Literatura académica sobre el tema "Orexin 1 receptor"

Orexins are peptide neurotransmitters which are produced in the lateral and posterior part of the hypothalamus in the brain. There are two Orexin receptors which has been identified till date viz. Orexin 1 (OX 1) and Orexin 2 (OX 2 receptor).

Abstract Hypothalamic prepro-orexin as well as pituitary and adrenal orexin receptors are gender-specifically expressed. To assess the regulation by gonadal steroids, we investigated the effect of 17β-estradiol in female and of testosterone in male rats on prepro-orexin and orexin receptor mRNA expression. Rats were either sham-operated or gonadectomized and subsequently treated with placebo, 17β-estradiol, or testosterone for 21 d. Tissue mRNA levels of prepro-orexin, orexin type-1 (OX1), and orexin type-2 (OX2) receptors were measured using quantitative real-time RT-PCR. In female rats, pituitary OX1 receptor mRNA levels were increased 12-fold after ovariectomy compared with sham- operated rats. The increase of pituitary OX1 receptor mRNA was inhibited by treatment with 17β-estradiol. Adrenal mRNA levels of OX2 receptors in ovariectomized rats were increased 2-fold compared with sham-operated rats and were also reduced by treatment with 17β-estradiol. In male rats, orchidectomy increased the mRNA levels of pituitary OX1 receptors compared with sham-operated rats. In contrast, adrenal OX2 receptor mRNA was reduced after orchidectomy. Testosterone treatment reversed the effect of orchidectomy on pituitary OX1 and adrenal OX2 receptors. In the hypothalamus, no differences were found in the mRNA levels of prepro-orexin, OX1, and OX2 receptors between sham-operated, placebo-treated, and steroid-treated female or male rats. Our results indicate that gonadal steroids differentially regulate pituitary OX1 receptors and adrenal OX2 receptors in male and female rats and may contribute to specific sex- dependent neuroendocrine and endocrine actions of orexins.

Orexins/hypocretins exert cardiovascular effects which are centrally mediated. In the present study, we tested whether orexins and their receptors may also act in an autocrine/paracrine manner in the heart exerting direct effects. Quantitative reverse transcription-PCR (RT-PCR), immunohistochemical and Western blot analyses revealed that the rat heart expresses orexins and orexin receptors (OXR). In isolated rat cardiomyocytes, only orexin-B (OR-B) caused an increase in contractile shortening, independent of diastolic or systolic calcium levels. A specific orexin receptor-2 (OX2R) agonist ([Ala11, d-Leu15]-Orexin B) exerted similar effects as OR-B, whereas a specific orexin receptor-1 (OX1R) antagonist (SB-408124) did not alter the responsiveness of OR-B. Treatment of the same model with OR-B resulted in a dose-dependent increase in myosin light chain and troponin-I (TnI) phosphorylation. Following ischaemia/reperfusion in the isolated Langendorff perfused rat heart model, OR-B, but not OR-A, exerts a cardioprotective effect; mirrored in an in vivo model as well. Unlike OR-A, OR-B was also able to induce extracellular signal-regulated kinase (ERK) 1/2 (ERK1/2) and Akt phosphorylation in rat myocardial tissue and ERK1/2 phosphorylation in human heart samples. These findings were further corroborated in an in vivo rat model. In human subjects with heart failure, there is a significant negative correlation between the expression of OX2R and the severity of the disease clinical symptoms, as assessed by the New York Heart Association (NYHA) functional classification. Collectively, we provide evidence of a distinct orexin system in the heart that exerts a cardioprotective role via an OR-B/OX2R pathway.

Abstract Two recently discovered hypothalamic peptides, orexin-A and orexin-B, play a role as mediators in the central mechanisms that regulate feeding behavior and sleep control. These peptides bind and activate two orexin receptors that belong to the G-protein coupled receptor superfamily. Morphological studies have detected mRNA expression of orexin receptors exclusively in the rat central nervous system. In this paper we demonstrate a strong level of expression of orexin receptor 1 and 2 in the adrenal medulla of the rat by RT-PCR immunohistochemistry. The results of the present study provide the first evidence showing that the adrenal medulla expresses orexin receptors, and thus appears to be a target tissue for orexins. This could open a new loop in which the central and autonomous nervous system may be involved in body weight homeostasis and sleep control.

Orexin-A and orexin-B, via their receptors orexin-1 receptor (OX1R) and orexin-2 receptor (OX2R) have been shown to play a role in the regulation of feeding, body weight, and energy expenditure. Adipose tissue also contributes significantly to the maintenance of body weight by interacting with a complex array of bioactive peptides; however, there are no data as yet on the expression of orexin components in adipose tissue. We, therefore, analyzed the expression of OX1R and OX2R in human adipose tissue and determined functional responses to orexin-A and orexin-B. OX1R and OX2R mRNA expression was detected in subcutaneous (s.c.) and omental adipose tissue and in isolated adipocytes. Protein for OX1R and OX2R was also detected in whole adipose tissue sections and lysates. Treatment with orexin-A, and orexin-B (100 nM, 24 h) resulted in a significant increase in peroxisome proliferator-activated receptors γ-2 mRNA expression in s.c. adipose tissue (P < 0.05). Hormone sensitive lipase mRNA was significantly reduced in omental adipose tissue with orexin-A and orexin-B treatment (P < 0.05). Glycerol release from omental adipose tissue was also significantly reduced with orexin-A treatment (P < 0.05). These findings demonstrate for the first time the presence of functional orexin receptors in human adipose tissue and suggest a role for orexins in adipose tissue metabolism and adipogenesis.

Orexin peptides comprise two neuropeptides, orexin A and orexin B, that bind two G-protein coupled receptors (GPCRs), orexin receptor 1 (OXR1) and orexin receptor 2 (OXR2). Although cell bodies that produce orexin peptides are localized in a small area comprising the lateral hypothalamus and adjacent regions, orexin-containing fibres project throughout the neuraxis. Although orexins were initially described as peptides that regulate feeding behaviour, research has shown that orexins are involved in diverse functions that range from the modulation of autonomic functions to higher cognitive functions, including reward-seeking, behaviour, attention, cognition, and mood. Furthermore, disruption in orexin signalling has been shown in mood disorders that are associated with low hedonic tone or anhedonia, including depression, anxiety, attention deficit hyperactivity disorder, and addiction. Notably, projections of orexin neurons overlap circuits involved in the modulation of hedonic tone. Evidence shows that orexins may potentiate hedonic behaviours by increasing the feeling of pleasure or reward to various signalling, whereas dysregulation of orexin signalling may underlie low hedonic tone or anhedonia. Further, orexin appears to play a key role in regulating behaviours in motivationally charged situations, such as food-seeking during hunger, or drug-seeking during withdrawal. Therefore, it would be expected that dysregulation of orexin expression or signalling is associated with changes in hedonic tone. Further studies investigating this association are warranted.

Abstract Orexins are hypothalamic neuropeptides primarily involved in the regulation of food intake and arousal states. In addition, a role for orexins as central neuroendocrine modulators of reproductive function has recently emerged. Prepro-orexin and orexin type-1 receptor mRNAs have been detected in the rat testis. This raises the possibility of additional peripheral actions of orexins in the control of reproductive axis, which remains so far unexplored. To analyze the biological effects and mechanisms of action of orexins in the male gonad, we evaluated testicular expression of orexin receptor 1 (OX1R) and orexin receptor 2 (OX2R) mRNAs in different experimental settings and the effect of orexin-A on testicular testosterone (T) secretion. Persistent expression of OX1R mRNA was demonstrated in the rat testis throughout postnatal development. In contrast, OX2R transcript was not detected at any developmental stage. Expression of OX1R mRNA persisted after selective elimination of mature Leydig cells and was detected in isolated seminiferous tubules at defined stages of the seminiferous epithelial cycle. In addition, testicular OX1R mRNA expression appeared to be under hormonal regulation; it was reduced by long-term hypophysectomy and partially restored by FSH replacement, whereas down-regulation was observed after exposure to increasing doses of the ligand in vitro. Moreover, OX1R mRNA expression was sensitive to neonatal imprinting by estrogen. Finally, orexin-A, in a dosedependent manner, significantly increased basal, but not human choriogonadotropin-stimulated, T secretion in vitro. A similar stimulatory effect was observed in vivo after intratesticular administration of orexin-A. In conclusion, our present results provide the first evidence for the regulated expression of OX1R mRNA and functional role of orexin-A in the rat testis. Overall, our data are suggestive of a novel site of action of orexins in the control of male reproductive axis.

Orexins, also called hypocretins, are newly discovered hypothalamic peptides that are thought to be involved in various physiological functions. In spite of the fact that orexin receptors, especially orexin receptor 2, are abundant in the hypothalamic paraventricular nucleus (PVN), the effects of orexins on PVN neurons remain unknown. Using a whole cell patch-clamp recording technique, we investigated the effects of orexin-B on PVN neurons of rat brain slices. Bath application of orexin-B (0.01–1.0 μM) depolarized 80.8% of type 1 ( n = 26) and 79.2% of type 2 neurons tested ( n = 24) in the PVN in a concentration-dependent manner. The effects of orexin-B persisted in the presence of TTX (1 μM), indicating that these depolarizing effects were generated postsynaptically. Addition of Cd2+(1 mM) to artificial cerebrospinal fluid containing TTX (1 μM) significantly reduced the depolarizing effect in type 2 neurons. These results suggest that orexin-B has excitatory effects on the PVN neurons mediated via a depolarization of the membrane potential.

Abstract In humans and rat, orexins orchestrate divergent actions through their G protein-coupled receptors, orexin-1 (OX1R) and orexin-2 (OX2R). Orexins also play an important physiological role in mouse, but the receptors through which they function are not characterized. To characterize the physiological role(s) of orexins in the mouse, we cloned and characterized the mouse orexin receptor(s), mOX1R and mOX2R, using rapid amplification of cDNA (mouse brain) ends, RT-PCR, and gene structure analysis. The mOX1R cDNA encodes a 416-amino acid (aa) receptor. We have identified two alternative C terminus splice variants of the mOX2R; mOX2αR (443 aa) and mOX2βR (460 aa). Binding studies in human embryonic kidney 293 cells transfected with mOX1R, mOX2αR, and the mOX2βR revealed specific, saturable sites for both orexin-A and -B. Activation of these receptors by orexins induced inositol triphosphate (IP3) turnover. However, human embryonic kidney 293 cells transfected with mOXRs demonstrated no cAMP response to either orexin-A or orexin-B challenge, although forskolin and GTPγS revealed a dose-dependent increase in cAMP. Although, orexin-A and -B showed no difference in binding characteristics between the splice variants; interestingly, orexin-B led to an increase in IP3 production at all concentrations in the mOX2βR variant. Orexin-A, however, showed no difference in IP3 production between the two variants. Additionally, in the mouse, we demonstrate that these splice variants are distributed in a tissue-specific manner, where OX2αR mRNA was undetectable in skeletal muscle and kidney. Moreover, food deprivation led to a greater increase in hypothalamic mOX2βR gene expression, compared with both mOX1R and mOX2αR. This potentially implicates a fundamental physiological role for these splice variants.

Abstract Orexin receptors play a role in regulation of sleep-wake-rhythm, food intake and energy homeostasis and they were long thought to be exclusively expressed in the nervous system. During the last years orexin receptors are being identified in a growing number of peripheral tissues. We have earlier detected orexin receptor 1 and 2 expression on human CD34+ blood stem and progenitor cells. Still, the sources of their physiological ligands, the peptides orexin A and B, seem to be restricted to the central nerve system to this date. The main downstream signaling pathways of the orexin receptors include Ca2+-dependent signaling associated with activation of mitogen-activated protein kinase (MAPK) and extracellular signal-related kinase 1/2 (ERK1/2) pathways. In an attempt to investigate if the receptors are functionally active in CD34+ stem and progenitor cells, we used live cell calcium imaging and stimulated purified CD34+ stem and progenitor cells with orexin A and B. Upon stimulation a massive intracellular calcium release was seen which could not been detected using cells preincubated with the Ca2+ chelator 1,2-bis(2-aminophenoxy) ethane-N,N,N′,N′-tetraacetic acid (BAPTA) or the selective OX1R-Antagonist SB334867 and CD34 negative cells. Additionally, upon stimulation with orexin A and B we found ERK (1/2) activation at a maximum 3 hours following incubation with orexin A whereas no effect was seen after stimulation with orexin B. To investigate a potential impact on the functional properties of human CD34+ cells we performed proliferation and apoptosis assays, migration and adhesion assays as well as colony forming and long-term culture assays. So far, no effects of orexin stimulation on the proliferation and apoptosis of CD34+ cells were apparent. Remarkably, stimulation with orexin A and B led to a significantly higher proportion of early pluripotent hematopoietic progenitor (CFU-GEMM) colonies and a significant reduction of erythroid precursors BFU-E (burst forming unit erythrocyte) and CFU-E (colony forming unit erythrocyte). A more immature phenotype of orexin-stimulated CD34+ cells is also reflected by array-based gene expression profiling. Long-term culture assays revealed a significantly higher frequency of LTC-IC (long-term-culture initiating cells) indicating also a more immature phenotype of orexin-stimulated cells and a greater repopulating capacity. The selective orexin receptor antagonist SB-334867 abrogated these effects. No differences could be observed regarding the migration towards SDF-1 with and without stimulation with orexin A and B. Still, orexin A and B led to a decrease in the adhesive capacity of CD34+ stem and progenitor cells to fibronectin coated dishes. Since orexin receptors are coupled to inhibitory G-proteins (Gi/q) and stimulatory G-proteins (Gs) dependent on the tissue, we incubated CD34+ cells with the selective inhibitor of Gi – proteins pertussis toxin concurrently to stimulation with orexins and observed no differences in the adhesive capacity of CD34+ cells compared to the unstimulated controls suggesting coupling of the orexin receptor 1 and 2 to Gi – proteins rather than Gs-proteins in CD34+ cells. Given this functional impact of the orexin system on CD34+ cells, we asked if orexins are secreted locally in the bone marrow or autocrine by CD34+ cells or if they are humorally transported to the bone marrow cavity. Using ELISA we did not find autocrine production of orexin by CD34+ cells whereas orexin could be detected in the serum obtained by bone marrow biopsies and peripheral blood pointing rather towards a humoral delivery of orexins to CD34+ cells. Taken together, our findings indicate a functional role of the orexin system in CD34+ stem and progenitor cells.