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Kim H, Min C, Jeong B, Lee KJ. Deciphering clock cell network morphology within the biological master clock, suprachiasmatic nucleus: From the perspective of circadian wave dynamics. PLoS Comput Biol 2022; 18:e1010213. [PMID: 35666776 PMCID: PMC9203024 DOI: 10.1371/journal.pcbi.1010213] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2021] [Revised: 06/16/2022] [Accepted: 05/16/2022] [Indexed: 11/18/2022] Open
Abstract
The biological master clock, suprachiasmatic nucleus (of rat and mouse), is composed of ~10,000 clock cells which are heterogeneous with respect to their circadian periods. Despite this inhomogeneity, an intact SCN maintains a very good degree of circadian phase (time) coherence which is vital for sustaining various circadian rhythmic activities, and it is supposedly achieved by not just one but a few different cell-to-cell coupling mechanisms, among which action potential (AP)-mediated connectivity is known to be essential. But, due to technical difficulties and limitations in experiments, so far very little information is available about the morphology of the connectivity at a cellular scale. Building upon this limited amount of information, here we exhaustively and systematically explore a large pool (~25,000) of various network morphologies to come up with some plausible network features of SCN networks. All candidates under consideration reflect an experimentally obtained 'indegree distribution' as well as a 'physical range distribution of afferent clock cells.' Then, importantly, with a set of multitude criteria based on the properties of SCN circadian phase waves in extrinsically perturbed as well as in their natural states, we select out appropriate model networks: Some important measures are, 1) level of phase dispersal and direction of wave propagation, 2) phase-resetting ability of the model networks subject to external circadian forcing, and 3) decay rate of perturbation induced "phase-singularities." The successful, realistic networks have several common features: 1) "indegree" and "outdegree" should have a positive correlation; 2) the cells in the SCN ventrolateral region (core) have a much larger total degree than that of the dorsal medial region (shell); 3) The number of intra-core edges is about 7.5 times that of intra-shell edges; and 4) the distance probability density function for the afferent connections fits well to a beta function. We believe that these newly identified network features would be a useful guide for future explorations on the very much unknown AP-mediated clock cell connectome within the SCN.
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Affiliation(s)
- Hyun Kim
- Department of Physics, Korea University, Seoul, Korea
| | - Cheolhong Min
- Department of Physics, Korea University, Seoul, Korea
| | - Byeongha Jeong
- University of Texas Southwestern Medical Center, Dallas, Texas, United States of America
| | - Kyoung J. Lee
- Department of Physics, Korea University, Seoul, Korea
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Entrainment of circadian rhythms of locomotor activity by ambient temperature cycles in the dromedary camel. Sci Rep 2020; 10:19515. [PMID: 33177571 PMCID: PMC7658228 DOI: 10.1038/s41598-020-76535-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/12/2020] [Accepted: 10/29/2020] [Indexed: 11/08/2022] Open
Abstract
In the dromedary camel, a well-adapted desert mammal, daily ambient temperature (Ta)-cycles have been shown to synchronize the central circadian clock. Such entrainment has been demonstrated by examining two circadian outputs, body temperature and melatonin rhythms. Locomotor activity (LA), another circadian output not yet investigated in the camel, may provide further information on such specific entrainment. To verify if daily LA is an endogenous rhythm and whether the desert Ta-cycle can entrain it, six dromedaries were first kept under total darkness and constant-Ta. Results showed that the LA rhythm free runs with a period of 24.8–24.9 h. After having verified that the light–dark cycle synchronizes LA, camels were subjected to a Ta-cycle with warmer temperatures during subjective days and cooler temperatures during subjective nights. Results showed that the free-running LA rhythm was entrained by the Ta-cycle with a period of exactly 24.0 h, while a 12 h Ta-cycle phase advance induced an inversion of the LA rhythm and advanced the acrophase by 9 h. Similarly, activity onset and offset were significantly advanced. All together, these results demonstrate that the Ta-cycle is a strong zeitgeber, able to entrain the camel LA rhythm, hence corroborating previous results concerning the Ta non-photic synchronization of the circadian master clock.
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Min C, Kim H, Choi W, Lee KJ. Diversity in the structure of action potential-mediated neural connectivity within rat supra chiasmatic nucleus. Eur J Neurosci 2019; 50:2814-2829. [PMID: 30968479 DOI: 10.1111/ejn.14417] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/05/2018] [Revised: 03/14/2019] [Accepted: 03/21/2019] [Indexed: 11/30/2022]
Abstract
Action potential (AP)-mediated cell-to-cell communication is essential for the frequency-locking and phase-synchronization of the clock cells within the biological master clock, suprachiasmatic nucleus (SCN). Nevertheless, the morphology of its network connectivity is largely unexplored. Here, with an optimized optogenetic light-stimulation and scanning protocol, we report some key characteristics of the inhibitory receptive field (IRF), the area which brings inhibitory synaptic currents to a given target cell, and basic statistics of the inhibitory network connections of rat SCN clock cells. ChR2 transfected, slice cultures of rat SCN were stimulated by a blue power LED light in a repetitive box-scanning modes, while a target cell was whole-cell patched. The registered inhibitory postsynaptic currents, which were brought by light-induced APs of presynaptic neurons, were mostly GABAergic. The sizes and shapes of IRFs of SCN cells were very diverse, and the number of presynaptic cells making up the IRF of a given target cell followed an exponential distribution with an average value of 8.9 approximately, according to our clustering analysis which is based on a hybrid measure D, combining the physical distance r and the difference in the current amplitudes of two different sites. Although this estimate inevitably depends on the construct of the measure D, it is found not so sensitive on the parameter w, which weighs the relative significance of the current amplitude different with respect to the physical distance r: The average number of presynaptic neurons varies < 26% over a significant range of 0 < w < 30. On average, the presynaptic connection number density around a target cell falls off as an exponentially decreasing function of r. But, its space constant (~210.7 μm) is quite large that long-range (>210.7 μm) neural connections are abundant (>66.9%) within the SCN.
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Affiliation(s)
- Cheolhong Min
- Department of Physics, Korea University, Seoul, Korea
| | - Hyun Kim
- Department of Physics, Korea University, Seoul, Korea
| | - Wonshik Choi
- Department of Physics, Korea University, Seoul, Korea.,Center for Molecular Spectroscopy and Dynamics, Institute for Basic Science, Seoul, Korea
| | - Kyoung J Lee
- Department of Physics, Korea University, Seoul, Korea
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Connectome of the Suprachiasmatic Nucleus: New Evidence of the Core-Shell Relationship. eNeuro 2018; 5:eN-NWR-0205-18. [PMID: 30283813 PMCID: PMC6168316 DOI: 10.1523/eneuro.0205-18.2018] [Citation(s) in RCA: 30] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/23/2018] [Revised: 09/05/2018] [Accepted: 09/07/2018] [Indexed: 11/21/2022] Open
Abstract
A brain clock, constituted of ∼20,000 peptidergically heterogeneous neurons, is located in the hypothalamic suprachiasmatic nucleus (SCN). While many peptidergic cell types have been identified, little is known about the connections among these neurons in mice. We first sought to identify contacts among major peptidergic cell types in the SCN using triple-label fluorescent immunocytochemistry (ICC). To this end, contacts among vasoactive intestinal polypeptide (VIP), gastrin-releasing peptide (GRP), and calretinin (CALR) cells of the core, and arginine vasopressin (AVP) and met-enkephalin (ENK) cells of the shell were analyzed. Some core-to-shell and shell-to-core communications are specialized. We found that in wild-type (WT) mice, AVP fibers make extremely sparse contacts onto VIP neurons but contacts in the reverse direction are numerous. In contrast, AVP fibers make more contacts onto GRP neurons than conversely. For the other cell types tested, largely reciprocal connections are made. These results point to peptidergic cell type-specific communications between core and shell SCN neurons. To further understand the impact of VIP-to-AVP communication, we next explored the SCN in VIP-deficient mice (VIP-KO). In these animals, AVP expression is markedly reduced in the SCN, but it is not altered in the paraventricular nucleus (PVN) and supraoptic nucleus (SON). Surprisingly, in VIP-KO mice, the number of AVP appositions onto other peptidergic cell types is not different from controls. Colchicine administration, which blocks AVP transport, restored the numbers of AVP neurons in VIP-KO to that of WT littermates. The results indicate that VIP has an important role in modulating AVP expression levels in the SCN in this mouse.
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Santana NNM, Barros MAS, Medeiros HHA, Santana MAD, Silva LL, Morais PLAG, Ladd FVL, Cavalcante JS, Lima RRM, Cavalcante JC, Costa MSMO, Engelberth RCJG, Nascimento Jr. ES. The Suprachiasmatic Nucleus and the Intergeniculate Leaflet of the Flat-Faced Fruit-Eating Bat ( Artibeus planirostris): Retinal Projections and Neurochemical Anatomy. Front Neuroanat 2018; 12:36. [PMID: 29867376 PMCID: PMC5962671 DOI: 10.3389/fnana.2018.00036] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/26/2017] [Accepted: 04/20/2018] [Indexed: 12/27/2022] Open
Abstract
In mammals, the suprachiasmatic nucleus (SCN) and the intergeniculate leaflet (IGL) are the main components of the circadian timing system. The SCN, classically known as the master circadian clock, generates rhythms and synchronizes them to environmental cues. The IGL is a key structure that modulates SCN activity. Strategies on the use of time by animals can provide important clues about how some species are adapted to competitive process in nature. Few studies have provided information about temporal niche in bats with special attention on the neural substrate underlies circadian rhythms. The aim of this study was to investigate these circadian centers with respect to their cytoarchitecture, chemical content and retinal projections in the flat-faced fruit-eating bat (Artibeus planirostris), a chiropteran endemic to South America. Unlike other species of phyllostomid bats, the flat-faced fruit-eating bat's peak of activity occurs 5 h after sunset. This raises several questions about the structure and function of the SCN and IGL in this species. We carried out a mapping of the retinal projections and cytoarchitectural study of the nuclei using qualitative and quantitative approaches. Based on relative optical density findings, the SCN and IGL of the flat-faced fruit-eating bat receive bilaterally symmetric retinal innervation. The SCN contains vasopressin (VP) and vasoactive intestinal polypeptide (VIP) neurons with neuropeptide Y (NPY), serotonin (5-HT) and glutamic acid decarboxylase (GAD) immunopositive fibers/terminals and is marked by intense glial fibrillary acidic protein (GFAP) immunoreactivity. The IGL contains NPY perikarya as well as GAD and 5-HT immunopositive terminals and is characterized by dense GFAP immunostaining. In addition, stereological tools were combined with Nissl stained sections to estimate the volumes of the circadian centers. Taken together, the present results in the flat-faced fruit-eating bat reveal some differences compared to other bat species which might explain the divergence in the hourly activity among bats in order to reduce the competitive potential and resource partitioning in nature.
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Affiliation(s)
- Nelyane N. M. Santana
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | | | - Helder H. A. Medeiros
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Melquisedec A. D. Santana
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Lara L. Silva
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Paulo L. A. G. Morais
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Fernando V. L. Ladd
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Jeferson S. Cavalcante
- Laboratory of Neurochemical Studies, Department of Physiology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Ruthnaldo R. M. Lima
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Judney C. Cavalcante
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Miriam S. M. O. Costa
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Rovena C. J. G. Engelberth
- Laboratory of Neurochemical Studies, Department of Physiology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
| | - Expedito S. Nascimento Jr.
- Laboratory of Neuroanatomy, Department of Morphology, Biosciences Center, Federal University of Rio Grande do Norte, Natal, Brazil
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Svobodova I, Bhattaracharya A, Ivetic M, Bendova Z, Zemkova H. Circadian ATP Release in Organotypic Cultures of the Rat Suprachiasmatic Nucleus Is Dependent on P2X7 and P2Y Receptors. Front Pharmacol 2018; 9:192. [PMID: 29559915 PMCID: PMC5845546 DOI: 10.3389/fphar.2018.00192] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/17/2017] [Accepted: 02/20/2018] [Indexed: 01/22/2023] Open
Abstract
The circadian rhythms in physiological and behavioral functions are driven by a pacemaker located in the suprachiasmatic nucleus (SCN). The rhythms continue in constant darkness and depend on cell-cell communication between neurons and glia. The SCN astrocytes generate also a circadian rhythm in extracellular adenosine 5′-triphosphate (ATP) accumulation, but molecular mechanisms that regulate ATP release are poorly understood. Here, we tested the hypothesis that ATP is released via the plasma membrane purinergic P2X7 receptors (P2X7Rs) and P2Y receptors (P2YRs) which have been previously shown to be expressed in the SCN tissue at transcriptional level. We have investigated this hypothesis using SCN organotypic cultures, primary cultures of SCN astrocytes, ATP bioluminescent assays, immunohistochemistry, patch-clamping, and calcium imaging. We found that extracellular ATP accumulation in organotypic cultures followed a circadian rhythm, with a peak between 24:00 and 04:00 h, and the trough at ~12:00 h. ATP rhythm was inhibited by application of AZ10606120, A438079, and BBG, specific blockers of P2X7R, and potentiated by GW791343, a positive allosteric modulator of this receptor. Double-immunohistochemical staining revealed high expression of the P2X7R protein in astrocytes of SCN slices. PPADS, a non-specific P2 antagonist, and MRS2179, specific P2Y1R antagonist, also abolished ATP rhythm, whereas the specific P2X4R blocker 5-BDBD was not effective. The pannexin-1 hemichannel blocker carbenoxolone displayed a partial inhibitory effect. The P2Y1R agonist MRS2365, and the P2Y2R agonist MRS2768 potentiated ATP release in organotypic cultures and increase intracellular Ca2+ level in cultured astrocytes. Thus, SCN utilizes multiple purinergic receptor systems and pannexin-1 hemichannels to release ATP.
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Affiliation(s)
- Irena Svobodova
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czechia
| | - Anirban Bhattaracharya
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czechia
| | - Milorad Ivetic
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czechia
| | - Zdenka Bendova
- Department of Physiology, Faculty of Science, Charles University, Prague, Czechia
| | - Hana Zemkova
- Department of Cellular and Molecular Neuroendocrinology, Institute of Physiology of the Czech Academy of Sciences, Prague, Czechia
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El Allali K, Achaâban MR, Piro M, Ouassat M, Challet E, Errami M, Lakhdar-Ghazal N, Calas A, Pévet P. The Suprachiasmatic Nucleus of the Dromedary Camel ( Camelus dromedarius): Cytoarchitecture and Neurochemical Anatomy. Front Neuroanat 2017; 11:103. [PMID: 29249943 PMCID: PMC5715321 DOI: 10.3389/fnana.2017.00103] [Citation(s) in RCA: 7] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2017] [Accepted: 10/27/2017] [Indexed: 12/05/2022] Open
Abstract
In mammals, biological rhythms are driven by a master circadian clock located in the suprachiasmatic nucleus (SCN) of the hypothalamus. Recently, we have demonstrated that in the camel, the daily cycle of environmental temperature is able to entrain the master clock. This raises several questions about the structure and function of the SCN in this species. The current work is the first neuroanatomical investigation of the camel SCN. We carried out a cartography and cytoarchitectural study of the nucleus and then studied its cell types and chemical neuroanatomy. Relevant neuropeptides involved in the circadian system were investigated, including arginine-vasopressin (AVP), vasoactive intestinal polypeptide (VIP), met-enkephalin (Met-Enk), neuropeptide Y (NPY), as well as oxytocin (OT). The neurotransmitter serotonin (5-HT) and the enzymes tyrosine hydroxylase (TH) and aromatic L-amino acid decarboxylase (AADC) were also studied. The camel SCN is a large and elongated nucleus, extending rostrocaudally for 9.55 ± 0.10 mm. Based on histological and immunofluorescence findings, we subdivided the camel SCN into rostral/preoptic (rSCN), middle/main body (mSCN) and caudal/retrochiasmatic (cSCN) divisions. Among mammals, the rSCN is unusual and appears as an assembly of neurons that protrudes from the main mass of the hypothalamus. The mSCN exhibits the triangular shape described in rodents, while the cSCN is located in the retrochiasmatic area. As expected, VIP-immunoreactive (ir) neurons were observed in the ventral part of mSCN. AVP-ir neurons were located in the rSCN and mSCN. Results also showed the presence of OT-ir and TH-ir neurons which seem to be a peculiarity of the camel SCN. OT-ir neurons were either scattered or gathered in one isolated cluster, while TH-ir neurons constituted two defined populations, dorsal parvicellular and ventral magnocellular neurons, respectively. TH colocalized with VIP in some rSCN neurons. Moreover, a high density of Met-Enk-ir, 5-HT-ir and NPY-ir fibers were observed within the SCN. Both the cytoarchitecture and the distribution of neuropeptides are unusual in the camel SCN as compared to other mammals. The presence of OT and TH in the camel SCN suggests their role in the modulation of circadian rhythms and the adaptation to photic and non-photic cues under desert conditions.
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Affiliation(s)
- Khalid El Allali
- Comparative Anatomy Unit/URAC49, Department of Biological and Pharmaceutical Veterinary Sciences, Hassan II Agronomy and Veterinary Medicine Institute, Rabat, Morocco
| | - Mohamed R Achaâban
- Comparative Anatomy Unit/URAC49, Department of Biological and Pharmaceutical Veterinary Sciences, Hassan II Agronomy and Veterinary Medicine Institute, Rabat, Morocco
| | - Mohammed Piro
- PMC-EC, Department of Medicine, Surgery and Reproduction, Hassan II Agronomy and Veterinary Medicine Institute, Rabat, Morocco
| | - Mohammed Ouassat
- Comparative Anatomy Unit/URAC49, Department of Biological and Pharmaceutical Veterinary Sciences, Hassan II Agronomy and Veterinary Medicine Institute, Rabat, Morocco
| | - Etienne Challet
- Neurobiology of Rhythms UPR 3212 CNRS, Institute for Cellular and Integrative Neurosciences, University of Strasbourg, Strasbourg, France
| | - Mohammed Errami
- Department of Biology, Faculty of Science, Abdelmalek Essaâdi University, Tétouan, Morocco
| | - Nouria Lakhdar-Ghazal
- Unit of Research on Biological Rhythms, Neuroscience and Environment, Faculty of Science, Mohammed V-Agdal University, Rabat, Morocco
| | - André Calas
- IINS, CNRS UMR 5297, University of Bordeaux, Bordeaux, France
| | - Paul Pévet
- Neurobiology of Rhythms UPR 3212 CNRS, Institute for Cellular and Integrative Neurosciences, University of Strasbourg, Strasbourg, France
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Yang JJ, Cheng RC, Cheng PC, Wang YC, Huang RC. K ATP Channels Mediate Differential Metabolic Responses to Glucose Shortage of the Dorsomedial and Ventrolateral Oscillators in the Central Clock. Sci Rep 2017; 7:640. [PMID: 28377630 PMCID: PMC5428822 DOI: 10.1038/s41598-017-00699-3] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2016] [Accepted: 03/08/2017] [Indexed: 12/29/2022] Open
Abstract
The suprachiasmatic nucleus (SCN) central clock comprises two coupled oscillators, with light entraining the retinorecipient vasoactive intestinal peptide (VIP)-positive ventrolateral oscillator, which then entrains the arginine vasopressin (AVP)-positive dorsomedial oscillator. While glucose availability is known to alter photic entrainment, it is unclear how the SCN neurones respond to metabolic regulation and whether the two oscillators respond differently. Here we show that the ATP-sensitive K+ (KATP) channel mediates differential responses to glucose shortage of the two oscillators. RT-PCR and electrophysiological results suggested the presence of Kir6.2/SUR1 KATP channels in the SCN neurones. Immunostaining revealed preferential distribution of Kir6.2 in the dorsomedial subregion and selective colocalization with AVP. Whole cell recordings with ATP-free pipette solution indicated larger tolbutamide-induced depolarisation and tolbutamide-sensitive conductance in dorsal SCN (dSCN) than ventral SCN (vSCN) neurones. Tolbutamide-sensitive conductance was low under perforated patch conditions but markedly enhanced by cyanide inhibition of mitochondrial respiration. Glucoprivation produced a larger steady-state inhibition in dSCN than vSCN neurones, and importantly hypoglycemia via opening KATP channels selectively inhibited the KATP-expressing neurones. Our results suggest that the AVP-SCN oscillator may act as a glucose sensor to respond to glucose shortage while sparing the VIP-SCN oscillator to remain in synch with external light-dark cycle.
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Affiliation(s)
- Jyh-Jeen Yang
- Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan, 33305, Taiwan
| | - Ruo-Ciao Cheng
- Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan, 33305, Taiwan
| | - Pi-Cheng Cheng
- Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan, 33305, Taiwan
| | - Yi-Chi Wang
- Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan, 33305, Taiwan
| | - Rong-Chi Huang
- Department of Physiology and Pharmacology, College of Medicine, Chang Gung University, Tao-Yuan, 33305, Taiwan. .,Healthy Aging Research Center, Chang Gung University, Tao-Yuan, 33305, Taiwan. .,Neuroscience Research Center, Chang Gung Memorial Hospital, Linkou Medical Center, Tao-Yuan, 33305, Taiwan.
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Bedont JL, Blackshaw S. Constructing the suprachiasmatic nucleus: a watchmaker's perspective on the central clockworks. Front Syst Neurosci 2015; 9:74. [PMID: 26005407 PMCID: PMC4424844 DOI: 10.3389/fnsys.2015.00074] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2014] [Accepted: 04/23/2015] [Indexed: 11/13/2022] Open
Abstract
The circadian system constrains an organism's palette of behaviors to portions of the solar day appropriate to its ecological niche. The central light-entrained clock in the suprachiasmatic nucleus (SCN) of the mammalian circadian system has evolved a complex network of interdependent signaling mechanisms linking multiple distinct oscillators to serve this crucial function. However, studies of the mechanisms controlling SCN development have greatly lagged behind our understanding of its physiological functions. We review advances in the understanding of adult SCN function, what has been described about SCN development to date, and the potential of both current and future studies of SCN development to yield important insights into master clock function, dysfunction, and evolution.
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Affiliation(s)
- Joseph L Bedont
- Department of Neuroscience, Johns Hopkins University School of Medicine Baltimore, MD, USA
| | - Seth Blackshaw
- Department of Neuroscience, Johns Hopkins University School of Medicine Baltimore, MD, USA ; Department of Ophthalmology, Johns Hopkins University School of Medicine Baltimore, MD, USA ; Department of Physiology, Johns Hopkins University School of Medicine Baltimore, MD, USA ; Department of Neurology, Johns Hopkins University School of Medicine Baltimore, MD, USA ; Center for High-Throughput Biology, Johns Hopkins University School of Medicine Baltimore, MD, USA
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Campos LMG, Cruz-Rizzolo RJ, Watanabe IS, Pinato L, Nogueira MI. Efferent projections of the suprachiasmatic nucleus based on the distribution of vasoactive intestinal peptide (VIP) and arginine vasopressin (AVP) immunoreactive fibers in the hypothalamus of Sapajus apella. J Chem Neuroanat 2014; 57-58:42-53. [PMID: 24727411 DOI: 10.1016/j.jchemneu.2014.03.004] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2013] [Revised: 03/08/2014] [Accepted: 03/09/2014] [Indexed: 02/01/2023]
Abstract
The suprachiasmatic nucleus (SCN), which is considered to be the master circadian clock in mammals, establishes biological rhythms of approximately 24 h that several organs exhibit. One aspect relevant to the study of the neurofunctional features of biological rhythmicity is the identification of communication pathways between the SCN and other brain areas. As a result, SCN efferent projections have been investigated in several species, including rodents and a few primates. The fibers originating from the two main intrinsic fiber subpopulations, one producing vasoactive intestinal peptide (VIP) and the other producing arginine vasopressin (AVP), exhibit morphological traits that distinguish them from fibers that originate from other brain areas. This distinction provides a parameter to study SCN efferent projections. In this study, we mapped VIP (VIP-ir) and AVP (AVP-ir) immunoreactive (ir) fibers and endings in the hypothalamus of the primate Sapajus apella via immunohistochemical and morphologic study. Regarding the fiber distribution pattern, AVP-ir and VIP-ir fibers were identified in regions of the tuberal hypothalamic area, retrochiasmatic area, lateral hypothalamic area, and anterior hypothalamic area. VIP-ir and AVP-ir fibers coexisted in several hypothalamic areas; however, AVP-ir fibers were predominant over VIP-ir fibers in the posterior hypothalamus and medial periventricular area. This distribution pattern and the receiving hypothalamic areas of the VIP-ir and AVP-ir fibers, which shared similar morphological features with those found in SCN, were similar to the patterns observed in diurnal and nocturnal animals. This finding supports the conservative nature of this feature among different species. Morphometric analysis of SCN intrinsic neurons indicated homogeneity in the size of VIP-ir neurons in the SCN ventral portion and heterogeneity in the size of two subpopulations of AVP-ir neurons in the SCN dorsal portion. The distribution of fibers and morphometric features of these neuronal populations are described and compared with those of other species in the present study.
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Affiliation(s)
- L M G Campos
- Department of Anatomy, Institute of Biomedical Science, University of São Paulo, SP, Brazil.
| | - R J Cruz-Rizzolo
- Department of Fundamental Sciences, São Paulo State University, Araçatuba, SP, Brazil
| | - Ii-Sei Watanabe
- Department of Anatomy, Institute of Biomedical Science, University of São Paulo, SP, Brazil
| | - L Pinato
- Department of Speech Language and Hearing Therapy, São Paulo State University, Marília, SP, Brazil
| | - M I Nogueira
- Department of Anatomy, Institute of Biomedical Science, University of São Paulo, SP, Brazil
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Immunocytochemical evidence for different patterns in daily rhythms of VIP and AVP peptides in the suprachiasmatic nucleus of diurnal Funambulus palmarum. Brain Res 2010; 1373:39-47. [PMID: 21156164 DOI: 10.1016/j.brainres.2010.12.018] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2010] [Revised: 12/03/2010] [Accepted: 12/07/2010] [Indexed: 12/25/2022]
Abstract
The suprachiasmatic nucleus (SCN) is the principal pacemaker that coordinates circadian rhythmicity in mammals. The studies on understanding the circadian system in diurnal rodents are limited. In this study, we have used the 3 striped South Indian Palm Squirrel (Funambulus palmarum). The locomotor activity showed a diurnal pattern of activity in LD 12:12, constant darkness (DD) and light (LL) conditions with circadian periods (τ) of 24.19 ± 0.1, 24.11 ± 0.03 and 24.92 ± 0.35 h respectively. Anatomical study of the brain revealed that this animal had short, thick and stout optic nerves with SCN elliptical in shape with a higher neuronal population as distinct from nocturnal rodents. Since the neuropeptides, vasoactive intestinal polypeptide (VIP) and arginine vasopressin (AVP) play important roles in photic entrainment and relay of information respectively in nocturnal rodents, we studied the distribution and daily rhythms of VIP-ir and AVP-ir in squirrel SCN. The VIP-ir and AVP-ir cells in the SCN showed a ventrolateral and dorsomedial distribution with daily rhythmicity in their levels. The peak time of VIP-ir rhythm was found ahead of AVP-ir. The VIP-ir levels were higher for longer duration than AVP-ir levels. The maximum and minimum VIP-ir levels were at ZT-6 and ZT-0 respectively and AVP-ir levels at ZT-12 and ZT-0 respectively. Thus, VIP and AVP maximum and minimum levels appeared 6 and 12h apart respectively in squirrel, though 12 and 8h apart in rat. These findings in the present report could be a step towards underpinning the mechanisms regulating diurnality.
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Nascimento ES, Souza AP, Duarte RB, Magalhães MA, Silva SF, Cavalcante JC, Cavalcante JS, Costa MS. The suprachiasmatic nucleus and the intergeniculate leaflet in the rock cavy (Kerodon rupestris): Retinal projections and immunohistochemical characterization. Brain Res 2010; 1320:34-46. [DOI: 10.1016/j.brainres.2010.01.034] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/07/2009] [Revised: 01/13/2010] [Accepted: 01/13/2010] [Indexed: 11/29/2022]
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13
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Girardet C, Blanchard MP, Ferracci G, Lévêque C, Moreno M, François-Bellan AM, Becquet D, Bosler O. Daily changes in synaptic innervation of VIP neurons in the rat suprachiasmatic nucleus: contribution of glutamatergic afferents. Eur J Neurosci 2010; 31:359-70. [PMID: 20074215 DOI: 10.1111/j.1460-9568.2009.07071.x] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
The daily temporal organization of rhythmic functions in mammals, which requires synchronization of the circadian clock to the 24-h light-dark cycle, is believed to involve adjustments of the mutual phasing of the cellular oscillators that comprise the time-keeper within the suprachiasmatic nucleus of the hypothalamus (SCN). Following from a previous study showing that the SCN undergoes day/night rearrangements of its neuronal-glial network that may be crucial for intercellular phasing, we investigated the contribution of glutamatergic synapses, known to play major roles in SCN functioning, to such rhythmic plastic events. Neither expression levels of the vesicular glutamate transporters nor numbers of glutamatergic terminals showed nycthemeral variations in the SCN. However, using quantitative imaging after combined immunolabelling, the density of synapses on neurons expressing vasoactive intestinal peptide, known as targets of the retinal input, increased during the day and both glutamatergic and non-glutamatergic synapses contributed to the increase (+36%). This was not the case for synapses made on vasopressin-containing neurons, the other major source of SCN efferents in the non-retinorecipient region. Together with electron microscope observations showing no differences in the morphometric features of glutamatergic terminals during the day and night, these data show that the light synchronization process in the SCN involves a selective remodelling of synapses at sites of photic integration. They provide a further illustration of how the adult brain may rapidly and reversibly adapt its synaptic architecture to functional needs.
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Affiliation(s)
- Clémence Girardet
- Centre de Recherche en Neurobiologie et Neurophysiologie de Marseille (CRN2M), CNRS-UMR 6231, Université de la Méditerranée, Faculté de Médecine Nord, Marseille, France
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14
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Bosler O, Girardet C, Sage-Ciocca D, Jacomy H, François-Bellan AM, Becquet D. Mécanismes de plasticité structurale associés à la synchronisation photique de l'horloge circadienne au sein du noyau suprachiasmatique. ACTA ACUST UNITED AC 2009; 203:49-63. [DOI: 10.1051/jbio:2009004] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022]
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15
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Kiss J, Csáki Á, Csaba Z, Halász B. Synaptic contacts of vesicular glutamate transporter 2 fibres on chemically identified neurons of the hypothalamic suprachiasmatic nucleus of the rat. Eur J Neurosci 2008; 28:1760-74. [DOI: 10.1111/j.1460-9568.2008.06463.x] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/26/2022]
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16
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Becquet D, Girardet C, Guillaumond F, François-Bellan AM, Bosler O. Ultrastructural plasticity in the rat suprachiasmatic nucleus. Possible involvement in clock entrainment. Glia 2008; 56:294-305. [PMID: 18080293 DOI: 10.1002/glia.20613] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Circadian rhythms in mammals are synchronized to the light (L)/dark (D) cycle through messages relaying in the master clock, the suprachiasmatic nucleus of the hypothalamus (SCN). Here, we provide evidence that the SCN undergoes rhythmic ultrastructural rearrangements over the 24-h cycle characterized by day/night changes of the glial, axon terminal, and/or somato-dendritic coverage of neurons expressing arginine vasopressin (AVP) or vasoactive intestinal peptide (VIP), the two main sources of SCN efferents. At nighttime, we noted an increase in the glial coverage of the dendrites of the VIP neurons (+29%) that was concomitant with a decrease in the mean coverage of the somata (-36%) and dendrites (-43%) of these neurons by axon terminals. Conversely, glial coverage of the dendrites of AVP neurons decreased (-19%) with parallel increase in the extent of somatal (+96%) and dendritic (+52%) membrane appositions involving these neurons. These plastic events were concomitant with daily fluctuations in quantitative expression of glial fibrillary acidic protein (GFAP), which were then used as an index of structural plasticity. The GFAP rhythm appeared to be strictly dependent on light entrainment, indicating that structural reorganization of the SCN may subserve synchronization of the clock to the L/D cycle. Other results presented reinforced this view while showing that circulating glucocorticoid hormones, which are known to modulate photic entrainment, were required to maintain amplitude of the GFAP rhythm to normal values.
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Affiliation(s)
- Denis Becquet
- CNRS-UMR 6544, IFR Jean-Roche, Faculté de médecine, Université de la Méditerranée, Marseille, France
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Belenky MA, Yarom Y, Pickard GE. Heterogeneous expression of gamma-aminobutyric acid and gamma-aminobutyric acid-associated receptors and transporters in the rat suprachiasmatic nucleus. J Comp Neurol 2008; 506:708-32. [PMID: 18067149 DOI: 10.1002/cne.21553] [Citation(s) in RCA: 83] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
The hypothalamic suprachiasmatic nucleus (SCN) is the primary mammalian circadian clock that regulates rhythmic physiology and behavior. The SCN is composed of a diverse set of neurons arranged in a tight intrinsic network. In the rat, vasoactive intestinal peptide (VIP)- and gastrin-releasing peptide (GRP)-containing neurons are the dominant cell phenotypes of the ventral SCN, and these cells receive photic information from the retina and the intergeniculate leaflet. Neurons expressing vasopressin (VP) are concentrated in the dorsal and medial aspects of the SCN. Although the VIP/GRP and VP cell groups are concentrated in different regions of the SCN, the separation of these cell groups is not absolute. The inhibitory neurotransmitter gamma-aminobutyric acid (GABA) is expressed in most SCN neurons irrespective of their location or peptidergic phenotype. In the present study, immunoperoxidase labeling, immunofluorescence confocal microscopy, and ultrastructural immunocytochemistry were used to examine the spatial distribution of several markers associated with SCN GABAergic neurons. Glutamate decarboxylase, a marker of GABA synthesis, and vesicular GABA transporter were more prominently observed in the ventral SCN. KCC2, a K(+)/Cl(-) cotransporter, was highly expressed in the ventral SCN in association with VIP- and GRP-producing neurons, whereas VP neurons in the dorsal SCN were devoid of KCC2. On the other hand, GABA(B) receptors were observed predominantly in VPergic neurons dorsally, whereas, in the ventral SCN, GABA(B) receptors were associated almost exclusively with retinal afferent fibers and terminals. The differential expression of GABAergic markers within the SCN suggests that GABA may play dissimilar roles in different SCN neuronal phenotypes.
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Affiliation(s)
- Michael A Belenky
- Department of Cell/Animal Biology, Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem, 91904 Israel.
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18
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Kalamatianos T, Kalló I, Piggins HD, Coen CW. Expression of VIP and/or PACAP receptor mRNA in peptide synthesizing cells within the suprachiasmatic nucleus of the rat and in its efferent target sites. J Comp Neurol 2004; 475:19-35. [PMID: 15176082 DOI: 10.1002/cne.20168] [Citation(s) in RCA: 55] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
The suprachiasmatic nucleus (SCN) contains the predominant circadian pacemaker in mammals. Considerable evidence indicates that VPAC(2) and PAC(1), receptors for vasoactive intestinal peptide (VIP) and pituitary adenylate cyclase-activating peptide (PACAP), play critical roles in maintaining and entraining circadian rhythms. Retinal projections to the rat SCN contain PACAP and terminate mostly in the ventral SCN, the site of VIP neurons. The incidence of VPAC(2) and PAC(1) mRNAs within distinct neuronal populations of the rat SCN has been determined using double-label in situ hybridization. VPAC(2) mRNA was detected in almost all arginine-vasopressin (AVP) neurons of the dorsomedial SCN and in 41% of the VIP neurons; somatostatin (SST) neurons, predominantly in dorsomedial and intermediate regions, showed a decreased incidence (23%). PAC(1) mRNA was present in nearly half of the VIP and SST neurons (45% and 40%, respectively) and in one-third of the AVP neurons (32%). Cells expressing VPAC(2) mRNA also were detected in diencephalic areas that receive VIP-immunoreactive SCN efferents, such as the peri-suprachiasmatic region, lateral subparaventricular zone, parvocellular hypothalamic paraventricular subdivisions, dorsomedial hypothalamic nucleus, and anterior thalamic paraventricular and paratenial nuclei. The extensive distribution of PAC(1) mRNA within the SCN suggests that actions of PACAP are not restricted to the predominantly retinorecipient region. The presence of VPAC(2) mRNA in nearly half the VIP neurons, in almost all the AVP neurons, and at sites receiving VIP-immunoreactive SCN efferents suggests that the SCN VIP neurons are coupled and/or autoregulated and also influence the AVP-containing dorsomedial SCN and distal sites via VPAC(2).
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MESH Headings
- Animals
- Efferent Pathways/chemistry
- Efferent Pathways/metabolism
- Gene Expression Regulation/physiology
- Male
- Peptide Biosynthesis/physiology
- RNA, Messenger/analysis
- RNA, Messenger/biosynthesis
- Rats
- Rats, Wistar
- Receptors, Pituitary Adenylate Cyclase-Activating Polypeptide
- Receptors, Pituitary Hormone/analysis
- Receptors, Pituitary Hormone/biosynthesis
- Receptors, Vasoactive Intestinal Peptide/analysis
- Receptors, Vasoactive Intestinal Peptide/biosynthesis
- Receptors, Vasoactive Intestinal Peptide, Type II
- Suprachiasmatic Nucleus/chemistry
- Suprachiasmatic Nucleus/metabolism
- Vasoactive Intestinal Peptide/analysis
- Vasoactive Intestinal Peptide/metabolism
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Belenky MA, Sagiv N, Fritschy JM, Yarom Y. Presynaptic and postsynaptic GABAA receptors in rat suprachiasmatic nucleus. Neuroscience 2003; 118:909-23. [PMID: 12732237 DOI: 10.1016/s0306-4522(03)00062-9] [Citation(s) in RCA: 37] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/27/2022]
Abstract
The mammalian suprachiasmatic nucleus (SCN), the brain's circadian clock, is composed mainly of GABAergic neurons, that are interconnected via synapses with GABA(A) receptors. Here we report on the subcellular localization of these receptors in the SCN, as revealed by an extensively characterized antibody to the alpha 3 subunit of GABA(A) receptors in conjunction with pre- and postembedding electron microscopic immunocytochemistry. GABA(A) receptor immunoreactivity was observed in neuronal perikarya, dendritic processes and axonal terminals. In perikarya and proximal dendrites, GABA(A) receptor immunoreactivity was expressed mainly in endoplasmic reticulum and Golgi complexes, while in the distal part of dendrites, immunoreaction product was associated with postsynaptic plasma membrane. Many GABAergic axonal terminals, as revealed by postembedding immunogold labeling, displayed GABA(A) receptor immunoreactivity, associated mainly with the extrasynaptic portion of their plasma membrane. The function of these receptors was studied in hypothalamic slices using whole-cell patch-clamp recording of the responses to minimal stimulation of an area dorsal to the SCN. Analysis of the evoked inhibitory postsynaptic currents showed that either bath or local application of 100 microM of GABA decreased GABAergic transmission, manifested as a two-fold increase in failure rate. This presynaptic effect, which was detected in the presence of the glutamate receptor blocker 6-cyano-7-nitroquinoxaline-2,3-dione and the selective GABA(B) receptor blocker CGP55845A, appears to be mediated via activation of GABA(A) receptors. Our results thus show that GABA(A) receptors are widely distributed in the SCN and may subserve both pre- and postsynaptic roles in controlling the mammalian circadian clock.
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Affiliation(s)
- M A Belenky
- Department of Cell and Animal Biology Institute of Life Sciences, Hebrew University of Jerusalem, Jerusalem 91904, Israel
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20
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Oukouchoud R, Vivien-Roels B, Pévet P, Lakhdar-Ghazal N. Testosterone-dependent and -independent mechanisms involved in the photoperiodic control of neuropeptide levels in the brain of the jerboa (Jaculus orientalis). Brain Res 2003; 967:63-72. [PMID: 12650966 DOI: 10.1016/s0006-8993(02)04213-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/23/2022]
Abstract
Vasoactive intestinal peptide (VIP) and neuropeptide Y (NPY) content in the suprachiasmatic nucleus have been shown to exhibit seasonal changes with an increase in late summer, the period of sexual quiescence in the jerboa (Jaculus orientalis). In this study, VIP content in the SCN and NPY and enkephaline (ENK) content in the geniculo-suprachiasmatic system have been assayed in wild-caught male jerboas (Jaculus orientalis) in order to determine whether these neuropeptides are controlled directly by photoperiod changes or indirectly by short photoperiod induced changes in circulating sex hormones levels. In agreement with previous studies seasonal variations occur in the VIP and NPY content in the SCN. Variations also occur in NPY content in the IGL with an increase in the period of sexual quiescence. In contrast, no seasonal changes are observed in Enk content in the IGL or the SCN. In short photoperiod conditions increases are observed in both VIP and NPY content in the SCN as well as NPY content in the IGL. Castration during the period of sexual activity (spring) or under long photoperiod which drastically reduces testosterone, also induced an increase in the levels of these neuropeptides. Testosterone implants which reproduce the sex hormonal status of the sexual activity period failed to prevent the short photoperiod-induced increase of VIP and NPY in the SCN and of NPY in the IGL. These results clearly show that the photoperiod modulates VIP and NPY in the geniculo-suprachiasmatic system both by testosterone-linked and testosterone-independent mechanisms.
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Affiliation(s)
- Rahma Oukouchoud
- Groupe de Recherche sur les Rythmes Biologiques, Unité de Neurosciences, Département de Biologie, Faculté des Sciences, Université Mohammed V, B.P. 1014, Avenue Ibn Battouta, 10000 Rabat, Morocco
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21
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Vacher CM, Frétier P, Créminon C, Seif I, De Maeyer E, Calas A, Hardin-Pouzet H. Monoaminergic control of vasopressin and VIP expression in the mouse suprachiasmatic nucleus. J Neurosci Res 2003; 71:791-801. [PMID: 12605405 DOI: 10.1002/jnr.10529] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/22/2022]
Abstract
We studied the effects of serotonin and noradrenaline on the expression of arginine-vasopressin (AVP) and vasoactive intestinal peptide (VIP) in the suprachiasmatic nucleus (SCN). We used transgenic Tg8 mice knockout for the MAO-A (monoamine oxidase A) gene, which are characterized by increased amounts of serotonin and noradrenaline in brain compared to wild-type mice (C3H). The MAO-A deficiency caused an increase in AVP and VIP expression (determined by immunohistochemistry, enzyme immunoassay, and in situ hybridization) compared to C3H mice. The number of peptidergic neurons was also increased. Inhibiting serotonin or noradrenaline synthesis in Tg8 mice by the administration of parachlorophenylalanine or alpha-methylparatyrosine, respectively, the amounts of AVP, VIP and their mRNAs were decreased, but not the number of peptidergic neurons. This study indicates that serotonin and noradrenaline stimulate AVP and VIP expression, and could participate in the differentiation of the neurochemical phenotype in the mouse SCN.
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Affiliation(s)
- C M Vacher
- Laboratoire de Neurobiologie des Signaux Intercellulaires, CNRS UMR 7101, Université Pierre et Marie Curie, Paris, France.
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22
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Abstract
The neurons of the mammalian suprachiasmatic nuclei (SCN) control circadian rhythms in molecular, physiological, endocrine, and behavioral functions. In the SCN, circadian rhythms are generated at the level of individual neurons. The last decade has provided a wealth of information on the genetic basis for circadian rhythm generation. In comparison, a modest but growing number of studies have investigated how the molecular rhythm is translated into neuronal function. Neuronal attributes have been measured at the cellular and tissue level with a variety of electrophysiological techniques. We have summarized electrophysiological research on neurons that constitute the SCN in an attempt to provide a comprehensive view on the current state of the art.
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Affiliation(s)
- Jeroen Schaap
- Department of Neurophysiology, Leiden University Medical School, RC Leiden, The Netherlands
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23
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Abstract
Calbindin-D(28K)-immunoreactive cells are tightly packed within a discrete region of the caudal aspect of the suprachiasmatic nuclei of hamsters. These cells receive direct retinal input and are Fos-positive in response to a light pulse. Knowledge of their afferent and efferent connections is necessary to understand suprachiasmatic nucleus organization. The first aim of the present study is to identify interconnections between calbindin and other peptidergic cells of the suprachiasmatic nuclei, using epi- and confocal microscopy and intra-suprachiasmatic nucleus tract tracing. The results indicate that essentially all calbindin cells receive numerous appositions from vasoactive intestinal polypeptide (VIP), neuropeptide Y and serotonin fibers and that most receive appositions from gastrin releasing peptide (GRP) and cholecystokinin (CCK) fibers. Reciprocal connections are seen from VIP, GRP and CCK cells but surprisingly, not from dorsomedial vasopressin cells. Injection of biotinylated dextran amine into the suprachiasmatic nucleus indicates that the ventrolateral suprachiasmatic nucleus projects to the entire nucleus, while the dorsal and medial regions of the suprachiasmatic nucleus project densely to most of the nucleus, except to the calbindin region. Analysis of colocalization of the peptides in the calbindin cell region shows that 91% of the substance P cells, 42% of the GRP cells and 60% of the VIP cells in the calbindin subnucleus coexpress calbindin-D(28K). Our results reveal a highly specialized topographical organization of connections among suprachiasmatic nucleus cells.
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Affiliation(s)
- J. Lesauter
- Department of Psychology, Barnard College, 3009 Broadway, New York, NY 10027, USA
| | - L. J. Kriegsfeld
- Department of Psychology, MC 5501, Columbia University, 1190 Amsterdam Avenue, New York, NY 10027, USA
| | - J. Hon
- Department of Psychology, Barnard College, 3009 Broadway, New York, NY 10027, USA
| | - R. Silver
- Department of Psychology, Barnard College, 3009 Broadway, New York, NY 10027, USA
- Department of Psychology, MC 5501, Columbia University, 1190 Amsterdam Avenue, New York, NY 10027, USA
- Department of Anatomy and Cell Biology, Columbia University, New York, NY 10032, USA
- Correspondence to: R. Silver, Columbia University, Department of Psychology, MC 5501, 1190 Amsterdam Avenue, New York, NY 10027, USA. Tel.: +1-212-854-5531; fax: +1-212-854-3609
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Expression of Period genes: rhythmic and nonrhythmic compartments of the suprachiasmatic nucleus pacemaker. J Neurosci 2001. [PMID: 11567064 DOI: 10.1523/jneurosci.21-19-07742.2001] [Citation(s) in RCA: 160] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The mammalian circadian clock lying in the suprachiasmatic nucleus (SCN) controls daily rhythms and synchronizes the organism to its environment. In all organisms studied, circadian timekeeping is cell-autonomous, and rhythmicity is thought to be generated by a feedback loop involving clock proteins that inhibit transcription of their own genes. In the present study, we examined how these cellular properties are organized within the SCN tissue to produce rhythmicity and photic entrainment. The results show that the SCN has two compartments regulating Period genes Per1, Per2, and Per3 mRNA expression differentially. One compartment shows endogenous rhythmicity in Per1, Per2, and Per3 mRNA expression. The other compartment does not have rhythmic mRNA expression but has gated light-induced Per1 and Per2 and high levels of endogenous nonrhythmic Per3 mRNA expression. These results reveal the occurrence of differential regulation of clock genes in two distinct SCN regions and suggest a potential mechanism for producing functional differences in distinct SCN subregions.
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Abstract
The suprachiasmatic nucleus (SCN) of the hypothalamus is the site of the pacemaker that controls circadian rhythms of a variety of physiological functions. Data strongly indicate the majority of the SCN neurons express self-sustaining oscillations that can be detected as rhythms in the spontaneous firing of individual neurons. The period of single SCN neurons in a dissociated cell culture is dispersed in a wide range (from 20h to 28h in rats), but that of the locomotor rhythm is close to 24h, suggesting individual oscillators are coupled to generate an averaged circadian period in the nucleus. Electrical coupling via gap junctions, glial regulation, calcium spikes, ephaptic interactions. extracellular ion flux, and diffusible substances have been discussed as possible mechanisms that mediate the interneuronal rhythm synchrony. Recently, GABA (gamma-aminobutyric acid), a major neurotransmitter in the SCN, was reported to regulate cellular communication and to synchronize rhythms through GABA(A) receptors. At present, subsequent intracellular processes that are able to reset the genetic loop of oscillations are unknown. There may be diverse mechanisms for integrating the multiple circadian oscillators in the SCN. This article reviews the knowledge about the various circadian oscillations intrinsic to the SCN, with particular focus on the intercellular signaling of coupled oscillators.
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Affiliation(s)
- T Shirakawa
- Department of Oral Functional Science, Hokkaido University Graduate School of Dental Medicine, Sapporo, Japan.
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26
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Ibata Y, Okamura H, Tanaka M, Tamada Y, Hayashi S, Iijima N, Matsuda T, Munekawa K, Takamatsu T, Hisa Y, Shigeyoshi Y, Amaya F. Functional morphology of the suprachiasmatic nucleus. Front Neuroendocrinol 1999; 20:241-68. [PMID: 10433864 DOI: 10.1006/frne.1999.0180] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
Abstract
In mammals, the biological clock (circadian oscillator) is situated in the suprachiasmatic nucleus (SCN), a small bilaterally paired structure just above the optic chiasm. Circadian rhythms of sleep-wakefulness and hormone release disappear when the SCN is destroyed, and transplantation of fetal or neonatal SCN into an arrhythmic host restores rhythmicity. There are several kinds of peptide-synthesizing neurons in the SCN, with vasoactive intestinal peptide, arginine vasopressin, and somatostatine neurons being most prominent. Those peptides and their mRNA show diurnal rhythmicity and may or may not be affected by light stimuli. Major neuronal inputs from retinal ganglion cells as well as other inputs such as those from the lateral geniculate nucleus and raphe nucleus are very important for entrainment and shift of circadian rhythms. In this review, we describe morphological and functional interactions between neurons and glial elements and their development. We also consider the expression of immediate-early genes in the SCN after light stimulation during subjective night and their role in the mechanism of signal transduction. The reciprocal interaction between the SCN and melatonin, which is synthesized in the pineal body under the influence of polysynaptic inputs from the SCN, is also considered. Finally, morphological and functional characteristics of clock genes, particularly mPers, which are considered to promote circadian rhythm, are reviewed.
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Affiliation(s)
- Y Ibata
- Department of Anatomy and Neurobiology, Kyoto Prefectural University of Medicine, Kawaramachi, Hirokoji, Kamikyoku, Kyoto, 602-8566, Japan
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