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Kirchner MK, Althammer F, Donaldson KJ, Cox DN, Stern JE. Changes in neuropeptide large dense core vesicle trafficking dynamics contribute to adaptive responses to a systemic homeostatic challenge. iScience 2023; 26:108243. [PMID: 38026155 PMCID: PMC10654599 DOI: 10.1016/j.isci.2023.108243] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/31/2023] [Revised: 08/28/2023] [Accepted: 10/16/2023] [Indexed: 12/01/2023] Open
Abstract
Neuropeptides are packed into large dense core vesicles (LDCVs) that are transported from the soma out into their processes. Limited information exists regarding mechanisms regulating LDCV trafficking, particularly during challenges to bodily homeostasis. Addressing this gap, we used 2-photon imaging in an ex vivo preparation to study LDCVs trafficking dynamics in vasopressin (VP) neurons, which traffic and release neuropeptide from their dendrites and axons. We report a dynamic bidirectional trafficking of VP-LDCVs with important differences in speed and directionality between axons and dendrites. Acute, short-lasting stimuli known to alter VP firing activity and axonal/dendritic release caused modest changes in VP-LDCVs trafficking dynamics. Conversely, chronic/sustained systemic osmotic challenges upregulated VP-LDCVs trafficking dynamic, with a larger effect in dendrites. These results support differential regulation of dendritic and axonal LDCV trafficking, and that changes in trafficking dynamics constitute a novel mechanism by which peptidergic neurons can efficiently adapt to conditions of increased hormonal demand.
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Affiliation(s)
- Matthew K. Kirchner
- Center for Neuroinflammation and Cardiometabolic Diseases, Georgia State University, Atlanta, GA 30303, USA
- Neuroscience Institute, Georgia State University, Atlanta, GA 30303, USA
| | - Ferdinand Althammer
- Center for Neuroinflammation and Cardiometabolic Diseases, Georgia State University, Atlanta, GA 30303, USA
- Institute of Human Genetics, Heidelberg University Hospital, 69120 Heidelberg, Germany
| | - Kevin J. Donaldson
- Neuroscience Institute, Georgia State University, Atlanta, GA 30303, USA
- Center for Neuromics, Georgia State University, Atlanta, GA 30303, USA
| | - Daniel N. Cox
- Neuroscience Institute, Georgia State University, Atlanta, GA 30303, USA
- Center for Neuromics, Georgia State University, Atlanta, GA 30303, USA
| | - Javier E. Stern
- Center for Neuroinflammation and Cardiometabolic Diseases, Georgia State University, Atlanta, GA 30303, USA
- Neuroscience Institute, Georgia State University, Atlanta, GA 30303, USA
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Aikins AO, Nguyen DH, Paundralingga O, Farmer GE, Shimoura CG, Brock C, Cunningham JT. Cardiovascular Neuroendocrinology: Emerging Role for Neurohypophyseal Hormones in Pathophysiology. Endocrinology 2021; 162:6247962. [PMID: 33891015 PMCID: PMC8234498 DOI: 10.1210/endocr/bqab082] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/19/2021] [Indexed: 11/19/2022]
Abstract
Arginine vasopressin (AVP) and oxytocin (OXY) are released by magnocellular neurosecretory cells that project to the posterior pituitary. While AVP and OXY currently receive more attention for their contributions to affiliative behavior, this mini-review discusses their roles in cardiovascular function broadly defined to include indirect effects that influence cardiovascular function. The traditional view is that neither AVP nor OXY contributes to basal cardiovascular function, although some recent studies suggest that this position might be re-evaluated. More evidence indicates that adaptations and neuroplasticity of AVP and OXY neurons contribute to cardiovascular pathophysiology.
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Affiliation(s)
- Ato O Aikins
- Department of Physiology and Anatomy, Graduate School of Biomedical Sciences, UNT Health Science Center, Fort Worth, TX 76107, USA
| | - Dianna H Nguyen
- Department of Physiology and Anatomy, Graduate School of Biomedical Sciences, UNT Health Science Center, Fort Worth, TX 76107, USA
- Texas College of Osteopathic Medicine, UNT Health Science Center, Fort Worth, TX 76107, USA
| | - Obed Paundralingga
- Department of Physiology and Anatomy, Graduate School of Biomedical Sciences, UNT Health Science Center, Fort Worth, TX 76107, USA
| | - George E Farmer
- Department of Physiology and Anatomy, Graduate School of Biomedical Sciences, UNT Health Science Center, Fort Worth, TX 76107, USA
| | - Caroline Gusson Shimoura
- Department of Physiology and Anatomy, Graduate School of Biomedical Sciences, UNT Health Science Center, Fort Worth, TX 76107, USA
| | - Courtney Brock
- Department of Physiology and Anatomy, Graduate School of Biomedical Sciences, UNT Health Science Center, Fort Worth, TX 76107, USA
| | - J Thomas Cunningham
- Department of Physiology and Anatomy, Graduate School of Biomedical Sciences, UNT Health Science Center, Fort Worth, TX 76107, USA
- Correspondence: J. Thomas Cunningham Department of Physiology & Anatomy CBH 338 UNT Health Science Center 3500 Camp Bowie Blvd Fort Worth, TX 76107, USA.
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Sheng W, Harden SW, Tan Y, Krause EG, Frazier CJ. Dendritic osmosensors modulate activity-induced calcium influx in oxytocinergic magnocellular neurons of the mouse PVN. eLife 2021; 10:e63486. [PMID: 34250900 PMCID: PMC8457833 DOI: 10.7554/elife.63486] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2020] [Accepted: 07/11/2021] [Indexed: 11/13/2022] Open
Abstract
Hypothalamic oxytocinergic magnocellular neurons have a fascinating ability to release peptide from both their axon terminals and from their dendrites. Existing data indicates that the relationship between somatic activity and dendritic release is not constant, but the mechanisms through which this relationship can be modulated are not completely understood. Here, we use a combination of electrical and optical recording techniques to quantify activity-induced calcium influx in proximal vs. distal dendrites of oxytocinergic magnocellular neurons located in the paraventricular nucleus of the hypothalamus (OT-MCNs). Results reveal that the dendrites of OT-MCNs are weak conductors of somatic voltage changes; however, activity-induced dendritic calcium influx can be robustly regulated by both osmosensitive and non-osmosensitive ion channels located along the dendritic membrane. Overall, this study reveals that dendritic conductivity is a dynamic and endogenously regulated feature of OT-MCNs that is likely to have substantial functional impact on central oxytocin release.
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Affiliation(s)
- Wanhui Sheng
- Department of Pharmacodynamics, College of Pharmacy, University of FloridaGainesvilleUnited States
| | - Scott W Harden
- Department of Pharmacodynamics, College of Pharmacy, University of FloridaGainesvilleUnited States
| | - Yalun Tan
- Department of Pharmacodynamics, College of Pharmacy, University of FloridaGainesvilleUnited States
- Department of Anesthesiology, School of Medicine, Stanford UniversityStanfordUnited States
| | - Eric G Krause
- Department of Pharmacodynamics, College of Pharmacy, University of FloridaGainesvilleUnited States
- Center for Integrative Cardiovascular and Metabolic Diseases, University of FloridaGainesvilleUnited States
- Evelyn F. and William L. McKnight Brain Institute, University of FloridaGainesvilleUnited States
| | - Charles J Frazier
- Department of Pharmacodynamics, College of Pharmacy, University of FloridaGainesvilleUnited States
- Center for Integrative Cardiovascular and Metabolic Diseases, University of FloridaGainesvilleUnited States
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Hagiwara D, Tochiya M, Azuma Y, Tsumura T, Hodai Y, Kawaguchi Y, Miyata T, Kobayashi T, Sugiyama M, Onoue T, Takagi H, Ito Y, Iwama S, Suga H, Banno R, Arima H. Arginine vasopressin-Venus reporter mice as a tool for studying magnocellular arginine vasopressin neurons. Peptides 2021; 139:170517. [PMID: 33647312 DOI: 10.1016/j.peptides.2021.170517] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/25/2020] [Revised: 02/16/2021] [Accepted: 02/17/2021] [Indexed: 11/20/2022]
Abstract
Arginine vasopressin (AVP) synthesized in the magnocellular neurons of the hypothalamus is transported through their axons and released from the posterior pituitary into the systemic circulation to act as an antidiuretic hormone. AVP synthesis and release are precisely regulated by changes in plasma osmolality. Magnocellular AVP neurons receive innervation from osmosensory and sodium-sensing neurons, but previous studies showed that AVP neurons per se are osmosensitive as well. In the current study, we made AVP-Venus reporter mice and showed that Venus was expressed exclusively in AVP neurons and was upregulated under water deprivation. In hypothalamic organotypic cultures from the AVP-Venus mice, Venus-labeled AVP neurons in the supraoptic and paraventricular nuclei survived for 1 month, and Venus expression was upregulated by forskolin. Furthermore, in dissociated Venus-labeled magnocellular neurons, treatment with NaCl, but not with mannitol, decreased Venus fluorescence in the soma of the AVP neurons. Thus, Venus expression in AVP-Venus transgenic mice, as well as in primary cultures, faithfully showed the properties of intrinsic AVP expression. These findings indicate that AVP-Venus mice as well as the primary hypothalamic cultures could be useful for studying magnocellular AVP neurons.
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Affiliation(s)
- Daisuke Hagiwara
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan.
| | - Masayoshi Tochiya
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Yoshinori Azuma
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Tetsuro Tsumura
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Yuichi Hodai
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Yohei Kawaguchi
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Takashi Miyata
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Tomoko Kobayashi
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Mariko Sugiyama
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Takeshi Onoue
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Hiroshi Takagi
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Yoshihiro Ito
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Shintaro Iwama
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Hidetaka Suga
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan
| | - Ryoichi Banno
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan; Research Center of Health, Physical Fitness and Sports, Nagoya University, Nagoya, 464-8601, Japan
| | - Hiroshi Arima
- Department of Endocrinology and Diabetes, Nagoya University Graduate School of Medicine, Nagoya, 466-8550, Japan.
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Tasker JG, Prager-Khoutorsky M, Teruyama R, Lemos JR, Amstrong WE. Advances in the neurophysiology of magnocellular neuroendocrine cells. J Neuroendocrinol 2020; 32:e12826. [PMID: 31917875 PMCID: PMC7192795 DOI: 10.1111/jne.12826] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/20/2019] [Revised: 01/02/2020] [Accepted: 01/07/2020] [Indexed: 02/06/2023]
Abstract
Hypothalamic magnocellular neuroendocrine cells have unique electrical properties and a remarkable capacity for morphological and synaptic plasticity. Their large somatic size, their relatively uniform and dense clustering in the supraoptic and paraventricular nuclei, and their large axon terminals in the neurohypophysis make them an attractive target for direct electrophysiological interrogation. Here, we provide a brief review of significant recent findings in the neuroplasticity and neurophysiological properties of these neurones that were presented at the symposium "Electrophysiology of Magnocellular Neurons" during the 13th World Congress on Neurohypophysial Hormones in Ein Gedi, Israel in April 2019. Magnocellular vasopressin (VP) neurones respond directly to hypertonic stimulation with membrane depolarisation, which is triggered by cell shrinkage-induced opening of an N-terminal-truncated variant of transient receptor potential vanilloid type-1 (TRPV1) channels. New findings indicate that this mechanotransduction depends on actin and microtubule cytoskeletal networks, and that direct coupling of the TRPV1 channels to microtubules is responsible for mechanical gating of the channels. Vasopressin neurones also respond to osmostimulation by activation of epithelial Na+ channels (ENaC). It was shown recently that changes in ENaC activity modulate magnocellular neurone basal firing by generating tonic changes in membrane potential. Both oxytocin and VP neurones also undergo robust excitatory synapse plasticity during chronic osmotic stimulation. Recent findings indicate that new glutamate synapses induced during chronic salt loading express highly labile Ca2+ -permeable GluA1 receptors requiring continuous dendritic protein synthesis for synapse maintenance. Finally, recordings from the uniquely tractable neurohypophysial terminals recently revealed an unexpected property of activity-dependent neuropeptide release. A significant fraction of the voltage-dependent neurohypophysial neurosecretion was found to be independent of Ca2+ influx through voltage-gated Ca2+ channels. Together, these findings provide a snapshot of significant new advances in the electrophysiological signalling mechanisms and neuroplasticity of the hypothalamic-neurohypophysial system, a system that continues to make important contributions to the field of neurophysiology.
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Affiliation(s)
- Jeffrey G. Tasker
- Department of Cell and Molecular Biology and Tulane Brain Institute, Tulane University, New Orleans, LA, USA
- Correspondence: Jeffrey Tasker, PhD, Tulane University, Cell and Molecular Biology Dept, 2000 Percival Stern Hall, New Orleans, LA 70118, USA; .; William Armstrong, PhD, University of Tennessee Health Science Center, Anatomy and Neurobiology Dept and Neuroscience Institute, 855 Monroe Ave, Memphis, TN 38163, USA;
| | | | - Ryoichi Teruyama
- Department of Biological Sciences, Louisiana State University, Baton Rouge, LA, USA
| | - José R. Lemos
- Department of Microbiology and Physiological Systems & Program in Neuroscience, University of Massachusetts Medical School, Worcester, MA, USA
| | - William E. Amstrong
- Department of Anatomy and Neurobiology and Neuroscience Institute, University of Tennessee Health Science Center, Memphis, TN, USA
- Correspondence: Jeffrey Tasker, PhD, Tulane University, Cell and Molecular Biology Dept, 2000 Percival Stern Hall, New Orleans, LA 70118, USA; .; William Armstrong, PhD, University of Tennessee Health Science Center, Anatomy and Neurobiology Dept and Neuroscience Institute, 855 Monroe Ave, Memphis, TN 38163, USA;
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Prager-Khoutorsky M, Choe KY, Levi DI, Bourque CW. Role of Vasopressin in Rat Models of Salt-Dependent Hypertension. Curr Hypertens Rep 2017; 19:42. [PMID: 28451854 DOI: 10.1007/s11906-017-0741-2] [Citation(s) in RCA: 17] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
PURPOSE OF REVIEW Dietary salt intake increases both plasma sodium and osmolality and therefore increases vasopressin (VP) release from the neurohypophysis. Although this effect could increase blood pressure by inducing fluid reabsorption and vasoconstriction, acute activation of arterial baroreceptors inhibits VP neurons via GABAA receptors to oppose high blood pressure. Here we review recent findings demonstrating that this protective mechanism fails during chronic high salt intake in rats. RECENT FINDINGS Two recent studies showed that chronic high sodium intake causes an increase in intracellular chloride concentration in VP neurons. This effect causes GABAA receptors to become excitatory and leads to the emergence of VP-dependent hypertension. One study showed that the increase in intracellular chloride was provoked by a decrease in the expression of the chloride exporter KCC2 mediated by local secretion of brain-derived neurotrophic factor and activation of TrkB receptors. Prolonged high dietary salt intake can cause pathological plasticity in a central homeostatic circuit that controls VP secretion and thereby contribute to peripheral vasoconstriction and hypertension.
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Affiliation(s)
- Masha Prager-Khoutorsky
- Department of Physiology, McGill University, McIntyre Medical Sciences Bldg., 3655 Promenade Sir-William Osler, Montreal, QC, H3G 1Y6, Canada
| | - Katrina Y Choe
- 2309 Gonda Neuroscience and Genetics Research Center, UCLA Department of Neurology, 695 Charles E. Young Dr. South, Los Angeles, CA, 90095, USA
| | - David I Levi
- Centre for Research in Neuroscience, Research Institute of the McGill University Health Center, Montreal General Hospital, 1650 Cedar Avenue, Montreal, QC, H3G 1A4, Canada
| | - Charles W Bourque
- Centre for Research in Neuroscience, Research Institute of the McGill University Health Center, Montreal General Hospital, 1650 Cedar Avenue, Montreal, QC, H3G 1A4, Canada.
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Kortus S, Srinivasan C, Forostyak O, Ueta Y, Sykova E, Chvatal A, Zapotocky M, Verkhratsky A, Dayanithi G. Physiology of spontaneous [Ca(2+)]i oscillations in the isolated vasopressin and oxytocin neurones of the rat supraoptic nucleus. Cell Calcium 2016; 59:280-8. [PMID: 27072326 PMCID: PMC4969632 DOI: 10.1016/j.ceca.2016.04.001] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/08/2016] [Revised: 03/31/2016] [Accepted: 04/05/2016] [Indexed: 01/26/2023]
Abstract
Supraoptic fluorescent vasopressin (AVP-eGFP) and oxytocin (OT-mRFP1) neurones exhibit distinct spontaneous [Ca2+]i oscillations. Vasopressin triggers [Ca2+]i oscillations, intensifies existing oscillations, and exceptionally stops oscillations. Hyper- or hypo-osmotic stimuli have an intensifying or inhibitory effect on oscillations, respectively. Nearly 90% of neurones from 3 or 5-day-dehydrated rats exhibit oscillations. More than 80% of OT-mRFP1 neurones from 3 to 6-day-lactating rats are oscillatory vs. about 44% in virgins.
The magnocellular vasopressin (AVP) and oxytocin (OT) neurones exhibit specific electrophysiological behaviour, synthesise AVP and OT peptides and secrete them into the neurohypophysial system in response to various physiological stimulations. The activity of these neurones is regulated by the very same peptides released either somato-dendritically or when applied to supraoptic nucleus (SON) preparations in vitro. The AVP and OT, secreted somato-dendritically (i.e. in the SON proper) act through specific autoreceptors, induce distinct Ca2+ signals and regulate cellular events. Here, we demonstrate that about 70% of freshly isolated individual SON neurones from the adult non-transgenic or transgenic rats bearing AVP (AVP-eGFP) or OT (OT-mRFP1) markers, produce distinct spontaneous [Ca2+]i oscillations. In the neurones identified (through specific fluorescence), about 80% of AVP neurones and about 60% of OT neurones exhibited these oscillations. Exposure to AVP triggered [Ca2+]i oscillations in silent AVP neurones, or modified the oscillatory pattern in spontaneously active cells. Hyper- and hypo-osmotic stimuli (325 or 275 mOsmol/l) respectively intensified or inhibited spontaneous [Ca2+]i dynamics. In rats dehydrated for 3 or 5 days almost 90% of neurones displayed spontaneous [Ca2+]i oscillations. More than 80% of OT-mRFP1 neurones from 3 to 6-day-lactating rats were oscillatory vs. about 44% (OT-mRFP1 neurones) in virgins. Together, these results unveil for the first time that both AVP and OT neurones maintain, via Ca2+ signals, their remarkable intrinsic in vivo physiological properties in an isolated condition.
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Affiliation(s)
- Stepan Kortus
- Department of Molecular Neurophysiology, Institute of Experimental Medicine, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czech Republic; Institute of Physiology, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czech Republic; Institute of Biophysics and Informatics, First Faculty of Medicine, Charles University in Prague, Salmovska 1, 12000 Prague, Czech Republic
| | - Chinnapaiyan Srinivasan
- Department of Molecular Neurophysiology, Institute of Experimental Medicine, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czech Republic
| | - Oksana Forostyak
- Department of Molecular Neurophysiology, Institute of Experimental Medicine, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czech Republic; Department of Neuroscience, Charles University, Second Medical Faculty, V Uvalu 84, 15006 Prague, Czech Republic
| | - Yoichi Ueta
- Department of Physiology, School of Medicine, University of Occupational and Environmental Health, Kitakyushu 807-8555, Japan
| | - Eva Sykova
- Department of Neuroscience, Charles University, Second Medical Faculty, V Uvalu 84, 15006 Prague, Czech Republic; Department of Neuroscience, Institute of Experimental Medicine, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czech Republic
| | - Alexandr Chvatal
- Department of Neuroscience, Charles University, Second Medical Faculty, V Uvalu 84, 15006 Prague, Czech Republic; Department of Cellular Neurophysiology, Institute of Experimental Medicine, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czech Republic
| | - Martin Zapotocky
- Institute of Physiology, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czech Republic; Institute of Biophysics and Informatics, First Faculty of Medicine, Charles University in Prague, Salmovska 1, 12000 Prague, Czech Republic
| | - Alexei Verkhratsky
- University of Manchester, School of Biological Sciences, D.4417 Michael Smith Building, Oxford Road, M13 9PT Manchester, United Kingdom; Achucarro Center for Neuroscience, IKERBASQUE, Basque Foundation for Science, 48011 Bilbao, Spain; Department of Neurosciences, University of the Basque Country UPV/EHU and CIBERNED, Leioa, Spain; University of Nizhny Novgorod, Nizhny Novgorod 603022, Russia.
| | - Govindan Dayanithi
- Department of Molecular Neurophysiology, Institute of Experimental Medicine, Czech Academy of Sciences, Videnska 1083, 14220 Prague, Czech Republic; Institut National de la Santé et de la Recherche Médicale, Unité de recherche U1198, Université Montpellier 2, 34095 Montpellier, France; Ecole Pratique des Hautes Etudes, Sorbonne, 75014 Paris, France.
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Gagnon A, Walsh M, Okuda T, Choe KY, Zaelzer C, Bourque CW. Modulation of spike clustering by NMDA receptors and neurotensin in rat supraoptic nucleus neurons. J Physiol 2014; 592:4177-86. [PMID: 25063824 DOI: 10.1113/jphysiol.2014.275602] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
Magnocellular neurosecretory cells (MNCs) in the rat supraoptic nucleus display clustered firing during hyperosmolality or dehydration. This response is beneficial because this type of activity potentiates vasopressin secretion from axon terminals in the neurohypophysis and thus promotes homoeostatic water reabsorption from the kidney. However, the mechanisms which lead to the generation of clustering activity in MNCs remain unknown. Previous work has shown that clustered firing can be induced in these neurons through the pharmacological activation of NMDA receptors (NMDARs) and that silent pauses observed during this activity are mediated by apamin-sensitive calcium activated potassium (SK) channels. However, it remains unknown if clustered firing can be induced in situ by endogenous glutamate release from axon terminals. Here we show that electrical stimulation of glutamatergic osmosensory afferents in the organum vasculosum lamina terminalis (OVLT) can promote clustering in MNCs via NMDARs and apamin-sensitive channels.We also show that the rate of spike clustering induced by NMDA varies as a bell-shaped function of voltage, and that partial inhibition of SK channels can increase cluster duration and reduce the rate of clustering. Finally,we show that MNCs express neurotensin type 2 receptors, and that activation of these receptors can simultaneously depolarize MNCs and suppress clustered firing induced by bath application of NMDA or by repetitive stimulation of glutamate afferents. These studies reveal that spike clustering can be induced in MNCs by glutamate release from afferent nerve terminals and that that this type of activity can be fine-tuned by neuromodulators such as neurotensin.
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Affiliation(s)
- Ariane Gagnon
- Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal QC, Canada H3G 1A4
| | - Michael Walsh
- Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal QC, Canada H3G 1A4
| | - Tika Okuda
- Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal QC, Canada H3G 1A4
| | - Katrina Y Choe
- Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal QC, Canada H3G 1A4
| | - Cristian Zaelzer
- Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal QC, Canada H3G 1A4
| | - Charles W Bourque
- Centre for Research in Neuroscience, Research Institute of the McGill University Health Centre, Montreal QC, Canada H3G 1A4
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Intact In Vitro Preparations of the Neonatal Rodent Cortex: Analysis of Cellular Properties and Network Activity. ISOLATED CENTRAL NERVOUS SYSTEM CIRCUITS 2012. [DOI: 10.1007/978-1-62703-020-5_10] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
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10
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Teruyama R, Sakuraba M, Kurotaki H, Armstrong WE. Transient receptor potential channel m4 and m5 in magnocellular cells in rat supraoptic and paraventricular nuclei. J Neuroendocrinol 2011; 23:1204-13. [PMID: 21848647 PMCID: PMC5703211 DOI: 10.1111/j.1365-2826.2011.02211.x] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The neurohypophysial hormones, vasopressin (VP) and oxytocin (OT), are synthesised by magnocellular cells in the supraoptic nucleus (SON) and the paraventricular nucleus (PVN) of the hypothalamus. The release of VP into the general circulation from the neurohypophysis increases during hyperosmolality, hypotension and hypovolaemia. VP neurones increase hormone release by increasing their firing rate as a result of adopting a phasic bursting. Depolarising after potentials (DAPs) following a series of action potentials are considered to be involved in the generation of the phasic bursts by summating to plateau potentials. We recently discovered a fast DAP (fDAP) in addition to the slower DAP characterised previously. Almost all VP neurones expressed the fDAP, whereas only 16% of OT neurones had this property, which implicates the involvement of fDAP in the generation of the firing patterns in VP neurones. Our findings obtained from electrophysiological experiments suggested that the ionic current underlying the fDAP is mediated by those of two closely-related Ca(2+) -activated cation channels: the melastatin-related subfamily of transient receptor potential channels, TRPM4 and TRPM5. In the present study, double/triple immunofluorescence microscopy and reverse transcriptase-polymerase chain reaction techniques were employed to evaluate whether TRPM4 and TRPM5 are specifically located in VP neurones. Using specific antibodies against these channels, TRPM5 immunoreactivity was found almost exclusively in VP neurones, but not in OT neurones in both the SON and PVN. The most prominent TRPM5 immunoreactivity was in the dendrites of VP neurones. By contrast, most TRPM4 immunoreactivity occurred in cell bodies of both VP and OT neurones. TRPM4 and TRPM5 mRNA were both found in a cDNA library derived from SON punches. These results indictate the possible involvement of TRPM5 in the generation of the fDAP, and these channels may play an important role in determining the distinct firing properties of VP neurones in the SON.
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Affiliation(s)
- R Teruyama
- Department of Biological Sciences, Louisiana State University, LA 70803, USA.
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Aguila FA, Oliveira-Pelegrin GR, Yao ST, Murphy D, Rocha MJA. Anteroventral third ventricle (AV3V) lesion affects hypothalamic neuronal nitric oxide synthase (nNOS) expression following water deprivation. Brain Res Bull 2011; 86:239-45. [PMID: 21840380 DOI: 10.1016/j.brainresbull.2011.07.020] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/20/2011] [Revised: 07/21/2011] [Accepted: 07/27/2011] [Indexed: 10/17/2022]
Abstract
Neuronal nitric oxide synthase (nNOS) has been reported to be up-regulated in the hypothalamic supraoptic nucleus (SON) during dehydration which in turn could increase nitric oxide (NO) production and consequently affect arginine vasopressin (AVP) secretion. The anteroventral third ventricle (AV3V) region has strong afferent connections with the SON. Herein we describe our analysis of the effects of an AV3V lesion on AVP secretion, and c-fos and nNOS expression in the SON following dehydration. Male Wistar rats had their AV3V region electrolytically lesioned or were sham operated. After 21 days they were submitted to dehydration or left as controls (euhydrated). Two days later, one group was anaesthetized, perfused and the brains were processed for Fos protein and nNOS immunohistochemistry (IHC). Another group was decapitated, the blood collected for hematocrit, osmolality, serum sodium and AVP plasma level analysis. The brains were removed for measurement of neurohypophyseal AVP content, and the SON was punched out and processed for nNOS detection by western blotting. The AV3V lesion reduced AVP plasma levels and c-fos expression in the SON following dehydration (P<0.05). Western blotting revealed an up-regulation of nNOS in the SON of control animals following dehydration, whereas such up-regulation was not observed in AV3V-lesioned rats (P<0.05). We conclude that the AV3V region plays a role in regulating the expression of nNOS in the SON of rats submitted to dehydration, and thus may affect the local nitric oxide production and the secretion of vasopressin.
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Affiliation(s)
- Fábio Alves Aguila
- Departamento de Morfologia, Universidade de São Paulo, Ribeirão Preto, São Paulo, Brazil
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12
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Abstract
Many neurons in the CNS display rhythmic patterns of activity to optimize excitation-secretion coupling. However, the mechanisms of rhythmogenesis are only partially understood. Magnocellular vasopressin (VP) neurons in the hypothalamus display a phasic activity that consists of alternative bursts of action potentials and silent periods. Previous observations from acute slices of adult hypothalamus suggested that VP cell rhythmicity depends on intrinsic membrane properties. However, such activity in vivo is nonregenerative. Here, we studied the mechanisms of VP neuron rhythmicity in organotypic slice cultures that, unlike acute slices, preserve functional synaptic connections. Comparative analysis of phasic firing of VP neurons in vivo, in acute slices, and in the cultures revealed that, in the latter, the activity was closely related to that observed in vivo. It was synaptically driven, essentially from glutamatergic inputs, and did not rely on intrinsic membrane properties. The glutamatergic synaptic activity was sensitive to osmotic challenges and kappa-opioid receptor activation, physiological stimuli known to affect phasic activity. Together, our data thus strongly suggest that phasic activity in magnocellular VP neurons is controlled by glutamatergic synaptic inputs rather than by intrinsic properties.
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13
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Armstrong WE, Wang L, Li C, Teruyama R. Performance, properties and plasticity of identified oxytocin and vasopressin neurones in vitro. J Neuroendocrinol 2010; 22:330-42. [PMID: 20210845 PMCID: PMC2910405 DOI: 10.1111/j.1365-2826.2010.01989.x] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The neurohypophysial hormones oxytocin (OT) and vasopressin (VP) originate from hypothalamic neurosecretory cells in the paraventricular and supraoptic (SON) nuclei. The firing rate and pattern of action potentials arising from these neurones determine the timing and quantity of peripheral hormone release. We have used immunochemical identification of biocytin-filled SON neurones in hypothalamic slices in vitro to uncover differences between OT and VP neurones in membrane and synaptic properties, firing patterns, and plasticity during pregnancy and lactation. In this review, we summarise some recent findings from this approach: (i) VP neuronal excitability is influenced by slow (sDAP) and fast (fDAP) depolarising afterpotentials that underlie phasic bursting activity. The fDAP may relate to a transient receptor potential (TRP) channel, type melastatin (TRPM4 and/or TRPM5), both of which are immunochemically localised more to VP neurones, and especially, to their dendrites. Both TRPM4 and TRPM5 mRNAs are found in the SON, but single cell reverse transcriptase-polymerisation suggests that TRPM4 might be the more prominent channel. Phasic bursting in VP neurones is little influenced by spontaneous synaptic activity in slices, being shaped largely by intrinsic currents. (ii) The firing pattern of OT neurones ranges from irregular to continuous, with the coefficient of variation determined by randomly distributed, spontaneous GABAergic, inhibitory synaptic currents (sIPSCs). These sIPSCs are four- to five-fold more frequent in OT versus VP neurones, and much more frequent than spontaneous excitatory synaptic currents. (iii) Both cell types express Ca(2+)-dependent afterhyperpolarisations (AHPs), including an apamin-sensitive, medium duration AHP and a slower, apamin-insensitive AHP (sAHP). In OT neurones, both AHPs are enhanced during pregnancy and lactation. During pregnancy, the plasticity of the sAHP is blocked by antagonism of central OT receptors. AHP enhancement is mimicked by exposing slices from day 19 pregnant rats to OT and oestradiol, suggesting that central OT and sex steroids programme this plasticity during pregnancy by direct hypothalamic actions. In conclusion, the differences in VP and OT neuronal function are underlain by differences in both membrane and synaptic properties, and differentially modulated by reproductive state.
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Affiliation(s)
- W E Armstrong
- Department of Anatomy and Neurobiology, University of Tennessee Health Science Center, Memphis, TN 38163, USA.
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14
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Roberts EM, Pope GR, Newson MJF, Landgraf R, Lolait SJ, O'Carroll AM. Stimulus-specific neuroendocrine responses to osmotic challenges in apelin receptor knockout mice. J Neuroendocrinol 2010; 22:301-8. [PMID: 20136689 DOI: 10.1111/j.1365-2826.2010.01968.x] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The expression of the novel peptide apelin and its receptor APJ within specific regions of the brain, in particular the magnocellular neurones of the hypothalamus and the circumventricular organs, has implicated the apelinergic system in mechanisms controlling fluid homeostasis. In addition, apelin and APJ are considered to be involved in controlling arginine vasopressin (AVP) secretion into the circulation and release within the hypothalamic-neurohypophysial system. To clarify the role of APJ during regulation of fluid homeostasis, we compared the effects of osmotic stimulation on the urinary concentrating capacities and central nervous system responses of salt-loaded (SL) and water-deprived (WD) female APJ knockout (APJ(-/-)) mice and wild-type controls. SL resulted in a significantly increased urine volume in APJ(-/-) mice compared to wild-type controls, whereas WD in APJ(-/-) mice failed to reduce urine volume as seen in wild-type controls. AVP transcripts in the supraoptic and paraventricular nuclei and plasma AVP concentrations were significantly attenuated in SL APJ(-/-) mice compared to SL wild-type, but increased comparably in wild-type and APJ(-/-) mice after WD. Analysis of c-fos mRNA expression in the median preoptic nucleus and subfornical organ in response to either WD or SL showed attenuated expression in APJ(-/-) compared to wild-type mice. These findings further implicate the apelinergic system in mechanisms controlling fluid homeostasis, particularly at a neuroendocrine level, and suggest stimulus-specific involvement in vasopressinergic activity.
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Affiliation(s)
- E M Roberts
- Henry Wellcome Laboratories for Integrative Neuroscience and Endocrinology, University of Bristol, Bristol, UK
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15
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Cuadra AE, Shan Z, Sumners C, Raizada MK. A current view of brain renin-angiotensin system: Is the (pro)renin receptor the missing link? Pharmacol Ther 2010; 125:27-38. [PMID: 19723538 PMCID: PMC2815255 DOI: 10.1016/j.pharmthera.2009.07.007] [Citation(s) in RCA: 59] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/20/2009] [Accepted: 07/20/2009] [Indexed: 02/07/2023]
Abstract
The renin-angiotensin system (RAS) plays a central role in the brain to regulate blood pressure (BP). This role includes the modulation of sympathetic nerve activity (SNA) that regulates vascular tone; the regulation of secretion of neurohormones that have a critical role in electrolyte as well as fluid homeostasis; and by influencing behavioral processes to increase salt and water intake. Based on decades of research it is clear that angiotensin II (Ang II), the major bioactive product of the RAS, mediates these actions largely via its Ang II type 1 receptor (AT1R), located within hypothalamic and brainstem control centers. However, the mechanisms of brain RAS function have been questioned, due in large part to low expression levels of the rate limiting enzyme renin within the central nervous system. Tissue localized RAS has been observed in heart, kidney tubules and vascular cells. Studies have also given rise to the hypothesis for localized RAS function within the brain, so that Ang II can act in a paracrine manner to influence neuronal activity. The recently discovered (pro)renin receptor (PRR) may be key in this mechanism as it serves to sequester renin and prorenin for localized RAS activity. Thus, the PRR can potentially mitigate the low levels of renin expression in the brain to propagate Ang II action. In this review we examine the regulation, expression and functional properties of the various RAS components in the brain with particular focus on the different roles that PRR may have in BP regulation and hypertension.
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Affiliation(s)
- Adolfo E Cuadra
- University of Florida College of Medicine, Department of Physiology and Functional Genomics, 100274 SW Archer Road, Gainesville, FL 32610, USA
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16
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Roberts EM, Newson MJF, Pope GR, Landgraf R, Lolait SJ, O'Carroll AM. Abnormal fluid homeostasis in apelin receptor knockout mice. J Endocrinol 2009; 202:453-62. [PMID: 19578099 PMCID: PMC2729781 DOI: 10.1677/joe-09-0134] [Citation(s) in RCA: 74] [Impact Index Per Article: 4.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Revised: 05/26/2009] [Accepted: 07/03/2009] [Indexed: 12/17/2022]
Abstract
The apelinergic system, comprised of apelin and its G protein-coupled receptor (APJ; APLNR as given in MGI Database), is expressed within key regions of the central nervous system associated with arginine vasopressin (AVP) synthesis and release as well as in structures involved in the control of drinking behaviour, including the magnocellular neurones of the hypothalamus, circumventricular organs, and the pituitary gland. This localisation is indicative of a possible functional role in fluid homeostasis. We investigated a role for APJ in the regulation of fluid balance using mice deficient for the receptor. Male APJ wild-type and knockout (APJ(-/-)) mice were housed in metabolic cages to allow determination of water intake and urine volume and osmolality. When provided with free access to water, APJ(-/-) mice drank significantly less than wild-types, while their urine volume and osmolality did not differ. Water deprivation for 24 h significantly reduced urine volume and increased osmolality in wild-type but not in APJ(-/-) mice. Baseline plasma AVP concentration increased comparably in both wild-type and APJ(-/-) mice following dehydration; however, APJ(-/-) mice were unable to concentrate their urine to the same extent as wild-type mice in response to the V2 agonist desmopressin. Analysis of c-fos (Fos as given in MGI Database) mRNA expression in response to dehydration showed attenuation of expression within the subfornical organ, accentuated expression in the paraventricular nucleus, but no differences in expression in the supraoptic nucleus nor median pre-optic nucleus in APJ(-/-) mice compared with wild-type. These findings demonstrate a physiological role for APJ in mechanisms of water intake and fluid retention and suggest an anti-diuretic effect of apelin in vivo.
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Effect of purines on calcium-independent acetylcholine release at the mouse neuromuscular junction. Neuroscience 2008; 154:1324-36. [PMID: 18534762 DOI: 10.1016/j.neuroscience.2008.04.056] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2008] [Revised: 04/29/2008] [Accepted: 04/29/2008] [Indexed: 01/29/2023]
Abstract
At the mouse neuromuscular junction, activation of adenosine A(1) and P2Y receptors inhibits acetylcholine release by an effect on voltage dependent calcium channels related to spontaneous and evoked secretion. However, an effect of purines upon the neurotransmitter-releasing machinery downstream of Ca(2+) influx cannot be ruled out. An excellent tool to study neurotransmitter exocytosis in a Ca(2+)-independent step is the hypertonic response. Intracellular recordings were performed on diaphragm fibers of CF1 mice to determine the action of the specific adenosine A(1) receptor agonist 2-chloro-N(6)-cyclopentyl-adenosine (CCPA) and the P2Y(12-13) agonist 2-methylthio-adenosine 5'-diphosphate (2-MeSADP) on the hypertonic response. Both purines significantly decreased such response (peak and area under the curve), and their effect was prevented by specific antagonists of A(1) and P2Y(12-13) receptors, 8-cyclopentyl-1,3-dipropylxanthine (DPCPX) and N-[2-(methylthioethyl)]-2-[3,3,3-trifluoropropyl]thio-5'-adenylic acid, monoanhydride with dichloromethylenebiphosphonic acid, tetrasodium salt (AR-C69931MX), respectively. Moreover, incubation of preparations only with the antagonists induced a higher response compared with controls, suggesting that endogenous ATP/ADP and adenosine are able to modulate the hypertonic response by activating their specific receptors. To search for the intracellular pathways involved in this effect, we studied the action of CCPA and 2-MeSADP in hypertonicity in the presence of inhibitors of several pathways. We found that the effect of CPPA was prevented by the calmodulin antagonist N-(6-aminohexil)-5-chloro-1-naphthalenesulfonamide hydrochloride (W-7) while that of 2-MeSADP was occluded by the protein kinase C antagonist chelerythrine and W-7. On the other hand, the inhibitors of protein kinase A (N-(2[pbromocinnamylamino]-ethyl)-5-isoquinolinesulfonamide, H-89) and phosphoinositide-3 kinase (PI3K) (2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one hydrochloride, LY-294002) did not modify the modulatory action in hypertonicity of both purines. Our results provide evidence that activation of A(1) and P2Y(12-13) receptors by CCPA and 2-MeSADP inhibits ACh release from mammalian motor nerve terminals through an effect on a Ca(2+)-independent step in the cascade of the exocytotic process. Since presynaptic calcium channels are intimately associated with components of the synaptic vesicle docking and fusion processes, further experiments could clarify if the actions of purines on calcium channels and on secretory machinery are related.
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Davies ML, Kirov SA, Andrew RD. Whole isolated neocortical and hippocampal preparations and their use in imaging studies. J Neurosci Methods 2007; 166:203-16. [PMID: 17765319 PMCID: PMC2100436 DOI: 10.1016/j.jneumeth.2007.07.012] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/18/2007] [Revised: 07/10/2007] [Accepted: 07/11/2007] [Indexed: 11/19/2022]
Abstract
This study shows that two whole isolated preparations from the young mouse, the neocortical 'slab' and the hippocampal formation, are useful for imaging studies requiring both global monitoring using light transmittance (LT) imaging and high resolution cellular monitoring using 2-photon laser scanning microscopy (2PLSM). These preparations share advantages with brain slices such as maintaining intrinsic neuronal properties and avoiding cardiac or respiratory movement. Important additional advantages include the maintenance of all local input and output pathways, the absence of surfaces injured by slicing and the preservation of three-dimensional tissue structure. Using evoked extracellular field recording, we demonstrate long-term (hours) viability of both whole preparations. We then show that propagating cortical events such as anoxic depolarization (AD) and spreading depression (SD) can be imaged in both preparations, yielding results comparable to those in brain slices but retaining the tissue's three-dimensional structure. Using transgenic mice expressing green fluorescent protein (GFP) in pyramidal and granule cell neurons, 2PLSM confirms that these preparations are free of the surface damage observed in sliced brain tissue. Moreover the neurons undergo swelling with accompanying dendritic beading following AD induced by simulated ischemia, similar to cortical damage described in vivo.
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Affiliation(s)
- Melissa L. Davies
- Department of Anatomy & Cell Biology and The Centre for Neuroscience Studies Queen’s University, Kingston, ON
| | - Sergei A. Kirov
- Department of Neurosurgery Medical College of Georgia, Augusta, GA
| | - R. David Andrew
- Department of Anatomy & Cell Biology and The Centre for Neuroscience Studies Queen’s University, Kingston, ON
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19
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Teruyama R, Armstrong WE. Calcium-dependent fast depolarizing afterpotentials in vasopressin neurons in the rat supraoptic nucleus. J Neurophysiol 2007; 98:2612-21. [PMID: 17715195 DOI: 10.1152/jn.00599.2007] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Oxytocin (OT) and vasopressin (VP) synthesizing magnocellular cells (MNCs) in the supraoptic nucleus (SON) display distinct firing patterns during the physiological demands for these hormones. Depolarizing afterpotentials (DAPs) in these neurons are involved in controlling phasic bursting in VP neurons. Our whole cell recordings demonstrated a Cs(+)-resistant fast DAP (fDAP; decay tau = approximately 200 ms), which has not been previously reported, in addition to the well-known Cs(+)-sensitive slower DAP (sDAP; decay tau = approximately 2 s). Immunoidentification of recorded neurons revealed that all VP neurons, but only 20% of OT neurons, expressed the fDAP. The activation of the fDAP required influx of Ca(2+) through voltage-gated Ca(2+) channels as it was strongly suppressed in Ca(2+)-free extracellular solution or by bath application of Cd(2+). Additionally, the current underlying the fDAP (I(fDAP)) is a Ca(2+)-activated current rather than a Ca(2+) current per se as it was abolished by strongly buffering intracellular Ca(2+) with BAPTA. The I-V relationship of the I(fDAP) was linear at potentials less than -60 mV but showed pronounced outward rectification near -50 mV. I(fDAP) is sensitive to changes in extracellular Na(+) and K(+) but not Cl(-). A blocker of Ca(2+)-activated nonselective cation (CAN) currents, flufenamic acid, blocked the fDAP, suggesting the involvement of a CAN current in the generation of fDAP in VP neurons. We speculate that the two DAPs have different roles in generating after burst discharges and could play important roles in determining the distinct firing properties of VP neurons in the SON neurons.
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Affiliation(s)
- Ryoichi Teruyama
- Department of Anatomy and Neurobiology, University of Tennessee, Health Science Center, TN 38163, USA.
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20
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Liu XH, Zhang W, Fisher TE. A novel osmosensitive voltage gated cation current in rat supraoptic neurones. J Physiol 2005; 568:61-8. [PMID: 16096339 PMCID: PMC1474758 DOI: 10.1113/jphysiol.2005.093773] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The magnocellular neurosecretory cells of the hypothalamus (MNCs) regulate water balance by releasing vasopressin and oxytocin as a function of plasma osmolality. Release is determined largely by the rate and pattern of action potentials generated in the MNC somata. Changes in firing are mediated in part by a stretch-inactivated non-selective cation current that causes the cells to depolarize when increased osmolality leads to cell shrinkage. We have obtained evidence for a new current that may regulate MNC firing during changes in external osmolality, using whole-cell patch clamp of acutely isolated rat MNC somata. In internal and external solutions lacking K+, with high concentrations of TEA, and with Na+ as the only likely permeant cation, the current appears as a slow inward current during depolarizations and yields a large tail current upon return to the holding potential of -80 mV. Approximately 60% of the MNCs tested (79 out of 134 cells) displayed a large increase in tail current density (from 5.2+/-0.9 to 10.5+/-1.4 pA pF-1; P<0.001) following an increase in external osmolality from 295 to 325 mosmol kg-1. The current is activated by depolarization to potentials above -60 mV and does not appear to depend on changes in internal Ca2+. The current is carried by Na+ under these conditions, but is blocked by Cs+ and Ba2+ and by internal K+, which suggests that the current could be a K+ current under physiological conditions. This current could play an important role in regulating the response of MNCs to osmolality.
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Affiliation(s)
- Xiao-Hong Liu
- Department of Physiology, College of Medicine, 107 Wiggins Road, University of Saskatchewan, Saskatoon, SK, Canada S7N 5E5
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21
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Ghamari-Langroudi M, Bourque CW. Muscarinic receptor modulation of slow afterhyperpolarization and phasic firing in rat supraoptic nucleus neurons. J Neurosci 2005; 24:7718-26. [PMID: 15342739 PMCID: PMC6729628 DOI: 10.1523/jneurosci.1240-04.2004] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
A slow posttrain afterhyperpolarization (sAHP) was studied in rat magnocellular neurosecretory cells (MNCs) in vitro. The sAHP was isolated from other afterpotentials by blocking the depolarizing afterpotential (DAP) with Cs(+) and the medium afterhyperpolarization (mAHP) with apamin. The sAHP amplitude increased logarithmically with activity ( approximately 3 mV per e-fold increase in number of impulses) and, when firing stopped, decayed exponentially with a time constant of 2 sec. The sAHP was associated with increased membrane conductance, and its amplitude varied linearly with voltage, reversing at the K(+) equilibrium potential. The sAHP was blocked by Cd(2+) but not by charybdotoxin or iberiotoxin, blockers of intermediate- and big-conductance-type Ca(2+)-dependent K(+) (K(Ca)) channels. The sAHP was reversibly inhibited by muscarine, an effect antagonized by atropine, indicating involvement of muscarinic cholinergic receptors. Muscarine did not affect Ca(2+)-dependent features of action potentials, DAPs, or the mAHP in MNCs, indicating selective modulation of K(Ca) channels causing the sAHP. Muscarinic inhibition of the sAHP enhanced plateau potentials and increased the mean firing rate and duration of afterdischarges that followed spike trains evoked from voltages near threshold. Similarly, the frequency and duration of the spontaneous phasic bursts that characterize physiologically activated vasopressin-releasing MNCs were enhanced by muscarine. MNCs thus express apamin- and voltage-insensitive K(Ca) channels that mediate an sAHP. The activity dependence and kinetics of the sAHP cause it to mask DAPs in a manner that attenuates the amplitude of plateau potentials. Muscarinic inhibition of the sAHP provides an effective mechanism for promoting phasic firing in MNCs.
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Affiliation(s)
- Masoud Ghamari-Langroudi
- Centre for Research in Neuroscience, Montreal General Hospital and McGill University, Montreal, Quebec H3G 1A4, Canada
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22
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Roper P, Callaway J, Armstrong W. Burst initiation and termination in phasic vasopressin cells of the rat supraoptic nucleus: a combined mathematical, electrical, and calcium fluorescence study. J Neurosci 2004; 24:4818-31. [PMID: 15152042 PMCID: PMC6729454 DOI: 10.1523/jneurosci.4203-03.2004] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Vasopressin secreting neurons of the rat hypothalamus discharge lengthy, repeating bursts of action potentials in response to physiological stress. Although many electrical currents and calcium-dependent processes have been isolated and analyzed in these cells, their interactions are less well fathomed. In particular, the mechanism of how each burst is triggered, sustained, and terminated is poorly understood. We present a mathematical model for the bursting mechanism, and we support our model with new simultaneous electrical recording and calcium imaging data. We show that bursts can be initiated by spike-dependent calcium influx, and we propose that the resulting elevation of bulk calcium inhibits a persistent potassium current. This inhibition depolarizes the cell above threshold and so triggers regenerative spiking and further calcium influx. We present imaging data to show that bulk calcium reaches a plateau within the first few seconds of the burst, and our model indicates that this plateau occurs when calcium influx is balanced by efflux and uptake into stores. We conjecture that the burst is terminated by a slow, progressive desensitization to calcium of the potassium leak current. Finally, we propose that the opioid dynorphin, which is known to be secreted from the somatodendritic region and has been shown previously to regulate burst length and phasic activity in these cells, is the autocrine messenger for this desensitization.
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Affiliation(s)
- Peter Roper
- Laboratory of Biological Modeling, National Institute of Diabetes and Digestive and Kidney Diseases, National Institutes of Health, Bethesda, Maryland 20892, USA.
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23
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Brown CH, Bull PM, Bourque CW. Phasic bursts in rat magnocellular neurosecretory cells are not intrinsically regenerative in vivo. Eur J Neurosci 2004; 19:2977-83. [PMID: 15182304 DOI: 10.1111/j.0953-816x.2004.03408.x] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Vasopressinergic hypothalamic magnocellular neurosecretory cells fire in phasic bursts. Burst initiation involves summation of postsynaptic potentials to generate action potentials. Action potentials are each followed by a nonsynaptic depolarizing after-potential that summates temporally to generate a plateau potential and so sustain activity throughout the burst. It is unknown whether this plateau potential exceeds spike threshold in vivo to cause intrinsic regenerative firing or simply approaches threshold to increase the probability that excitatory postsynaptic potentials will trigger further action potentials. Here we show that pharmacological blockade of ionotropic glutamatergic transmission by microdialysis application of kynurenic acid into the supraoptic nucleus of anaesthetized rats prevents spontaneous bursts and bursts (after-discharge) evoked by short trains of antidromically stimulated action potentials in magnocellular neurosecretory cells. Even during prolonged depolarization induced by 1 m NaCl infusion, kynurenic acid microdialysis application still blocked after-discharge. The ability of kynurenic acid to block after-discharge during osmotic stimulation was not caused by an unmasking of inhibitory postsynaptic potentials as kynurenic acid was equally effective in the presence of the ionotropic gamma-aminobutyric acid receptor antagonist, bicuculline, nor did it result from inhibition of plateau potential amplitude as this was unaffected by kynurenic acid and bicuculline in vitro, as was after-discharge evoked in vitro. We conclude that phasic bursts are nonregenerative in vivo but rather require continued excitatory synaptic input activity superimposed upon a subthreshold plateau potential to sustain burst activity.
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Affiliation(s)
- Colin H Brown
- School of Biomedical and Clinical Laboratory Sciences, University of Edinburgh, Hugh Robson Building, George Square, Edinburgh EH8 9XD, Scotland, UK.
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24
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Oliveira GR, Franci CR, Rodovalho GV, Franci JAA, Morris M, Rocha MJA. Alterations in the central vasopressin and oxytocin axis after lesion of a brain osmotic sensory region. Brain Res Bull 2004; 63:515-20. [PMID: 15249117 DOI: 10.1016/j.brainresbull.2004.04.009] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/06/2004] [Revised: 04/15/2004] [Accepted: 04/19/2004] [Indexed: 11/16/2022]
Abstract
The anteroventral region of the third ventricle (AV3V) is critical in mediating osmotic sensitivity. AV3V lesions increase plasma osmolality and block osmotic-induced vasopressin (VP) and oxytocin (OT) secretion. The aim was to evaluate the effects of AV3V lesions on neurosecretion under control/water replete conditions and after 48 h dehydration. The focus was on central peptidergic changes with measurement of OT and VP content in the hypothalamic paraventricular (PVN) and supraoptic (OT) regions and the posterior pituitary. AV3V-lesioned rats exhibited an elevated plasma osmolality and higher OT content in SON and PVN. There was an increase in VP content in PVN, but no change in SON. As predicted, the plasma peptide response to dehydration was absent in lesioned animals. However, dehydration produced depletion in posterior pituitary VP in lesioned animals with no change in OT. No changes in nuclear VP and OT levels were seen after dehydration. These results demonstrate that AV3V lesions alter the VP and OT neurosecretory system, seen as a blockade of osmotic-induced release and an increase in basal nuclear peptide content. The data indicate that interruption of the osmotic sensory system affects the central neurosecretory axis, resulting in a backup in content and likely changes in synthesis and processing.
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Affiliation(s)
- Gabriela R Oliveira
- Departamento de Morfologia, Estomatologia e Fisiologia da Faculdade de Odontologia de Ribeirão Preto, Universidade de São Paulo, Av. do Café s/n, CEP 14049-900 Ribeirão Preto, Brazil
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Priming of excitatory synapses by alpha1 adrenoceptor-mediated inhibition of group III metabotropic glutamate receptors. J Neurosci 2003. [PMID: 12867506 DOI: 10.1523/jneurosci.23-15-06223.2003] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Adaptive responses mediated by the hypothalamus require sustained activation until homeostasis is achieved. Increases in excitatory drive to the magnocellular neuroendocrine cells that mediate these responses, however, result in the activation of a presynaptic metabotropic glutamate receptor (mGluR) that curtails synaptic excitability. Recent evidence that group III mGluRs can be inhibited by protein kinase C prompted us to test the hypothesis that activation of PKC by noradrenaline (NA) inhibits group III mGluRs and increases excitatory synaptic input to these cells. To examine the effects of NA on miniature EPSCs (mEPSCs), we obtained whole-cell recordings from magnocellular vasopressin and oxytocin neurons in the paraventricular nucleus of the hypothalamus. All of the neurons tested in the current study displayed an alpha1 adrenoceptor-mediated increase in mEPSC frequency in response to NA (1-200 microm). The excitatory effects of NA were mimicked by the phorbol ester PMA and blocked by the PKC inhibitor calphostin C. The activation of PKC inhibits the efficacy of group III mGluRs, resulting in an increase in mEPSC frequency in response to a subsequent exposure to NA. By removing feedback inhibition, this mechanism effectively primes the synapses such that subsequent activation is more efficacious. The novel form of synaptic rescaling afforded by this cross-talk between distinct metabotropic receptors provides a means by which ascending catecholamine inputs can facilitate the control of homeostasis by hypothalamic networks.
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26
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Gordon GRJ, Bains JS. Priming of excitatory synapses by alpha1 adrenoceptor-mediated inhibition of group III metabotropic glutamate receptors. J Neurosci 2003; 23:6223-31. [PMID: 12867506 PMCID: PMC6740556] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/03/2023] Open
Abstract
Adaptive responses mediated by the hypothalamus require sustained activation until homeostasis is achieved. Increases in excitatory drive to the magnocellular neuroendocrine cells that mediate these responses, however, result in the activation of a presynaptic metabotropic glutamate receptor (mGluR) that curtails synaptic excitability. Recent evidence that group III mGluRs can be inhibited by protein kinase C prompted us to test the hypothesis that activation of PKC by noradrenaline (NA) inhibits group III mGluRs and increases excitatory synaptic input to these cells. To examine the effects of NA on miniature EPSCs (mEPSCs), we obtained whole-cell recordings from magnocellular vasopressin and oxytocin neurons in the paraventricular nucleus of the hypothalamus. All of the neurons tested in the current study displayed an alpha1 adrenoceptor-mediated increase in mEPSC frequency in response to NA (1-200 microm). The excitatory effects of NA were mimicked by the phorbol ester PMA and blocked by the PKC inhibitor calphostin C. The activation of PKC inhibits the efficacy of group III mGluRs, resulting in an increase in mEPSC frequency in response to a subsequent exposure to NA. By removing feedback inhibition, this mechanism effectively primes the synapses such that subsequent activation is more efficacious. The novel form of synaptic rescaling afforded by this cross-talk between distinct metabotropic receptors provides a means by which ascending catecholamine inputs can facilitate the control of homeostasis by hypothalamic networks.
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Affiliation(s)
- Grant R J Gordon
- Neuroscience Research Group, Department of Physiology and Biophysics, University of Calgary, Alberta, T2N 4N1, Canada
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27
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O'Carroll AM, Lolait SJ. Regulation of rat APJ receptor messenger ribonucleic acid expression in magnocellular neurones of the paraventricular and supraopric nuclei by osmotic stimuli. J Neuroendocrinol 2003; 15:661-6. [PMID: 12787050 DOI: 10.1046/j.1365-2826.2003.01044.x] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
The novel apelin receptor (APJ receptor, APJR) has a restricted expression in the central nervous system suggestive of an involvement in the regulation of body fluid homeostasis. The endogenous ligand for APJR, apelin, is also highly concentrated in regions that are involved in the control of drinking behaviour. While the physiological roles of APJR and apelin are not fully known, apelin has been shown to stimulate drinking behaviour in rats and to have a regulatory effect on vasopressin release from magnocellular neurones of the hypothalamic paraventricular (PVN) and supraoptic (SON) nuclei. To determine the role of APJR in the regulation of water balance, this study examined the effects of osmotic stimulation on the expression of APJR mRNA in the magnocellular PVN (mPVN) and SON of salt-loaded and water-deprived rats. Intake of 2% NaCl and water deprivation for 48 h induced expression of APJR mRNA in the mPVN and SON. Using dual-label in situ hybridization histochemistry, we also investigated whether APJR is colocalized within vasopressin neurones in control, salt-loaded and water-deprived rats. APJR mRNA was found to colocalize with a small population of vasopressin-containing magnocellular neurones in control and water-deprived rats. Salt-loading resulted in an increased colocalization of APJR and vasopressin mRNAs in the SON. These data verify a role for APJ receptors in body fluid regulation and suggest a role for apelin in the regulation of vasopressin-containing neurones via a local autocrine/paracrine action of the peptide.
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Affiliation(s)
- A-M O'Carroll
- University Research Centre for Neuroendocrinology, University of Bristol, Bristol, UK
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28
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Suzuki K, Grinnell AD, Kidokoro Y. Hypertonicity-induced transmitter release at Drosophila neuromuscular junctions is partly mediated by integrins and cAMP/protein kinase A. J Physiol 2002; 538:103-19. [PMID: 11773320 PMCID: PMC2290025 DOI: 10.1113/jphysiol.2001.012901] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022] Open
Abstract
The frequency of quantal transmitter release increases upon application of hypertonic solutions. This effect bypasses the Ca(2+) triggering step, but requires the presence of key molecules involved in vesicle fusion, and hence could be a useful tool for dissecting the molecular process of vesicle fusion. We have examined the hypertonicity response at neuromuscular junctions of Drosophila embryos in Ca(2+)-free saline. Relative to wild-type, the response induced by puff application of hypertonic solution was enhanced in a mutant, dunce, in which the cAMP level is elevated, or in wild-type embryos treated with forskolin, an activator of adenylyl cyclase, while protein kinase A (PKA) inhibitors decreased it. The response was also smaller in a mutant, DC0, which lacks the major subunit of PKA. Thus the cAMP/PKA cascade is involved in the hypertonicity response. Peptides containing the sequence Arg-Gly-Asp (RGD), which inhibit binding of integrins to natural ligands, reduced the response, whereas a peptide containing the non-binding sequence Arg-Gly-Glu (RGE) did not. A reduced response persisted in a mutant, myospheroid, which expresses no integrins, and the response in DC0 was unaffected by RGD peptides. These data indicate that there are at lease two components in the hypertonicity response: one that is integrin mediated and involves the cAMP/PKA cascade, and another that is not integrin mediated and does not involve the cAMP/PKA cascade.
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Affiliation(s)
- Kazuhiro Suzuki
- Institute for Behavioral Sciences, Gunma University School of Medicine, 3-39-22 Showa-machi, Maebashi, 371-8511, Japan
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29
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Johnson RF, Beltz TG, Sharma RV, Xu Z, Bhatty RA, Johnson AK. Agonist activation of cytosolic Ca2+ in subfornical organ cells projecting to the supraoptic nucleus. Am J Physiol Regul Integr Comp Physiol 2001; 280:R1592-9. [PMID: 11294785 DOI: 10.1152/ajpregu.2001.280.5.r1592] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
The subfornical organ (SFO) is sensitive to both ANG II and ACh, and local application of these agents produces dipsogenic responses and vasopressin release. The present study examined the effects of cholinergic drugs, ANG II, and increased extracellular osmolarity on dissociated, cultured cells of the SFO that were retrogradely labeled from the supraoptic nucleus. The effects were measured as changes in cytosolic calcium in fura 2-loaded cells by using a calcium imaging system. Both ACh and carbachol increased intracellular ionic calcium concentration ([Ca2+]i). However, in contrast to the effects of muscarinic receptor agonists on SFO neurons, manipulation of the extracellular osmolality produced no effects, and application of ANG II produced only moderate effects on [Ca2+]i in a few retrogradely labeled cells. The cholinergic effects on [Ca2+]i could be blocked with the muscarinic receptor antagonist atropine and with the more selective muscarinic receptor antagonists pirenzepine and 4-diphenylacetoxy-N-methylpiperdine methiodide (4-DAMP). In addition, the calcium in the extracellular fluid was required for the cholinergic-induced increase in [Ca2+]i. These findings indicate that ACh acts to induce a functional cellular response in SFO neurons through action on a muscarinic receptor, probably of the M1 subtype and that the increase of [Ca2+]i, at least initially, requires the entry of extracellular Ca2+. Also, consistent with a functional role of M1 receptors in the SFO are the results of immunohistochemical preparations demonstrating M1 muscarinic receptor-like protein present within this forebrain circumventricular organ.
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Affiliation(s)
- R F Johnson
- Department of Psychology, Pharmacology, Exercise Science, University of Iowa, Iowa City, Iowa 52242, USA
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30
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Kashani AH, Chen BM, Grinnell AD. Hypertonic enhancement of transmitter release from frog motor nerve terminals: Ca2+ independence and role of integrins. J Physiol 2001; 530:243-52. [PMID: 11208972 PMCID: PMC2278411 DOI: 10.1111/j.1469-7793.2001.0243l.x] [Citation(s) in RCA: 42] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/27/2022] Open
Abstract
Hyperosmotic solutions cause markedly enhanced spontaneous quantal release of neurotransmitter from many nerve terminals. The mechanism of this enhancement is unknown. We have investigated this phenomenon at the frog neuromuscular junction with the aim of determining the degree to which it resembles the modulation of release by stretch, which has been shown to be mediated by mechanical tension on integrins. The hypertonicity enhancement, like the stretch effect, does not require Ca2+ influx or release from internal stores, although internal release may contribute to the effect. The hypertonicity effect is sharply reduced (but not eliminated) by peptides containing the RGD sequence, which compete with native ligands for integrin bonds. There is co-variance in the magnitude of the stretch and osmotic effects; that is, individual terminals exhibiting a large stretch effect also show strong enhancement by hypertonicity, and vice versa. The stretch and osmotic enhancements also can partially occlude each other. There remain some clear-cut differences between osmotic and stretch forms of modulation: the larger range of enhancement by hypertonic solutions, the relative lack of effect of osmolarity on evoked release, and the reported higher temperature sensitivity of osmotic enhancement. Nevertheless, our data strongly implicate integrins in a significant fraction of the osmotic enhancement, possibly acting via the same mechanism as stretch modulation.
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Affiliation(s)
- A H Kashani
- Department of Physiology, Jerry Lewis Neuromuscular Research Center, UCLA School of Medicine, University of California, Los Angeles, CA 90095, USA
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31
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Currás-Collazo MC, Chin C, Díaz G, Stivers C, Bozzetti L, Tran LY, Kíaz G. Immunolabeling reveals cellular localization of the N-methyl-D-aspartate receptor subunit NR2B in neurosecretory cells but not astrocytes of the rat magnocellular nuclei. J Comp Neurol 2000; 427:93-108. [PMID: 11042593 DOI: 10.1002/1096-9861(20001106)427:1<93::aid-cne6>3.0.co;2-8] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Previous studies suggest that activation of N-methyl-D-aspartate (NMDA) receptors facilitates phasic firing and spike clustering displayed by magnocellular neuroendocrine cells (MNCs) of the supraoptic (SON) and paraventricular nucleus of the hypothalamus (PVN). Osmotic stimulation produces similar activity patterns which, in turn, can lead to enhanced release of vasopressin and oxytocin from MNCs. Our laboratory has shown that dehydration regulates the expression of the NMDA receptor subunits, NR1 and NR2B, in the SON and PVN, suggesting their involvement in osmoregulation. In the present study, we examined the cellular localization of NR2B, one of the glutamate-binding subunits of the NMDA receptor, with an NR2B-specific antibody. Using double-label immunohistochemistry and three different detection methods with metallic, peroxidase, and fluorescence markers, it was found that both vasopressin and oxytocin-producing MNC populations synthesize NR2B. The incidence of NR2B colocalization with vasopressin-neurophysin in the SON and lateral magnocellular PVN (PVL) was 0.95 and 0.91, respectively. For oxytocin-neurophysin, the corresponding values were 0.97 and 0.95, respectively. Furthermore, the extent of colocalization in MNCs of the SON, PVL, retrochiasmatic SON, and accessory neurosecretory nuclei was similar. Astrocytes associated with the SON, and identified with antibodies targeting glial fibrillary acidic protein (GFAP) or vimentin, were not colabeled with NR2B. Our results demonstrate that NR2B protein is expressed by almost all MNCs and that it is equally prevalent in vasopressinergic and oxytocinergic populations of various magnocellular neuroendocrine nuclei supporting a role of NMDA receptors in MNC-mediated neurosecretory processes. Although NR2B may form part of functional NMDA receptors on MNCs, it is probably not present on astrocytes associated with nearby MNCs.
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Affiliation(s)
- M C Currás-Collazo
- Department of Neuroscience, University of California at Riverside, Riverside, California 92521, USA.
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32
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Hussy N, Deleuze C, Desarménien MG, Moos FC. Osmotic regulation of neuronal activity: a new role for taurine and glial cells in a hypothalamic neuroendocrine structure. Prog Neurobiol 2000; 62:113-34. [PMID: 10828380 DOI: 10.1016/s0301-0082(99)00071-4] [Citation(s) in RCA: 158] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Maintenance of osmotic pressure is a primary regulatory process essential for normal cell function. The osmolarity of extracellular fluids is regulated by modifying the intake and excretion of salts and water. A major component of this regulatory process is the neuroendocrine hypothalamo-neurohypophysial system, which consists of neurons located in the paraventricular and supraoptic nuclei. These neurons synthesize the neurohormones vasopressin and oxytocin and release them in the blood circulation. We here review the mechanisms responsible for the osmoregulation of the activity of these neurons. Notably, the osmosensitivity of the supraoptic nucleus is described including the recent data that suggests an important participation of taurine in the transmission of the osmotic information. Taurine is an amino acid mainly known for its involvement in cell volume regulation, as it is one of the major inorganic osmolytes used by cells to compensate for changes in extracellular osmolarity. In the supraoptic nucleus, taurine is highly concentrated in astrocytes, and released in an osmodependent manner through volume-sensitive anion channels. Via its agonist action on neuronal glycine receptors, taurine is likely to contribute to the inhibition of neuronal activity induced by hypotonic stimuli. This inhibitory influence would complement the intrinsic osmosensitivity of supraoptic neurons, mediated by excitatory mechanoreceptors activated under hypertonic conditions. These observations extend the role of taurine from the regulation of cell volume to that of the whole body fluid balance. They also point to a new role of supraoptic glial cells as active components in a neuroendocrine regulatory loop.
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Affiliation(s)
- N Hussy
- Biologie des Neurones Endocrines CNRS-UPR 9055 CCIPE, 141 rue de la Cardonille 34094 Cedex 5, Montpellier, France.
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33
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Izawa S, Inoue K, Adachi A, Funahashi M. Activity of neurons in the nucleus of the solitary tract of rats: effect of osmotic and mechanical stimuli. Neurosci Lett 2000; 288:33-6. [PMID: 10869809 DOI: 10.1016/s0304-3940(00)01193-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Patch-clamp recordings were used to examine the osmosensitivity and mechanosensitivity of neurons in the caudal part of the nucleus tractus solitarius in coronal slices from rat brain. Firing rates and membrane potentials were measured as slices were exposed to perfusate which varied in its osmolality and/or sodium concentration. In all cells tested, the responses to change in the sodium concentration of perfusate were duplicated by osmolality changes of sucrose or mannitol. When nucleus tractus solitarius cells were tested with changes in pressure applied via the pipette, responses to positive or negative pressure paralleled their responses to osmotic stimulation. We suggest that a mechanosensitive receptor exists on osmosensitive neurons within the nucleus tractus solitarius, and this receptor may be responsible for changes in the firing rate and membrane potential which occur in the nucleus tractus solitarius neurons.
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Affiliation(s)
- S Izawa
- Department of Operative Dentistry, Okayama University Dental School, Japan
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34
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Currás-Collazo MC, Dao J. Osmotic activation of the hypothalamo-neurohypophysial system reversibly downregulates the NMDA receptor subunit, NR2B, in the supraoptic nucleus of the hypothalamus. BRAIN RESEARCH. MOLECULAR BRAIN RESEARCH 1999; 70:187-96. [PMID: 10407167 DOI: 10.1016/s0169-328x(99)00129-1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
NMDA receptor activation produces a characteristic pattern of neuronal firing in magnocellular neuroendocrine cells (MNCs) of the supraoptic nucleus of the hypothalamus (SON) which has been associated with greater hormone release in vivo and in vitro. In addition, i.c.v. administered NMDA receptor blockers suppress the dehydration-induced rise in plasma vasopressin and drinking. To investigate the role of NMDA receptor subunits in the neuroendocrine functions of the magnocellular neuroendocrine cells of the hypothalamus, we examined the effects of osmotic stimulation on the protein expression of the NMDA receptor subunits, NR1 and NR2B, important in binding glycine and glutamate, respectively. Homogenates of SON, paraventricular nucleus of the hypothalamus (PVN), cortex and lateral hypothalamus from control rats and rats given 2% saline water to drink for 4-10 days were subjected to SDS-PAGE and Western blot analysis. This saline water drinking regimen produced a significant rise in plasma osmolality levels. NR1 and NR2B immunoreactivity was detected in SON, PVN, lateral hypothalamus and cortex but not in liver homogenates using subunit-specific polyclonal antibodies and quantified using computer-assisted densitometry. Mean NR2B immunoreactivity was significantly lower in SON (29%) and PVN homogenates (23%) from saline-treated rats than in those from control rats. In addition, the effect of dehydration on NR2B was regionally specific since no significant changes in NR2B expression were observed in homogenates of cortex and lateral hypothalamus. Rehydration allowed recovery of plasma osmolality as well as NR2B protein levels in the SON. These results suggest that changes in NMDA receptor subunit expression contribute to the plasticity manifested by in magnocellular neuroendocrine cells in response to osmotic activation of the hypothalamo-neurohypophysial system. In addition, our results indicate that NMDA receptors on SON and PVN MNCs may contribute to neuroendocrinological functions associated with body fluid homeostasis.
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Affiliation(s)
- M C Currás-Collazo
- Department of Neuroscience, University of California at Riverside, Riverside, CA 92521, USA.
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35
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Rocha MJ, Beltz TG, Dornelles RC, Johnson AK, Franci CR. Anteroventral third ventricle (AV3V) lesions alter c-fos expression induced by salt loading. Brain Res 1999; 829:197-200. [PMID: 10350549 DOI: 10.1016/s0006-8993(99)01366-9] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Lesion of the anteroventral third-ventricle region (AV3VX) reduced saline consumption. Salt loading in AV3VX rats resulted in reduced but not completely abolished c-fos expression in the supraoptic and paraventricular nuclei. Intrinsic osmosensitivity of the magnocellular neurons, or input from other brain areas, such as the subfornical and median preoptic nuclei, may account for this residual c-fos expression. These regions showed c-fos expression following salt loading.
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Affiliation(s)
- M J Rocha
- Departamento de Fisiologia, Faculdade de Medicina de Ribeirão Preto, Universidade de São Paulo, Av. Bandeirantes, 3900, CEP 14049-900, Ribeirão Preto, SP, Brazil.
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36
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Leng G, Brown CH, Russell JA. Physiological pathways regulating the activity of magnocellular neurosecretory cells. Prog Neurobiol 1999; 57:625-55. [PMID: 10221785 DOI: 10.1016/s0301-0082(98)00072-0] [Citation(s) in RCA: 230] [Impact Index Per Article: 9.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
Magnocellular oxytocin and vasopressin cells are among the most extensively studied neurons in the brain; their large size and high synthetic capacity, their discrete, homogeneous distribution and the anatomical separation of their terminals from their cell bodies, and the ability to determine their neuronal output readily by measurements of hormone concentration in the plasma, combine to make these systems amenable to a wide range of fundamental investigations. While vasopressin cells have intrinsic burst-generating properties, oxytocin cells are organized within local pattern-generating networks. In this review we consider the rôle played by particular afferent pathways in the regulation of the activity of oxytocin and vasopressin cells. For both cell types, the effects of changes in the activity of synaptic input can be complex.
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Affiliation(s)
- G Leng
- Department of Physiology, University Medical School, Edinburgh, UK.
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37
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Bourque CW. Osmoregulation of vasopressin neurons: a synergy of intrinsic and synaptic processes. PROGRESS IN BRAIN RESEARCH 1999; 119:59-76. [PMID: 10074781 DOI: 10.1016/s0079-6123(08)61562-9] [Citation(s) in RCA: 80] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The release of vasopressin into the general circulation varies as a function of plasma osmolality and therefore plays a major role in systemic osmoregulation. In vivo, the secretion of this hormone in the neurohypophysis is primarily determined by the rate of action potential discharge of the magnocellular neurosecretory cells (MNCs) in the hypothalamus. Experiments done over the past 20 years have clarified much of the neurophysiological basis underlying this important osmoregulatory reflex. As discussed here, recent findings indicate that the regulation of the firing rate of MNCs during changes in systemic osmolality involves the concerted modulation of mechanosensitive ion channels in MNCs, as well as excitatory glutamatergic inputs derived from forebrain regions such as the organum vasculosum of the lamina terminalis.
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Affiliation(s)
- C W Bourque
- Centre for Research in Neuroscience, Montreal General Hospital, QC, Canada
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38
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Bains JS, Ferguson AV. Activation of N-methyl-D-aspartate receptors evokes calcium spikes in the dendrites of rat hypothalamic paraventricular nucleus neurons. Neuroscience 1999; 90:885-91. [PMID: 10218788 DOI: 10.1016/s0306-4522(98)00525-9] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
Abstract
Activation of dendritic voltage-dependent calcium (Ca2+) conductances in neuroendocrine cells of the hypothalamus may underlie previously documented Ca2+ spikes in these cells. The present study, in which whole-cell recordings were obtained from paraventricular nucleus neurons in a hypothalamic slice preparation, addresses this issue by directly activating dendritic N-methyl-D-aspartate receptors in the presence of tetrodotoxin. Application of tetrodotoxin abolished spontaneous action potentials in all paraventricular nucleus neurons tested (n = 27). Following tetrodotoxin, spikes were evoked by depolarizing current pulses, in an all-or-none fashion in the majority of cells (n = 20). Removal of extracellular Ca2+ (n = 6) or addition of 500 microM CdCl2 (n = 4) abolished the spikes in response to pulses. Repetitive spiking activity (in tetrodotoxin) was also observed following N-methyl-D-aspartate agonist application in 75% of the cells tested (n = 15). The spikes, underscored by a slow membrane depolarization, were abolished by the administration of CdCl2 (n = 4). N-Methyl-D-aspartate agonist elicited a slow inward current in cells voltage-clamped at -60 mV (n = 5). Additionally, larger amplitude, transient inward currents were observed near the onset of the response. The activation threshold to elicit spikes following N-methyl-D-aspartate agonist application was significantly more negative (-54.6+/-3.6 mV) than the potential at which spikes were initiated as a result of depolarizing current injection (-32.3+/-1.8 mV; Student's t-test: P < 0.0001). In contrast to this, Na+ spikes in control solution had an invariable threshold (-49.6+/-0.7 mV vs -51.5+/-1.2 mV; P > 0.05), regardless of the stimulus used to initiate the spikes. These observations suggest that direct activation of N-methyl-D-aspartate receptors located on the dendrites of paraventricular nucleus neurons triggers Ca2+ spikes. Although the precise function of these spikes is unclear, previous data reporting dendritic neuropeptide release in the paraventricular nucleus raise the possibility that dendritically initiated spikes may serve as a local signal to trigger such release.
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Affiliation(s)
- J S Bains
- Department of Physiology, Queen's University, Kingston, Ontario, Canada
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39
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Currás MC, Rack PG, Meeker RB. Channel properties of NMDA receptors on magnocellular neuroendocrine cells cultured from the rat supraoptic nucleus. Brain Res 1998; 789:181-93. [PMID: 9573359 DOI: 10.1016/s0006-8993(97)01409-1] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Application of N-methyl-D-aspartate (NMDA) to the supraoptic nucleus of the hypothalamus (SON) generates clustered firing that may be important in hormone release. However, synaptically evoked EPSPs recorded from SON neurons exhibit varying contributions from NMDA receptors. We used the high resolution of single-channel recording to examine the receptor and ion channel properties of NMDA receptors expressed by SON neurons in 'punch' culture. Biocytin introduced into individual neurons during patch clamp recording revealed large (32.1+/-3.3 micron), oblong somas and bipolar extensions typical of magnocellular neuroendocrine cells (MNCs). Rapid application of NMDA (100-300 microM) in the presence of 10 microM glycine to outside-out macropatches resulted in openings with an average conductance of 46. 9 pS and reversal potential of +3.9 mV. Increasing glycine from 0.03 to 30 microM increased the apparent frequency, duration and occurrence of overlapping NMDA-elicited openings. NMDA responses were inhibited by Mg2+ in a voltage-dependent manner and by the NMDA-site antagonist, D-(-)-2-amino-5-phosphonovaleric acid (D-APV). Application of saturating NMDA or glycine alone with the glycine-site antagonist, 5,7-dichlorokynurenate (DCK) or with D-APV, respectively, did not result in agonist-induced openings. NR1 immunoreactivity was observed in large neurons (>25 micron) with MNC-like morphology. These single-channel and immunocytochemical data confirm the presence of functional NR1-containing NMDA receptors in MNCs.
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Affiliation(s)
- M C Currás
- Department of Neuroscience, University of California at Riverside, Riverside, CA 92521, USA.
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40
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Inenaga K, Honda E, Hirakawa T, Nakamura S, Yamashita H. Glutamatergic synaptic inputs to mouse supraoptic neurons in calcium-free medium in vitro. J Neuroendocrinol 1998; 10:1-7. [PMID: 9510053 DOI: 10.1046/j.1365-2826.1998.00662.x] [Citation(s) in RCA: 23] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
The effects of Ca2+-free perfusion medium on excitatory postsynaptic currents (EPSCs) and potentials (EPSPs) were studied by whole-cell recordings from neurons of the supraoptic nucleus (SON) in trimmed slice preparations of mouse hypothalamus. EPSCs evoked with either focal stimulation to the SON or perfusion of slices with high K+-medium, spontaneous EPSCs (sEPSCs) and miniature EPSCs (mEPSCs) recorded from neurons of the SON were blocked by the glutamate receptor antagonist kynurenic acid (1 mM). While EPSCs evoked by focal stimulation were abolished in the presence of Ca2+-free perfusion medium; sEPSCs and mEPSCs remained. Neither the frequency nor the amplitude of the sEPSCs and mEPSCs significantly changed during the application of Ca2+-free perfusion medium. Perfusion of slices with high K+-medium increased the mEPSC frequency compared with that recorded in normal Ca2+-containing perfusion medium. In contrast, mEPSC frequency did not change during perfusion with Ca2+-free high K+-medium. In current-clamp mode sEPSPs were observed during the perfusion with Ca2+-free medium. Some sEPSPs recorded in Ca2+-free medium were sufficiently large to evoke action potentials. These results imply that spontaneous glutamatergic synaptic inputs to the hypothalamic neurosecretory cells exist in Ca2+-free perfusion medium. Thus, the present study suggests that Ca2+-free medium does not always block the synaptic transmission in hypothalamic slice preparations.
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Affiliation(s)
- K Inenaga
- Department of Physiology, Kyushu Dental College, Kitakyushu, Japan
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41
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Khalilov I, Esclapez M, Medina I, Aggoun D, Lamsa K, Leinekugel X, Khazipov R, Ben-Ari Y. A novel in vitro preparation: the intact hippocampal formation. Neuron 1997; 19:743-9. [PMID: 9354321 DOI: 10.1016/s0896-6273(00)80956-3] [Citation(s) in RCA: 118] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The intact hippocampal formation (IHF) of neonatal or young rats can be kept alive for an extended period in a fully submerged chamber with excellent morphological preservation. Field or patch-clamp recordings, intracellular Ca2+ measurements, and 3-D reconstruction of biocytin-filled neurons can be performed routinely. The generation and propagation of network-driven activities can be studied within the IHF or between connected intact structures such as the septum and the hippocampus or two hippocampi, and the use of a dual chamber enables the application of drugs separately to each structure. This preparation will be useful to study intact neuronal networks in the developing hippocampus in vitro.
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Affiliation(s)
- I Khalilov
- INSERM U 29 Hôpital de Port Royal, Paris, France
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42
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Decavel C, Curras MC. Increased expression of the N-methyl-D-aspartate receptor subunit, NR1, in immunohistochemically identified magnocellular hypothalamic neurons during dehydration. Neuroscience 1997; 78:191-202. [PMID: 9135100 DOI: 10.1016/s0306-4522(96)00544-1] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
N-Methyl-D-aspartate receptors are thought to be involved in synaptic signaling within the hypothalamo-neurohypophysial system, but the extent and nature of their involvement has not been determined. In this study, in the rat, we evaluated the effect of hyperosmotic stimulation on the N-methyl-D-aspartate receptor subunit, NR1, which confers function to N-methyl-D-aspartate receptor heteromers. Co-localization of immunoreactivity for NR1 and vasopressin- or oxytocin-associated neurophysin in magnocellular neurons of the supraoptic and paraventricular hypothalamic nuclei was accomplished using double-label immunohistochemistry. Our results show that vasopressin- and oxytocin-neurophysin-positive populations contained detectable levels of NR1 labeling. Using NR1 labeling as a measure of N-methyl-D-aspartate receptor density, we examined the effect of dehydration in these nuclei. Using computer-assisted densitometry, we found significantly greater NR1 labeling densities in the magnocellular regions of both the supraoptic and paraventricular nuclei of saline-treated rats than of control rats. This increase was not due to methodological factors, since no changes in NR1 labeling density were found in a nearby nucleus, the nucleus reuniens. Western blot analysis showed similar selective increases in NR1 labeling in homogenates from the supraoptic nucleus, paraventricular nucleus and in some cases from the anterior hypothalamic area. In both immunohistochemical and western blotting experiments we did not observe a dehydration-induced increase in NR1 in other brain areas examined. Our results showing an up-regulation of NR1-containing N-methyl-D-aspartate receptors during dehydration suggest that these receptors are involved in the regulation of body water and may represent an adaptive physiological response following activation of the hypothalamo-neurohypophysial axis. In addition, these results suggest that the functional expression of N-methyl-D-aspartate receptors is dynamic and may be modified according to the physiological state of the animal.
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Affiliation(s)
- C Decavel
- Department of Neuroscience, University of California at Riverside, 92521, U.S.A
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43
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Oliet SH, Bourque CW. Gadolinium uncouples mechanical detection and osmoreceptor potential in supraoptic neurons. Neuron 1996; 16:175-81. [PMID: 8562082 DOI: 10.1016/s0896-6273(00)80034-3] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023]
Abstract
Stretch-sensitive ion channels are ubiquitous, yet evidence of their role in mechanotransduction remains scarce. The presence of stretch-inactivated cation channels in supraoptic neurons is consistent with the osmoreceptor potentials regulating vasopressin release. However, whether osmosensitivity depends on mechanical gating and ion flux through stretch-inactivated channels is unknown. Here we report that changes in channel open probability associated either with modification of pipette pressure or with external osmolality selectivity result from variations in closed time. While channel mechanosensitivity and osmotically evoked changes in cell volume are not affected by gadolinium, similar concentrations of the lanthanide inhibit cation permeation through the single channels and macroscopic osmoreceptor potentials. Mechanotransduction through stretch-inactivated channels is therefore necessary for osmoreception in supraoptic neurons.
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Affiliation(s)
- S H Oliet
- Centre for Research in Neuroscience, Montreal General Hospital, McGill University, Quebec, Canada
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44
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Kazakov VN, Kravtsov PY, Kuznetsov I�, Tereshchenko AV. Responses of neurons of the preoptic region to an increase in systemic blood pressure in cats. NEUROPHYSIOLOGY+ 1995. [DOI: 10.1007/bf01053087] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/25/2022]
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45
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Munro G, Ludwig M, Landgraf R, Russell JA. Opioids influence neurohypophysial but not central oxytocin release following direct hyperosmotic stimulation of the supraoptic nucleus in urethane-anaesthetised rats. Neuropeptides 1994; 27:121-7. [PMID: 7991066 DOI: 10.1016/0143-4179(94)90052-3] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
Microdialysis was used to apply an osmotic stimulus (0.5 M NaCl-aCSF) into both supraoptic nuclei (SON) to investigate the role of endogenous opioid peptides in the control of both central and peripheral oxytocin release in response to this stimulus. There were no differences in central peptide release during direct hyperosmotic stimulation between groups of rats given either vehicle, morphine (5 mg/kg) or naloxone (5 mg/kg) intravenously. Naloxone potentiated oxytocin release into blood; this suggests that endogenous opioid peptides at the level of the neurohypophysis, but not in the SON are important modulators of oxytocin release to this stimulus. However morphine blocked oxytocin release into blood indicative of a central inhibitory action on the firing rate of oxytocin neurones, contrasted with insensitivity to morphine of oxytocin secretion from the dendrites stimulated directly by hyperosmolarity.
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Affiliation(s)
- G Munro
- Department of Physiology, University Medical School, Edinburgh, UK
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46
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Firing activity of preoptic and supraoptic neurons upon mild alterations in osmo- and glucohomeostasis. NEUROPHYSIOLOGY+ 1994. [DOI: 10.1007/bf01054510] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/25/2022]
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47
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Abstract
We describe here an isolated and perfused in vitro adult guinea-pig whole brain preparation which is an extension of the previously described in vitro brainstem-cerebellum preparation. Viability was tested by the analysis of trans-synaptic responses along the visual pathways following the electrical stimulation of the optic nerve or the optic radiations. The evoked field potentials were recorded in the dorsal lateral geniculate, the superior colliculus and the visual cortex. The distribution of extracellular currents was studied using current source density analysis, in order to determine the amplitude, time course and spatial organization of the synaptic activity at these sites. The study indicates that field potentials were very similar to those described in vivo. These data demonstrate the survival of a complex adult sensory system in vitro and suggest that this preparation can be used for the analysis of multisynaptic circuits in the mammalian brain.
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Affiliation(s)
- M Mühlethaler
- Laboratoire de Psychophysiologie, Département de Physiologie, CMU, Genève, Switzerland
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48
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Smith DW, Day TA. Neurochemical identification of fos-positive neurons using two-colour immunoperoxidase staining. J Neurosci Methods 1993; 47:73-83. [PMID: 8100600 DOI: 10.1016/0165-0270(93)90023-k] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/28/2023]
Abstract
The discovery of immediate early genes (IEG) has provided neuroscientists with a new functional mapping technique. Labelling of neural tissue for the protein product of IEG provides an activity map with single-cell resolution. When combined with labelling for the chemical identity of the neuron, this provides a powerful tool for the investigation of specific cell populations along a neuraxis. Here we describe in detail a method which allows simultaneous bright-field visualization of neurochemically identified cells displaying increased IEG expression. This technique is evaluated in tissue from rats subjected to stimuli known to induce the expression of the IEG c-fos in various medullary catecholaminergic and hypothalamic neurosecretory cell groups. A 2-colour immunoperoxidase technique was used to visualize Fos, the nuclear protein product of c-fos, and the cytoplasmic antigens tyrosine hydroxylase (TH), phenylethanolamine N-methyl transferase (PNMT), oxytocin (OT) and vasopressin (VP). This involved simultaneous application of primary antibodies raised in different species followed by sequential application of appropriate biotinylated secondary antibodies and the avidin-biotin-peroxidase technique. Fos was visualized with nickel-intensified diaminobenzidine (Ni-DAB) in the first sequence while TH, PNMT, OT or VP were visualized with DAB alone, resulting in readily distinguishable black and amber reaction products, respectively. This dual immunoperoxidase technique is time saving compared to techniques using sequential application of primary antibodies and avoids the disadvantages associated with fluorescence techniques.
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Affiliation(s)
- D W Smith
- Department of Physiology and Pharmacology, University of Queensland, Australia
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49
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Erickson KR, Ronnekleiv OK, Kelly MJ. Electrophysiology of guinea-pig supraoptic neurones: role of a hyperpolarization-activated cation current in phasic firing. J Physiol 1993; 460:407-25. [PMID: 8487202 PMCID: PMC1175220 DOI: 10.1113/jphysiol.1993.sp019478] [Citation(s) in RCA: 54] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/31/2023] Open
Abstract
1. Immunocytochemically identified magnocellular neurosecretory cells (MNCs) in the guinea-pig supraoptic nucleus (SON) were studied using the in vitro intracellular recording technique. Cells were identified as containing arginine vasopressin (AVP) or oxytocin (OT) following recordings made with biocytin-filled electrodes. Both AVP and OT MNCs demonstrated a fusiform or pyramidal shape (15-20 microns by 26-39 microns), with two to three processes. There were no significant differences in the proportion of AVP and OT cells in the retrochiasmatic (caudal) versus the rostral slices. 2. No significant differences in passive membrane properties were observed between AVP and OT cells, except that AVP cells exhibited a significantly broader action potential width (1.51 +/- 0.1 ms, n = 11) than did OT cells (1.01 +/- 0.08 ms, n = 7). 3. Firing patterns were recorded for 100 MNCs, 41% of which fired in a phasic manner (repeated clustering of action potentials into bursts). Of the seventy-seven cells which were immunocytochemically identified, only AVP-containing MNCs displayed phasic firing. Phasic firing occurred only in MNCs demonstrating a depolarizing potential which followed hyperpolarizing after-potentials (HAPs). The presence of the depolarizing potential was not always associated with phasic firing, however, as both OT cells and non-phasic AVP cells sometimes exhibited a depolarizing potential. 4. In 160 MNCs examined for the presence of the time-dependent inward rectification (TDR in current clamp, or Ih in voltage clamp), a significant difference in the proportion of cells expressing the Ih was observed in the two cell types. The Ih was expressed in forty-five of fifty-four AVP MNCs (83%) and in six of fifteen OT MNCs (40%). No significant association was found with firing pattern. 5. The Ih exhibited properties similar to those found in other CNS and peripheral tissues. It appeared on steps to potentials more hyperpolarized than -65 mV. It was augmented by raising the extracellular potassium concentration, blocked by 2 mM CsCl, and insensitive to 100-500 microM BaCl2. Activation followed a single exponential, and the time constant of activation was voltage dependent. 6. The adenylate cyclase activator forskolin increased the Ih and shifted its activation curve to more depolarized levels. In cells recorded for several hours, the Ih varied in amplitude, suggesting intrinsic modulation, possibly by intracellular second messenger systems. The Ih in guinea-pig SON MNCs appears to serve an excitatory role, bringing cells closer to firing threshold.
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Affiliation(s)
- K R Erickson
- Department of Physiology, Oregon Health Sciences University, Portland 97201
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50
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Hu B, Bourque CW. NMDA receptor-mediated rhythmic bursting activity in rat supraoptic nucleus neurones in vitro. J Physiol 1992; 458:667-87. [PMID: 1302282 PMCID: PMC1175178 DOI: 10.1113/jphysiol.1992.sp019440] [Citation(s) in RCA: 120] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022] Open
Abstract
1. Intracellular recordings were obtained from 112 supraoptic nucleus magnocellular neurosecretory cells (MNCs) in superfused explants of rat hypothalamus maintained in vitro. The effects of glutamate receptor agonists and antagonists were examined at 32-34 degrees C. 2. In control solutions, spontaneously active (> 5 Hz) phasic or continuous neurones showed interspike interval distributions slightly skewed toward short intervals, but did not feature pauses in the 0.4-2 s range. Current injection to alter the rate of cell discharge shifted the histograms according to the mean firing rate, but failed to induce intermittent pauses in the 0.4-2 s range. 3. Application of N-methyl-D-aspartate (NMDA) induced a mode of firing in which bimodal interspike interval distributions reflected a high incidence of clusters of short interspike intervals (0.5-1.5 s) recurring every 1-3 s. In contrast, firing evoked by application of D,L-alpha-amino-3-hydroxy-5-methyl-4-isoxalone propionic acid (AMPA) was not associated with a clustering of impulse discharge. 4. The putative endogenous excitatory amino acid transmitters L-glutamate, L-aspartate and quinolinate all mimicked the effects of NMDA. Clustered spiking responses to these agents were reversibly blocked by D,L-2-amino-5-phosphono-valerate (APV), but not by 6-cyano-7-nitroquinoxaline-2,3-dione (CNQX). In contrast, the non-NMDA receptor ligands kainate and quisqualate caused CNQX-sensitive increases in firing rate, but these responses were not associated with the appearance of clustered activity. 5. When applied to cells showing negative resting potentials (< -70 mV), or to neurones hyperpolarized by current injection, responses to NMDA consisted of rhythmic (approximately 1 Hz) voltage oscillations associated with bursts of spike discharge. In the presence of TTX, NMDA could induce subthreshold voltage oscillations in the absence of action potentials. 6. Application of a voltage clamp to potentials between -75 and -55 mV during rhythmic bursting responses failed to reveal any rhythmic oscillation of the membrane current. In all cases, rhythmic bursting activity resumed upon returning to the current-clamp mode. 7. Rhythmic bursting responses to NMDA application were abolished in Mg(2+)-free solutions, suggesting that the voltage dependence of NMDA channels served to promote regenerative voltage changes throughout the cycle. The NMDA-induced current itself, however, did not appear to decrease with time, suggesting that a distinct, outward current, was necessary to initiate the repolarizing phase of each cycle.(ABSTRACT TRUNCATED AT 400 WORDS)
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Affiliation(s)
- B Hu
- Center for Research in Neuroscience, Montreal General Hospital, P.Q., Canada
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