severe pain attacks have already been proposed. Supported by endocrinological and radiological findings as well as the chronobiological features, predominant theories revolve around central pathology of the hypothalamus. We aimed to investigate the clinical presentation of chronobiological features, the presence of concurrent sleep disorders and the relationship with particular sleep phases or phenomena, the possible role of hypocretin as well as the possible involvement of cardiac autonomic control. We conducted a questionnaire survey on 275 cluster headache patients and 145 controls as well an in-patient sleep study including 40 CH-patients and 25 healthy controls. The findings include: A distinct circannual connection between cluster occurrence and the amount of daylight, substantially poorer sleep quality in patients compared to controls which was present not only inside the clusters but also outside, affected REM-sleep in patients without a particular temporal connection to nocturnal attacks, equal prevalence of sleep apnea in both patient and control groups, reduced levels of hypocretin-1 in the cerebrospinal fluid of patients and finally a blunted response to the change from supine to tilted position in the head-up tilt table test indicating a weakened sympathoexcitatory or stronger parasympathetic drive. Overall, these findings support a theory of involvement of dysregulation in hypothalamic and brainstem nuclei in cluster headache pathology. Further, it is made plausible that the headache attacks are but one aspect of a more complex syndrome of central dysregulation manifesting as sleep-related complaints, sub-clinical autonomic dysregulation and of course the severe attacks of unilateral headache. Future endeavors should focus on pathological changes which persist in the attack-free periods but also heed the possibility of long-lived, cluster-induced pathology.

Roles of the orexin system in central motor control

The neuropeptides orexin-A and orexin-B are produced by one group of neurons located in the lateral hypothalamic/perifornical area. However, the orexins are widely released in entire brain including various central motor control structures. Especially, the loss of orexins has been demonstrated to associate with several motor deficits. Here, we first summarize the present knowledge that describes the anatomical and morphological connections between the orexin system and various central motor control structures. In the next section, the direct influence of orexins on related central motor control structures is reviewed at molecular, cellular, circuitry, and motor activity levels. After the summarization, the characteristic and functional relevance of the orexin system's direct influence on central motor control function are demonstrated and discussed. We also propose a hypothesis as to how the orexin system orchestrates central motor control in a homeostatic regulation manner. Besides, the importance of the orexin system's phasic modulation on related central motor control structures is highlighted in this regulation manner. Finally, a scheme combining the homeostatic regulation of orexin system on central motor control and its effects on other brain functions is presented to discuss the role of orexin system beyond the pure motor activity level, but at the complex behavioral level.

Reduced CSF hypocretin-1 levels are associated with cluster headache

Background

Cluster headache (CH) is a debilitating disorder characterized by unilateral, severe pain attacks with accompanying autonomic symptoms, often waking the patient from sleep. As it exhibits strong chronobiological traits and genetic studies have suggested a link with the hypocretin (HCRT) system, the objective of this study was to investigate HCRT-1 in CH patients.

Methods

Cerebrospinal fluid HCRT-1 concentration was measured in 12 chronic and 14 episodic CH patients during an active bout, and in 27 healthy controls. The patients were well characterized and clinical features compared to the HCRT concentration.

Results

We found significantly lower HCRT levels both in chronic ( p = 0.0221) and episodic CH ( p = 0.0005) patients compared with controls. No significant relationship was found with other clinical features.

Conclusions

This is the first report of significantly reduced HCRT concentrations in CH patients. We speculate that decreased HCRT may reflect insufficient antinociceptive activity of the hypothalamus. The mechanism of the antinociceptive effect of HCRT is not known and requires further investigation. This study supports the hypothesis of a connection between arousal regulation and CH.

Sleep in trigeminal autonomic cephalagias: a review

PURPOSE OF REVIEW

Sleep and cluster headache (CH) are believed to be interconnected but the precise relation to the other trigeminal autonomic cephalalgias (TACs) is uncertain and complex. A better understanding of these relations may eventually lead to a clarification of the underlying mechanisms and eventually to more effective therapeutic regimens. This review aims to evaluate the existing literature on the subject of TACs and sleep. An association between episodic CH and distinct macrostructural sleep phases, especially the relation to rapid eye movement (REM) sleep, has been described in some older studies but could not be confirmed in other, more recent studies. Investigations into the microstructure of sleep in these patients are lacking. Only a few case reports exist on the relation between sleep and other TACs.

SUMMARY

Recent studies do not find an association between CH and REM sleep. One older study suggests chronic paroxysmal hemicranias may be locked to REM sleep but otherwise the relation is unknown. Reports indicate that CH and obstructive sleep apnoea are associated in some individuals but results are diverging. Single cases show improvement of CH upon treatment of sleep apnoea, but the causal relationship remains in question. Other TACs are probably not connected to sleep and strictly nocturnal attacks should prompt investigations for secondary causes. The relation between CH and sleep is, however, fascinating and detailed sleep studies in carefully diagnosed patients are warranted.

Role of lateral hypothalamus in two aspects of attention in associative learning

Orexin (hypocretin) and melanin-concentrating hormone (MCH) neurons are unique to the lateral hypothalamic (LH) region, but project throughout the brain. These cell groups have been implicated in a variety of functions, including reward learning, responses to stimulants, and the modulation of attention, arousal and the sleep/wakefulness cycle. Here, we examined roles for LH in two aspects of attention in associative learning shown previously to depend on intact function in major targets of orexin and MCH neurons. In experiments 1 and 2, unilateral orexin-saporin lesions of LH impaired the acquisition of conditioned orienting responses (ORs) and bilaterally suppressed FOS expression in the amygdala central nucleus (CeA) normally observed in response to food cues that provoke conditioned ORs. Those cues also induced greater FOS expression than control cues in LH orexin neurons, but not in MCH neurons. In experiment 3, unilateral orexin-saporin lesions of LH eliminated the cue associability enhancements normally produced by the surprising omission of an expected event. The magnitude of that impairment was positively correlated with the amount of LH damage and with the loss of orexin neurons in particular, but not with the loss of MCH neurons. We suggest that the effects of the LH orexin-saporin lesions were mediated by their effect on information processing in the CeA, known to be critical to both behavioral phenomena examined here. The results imply close relations between LH motivational amplification functions and attention, and may inform our understanding of disorders in which motivational and attentional impairments co-occur.

Effects of hypocretin/orexin cell transplantation on narcoleptic-like sleep behavior in rats

The sleep disorder narcolepsy is now considered a neurodegenerative disease because there is a massive loss of neurons containing the neuropeptide hypocretin/orexin (HCRT). In consequence, narcoleptic patients have very low cerebrospinal fluid (CSF) levels of HCRT. Studies in animal models of narcolepsy have shown the neurophysiological role of the HCRT system in the development of this disease. For example, the injection of the neurotoxin named hypocretin-2-saporin (HCRT2/SAP) into the lateral hypothalamus (LH) destroys the HCRT neurons, therefore diminishes the contents of HCRT in the CSF and induces narcoleptic-like behavior in rats. Transplants of various cell types have been used to induce recovery in a variety of neurodegenerative animal models. In models such as Parkinson's disease, cell survival has been shown to be small but satisfactory. Similarly, cell transplantation could be employed to implant grafts of HCRT cells into the LH or even other brain regions to treat narcolepsy. Here, we report for the first time that transplantation of HCRT neurons into the LH of HCRT2/SAP-lesioned rats diminishes narcoleptic-like sleep behavior. Therefore, cell transplantation may provide an effective method to treat narcolepsy.

Why does sleep stop migraine?

The relationship between sleep and migraine headaches is complex. Changes in sleep patterns can trigger migraine attacks, and sleep disorders may be associated with increased migraine frequency. Furthermore, migraine patients and their doctors very consistently report that sleep relieves already established migraine attacks. Herein we will try to answer the question, "Why does sleep stop migraine?" Since evidence for this relationship is largely based on empirical clinical observation, we will not provide a clinical review of the association. Instead, we will focus on the pathophysiology of migraine attacks and its intersections with sleep biology.

Migraine & paediatric obesity: a plausible link?

Obesity and migraine are both highly prevalent disorders in the general population, influenced by genetic and environmental risk factors. In recent studies, obesity was found to be a strong risk factor for transformed migraine and, among migraineurs, obesity was associated with frequent headaches and higher disability scores. Suggested mechanisms included: (i) obesity as a pro-inflammatory state may be associated with neurovascular inflammation in patients with migraine; (ii) elevated levels of plasma calcitonin gene-related peptide (CGRP) in obese individuals may play a role as an important post-synaptic mediator of trigeminovascular inflammation in migraine; (iii) dismodulation in the hypothalamic neuropeptide, orexin, in obese persons may be associated with increased susceptibility to neurogenic inflammation causing migraine attacks; and (iv) leptin and adiponectin can activate proinflammatory cytokine release that is involved in the pathogenesis of migraine. In addition, both conditions are associated with psychiatric co-morbidities, such as depression and anxiety, that can further increase headache frequency and disability. Therefore, the effect of obesity on migraine outcome is important. Weight and BMI should be measured and calculated in all children presenting with migraine, and weight control should be a part of the treatment.

Sympathetic and cardiovascular changes during sleep in narcolepsy with cataplexy patients

OBJECTIVE

Neural mechanisms underlying sleep-onset rapid eye movement (REM) periods (SOREMPs) in narcolepsy and the role of hypocretin in driving sympathetic changes during sleep are misunderstood. We aimed to characterize autonomic changes during sleep in narcolepsy with cataplexy (NC) patients to clarify the nature of SOREMP events and the effect of hypocretin deficiency on sympathetic activity during sleep.

METHODS

We observed 13 hypocretin-deficient NC patients and five healthy controls who underwent nocturnal video-polysomnography (v-PSG) with blood pressure (BP) recording, heart rate (HR), skin sympathetic activity (SSA), and muscle sympathetic nerve activity (MSNA) from the peroneal nerve by microneurography.

RESULTS

Compared to wake, control participants displayed a progressive significant decrease of BP and sympathetic activities during nonrapid eye movement (NREM) sleep and an increase of autonomic activity during REM sleep, as expected. NC patients showed: (1) a decrease of sympathetic activities during SOREMP comparable to NREM sleep stage 1 (N1) but in contrast to the increased activity typical of REM sleep; and (2) physiologic sympathetic change during the following sleep stages with a progressive decrease during NREM sleep stage 2 (N2) and NREM sleep stage 3 (N3) and a clear increase in REM sleep, though BP did not show the physiologic decrease during sleep (nondipper pattern).

CONCLUSIONS

SOREMPs in NC patients lack the sympathetic activation occurring during physiologic REM sleep, thus suggesting a dissociated REM sleep condition. In addition, our data indicated that hypocretin plays a limited role in the regulation of sympathetic changes during sleep.

Sex differences in circadian timing systems: implications for disease

Virtually every eukaryotic cell has an endogenous circadian clock and a biological sex. These cell-based clocks have been conceptualized as oscillators whose phase can be reset by internal signals such as hormones, and external cues such as light. The present review highlights the inter-relationship between circadian clocks and sex differences. In mammals, the suprachiasmatic nucleus (SCN) serves as a master clock synchronizing the phase of clocks throughout the body. Gonadal steroid receptors are expressed in almost every site that receives direct SCN input. Here we review sex differences in the circadian timing system in the hypothalamic-pituitary-gonadal axis (HPG), the hypothalamic-adrenal-pituitary (HPA) axis, and sleep-arousal systems. We also point to ways in which disruption of circadian rhythms within these systems differs in the sexes and is associated with dysfunction and disease. Understanding sex differentiated circadian timing systems can lead to improved treatment strategies for these conditions.

Synaptic interactions between perifornical lateral hypothalamic area, locus coeruleus nucleus and the oral pontine reticular nucleus are implicated in the stage succession during sleep-wakefulness cycle

The perifornical area in the posterior lateral hypothalamus (PeFLH) has been implicated in several physiological functions including the sleep-wakefulness regulation. The PeFLH area contains several cell types including those expressing orexins (Orx; also known as hypocretins), mainly located in the PeF nucleus. The aim of the present study was to elucidate the synaptic interactions between Orx neurons located in the PeFLH area and different brainstem neurons involved in the generation of wakefulness and sleep stages such as the locus coeruleus (LC) nucleus (contributing to wakefulness) and the oral pontine reticular nucleus (PnO) nucleus (contributing to REM sleep). Anatomical data demonstrated the existence of a neuronal network involving the PeFLH area, LC, and the PnO nuclei that would control the sleep-wake cycle. Electrophysiological experiments indicated that PeFLH area had an excitatory effect on LC neurons. PeFLH stimulation increased the firing rate of LC neurons and induced an activation of the EEG. The excitatory effect evoked by PeFLH stimulation in LC neurons was blocked by the injection of the Orx-1 receptor antagonist SB-334867 into the LC. Similar electrical stimulation of the PeFLH area evoked an inhibition of PnO neurons by activation of GABAergic receptors because the effect was blocked by bicuculline application into the PnO. Our data also revealed that the LC and PnO nuclei exerted a feedback control on neuronal activity of PeFLH area. Electrical stimulation of LC facilitated firing activity of PeFLH neurons by activation of catecholaminergic receptors whereas PnO stimulation inhibited PeFLH neurons by activation of GABAergic receptors. In conclusion, Orx neurons of the PeFLH area seem to be an important organizer of the wakefulness and sleep stages in order to maintain a normal succession of stages during the sleep-wakefulness cycle.

Evaluation of potential PET imaging probes for the orexin 2 receptors

A wide range of central nervous system (CNS) disorders, particularly those related to sleep, are associated with the abnormal function of orexin (OX) receptors. Several orexin receptor antagonists have been reported in recent years, but currently there are no imaging tools to probe the density and function of orexin receptors in vivo. To date there are no published data on the pharmacokinetics (PK) and accumulation of some lead orexin receptor antagonists. Evaluation of CNS pharmacokinetics in the pursuit of positron emission tomography (PET) radiotracer development could be used to elucidate the association of orexin receptors with diseases and to facilitate the drug discovery and development. To this end, we designed and evaluated carbon-11 labeled compounds based on diazepane orexin receptor antagonists previously described. One of the synthesized compounds, [(11)C]CW4, showed high brain uptake in rats and further evaluated in non-human primate (NHP) using PET-MR imaging. PET scans performed in a baboon showed appropriate early brain uptake for consideration as a radiotracer. However, [(11)C]CW4 exhibited fast kinetics and high nonspecific binding, as determined after co-administration of [(11)C]CW4 and unlabeled CW4. These properties indicate that [(11)C]CW4 has excellent brain penetrance and could be used as a lead compound for developing new CNS-penetrant PET imaging probes of orexin receptors.

[Migraine and hypothalamus]

Migraine is a complex brain disease. The "generator" of the migrainous attacks remains a subject of debate, but the hypothalamus, with its multiple connections with the other parts of the central nervous system and its controls on the pituitary gland and the autonomic nervous system, is a very serious candidate. Many of the premonitory symptoms of migraine attacks find their origin in the hypothalamus. The hormonal changes which occur during feminine genital life and which impact on the life of the migrainous women have their origin in the hypothalamus. The hypothalamus exerts control over the balance between the parasympathetic and orthosympathetic systems. Orexine, hormones originating in the hypothalamic, are involved in sleep regulation, thermoregulation and neuroendocrine and nociceptive functions. They could play a crucial role in the origin of the migrainous attack and might explain the influence of sleep, eating habits and excessive weight in the occurrence of attacks. Hypothalamic cerebral activation via H2 15OPET activity, suspected by clinical and experimental arguments as a possible trigger for migraine, has been demonstrated during spontaneous attacks. However, no conclusion can be made however as to whether this activation is the cause or the consequence of the migrainous pain.

Radiosynthesis and evaluation of [11C]EMPA as a potential PET tracer for orexin 2 receptors

EMPA is a selective antagonist of orexin 2 (OX2) receptors. Previous literature with [(3)H]-EMPA suggest that it may be used as an imaging agent for OX2 receptors; however, brain penetration is known to be modest. To evaluate the potential of EMPA as a PET radiotracer in non-human primate (as a step to imaging in man), we radiolabeled EMPA with carbon-11. Radiosynthesis of [(11)C]N-ethyl-2-(N-(6-methoxypyridin-3-yl)-2-methylphenylsulfonamido)-N-(pyridin-3-ylmethyl)acetamide ([(11)C]EMPA), and evaluation as a potential PET tracer for OX2 receptors is described. Synthesis of an appropriate non-radioactive O-desmethyl precursor was achieved from EMPA with sodium iodide and chlorotrimethylsilane. Selective O-methylation using [(11)C]CH3I in the presence of cesium carbonate in DMSO at room temp afforded [(11)C]EMPA in 1.5-2.5% yield (non-decay corrected relative to trapped [(11)C]CH3I at EOS) with ≥95% chemical and radiochemical purities. The total synthesis time was 34-36min from EOB. Studies in rodent suggested that uptake in tissue was dominated by nonspecific binding. However, [(11)C]EMPA also showed poor uptake in both rats and baboon as measured with PET imaging.

Human hypocretin and melanin-concentrating hormone levels are linked to emotion and social interaction

The neurochemical changes underlying human emotions and social behaviour are largely unknown. Here we report on the changes in the levels of two hypothalamic neuropeptides, hypocretin-1 and melanin-concentrating hormone, measured in the human amygdala. We show that hypocretin-1 levels are maximal during positive emotion, social interaction and anger, behaviours that induce cataplexy in human narcoleptics. In contrast, melanin-concentrating hormone levels are minimal during social interaction, but are increased after eating. Both peptides are at minimal levels during periods of postoperative pain despite high levels of arousal. Melanin-concentrating hormone levels increase at sleep onset, consistent with a role in sleep induction, whereas hypocretin-1 levels increase at wake onset, consistent with a role in wake induction. Levels of these two peptides in humans are not simply linked to arousal, but rather to specific emotions and state transitions. Other arousal systems may be similarly emotionally specialized.

Twenty-five lessons from computational neuromodulation

Neural processing faces three rather different, and perniciously tied, communication problems. First, computation is radically distributed, yet point-to-point interconnections are limited. Second, the bulk of these connections are semantically uniform, lacking differentiation at their targets that could tag particular sorts of information. Third, the brain's structure is relatively fixed, and yet different sorts of input, forms of processing, and rules for determining the output are appropriate under different, and possibly rapidly changing, conditions. Neuromodulators address these problems by their multifarious and broad distribution, by enjoying specialized receptor types in partially specific anatomical arrangements, and by their ability to mold the activity and sensitivity of neurons and the strength and plasticity of their synapses. Here, I offer a computationally focused review of algorithmic and implementational motifs associated with neuromodulators, using decision making in the face of uncertainty as a running example.