Hypocretin Neurons Research Articles

The Role of T Cells in the Pathogenesis of Narcolepsy Type 1: A Narrative Review

Narcolepsy type 1 (NT1) is an uncommon, persistent sleep disorder distinguished by significant daytime sleepiness, episodes of cataplexy, and irregularities in rapid eye movement sleep. The etiology of NT1 is linked to the destruction of hypothalamic neurons responsible for the synthesis of the wake-promoting neuropeptide known as hypothalamic orexin. The pathophysiological mechanisms underlying NT1 remain inadequately elucidated; however, a model that incorporates the interplay of genetic predisposition, environmental influences, immune system factors, and a deficiency in hypocretin (HCRT) provides a framework for elucidating the pathogenesis of NT1. The prevalence of NT1 has been observed to rise following influenza A (H1N1) pdm09 and the administration of the Pandemrix influenza vaccine. The strong association between narcolepsy and the HLA-DQB1*06:02 allele strongly indicates an autoimmune etiology for this condition. Increasing evidence suggests that T cells play a critical role in this autoimmune-mediated HCRT neuronal loss. Studies have identified specific T cell subsets, including CD4+ and CD8+ T cells, that target HCRT neurons, contributing to their destruction. Clarifying the pathogenesis of NT1 driven by autoimmune T cells is crucial for the development of effective therapeutic interventions for this disorder. This review examines the risk factors associated with the pathogenesis of NT1, explores the role of T cells within the immune system in the progression of NT1, and evaluates immune-mediated animal models alongside prospective immunotherapeutic strategies.

Hypocretin-1 receptor antagonism improves inhibitory control during the Go/No-Go task in highly motivated, impulsive male mice.

Motivation and inhibitory control are dominantly regulated by the dopaminergic (DA) and noradrenergic (NA) systems, respectively. Hypothalamic hypocretin (orexin) neurons provide afferent inputs to DA and NA nuclei and hypocretin-1 receptors (HcrtR1) are implicated in reward and addiction. However, the role of the HcrtR1 in inhibitory control is not well understood. To determine the effects of HcrtR1 antagonism and motivational state in inhibitory control using the go/no-go task in mice. n = 23 male C57Bl/6JArc mice were trained in a go/no-go task. Decision tree dendrogram analysis of training data identified more and less impulsive clusters of animals. A HcrtR1 antagonist (BI001, 12.5mg/kg, per os) or vehicle were then administered 30min before go/no-go testing, once daily for 5 days, under high (food-restricted) and low (free-feeding) motivational states in a latin-square crossover design. Compound exposure levels were assessed in a satellite group of animals. HcrtR1 antagonism increased go accuracy and decreased no-go accuracy in free-feeding animals overall, whereas it decreased go accuracy and increased no-go accuracy only in more impulsive, food restricted mice. HcrtR1 antagonism also showed differential effects in premature responding, which was increased in response to the antagonist in free-feeding, less impulsive animals, and decreased in food restricted, more impulsive animals. HcrtR1 receptor occupancy by BI001 was estimated at ~ 66% during the task. These data indicate that hypocretin signalling plays roles in goal-directed behaviour and inhibitory control in a motivational state-dependant manner. While likely not useful in all settings, HcrtR1 antagonism may be beneficial in improving inhibitory control in impulsive subpopulations.

A Review of Current and Future Pharmacologic Treatments for Narcolepsy

IntroductionNarcolepsy is a rare but disabling neurological disorder involving disruption of the sleep-wake cycle that is often under- or misdiagnosed (Barateau L, et al. J Sleep Res. 2022;31(4):e13631). It is characterized by a classical tetrad of excessive daytime sleepiness (EDS), cataplexy, hypnagogic hallucinations, and sleep paralysis. Narcolepsy is divided into 3 types: Narcolepsy Type 1 (NT1); Narcolepsy Type 2 (NT2); and Secondary Narcolepsy. The pathophysiology remains unclear but is primarily associated with loss of hypocretin (orexin) neurons involving autoimmune and genetic risk factors, particularly for NT1.ObjectivesTo review the currently available therapies for the treatment of narcolepsy.MethodsThe extant literature was reviewed and discussed in the context of clinical relevance.ResultsTreatment historically has included medications developed for the treatment of other conditions such as psychostimulants (methylphenidate, modafinil/armodafinil, pemoline) and antidepressants (SSRIs,TCAs). These agents are also associated with limiting side effects in practice. In more recent years a variety of specific treatments have been approved that act on diverse pathways. Pitolisant, a histamine H3 receptor inverse agonist, is approved for the treatment of EDS or cataplexy in adult patients with narcolepsy (and children> 6 years in European Union) (Keam SJ.Paediatr Drugs. 2023;25(4):483-488). Solriamfetol, a dopamine and norepinephrine reuptake inhibitor (DNRI) is indicated to improve wakefulness in adult patients with EDS associated with narcolepsy or obstructive sleep apnea (OSA) (Winter Y, et al. Sleep Med. 2023;103:138-143). Sodium oxybate (SXB), a GABAB receptor agonist, is approved for the treatment of cataplexy associated with narcolepsy and (EDS) in patients 7 years or older (Bogan RK, et al. CNS Drugs. 2023;37(4):323-335). Current research focuses on on-peptide hypocretin receptor-2 agonists (Saitoh T, Sakurai T. Peptides. 2023;167:171051).ConclusionsDespite limited understanding of the pathophysiology of narcolepsy there have been substantial advances in the pharmacotherapy, including medications now approved for children. Early diagnosis and treatment are associated with better outcomes. In view of the chronic and disabling morbidity associated with narcolepsy further research and better access to appopriate medications is necessary.Disclosure of InterestNone Declared

A direct estrogenic involvement in the expression of human hypocretin

Hypocretin is synthesized exclusively in the hypothalamus and distributes inputs to several areas of the brain, which may play an important role in depression. Our previous study showed that hypocretin-1 was increased in the lateral hypothalamus in female patients with depression compared to female controls. Estrogen acts through estrogen receptor (ER)α and ERβ. We studied the possibility of a direct action of estrogen receptors on the expression of human hypocretin. We found that hypocretin-1 plasma levels were significantly higher in female patients with depression than in female controls. Female depression estrogen receptors and hypocretin are colocalized in the human lateral hypothalamus, PC12, and SK-N-SH cells. The estrogen receptor response elements (ERE) that exist in the hypocretin promoter region may directly regulate the gene expression of hypocretin. The synchronicity of change of hypocretin and estradiol both in hypothalamus and plasma was verified in female rats. In the presence of estradiol, specific binding occurs between the recombinant human ER and hypocretin-ERE. Expression of ER combined with estradiol repressed hypocretin promoter activity via the ERE. In conclusion, we found that estradiol may directly affect hypocretin neurons in the human hypothalamus via ER binding to the hypocretin-ERE, which may lead to the sex-specific pathogenesis of depression.

Embryonic ethanol exposure and optogenetic activation of hypocretin neurons stimulate similar behaviors early in life associated with later alcohol consumption

The initiation of alcohol use early in life is one of the strongest predictors of developing a future alcohol use disorder. Clinical studies have identified specific behaviors during early childhood that predict an increased risk for excess alcohol consumption later in life. These behaviors, including increased hyperactivity, anxiety, novelty-seeking, exploratory behavior, impulsivity, and alcohol-seeking, are similarly stimulated in children and adolescent offspring of mothers who drink alcohol during pregnancy. Here we tested larval zebrafish in addition to young pre-weanling rats and found this repertoire of early behaviors along with the overconsumption of alcohol during adolescence to be increased by embryonic ethanol exposure. With hypocretin/orexin (Hcrt) neurons known to be stimulated by ethanol and involved in mediating these alcohol-related behaviors, we tested their function in larval zebrafish and found optogenetic activation of Hcrt neurons to stimulate these same early alcohol-related behaviors and later alcohol intake, suggesting that these neurons have an important role in producing these behaviors. Together, these results show zebrafish to be an especially useful animal model for investigating the diverse neuronal systems mediating behavioral changes at young ages that are produced by embryonic ethanol exposure and predict an increased risk for developing alcohol use disorder.

Altered reinforcement learning in Narcolepsy type I and other central disorders of hypersomnolence

Cognitive impairments are described in central disorders of hypersomnolence (CDH), but studies remain very limited and largely focused on narcolepsy type 1 (NT1). The precise nature and origin of these cognitive impairments is poorly understood. Specifically, impaired decision making under ambiguity has been reported in NT1 and suggested to be caused by dysregulation of the direct projections of hypocretin neurons to the dopamine network. However, the decision-making tasks used previously embed different cognitive functions that are difficult to isolate.This study aims to test reinforcement learning in participants with NT1 and with other (non-hypocretin deficient) CDH in a task known to directly depend on the dopamine system. Participants with NT1 (N = 27), other CDH (N = 34, including narcolepsy type 2 and idiopathic hypersomnia, matched with NT1 participants for sleepiness severity), and healthy participants (N = 34) took part in the study.Results showed that all groups had normal and similar positive reinforcement learning, a pattern not suggestive of dopamine deficiency. However, both participants with NT1 and other CDH had decreased learning abilities to avoid losses. This decreased negative reinforcement learning in participants with CDH was associated with the alteration of vigilance.This study provides new insights into the nature of decision making impairment in people with CDH and suggests that these alterations could be minimized by restoring adequate vigilance.

Hypocretin/orexin neurons encode social discrimination and exhibit a sex-dependent necessity for social interaction

The hypothalamus plays a crucial role in the modulation of social behavior by encoding internal states. The hypothalamic hypocretin/orexin neurons, initially identified as regulators of sleep and appetite, are important for emotional and motivated behaviors. However, their role in social behavior remains unclear. Using fiber photometry and behavioral analysis, we show here that hypocretin neurons differentially encode social discrimination based on the nature of social encounters. The optogenetic inhibition of hypocretin neuron activity or blocking of hcrt-1 receptors reduces the amount of time mice are engaged in social interaction in males but not in females. Reduced hcrt-1 receptor signaling during social interaction is associated with altered activity in the insular cortex and ventral tegmental area in males. Our data implicating hypocretin neurons as sexually dimorphic regulators within social networks have significant implications for the treatment of neuropsychiatric diseases with social dysfunction, particularly considering varying prevalence among sexes.

Control and coding of pupil size by hypothalamic orexin neurons

Brain orexin (hypocretin) neurons are implicated in sleep–wake switching and reward-seeking but their roles in rapid arousal dynamics and reward perception are unclear. Here, cell-specific stimulation, deletion and in vivo recordings revealed strong correlative and causal links between pupil dilation—a quantitative arousal marker—and orexin cell activity. Coding of arousal and reward was distributed across orexin cells, indicating that they specialize in rapid, multiplexed communication of momentary arousal and reward states.

Narcolepsy and Idiopathic Hypersomnia.

Narcolepsy types 1 and 2 and idiopathic hypersomnia are primary Central Nervous System (CNS) disorders of hypersomnolence characterized by profound daytime sleepiness and/or excessive sleep need. Onset of symptoms begins typically in childhood or adolescence, and children can have unique presentations compared with adults. Narcolepsy type 1 is likely caused by immune-mediated loss of orexin (hypocretin) neurons in the hypothalamus; however, the causes of narcolepsy type 2 and idiopathic hypersomnia are unknown. Existing treatments improve daytime sleepiness and cataplexy but there is no cure for these disorders.

Progress of autonomic disturbances in narcolepsy type 1.

Narcolepsy type 1 is a kind of sleep disorder characterized by a specific loss of hypocretin neurons in the lateral hypothalamus and reduced levels of hypocretin-1 in the cerebrospinal fluid. Hypocretin deficiency is associated with autonomic disorders. This article summarizes the autonomic disorders and possible mechanisms associated with narcolepsy type 1. Patients with narcolepsy type 1 often have various systemic autonomic symptoms, including non-dipping blood pressure, reduced heart rate variability, dynamic cerebral autoregulation impairment, reduced gastric motility and emptying, sleep-related erectile dysfunction, skin temperature abnormalities, and blunted pupillary light reflex. Similar findings should strengthen the recognition and intervention of these disturbances in clinical practice. In addition to hypocretin deficiency, current evidence also indicates that pharmacological therapy (including psychostimulants and anti-cataplectic drugs) and comorbidities may contribute to the alterations of autonomic system observed in narcolepsy type 1.

Optogenetic and pharmacological interventions link hypocretin neurons to impulsivity in mice

Neurons in the lateral hypothalamus expressing the neuropeptide Hypocretin, also known as orexin, are known critical modulators of arousal stability. However, their role in the different components of the arousal construct such as attention and decision making is poorly understood. Here we study Hypocretin neuronal circuit dynamics during stop action impulsivity in a Go/NoGo task in mice. We show that Hypocretin neuronal activity correlates with anticipation of reward. We then assessed the causal role of Hypocretin neuronal activity using optogenetics in a Go/NoGo task. We show that stimulation of Hypocretin neurons during the cue period dramatically increases the number of premature responses. These effects are mimicked by amphetamine, reduced by atomoxetine, a norepinephrine uptake inhibitor, and blocked by a Hypocretin receptor 1 selective antagonist. We conclude that Hypocretin neurons have a key role in the integration of salient stimuli during wakefulness to produce appropriate and timely responses to rewarding and aversive cues.

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.

Diurnal changes in blood pressure and heart rate in children with narcolepsy with cataplexy.

The hypocretin neurons in the lateral hypothalamus are connected not only to brain alertness systems but also to brainstem nuclei that regulate blood pressure and heart rate. The premise is that regulation of blood pressure and heart rate is altered and affected by methylphenidate, a stimulant drug in children with narcolepsy with cataplexy. The changes in 24-hr ambulatory systolic and diastolic blood pressure and heart rate were compared among pre-treated narcolepsy with cataplexy patients (40 males, 10 females), with mean age 10.4 ± 3.5 years (M ± SD, range 5-17 years) with values from 100 archival age-sex-body mass index matched controls. Patients had a lower diurnal systolic blood pressure (-6.5 mmHg; p=0.000) but higher heart rate (+11.0bpm; p=0.000), particularly evident in the waketime, while diastolic blood pressure was comparable. With methylphenidate (18 mg sustained release at 08:00 hours), patients with narcolepsy with cataplexy had higher systolic blood pressure (+4.6 mmHg, p=0.015), diastolic blood pressure (+3.3 mmHg, p=0.005) and heart rate (+7.1bpm, p=0.028) during wake time, but nighttime cardiovascular values were unchanged from pre-treated values; amplitude variation in cardiovascular values was unchanged over 24 hr. In conclusion, children with narcolepsy with cataplexy had downregulation blood pressure profile but a higher heart rate, and lesser non-dipping profiles. Daytime methylphenidate treatment increases only waketime blood pressure and further elevated heart rate values.

Narcolepsy.

This article addresses the clinical presentation, diagnosis, pathophysiology and management of narcolepsy type 1 and 2, with a focus on recent findings. A low level of hypocretin-1/orexin-A in the cerebrospinal fluid is sufficient to diagnose narcolepsy type 1, being a highly specific and sensitive biomarker, and the irreversible loss of hypocretin neurons is responsible for the main symptoms of the disease: sleepiness, cataplexy, sleep-related hallucinations and paralysis, and disrupted nocturnal sleep. The process responsible for the destruction of hypocretin neurons is highly suspected to be autoimmune, or dysimmune. Over the last two decades, remarkable progress has been made for the understanding of these mechanisms that were made possible with the development of new techniques. Conversely, narcolepsy type 2 is a less well-defined disorder, with a variable phenotype and evolution, andfew reliable biomarkers discovered so far. There is a dearth of knowledge about this disorder, and its aetiology remains unclear and needs to be further explored. Treatment of narcolepsy is still nowadays only symptomatic, targeting sleepiness, cataplexy and disrupted nocturnal sleep. However, new psychostimulants have been recently developed, and the upcoming arrival of non-peptide hypocretin receptor-2 agonists should be a revolution in the management of this rare sleep disease, and maybe also for disorders beyond narcolepsy.

Neuroanatomical Basis for the Orexinergic Modulation of Anesthesia Arousal and Pain Control.

Hypothalamic orexin (hypocretin) neurons play crucial roles in arousal control. Their involvement in anesthesia and analgesia remains to be better understood. In order to enhance our view on the neuroanatomy, we systematically mapped the projections of orexin neurons with confocal microscope and light sheet microscope. We specifically expressed optogenetic opsins tagged with fluorescence markers in orexin neurons through adeno-associated viral infection in the mouse brain. The imaging results revealed fine details and novel features of the orexin projections throughout the brain, particularly related to the nuclei regulating arousal and pain. We then optogenetically activated orexin neurons in the lateral hypothalamus to study the effects on anesthesia-related behaviors. cFos staining showed that optogenetic stimulation can activate orexin neurons in the ChR2-mCherry group, but not the control mCherry group (62.86 ± 3.923% vs. 7.9 ± 2.072%; P < 0.0001). In behavior assays, optogenetic stimulation in the ChR2-mCherry group consistently elicited robust arousal from light isoflurane anesthesia (9.429 ± 3.804 s vs. 238.2 ± 17.42 s; P < 0.0001), shortened the emergence time after deep isoflurane anesthesia (109.5 ± 13.59 s vs. 213.8 ± 21.77 s; P = 0.0023), and increased the paw withdrawal latency in a hotplate test (11.45 ± 1.185 s vs. 8.767 ± 0.7775; P = 0.0317). The structural details of orexin fibers established the neuroanatomic basis for studying the role of orexin in anesthesia and analgesia.

Sex-related differences within sleep-wake dynamics, cataplexy, and EEG fast-delta power in a narcolepsy mouse model.

Narcolepsy type 1 (NT1) is a sleep-wake disorder caused by selective loss of hypocretin (HCRT, also called orexin) neurons. Although the prevalence of NT1 is equal in men and women, sex differences in NT1 symptomatology have been reported in humans and other species. Yet, most preclinical studies fail to include females, resulting in gender bias within translational drug development. We used hcrt-tTA;TetO DTA mice (NT1 mice) that lose their HCRT neurons upon dietary doxycycline removal to examine in detail the effect of sex on NT1 symptoms and sleep-wake characteristics. We recorded 24-h electroencephalography (EEG), electromyography (EMG), and video in adult male and female NT1 mice for behavioral state quantification. While conducting this study, we recognized another type of behavioral arrest different from cataplexy: shorter lasting and with high δ power. We termed these delta attacks and propose a set of criteria for quantifying these in future research. Our findings show that both sexes exhibit high behavioral state instability, which was markedly higher in females with more behavioral arrests interrupting the wake episodes. Females exhibited increased wake at the expense of sleep during the dark phase, and decreased rapid eye movement (REM) sleep during the 24-h day. During the dark phase, fast-δ (2.5-4 Hz) in non-rapid eye movement (NREM) sleep and θ (6-10 Hz) EEG spectral power in REM sleep were lower in females compared to males. We demonstrate that biologically driven sex-related differences exist in the symptomatology of NT1 mice which calls for including both sexes in future research.

Selective requirement for polycomb repressor complex 2 in the generation of specific hypothalamic neuronal subtypes.

ABSTRACTThe hypothalamus displays staggering cellular diversity, chiefly established during embryogenesis by the interplay of several signalling pathways and a battery of transcription factors. However, the contribution of epigenetic cues to hypothalamus development remains unclear. We mutated the polycomb repressor complex 2 gene Eed in the developing mouse hypothalamus, which resulted in the loss of H3K27me3, a fundamental epigenetic repressor mark. This triggered ectopic expression of posteriorly expressed regulators (e.g. Hox homeotic genes), upregulation of cell cycle inhibitors and reduced proliferation. Surprisingly, despite these effects, single cell transcriptomic analysis revealed that most neuronal subtypes were still generated in Eed mutants. However, we observed an increase in glutamatergic/GABAergic double-positive cells, as well as loss/reduction of dopamine, hypocretin and Tac2-Pax6 neurons. These findings indicate that many aspects of the hypothalamic gene regulatory flow can proceed without the key H3K27me3 epigenetic repressor mark, but points to a unique sensitivity of particular neuronal subtypes to a disrupted epigenomic landscape.

Losing sleep with age.

Hypocretin neuron hyperexcitability underlies disrupted sleep quality associated with age.

Hypocretin/Orexin Interactions with Norepinephrine Contribute to the Opiate Withdrawal Syndrome.

We previously found that human heroin addicts and mice chronically exposed to morphine exhibit a significant increase in the number of detected hypocretin/orexin (Hcrt)-producing neurons. However, it remains unknown how this increase affects target areas of the hypocretin system involved in opioid withdrawal, including norepinephrine containing structures locus coeruleus (LC) and A1/A2 medullary regions. Using a combination of immunohistochemical, biochemical, imaging, and behavioral techniques, we now show that the increase in detected hypocretin cell number translates into a significant increase in hypocretin innervation and tyrosine hydroxylase (TH) levels in the LC without affecting norepinephrine-containing neuronal cell number. We show that the increase in TH is completely dependent on Hcrt innervation. The A1/A2 regions were unaffected by morphine treatment. Manipulation of the Hcrt system may affect opioid addiction and withdrawal.SIGNIFICANCE STATEMENT Previously, we have shown that the hypothalamic hypocretin system undergoes profound anatomic changes in human heroin addicts and in mice exposed to morphine, suggesting a role of this system in the development of addictive behaviors. The locus coeruleus plays a key role in opioid addiction. Here we report that the hypothalamic hypocretin innervation of the locus coeruleus increases dramatically with morphine administration to mice. This increase is correlated with a massive increase in tyrosine hydroxylase expression in locus coeruleus. Elimination of hypocretin neurons prevents the tyrosine hydroxylase increase in locus coeruleus and dampens the somatic and affective components of opioid withdrawal.

Activation of Hypocretin Neurons in Endometriosis.

Endometriosis is a gynecological disease affecting 6-10% of women of reproductive age. In addition to gynecologic symptoms, endometriosis is associated with various systemic effects, including inflammation, altered body weight, and behavioral changes. Previous murine studies demonstrate that endometriosis is causally inked to increased pain sensitization, behavioral changes, and low body mass index (BMI). One possible cellular target that may mediate some of these findings is the hypocretin/orexin neurons. This neuronal system plays a role in regulating wakefulness/sleep cycles, pain perception, and appetite. We hypothesize that endometriosis alters activity level of the hypocretin/orexin (Hcrt) neuronal system. Mice underwent endometriosis induction surgeries (endo) or sham surgeries (sham) for the development of the experimental model. Immunocytochemistry was performed on harvested samples from the lateral hypothalamus, and activation levels of Hcrt cells were examined by quantifying the expression of phosphorylation of cAMP-responsive element binding protein (CREB) in these cells after an acute stress in sham and endo mice. Mice with endometriosis had greater Hcrt neurons activation than sham mice. Mice with endometriosis fed with high fat diet showed a lower fat/body weight and fat/lean tissue ratio compared to mice without endometriosis. There was no significant difference in food intake between sham and endometriosis mice. These results demonstrate that endometriosis is associated with low body mass and increased hypocretin/orexin activity, which could be implicated in the behavioral changes and to differences in body composition.