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Orexins (orexin-A and orexin-B) are neuropeptides that are reduced in narcolepsy, a sleep disorder that is characterized by excessive daytime sleepiness, sudden sleep attacks and cataplexy. However, it remains unclear how orexins in the brain and orexin neurons are reduced in narcolepsy. Orexin-A has two closely located intramolecular disulfide bonds and is prone to misfolding due to the formation of incorrect disulfide bonds. Protein disulfide isomerase (PDI) possesses disulfide interchange activity. PDI can modify misfolded orexin-A to its native form by rearrangement of two disulfide bonds. We have previously demonstrated that sleep deprivation and a high fat diet increase nitric oxide in the brain. This increase triggers S-nitrosation and inactivation of PDI, leading to aggregation of orexin-A and reduction of orexin neurons. However, the relationship between PDI inactivation and loss of orexin neurons has not yet been fully elucidated. In the present study, we used a PDI inhibitor, cystamine, to elucidate the precise molecular mechanism by which PDI inhibition reduces the number of orexin neurons. In rat hypothalamic slice cultures, cystamine induced selective depletion of orexin-A, but not orexin-B and melanin-concentrating hormone. Moreover, cystamine triggered aggregation of orexin-A, but not orexin-B in the Golgi apparatus of hypothalamic slice cultures and in vivo mouse brains. However, cystamine did not induce endoplasmic reticulum (ER) stress, and an ER stress inducer did not trigger aggregation of orexin-A in slice cultures. Finally, we demonstrated that cystamine significantly decreased extracellular secretion of orexin-A in AD293 cells overexpressing prepro-orexin. These findings suggest that cystamine-induced PDI inhibition induces selective depletion, aggregation in the Golgi apparatus and impaired secretion of orexin-A. These effects may represent an initial step in the pathogenesis of narcolepsy. [ABSTRACT FROM AUTHOR]

Objective: To evaluate the protective effect of orexin-A on the cerebral ischemia reperfusion injury in rats. Methods: The physiological parameters were observed to define time rang by six rats before MCAO and after MCAO 2h, 24 h. Twenty rats were randomly divided into middle cerebral artery occlusion (MCAO) group, vehicle group, orexin-A 50 μg/kg and orexin-A 100 μg/kg group (n=5). Neurological dysfunction scores (NDS) and infarct volume were measured at 24h after ischemia-reperfusion. The other sixty rats were also divided into 4 groups (n=15 each group), the level of glutathione peroxidase (GSH-PX) and maleic diadehyde (MDA) in brain plasm were detected pre-operation and at 6h, 24 h after ischemia-reperfusion (n=5 each time point). Results:① No significant differentce was found in the pyhsiological parameters ofrats before MCAO and at 2h ,24h after MCAO (P>0.05), suggesting that the follow indexes of cerebral protection hadn't been influenced within 24h after MCAO.② Compared with the MCAO group and vehicle group, the NDS (P<0.05) and the percentage of brain infarct were better in the orexin-A 50 and 100 μg/kg group (P<0.05); the concentration of GSH-PX was increased and MDA was decreased in orexin-A 50 and 100 μg/kg group (P<0.05). Conclusion: Orexin-A might play a protective role in the cerebral ischemia reperfusion injury in rats by increasing the concentration of antiperoxidase and decreasing the level of oxygen free radicals. [ABSTRACT FROM AUTHOR]

Orexin (hypocretin) neuropeptides play a pivotal role in expression of opioid withdrawal signs. Hypothalamic orexinergic neurons provide dense afferents for the nucleus locus coeruleus (LC). Somatic signs of opioid withdrawal are associated with the enhanced activity of LC neurons. In addition, intra-LC administration of orexin-A leads to the hyperactivity of LC neurons. The present study was an attempt to investigate whether intra-LC microinjection of orexin-A induces morphine withdrawal-like signs in both morphine dependent and control rats. To end this, adult male Wistar rats weighing 250–300 g were used. For induction of morphine dependence, animals received morphine sulfate subcutaneously (10 mg/kg, s.c.) at an interval of 12 h for 9 days. On day 10, intra-LC orexin injection (100 μM, 200 nl) was carried out two hours after last morphine administration. Morphine withdrawal-like signs were assessed in a transparent Plexiglas test chamber (30 cm diameter, 50 cm height) for 25 min. Orexin-A microinjection induced some morphine withdrawal-like signs in both morphine dependent (chewing, scratching, rearing, teeth chattering, wet-dog shake and paw tremor) and control (chewing, scratching, rearing, sniffing, wet-dog shake and head tremor) rats. Furthermore, microinjection of SB-334867, a selective orexin type-1 receptor antagonist before orexin-A significantly suppressed orexin-induced morphine withdrawal-like signs. It seems that orexin-A, via increasing the activity of LC neurons, mediates the induction of some morphine withdrawal-like signs independent of morphine dependence. [ABSTRACT FROM AUTHOR]

Parkinson's disease (PD) is a common neurodegenerative disorder that is characterized by progressive and selective death of dopaminergic neurons. Multifunctional neuropeptide orexin-A is involved in many biological events of the body. It has been shown that orexin-A has protective effects in neurodegenerative disease such as PD. However, its cellular mechanisms have not yet been fully clarified. Here, we investigated the intracellular signaling pathway of orexin-A neuroprotection in 6-hydroxydopamine (6-OHDA)-induced SH-SY5H cells damage as an in vitro model of PD. The cells were incubated with 150 μM 6-OHDA, and the viability was examined by 3-[4,5-dimethyl-2-thiazolyl]-2,5-diphenyl-2-tetrazolium bromide (MTT) assay. Mitochondrial membrane potential and intracellular calcium were measured by fluorescent probes. Western blotting was also used to determine cyclooxygenase type 2 (COX-2), nuclear factor erythroid 2 related factor 2 (Nrf2), and HSP70 protein levels. The data showed that 6-OHDA has decreasing effects on cell viability, Nrf2, and HSP70 protein expression and increases the level of mitochondrial membrane potential, intracellular calcium, and COX-2 protein. Orexin-A (500 pM) significantly attenuated the 6-OHDA-induced cell damage. Furthermore, Orexin-A significantly prevented the mentioned effects of 6-OHDA on SH-SY5Y cells. Orexin 1 receptor antagonist (SB3344867), PKC, and PI3-kinase (PI3K) inhibitors (chelerythrin and LY294002, respectively) could suppress the orexin-A neuroprotective effect. In contrast, blockage of PKA by a selective inhibitor (KT5720) had no effects on the orexin protection. The results suggest that orexin-A protective effects against 6-OHDA-induced neurotoxicity are performed via its receptors, PKC and PI3K signaling pathways. [ABSTRACT FROM AUTHOR]

Objective: To investigate the effect of the orexin-A on nycterohemeral food intake in rats. Methods: Male wistar rats were randomly assigned to accept a single intracerebroventricul-ar (ICV) injection, continuous ICV injection and perineural injection, dosed in the daytime and dark phase, then measured the food intake of rats during the whole day of various phases and corresponding biochemical indexes. Results: Compared with NS group, inject orexin-A into ICV in the light phase (08:00) dose-dependently increased food intake following the next 4 h in rats (P<0.05). Food consumption of rats was unchanged after a single administered ICV with orexin- A in the early dark times (18:00) (P＞0.05). Compared with NS group, administered orexin-A into ICV in the light times (12:00) increased food consumption following the next 4 h in rats (P<0.05). Continuous administered ICV with orexin-A significantly increased the food intakes during the light phase (P＜0.05), and reduced it during the dark phase (P＜0.05), but total 24 h food intake was moving (P＞ 0.05). The level of the temperature of brown adipose tissue, peripheral blood glucose, plasma leptin and other indexes were not changed after ICV infusion of orexin-A. Conclusions: The regulation of Orexin-A on food intake in rats was circadian rhythm. [ABSTRACT FROM AUTHOR]

Orexins, also known as hypocretins, play a regulatory role in the sleep-wake cycle by activating orexin receptors. Previous animal studies have shown that sleep deprivation can elevate orexinergic peptide levels. However, the relationship between insomnia disorder and orexin-A levels in humans has not been explored. In the current study, we examined plasma orexin-A levels in patients with insomnia disorder and in normal sleepers. We also studied the possible mechanisms underlying changes in orexin-A levels between the study groups; this included investigations of prepro-orexin and orexin receptor gene polymorphisms as well as exploration of other variables. We measured plasma orexin-A levels in 228 patients with insomnia disorder and 282 normal sleepers. The results indicated that the patients with insomnia disorder had significantly higher orexin-A levels than normal sleepers (63.42 ± 37.56 vs. 54.84 ± 23.95 pg/ml). A positive relationship was detected between orexin-A level and age in patients with insomnia disorder. Orexin-A levels were elevated in relation to course of insomnia, as well as in relation to increased Insomnia Severity Index score. None of the evaluated prepro-orexin gene single nucleotide polymorphisms were informative between the two study populations. After sequencing all orexin receptor exons, one variation (rs2271933) in the OX1R gene and one variation (rs2653349) in the OX2R gene were found. However, no significant differences were found in either genotypic or allelic frequency distributions between the two study groups. It is suggested that the increased plasma orexin-A levels in patients with insomnia disorder are associated with the course and severity of insomnia, but not with prepro-orexin and orexin receptor gene polymorphisms. [ABSTRACT FROM AUTHOR]

Orexin-A, which is an endogenous neuropeptide, is reported to have a protective role in ischemic stroke. High-concentration glutamic acid (Glu) induced by hypoxia injury in ischemic stroke can be inhibited by glial glutamate transporter GLT-1 which is only expressed in astroglia cells. A previous study reported that Orexin-A may regulate GLT-1 expression. However, the role of orexin-A in the regulation of GLT-1 in ischemic stroke still remains unclear. In this study, we aimed to investigate the effect and the underlying mechanism of orexin-A on Glu uptake in astrocytes in vitro and this effect on protecting the neurons from anoxia/hypoglycemic injury. The expression of GLT-1 significantly increased in the astrocytes with orexin-A treatment under anoxia/hypoglycemic conditions, promoting the uptake of Glu and inhibiting the apoptosis of co-cultured cells of astrocytes and neurons. However, these effects were significantly weakened by treatment with orexin-A receptor 1 (OX1R) antagonist. Orexin-A significantly up-regulated the expressions of PKCα and ERK1/2 under anoxia/hypoglycemic conditions in astrocytes, whereas the OX1R antagonist markedly reversed the effect. Furthermore, PKCα or ERK1/2 inhibitor significantly constrained the GLT-1 expression in astrocytes and facilitated the apoptosis of co-cultured cells, and GLT-1 overexpression could reverse those effects of PKCα or ERK1/2 inhibitor. Taken together, orexin-A promoted the GLT-1 expression via OX1R/PKCα/ERK1/2 pathway in astrocytes and protected co-cultured cells against anoxia/hypoglycemic injury. [ABSTRACT FROM AUTHOR]

Opiate withdrawal syndrome is temporally associated with the hyperactivity of locus coeruleus neurons. Previous studies have shown that this hyperactivity, at least in part, results from the activity of excitatory afferents which mainly include the orexinergic neurons of hypothalamus and glutamatergic neurons of paragigantocellularis (PGi) nucleus. The effect of intra LC orexin type 1 receptor antagonism was investigated on expression of glutamate-induced morphine withdrawal-like signs in rats. Regarding the involvement of both orexin and LC in modulation of circadian rhythm, experimental procedures were performed during the rest (day) and the active (night) phases. Male Wistar rats (250–300 g) received escalating doses (6, 16, 26, 36, 46, 56, 66 mg/kg, 2 ml/kg) of morphine sulfate subcutaneously for 7 days. Then, glutamate (100 nM, 200 nl) was microinjected into the LC region and the subsequent behavioral manifestations were visually monitored in both rest and active phases. SB-334867 (as a selective orexin type 1 receptor antagonist) was microinjected into the LC prior to glutamate administration. Results indicate that intra-LC microinjection of glutamate elicits morphine withdrawal-like behavioral signs in rats. It is noteworthy that this effect was significantly suppressed in rats pretreated with SB-334867 only during the active phase. It could be concluded that orexin-A plays a role in expression of glutamate-induced opiate withdrawal-like signs and differential orexinergic tone during the rest and active phases might explain the observed difference in activity of LC neurons. [ABSTRACT FROM AUTHOR]

Introduction: Chaihu-Longgu-Muli decoction (CLMD) is a well-used ancient formula originally recorded in the "Treatise on Febrile Diseases" written by the founding theorist of Traditional Chinese Medicine, Doctor Zhang Zhongjing. While it has been used extensively as a therapeutic treatment for neuropsychiatric disorders, such as insomnia, anxiety and dementia, its mechanisms remain unclear., Methods: In order to analyze the therapeutic mechanism of CLMD in chronic renal failure and insomnia, An adenine diet-induced chronic kidney disease (CKD) model was established in mice, Furthermore, we analyzed the impact of CLMD on sleep behavior and cognitive function in CKD mice, as well as the production of insomnia related regulatory proteins and inflammatory factors., Results: CLMD significantly improved circadian rhythm and sleep disturbance in CKD mice. The insomnia related regulatory proteins, Orexin, Orexin R1, and Orexin R2 in the hypothalamus of CKD mice decreased significantly, while Orexin and its receptors increased remarkably after CLMD intervention. Following administration of CLMD, reduced neuron loss and improved learning as well as memory ability were observed in CKD mice. And CLMD intervention effectively improved the chronic inflflammatory state of CKD mice., Discussion: Our results showed that CLMD could improve sleep and cognitive levels in CKD mice. The mechanism may be related to the up-regulation of Orexin-A and increased phosphorylation level of CaMKK2/AMPK, which further inhibits NF-κB downstream signaling pathways, thereby improving the disordered inflammatory state in the central and peripheral system. However, More research is required to confirm the clinical significance of the study., Competing Interests: The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Cao, Peng, Li, Ding, Wang, Wang, Xiong, Xiong, Li and Song.)

Objective: This study was designed to analyze the associations of serum Orexin-A level with cognitive function and serum inflammatory cytokines in epileptic patients., Methods: Totally 77 epileptic patients treated in Suqian First Hospital between January 2019 and January 2022 were retrospectively analyzed as the observation group, and 65 healthy individuals who had a physical examination in Suqian First Hospital during the same period were enrolled as the control group. The Mini-Mental State Examination (MMSE) was conducted in participants in the two groups, and the enzyme-linked immunosorbent assay (ELISA) was conducted for quantifying serum Orexin-A, interleukin-1β (IL-1β), interleukin-6 (IL-6), and tumor necrosis factor-α (TNF-α). Additionally, the Pearson correlation test was used for analyzing the associations of Orexin-A with MMSE, IL-1β, IL-6, and TNF-α in the patients, and receiver operating characteristic (ROC) curves were drawn for determining the diagnostic value of Orexin-A in epilepsy and cognitive dysfunction in epileptic patients. The independent risk factors for cognitive impairment in epileptic patients were analyzed by multivariate logistic regression analysis., Results: Epileptic patients showed a significantly lower serum Orexin-A level than the control group (P < 0.05), and the area under the curve (AUC) of Orexin-A in epilepsy diagnosis was 0.879. Additionally, epileptic patients had notably lower MMSE scores than the control group (P < 0.05). The Pearson correlation test revealed a positive association of Orexin-A with MMSE score and negative correlations of Orexin-A with IL-1β, IL-6, and TNF-α levels (P < 0.05). The AUC of Orexin-A in diagnosing cognitive dysfunction in epileptic patients was 0.908. According to multivariate analysis, lower education level, more severe EEG abnormalities and a lower Orexin-A level were independent risk factors for cognitive impairment in epileptic patients., Conclusion: Orexin-A can act as a diagnostic marker for epileptic patients, and its level is positively related with cognitive function of patients, but negatively related to the degree of inflammation. It is promising to be an early warning index for epilepsy and cognitive dysfunction in patients., Competing Interests: None., (AJTR Copyright © 2023.)

Introduction: Orexin neuropeptide has a role in opioid withdrawal behaviors. Orexin-expressing neurons that are present in the hypothalamic nuclei send dense projections to the Locus Coeruleus (LC). Withdrawal syndrome is temporally associated with hyperactivity of LC neurons. LC neurons do not show withdrawal-induced hyperactivity in brain slices from morphine-dependent rats. Thus, it has been suggested that the increase in LC neuronal activity seen in vivo is mediated by extrinsic factors. Therefore, this study was carried out to find whether LC microinjection of orexin-A can induce withdrawal behaviors. Method: Adult male Wistar rats were used in this study. Intra-LC microinjection of orexin-A or orexin-A vehicle was performed one week after LC cannulation. Thereafter, somatic signs of withdrawal were evaluated during a period of 25 min.Findings: Orexin-A induced several signs of morphine withdrawal. Conclusion: It may be concluded that orexin at LC acts as an extrinsic factor in the expression of morphine withdrawal syndrome.

[Display omitted] • Prolonged effect of acute morphine treatment on LC neurons was studied. • Acute morphine exposure decreased firing rate of LC neurons after 24 h. • In LC, the rise and decay slopes of action potential were decreased and half-width was increased by morphine. • Morphine injection did not affect first spike latency and rheobase current in LC neurons. • Morphine injection prevented the excitatory effect of OXA on postsynaptic currents of LC neurons. Administration of morphine is associated with critical complications in clinic which primarily includes the development of dependence and tolerance even following a single dose (acute) exposure. Behavioral and electrophysiological studies support the significant role of locus coeruleus (LC) neurons in tolerance and dependence following chronic morphine exposure. The current study was designed to explore the electrophysiological properties of the LC neurons following acute morphine exposure. In-vitro whole-cell patch-clamp recordings were performed in LC neurons 24 h after intraperitoneal morphine injection. Acute morphine injection significantly decreased the spontaneous firing rate of LC neurons, the rising and decay slopes of action potentials, and consequently increased the action potential duration. In addition, morphine treatment did not alter the rheobase current and first spike latency while affected the inhibitory postsynaptic currents elicited in response to orexin-A. In fact, single morphine exposure could inhibit the disinhibitory effect of orexin-A on LC neurons. [ABSTRACT FROM AUTHOR]

AIM: Orexin, a neuropeptide, regulates sleep-wake cycle, energy homeostasis, analgesia, learning, and memory. Orexins cause depolarization in neurons and increase in firing frequencies of neurons. In the present study, we aimed to investigate the effect of Orexin-A, an orexin receptor agonist, on absence epilepsy models of WAG/Rij rats. METHODS: The rats were anesthetized with ketamine (90 mg/kg) and xylazine (10 mg/kg), and electrodes were placed after the coordinates were determined according to the bregma points of animals placed on the stereotaxic device. Records were taken from the operated animals after a 7-day recovery period. After 3 hours of baseline recording, 4, 8, and 16 μg doses of Orexin-A were injected intracerebroventricular (i.s.v.) and recorded for another 3 hours. RESULTS: The number of spike-wave discharges (SWDs) ± SEM 140th minute value after DMSO was 66.6 ± 4.7 clusters/20 min. Orexin-A (4 μg, 1.33 μl) post-injection SWDs 140th minute value was 27.9 ± 8.7 and when compared with control group, it was observed that it decreased statistically from the 100th minute to the end of the recording (p<0.05). Orexin-A (8 μg, 2.66 μl) postinjection SWD's 140th-minute value was 17.9 ± 8.9 and postinjection from the 20th minute it was found to decrease the number of SWDs according to control group. Orexin-A (16 μg, 5.33 μl) post-injection SWDs 140th minute value 19.6 ± 6.0, and it was observed that the number of SWDs was statistically reduced compared to control group from the 20th minute after the injection. CONCLUSION: Although the effect of 4 μg of Orexin-A has weak, all doses of Orexin-A showed anticonvulsant effects. Since there was no statistical difference in effect between 8 μg and 16 μg, the lower dose of 8 μg was accepted as the effective dose. The results of the study of Celli et al. support our study. [ABSTRACT FROM AUTHOR]

Irisin, the soluble secreted form of fibronectin type III domain containing 5 (FNDC5)-cleaved product, is a recently identified adipo-myokine that has been indicated as a possible link between physical exercise and energetic homeostasis. The co-localization of irisin with neuropeptide Y in hypothalamic sections of paraventricular nucleus, which receives NPY/AgRP projections from the arcuate nucleus, suggests a possible role of irisin in the central regulation of energy balance. In this context, in the present work we studied the effects of intra-hypothalamic irisin (1 μl, 50–200 nmol/l) administration on feeding and orexigenic [agouti-related peptide (AgRP), neuropeptide Y (NPY) and orexin-A] and anorexigenic [cocaine and amphetamine-regulated transcript (CART) and proopiomelanocortin (POMC)] peptides in male Sprague-Dawley rats. Furthermore, we evaluated the effects of irisin on hypothalamic dopamine (DA), norepinephrine (NE) and serotonin (5-hydroxytryptamine, 5-HT) concentrations and plasma NE levels. Compared to vehicle, irisin injected rats showed decreased food intake, possibly mediated by stimulated CART and POMC and inhibited DA, NE and orexin-A, in the hypothalamus. We also found increased plasma NE levels, supporting a role for sympathetic nervous system stimulation in mediating increased oxygen consumption by irisin. [ABSTRACT FROM AUTHOR]

Orexins are hypothalamic neuropeptides involved in the central regulation of feeding behavior, sleep-wake cycle and other physiological functions. Orexin-A can regulate energy metabolism and increase glucose uptake, suggesting a role in glucose metabolism. In this study, we investigated the effects of orexin-A on GLUT4 mRNA and protein levels and the intracellular signaling mechanisms mediating orexin-A activity in the hepatocytes of grouper. Our results demonstrate that intraperitoneal injection of orexin-A increased the expression of GLUT4 in the liver, and this effect was significantly enhanced by co-injection of glucose. Treatment of primary cultured hepatocytes with either orexin-A or glucose alone had no effect on the expression of GLUT4, while co-treatment with orexin-A and glucose significantly increased the expression of GLUT4. This stimulatory effect was partially blocked by inhibitors to ERK1/2, JNK or p38 MAPK and was further blocked by an orexin receptor antagonist, which indicates that orexin-A could stimulate the expression of GLUT4 in a glucose dependent manner in primary hepatocytes via ERK1/2, JNK and p38 signaling. Our results suggest that orexin-A could play a pivotal role in stimulating glucose utilization in grouper, for a long-term goal, which might be useful in reducing costs in the aquaculture industry. [ABSTRACT FROM AUTHOR]

Orexin is a member of neuropeptides which was first identified in the hypothalamus. The globus pallidus is a key structure in the basal ganglia, which is involved in both normal motor function and movement disorders. Morphological studies have shown the expression of both OX1 and OX2 receptors in the globus pallidus. Employing single unit extracellular recordings and behavioural tests, the direct in vivo electrophysiological and behavioural effects of orexin-A in the globus pallidus were studied. Micro-pressure administration of orexin-A significantly increased the spontaneous firing rate of pallidal neurons. Correlation analysis revealed a negative correlation between orexin-A induced excitation and the basal firing rate. Furthermore, application of the specific OX1 receptor antagonist, SB-334867, decreased the firing rate of pallidal neurons, suggesting that endogenous orexinergic systems modulate the firing activity of pallidal neurons. Orexin-A increased the excitability of pallidal neurons through both OX1 and OX2 receptors. In 6-hydroxydopamine parkinsonian rats, orexin-A-induced increase in firing rate of pallidal neurons was stronger than that in normal rats. Immunostaining revealed positive OX1 receptor expression in the globus pallidus of both normal and parkinsonian rats. Finally, postural test showed that unilateral microinjection of orexin-A led to contralateral deflection in the presence of systemic haloperidol administration. Further elevated body swing test revealed that pallidal orexin-A and SB-334867 induced contralateral-biased swing and ipsilateral-biased swing respectively. Based on the electrophysiological and behavioural findings of orexin-A in the globus pallidus, the present findings may provide a rationale for the pathogenesis and treatment of Parkinson's disease. [ABSTRACT FROM AUTHOR]

Orexin-A is mainly produced in the lateral hypothalamus (LHA) and the perifornical area (PeF). Here, we aim to elucidate the effects of orexin-A in the hippocampus (Hi) on gastric distention (GD)-sensitive neurons and gastric motility, and potential regulation mechanisms by the PeF. Retrograde tracing and fluorescent-immunohistochemical staining were used to determine orexin-A neuronal projections. Single unit discharges in the Hi were recorded extracellularly and gastric motility in conscious rats was monitored during administration of orexin-A to the Hi or electrical stimulation of the PeF. Orexin-A administration to the Hi excited most of the GD-excitatory (GD-E) neurons and GD-inhibitory (GD-I) neurons, and increased gastric motility in a dose-dependent manner. All of effects induced by orexin-A could be partly blocked by pretreatment with orexin-A antagonist, SB-334867. Electrical stimulation of the PeF excited the majority of the orexin-A-responsive GD neurons in the Hi and promoted gastric motility. Additionally, pretreatment with SB-334867 in the Hi increased the firing rate of GDI and GDE neurons following electrical stimulation of the PeF. These findings suggest that orexin-A could regulate activities of GD-sensitive neurons and gastric motility. Furthermore, the PeF may be involved in this regulatory pathway. [ABSTRACT FROM AUTHOR]

Hypothalamic orexin neurons project to numerous brain areas, including the ventral tegmental area (VTA), which is involved in motivation and food-seeking behavior. Here we address how exogenously administered orexin-A and endogenous orexin 1 receptor (OX1R) activation in the VTA affects feeding behavior. We hypothesized that orexin-A and OX1R antagonist SB334867 delivered to the VTA, at doses that were subthreshold for effect when injected into the ventricle, would affect intake of palatable foods in multiple test situations. We first used a hedonic feeding model in which satiated rats selectively consume a high-fat diet (HFD). Intra-VTA orexin-A stimulated additional consumption of chow and increased HFD intake in this model. In ad libitum-fed rats given daily 30-min test sessions, intra-VTA orexin-A also increased intake of HFD and 0.1 M sucrose. Further analysis of licking patterns revealed that that VTA orexin-A increased meal size and licking burst size only toward the end of the meal. Consistent with this finding, a subthreshold dose of VTA orexin-A prevented intake suppression induced by gastrointestinal nutrient infusion. Surprisingly, intra-VTA orexin-A had no effect on operant responding for sucrose pellets on a progressive ratio schedule of reinforcement. A role for endogenous VTA OX1R stimulation is supported by our finding that bilateral VTA injection of the selective OX1R antagonist SB334867 suppressed 0.1 M sucrose intake. Together, our data suggest that OX1R activity in the VTA facilitates food intake, potentially by counteracting postingestive negative feedback that would normally suppress feeding later in a meal. [ABSTRACT FROM AUTHOR]

Hypocretin-1 (HC, orexin-A) is a neuropeptide involved in regulating physiological functions of sleep, appetite and arousal, and it has been shown that intranasal (IN) administration can target HC to the brain. Recent clinical studies have shown that IN HC has functional effects in human clinical trials. In this study, we use rats to determine whether IN HC has an immediate effect on food consumption and locomotor activity, whether distribution in the brain after IN delivery is dose-dependent, and whether MAPK and PDK1 are affected after IN delivery. Food intake and wheel-running activity were quantified for 24 h after IN delivery. Biodistribution was determined 30 min after IN delivery of both a high and low dose of 125I-radiolabelled HC throughout the brain and other bodily tissues, while Western blots were used to quantify changes in cell signaling pathways (MAPK and PDK1) in the brain. Intranasal HC significantly increased food intake and wheel activity within 4 h after delivery, but balanced out over the course of 24 h. The distribution studies showed dose-dependent delivery in the CNS and peripheral tissues, while PDK1 was significantly increased in the brain 30 min after IN delivery of HC. This study adds to the growing body of evidence that IN administration of HC is a promising strategy for treatment of HC related behaviors. [ABSTRACT FROM AUTHOR]

The orexins system consists of two G-protein coupled receptors (the orexin-1 and the orexin-2 receptor) and two neuropeptides, orexin-A and orexin-B. Orexin-A is an excitatory neuropeptide that regulates arousal, wakefulness and appetite. Recent studies have shown that orexin-A may promote gastric motility. We aim to explore the effects of orexin-A on the gastric -distension (GD) sensitive neurons and gastric motility in the lateral hypothalamic area (LHA), and the possible regulation by the paraventricular nucleus (PVN). Extracellular single unit discharges were recorded and the gastric motility was monitored by administration of orexin-A into the LHA and electrical stimulation of the PVN. There were GD neurons in the LHA, and administration of orexin-A to the LHA could increase the firing rate of both GD-excitatory (GD-E) and GD-inhibited (GD-I) neurons. The gastric motility was significantly enhanced by injection of orexin-A into the LHA with a dose dependent manner, which could be completely abolished by pre-treatment with orexin-A receptor antagonist SB334867. Electrical stimulation of the PVN could significantly increase the firing rate of GD neurons responsive to orexin-A in the LHA as well as promote gastric motility of rats. However, those effects could be partly blocked by pre-treatment with SB334867 in the LHA. It is suggested that orexin-A plays an important role in promoting gastric motility via LHA. The PVN may be involved in regulation of LHA on gastric motility. [ABSTRACT FROM AUTHOR]

It is widely accepted that the spinal trigeminal nuclear complex, especially the subnucleus caudalis (Vc), receives input from orofacial structures. The neuropeptides orexin-A and -B are expressed in multiple neuronal systems. Orexin signaling has been implicated in pain-modulating system as well as learning and memory processes. Orexin 1 receptor (OX1R) has been reported in trigeminal nucleus caudalis. However, its roles in trigeminal pain modulation have not been elucidated so far. This study was designed to investigate the role of Vc OX1R in the modulation of orofacial pain as well as pain-induced learning and memory deficits. Orofacial pain was induced by subcutaneous injection of capsaicin in the right upper lip of the rats. OX1R agonist (orexin-A) and antagonist (SB-334867-A) were microinjected into Vc prior capsaicin administration. After recording nociceptive times, learning and memory was investigated using Morris water maze (MWM) test. The results indicated that, orexin-A (150 pM/rat) significantly reduced the nociceptive times, while SB334867-A (80 nM/rat) exaggerated nociceptive behavior in response to capsaicin injection. In MWM test, capsaicin-treated rats showed a significant learning and memory impairment. Moreover, SB-334867-A (80 nM/rat) significantly exaggerated learning and memory impairment in capsaicin-treated rats. However, administration of orexin-A (100 pM/rat) prevented learning and memory deficits. Taken together, these results indicate that Vc OX1R was at least in part involved in orofacial pain transmission and orexin-A has also a beneficial inhibitory effect on orofacial pain-induced deficits in abilities of spatial learning and memory. [ABSTRACT FROM AUTHOR]

Objective: To investigate the effect of orexin-A microinjected into the paraventricular nucleus of the hypothalamus (PVN) on body weight in rats. Methods: Chronic guide cannulae were implanted into PVN of rats. Orexin-A was microinjected into the brain site. The effect of orexin-A on body weight in rats was detected. Results: The loss of body weight in orexin-A-treated rats was more significantly than their vehicle-injected counterparts (P<0.05）, but they had no difference in food intake (P＞0.05). The rats were more significantly active after intra-PVN orexin microinjection compared to vehicle（P<0.05）. Conclusion: Orexin-A microinjected into the paraventricular nucleus of the hypothalamus (PVN) can induce weight loss in rats through producing negative energy balance via the increase of physical activity. [ABSTRACT FROM AUTHOR]

The aim of present study was to investigate the involvement of orexin-A neuropeptide in naloxone-induced morphine withdrawal syndrome via modulating neurons bearing GABA A receptors. The locus coeruleus (LC) is a sensitive site for expression of the somatic aspects of morphine withdrawal. Intra-LC microinjection of GABA A receptor agonist attenuates morphine withdrawal signs in rats. Here we studied the influence of LC orexin type 1 receptors blockade by SB-334867 in presence of bicuculline, a GABA A receptor antagonist, on naloxone-induced morphine withdrawal syndrome. Adult male Wistar rats, weighing 250–300 g, were rendered dependent on morphine by subcutaneous (s.c.) injection of increasing morphine doses (6, 16, 26, 36, 46, 56 and 66 mg/kg, 2 ml/kg) at set intervals of 24 h for 7 days. On 8th day, naloxone (3 mg/kg, s.c.) was injected and the somatic signs of morphine withdrawal were evaluated. Intra-LC microinjections (0.2 μl) of either bicuculline (15 μM) or SB-334867 (3 mM) or a combination of both chemicals were done immediately before naloxone injection. Intra-LC microinjection of bicuculline (15 μM) had no significant effect on morphine withdrawal signs, whereas intra-LC microinjection of SB-334867 considerably attenuated morphine withdrawal signs. However, the effect of SB-334867 in attenuating naloxone-induced morphine withdrawal signs was blocked in presence of bicuculline. This finding, for the first time, indicated that orexin-A may participate in expression of naloxone-induced morphine withdrawal syndrome partly through decreasing the activity of neurons bearing GABA A receptors. [ABSTRACT FROM AUTHOR]

Objective: To observe the effect and mechanism of intracerebroventricular(icv) injection of Orexin-A on gastric motility in rats. Methods: 50 adult male rats were randomly divided into five groups, namely normal saline(NS), 1 μg, 5 μg, 10 μg and 20 μg group. Two strain gauge transducers were attached on the antrum and duodenum to record circular muscle contractions. Spontaneous gastroduodenal contractions were recorded in freely moving conscious rats. Through icv injection of OXA, observed the changes in the gastrointestinal circular muscle motion wave form and duration in rats. 10 rats were randomly divided into two groups, one group with subcutaneous injection of NS + icv injection of 10 μg OXA, another group with subcutaneous injection of atropine + icv injection of 10 μg OXA, to observe the effects on gastrointestinal motility. Similarly selecting 10 rats were divided into sham group + 10 μg OXA group,vagotomy + 10 μg OXA group, which was used to elucidate the neural pathways of OXA. Then selecting 10 rats, first icv injection of NS then icv injection of OXA antagonist SB334867, observed the effect of endogenous OXA on gastrointestinal motility. Results: OXA(1-20 μg) disrupted the interdigestive phase III-like contractions and induced an irregular postprandial-like motility pattern in the stomach and duodenum. The stimulatory effect of OXA on gastroduodenal postprandial-like motility pattern was abolished by atropine and truncal vagotomy(P<0.05). Central administration(icv) of selective OXA receptor antagonist, SB-334867(16 μg), enhanced gastric spontaneous phase III-like contractions(P<0.05). Conclusion: Central administration of OXA changes GI motor pattern from interdigestive to postprandial via the vagal cholinergic pathways. Endogenous OXA may inhibit in interdigestive GI motility in rats. [ABSTRACT FROM AUTHOR]

Background and aims Orexins/hypocretins are orexigenic peptides implicated in the regulation of feeding behavior and the sleep/wake cycle. Little is known about the functioning of these peptides in anorexia nervosa (AN). The aims of the current study were to evaluate the extent to which orexin-A might be linked to sleep and treatment outcome in AN. Method Fasting plasma orexin-A concentrations were measured in 48 females with AN at the start of a day hospital treatment and in 98 normal-eater/healthy-weight controls. The Pittsburgh Sleep Quality Index was administered at the beginning of the treatment as a measure of sleep quality. Other psychopathological variables were evaluated with the Symptom Checklist-Revised (SCL90R) and the Eating Disorder Inventory-2 (EDI). Patients were assessed at the start and end of treatment by means of commonly used diagnostic criteria and clinical questionnaires. Results The AN patients presented more sleep disturbances and poorer overall sleep quality than did the healthy controls ( p = .026) but there were no global differences between groups in plasma orexin-A concentrations ( p = .071). In the AN sample, orexin-A concentrations were associated with greater sleep disturbances (| r | = .30), sleep inefficiency (| r | = .22) and poorer overall sleep (| r | = .22). Structural Equation Modeling (SEM) showed that both elevated orexin-A concentrations and inadequate sleep predicted poorer treatment outcome. Conclusion Plasma orexin-A concentrations contribute to poor sleep quality in AN, and both of these variables are associated with therapy response. [ABSTRACT FROM AUTHOR]

This study investigated the effect of orexin-A on the renal dysfunction and histological damage induced by ischaemia/reperfusion at an early stage. Pentobarbital anaesthetised rats were prepared for measuring renal functional variables. Ischaemia was induced by bilateral renal artery clamping for 30 min followed by a 1-h reperfusion period. In orexin-treated rats, it was infused (i.v.) at 500 pmol kg min from starting pre-ischaemic (pretreatment) clearance period. The left kidney was examined using light microscopy. The renal ischaemic challenge resulted in major histological damages, which were associated with decreased creatinine clearance, absolute potassium-excretion and effective free-water reabsorption, but increased fractional sodium-excretion and urine flow during reperfusion period. In orexin-treated rats, the histological damage to the kidneys was improved along with the decrease in creatinine clearance and increase in fractional sodium-excretion being smaller, but the increase in urine flow being larger than those of the non-treated rats, while absolute potassium-excretion and effective free-water reabsorption were equal to those of the sham-operated rats. Orexin-A exhibited a renoprotective effect against ischaemia/reperfusion-induced lesions probably via inhibition of post-ischaemic intrarenal vasoconstriction. [ABSTRACT FROM AUTHOR]

Objective: The aim of the study was to demonstrate whether blood Orexin A levels (OX-AL), which are a marker of hypothalamic activity, are altered in patients with migraine and whether they differ ictally and interictally and with the chronification of migraine. Materials and Methods: A total of 113 patients participated in this study. Orexin A blood samples were taken during a headache-free interval. In 17 patients with episodic migraine a second blood sample for Orexin A was taken during an attack of migraine. Results: OX-AL were lower in episodic migrane compared to controls but did not differ during an attack and the interictal period. Conclusion: Our findings of low OX-AL in episodic migrane both ictally and interictally, similar levels of OX-AL in chronic migraine and tension-type headache compared to controls may suggest that OX-AL is probably not released in response to acute pain but its basal levels may modulate the susceptibility to pain. Basal OX-AL are low in patients with episodic migrane which could reflect a suppression of the orexinergic system due to hypothalamic dysfunction but increase with chronification possibly in response to lower Orexin-A receptor density secondary to neurodegeneration. Further larger studies may shed more light on the role of the orexinergic system and the hypothalamus in migraine and the chronification of it. [ABSTRACT FROM AUTHOR]

Objectives: To investigate the role of the locus coeruleus (LC) in enhanced orexin-A induced spontaneous activities of obesity-resistant rats and its mechanism and further explore whether LC associated with obesity resistance. Methods: Male Sprague-Dawley and selectively bred OR rats were used. A 26-gauge stainless steel cannula was directed towards the LC of rats. Orexin-A and the vehicle was injected through the cannula tract. And then, measured SPA, Indirect Calorimetry, total fat and fat-free mass. Adiposity was expressed by percent body fat. Results: Compared with SD rats, the OR rats had significantly lower body weight, fat and fat-free mass (P<0.05). OR rats showed significantly less adiposity (P<0.05) than SD rats. OR rats spent more time ambulating at 3 month of age and spent more time vertical at 6 months of age. This resulted in OR rats spending significantly more time moving as increase of age (P<0.05). After the injection of orexin-A, SPA of OR rats was higher than SD rats cause ambulating of OR rats significantly more than vertical activities. The OR rats have higher SPA, lower body weight, and yet the same daily energy expenditure as Sprague-Dawley rats which suggests that OR rats expend more energy on activities during the dark period. In OR rats, the two highest doses of orexin-A increased SPA significantly (P ＜0.05 for both doses) and this was dose dependent. In contrast, in Sprague-Dawley rats only the highest dose of orexin-A significantly increased SPA relative to vehicle (P ＜0.05). The two highest doses of orexin-A significantly increased SPA more robustly in OR rats relative to SD rats (250 pmol: P＜0.05; 500 pmol: P＜0.05). Conclusion: Orexin-A infused into the LC stimulated SPA and related to obesity resistance. [ABSTRACT FROM AUTHOR]

The aim of this study was to evaluate the effects of orexin-A (OX-A) on behavioral and pathological parameters and on gene expression of some multiple sclerosis-related peptides in a model of experimental autoimmune encephalomyelitis (EAE). EAE was induced by subcutaneous administration of MOG 35–55. Following immunization, the treatment was initiated by using SB.334867 (orexin-1 receptor antagonist) and/or OX-A. Locomotor activity and exploratory behaviors were monitored using open field and T-maze continuous alternation task (T-CAT) respectively. Pain sensitivity was assessed by hot-plate test. Histopathological assessments were performed by H&E staining. The expression of TGF-β, MBP, MMP-9, IL-12, iNOS and MCP-1 were measured using real-time PCR method in lumbar spinal cord. OX-A administration in EAE mice remarkably attenuated the clinical symptoms, increased latency response in hot plate test, inhibited infiltration of inflammatory cells, up-regulated mRNA expression of TGF-β as well as MBP and down-regulated mRNA expression of iNOS, MMP-9 and IL-12. In contrast SB.334867 administration in EAE mice deteriorated the clinical symptoms, decreased the alternation in T-CAT, increased infiltration of inflammatory cells, down-regulated mRNA expression of TGF-β and MBP and up-regulated mRNA expression of iNOS. Results of this study suggest that the orexinergic system might be involved in pathological development of EAE. These findings suggest orexinergic system as a potential target for treatment of multiple sclerosis. [ABSTRACT FROM AUTHOR]

Objective: To investigate the effects of the fourth ventricle injection of orexin-A (OXA) on food-conditioned place preference in rats. Method: 30 SD male rats were randomly divided into three groups: the control group, low-dose group and high-dose group. The fourth ventricle were injected with saline (NS), orexin-A or orexin-A receptor antagonist SB334867, observed changes of sucrose lever presses and breakpoint of rats. Then selecting 15 rats with fourth ventricle injection orexin-A or SB334867 was observed the effects on HF food intake during daily 1-h tests. At last, 30 rats with fourth ventricle injection orexin-A or SB334867, the rats were placed in conditioned place preference box to detect expression of the place preference of rats with HF food. Results: Compared with the control group, after 24 hours of fasting, The sucrose lever presses and breakpoint of rats were significantly increased through fourth ventricle injection of orexin-A (P<0.05). But SB334867 significantly reduced sucrose lever presses and breakpoint (P<0.05). The HF intake of rats was significantly increased with fourth ventricle injection of orexin-A (P<0.05), while SB334867 did not affect the HF intake, however SB334867 would inhibit chow intake (P<0.05). The expression of HF food-conditioned place preference of rats was enhanced through fourth ventricle injection of orexin-A, while SB334867 inhibited this effect(P<0.05). Conclusion: The Fourth ventricle injection of Orexin-A may affect feeding behavior in rats, increase the intake of HF food, and enhance the expression of HF food-conditioned place preference. [ABSTRACT FROM AUTHOR]

Objective: To investigate whether the rats given glucose in the intermittent access model(IAM) can cause hedonic feeding including bingeing, and the influence of nucleus accumbens and lateral hypothalamic(LHA) orexin(ORX)neurons on fructose eating behavior. Methods: The IAM rats were given 4 %, 8 % or 12 % fructose or Saline(NS). And the fructose intake and fructose eating behavior were observed and recorded in the rats. The receptors number(Bmax) and receptor affinity(Kd) of dopamine D1R and D2R were analyzed in the nucleus accumbens shell, nucleus accumbens core and dorsal striatum. The C-Fos neurons immunoreactivity(Fos-IR)were recorded in paraventricular nucleus, amygdala, nucleus accumbens of related nucleus of the long-term and short-term IAM rat. Food intake was observed while administration of OX1 R antagonist SB334867 in the long term IAM rats. Results: The rats given fructose solutions displayed fructose bingeing but unaltered DA D1R or D2R number following long-term exposure to the IAM. Fructose bingeing rats, as compared to chow bingeing controls, exhibited reduced nucleus accumbens neuron activation, as determined by c-Fos-immunoreactivity. Following short-term access to the IAM, rats exhibited bingeing but unchanged Fos-IR. Fructose bingeing and food intake were significantly reduced while OX1 R antagonist SB-334867(30 mg/kg) were administrated for 21 days in the IAM rats.Conclusion: Long-term fructose bingeing can increase the release of Orexin, reduce the nucleus accumbens Orexin neuron activation,enhance the lateral nucleus Orexin neurons activation. [ABSTRACT FROM AUTHOR]

Objective: To investigate the central and peripheral effects of endogenous Orexin-A(OXA) on gastric motility in rats.Methods: Selecting adult Wistar rats for the study, the synthesis of endogenous OXA was induced by fasting. Plasma OXA concentration was measured by radioimmunoassay. Rats were pretreated with OXA receptor antagonist SB-334867 prior to measurement to observe the effect of OXA.Vagotomy was used to observe vagus nerve-mediated effects. Gastric emptying was measured by spectrophotometric methods. One strain gauge transducers were attached on the antrum to record interdigestive gastric motility. Preproorexin(PPO)expression in stomach and hypothalamus were tested by Western blot. Results: After fasting 18 h, the level of plasma OXA and PPO protein expression were significantly increased(P<0.05). The highest level of plasma OXA and PPO protein expression appeared in 36 h fasting groups(P<0.01). Endogenous OXA promoted gastric emptying(P<0.05), inhibited gastric interdigestive motility(P<0.05). As these effects were abolished with injection of SB-334867, but no effect on PPO expression. Vagotomy surgery did not block endogenous OXA-mediated effects(P>0.05). Conclusion: Fasting can induce the synthesis of endogenous OXA. Endogenous OXA can accelerate gastric emptying, but it suppressed interdigestive gastric motility. [ABSTRACT FROM AUTHOR]

Objective(s): Reduction of pharmacological effectiveness or tolerance appears following repeated administration of many analgesic drugs. We investigated tolerance to anti-nociceptive effects of orexin-A, an endogenous potent analgesic peptide using the hot-plate test. Materials and Methods: Orexin-A was microinjected ICV (intracerebroventricular) with an interval of 12 hr for 7 continuous days and its anti-nociceptive responses were measured on days 1, 4 and 7 using the hot-plate test following the first day of administration. Orexin-A was used at a dose of 100 pmol to induce analgesic effects. Results: ICV administration of orexin-A produced an effective anti-nociception on the first day of experiment as measured by hot-plate 5, 15, and 30 min after the injection, in comparison with both baselines (hot-plate test one day before the beginning of orexin-A administration and control, saline- administrated group). However, repeated administration of orexin-A on the following days revealed a significant reduction in this analgesic effect during day 4 to day 7. However, to rule out any associative tolerance resulting from learning related to experimental procedures and/or environmental cues, a single injection of orexin-A was administrated to animals of control group (which were receiving saline during 7 days of experiments) and the analgesic effect was observed. Conclusion: These results, for the first time, indicated the appearance of tolerance to anti-nociceptive effects of orexin-A, following repeated administrations of this agent. [ABSTRACT FROM AUTHOR]