201
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Tsujino N, Sakurai T. Orexin/hypocretin: a neuropeptide at the interface of sleep, energy homeostasis, and reward system. Pharmacol Rev 2010; 61:162-76. [PMID: 19549926 DOI: 10.1124/pr.109.001321] [Citation(s) in RCA: 336] [Impact Index Per Article: 24.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Recent studies have implicated the orexin system as a critical regulator of sleep/wake states as well as feeding behavior and reward processes. Orexin deficiency results in narcolepsy in humans, dogs, and rodents, suggesting that the orexin system is particularly important for maintenance of wakefulness. In addition, orexin deficiency also cause abnormalities in energy homeostasis and reward systems. Orexin activates waking active monoaminergic and cholinergic neurons in the hypothalamus and brainstem regions to maintain a long, consolidated waking period. Orexin neurons receive abundant input from the limbic system. Orexin neurons also have reciprocal links with the hypothalamic arcuate nucleus, which regulates feeding. Moreover, the responsiveness of orexin neurons to peripheral metabolic cues, such as leptin and glucose, suggest that these neurons have important role as a link between the energy homeostasis and vigilance states. Orexin neurons also have a link with the dopaminergic reward system in the ventral tegmental nucleus. These findings suggest that the orexin system interacts with systems that regulate emotion, reward, and energy homeostasis to maintain proper vigilance states. Therefore, this system may be a potentially important therapeutic target for treatment of sleep disorder, obesity, emotional stress, and addiction.
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Affiliation(s)
- Natsuko Tsujino
- Department of Molecular Neuroscience and Integrative Physiology, Graduate School of Medical Science, Kanazawa University, 13-1 Takaramachi, Kanazawa-shi, Ishikawa 920-8640, Japan
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202
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Abstract
Orexin-A (hypocretin-1) and orexin-B (hypocretin-2) are hypothalamic neuropeptides that play key roles in the regulation of wakefulness, feeding, reward, autonomic functions and energy homeostasis. To control these functions indispensable for survival, orexin-expressing neurones integrate peripheral metabolic signals, interact with many types of neurones in the brain and modulate their activities via the activation of orexin-1 receptor or orexin-2 receptor. In addition, a new functional role of orexin is emerging in the regulation of insulin and leptin sensitivities responsible for whole-body glucose metabolism. Recent evidence indicates that orexin efficiently protects against the development of peripheral insulin resistance induced by ageing or high-fat feeding in mice. In particular, the orexin receptor-2 signalling appears to confer resistance to diet-induced obesity and insulin insensitivity by improving leptin sensitivity. In fact, the expression of orexin gene is known to be down-regulated by hyperglycaemia in the rodent model of diabetes, such as ob/ob and db/db mice. Moreover, the levels of orexin receptor-2 mRNA have been shown to decline in the brain of mice along with ageing. These suggest that hyperglycaemia due to insulin insensitivity during ageing or by habitual consumption of a high-fat diet leads to the reduction in orexin expression in the hypothalamus, thereby further exacerbating peripheral insulin resistance. Therefore, orexin receptor controlling hypothalamic insulin/leptin actions may be a new target for possible future treatment of hyperglycaemia in patients with type 2 diabetes.
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Affiliation(s)
- H Tsuneki
- Department of Clinical Pharmacology, University of Toyama, Toyama, Japan
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203
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Dias MB, Li A, Nattie E. The orexin receptor 1 (OX1R) in the rostral medullary raphe contributes to the hypercapnic chemoreflex in wakefulness, during the active period of the diurnal cycle. Respir Physiol Neurobiol 2010; 170:96-102. [PMID: 19995618 PMCID: PMC2844074 DOI: 10.1016/j.resp.2009.12.002] [Citation(s) in RCA: 48] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2009] [Revised: 11/09/2009] [Accepted: 12/02/2009] [Indexed: 10/20/2022]
Abstract
It has been shown that orexin plays an important role in the hypercapnic chemoreflex during wakefulness, and OX(1)Rs in the retrotrapezoid nucleus (RTN) participate in this mechanism. We hypothesized that OX(1)R in the rostral medullary raphe (MR) also contributes to the hypercapnic chemoreflex. We studied the effects on ventilation in air and in 7% CO(2) of focal antagonism of OX(1)R in the rostral MR by microdialysis of SB-334867 in rats during wakefulness and NREM sleep, under dark and light periods. During wakefulness in the dark period, but not in the light period, SB-334867 caused a 16% reduction of the hyperventilation induced by 7% CO(2) compared with vehicle. There was no significant effect in sleep. The basal ventilation, body temperature and V(O2) were not affected. No effect was observed in a separate group of animals which had the microdialysis probe misplaced (peri-raphe). We conclude that OX(1)R in the rostral medullary raphe contribute to the hypercapnic chemoreflex in wakefulness, during the dark period in rats.
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Affiliation(s)
- Mirela Barros Dias
- Department of Physiology, Dartmouth Medical School, Lebanon, NH 03756-0001, USA
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204
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Guyenet PG, Stornetta RL, Abbott SBG, Depuy SD, Fortuna MG, Kanbar R. Central CO2 chemoreception and integrated neural mechanisms of cardiovascular and respiratory control. J Appl Physiol (1985) 2010; 108:995-1002. [PMID: 20075262 DOI: 10.1152/japplphysiol.00712.2009] [Citation(s) in RCA: 103] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023] Open
Abstract
In this review, we examine why blood pressure (BP) and sympathetic nerve activity (SNA) increase during a rise in central nervous system (CNS) P(CO(2)) (central chemoreceptor stimulation). CNS acidification modifies SNA by two classes of mechanisms. The first one depends on the activation of the central respiratory controller (CRG) and causes the much-emphasized respiratory modulation of the SNA. The CRG probably modulates SNA at several brain stem or spinal locations, but the most important site of interaction seems to be the caudal ventrolateral medulla (CVLM), where unidentified components of the CRG periodically gate the baroreflex. CNS P(CO(2)) also influences sympathetic tone in a CRG-independent manner, and we propose that this process operates differently according to the level of CNS P(CO(2)). In normocapnia and indeed even below the ventilatory recruitment threshold, CNS P(CO(2)) exerts a tonic concentration-dependent excitatory effect on SNA that is plausibly mediated by specialized brain stem chemoreceptors such as the retrotrapezoid nucleus. Abnormally high levels of P(CO(2)) cause an aversive interoceptive awareness in awake individuals and trigger arousal from sleep. These alerting responses presumably activate wake-promoting and/or stress-related pathways such as the orexinergic, noradrenergic, and serotonergic neurons. These neuronal groups, which may also be directly activated by brain acidification, have brainwide projections that contribute to the CO(2)-induced rise in breathing and SNA by facilitating neuronal activity at innumerable CNS locations. In the case of SNA, these sites include the nucleus of the solitary tract, the ventrolateral medulla, and the preganglionic neurons.
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908-0735, USA.
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205
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Buckler KJ. Two-pore domain k(+) channels and their role in chemoreception. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 661:15-30. [PMID: 20204721 DOI: 10.1007/978-1-60761-500-2_2] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
A number of tandem P-domain K(+)- channels (K(2)P) generate background K(+)-currents similar to those found in enteroreceptors that sense a diverse range of physiological stimuli including blood pH, carbon dioxide, oxygen, potassium and glucose. This review presents an overview of the properties of both cloned K(2)P tandem-P-domain K-channels and the endogenous chemosensitive background K-currents found in central chemoreceptors, peripheral chemoreceptors, the adrenal gland and the hypothalamus. Although the identity of many of these endogenous channels has yet to be confirmed they show striking similarities to a number of K(2)P channels especially those of the TASK subgroup. Moreover these channels seem often (albeit not exclusively) to be involved in pH and nutrient/metabolic sensing.
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Affiliation(s)
- Keith J Buckler
- Department of Physiology Anatomy and Genetics, University of Oxford, Parks Road, Oxford, OX1 3PT, UK.
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206
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Corcoran A, Richerson G, Harris M. Modulation of respiratory activity by hypocretin-1 (orexin A) in situ and in vitro. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 669:109-13. [PMID: 20217331 PMCID: PMC3858080 DOI: 10.1007/978-1-4419-5692-7_22] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Release of hypocretins (orexins) by neurons in the lateral hypothalamus is an important contributor to arousal state, thermoregulation, feeding behavior, and has recently been proposed to play a role in breathing and central chemosensitivity. Using the in situ arterially perfused juvenile rat preparation, we determined the effect of hypocretin-1 (hcrt-1) and SB-408124 (antagonist for hypocretin receptor subtype 1, hcrt-r1) on phrenic nerve activity, a neural correlate of breathing (neuroventilation), and the neuroventilatory sensitivity to CO(2). Application of hcrt-1 through the perfusate had little effect on baseline firing. Blocking hcrt-r1, however, prevented the phrenic burst frequency response normally associated with hypercapnia. These data suggest that endogenous hypocretinergic modulation enhances neuroventilatory chemosensitivity. Further studies using the in vitro medullary slice preparation explored the effect of hcrt-1 on hypoglossal nerve activity, a correlate of ventilation in vitro. Application of exogenous hcrt-1 failed to significantly alter hypoglossal burst output in neonatal rat slices, indicating that this portion of the neuroventilatory circuit is insensitive to hcrt-1. Taken together, these data suggest that hcrt-1 is a modulator of central chemosensitivity.
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Affiliation(s)
- Andrea Corcoran
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK, USA,
| | - George Richerson
- Department of Neurology, Yale University, New Haven, CT, USA, , Veterans Affairs Medical Center, West Haven, CT, USA
| | - Michael Harris
- Department of Biology and Wildlife, University of Alaska Fairbanks, Fairbanks, AK, USA,
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207
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Kuwaki T. Hypothalamic modulation of breathing. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2010; 669:243-7. [PMID: 20217358 DOI: 10.1007/978-1-4419-5692-7_49] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/12/2022]
Abstract
Hypothalamus has long been known to be involved in the regulation of breathing. For example, many neurons are activated by hypoxia and hypercapnia and stimulation to the hypothalamus increases respiration. However, precise characters of these neurons have not well understood until recently presumably because hypothalamus is a heterogeneous structure intermingly containing many kind of neurotransmitters. The situation has dramatically changed by a discovery of hypothalamic neuropeptide orexin in 1998 and subsequent development of orexin-knockout mice in 1999. Here I summarize our recent discovery of the possible contribution of orexin to the vigilance-state-dependent adjustment of central respiratory regulation. Orexin-deficient mice show an attenuated hypercapnic ventilatory response during the awake but not during the sleep period, whereas basal ventilation remained normal, irrespective of the vigilance state. Orexin supplementation remedied the defect, and the administration of an orexin receptor antagonist to wild-type mice mimicked the abnormality. Hypercapnic stimulation activated orexinergic neurons in the wild-type mice. Orexin-deficient mice also showed frequent sleep apneas and loss of repetitive intermittent hypoxia-induced ventilatory and phrenic long-term facilitation. Hence, it is possible that the orexin system is one of the essential modulators required for coordinating the circuits controlling respiration and behavior.
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Affiliation(s)
- Tomoyuki Kuwaki
- Department of Physiology, Kagoshima University Graduate School of Medical and Dental Sciences, Kagoshima, Japan.
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208
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Boutrel B, Cannella N, de Lecea L. The role of hypocretin in driving arousal and goal-oriented behaviors. Brain Res 2009; 1314:103-11. [PMID: 19948148 DOI: 10.1016/j.brainres.2009.11.054] [Citation(s) in RCA: 97] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/25/2009] [Revised: 11/13/2009] [Accepted: 11/20/2009] [Indexed: 12/29/2022]
Abstract
The hypocretins (Hcrts), also called orexins, are two neuropeptides secreted by a few thousand neurons restricted to the lateral hypothalamus. The Hcrt peptides bind to two receptors located in nuclei associated with diverse cognitive and physiological functions. Experimental evidence has demonstrated that the physiological roles of hypocretins extend far beyond its initial role in food consumption and has emerged as a key system in the fields of sleep disorders and drug addiction. Here, we discuss recent evidence demonstrating a key role of hypocretin in the motivation for reward seeking in general, and drug taking in particular, and we delineate a physiological framework for this peptidergic system in orchestrating the appropriate levels of alertness required for the elaboration and the execution of goal-oriented behaviors. We propose a general role for hypocretins in mediating arousal, especially when an organism must respond to unexpected stressors and environmental challenges, which serve to shape survival behaviors. We also discuss the limit of the current experimental paradigms to address the question of how a system normally involved in the regulation of vigilance states and hyperarousal may promote a pathological state that elicits compulsive craving and relapse to drug seeking.
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Affiliation(s)
- Benjamin Boutrel
- Center for Psychiatric Neuroscience, CHUV-Department of Psychiatry, Site de Cery, CH-1008 Prilly-Lausanne, Switzerland.
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209
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Guyenet PG, Bayliss DA, Stornetta RL, Fortuna MG, Abbott SBG, DePuy SD. Retrotrapezoid nucleus, respiratory chemosensitivity and breathing automaticity. Respir Physiol Neurobiol 2009; 168:59-68. [PMID: 19712903 PMCID: PMC2734912 DOI: 10.1016/j.resp.2009.02.001] [Citation(s) in RCA: 69] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/04/2009] [Revised: 02/03/2009] [Accepted: 02/05/2009] [Indexed: 10/21/2022]
Abstract
Breathing automaticity and CO(2) regulation are inseparable neural processes. The retrotrapezoid nucleus (RTN), a group of glutamatergic neurons that express the transcription factor Phox2b, may be a crucial nodal point through which breathing automaticity is regulated to maintain CO(2) constant. This review updates the analysis presented in prior publications. Additional evidence that RTN neurons have central respiratory chemoreceptor properties is presented, but this is only one of many factors that determine their activity. The RTN is also regulated by powerful inputs from the carotid bodies and, at least in the adult, by many other synaptic inputs. We also analyze how RTN neurons may control the activity of the downstream central respiratory pattern generator. Specifically, we review the evidence which suggests that RTN neurons (a) innervate the entire ventral respiratory column and (b) control both inspiration and expiration. Finally, we argue that the RTN neurons are the adult form of the parafacial respiratory group in neonate rats.
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Affiliation(s)
- Patrice G Guyenet
- Department of Pharmacology, University of Virginia, Charlottesville, VA 22908, USA.
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210
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Erlichman JS, Boyer AC, Reagan P, Putnam RW, Ritucci NA, Leiter JC. Chemosensory responses to CO2 in multiple brain stem nuclei determined using a voltage-sensitive dye in brain slices from rats. J Neurophysiol 2009; 102:1577-90. [PMID: 19553484 DOI: 10.1152/jn.00381.2009] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We used epifluorescence microscopy and a voltage-sensitive dye, di-8-ANEPPS, to study changes in membrane potential during hypercapnia with or without synaptic blockade in chemosensory brain stem nuclei: the locus coeruleus (LC), the nucleus of the solitary tract, lateral paragigantocellularis nucleus, raphé pallidus, and raphé obscurus and, in putative nonchemosensitive nuclei, the gigantocellularis reticular nucleus and the spinotrigeminal nucleus. We studied the response to hypercapnia in LC cells to evaluate the performance characteristics of the voltage-sensitive dye. Hypercapnia depolarized many LC cells and the voltage responses to hypercapnia were diminished, but not eradicated, by synaptic blockade (there were intrinsically CO2-sensitive cells in the LC). The voltage response to hypercapnia was substantially diminished after inhibiting fast Na+ channels with tetrodotoxin. Thus action potential-related activity was responsible for most of the optical signal that we detected. We systematically examined CO2 sensitivity among cells in brain stem nuclei to test the hypothesis that CO2 sensitivity is a ubiquitous phenomenon, not restricted to nominally CO2 chemosensory nuclei. We found intrinsically CO2 sensitive neurons in all the nuclei that we examined; even the nonchemosensory nuclei had small numbers of intrinsically CO2 sensitive neurons. However, synaptic blockade significantly altered the distribution of CO2-sensitive cells in all of the nuclei so that the cellular response to CO2 in more intact preparations may be difficult to predict based on studies of intrinsic neuronal activity. Thus CO2-sensitive neurons are widely distributed in chemosensory and nonchemosensory nuclei and CO2 sensitivity is dependent on inhibitory and excitatory synaptic activity even within brain slices. Neuronal CO2 sensitivity important for the behavioral response to CO2 in intact animals will thus be determined as much by synaptic mechanisms and patterns of connectivity throughout the brain as by intrinsic CO2 sensitivity.
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211
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González JA, Jensen LT, Doyle SE, Miranda-Anaya M, Menaker M, Fugger L, Bayliss DA, Burdakov D. Deletion of TASK1 and TASK3 channels disrupts intrinsic excitability but does not abolish glucose or pH responses of orexin/hypocretin neurons. Eur J Neurosci 2009; 30:57-64. [PMID: 19508695 DOI: 10.1111/j.1460-9568.2009.06789.x] [Citation(s) in RCA: 52] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The firing of hypothalamic hypocretin/orexin neurons is vital for normal sleep-wake transitions, but its molecular determinants are not well understood. It was recently proposed that TASK (TWIK-related acid-sensitive potassium) channels [TASK1 (K(2P)3.1) and/or TASK3 (K(2P)9.1)] regulate neuronal firing and may contribute to the specialized responses of orexin neurons to glucose and pH. Here we tested these theories by performing patch-clamp recordings from orexin neurons directly identified by targeted green fluorescent protein labelling in brain slices from TASK1/3 double-knockout mice. The deletion of TASK1/3 channels significantly reduced the ability of orexin cells to generate high-frequency firing. Consistent with reduced excitability, individual action potentials from knockout cells had lower rates of rise, higher thresholds and more depolarized after-hyperpolarizations. However, orexin neurons from TASK1/3 knockout mice retained typical responses to glucose and pH, and the knockout animals showed normal food-anticipatory locomotor activity. Our results support a novel role for TASK genes in enhancing neuronal excitability and promoting high-frequency firing, but suggest that TASK1/3 subunits are not essential for orexin cell responses to glucose and pH.
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Affiliation(s)
- J A González
- Department of Pharmacology, University of Cambridge, Cambridge CB2 1 PD, UK
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212
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Sunanaga J, Deng BS, Zhang W, Kanmura Y, Kuwaki T. CO2 activates orexin-containing neurons in mice. Respir Physiol Neurobiol 2009; 166:184-6. [DOI: 10.1016/j.resp.2009.03.006] [Citation(s) in RCA: 60] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/02/2009] [Revised: 03/05/2009] [Accepted: 03/07/2009] [Indexed: 10/21/2022]
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213
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Kuwaki T. Orexinergic modulation of breathing across vigilance states. Respir Physiol Neurobiol 2009; 164:204-12. [PMID: 18455970 DOI: 10.1016/j.resp.2008.03.011] [Citation(s) in RCA: 68] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/26/2008] [Revised: 03/23/2008] [Accepted: 03/24/2008] [Indexed: 10/22/2022]
Abstract
Basal respiration and respiratory reflex regulations are considerably different during the awake and sleep states. Tidal volume and respiratory frequency diminish during sleep, and hypoxic and hypercapnic ventilatory responses also decline during sleep. Reduced metabolic demand during sleep cannot completely explain these phenomena because PaCO2 increases during sleep. In this review, I will summarize our recent discovery of the possible contribution of orexin, a hypothalamic neuropeptide, to the vigilance state-dependent adjustment of central respiratory regulation. Orexin-deficient mice show an attenuated hypercapnic ventilatory response during the awake but not during the sleep period, whereas basal ventilation remained normal, irrespective of the vigilance state. Orexin supplementation remedied the defect, and the administration of an orexin receptor antagonist to wild-type mice mimicked the abnormality. Orexin-deficient mice also showed frequent sleep apneas and loss of repetitive intermittent hypoxia-induced ventilatory long-term facilitation. Hence, it is possible that the orexin system is one of the essential modulators required for coordinating the circuits controlling respiration and behavior.
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Affiliation(s)
- Tomoyuki Kuwaki
- Department of Molecular & Integrative Physiology, Chiba University Graduate School of Medicine, Inohana 1-8-1, Chuo-ku, Chiba 260-8670, Japan.
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214
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González JA, Horjales-Araujo E, Fugger L, Broberger C, Burdakov D. Stimulation of orexin/hypocretin neurones by thyrotropin-releasing hormone. J Physiol 2009; 587:1179-86. [PMID: 19204048 PMCID: PMC2674990 DOI: 10.1113/jphysiol.2008.167940] [Citation(s) in RCA: 46] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2008] [Accepted: 01/27/2009] [Indexed: 02/01/2023] Open
Abstract
Central orexin/hypocretin neurones are critical for sustaining consciousness: their firing stimulates wakefulness and their destruction causes narcolepsy. We explored whether the activity of orexin cells is modulated by thyrotropin-releasing hormone (TRH), an endogenous stimulant of wakefulness and locomotor activity whose mechanism of action is not fully understood. Living orexin neurones were identified by targeted expression of green fluorescent protein (GFP) in acute brain slices of transgenic mice. Using whole-cell patch-clamp recordings, we found that TRH robustly increased the action potential firing rate of these neurones. TRH-induced excitation persisted under conditions of synaptic isolation, and involved a Na(+)-dependent depolarization and activation of a mixed cation current in the orexin cell membrane. By double-label immunohistochemistry, we found close appositions between TRH-immunoreactive nerve terminals and orexin-A-immunoreactive cell bodies. These results identify a new physiological modulator of orexin cell firing, and suggest that orexin cell excitation may contribute to the arousal-enhancing actions of TRH.
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Affiliation(s)
- J Antonio González
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge CB2 1PD, UK
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215
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Dias MB, Li A, Nattie EE. Antagonism of orexin receptor-1 in the retrotrapezoid nucleus inhibits the ventilatory response to hypercapnia predominantly in wakefulness. J Physiol 2009; 587:2059-67. [PMID: 19273574 DOI: 10.1113/jphysiol.2008.168260] [Citation(s) in RCA: 78] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022] Open
Abstract
Recent data from transgenic mice suggest that orexin plays an important role in the ventilatory response to CO(2) during wakefulness. We hypothesized that orexin receptor-1 (OX(1)R) in the retrotrapezoid nucleus (RTN) contributes to chemoreception. In unanaesthetized rats, we measured ventilation using a whole-body plethysmograph, together with EEG and EMG. We dialysed the vehicle and then SB-334867 (OX(1)R antagonist) into the RTN to focally inhibit OX(1)R and studied the effects of both treatments on breathing in air and in 7% CO(2). During wakefulness, SB-334867 caused a 30% reduction of the hyperventilation induced by 7% CO(2) (mean +/- S.E.M., 135 +/- 10 ml (100 g)(-1) min(-1)) compared with vehicle (182 +/- 10 ml (100 g)(-1) min(-1)) (P < 0.01). This effect was due to both decreased tidal volume and breathing frequency. There was a much smaller, though significant, effect in sleep (9% reduction). Neither basal ventilation nor oxygen consumption was affected. The number and duration of apnoeas were similar between control and treatment periods. No effect was observed in a separate group of animals who had the microdialysis probe misplaced (peri-RTN). We conclude that projections of orexin-containing neurons to the RTN contribute, via OX(1)Rs in the region, to the hypercapnic chemoreflex control during wakefulness and to a lesser extent, non-rapid eye movement sleep.
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Affiliation(s)
- Mirela Barros Dias
- Department of Physiology, Dartmouth Medical School, Lebanon, NH 03756-0001, USA
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216
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Williams RH, Burdakov D. Silencing of ventromedial hypothalamic neurons by glucose-stimulated K(+) currents. Pflugers Arch 2009; 458:777-83. [PMID: 19238426 DOI: 10.1007/s00424-009-0650-6] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/13/2008] [Revised: 02/04/2009] [Accepted: 02/08/2009] [Indexed: 01/09/2023]
Abstract
Glucose sensing by neurons of the ventromedial hypothalamus (VMH) plays a central role in the regulation of body energy balance. Physiological rises in extracellular glucose levels hyperpolarise and inhibit a group of VMH neurons. This specialised sensing response is currently thought to involve glucose-induced activation of chloride channels, but alternative mechanisms have not been explored in detail. In this study, we converted all chloride channels from inhibitory to excitatory by filling the cytosol of VMH neurons with a high concentration of chloride. Despite this, some VMH neurons were still strongly hyperpolarised and inhibited by glucose. Voltage-clamp analysis revealed that this was due to glucose-induced activation of K(+)-selective currents of sufficient size to cause complete inhibition of whole-cell electrical activity. These K(+) currents exhibited leak-like biophysical properties and were inhibited by extracellular acidification. Our data support the idea that glucose-stimulated K(+) currents contribute to sugar-induced suppression of firing in the VMH.
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Affiliation(s)
- Rhiannan H Williams
- Department of Pharmacology, University of Cambridge, Tennis Court Road, Cambridge, CB2 1PD, UK
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217
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Abstract
Glucose-inhibited neurones are an integral part of neurocircuits regulating cognitive arousal, body weight and vital adaptive behaviours. Their firing is directly suppressed by extracellular glucose through poorly understood signalling cascades culminating in opening of post-synaptic K(+) or possibly Cl(-) channels. In mammalian brains, two groups of glucose-inhibited neurones are best understood at present: neurones of the hypothalamic arcuate nucleus (ARC) that express peptide transmitters NPY and agouti-related peptide (AgRP) and neurones of the lateral hypothalamus (LH) that express peptide transmitters orexins/hypocretins. The activity of ARC NPY/AgRP neurones promotes food intake and suppresses energy expenditure, and their destruction causes a severe reduction in food intake and body weight. The physiological actions of ARC NPY/AgRP cells are mediated by projections to numerous hypothalamic areas, as well as extrahypothalamic sites such as the thalamus and ventral tegmental area. Orexin/hypocretin neurones of the LH are critical for normal wakefulness, energy expenditure and reward-seeking, and their destruction causes narcolepsy. Orexin actions are mediated by highly widespread central projections to virtually all brain areas except the cerebellum, including monosynaptic innervation of the cerebral cortex and autonomic pre-ganglionic neurones. There, orexins act on two specific G-protein-coupled receptors generally linked to neuronal excitation. In addition to sensing physiological changes in sugar levels, the firing of both NPY/AgRP and orexin neurones is inhibited by the 'satiety' hormone leptin and stimulated by the 'hunger' hormone ghrelin. Glucose-inhibited neurones are thus well placed to coordinate diverse brain states and behaviours based on energy levels.
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Affiliation(s)
- D Burdakov
- Department of Pharmacology, University of Cambridge, Cambridge, UK.
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218
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Role of chemoreceptors in mediating dyspnea. Respir Physiol Neurobiol 2008; 167:9-19. [PMID: 19118647 DOI: 10.1016/j.resp.2008.12.002] [Citation(s) in RCA: 56] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/30/2008] [Revised: 11/26/2008] [Accepted: 12/04/2008] [Indexed: 11/22/2022]
Abstract
Dyspnea, or the uncomfortable awareness of respiratory distress, is a common symptom experienced by most people at some point during their lifetime. It is commonly encountered in individuals with pulmonary disease, such as chronic obstructive pulmonary disease (COPD), but can also be seen in healthy individuals after strenuous exercise, at altitude or in response to psychological stress. Dyspnea is a multifactorial sensation involving the brainstem, cortex, and limbic system, as well as mechanoreceptors, irritant receptors and chemoreceptors. Chemoreceptors appear to contribute to the sensation of dyspnea in two ways. They stimulate the respiratory control system in response to hypoxia and/or hypercapnia, and the resultant increase respiratory motor output can be consciously perceived as unpleasant. They also can induce the sensation of dyspnea through an as yet undetermined mechanism-potentially via direct ascending connections to the limbic system and cortex. The goal of this article is to briefly review how changes in blood gases reach conscious awareness and how chemoreceptors are involved in dyspnea.
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219
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Abstract
Sleep disturbances are associated with hormonal imbalances and may result in metabolic disorders including obesity and diabetes. Therefore, circuits controlling both sleep and metabolism are likely to play a role in these physiopathological conditions. The hypocretin (Hcrt) system is a strong candidate for mediating both sleep and metabolic imbalances because Hcrt neurons are sensitive to metabolic hormones, including leptin and ghrelin, and modulate arousal and goal-orientated behaviours. This review discusses the role of Hcrt neurons as a sensors of energy balance and arousal and proposes new ways of probing local hypothalamic circuits regulating sleep and metabolism with unprecedented cellular specificity and temporal resolution.
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Affiliation(s)
- Antoine Adamantidis
- Department of Psychiatry and Behavioral Sciences, Stanford University School of Medicine, Palo Alto, CA 94304-5742, USA.
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220
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The dual role of the orexin/hypocretin system in modulating wakefulness and respiratory drive. Curr Opin Pulm Med 2008; 14:512-8. [PMID: 18812827 DOI: 10.1097/mcp.0b013e32831311d3] [Citation(s) in RCA: 36] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/21/2022]
Abstract
PURPOSE OF REVIEW Today, numerous studies show that orexin peptides act as regulators of many functions including the control of sleep-wake states, breathing, and central chemosensitivity. However, little is known on neuronal mechanisms by which orexin regulates breathing in a state-dependent manner. This review summarizes recent data on the control of neuronal circuits by orexin, with a special emphasis on breathing, central chemosensitivity, and obstructive sleep apneas. RECENT FINDINGS Activity of hypothalamic orexinergic neurons is subjected to maturation and is mandatory to maintain long bouts of wakefulness in adults. At wake onset, this activity progressively builds up as a result of synaptic interactions and reinforces the awake state. Orexin deficiency attenuates the hypercapnic reflex only during wakefulness and is correlated with an increase in sleep apneas. Intrinsic sensitivity to CO2/pH of orexin neurons may impact on brainstem chemosensitive neurons, and this effect likely involves TWIK (tandem of P domains in a weak inwardly rectifying K+ channel)-related acid sensitive K+ (TASK)-like potassium currents. SUMMARY Orexin signaling is directly involved in the control of upper airway patency in particular during wakefulness, whereas decreasing activity of orexinergic neurons may contribute to upper airway collapse during sleep causing obstructive sleep apnea. Future research should focus on the role of orexin in upper airway control, which may lead to new clinical strategies for treating breathing disorders associated with sleep.
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221
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Adamantidis A, de Lecea L. Sleep and metabolism: shared circuits, new connections. Trends Endocrinol Metab 2008; 19:362-70. [PMID: 18938086 DOI: 10.1016/j.tem.2008.08.007] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2008] [Revised: 08/27/2008] [Accepted: 08/27/2008] [Indexed: 01/05/2023]
Abstract
Association between sleep disturbances and hormonal imbalances can result in metabolic disorders, including obesity and diabetes. The hypothalamus is likely to play a part in these pathophysiological conditions because it contains sleep-wake circuits that are sensitive to metabolic hormones, including leptin and ghrelin. Thus, shared hypothalamic circuits such as the hypocretin and melanin-concentrating hormone systems are strong candidates for mediating both sleep and metabolic imbalances. This review reveals new roles for these systems as sensors and effectors of sleep and wakefulness, and discusses their plasticity in regulating sleep and energy balance. New optical tools that remotely control neuronal circuit activity provide an effective means to understand the cooperativity of shared circuits in regulating hypothalamic functions such as sleep and metabolism.
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Affiliation(s)
- Antoine Adamantidis
- Department of Psychiatry, Stanford University School of Medicine, Palo Alto, CA 94304-5742, USA.
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222
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Kuwaki T, Zhang W, Nakamura A, Deng BS. Emotional and state-dependent modification of cardiorespiratory function: Role of orexinergic neurons. Auton Neurosci 2008; 142:11-6. [DOI: 10.1016/j.autneu.2008.03.004] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2008] [Revised: 03/12/2008] [Accepted: 03/13/2008] [Indexed: 10/22/2022]
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223
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Current World Literature. Curr Opin Pulm Med 2008; 14:600-2. [DOI: 10.1097/mcp.0b013e328316ea6b] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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224
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Abstract
It was suggested half a century ago that electrical impulses from the lateral hypothalamic area stimulate breathing. It is now emerging that these effects may be mediated, at least in part, by neurons containing orexin neuropeptides (also known as hypocretins). These cells promote wakefulness and consciousness, and their loss results in narcolepsy. Recent data also show that orexin neurons directly project to respiratory centres in the brainstem, which express orexin receptors, and where injection of orexin stimulates breathing. Because orexin neurons receive inputs that signal metabolic, sleep/wake and emotional states, it is tempting to speculate that they may regulate breathing according to these parameters. Knockout of the orexin gene in mice reduces CO2-induced increases in breathing by approximately 50% and increases the frequency of spontaneous sleep apneas. The relationship between orexins and breathing may be bidirectional: the rate of breathing controls acid and CO2 levels, and these signals alter the electrical activity of orexin neurons in vitro. Overall, these findings suggest that orexins are important for the regulation of breathing and may potentially play a role in the pathophysiology and medical treatment of respiratory disorders.
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225
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Abstract
OBJECTIVE Glucose sensing by specialized neurons of the hypothalamus is vital for normal energy balance. In many glucose-activated neurons, glucose metabolism is considered a critical step in glucose sensing, but whether glucose-inhibited neurons follow the same strategy is unclear. Orexin/hypocretin neurons of the lateral hypothalamus are widely projecting glucose-inhibited cells essential for normal cognitive arousal and feeding behavior. Here, we used different sugars, energy metabolites, and pharmacological tools to explore the glucose-sensing strategy of orexin cells. RESEARCH DESIGN AND METHODS We carried out patch-clamp recordings of the electrical activity of individual orexin neurons unambiguously identified by transgenic expression of green fluorescent protein in mouse brain slices. RESULTS- We show that 1) 2-deoxyglucose, a nonmetabolizable glucose analog, mimics the effects of glucose; 2) increasing intracellular energy fuel production with lactate does not reproduce glucose responses; 3) orexin cell glucose sensing is unaffected by glucokinase inhibitors alloxan, d-glucosamine, and N-acetyl-d-glucosamine; and 4) orexin glucosensors detect mannose, d-glucose, and 2-deoxyglucose but not galactose, l-glucose, alpha-methyl-d-glucoside, or fructose. CONCLUSIONS Our new data suggest that behaviorally critical neurocircuits of the lateral hypothalamus contain glucose detectors that exhibit novel sugar selectivity and can operate independently of glucose metabolism.
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Johnson SM, Haxhiu MA, Richerson GB. GFP-expressing locus ceruleus neurons from Prp57 transgenic mice exhibit CO2/H+ responses in primary cell culture. J Appl Physiol (1985) 2008; 105:1301-11. [PMID: 18635881 PMCID: PMC2576037 DOI: 10.1152/japplphysiol.90414.2008] [Citation(s) in RCA: 38] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/17/2008] [Accepted: 07/12/2008] [Indexed: 11/22/2022] Open
Abstract
The locus ceruleus (LC) contains neurons that increase their firing rate (FR) in vitro when exposed to elevated CO(2)/H(+) and have been proposed to influence the respiratory network to make compensatory adjustments in ventilation. Prp57 transgenic mice express green fluorescent protein (GFP) in the LC and were used to isolate, culture, and target LC neurons for electrophysiological recording. We hypothesized that GFP-LC neurons would exhibit CO(2)/H(+) chemosensitivity under primary culture conditions, evidenced as a change in FR. This is the first study to quantify CO(2)/H(+) responses in LC neuron FR in cell culture. Neurons were continuously bathed with solutions containing antagonists of glutamate and GABA receptors, and the acid-base status was changed from control (5% CO(2); pH approximately 7.4) to hypercapnic acidosis (9% CO(2); pH approximately 7.2) and hypocapnic alkalosis (3% CO(2); pH approximately 7.6). FR was quantified during perforated patch current clamp recordings. Approximately 86% of GFP-LC neurons were stimulated, and approximately 14% were insensitive to changes in CO(2)/H(+). The magnitude of the response of these neurons depended on the baseline FR, ranging from 155.9 +/- 6% when FR started at 2.95 +/- 0.49 Hz to 381 +/- 55.6% when FR started at 1.32 +/- 0.31 Hz. These results demonstrate that cultured LC neurons from Prp57 transgenic mice retain functional sensing molecules necessary for CO(2)/H(+) responses. Prp57 transgenic mice will serve as a valuable model to delineate mechanisms involved in CO(2)/H(+) responsiveness in catecholaminergic neurons.
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Affiliation(s)
- Shereé M Johnson
- Department of Physiology and Biophysics, Howard University College of Medicine, 520 W Street Northwest, Washington, DC 20059, USA.
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227
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Nattie E, Li A. Muscimol dialysis into the caudal aspect of the Nucleus tractus solitarii of conscious rats inhibits chemoreception. Respir Physiol Neurobiol 2008; 164:394-400. [PMID: 18824146 DOI: 10.1016/j.resp.2008.09.004] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2008] [Revised: 09/01/2008] [Accepted: 09/02/2008] [Indexed: 01/31/2023]
Abstract
We studied the effects on chemoreception of bilateral focal inhibition of the caudal Nucleus tractus solitarii (cNTS) by microdialysis of muscimol (0.5 mM) in rats during wakefulness and NREM sleep at two temperatures, 24 degrees C and 30 degrees C, just below and within the thermoneutral zone, respectively. Body temperature and VO2 did not differ at these two temperatures. The CO2 response (% increase in V(E)/VO2) did not differ at 24 degrees C vs. 30 degrees C and muscimol inhibited the CO2 response equally at both temperatures. In contrast, the hypoxic response (% increase in V(E)/VO2) was greater at 30 degrees C than at 24 degrees C and muscimol inhibited it only at 30 degrees C. These effects were similar in wakefulness and NREM sleep. We conclude that: (1) ambient temperature can affect the V(E)/VO2 response to hypoxia but not hypercapnia and (2) at 24 degrees C muscimol in the cNTS affects the CO2 response but not the hypoxic response providing indirect support for the presence of chemoreception within the NTS.
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Affiliation(s)
- Eugene Nattie
- Department of Physiology, Dartmouth Medical School, Lebanon, NH 03756, United States.
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228
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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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229
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Hodges MR, Richerson GB. Interaction between defects in ventilatory and thermoregulatory control in mice lacking 5-HT neurons. Respir Physiol Neurobiol 2008; 164:350-7. [PMID: 18775520 DOI: 10.1016/j.resp.2008.08.003] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2008] [Revised: 08/08/2008] [Accepted: 08/11/2008] [Indexed: 11/28/2022]
Abstract
We have previously shown that mice with near-complete absence of 5-HT neurons (Lmx1bf/f/p) display a blunted hypercapnic ventilatory response (HCVR) and impaired cold-induced thermogenesis, but have normal baseline ventilation (), core body temperature (TCore) and hypoxic ventilatory responses (HVR) at warm ambient temperatures (TAmb; 30 degrees C). These results suggest that 5-HT neurons are an important site for integration of ventilatory, metabolic and temperature control. To better define this integrative role, we now determine how a moderate cold stress (TAmb of 25 degrees C) influences ventilatory control in adult Lmx1bf/f/p mice. During whole animal plethysmographic recordings at 25 degreesC, baseline , metabolic rate , and TCore of Lmx1bf/f/p mice were reduced (P < 0.001) compared to wild type (WT) mice. Additionally, the HCVR was reduced in Lmx1bf/f/p mice during normoxic (-33.1%) and hyperoxic (-40.9%) hypercapnia. However, in Lmx1bf/f/p mice was equal to that in WT mice while breathing 10% CO2, indicating that non-5-HT neurons may play a dominant role during extreme hypercapnia. Additionally, ventilation was decreased during hypoxia in Lmx1bf/f/p mice compared to WT mice at 25 degrees C due to decreased TCore. These data suggest that a moderate cold stress in Lmx1bf/f/p mice leads to further dysfunction in ventilatory control resulting from failure to adequately maintain TCore. We conclude that 5-HT neurons contribute to the hypercapnic ventilatory response under physiologic, more than during extreme levels of CO2, and that mild cold stress further compromises ventilatory control in Lmx1bf/f/p mice as a result of defective thermogenesis.
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Affiliation(s)
- Matthew R Hodges
- Department of Neurology, Yale University School of Medicine, New Haven, CT 06520, United States.
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230
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Abstract
Brain glucose sensing is critical for healthy energy balance, but how appropriate neurocircuits encode both small changes and large background values of glucose levels is unknown. Here, we report several features of hypothalamic orexin neurons, cells essential for normal wakefulness and feeding: (i) A distinct group of orexin neurons exhibits only transient inhibitory responses to sustained rises in sugar levels; (ii) this sensing strategy involves time-dependent recovery from inhibition via adaptive closure of leak-like K(+) channels; (iii) combining transient and sustained glucosensing allows orexin cell firing to maintain sensitivity to small fluctuations in glucose levels while simultaneously encoding a large range of baseline glucose concentrations. These data provide insights into how vital behavioral orchestrators sense key features of the internal environment while sustaining a basic activity tone required for the stability of consciousness.
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231
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Molnár T, Barabás P, Héja L, Fekete EK, Lasztóczi B, Szabó P, Nyitrai G, Simon-Trompler E, Hajós F, Palkovits M, Kardos J. gamma-Hydroxybutyrate binds to the synaptic site recognizing succinate monocarboxylate: a new hypothesis on astrocyte-neuron interaction via the protonation of succinate. J Neurosci Res 2008; 86:1566-76. [PMID: 18189322 DOI: 10.1002/jnr.21608] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Succinate (SUC), a citrate (CIT) cycle intermediate, and carbenoxolone (CBX), a gap junction inhibitor, were shown to displace [3H]gamma-hydroxybutyrate ([3H]GHB), which is specifically bound to sites present in synaptic membrane subcellular fractions of the rat forebrain and the human nucleus accumbens. Elaboration on previous work revealed that acidic pH-induced specific binding of [3H]SUC occurs, and it has been shown to have a biphasic displacement profile distinguishing high-affinity (K(i,SUC) = 9.1 +/- 1.7 microM) and low-affinity (K(i,SUC) = 15 +/- 7 mM) binding. Both high- and low- affinity sites were characterized by the binding of GHB (K(i,GHB) = 3.9 +/- 0.5 microM and K(i,GHB) = 5.0 +/- 2.0 mM) and lactate (LAC; K(i,LAC) = 3.9 +/- 0.5 microM and K(i,LAC) = 7.7 +/- 0.9 mM). Ligands, including the hemiester ethyl-hemi-SUC, and the gap junction inhibitors flufenamate, CBX, and the GHB binding site-selective NCS-382 interacted with the high-affinity site (in microM: K(i,EHS) = 17 +/- 5, K(i,FFA) = 24 +/- 13, K(i,CBX) = 28 +/- 9, K(i,NCS-382) = 0.8 +/- 0.1 microM). Binding of the Na+,K+-ATPase inhibitor ouabain, the proton-coupled monocarboxylate transporter (MCT)-specific alpha-cyano-hydroxycinnamic acid (CHC), and CIT characterized the low-affinity SUC binding site (in mM: K(i,ouabain) = 0.13 +/- 0.05, K(i,CHC) = 0.32 +/- 0.07, K(i,CIT) = 0.79 +/- 0.20). All tested compounds inhibited [3H]SUC binding in the human nucleus accumbens and had K(i) values similar to those observed in the rat forebrain. The binding process can clearly be recognized as different from synaptic and mitochondrial uptake or astrocytic release of SUC, GHB, and/or CIT by its unique GHB selectivity. The transient decrease of extracellular SUC observed during epileptiform activity suggested that the function of the synaptic target recognizing protonated succinate monocarboxylate may vary under different (patho)physiological conditions. Furthermore, we put forward a hypothesis on the synaptic activity-regulated signaling between astrocytes and neurons via SUC protonation.
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Affiliation(s)
- Tünde Molnár
- Department of Neurochemistry, Institute of Biomolecular Chemistry, Chemical Research Center, Hungarian Academy of Sciences, Budapest, Hungary
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Bourgin P, Zeitzer JM, Mignot E. CSF hypocretin-1 assessment in sleep and neurological disorders. Lancet Neurol 2008; 7:649-62. [DOI: 10.1016/s1474-4422(08)70140-6] [Citation(s) in RCA: 71] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
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233
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Hodges MR, Tattersall GJ, Harris MB, McEvoy SD, Richerson DN, Deneris ES, Johnson RL, Chen ZF, Richerson GB. Defects in breathing and thermoregulation in mice with near-complete absence of central serotonin neurons. J Neurosci 2008; 28:2495-505. [PMID: 18322094 PMCID: PMC6671195 DOI: 10.1523/jneurosci.4729-07.2008] [Citation(s) in RCA: 259] [Impact Index Per Article: 16.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/18/2007] [Revised: 01/21/2008] [Accepted: 01/21/2008] [Indexed: 01/28/2023] Open
Abstract
Serotonergic neurons project widely throughout the CNS and modulate many different brain functions. Particularly important, but controversial, are the contributions of serotonin (5-HT) neurons to respiratory and thermoregulatory control. To better define the roles of 5-HT neurons in breathing and thermoregulation, we took advantage of a unique conditional knock-out mouse in which Lmx1b is genetically deleted in Pet1-expressing cells (Lmx1b(f/f/p)), resulting in near-complete absence of central 5-HT neurons. Here, we show that the hypercapnic ventilatory response in adult Lmx1b(f/f/p) mice was decreased by 50% compared with wild-type mice, whereas baseline ventilation and the hypoxic ventilatory response were normal. In addition, Lmx1b(f/f/p) mice rapidly became hypothermic when exposed to an ambient temperature of 4 degrees C, decreasing core temperature to 30 degrees C within 120 min. This failure of thermoregulation was caused by impaired shivering and nonshivering thermogenesis, whereas thermosensory perception and heat conservation were normal. Finally, intracerebroventricular infusion of 5-HT stimulated baseline ventilation, and rescued the blunted hypercapnic ventilatory response. These data identify a previously unrecognized role of 5-HT neurons in the CO(2) chemoreflex, whereby they enhance the response of the rest of the respiratory network to CO(2). We conclude that the proper function of the 5-HT system is particularly important under conditions of environmental stress and contributes significantly to the hypercapnic ventilatory response and thermoregulatory cold defense.
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Affiliation(s)
- Matthew R Hodges
- Department of Neurology, Yale University, New Haven, Connecticut 06520, USA.
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234
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Abstract
The 'distributed chemoreception theory' attributes the central chemoreflex (the stimulation of breathing by CNS acidification) to the cumulative effects of pH on multiple classes of respiratory neurons as well as on their tonic sources of drive. Opinions differ as to how many classes of pH-sensitive neurons contribute to the central chemoreflex but the number of candidates is high and growing fast. The 'specialized chemoreceptor theory', endorsed here, attributes the chemoreflex to a limited number of specialized neurons. These neurons (the central chemoreceptors) would drive a respiratory pattern generator that is not or minimally activated by acidification. In this review we first describe the properties of the retrotrapezoid nucleus (RTN) and argue that this nucleus may contain the most important central chemoreceptors. Next, we subject the assumptions that underlie the distributed chemoreception theory to a critical analysis. We propose several explanations for the apparent contradiction between the two competing theories of central chemoreception. We attribute much of the current controversy to premature extrapolations of the effects of acidification on neurons recorded in vitro (chemosensitivity) and to a semantic confusion between chemosensitivity and chemoreception (the mechanism by which CO(2) or pH activates breathing in vivo).
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Affiliation(s)
- Patrice G Guyenet
- University of Virginia Health System, P.O. Box 800735, 1300 Jefferson Park Avenue, Charlottesville, VA 22908-0735, USA.
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235
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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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Terada J, Nakamura A, Zhang W, Yanagisawa M, Kuriyama T, Fukuda Y, Kuwaki T. Ventilatory long-term facilitation in mice can be observed during both sleep and wake periods and depends on orexin. J Appl Physiol (1985) 2007; 104:499-507. [PMID: 18032578 DOI: 10.1152/japplphysiol.00919.2007] [Citation(s) in RCA: 73] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Respiratory long-term facilitation (LTF) is a long-lasting (>1 h) augmentation of respiratory motor output that occurs even after cessation of hypoxic stimuli, is serotonin-dependent, and is thought to prevent sleep-disordered breathing such as sleep apnea. Raphe nuclei, which modulate several physiological functions through serotonin, receive dense projections from orexin-containing neurons in the hypothalamus. We examined possible contributions of orexin to ventilatory LTF by measuring respiration in freely moving prepro-orexin knockout mice (ORX-KO) and wild-type (WT) littermates before, during, and after exposure to intermittent hypoxia (IH; 5 x 5 min at 10% O2), sustained hypoxia (SH; 25 min at 10% O2), or sham stimulation. Respiratory data during quiet wakefulness (QW), slow wave sleep (SWS), and rapid-eye-movement sleep were separately calculated. Baseline ventilation before hypoxic stimulation and acute responses during stimulation did not differ between the ORX-KO and WT mice, although ventilation depended on vigilance state. Whereas the WT showed augmented minute ventilation (by 20.0 +/- 4.5% during QW and 26.5 +/- 5.3% during SWS; n = 8) for 2 h following IH, ORX-KO showed no significant increase (by -3.1 +/- 4.6% during QW and 0.3 +/- 5.2% during SWS; n = 8). Both genotypes showed no LTF after SH or sham stimulation. Sleep apnea indexes did not change following IH, even when LTF appeared in the WT mice. We conclude that LTF occurs during both sleep and wake periods, that orexin is necessary for eliciting LTF, and that LTF cannot prevent sleep apnea, at least in mice.
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Affiliation(s)
- Jiro Terada
- Dept. of Molecular & Integrative Physiology, Chiba Univ. Graduate School of Medicine, 1-8-1 Chuo-ku, Chiba 260-8670, Japan
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237
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The TASK background K2P channels: chemo- and nutrient sensors. Trends Neurosci 2007; 30:573-80. [PMID: 17945357 DOI: 10.1016/j.tins.2007.08.003] [Citation(s) in RCA: 63] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/14/2007] [Revised: 07/30/2007] [Accepted: 08/13/2007] [Indexed: 11/23/2022]
Abstract
Specialized chemo- and nutrient-sensing cells share a common electrophysiological mechanism by transducing low O(2), high CO(2) and low glucose stimuli into a compensatory cellular response: the closing of background K(+) channels encoded by the K(2P) subunits. Inhibition of the TASK K(2P) channels by extracellular acidosis leads to an increased excitability of brainstem respiratory neurons. Moreover, hypoxic down-modulation of TASK channels is implicated in the activation of glomus cells in the carotid body. Stimulation of both types of cell leads to an enhanced ventilation and to cardiocirculatory adjustments. Differential modulation of TASK channels by acidosis and high glucose alters excitability of the hypothalamic orexin neurons, which influence arousal, food seeking and breathing. These recent results shed light on the role of TASK channels in sensing physiological stimuli.
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238
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Deng BS, Nakamura A, Zhang W, Yanagisawa M, Fukuda Y, Kuwaki T. Contribution of orexin in hypercapnic chemoreflex: evidence from genetic and pharmacological disruption and supplementation studies in mice. J Appl Physiol (1985) 2007; 103:1772-9. [PMID: 17717124 DOI: 10.1152/japplphysiol.00075.2007] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
We have previously shown that hypercapnic chemoreflex in prepro-orexin knockout mice (ORX-KO) is attenuated during wake but not sleep periods. In that study, however, hypercapnic stimulation had been chronically applied for 6 h because of technical difficulty in changing the composition of the inspired gas mixture without distorting the animal's vigilance states. In the present study we examined possible involvement of orexin in acute respiratory chemoreflex during wake periods. Ventilation was recorded together with electroencephalography and electromyography before and after intracerebroventricular administration of orexin or an orexin receptor antagonist, SB-334867. A hypercapnic (5 or 10% CO(2)) or hypoxic (15 or 10% O(2)) gas mixture was introduced into the recording chamber for 5 min. Respiratory parameters were analyzed only for quiet wakefulness. When mice breathed normal room air, orexin-A and orexin-B but not vehicle or SB-334867 increased minute ventilation in both ORX-KO and wild-type (WT) mice. As expected, hypercapnic chemoreflex in vehicle-treated ORX- KO mice (0.22 +/- 0.03 mlxmin(-1)xg(-1)x% CO(2)(-1)) was significantly blunted compared with that in WT mice (0.51 +/- 0.05 mlxmin(-1)xg(-1)x% CO(2)(-1)). Supplementation of orexin-A or -B (3 nmol) partially restored the hypercapnic chemoreflex in ORX-KO mice (0.28 +/- 0.03 mlxmin(-1).g(-1)x% CO(2)(-1) for orexin-A and 0.32 +/- 0.04 mlxmin(-1)xg(-1)x% CO(2)(-1) for orexin-B). In addition, injection of SB-334867 (30 nmol) in WT mice decreased the hypercapnic chemoreflex (0.39 +/- 0.04 mlxmin(-1)xg(-1)x% CO(2)(-1)). On the other hand, hypoxic chemoreflex in vehicle-treated ORX-KO and SB-334867-treated WT mice was not different from that in corresponding controls. Our findings suggest that orexin plays a crucial role in CO(2) sensitivity at least during wake periods in mice.
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Affiliation(s)
- Ben-Shiang Deng
- Dept. of Molecular & Integrative Physiology, Chiba Univ. Graduate School of Medicine, 1-8-1 Chuo-ku, Chiba 260-8670, Japan
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Orexin neurons on acid. Nat Rev Neurosci 2007. [DOI: 10.1038/nrn2198] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
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