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Williams KS, Diniz Behn CG. Dynamic Interactions between Orexin and Dynorphin May Delay Onset of Functional Orexin Effects: A Modeling Study. J Biol Rhythms 2011; 26:171-81. [DOI: 10.1177/0748730410395471] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/25/2022]
Abstract
Orexin (also known as hypocretin) neurons play a key role in regulating sleep-wake behavior, but the links between orexin neuron electrophysiology and function have not been explored. Orexin neurons are wake-active, and spiking activity in orexin neurons may anticipate transitions to wakefulness by several seconds. However, it is suggested that while the orexin system is necessary to maintain sustained wake bouts, orexin has little effect on brief wake bouts. In vitro experiments investigating the actions of orexin and dynorphin, a colocalized neuropeptide, on orexin neurons indicate that the dynamics of desensitization to dynorphin may represent a mechanism for modulating local network activity and resolving the apparent discrepancy between the onset of firing in orexin neurons and the onset of functional orexin effects. To investigate the role of dynorphin on orexin neuron activity, a Hodgkin-Huxley—type model orexin neuron was developed in which baseline electrophysiology, orexin/dynorphin action, and dynorphin desensitization were closely tied to experimental data. In this model framework, model orexin neuron responses to orexin/dynorphin action were calibrated by simulating the physiologic effects of static orexin and dynorphin bath application on orexin neurons. Then behavior in a small network of model orexin neurons was simulated with pure orexin, pure dynorphin, or combined orexin and dynorphin coupling based on the mechanisms established in the static case. It was found that the dynamics of desensitization to dynorphin can mediate a clear shift from a network in which firing is suppressed by dynorphin-mediated inhibition to a network of neurons with high firing rates sustained by orexin-mediated excitation. The findings suggest that dynamic interactions between orexin and dynorphin at transitions from sleep to wake may delay onset of functional orexin effects.
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Affiliation(s)
- Katherine S. Williams
- Department of Mathematics, University of Michigan, Ann Arbor, MI, Department of Mathematics, The Ohio State University, Columbus, OH
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52
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Abstract
PURPOSE The mechanisms through which general anesthetics cause reversible loss of consciousness are characterized poorly. In this review, we examine the evidence that anesthetic-induced loss of consciousness may be caused by actions on the neuronal pathways that produce natural sleep. PRINCIPAL FINDINGS It is clear that many general anesthetics produce effects in the brain (detected on electroencephalogram recordings) that are similar to those seen during non-rapid eye movement non-(REM) sleep. Gamma aminobutyric acid (GABA)ergic hypnogenic neurons are thought to be critical for generating non-REM sleep through their inhibitory projections to wake-active regions of the brain. The postsynaptic GABA(A) receptor is a major molecular target of many anesthetics and thus may be a point of convergence between natural sleep and anesthesia. Furthermore, we also present growing evidence in this review that modulating wake-active neurotransmitter (e.g., acetylcholine, histamine) release can impact on anesthesia, supporting the idea that this point of convergence is at the level of the brain arousal systems. CONCLUSIONS While it is clear that general anesthetics can have effects at various points in the sleep-wake circuitry, it remains to be seen which points are true anesthetic targets. It will be challenging to separate non-specific effects on baseline arousal from a causal mechanism. Sophisticated experimental approaches are necessary to address basic mechanisms of sleep and anesthesia and should advance our understanding in both of these fields.
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Abstract
Orexin neurons (hypocretin neurons) have a critical role in the regulation of sleep/wakefulness, especially in the maintenance of arousal. Here, we revealed that orexin neurons are directly and indirectly activated by orexin via the orexin 2 receptor (OX2R). Orexin B (1 μM) induced depolarization in orexin neurons, which was still observed in the presence of TTX (1 μM), AP-5 (50 μM), and CNQX (20 μM). In addition, orexin B induced inward currents in the presence of TTX, suggesting a direct activation of orexin neurons. Although orexin B application induced depolarization in orexin neurons of OX1R knock-out mice at comparable levels to wild-type mice, the observation that orexin B failed to depolarize orexin neurons in the OX2R knock-out mice suggested that OX2R was a primary receptor for this response. Moreover, immunoelectron microscopic analyses revealed direct contacts among orexin neurons, which exhibited structural similarities to the glutamatergic synapses. Together, these results suggest that orexin neurons form a positive-feedback circuit through indirect and direct pathways, which results in the preservation of the orexin neuron network at a high activity level and/or for a longer period. Therefore, the activation of orexin neurons through OX2R might have an important role in the maintenance of arousal.
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54
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Nuñez A, Rodrigo-Angulo ML, Andrés ID, Garzón M. Hypocretin/Orexin neuropeptides: participation in the control of sleep-wakefulness cycle and energy homeostasis. Curr Neuropharmacol 2010; 7:50-9. [PMID: 19721817 PMCID: PMC2724663 DOI: 10.2174/157015909787602797] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/24/2008] [Revised: 08/19/2008] [Accepted: 09/17/2008] [Indexed: 11/28/2022] Open
Abstract
Hypocretins or orexins (Hcrt/Orx) are hypothalamic neuropeptides that are synthesized by neurons located mainly in the perifornical area of the posterolateral hypothalamus. These hypothalamic neurons are the origin of an extensive and divergent projection system innervating numerous structures of the central nervous system. In recent years it has become clear that these neuropeptides are involved in the regulation of many organic functions, such as feeding, thermoregulation and neuroendocrine and cardiovascular control, as well as in the control of the sleep-wakefulness cycle. In this respect, Hcrt/Orx activate two subtypes of G protein-coupled receptors (Hcrt/Orx1R and Hcrt/Orx2R) that show a partly segregated and prominent distribution in neural structures involved in sleep-wakefulness regulation. Wakefulness-enhancing and/or sleep-suppressing actions of Hcrt/Orx have been reported in specific areas of the brainstem. Moreover, presently there are animal models of human narcolepsy consisting in modifications of Hcrt/Orx receptors or absence of these peptides. This strongly suggests that narcolepsy is the direct consequence of a hypofunction of the Hcrt/Orx system, which is most likely due to Hcrt/Orx neurons degeneration. The main focus of this review is to update and illustrate the available data on the actions of Hcrt/Orx neuropeptides with special interest in their participation in the control of the sleep-wakefulness cycle and the regulation of energy homeostasis. Current pharmacological treatment of narcolepsy is also discussed.
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Affiliation(s)
- A Nuñez
- Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina, Universidad Autónoma de Madrid, Madrid, Spain.
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Abstract
Orexin/hypocretin neurones in the posterior hypothalamus are mutually connected with noradrenergic, serotonergic, dopaminergic, histaminergic, and cholinergic neurone systems. They activate these targets by direct post-synaptic and indirect pre-synaptic mechanisms and in turn receive inhibitory feedback and excitatory feed forward control. With respect to behavioural state control, orexin/hypocretin neurones are conducting the orchestra of biogenic amines. This review highlights the role of these players in the control of energy administration, sleep-wake architecture, cortical activation, plasticity, and memory functions in health and disease.
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Affiliation(s)
- K S Eriksson
- Department of Neurophysiology, Heinrich-Heine-University, Dusseldorf, Germany
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56
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Arrigoni E, Mochizuki T, Scammell TE. Activation of the basal forebrain by the orexin/hypocretin neurones. Acta Physiol (Oxf) 2010; 198:223-35. [PMID: 19723027 DOI: 10.1111/j.1748-1716.2009.02036.x] [Citation(s) in RCA: 67] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The orexin neurones play an essential role in driving arousal and in maintaining normal wakefulness. Lack of orexin neurotransmission produces a chronic state of hypoarousal characterized by excessive sleepiness, frequent transitions between wake and sleep, and episodes of cataplexy. A growing body of research now suggests that the basal forebrain (BF) may be a key site through which the orexin-producing neurones promote arousal. Here we review anatomical, pharmacological and electrophysiological studies on how the orexin neurones may promote arousal by exciting cortically projecting neurones of the BF. Orexin fibres synapse on BF cholinergic neurones and orexin-A is released in the BF during waking. Local application of orexins excites BF cholinergic neurones, induces cortical release of acetylcholine and promotes wakefulness. The orexin neurones also contain and probably co-release the inhibitory neuropeptide dynorphin. We found that orexin-A and dynorphin have specific effects on different classes of BF neurones that project to the cortex. Cholinergic neurones were directly excited by orexin-A, but did not respond to dynorphin. Non-cholinergic BF neurones that project to the cortex seem to comprise at least two populations with some directly excited by orexin-A that may represent wake-active, GABAergic neurones, whereas others did not respond to orexin-A but were inhibited by dynorphin and may be sleep-active, GABAergic neurones. This evidence suggests that the BF is a key site through which orexins activate the cortex and promote behavioural arousal. In addition, orexins and dynorphin may act synergistically in the BF to promote arousal and improve cognitive performance.
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Affiliation(s)
- E Arrigoni
- Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA 02215, USA.
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Kantor S, Mochizuki T, Janisiewicz AM, Clark E, Nishino S, Scammell TE. Orexin neurons are necessary for the circadian control of REM sleep. Sleep 2009; 32:1127-34. [PMID: 19750917 PMCID: PMC2737570 DOI: 10.1093/sleep/32.9.1127] [Citation(s) in RCA: 72] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023] Open
Abstract
STUDY OBJECTIVES The orexin-producing neurons are hypothesized to be essential for the circadian control of sleep/wake behavior, but it remains unknown whether these rhythms are mediated by the orexin peptides or by other signaling molecules released by these neurons such as glutamate or dynorphin. To determine the roles of these neurotransmitters, we examined the circadian rhythms of sleep/wake behavior in mice lacking the orexin neurons (ataxin-3 [Atx] mice) and mice lacking just the orexin neuropeptides (orexin knockout [KO] mice). DESIGN We instrumented mice for recordings of sleep-wake behavior, locomotor activity (LMA), and body temperature (Tb) and recorded behavior after 6 days in constant darkness. RESULTS The amplitude of the rapid eye movement (REM) sleep rhythm was substantially reduced in Atx mice but preserved in orexin KO mice. This blunted rhythm in Atx mice was caused by an increase in the amount of REM sleep during the subjective night (active period) due to more transitions into REM sleep and longer REM sleep episodes. In contrast, the circadian variations of Tb, LMA, Wake, non-REM sleep, and cataplexy were normal, suggesting that the circadian timekeeping system and other output pathways are intact in both Atx and KO mice. CONCLUSIONS These results indicate that the orexin neurons are necessary for the circadian suppression of REM sleep. Blunting of the REM sleep rhythm in Atx mice but not in orexin KO mice suggests that other signaling molecules such as dynorphin or glutamate may act in concert with orexins to suppress REM sleep during the active period.
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Affiliation(s)
- Sandor Kantor
- Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA
| | | | | | - Erika Clark
- Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA
| | - Seiji Nishino
- Department of Psychiatry, Stanford University, Palo Alto, CA
| | - Thomas E. Scammell
- Department of Neurology, Beth Israel Deaconess Medical Center, Boston, MA
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58
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Abstract
The appropriate time and place for sleep and waking are important factors for survival. Sleep and waking, rest and activity, flight and fight, feeding, and reproduction are all organized in relation to the day and night. A biological clock, the suprachiasmatic nucleus (SCN), synchronized by photic influences and other environmental cues, provides an endogenous timing signal that entrains circadian body rhythms and is complemented by a homeostatic sleep pressure factor. Cholinergic, catecholaminergic, serotonergic, and histaminergic nuclei control wakefulness and mutually interact with the SCN as well as sleep- and wake-promoting neurons in the hypothalamus to form a bistable switch that controls the timing of behavioral state transitions. Hypocretin neurons integrate circadian-photic and nutritional-metabolic influences and act as a conductor in the aminergic orchestra. Their loss causes narcolepsy, a disease conferring the inability to separate sleep and waking. Their role in appetitive behavior, stress, and memory functions is important to our understanding of addiction and compulsion.
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Affiliation(s)
- Oliver Selbach
- Department of Physiology, Heinrich-Heine-University, Düsseldorf, Germany
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59
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Parmentier R, Kolbaev S, Klyuch BP, Vandael D, Lin JS, Selbach O, Haas HL, Sergeeva OA. Excitation of histaminergic tuberomamillary neurons by thyrotropin-releasing hormone. J Neurosci 2009; 29:4471-83. [PMID: 19357273 PMCID: PMC3198719 DOI: 10.1523/jneurosci.2976-08.2009] [Citation(s) in RCA: 51] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2008] [Revised: 03/04/2009] [Accepted: 03/05/2009] [Indexed: 11/21/2022] Open
Abstract
The histaminergic tuberomamillary nucleus (TMN) controls arousal and attention, and the firing of TMN neurons is state-dependent, active during waking, silent during sleep. Thyrotropin-releasing hormone (TRH) promotes arousal and combats sleepiness associated with narcolepsy. Single-cell reverse-transcription-PCR demonstrated variable expression of the two known TRH receptors in the majority of TMN neurons. TRH increased the firing rate of most (ca 70%) TMN neurons. This excitation was abolished by the TRH receptor antagonist chlordiazepoxide (CDZ; 50 mum). In the presence of tetrodotoxin (TTX), TRH depolarized TMN neurons without obvious change of their input resistance. This effect reversed at the potential typical for nonselective cation channels. The potassium channel blockers barium and cesium did not influence the TRH-induced depolarization. TRH effects were antagonized by inhibitors of the Na(+)/Ca(2+) exchanger, KB-R7943 and benzamil. The frequency of GABAergic spontaneous IPSCs was either increased (TTX-insensitive) or decreased [TTX-sensitive spontaneous IPSCs (sIPSCs)] by TRH, indicating a heterogeneous modulation of GABAergic inputs by TRH. Facilitation but not depression of sIPSC frequency by TRH was missing in the presence of the kappa-opioid receptor antagonist nor-binaltorphimine. Montirelin (TRH analog, 1 mg/kg, i.p.) induced waking in wild-type mice but not in histidine decarboxylase knock-out mice lacking histamine. Inhibition of histamine synthesis by (S)-alpha-fluoromethylhistidine blocked the arousal effect of montirelin in wild-type mice. We conclude that direct receptor-mediated excitation of rodent TMN neurons by TRH demands activation of nonselective cation channels as well as electrogenic Na(+)/Ca(2+) exchange. Our findings indicate a key role of the brain histamine system in TRH-induced arousal.
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Affiliation(s)
- Regis Parmentier
- Department of Neurophysiology, Heinrich Heine University, D-40001 Duesseldorf, Germany, and
- Inserm, U628, Physiologie Intégrée du Système d'Éveil, 69373 Lyon Cedex 08, France
| | - Sergej Kolbaev
- Department of Neurophysiology, Heinrich Heine University, D-40001 Duesseldorf, Germany, and
| | - Boris P. Klyuch
- Department of Neurophysiology, Heinrich Heine University, D-40001 Duesseldorf, Germany, and
| | - David Vandael
- Department of Neurophysiology, Heinrich Heine University, D-40001 Duesseldorf, Germany, and
| | - Jian-Sheng Lin
- Inserm, U628, Physiologie Intégrée du Système d'Éveil, 69373 Lyon Cedex 08, France
| | - Oliver Selbach
- Department of Neurophysiology, Heinrich Heine University, D-40001 Duesseldorf, Germany, and
| | - Helmut L. Haas
- Department of Neurophysiology, Heinrich Heine University, D-40001 Duesseldorf, Germany, and
| | - Olga A. Sergeeva
- Department of Neurophysiology, Heinrich Heine University, D-40001 Duesseldorf, Germany, and
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60
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61
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Abstract
Histamine is a transmitter in the nervous system and a signaling molecule in the gut, the skin, and the immune system. Histaminergic neurons in mammalian brain are located exclusively in the tuberomamillary nucleus of the posterior hypothalamus and send their axons all over the central nervous system. Active solely during waking, they maintain wakefulness and attention. Three of the four known histamine receptors and binding to glutamate NMDA receptors serve multiple functions in the brain, particularly control of excitability and plasticity. H1 and H2 receptor-mediated actions are mostly excitatory; H3 receptors act as inhibitory auto- and heteroreceptors. Mutual interactions with other transmitter systems form a network that links basic homeostatic and higher brain functions, including sleep-wake regulation, circadian and feeding rhythms, immunity, learning, and memory in health and disease.
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Affiliation(s)
- Helmut L Haas
- Institute of Neurophysiology, Heinrich-Heine-University, Duesseldorf, Germany.
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62
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Watson CJ, Soto-Calderon H, Lydic R, Baghdoyan HA. Pontine reticular formation (PnO) administration of hypocretin-1 increases PnO GABA levels and wakefulness. Sleep 2008; 31:453-64. [PMID: 18457232 DOI: 10.1093/sleep/31.4.453] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
STUDY OBJECTIVES GABAergic transmission in the oral part of the pontine reticular formation (PnO) increases wakefulness. The hypothalamic peptide hypocretin-1 (orexin A) promotes wakefulness, and the PnO receives hypocretinergic input. The present study tested the hypothesis that PnO administration of hypocretin-1 increases PnO GABA levels and increases wakefulness. This study also tested the hypothesis that wakefulness is either increased or decreased, respectively, by PnO administration of drugs known to selectively increase or decrease GABA levels. DESIGN Awithin-subjects design was used for microdialysis and microinjection experiments. SETTING University of Michigan. PATIENTS OR PARTICIPANTS Experiments were performed using adult male Crl:CD (SD)IGS BR (Sprague-Dawley) rats (n=46). INTERVENTIONS PnO administration of hypocretin-1, nipecotic acid (a GABA uptake inhibitor that increases extracellular GABA levels), 3-mercaptopropionic acid (a GABA synthesis inhibitor that decreases extracellular GABA levels; 3-MPA), and Ringer solution (vehicle control). MEASUREMENTS AND RESULTS Dialysis administration of hypocretin-1 to the PnO caused a statistically significant, concentration-dependent increase in PnO GABA levels. PnO microinjection of hypocretin-1 or nipecotic acid caused a significant increase in wakefulness and a significant decrease in non-rapid eye movement (NREM) sleep and REM sleep. Microinjecting 3-MPA into the PnO caused a significant increase in NREM sleep and REM sleep and a significant decrease in wakefulness. CONCLUSIONS An increase or a decrease in PnO GABA levels causes an increase or decrease, respectively, in wakefulness. Hypocretin-1 may promote wakefulness, at least in part, by increasing GABAergic transmission in the PnO.
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Affiliation(s)
- Christopher J Watson
- Department ofAnesthesiology, University ofMichigan, Ann Arbor, MI 48109-5615, USA
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63
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Ohno K, Sakurai T. Orexin neuronal circuitry: role in the regulation of sleep and wakefulness. Front Neuroendocrinol 2008; 29:70-87. [PMID: 17910982 DOI: 10.1016/j.yfrne.2007.08.001] [Citation(s) in RCA: 201] [Impact Index Per Article: 12.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/10/2007] [Revised: 08/06/2007] [Accepted: 08/08/2007] [Indexed: 11/26/2022]
Abstract
Orexin A and orexin B were initially identified as endogenous ligands for two orphan G protein-coupled receptors [104]. They were initially recognized as regulators of feeding behavior in view of their exclusive production in the lateral hypothalamic area (LHA), a region known as the feeding center, and their pharmacological activity [104,30,49,107]. Subsequently, the finding that orexin deficiency causes narcolepsy in humans and animals suggested that these hypothalamic neuropeptides play a critical role in regulating sleep/wake cycle [22,46,71,95,117]. These peptides activate waking-active monoaminergic and cholinergic neurons in the hypothalamus/brain stem regions to maintain a long, consolidated awake period. Recent studies on efferent and afferent systems of orexin neurons, and phenotypic characterization of genetically modified mice in the orexin system further suggested roles of orexin in the coordination of emotion, energy homeostasis, reward system, and arousal [3,80,106,137]. A link between the limbic system and orexin neurons might be important for increasing vigilance during emotional stimuli. Orexin neurons are also regulated by peripheral metabolic cues, including ghrelin, leptin, and glucose, suggesting that they might have important roles as a link between energy homeostasis and vigilance states [137]. Recent research has also implicated orexins in reward systems and the mechanisms of drug addiction [13,48,91]. These observations suggest that orexin neurons sense the outer and inner environment of the body, and maintain proper wakefulness of animals for survival. This review discusses the mechanism by which orexins maintain sleep/wakefulness states, and how this mechanism relates to other systems that regulate emotion, reward, and energy homeostasis.
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Affiliation(s)
- Kousaku Ohno
- Department of Pharmacology, Institute of Basic Medical Science, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan
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64
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Hou RH, Langley RW, Szabadi E, Bradshaw CM. Comparison of diphenhydramine and modafinil on arousal and autonomic functions in healthy volunteers. J Psychopharmacol 2007; 21:567-78. [PMID: 17092978 DOI: 10.1177/0269881106071022] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Arousal is regulated by the interplay between wakefulness- and sleep-promoting nuclei. Major wakefulness-promoting nuclei are the histaminergic tuberomamillary nucleus (TMN) of the hypothalamus and the noradrenergic locus coeruleus (LC) of the pons, which also play a role in autonomic regulation. First generation antihistamines, such as diphenhydramine, are likely to cause sedation by blocking excitatory H1 histamine receptors in the cerebral cortex, and the anti-narcolepsy drug modafinil may promote wakefulness by activating the locus coeruleus. We compared the effects of single doses of diphenhydramine (75 mg) and modafinil (200 mg) on arousal and autonomic functions in 16 healthy male volunteers, using a placebo-controlled, balanced, double-blind design. Arousal was assessed by critical flicker fusion frequency (CFFF), visual analogue scales (VAS) and pupillary fatigue waves (Pupillographic Sleepiness Test (PST)). Autonomic functions measured included resting pupil diameter, light and darkness reflex responses, blood pressure, heart rate and salivation. Data were analysed with ANOVA, with multiple comparisons. Diphenhydramine had sedative effects as shown by reductions in CFFF, VAS alertness ratings and increases of the indices of pupillary fatigue. Modafinil had alerting effects as indicated by reductions in the measures of pupillary fatigue. Comparison of pre-post medication changes in pupil diameter showed a decrease after diphenhydramine and an increase after modafinil. Diphenhydramine reduced salivation, and modafinil increased systolic blood pressure. In conclusion, diphenhydramine and modafinil evoked opposite effects on arousal and sympathetic functions, which are likely to reflect their interaction with the central histaminergic and noradrenergic systems. Hyposalivation by diphenhydramine is likely to be due to its additional anticholinergic property.
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Affiliation(s)
- R H Hou
- Psychopharmacology Section, Division of Psychiatry, University of Nottingham Medical School, Queen's Medical Centre, Nottingham, UK
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65
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Bengtsson MW, Mäkelä K, Sjöblom M, Uotila S, Akerman KEO, Herzig KH, Flemström G. Food-induced expression of orexin receptors in rat duodenal mucosa regulates the bicarbonate secretory response to orexin-A. Am J Physiol Gastrointest Liver Physiol 2007; 293:G501-9. [PMID: 17585016 DOI: 10.1152/ajpgi.00514.2006] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Presence of appetite-regulating peptides orexin-A and orexin-B in mucosal endocrine cells suggests a role in physiological control of the intestine. Our aim was to characterize orexin-induced stimulation of duodenal bicarbonate secretion and modulation of secretory responses and mucosal orexin receptors by overnight food deprivation. Lewis x Dark Agouti rats were anesthetized and proximal duodenum cannulated in situ. Mucosal bicarbonate secretion (pH stat) and mean arterial blood pressure were continuously recorded. Orexin-A was administered intra-arterially close to the duodenum, intraluminally, or into the brain ventricles. Total RNA was extracted from mucosal specimens, reverse transcribed to cDNA and expression of orexin receptors 1 and 2 (OX1 and OX2) measured by quantitative real-time PCR. OX1 protein was measured by Western blot. Intra-arterial orexin-A (60-600 nmol.h(-1).kg(-1)) increased (P < 0.01) the duodenal secretion in fed but not in fasted animals. The OX1 receptor antagonist SB-334867, which was also found to have a partial agonist action, abolished the orexin-induced secretory response but did not affect secretion induced by the muscarinic agonist bethanechol. Atropine, in contrast, inhibited bethanechol but not orexin-induced secretion. Orexin-A infused into the brain ventricles (2-20 nmol.kg(-1).h(-1)) or added to luminal perfusate (1.0-100 nM) did not affect secretion, indicating that orexin-A acts peripherally and at basolateral receptors. Overnight fasting decreased mucosal OX1 and OX2 mRNA expression (P < 0.01) as well as OX1 protein expression (P < 0.05). We conclude that stimulation of secretion by orexin-A may involve both receptor types and is independent of cholinergic pathways. Intestinal OX receptors and secretory responses are markedly related to food intake.
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MESH Headings
- Animals
- Atropine/pharmacology
- Benzoxazoles/administration & dosage
- Bethanechol/pharmacology
- Bicarbonates/metabolism
- Cerebral Ventricles/drug effects
- Cerebral Ventricles/metabolism
- Crosses, Genetic
- Dose-Response Relationship, Drug
- Duodenum/drug effects
- Duodenum/metabolism
- Eating/physiology
- Food Deprivation
- Hydrogen-Ion Concentration
- Infusions, Intra-Arterial
- Intestinal Mucosa/drug effects
- Intestinal Mucosa/metabolism
- Intestinal Secretions/metabolism
- Intracellular Signaling Peptides and Proteins/administration & dosage
- Intracellular Signaling Peptides and Proteins/metabolism
- Male
- Muscarinic Agonists/pharmacology
- Muscarinic Antagonists/pharmacology
- Naphthyridines
- Neuropeptides/administration & dosage
- Neuropeptides/metabolism
- Orexin Receptors
- Orexins
- RNA, Messenger/metabolism
- Rats
- Rats, Inbred Lew
- Receptors, G-Protein-Coupled/biosynthesis
- Receptors, G-Protein-Coupled/drug effects
- Receptors, G-Protein-Coupled/genetics
- Receptors, Neuropeptide/biosynthesis
- Receptors, Neuropeptide/drug effects
- Receptors, Neuropeptide/genetics
- Time Factors
- Up-Regulation
- Urea/administration & dosage
- Urea/analogs & derivatives
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Affiliation(s)
- Magnus W Bengtsson
- Dept. of Neuroscience, Division of Physiology, Uppsala University, BMC, PO Box 572, SE-751 23 Uppsala, Sweden
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66
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Arrang JM, Morisset S, Gbahou F. Constitutive activity of the histamine H3 receptor. Trends Pharmacol Sci 2007; 28:350-7. [PMID: 17573125 DOI: 10.1016/j.tips.2007.05.002] [Citation(s) in RCA: 106] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/03/2006] [Revised: 04/12/2007] [Accepted: 05/25/2007] [Indexed: 11/27/2022]
Abstract
Constitutive activity has been mainly recorded for numerous overexpressed and/or mutated receptors. The histamine H(3) receptor (H(3)R) is a target of choice to study the physiological relevance of this process. In rodent brain, postsynaptic H(3)Rs show high constitutive activity, and presynaptic H(3) autoreceptors that show constitutive activity have a predominant role in inhibiting the activity of histamine neurons. H(3)R inverse agonists abrogate this constitutive brake and enhance histamine release in vivo. Some of these inverse agonists have entered clinical trials for the treatment of cognitive and food intake disorders. Studies performed in vitro and in vivo with proxyfan show that this H(3)R ligand is a 'protean agonist' - that is, a ligand with a spectrum of activity ranging from full agonism to full inverse agonism depending on the level of H(3)R constitutive activity. Consistent with its physiological and therapeutic relevance, the constitutive activity of H(3)R thus has a major function in the brain and regulates the activity of H(3)R-targeted drugs.
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Affiliation(s)
- Jean-Michel Arrang
- INSERM, Unité de Neurobiologie et Pharmacologie Moléculaire (U 573), Centre Paul Broca, 75014 Paris, France.
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67
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Abstract
The primary headaches are a group of distinct individually characterized attack forms, which although varying in presentation, share some common anatomical basis responsible for the pain component of the attack. The hypothalamus is known to modulate a multitude of functions and has been shown to be involved in the pathophysiology of a variety of primary headaches including cluster headache and chronic migraine. It seems likely that it may be involved in other primary headache disorders due to their episodic nature and may underlie many of their diverse symptoms. We discuss the hypothalamic involvement in the modulation of trigeminovascular processing and examine the involvement of the hypothalamic orexinergic system as a key regulator of this function.
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Affiliation(s)
- Philip Holland
- Headache Group, Institute of Neurology, The National Hospital for Neurology and Neurosurgery, London, UK
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68
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Li Y, van den Pol AN. Differential target-dependent actions of coexpressed inhibitory dynorphin and excitatory hypocretin/orexin neuropeptides. J Neurosci 2007; 26:13037-47. [PMID: 17167093 PMCID: PMC6674960 DOI: 10.1523/jneurosci.3380-06.2006] [Citation(s) in RCA: 112] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/03/2023] Open
Abstract
The hypocretin/orexin arousal system plays a key role in maintaining an alert wake state. The hypocretin peptide is colocalized with an opioid peptide, dynorphin. As dynorphin may be coreleased with hypocretin, we asked what action simultaneous stimulation with the excitatory neuropeptide hypocretin and the inhibitory peptide dynorphin might exert on cells postsynaptic to hypocretin axons, including hypocretin neurons. Hypocretin neurons received direct synaptic contact from other hypocretin neurons but showed little direct response to hypocretin. Here, we show that mouse hypocretin neurons are acutely sensitive to dynorphin. Dynorphin inhibits the hypocretin system by direct postsynaptic actions (hyperpolarization, decreased spike frequency, increased GIRK (G-protein-gated inwardly rectifying K+ channel) current, and attenuated calcium current, and indirectly by reducing excitatory synaptic tone. Interestingly, a selective antagonist of kappa-opioid receptors enhanced activity of the hypocretin system, suggesting ongoing depression by endogenous hypothalamic opioids. Electrical stimulation of hypothalamic microslices that contained hypocretin cells and their axons evoked dynorphin release. Costimulation with dynorphin and hypocretin had three different effects on neurons postsynaptic to hypocretin axons: direct response to only one or the other of the two peptides [hypocretin cells respond to dynorphin, arcuate neuropeptide Y (NPY) cells respond to hypocretin], differential desensitization causing shift from inhibitory current to excitatory current with repeated coexposure (melanin-concentrating hormone neurons), synergistic direct excitation by hypocretin and presynaptic attenuation of inhibition by dynorphin (arcuate NPY neurons). These results suggest that hypocretin neurons may be able to exercise a high degree of modulatory control over postsynaptic targets using multiple neuropeptides with target-dependent actions.
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Affiliation(s)
- Ying Li
- Department of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut 06520
| | - Anthony N. van den Pol
- Department of Neurosurgery, Yale University School of Medicine, New Haven, Connecticut 06520
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69
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Chen L, Thakkar MM, Winston S, Bolortuya Y, Basheer R, McCarley RW. REM sleep changes in rats induced by siRNA-mediated orexin knockdown. Eur J Neurosci 2006; 24:2039-48. [PMID: 17067300 PMCID: PMC2394504 DOI: 10.1111/j.1460-9568.2006.05058.x] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Short interfering RNAs (siRNA) targeting prepro-orexin mRNA were microinjected into the rat perifornical hypothalamus. Prepro-orexin siRNA-treated rats had a significant (59%) reduction in prepro-orexin mRNA compared to scrambled siRNA-treated rats 2 days postinjection, whereas prodynorphin mRNA was unaffected. The number of orexin-A-positive neurons on the siRNA-treated side decreased significantly (23%) as compared to the contralateral control (scrambled siRNA-treated) side. Neither the colocalized dynorphin nor the neighbouring melanin-concentrating hormone neurons were affected. The number of orexin-A-positive neurons on the siRNA-treated side did not differ from the number on the control side 4 or 6 days postinjection. Behaviourally, there was a persistent (approximately 60%) increase in the amount of time spent in rapid eye movement (REM) sleep during the dark (active) period for 4 nights postinjection, in rats treated with prepro-orexin siRNA bilaterally. This increase occurred mainly because of an increased number of REM episodes and decrease in REM-to-REM interval. Cataplexy-like episodes were also observed in some of these animals. Wakefulness and NREM sleep were unaffected. The siRNA-induced increase in REM sleep during the dark cycle reverted to control values on the 5th day postinjection. In contrast, the scrambled siRNA-treated animals only had a transient increase in REM sleep for the first postinjection night. Our results indicate that siRNA can be usefully employed in behavioural studies to complement other loss-of-function approaches. Moreover, these data suggest that the orexin system plays a role in the diurnal gating of REM sleep.
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Affiliation(s)
- Lichao Chen
- Department of Psychiatry, Harvard Medical School, Boston VA Healthcare System, 940 Belmont Street, Brockton, MA 02301, USA
| | - Mahesh M. Thakkar
- Department of Neurology, University of Missouri, Harry Truman Memorial VA Hospital, 800 Hospital Drive, Columbia, MO 65203, USA
| | - Stuart Winston
- Department of Psychiatry, Harvard Medical School, Boston VA Healthcare System, 940 Belmont Street, Brockton, MA 02301, USA
| | - Yunren Bolortuya
- Department of Psychiatry, Harvard Medical School, Boston VA Healthcare System, 940 Belmont Street, Brockton, MA 02301, USA
| | - Radhika Basheer
- Department of Psychiatry, Harvard Medical School, Boston VA Healthcare System, 940 Belmont Street, Brockton, MA 02301, USA
| | - Robert W. McCarley
- Department of Psychiatry, Harvard Medical School, Boston VA Healthcare System, 940 Belmont Street, Brockton, MA 02301, USA
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70
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Nuñez A, Moreno-Balandrán ME, Rodrigo-Angulo ML, Garzón M, De Andrés I. Relationship between the perifornical hypothalamic area and oral pontine reticular nucleus in the rat. Possible implication of the hypocretinergic projection in the control of rapid eye movement sleep. Eur J Neurosci 2006; 24:2834-42. [PMID: 17116163 DOI: 10.1111/j.1460-9568.2006.05159.x] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The perifornical (PeF) area in the posterior lateral hypothalamus has been implicated in several physiological functions including the regulation of sleep-wakefulness. Some PeF neurons, which contain hypocretin, have been suggested to play an important role in sleep-wake regulation. The aim of the present study was to examine the effect of the PeF area and hypocretin on the electrophysiological activity of neurons of the oral pontine reticular nucleus (PnO), which is an important structure in the generation and maintenance of rapid eye movement sleep. PnO neurons were recorded in urethane-anesthetized rats. Extracellular recordings were performed by means of tungsten microelectrodes or barrel micropipettes. Electrical stimulation of the ipsilateral PeF area elicited orthodromic responses in both type I (49%) and type II (58%) electrophysiologically characterized PnO neurons, with a mean latency of 13.0 +/- 2 and 8.3 +/- 5 ms, respectively. In six cases, antidromic spikes were evoked in type I PnO neurons with a mean latency of 3.2 +/- 0.4 ms, indicating the existence of PnO neurons that projected to the PeF area. Anatomical studies showed retrogradely labeled neurons in the PeF area from the PnO. Some of these neurons projecting to the PnO contained hypocretin (17.8%). Iontophoretic application of hypocretin-1 through a barrel micropipette in the PnO induced an inhibition, which was blocked by a previous iontophoretic application of bicuculline, indicating that the inhibitory action of hypocretin-1 may be due to activation of GABA(A) receptors. These data suggest that the PeF area may control the generation of rapid eye movement sleep through a hypocretinergic projection by inhibiting the activity of PnO neurons.
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Affiliation(s)
- A Nuñez
- Departamento de Anatomía, Histología y Neurociencia, Facultad de Medicina, Universidad Autónoma de Madrid, C/Arzobispo Morcillo 4, 28029 Madrid, Spain.
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71
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Sergeeva OA, Klyuch BP, Fleischer W, Eriksson KS, Korotkova TM, Siebler M, Haas HL. P2Y receptor-mediated excitation in the posterior hypothalamus. Eur J Neurosci 2006; 24:1413-26. [PMID: 16965543 DOI: 10.1111/j.1460-9568.2006.05027.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Histaminergic neurons located in the posterior hypothalamus (tuberomamillary nucleus, TMN) project widely through the whole brain controlling arousal and attention. They are tonically active during wakefulness but cease firing during sleep. As a homeostatic theory of sleep involves ATP depletion and adenosine accumulation in the brain, we investigated the role of ATP and its analogues as well as adenosine on neuronal activity in the TMN. We show increased firing of rat TMN neurons by ATP, ADP, UTP and 2meSATP, indicating activation of receptors belonging to the P2Y family. Adenosine affected neither membrane potential nor firing of these cells. Single-cell reverse transcriptase-polymerase chain reaction revealed that P2Y1 and P2Y4 are prevailing receptors in TMN neurons. P2Y1 receptor mRNA was detected with a higher frequency in 2-week-old than in 4-week-old rats; in accordance, 2meSATP was more potent than ATP. Semi-quantitative real-time polymerase chain reaction revealed a developmental downregulation of mRNA levels for P2Y1 and P2Y4 receptors. Immunocytochemistry demonstrated neuronal and glial localization of the P2Y1 receptor protein. Network activity measured with multielectrode arrays in primary cultures made from the posterior hypothalamus was enhanced by UTP and 2meSATP (P2Y4 and P2Y1 agonists, respectively). ATP caused an inhibition of firing, which was reversed in the presence of suramin or gabazine [gamma-aminobutyric acid (GABA)A receptor antagonist], indicating that GABAergic neurons are preferentially activated by ATP in this network. Excitation of the wake-active TMN neurons by nucleotides and the lack of adenosine action may be important factors in sleep-wake regulation.
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MESH Headings
- Action Potentials/drug effects
- Action Potentials/physiology
- Adenine Nucleotides/pharmacology
- Adenosine Diphosphate/analogs & derivatives
- Adenosine Diphosphate/pharmacology
- Animals
- Animals, Newborn
- Dose-Response Relationship, Drug
- Drug Interactions
- Gene Expression/drug effects
- Histamine/metabolism
- Hypothalamus, Posterior/cytology
- Hypothalamus, Posterior/drug effects
- Hypothalamus, Posterior/physiology
- Imidazoles/pharmacology
- Immunohistochemistry/methods
- In Vitro Techniques
- Male
- Methylhistamines/pharmacology
- Microtubule-Associated Proteins/metabolism
- Purinergic P2 Receptor Antagonists
- Pyridoxal Phosphate/analogs & derivatives
- Pyridoxal Phosphate/pharmacology
- RNA, Messenger/metabolism
- Rats
- Receptors, Metabotropic Glutamate/metabolism
- Receptors, Purinergic P2/classification
- Receptors, Purinergic P2/genetics
- Receptors, Purinergic P2/physiology
- Reverse Transcriptase Polymerase Chain Reaction/methods
- Temperature
- Thiorphan/analogs & derivatives
- Thiorphan/pharmacology
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Affiliation(s)
- Olga A Sergeeva
- Department of Neurophysiology, Heinrich-Heine-Universität, POB 101007, D-40001 Düsseldorf, Germany.
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72
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Abstract
Spontaneous physical activity is activity that is non-volitional, or subconscious, such as fidgeting and shifting in one's seat, and time spent moving (standing and ambulating). Recent evidence indicates that spontaneous physical activity, and the resulting thermogenesis (non-exercise activity thermogenesis) may be regulated by brain systems. A large number of brain areas, with their associated neurotransmitter populations and connectivity, participate in the regulation of feeding behavior by acting as energy sensing and modulating centers. Although less well characterized, it is likely that a multitude of neurotransmitters and brain areas act to mediate spontaneous physical activity. These two behaviors, feeding and spontaneous physical activity, affect energy intake and expenditure and thus are important to body weight. Interestingly, often the two behaviors are affected simultaneously; when feeding is affected, so too is spontaneous physical activity, and both food intake and physical activity (whether spontaneous or volitional) influence activity of brain areas important to both. Several brain areas and neuropeptides are important to feeding and spontaneous physical activity. The lateral hypothalamus is one area that appears important to both behaviors, as stimulation or lesion of this region produces alterations in feeding behavior and spontaneous physical activity. Orexin neurons, with their central location in the lateral hypothalamus, widespread projections and connectivity to other brain areas important to energy homeostasis, are well situated to perform an integrative function. This review focuses on how hypothalamic orexins participate in both feeding and spontaneous physical activity, and provides potential models for the integration of signals important to both.
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Affiliation(s)
- Catherine M Kotz
- Veterans Affairs Medical Center, One Veterans Drive, GRECC (11G), Minneapolis, MN 55417, USA.
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73
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Abstract
The finding of orexin (hypocretin) deficiency in patients with narcolepsy suggests that this hypothalamic neuropeptide plays a crucial role in regulating and maintaining sleep/wakefulness states and energy homeostasis. Orexin might be especially important for stabilization of behavioral states, because the major symptom in narcolepsy is instability of each behavioral state, which results in sleep/wakefulness fragmentation. The efferent and afferent systems of orexin neurons suggest interactions between these cells and arousal/sleep-wakefulness centers in the brainstem as well as important feeding centers in the hypothalamus. Electrophysiological studies have shown that orexin neurons are regulated by monoamines and acetylcholine as well as metabolic cues, including leptin, glucose, and ghrelin. Thus, orexin neurons have the requisite functional interactions with hypothalamic feeding pathways and monoaminergic/cholinergic centers, and provide a critical link between peripheral energy balance and the central mechanisms that coordinate sleep/wakefulness and motivated behavior such as food seeking.
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Affiliation(s)
- Takeshi Sakurai
- Department of Pharmacology, Institute of Basic Medical Sciences, University of Tsukuba, Ibaraki 305-8575, Japan.
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74
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Abstract
This paper is the 27th consecutive installment of the annual review of research concerning the endogenous opioid system, now spanning over 30 years of research. It summarizes papers published during 2004 that studied the behavioral effects of molecular, pharmacological and genetic manipulation of opioid peptides, opioid receptors, opioid agonists and opioid antagonists. The particular topics that continue to be covered include the molecular-biochemical effects and neurochemical localization studies of endogenous opioids and their receptors related to behavior, and the roles of these opioid peptides and receptors in pain and analgesia; stress and social status; tolerance and dependence; learning and memory; eating and drinking; alcohol and drugs of abuse; sexual activity and hormones, pregnancy, development and endocrinology; mental illness and mood; seizures and neurologic disorders; electrical-related activity and neurophysiology; general activity and locomotion; gastrointestinal, renal and hepatic functions; cardiovascular responses; respiration and thermoregulation; and immunological responses.
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Affiliation(s)
- Richard J Bodnar
- Department of Psychology and Neuropsychology Doctoral Sub-Program, Queens College, City University of New York, Flushing, NY 11367, USA.
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75
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Abstract
Since their discovery in 1998, the hypocretins (orexins)-peptides that are produced by a group of neurons situated in the posterolateral hypothalamus--have been shown to excite many CNS areas including many neuronal systems that regulate sleep and wakefulness. Animal studies indicate that hypocretins play a part in the regulation of various functions including arousal, muscle tone, locomotion, regulation of feeding behaviour, and neuroendocrine and autonomic functions. A link between hypocretin deficiency and narcoleptic symptoms was first shown in canine and rodent models of narcolepsy. Hypocretin deficiency, as shown by low or absent concentrations in CSF, was subsequently found in 90% of patients with sporadic narcolepsy-cataplexy, and less commonly in familial narcolepsy. In most other sleep-wake and neurological disorders, hypocretin concentrations are normal. Low concentrations were also found in hypothalamic disorders, acute traumatic brain injury, and a few other disorders. The exact function of the hypocretin system in sleep-wake regulation and its pathophysiological role in hypocretin-deficient and non-deficient narcolepsy as well as in non-narcoleptic, hypocretin-deficiency syndromes remain unclear.
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Affiliation(s)
- Christian R Baumann
- Department of Neurology, University Hospital, Frauenklinikstrasse 26, 8091 Zürich, Switzerland
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76
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Crocker A, España RA, Papadopoulou M, Saper CB, Faraco J, Sakurai T, Honda M, Mignot E, Scammell TE. Concomitant loss of dynorphin, NARP, and orexin in narcolepsy. Neurology 2005; 65:1184-8. [PMID: 16247044 PMCID: PMC2254145 DOI: 10.1212/01.wnl.0000168173.71940.ab] [Citation(s) in RCA: 212] [Impact Index Per Article: 11.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022] Open
Abstract
BACKGROUND Narcolepsy with cataplexy is associated with a loss of orexin/hypocretin. It is speculated that an autoimmune process kills the orexin-producing neurons, but these cells may survive yet fail to produce orexin. OBJECTIVE To examine whether other markers of the orexin neurons are lost in narcolepsy with cataplexy. METHODS We used immunohistochemistry and in situ hybridization to examine the expression of orexin, neuronal activity-regulated pentraxin (NARP), and prodynorphin in hypothalami from five control and two narcoleptic individuals. RESULTS In the control hypothalami, at least 80% of the orexin-producing neurons also contained prodynorphin mRNA and NARP. In the patients with narcolepsy, the number of cells producing these markers was reduced to about 5 to 10% of normal. CONCLUSIONS Narcolepsy with cataplexy is likely caused by a loss of the orexin-producing neurons. In addition, loss of dynorphin and neuronal activity-regulated pentraxin may contribute to the symptoms of narcolepsy.
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Affiliation(s)
- A Crocker
- Department of Neurology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, MA, USA
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77
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Baumann CR, Bassetti CL. Hypocretins (orexins): clinical impact of the discovery of a neurotransmitter. Sleep Med Rev 2005; 9:253-68. [PMID: 15979356 DOI: 10.1016/j.smrv.2005.01.005] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Abstract
Hypothalamic excitatory hypocretin (orexin) neurons have been discovered in 1998 and found to have widespread projections to basal forebrain, monoaminergic and cholinergic brainstem, and spinal cord regions. The hypocretin system is influenced both neuronally (e.g. suprachiasmatic nucleus, GABAergic, cholinergic and aminergic brainstem nuclei) as well as metabolically (e.g. glucose, ghrelin, and leptin). Physiologically the hypocretin system has been implicated in the regulation of behaviours that are associated with wakefulness, locomotion, and feeding. A role in REM sleep, neuroendocrine, autonomic and metabolic functions has also been suggested. Pathophysiologically a deficient hypocretin neurotransmission has been found in human narcolepsy and (engineered) animal models of the disorder. Different mechanisms are involved including (1) degeneration of hypocretin neurons (mice), (2) hypocretin ligand deficiency (humans, mice, dogs), (3) hypocretin receptor deficiency (mice, dogs). Reports of low hypocretin-1 cerebrospinal fluid levels in neurologic conditions (e.g. Guillain-Barré syndrome, traumatic brain injury, hypothalamic lesions) with and without sleep-wake disturbances and, on the other hand, observations of normal levels in about 11% of narcoleptics raise questions about the exact nature and pathophysiological base of the link between hypocretin deficiency and clinical manifestations in human narcolepsy.
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Affiliation(s)
- Christian R Baumann
- Neurologische Klinik, Universitätsspital Zürich, Frauenklinikstrasse 26, CH-8091 Zürich, Switzerland
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78
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Abstract
Performance enhancing agents are prohibited in athletic competition so that only athletic skills can determine outcomes. Modafinil is a novel non-addicting psychostimulant approved for treatment of narcolepsy. Does its use, especially for medical indications, violate the Olympic Movement Anti-Doping Code? This is discussed with reference to a current high profile case.
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Affiliation(s)
- K R Kaufman
- Department of Psychiatry, UMDNJ-Robert Wood Johnson Medical School, New Brunswick, NJ, USA.
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79
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Hara J, Yanagisawa M, Sakurai T. Difference in obesity phenotype between orexin-knockout mice and orexin neuron-deficient mice with same genetic background and environmental conditions. Neurosci Lett 2005; 380:239-42. [PMID: 15862893 DOI: 10.1016/j.neulet.2005.01.046] [Citation(s) in RCA: 146] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/25/2004] [Revised: 12/16/2004] [Accepted: 01/15/2005] [Indexed: 12/31/2022]
Abstract
Orexins are a pair of neuropeptides expressed by a population of neurons located in the lateral hypothalamic area (LHA). Prepro-orexin- or orexin receptor type 2-deficient animals exhibit a phenotype remarkably similar to the human sleep disorder, narcolepsy, which is characterized by sleep/wakefulness fragmentation. Human narcolepsy is known to be associated with metabolic abnormalities, including an increased frequency of obesity and non-insulin-dependent diabetes mellitus. Complex disruption of energy homeostasis in orexin neuron-deficient transgenic mice (orexin/ataxin-3 mice) is also manifested as late-onset obesity despite eating less. Here, we report that the development of obesity in orexin neuron-ablated narcoleptic mice is critically dependent on their genetic background and environmental factors, and the phenotype is different from that of prepro-orexin knockout mice even under the same genetic background and environmental factors, suggesting that factors that co-localize in orexin neurons might have important roles in the regulation of energy homeostasis. Our observation also suggests that the obesity observed in orexin neuron-deficient narcolepsy is dependent on the genetic background and environmental factors.
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Affiliation(s)
- Junko Hara
- Institute of Basic Medical Sciences, Department of Pharmacology, University of Tsukuba, Ibaraki 305-8575, Japan
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80
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Abstract
Orexins, which were initially identified as endogenous peptide ligands for two orphan G-protein coupled receptors (GPCRs), have been shown to have an important role in the regulation of energy homeostasis. Furthermore, the discovery of orexin deficiency in narcolepsy patients indicated that orexins are highly important factors for the sleep/wakefulness regulation. The efferent and afferent systems of orexin-producing neurons suggest interactions between these cells and arousal centers in the brainstem as well as important feeding centers in the hypothalamus. Electrophysiological studies have shown that orexin neurons are regulated by humoral factors, including leptin, glucose, and ghrelin as well as monoamines and acetylcholin. Thus, orexin neurons have functional interactions with hypothalamic feeding pathways and monoaminergic/cholinergic centers to provide a link between peripheral energy balance and the CNS mechanisms that coordinate sleep/wakefulness states and motivated behavior such as food seeking.
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Affiliation(s)
- Takeshi Sakurai
- Department of Pharmacology, Institute of Basic Medical Science, University of Tsukuba, Tsukuba, Ibaraki 305-8575, Japan.
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81
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Hong ZY, Huang ZL, Qu WM, Eguchi N, Urade Y, Hayaishi O. An adenosine A2A receptor agonist induces sleep by increasing GABA release in the tuberomammillary nucleus to inhibit histaminergic systems in rats. J Neurochem 2005; 92:1542-9. [PMID: 15748171 DOI: 10.1111/j.1471-4159.2004.02991.x] [Citation(s) in RCA: 93] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The adenosine A(2A) receptor (A(2A)R) has been demonstrated to play a crucial role in the regulation of the sleep process. However, the molecular mechanism of the A(2A)R-mediated sleep remains to be elucidated. Here we used electroencephalogram and electromyogram recordings coupled with in vivo microdialysis to investigate the effects of an A(2A)R agonist, CGS21680, on sleep and on the release of histamine and GABA in the brain. In freely moving rats, CGS21680 applied to the subarachnoid space underlying the rostral basal forebrain significantly promoted sleep and inhibited histamine release in the frontal cortex. The histamine release was negatively correlated with the amount of non-rapid eye movement sleep (r = - 0.652). In urethane-anesthetized rats, CGS21680 inhibited histamine release in both the frontal cortex and medial pre-optic area in a dose-dependent manner, and increased GABA release specifically in the histaminergic tuberomammillary nucleus but not in the frontal cortex. Moreover, the CGS21680-induced inhibition of histamine release was antagonized by perfusion of the tuberomammillary nucleus with a GABA(A) antagonist, picrotoxin. These results suggest that the A(2A)R agonist induced sleep by inhibiting the histaminergic system through increasing GABA release in the tuberomammillary nucleus.
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Affiliation(s)
- Zong-Yuan Hong
- School of Life Science, University of Science and Technology of China, Hefei, Anhui, China
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82
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Bentivoglio M, Morelli M. Chapter I The organization and circuits of mesencephalic dopaminergic neurons and the distribution of dopamine receptors in the brain. HANDBOOK OF CHEMICAL NEUROANATOMY 2005. [DOI: 10.1016/s0924-8196(05)80005-3] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
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83
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Abstract
African trypanosomiasis or sleeping sickness is hallmarked by sleep and wakefulness disturbances. In contrast to other infections, there is no hypersomnia, but the sleep pattern is fragmented. This overview discusses that the causative agents, the parasites Trypanosoma brucei, target circumventricular organs in the brain, causing inflammatory responses in hypothalamic structures that may lead to dysfunctions in the circadian-timing and sleep-regulatory systems.
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