Orexin Research Articles

Positive association between plasmatic levels of orexin A and the endocannabinoid-derived 2-arachidonoyl lysophosphatidic acid in Alzheimer's disease.

A regular sleep-wake cycle plays a positive function that preserves synaptic plasticity and brain activity from neuropathological injuries. The hypothalamic neuropeptide orexin-A (OX-A) is central in sleep-wake regulation and has been found to be over-expressed in the cerebrospinal fluid (CSF) of patients with Alzheimer's disease (AD) suffering from sleep disturbances. OX-A promotes the biosynthesis of 2-arachidonoylglycerol (2-AG), which, in turn, could be phosphorylated to 2-arachidonoyl lysophosphatidic acid (2-AGP). The reorganization of the actin cytoskeleton during neurite retraction is one of the best-characterized effects of lysophosphatidic acids. However, less information is available regarding the reorganization of the neuronal microtubule network in response to OX-A-induced 2-AG and, possibly consequent, 2-AGP production in AD patients. This is of special relevance also considering that higher 2-AG levels are reported in the CSF of AD patients. Here, we found a positive correlation between OX-A and 2-AGP concentrations in the plasma, and an increase of 2-AGP levels in the CSF of AD patients. Furthermore, a negative correlation between the plasmatic 2-AGP levels and the mini-mental state examination score is also revealed in AD patients. By moving from the human patients to in vitro and in vivo models of AD we investigated the molecular pathway linking OX-A, 2-AG and 2-AGP to the phosphorylation of pT231-Tau, which is a specific early plasma biomarker of this disorder. By LC-MS analysis we show that OX-A, via OX-1R, induces 2-AG biosynthesis via DAGLα, and in turn 2-AG is converted to 2-AGP in primary hippocampal neurons. By confocal microscopy and western blotting assay we found an OX-A- or 2-AGP-mediated phosphorylation of Tau at threonine 231 residue, in a manner prevented by LPA1R (2-AGP receptor) or OX1R (OX-A receptor) antagonism with AM095 or SB334867, respectively. Finally, by patch-clamp recording we documented that 2-AGP-mediated pT231-Tau phosphorylation impairs glutamatergic transmission in the mouse hippocampus. Although further additional research is still required to clarify the potential role of orexin signaling in neurodegeneration, this study provides evidence that counteraction of aberrant OX-A signaling, also via LPA-1R antagonism, may be beneficial in the mild-to-moderate age-related cognitive decline associated with sleep disturbances.

A Bitter Experience That Enlightens the Future: COVID-19 Neurological Affection and Perspectives on the Orexigenic System

The history of coronaviruses revealed that these viruses caused multiple outbreaks in the past, including a previous severe acute respiratory syndrome (SARS) outbreak in 2003. In 2019, a novel SARS virus, SARS-CoV-2, started a drastic pandemic that, up till now, keeps peaking in successive waves owing to the mutational ability of the virus versus the short-term immunity against it. Although the angiotensin-converting enzyme 2 (ACE2) is the gate through which the virus gets access to human cells, yet ACE2 is deemed protective in lung injury yielding vasodilator, anti-fibrotic, and anti-inflammatory peptides. The viral-provoked ACE2 downregulation aggravated a subsequent potentially lethal cytokine storm. Both the tumor necrosis factor-alpha (TNF-α) receptor (TNFR), activated by the proinflammatory cytokine, TNF-α, released during coronavirus disease 2019 (COVID-19), and ACE2 are cleaved by tumor necrosis convertase enzyme (TACE) to render respective soluble decoy mediators. Several risk factors were linked to COVID-19 morbidity and neurological affection, including obesity and diabetes mellitus (DM), attributed toACE2 overexpression in obesity, a low-grade inflammatory state with both obesity and DM, and defective lung reparative machinery, added to low tissue-to-lung ACE2 expression in DM. The ACE2 shedding by SARS-CoV-2 upon its entry into the brain, together with the inflammatory cytokines invading the brain, predispose to such neurological affection. However, ACE2 was not sufficient to justify the occurrence of neurological disorders with COVID-19, owing to its lower brain expression, relative to other tissues. Other mediators should have contributed to such neurological disorders, of which, orexins (OXs) are discussed, owing to multiple functional similarities to ACE2. Eventually, this review highlights such similarities selected according to their possible relevance to COVID-19 symptomatology and pathology. Both ACE2 and OXs confer anti-inflammatory benefits, reduce cerebral endothelial dysfunction, promote neuronal survival and neurogenesis, and add to their therapeutic potentiality in sepsis. Both ACE2 and OXs assist in moderating the stress responses and the stress-activated hypothalamic-pituitary-adrenal axis. Both ACE2 and OXs are affected by obesity and DM. The loss of ACE2 and OXs signaling was suggested in neuro-inflammatory and neurodegenerative diseases. Of interest is the abundance of OXs in the dissemination routes to the brain, namely, the peripheral olfactory and the enteric systems. The presumptive role of OXs as analgesics and antipyretics might add to their favorable profile. Advantageously, the availability of OXs agonists and antagonists makes it applicable to corroborate or abrogate the future utility of targeting the orexigenic system in terms of COVID-19 neurological affection. Elaborative work, exploring in vitro and in vivo models, is recommended to identify or deny such perspective involvement.

The association between serum orexin-A levels and sleep quality in pregnant women

Objective/backgroundOrexin has been shown to regulate the sleep-wake cycle, and it may play a major role in the pathogenesis of sleep disorders; however, its role in sleep disorders in pregnant women remains unclear. We aimed to assess the relationship between serum orexin-A (OXA) levels and sleep quality in pregnant women. Patients/methodsThis study comprised 214 enrolled pregnant women (poor sleep quality, n = 125; no poor sleep quality, n = 89). We assessed participants’ sleep quality and depression and anxiety levels. OXA levels were measured using enzyme-linked immunosorbent assay. ResultsWomen in the poor sleep quality group showed higher serum OXA levels (0.33[0.3] vs. 0.27[0.11], P < 0.001) than those in the no poor sleep quality group. Binary regression analysis showed that the higher the OXA levels (odds ratio [OR] 1.385, 95% CI [confidence interval] 1.160–1.655) and Zung Self-Rating Anxiety Scale scores (OR 1.073, 95% CI 1.009–1.140), the greater the risk of sleep quality in pregnant women. First-trimester OXA levels differed significantly from those in the second and third trimesters (P < 0.05). ConclusionSerum OXA levels were higher in pregnant women with poor sleep quality than in those without poor sleep quality. OXA levels were also higher in the second and third trimesters than in the first trimester.

Investigating a role of orexin and ‘cocaine- and amphetamine-regulated transcript’ in the nucleus accumbens shell in binge eating of male rats and the relationship with impulsivity

Binge eating disorder (BED) is the most prevalent eating disorder in the adult population. It is characterized by recurrent episodes of uncontrollable overconsumption of palatable food (PF). BED is connected to several comorbidities such as obesity, major depression, and substance use disorder, and was linked to heightened levels of impulsivity. The neurobiological basis of BED is however still vaguely known. Binge eating (BE) occurs without homeostatic needs, and therefore, relates to hedonic consumption of PF. A major brain structure in the control of hedonic feeding, and part of the network regulating impulsive action, is the nucleus accumbens shell (NAcSh). The present study in rats assessed the influence of trait impulsivity on the development of BE-like feeding and the role of the orexigenic neuropeptide orexin (OX) and the anorexigenic neuropeptide cocaine- and amphetamine-regulated transcript (CART) within the NAcSh in a BE-model. The rats were initially ranked for their trait impulsivity based on a screening in the 5-choice serial reaction time task. They were subsequently introduced into a limited access-model to establish BE-like feeding with pure vegetable fat to examine a correlation between trait impulsivity and the development of BE-like feeding. The effect of bilateral infusions of the OX 1-receptor (OX1R) antagonist SB-334867 (SB) and CART-antibodies (CART-ABs) into the NAcSh was examined in relation to trait impulsivity. Further, accumbal OX1R density was evaluated by immunohistochemical staining in rats with normal and BE-like feeding behavior. We found that all animals developed stable BE-like PF intake, independent of trait impulsivity and without differences in the dynamics. The blockade of accumbal OX1Rs effectively reduced PF intake only in the control group that had daily access to PF, with impulsivity trait as a decisive factor, pointing towards alterations in orexinergic transmission in the NAcSh of rats bingeing on pure fat. This was corroborated by a lower density of OX1Rs in the NAcSh of rats with BE-like feeding behavior, precisely, in low-impulsive bingeing rats. Regardless of impulsivity trait, antagonizing CART in the NAcSh did not affect PF intake of control or bingeing animals. This suggests that endogenous accumbal CART does not influence consummatory behavior in ad libitum-fed rats with access to fat, under both normal and BE-like feeding patterns.

Hypocretin/orexin influences chronic sleep disruption injury in the hippocampus.

Chronic sleep disruption is a risk factor for Alzheimer’s disease (AD), yet mechanisms by which sleep disturbances might promote or exacerbate AD are not understood. Short-term sleep loss acutely increases hippocampal amyloid β (Aβ) in wild type (WT) mice and long-term sleep loss increases amyloid plaque in AD transgenic mouse models. Both effects can be influenced by the wake-promoting neuropeptide, hypocretin (HCRT), but whether HCRT influences amyloid accumulation independent of sleep and wake timing modulation remains unclear. Here, we induced chronic fragmentation of sleep (CFS) in WT and HCRT-deficient mice to elicit similar arousal indices, sleep bout lengths and sleep bout numbers in both genotypes. We then examined the roles of HCRT in CFS-induced hippocampal Aβ accumulation and injury. CFS in WT mice resulted in increased Aβ42 in the hippocampus along with loss of cholinergic projections and loss of locus coeruleus neurons. Mice with HCRT deficiency conferred resistance to CFS Aβ42 accumulation and loss of cholinergic projections in the hippocampus yet evidenced similar CFS-induced loss of locus coeruleus neurons. Collectively, the findings demonstrate specific roles for orexin in sleep disruption hippocampal injury.Significance statementChronic fragmentation of sleep (CFS) occurs in common conditions, including sleep apnea syndromes and chronic pain disorders, yet CFS can induce neural injury. Our results demonstrate that under conditions of sleep fragmentation, hypocretin/orexin is essential for the accumulation of amyloid-β and loss of cholinergic projections in the hippocampus observed in response to CFS yet does not influence locus coeruleus neuron response to CFS.

Male mice engaging differently in emotional eating present distinct plasmatic and neurological profiles

ABSTRACT Objective: Stressed individuals tend to turn to calorie-rich food, also known as ‘comfort food’ for the temporary relief it provides. The emotional eating drive is highly variable among subjects. Using a rodent model, we explored the plasmatic and neurobiological differences between ‘high and low emotional eaters’ (HEE and LEE). Methods: 40 male mice were exposed for 5 weeks to a protocol of unpredictable chronic mild stress. Every 3 or 4 days, they were submitted to a 1-h restraint stress, immediately followed by a 3-h period during which a choice between chow and chocolate sweet cereals was proposed. The dietary intake was measured by weighing. Plasmatic and neurobiological characteristics were compared in mice displaying high vs low intakes. Results: Out of 40 mice, 8 were considered as HEE because of their high post-stress eating score, and 8 as LEE because of their consistent low intake. LEE displayed higher plasma corticosterone and lower levels of NPY than HEE, but acylated and total ghrelin were similar in both groups. In the brain, the abundance of NPY neurons in the arcuate nucleus of the hypothalamus was similar in both groups, but was higher in the ventral hippocampus and the basal lateral amygdala of LEE. The lateral hypothalamus LEE had also more orexin (OX) positive neurons. Both NPY and OX are orexigenic peptides and mood regulators. Discussion: Emotional eating difference was reflected in plasma and brain structures implicated in emotion and eating regulation. These results concur with the psychological side of food consumption.

Antagonism of the orexin receptors in the ventral tegmental area diminished the stress-induced analgesia in persistent inflammatory pain

As a part of descending pain inhibitory system, orexin (OXs) in the ventral tegmental area (VTA) are implicated in nociceptive responses. The current study aimed to evaluate the role of OX receptors (OXRs) in the VTA in stress-induced analgesia in persistent inflammatory pain. Ninety-nine adult male Wistar rats underwent forced swim stress (FSS) following intra-VTA infusion of various doses of SB334867 or TCS OX2 29 (1, 3, 10, and 30 nmol/0.3 μL) as an OX1R or OX2R antagonist, respectively. The nociceptive threshold was evaluated using the formalin test as an animal model of persistent inflammatory pain. Current results demonstrated FSS as acute stress produced analgesic responses in the persistent inflammatory pain. Moreover, either OX1R or OX2R antagonist infusion in the VTA hindered the FSS-induced analgesia in both early and late phases. The inhibitory effect of SB334768 in the FSS-induced analgesia was stronger than TCS OX2 29 in both early and late phases of the formalin test. Neither SB334768 nor TCS OX2 29 alone affects pain-related behaviors in formalin tests. Intra-VTA microinjection of each treatment could not modify locomotion in rats. The findings suggest that OX1R and OX2R in the VTA are implicated in FSS-induced analgesia mechanisms.

Low-intensity focused ultrasound attenuates early traumatic brain injury by OX-A/NF-κB/NLRP3 signaling pathway.

Background: Traumatic brain injury (TBI) is a serious hazard to human health and is characterized by high rates of disability and mortality. It is necessary to explore new effective treatment methods to reduce the impact of TBI on individuals and society. As an emerging neuromodulation technique, ultrasound is used to treat some neurological diseases, but the neuroprotective mechanism of low-intensity focused ultrasound (LIFUS) in TBI remains unclear. We aimed to investigate the protective effects and potential mechanisms of LIFUS in TBI.Methods: A rat model of TBI was established using the free-fall method. After establishing the TBI model, the hypothalamus region was covered with LIFUS radiation, and an orexin receptor 1 (OXR1) antagonist (SB334867) was injected intraperitoneally. Neurobehavioral examination, Nissl staining, hematoxylin and eosin staining of the brain tissue, and brain water content, were performed 3 days later. Western blotting, quantitative real-time polymerase chain reaction, immunofluorescence staining, and immunohistochemical staining, were used to evaluate the neuroprotective mechanisms of LIFUS.Results: LIFUS improved tissue damage, neurological deficits, and brain edema. LIFUS can increase the expression of orexin-A (OX-A) and OXR1, significantly inhibit the activation of nuclear factor-κB (NF-κB) protein and nucleotide-binding domain-like receptor protein 3 (NLRP3) inflammasome after TBI, and reduce the release of pro-inflammatory factors after TBI; however, SB334867 can reverse this effect.Conclusions: This study suggests that LIFUS may play a neuroprotective role by promoting the release of OX-A from the hypothalamus and inhibiting the inflammatory response after TBI through the OX-A /NF-κB/NLRP3 pathway.

CO2 exposure enhances Fos expression in hypothalamic neurons in rats during the light and dark phases of the diurnal cycle.

Orexinergic (OX) neurons in the lateral hypothalamus (LH), perifornical area (PFA) and dorsomedial hypothalamus (DMH) play a role in the hypercapnic ventilatory response, presumably through direct inputs to central pattern generator sites and/or through interactions with other chemosensitive regions. OX neurons can produce and release orexins, excitatory neuropeptides involved in many functions, including physiological responses to changes in CO2/pH. Thus, in the present study, we tested the hypothesis that different nuclei (LH, PFA and DMH) where the orexinergic neurons are located, show distinct activation by CO2 during the light-dark cycle phases. For this purpose, we evaluated the Fos and OXA expression by immunohistochemistry to identify neurons that co-localize Fos + OXA in the LH, LPeF, MPeF and DMH in the light-inactive and dark-active phase in Wistar rats subjected to 3h of normocapnia or hypercapnia (7% CO2). Quantitative analyses of immunoreactive neurons show that hypercapnia caused an increase in the number of neurons expressing Fos in the LH, LPeF, MPeF and DMH in the light and dark phases. In addition, the number of Fos + OXA neurons increased in the LPeF and DMH independently of the phases of the diurnal cycle; whereas in the MPeF, this increase was observed exclusively in the light phase. Thus, we suggest that OX neurons are selectively activated by hypercapnia throughout the diurnal cycle, reinforcing the differential role of nuclei in the hypothalamus during central chemosensitivity.

Hypothalamic orexinergic neuron changes during the hibernation of the Syrian hamster

Hibernation in small mammals is a highly regulated process with periods of torpor involving drops in body temperature and metabolic rate, as well as a general decrease in neural activity, all of which proceed alongside complex brain adaptive changes that appear to protect the brain from extreme hypoxia and low temperatures. All these changes are rapidly reversed, with no apparent brain damage occurring, during the short periods of arousal, interspersed during torpor—characterized by transitory and partial rewarming and activity, including sleep activation, and feeding in some species. The orexins are neuropeptides synthesized in hypothalamic neurons that project to multiple brain regions and are known to participate in the regulation of a variety of processes including feeding behavior, the sleep-wake cycle, and autonomic functions such as brown adipose tissue thermogenesis. Using multiple immunohistochemical techniques and quantitative analysis, we have characterized the orexinergic system in the brain of the Syrian hamster—a facultative hibernator. Our results revealed that orexinergic neurons in this species consisted of a neuronal population restricted to the lateral hypothalamic area, whereas orexinergic fibers distribute throughout the rostrocaudal extent of the brain, particularly innervating catecholaminergic and serotonergic neuronal populations. We characterized the changes of orexinergic cells in the different phases of hibernation based on the intensity of immunostaining for the neuronal activity marker C-Fos and orexin A (OXA). During torpor, we found an increase in C-Fos immunostaining intensity in orexinergic neurons, accompanied by a decrease in OXA immunostaining. These changes were accompanied by a volume reduction and a fragmentation of the Golgi apparatus (GA) as well as a decrease in the colocalization of OXA and the GA marker GM-130. Importantly, during arousal, C-Fos and OXA expression in orexinergic neurons was highest and the structural appearance and the volume of the GA along with the colocalization of OXA/GM-130 reverted to euthermic levels. We discuss the involvement of orexinergic cells in the regulation of mammalian hibernation and, in particular, the possibility that the high activation of orexinergic cells during the arousal stage guides the rewarming as well as the feeding and sleep behaviors characteristic of this phase.

Electrophysiological characterization of medial preoptic neurons in lactating rats and its modulation by hypocretin-1

The medial preoptic area (mPOA) undergoes through neuroanatomical changes across the postpartum period, during which its neurons play a critical role in the regulation of maternal behavior. In addition, this area is also crucial for sleep-wake regulation. We have previously shown that hypocretins (HCRT) within the mPOA facilitate active maternal behaviors in postpartum rats, while the blockade of endogenous HCRT in this area promotes nursing and sleep. To explore the mechanisms behind these HCRT actions, we aimed to evaluate the effects of juxta-cellular HCRT-1 administration on mPOA neurons in urethane-anesthetized postpartum and virgin female rats. We recorded mPOA single units and the electroencephalogram (EEG) and applied HCRT-1 juxta-cellular by pressure pulses. Our main results show that the electrophysiological characteristics of the mPOA neurons and their relationship with the EEG of postpartum rats did not differ from virgin rats. Additionally, neurons that respond to HCRT-1 had a slower firing rate than those that did not. In addition, administration of HCRT increased the activity in one group of neurons while decreasing it in another, both in postpartum and virgin rats. This study suggests that the mechanisms by which HCRT modulate functions controlled by the mPOA involve different cell populations.

Hypothalamic orexinergic neurons modulate pain and itch in an opposite way: pain relief and itch exacerbation

Pain and itch are recognized as antagonistic sensations; pain suppresses itch and inhibition of pain generates itch. There is still a lack of evidence about the neural mechanism of the interaction between pain and itch in the central nervous system. In this study, we focused on the orexin (ORX) neurons in the lateral hypothalamus (LH), which mediate various “defense responses” when animals confront stressors. We found that the scratching behaviors induced by the pruritogen were significantly suppressed in ORX-neuron-ablated (ORX-abl) mice. The exaggerated pain behavior and attenuated itch behavior observed in ORX-abl mice indicated that ORX neurons modulate pain and itch in an opposite way, i.e., pain relief and itch exacerbation. In addition, most of the ORX neurons responded to both pain and itch input. Our results suggest that ORX neurons inversely regulate pain- and itch-related behaviors, which could be understood as a defense response to cope with stress environment.

Orexin system in the ventral tegmental area is implicated in the rewarding properties of methamphetamine

Overwhelming evidence has revealed that the orexins (OXs) and their receptors in the mesolimbic system participate in modulating psychostimulants and rewarding impacts. The current study aimed to elucidate the role of OX receptors in the ventral tegmental area (VTA) in the acquisition and expression phases of methamphetamine (METH)-induced conditioned place preference (CPP). In the first set of experiments, animals bilaterally received OX receptor 1 (SB 334867) or OX receptor 2 (TCS OX2 29) antagonist (1, 3, 10, and 30 nmol/0.3 μL DMSO 12%) in the VTA before each METH session over the acquisition phase to evaluate the role of OX receptors in the acquisition of METH-induced CPP. In the next set of experiments, animals bilaterally received antagonists at the same doses in the VTA before the post-conditioning test to illustrate the role of OX receptors in the expression of METH-induced CPP. Current data demonstrated that administering both antagonists in the VTA diminished both acquisition and expression phases of METH-induced CPP. However, the suppressive effects of both OX receptor antagonists were more potent in the acquisition phase of METH-CPP than those in the expression phase. Overall, it seems that the OX receptors in the VTA are implicated in developing the rewarding properties of METH.

The Role of Orexin-A in Water Intake in Water-deprived Rats

Background: The lateral hypothalamus (LH), which produces orexin, is vital for body solution homeostasis. Lateral hypothalamus (LH) lesion causes adipsia and its stimulation increases water intake. Objective: This study aimed to investigate the effect of an intracerebroventricular (ICV) injection of orexin-A (OXA) on water-drinking behavior in water-deprived rats. Metods: A total of 32 male Wistar rats (220–250 g) were used and divided into 4 groups, control (no injection), vehicle (Normal saline, 5 µL), OXA (30 µg/rat), SB-334867 (OXA receptor selective antagonist, 30 µg/rat). After the microinjection of drugs or vehicles in the right lateral ventricle, each rat was placed individually into the metabolic cage and the amount of water intake, the delay time for the first water intake, and the referral number for water intake were recorded for 4 h. Findings: This study showed that ICV administration of OXA increased both water intake and the referral number for water intake in water-deprived animals (P&lt;0.05). On the other hand, ICV administration of SB-334867 decreased water intake compared to vehicle and control groups. Conclusion: It can be concluded that OXA has a regulatory role in water drinking behavior in water-depriving states.

Agonists and antagonists of the orexinergic system: therapeutic molecules of the future - a narrative review

&lt;p&gt;The orexinergic system involves orexin (OX) neurons, OX peptides, and OX receptors. OX neurons are located throughout the central nervous tissue (including many nuclei) and the peripheral nervous tissue and organs. These neurons are critically involved in the sleepwake transition, cardiorespiratory, and autonomic regulations. OX antagonists include selective OX type 1 receptor (OX1R) antagonists, selective OX type 2 receptor (OX2R) antagonists, and dual OX1/2R antagonists. Similarly, OX agonists include dual OX1/2R agonists and selective OX1R or OX2R agonists. Recent understandings of the therapeutic mechanism of OX have led to possible therapeutic options in diseases such as insomnia, narcolepsy, psychiatric disorders, and neurodegenerative diseases. This review focuses on the therapeutic roles of OXs as agonists or antagonists in animal models and human patients, which can lead to possible avenues related to their application in health and disease.&lt;/p&gt;

The Orexin-A/OX1R System Induces Cell Death in Pancreatic Cancer Cells Resistant to Gemcitabine and Nab-Paclitaxel Treatment.

Pancreatic ductal adenocarcinoma (PDAC) represents the fourth cause of cancer-associated death in the West. This type of cancer has a very poor prognosis notably due to the development of chemoresistance when treatments including gemcitabine and Abraxane (Nab-paclitaxel) were prescribed. The identification of new treatment circumventing this chemoresistance represents a key challenge. Previous studies demonstrated that the activation of orexin receptor type 1 (OX1R), which was ectopically expressed in PDAC, by its natural ligand named orexin-A (OxA), led to anti-tumoral effect resulting in the activation of mitochondrial pro-apoptotic mechanism. Here, we demonstrated that OxA inhibited the pancreatic cancer cell (AsPC-1) growth and inhibited the tumor volume in preclinical models as effectively as gemcitabine and Nab-paclitaxel. Moreover, the combination therapy including OxA plus gemcitabine or OxA plus Nab-paclitaxel was additive on the inhibition of cancer cell growth and tumor development. More importantly, the treatment by OxA of chemoresistant tumors to gemcitabine or Nab-paclitaxel obtained by successive xenografts in mice revealed that OxA was able to induce a strong inhibition of tumor development, whereas no OxA resistance was identified in tumors. The OX1R/OxA system might be an innovative and powerful alternative treatment of chemoresistant PDAC.

Hippocampal orexin-1 and endocannabinoid-1 receptors underlie the kainate-induced occlusion in theta-burst long- term potentiation

IntroductionSeizures may result from the hyperexcitable neuronal activity of the brain. Multiple neurotransmitter receptors, including orexin (OX) and endocannabinoids interfere with forming the synaptic responses linked to the seizures. Therefore, this study investigates the involvement of OX-1 (OX1R) and endocannbinoid-1 (CB1R) receptors in the kainate- induced excitability in the synaptic field responses. Material and methodsTheta pattern used to stimulate Schaffer collaterals and then metal microelectrodes to record the CA1 field excitatory postsynaptic potentials (fEPSPs). Input/ output stimulation and responses and paired- pulse (PP) stimuli employed to measure the state of synaptic activity in normal and kainate- induced seizure-like hyperexcitable activities and the slope of fEPSPs used as a measure of the change in the synaptic activity. Furthermore, agonists and antagonists of OX and endocannabinoids infused to investigate the involvement of their receptors. ResultThe results showed that kainate application increased the fEPSP slope either in input stimuli with different intensities/output synaptic responses (I/O), or test pulse stimulated baseline synaptic responses (BSR) and, hence, increased the excitability of field responses in the CA1 region. However, neither kainate nor theta burst stimulation (TBS) could alter the PP stimuli -induced synaptic responses. TBS increased the fEPSP slope of the kainate-applied I/O and BSR, however, the increase was not high enough in BSR to be classified as long-term potentiation (LTP). The single-antagonist OX1R and CB1R administration prevented TBS- induced potentiation and partially recovered the effect by adding eCB or OX agonists in kainate-injected animals. In contrast, OX or combined eCB-OX antagonist application group demonstrated nearly full recovery of LTP induction. ConclusionOur study concludes that blockade of OX1 or CB1 prevents the induction of LTP, and OX infusion or both receptor blockade recovers the LTP.

Effects of dietary pantothenic acid on growth, antioxidant ability and innate immune response in juvenile black carp

An 8-week feeding study was conducted to examine how dietary pantothenic acid (PA) affects growth, antioxidant ability and innate immunity in juvenile black carp (Mylopharyngodon piceus). Juvenile fish (7.35 ± 0.06 g) were fed diets with PA at 0, 5, 10, 20, 40 and 80 mg/kg, respectively. The highest weight gain (WG), specific growth rate (SGR) and protein efficiency ratio (PER) were obtained with 10 mg/kg dietary PA (p < 0.05), as well as the lowest feed conversion ratio (FCR). Adequate dietary PA (10 and 20 mg/kg) markedly upregulated neuropeptide Y (NPY), orexin (ORX) and ghrelin (GRL) and downregulated cholecystokinin (CCK) in the brain of these animals (p < 0.05). Intestinal sodium-dependent multivitamin transporter (SMVT) expression and α amylase, trypsin, chymotrypsin and lipase activities were all improved after supplementation of PA at 10 or 20 mg/kg (p < 0.05). In addition, adequate dietary PA (10 and 20 mg/kg) significantly increased the activities of antioxidant enzymes such as superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX) and glutathione reductase (GR), as well as the amounts of reduced glutathione (GSH) and total antioxidant capacity (T-AOC) in the liver of these animals (p < 0.05). Meanwhile, liver glutathione S-transferase (GST) activity and malondialdehyde (MDA) amounts levels were both markedly decreased with dietary PA at 10 or 20 mg/kg (p < 0.05). Furthermore, adequate dietary PA significantly elevated the mRNA amounts of NFE2-related nuclear factor 2 (Nrf2) and downregulated Kelch-like-ECH-associated protein 1a (Keap1a) and Keap1b (p < 0.05), and remarkably upregulated innate defense molecules, including lysozyme (LYZ), natural resistance-associated macrophage protein (NRAMP), liver-expressed antimicrobial peptide 2 (LEAP-2), hepcidin (HEPC), complement 3 (C3) and complement 9 (C9) in the liver (p < 0.05). Meanwhile, elevated dietary PA resulted in increased LYZ activity and C3 content and decreased aspartate aminotransferase (ALT) and aspartate aminotransferase (AST) activities in serum samples from juvenile black carp compared with the groups fed PA-deficient diets (p < 0.05). Moreover, 10, 20 and 40 mg/kg PA-containing diets starkly downregulated intestinal interleukin 8 (IL-8) and IL-11 at the mRNA level in comparison with the PA-deficient diet (0 mg/kg) (p < 0.05). However, PA supplementation at 10, 20 or 40 mg/kg resulted in increased intestinal zonula occludens-1 (ZO-1), ZO-2, ZO-3, claudin 3, claudin 4, claudin 8, claudin 15 and occludin mRNA levels in M. piceus in comparison with the 0 mg/kg PA group (p < 0.05). Jointly, the above findings suggested adequate dietary PA (10 and 20 mg/kg) enhances feed utilization and growth performance, as well as antioxidant capacities and non-specific immune reactions in juvenile M. piceus.

Orexin Signaling: A Complex, Multifaceted Process.

The orexin system comprises two G protein-coupled receptors, OX1 and OX2 receptors (OX1R and OX2R, respectively), along with two endogenous agonists cleaved from a common precursor (prepro-orexin), orexin-A (OX-A) and orexin-B (OX-B). For the receptors, a complex array of signaling behaviors has been reported. In particular, it becomes obvious that orexin receptor coupling is very diverse and can be tissue-, cell- and context-dependent. Here, the early signal transduction interactions of the orexin receptors will be discussed in depth, with particular emphasis on the direct G protein interactions of each receptor. In doing so, it is evident that ligands, additional receptor-protein interactions and cellular environment all play important roles in the G protein coupling profiles of the orexin receptors. This has potential implications for our understanding of the orexin system’s function in vivo in both central and peripheral environments, as well as the development of novel agonists, antagonists and possibly allosteric modulators targeting the orexin system.

Amygdalar CB2 cannabinoid receptor mediates fear extinction deficits promoted by orexin-A/hypocretin-1

Anxiety and stress disorders are often characterized by an inability to extinguish learned fear responses. Orexins/hypocretins are involved in the modulation of aversive memories, and dysregulation of this system may contribute to the aetiology of anxiety disorders characterized by pathological fear. The mechanisms by which orexins regulate fear are unknown. Here we investigated the role of the endogenous cannabinoid system in the impaired fear extinction induced by orexin-A (OXA) in male mice. The selective inhibitor of 2-arachidonoylglycerol (2-AG) biosynthesis O7460 abolished the fear extinction deficits induced by OXA. Accordingly, increased 2-AG levels were observed in the amygdala and hippocampus of mice treated with OXA that do not extinguish fear, suggesting that high levels of this endocannabinoid are related to poor extinction. Impairment of fear extinction induced by OXA was associated with increased expression of CB2 cannabinoid receptor (CB2R) in microglial cells of the basolateral amygdala. Consistently, the intra-amygdala infusion of the CB2R antagonist AM630 completely blocked the impaired extinction promoted by OXA. Microglial and CB2R expression depletion in the amygdala with PLX5622 chow also prevented these extinction deficits. These results show that overactivation of the orexin system leads to impaired fear extinction through 2-AG and amygdalar CB2R. This novel mechanism could be of relevance for the development of novel potential approaches to treat diseases associated with inappropriate retention of fear, such as post-traumatic stress disorder, panic anxiety and phobias.