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Moiseev KY, Spirichev AA, Vishnyakova PA, Pankrasheva LG, Masliukov PM. Changes of discharge properties of neurons from dorsomedial hypothalamic nuclei during aging in rats. Neurosci Lett 2021; 762:136168. [PMID: 34389479 DOI: 10.1016/j.neulet.2021.136168] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/04/2021] [Revised: 07/28/2021] [Accepted: 08/05/2021] [Indexed: 10/20/2022]
Abstract
The hypothalamus is a vital brain center that is participated in the integration of the endocrine and nervous systems and control of the homeostasis and aging. Spontaneous firing activity from single neurons of the dorsomedial hypothalamic nucleus (DMN) was studied extracellularly in vivo in urethane-anaesthetized rats. The discharge patterns of the majority of DMN neurons were irregular, including periods of relatively stable activity interrupted by pauses. Based on the features of interval interspike histogram, we have selected neurons with an irregular arrhythmic activity (50% in young, 46% in adult and 44% in aged rats), with a constant rhythmic activity (18% of neurons in young, 19% in adult and 23% in aged rats), with a wide interspike interval distribution (22% in young, 26% in adult and 25% in aged rats) and cells with bursts of two or three spikes (10% in young, 9% in adult and 8% in aged rats). The firing rate of DMN neurons was 2.5 ± 0.12 Hz in young and 2.4 ± 0.21 Hz in adult rats and significantly decreased to 1.8 ± 0.17 Hz in aged rats.
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Spike Activity in the Ventromedial Nucleus of Rat Hypothalamus during Aging. Bull Exp Biol Med 2021; 171:251-253. [PMID: 34173105 DOI: 10.1007/s10517-021-05205-4] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/22/2020] [Indexed: 10/21/2022]
Abstract
Spike activity of neurons in the ventromedial nucleus (VMN) of the hypothalamus in adult (6-8 months) and aged (2 years) male rats was studied by the in vivo extracellular method using stereotaxic insertion of microelectrodes. In all animals, firing frequency of most VMN neurons increased in response to glucose administration. However, in aged rats, the mean baseline and glucose-induced spike frequencies of VMN neurons were lower than in adult animals. These results support the hypothesis that aging is associated with a decrease in the functional activity of hypothalamic neurons.
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Silveira MA, Burger LL, DeFazio RA, Wagenmaker ER, Moenter SM. GnRH Neuron Activity and Pituitary Response in Estradiol-Induced vs Proestrous Luteinizing Hormone Surges in Female Mice. Endocrinology 2017; 158:356-366. [PMID: 27911605 PMCID: PMC5413083 DOI: 10.1210/en.2016-1771] [Citation(s) in RCA: 25] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 10/17/2016] [Accepted: 12/01/2016] [Indexed: 12/18/2022]
Abstract
During the female reproductive cycle, estradiol exerts negative and positive feedback at both the central level to alter gonadotropin-releasing hormone (GnRH) release and at the pituitary to affect response to GnRH. Many studies of the neurobiologic mechanisms underlying estradiol feedback have been done on ovariectomized, estradiol-replaced (OVX+E) mice. In this model, GnRH neuron activity depends on estradiol and time of day, increasing in estradiol-treated mice in the late afternoon, coincident with a daily luteinizing hormone (LH) surge. Amplitude of this surge appears lower than in proestrous mice, perhaps because other ovarian factors are not replaced. We hypothesized GnRH neuron activity is greater during the proestrous-preovulatory surge than the estradiol-induced surge. GnRH neuron activity was monitored by extracellular recordings from fluorescently tagged GnRH neurons in brain slices in the late afternoon from diestrous, proestrous, and OVX+E mice. Mean GnRH neuron firing rate was low on diestrus; firing rate was similarly increased in proestrous and OVX+E mice. Bursts of action potentials have been associated with hormone release in neuroendocrine systems. Examination of the patterning of action potentials revealed a shift toward longer burst duration in proestrous mice, whereas intervals between spikes were shorter in OVX+E mice. LH response to an early afternoon injection of GnRH was greater in proestrous than diestrous or OVX+E mice. These observations suggest the lower LH surge amplitude observed in the OVX+E model is likely not attributable to altered mean GnRH neuron activity, but because of reduced pituitary sensitivity, subtle shifts in action potential pattern, and/or excitation-secretion coupling in GnRH neurons.
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Affiliation(s)
- Marina A Silveira
- Department of Anatomy, Institute of Biomedical Sciences, University of São Paulo, São Paulo, SP, Brazil
- Departments of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan
| | - Laura L Burger
- Departments of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan
| | - R Anthony DeFazio
- Departments of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan
| | - Elizabeth R Wagenmaker
- Departments of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan
| | - Suzanne M Moenter
- Departments of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan
- Internal Medicine, University of Michigan, Ann Arbor, Michigan
- Obstetrics and Gynecology, University of Michigan, Ann Arbor, Michigan
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Nunemaker CS, Satin LS. Episodic hormone secretion: a comparison of the basis of pulsatile secretion of insulin and GnRH. Endocrine 2014; 47:49-63. [PMID: 24610206 PMCID: PMC4382805 DOI: 10.1007/s12020-014-0212-3] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/04/2014] [Accepted: 02/13/2014] [Indexed: 01/01/2023]
Abstract
Rhythms govern many endocrine functions. Examples of such rhythmic systems include the insulin-secreting pancreatic beta-cell, which regulates blood glucose, and the gonadotropin-releasing hormone (GnRH) neuron, which governs reproductive function. Although serving very different functions within the body, these cell types share many important features. Both GnRH neurons and beta-cells, for instance, are hypothesized to generate at least two rhythms endogenously: (1) a burst firing electrical rhythm and (2) a slower rhythm involving metabolic or other intracellular processes. This review discusses the importance of hormone rhythms to both physiology and disease and compares and contrasts the rhythms generated by each system.
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Affiliation(s)
- Craig S. Nunemaker
- Division of Endocrinology and Metabolism, Department of, Medicine, University of Virginia, P.O. Box 801413, Charlottesville, VA 22901, USA,
| | - Leslie S. Satin
- Pharmacology Department, University of Michigan Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
- Brehm Diabetes Research Center, University of Michigan, Medical School, 5128 Brehm Tower, Ann Arbor, MI 48105, USA
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Van Dijck G, Van Hulle MM, Heiney SA, Blazquez PM, Meng H, Angelaki DE, Arenz A, Margrie TW, Mostofi A, Edgley S, Bengtsson F, Ekerot CF, Jörntell H, Dalley JW, Holtzman T. Probabilistic identification of cerebellar cortical neurones across species. PLoS One 2013; 8:e57669. [PMID: 23469215 PMCID: PMC3587648 DOI: 10.1371/journal.pone.0057669] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2012] [Accepted: 01/24/2013] [Indexed: 02/02/2023] Open
Abstract
Despite our fine-grain anatomical knowledge of the cerebellar cortex, electrophysiological studies of circuit information processing over the last fifty years have been hampered by the difficulty of reliably assigning signals to identified cell types. We approached this problem by assessing the spontaneous activity signatures of identified cerebellar cortical neurones. A range of statistics describing firing frequency and irregularity were then used, individually and in combination, to build Gaussian Process Classifiers (GPC) leading to a probabilistic classification of each neurone type and the computation of equi-probable decision boundaries between cell classes. Firing frequency statistics were useful for separating Purkinje cells from granular layer units, whilst firing irregularity measures proved most useful for distinguishing cells within granular layer cell classes. Considered as single statistics, we achieved classification accuracies of 72.5% and 92.7% for granular layer and molecular layer units respectively. Combining statistics to form twin-variate GPC models substantially improved classification accuracies with the combination of mean spike frequency and log-interval entropy offering classification accuracies of 92.7% and 99.2% for our molecular and granular layer models, respectively. A cross-species comparison was performed, using data drawn from anaesthetised mice and decerebrate cats, where our models offered 80% and 100% classification accuracy. We then used our models to assess non-identified data from awake monkeys and rabbits in order to highlight subsets of neurones with the greatest degree of similarity to identified cell classes. In this way, our GPC-based approach for tentatively identifying neurones from their spontaneous activity signatures, in the absence of an established ground-truth, nonetheless affords the experimenter a statistically robust means of grouping cells with properties matching known cell classes. Our approach therefore may have broad application to a variety of future cerebellar cortical investigations, particularly in awake animals where opportunities for definitive cell identification are limited.
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Affiliation(s)
- Gert Van Dijck
- Computational Neuroscience Research Group, Laboratory for Neuro- en Psychophysiology, K.U. Leuven School of Medicine, Leuven, Belgium
- Department of Psychology, Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge, United Kingdom
| | - Marc M. Van Hulle
- Computational Neuroscience Research Group, Laboratory for Neuro- en Psychophysiology, K.U. Leuven School of Medicine, Leuven, Belgium
| | - Shane A. Heiney
- Department of Otolaryngology, Washington University, St. Louis, Missouri, United States of America
| | - Pablo M. Blazquez
- Department of Otolaryngology, Washington University, St. Louis, Missouri, United States of America
| | - Hui Meng
- Department of Neurobiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Dora E. Angelaki
- Department of Neurobiology, Washington University School of Medicine, St. Louis, Missouri, United States of America
| | - Alexander Arenz
- The Division of Neurophysiology, The National Institute for Medical Research, London, United Kingdom
| | - Troy W. Margrie
- The Division of Neurophysiology, The National Institute for Medical Research, London, United Kingdom
- Department of Neuroscience, Physiology and Pharmacology, University College London, London, United Kingdom
| | - Abteen Mostofi
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom
| | - Steve Edgley
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom
| | - Fredrik Bengtsson
- Department of Experimental Medical Science, Section for Neuroscience, Lund University, Lund, Sweden
| | - Carl-Fredrik Ekerot
- Department of Experimental Medical Science, Section for Neuroscience, Lund University, Lund, Sweden
| | - Henrik Jörntell
- Department of Experimental Medical Science, Section for Neuroscience, Lund University, Lund, Sweden
- NeuroNano Research Center, Lund, Sweden
| | - Jeffrey W. Dalley
- Department of Psychiatry, University of Cambridge, Addenbrooke's Hospital, Cambridge, United Kingdom
- Department of Psychology, Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge, United Kingdom
| | - Tahl Holtzman
- Department of Physiology, Development and Neuroscience, University of Cambridge, Cambridge, United Kingdom
- Department of Psychology, Behavioural and Clinical Neuroscience Institute, University of Cambridge, Cambridge, United Kingdom
- * E-mail:
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Wang Y, Kuehl-Kovarik MC. Estradiol directly attenuates sodium currents and depolarizing afterpotentials in isolated gonadotropin-releasing hormone neurons. Brain Res 2012; 1436:81-91. [PMID: 22209345 DOI: 10.1016/j.brainres.2011.12.013] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/16/2011] [Revised: 11/23/2011] [Accepted: 12/07/2011] [Indexed: 10/14/2022]
Abstract
The gonadotropin-releasing hormone (GnRH) neuron is the pivotal control center in a tightly regulated reproductive axis. The release of GnRH controls estradiol production by the ovary, and estradiol acts at the hypothalamus to regulate GnRH release. However, the mechanisms of estradiol feedback are just beginning to be understood. We have previously shown that estradiol administered to the female mouse modulates sodium currents in fluorescently-labeled GnRH neurons. In the current studies, estradiol (1 nM) was applied directly, for 16-24h, to hypothalamic cultures from young or aged female ovariectomized mice. The direct application of estradiol modulated a tetrodotoxin-sensitive sodium current in isolated GnRH neurons from both young and aged animals. Estradiol, and the specific estrogen receptor-β agonist DPN, decreased current amplitude measured in the morning (AM), but had no effect on afternoon currents. These compounds also decreased the rise and decay slope of the current response, increased the width of the current, and increased action potential width in AM recordings. In addition, estradiol decreased the amplitude of the depolarizing afterpotential (DAP); this effect was not time-of-day dependent. The ER-β agonist DPN did not mimic the effect of estradiol on DAPs, and the modulation of DAPs by estradiol was no longer present in cells from postreproductive animals. These results indicate that estradiol can affect the physiology of GnRH neurons via multiple pathways that are differentially regulated during the transition to reproductive senescence, suggesting that estradiol regulation of GnRH neuronal output is modulated during the aging process.
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Affiliation(s)
- Yong Wang
- Department of Biological Engineering, University of Missouri, Dalton Cardiovascular Research Center, 134 Research Park Drive, Columbia, MO 65211, USA
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Abstract
Reading the spike coding of hypothalamic neurones presents a considerable challenge because they exhibit highly irregular firing patterns. Electrophysiologists working in the motor and sensory systems, in which neurones fire more regularly, have devised satisfactory methods to describe the firing of cells, although the statistical assumptions that underlie the methods do not apply to hypothalamic neurones. Measurement of neural activity is nevertheless vital to characterise the activity of neuroendocrine cells. It has thus become necessary to develop methods suitable for the analysis of the highly irregular spike discharge patterns of both spontaneous and stimulus-evoked firing of hypothalamic neurones. We review techniques used to meet this challenge and demonstrate their considerable capacity to address important physiological questions. We also introduce a novel approach for valid statistical estimation of the information conveyed by the response of a single neurone to a periodic stimulus. The approach demonstrated significant diurnal rhythms of synaptic connectivity between hypothalamic nuclei.
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Affiliation(s)
- G S Bhumbra
- Department of Neuroscience, Physiology, and Pharmacology, University College London, London, UK.
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Moenter SM. Identified GnRH neuron electrophysiology: a decade of study. Brain Res 2010; 1364:10-24. [PMID: 20920482 DOI: 10.1016/j.brainres.2010.09.066] [Citation(s) in RCA: 55] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2010] [Revised: 09/15/2010] [Accepted: 09/17/2010] [Indexed: 12/27/2022]
Abstract
Over the past decade, the existence of transgenic mouse models in which reporter genes are expressed under the control of the gonadotropin-releasing hormone (GnRH) promoter has made possible the electrophysiological study of these cells. Here, we review the intrinsic and synaptic properties of these cells that have been revealed by these approaches, with a particular regard to burst generation. Advances in our understanding of neuromodulation of GnRH neurons and synchronization of this network are also discussed.
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Affiliation(s)
- Suzanne M Moenter
- Department of Molecular and Integrative Physiology, 7725 Med Sci II, 1301 E Catherine St., Ann Arbor, MI 48109-5622, USA.
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Wang Y, Kuehl-Kovarik MC. Flufenamic acid modulates multiple currents in gonadotropin-releasing hormone neurons. Brain Res 2010; 1353:94-105. [PMID: 20655884 DOI: 10.1016/j.brainres.2010.07.047] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2010] [Revised: 07/12/2010] [Accepted: 07/14/2010] [Indexed: 11/26/2022]
Abstract
Reproduction in mammals is dependent upon the appropriate neurosecretion of gonadotropin-releasing hormone (GnRH), yet the endogenous generation of activity underlying GnRH secretion remains poorly understood. We have demonstrated that the depolarizing afterpotential (DAP), which modulates bursting activity, is reduced in isolated GnRH neurons from aged animals. Calcium-activated non-specific cation (CAN) channels contribute to the DAP in other vertebrate neurosecretory cells. We used the CAN channel blocker flufenamic acid (FFA) to examine the contribution of CAN channels to the DAP in GnRH neurons during aging. Recordings were performed on isolated fluorescent GnRH neurons from young, middle-aged and aged female mice. Flufenamic acid inhibited spontaneous activity, but significantly increased the DAP in neurons from young and middle-aged animals. Apamin did not significantly potentiate the DAP, but did reduce the effects of FFA, suggesting that the increased DAP is partially due to blockade of apamin-sensitive SK channels. Flufenamic acid increased the current underlying the DAP (I(ADP)) and decreased the preceding fast outward current (I(OUT)) at all ages. These current responses were not affected by apamin, but TEA evoked similar changes. Thus, a potassium current, likely mediated through BK channels, contributes to the fast AHP and appears to offset the DAP; this current is sensitive to FFA, but insensitive to age. The effect of FFA on the DAP, but not I(ADP), is diminished in aged animals, possibly reflecting an age-related modulation of the apamin-sensitive SK channel. Future studies will examine the expression of SK channels during the aging process in GnRH neurons.
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Affiliation(s)
- Yong Wang
- Department of Biological Engineering, University of Missouri, Dalton Cardiovascular Research Center, Columbia, MO 65211, USA
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Estradiol attenuates multiple tetrodotoxin-sensitive sodium currents in isolated gonadotropin-releasing hormone neurons. Brain Res 2010; 1345:137-45. [PMID: 20580637 DOI: 10.1016/j.brainres.2010.05.031] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/05/2010] [Revised: 05/06/2010] [Accepted: 05/11/2010] [Indexed: 12/19/2022]
Abstract
Secretion from gonadotropin-releasing hormone (GnRH) neurons is necessary for the production of gametes and hormones from the gonads. Subsequently, GnRH release is regulated by steroid feedback. However, the mechanisms by which steroids, specifically estradiol, modulate GnRH secretion are poorly understood. We have previously shown that estradiol administered to the female mouse decreases inward currents in fluorescently labeled GnRH neurons. The purpose of this study was to examine the contribution of sodium currents in the negative feedback action of estradiol. Electrophysiology was performed on GnRH neurons dissociated from young, middle-aged, or old female mice. All mice were ovariectomized; half were estradiol replaced. The amplitude of the sodium current underlying the action potential was significantly decreased in GnRH neurons from young estradiol-treated animals. In addition, in vivo estradiol significantly decreased the transient sodium current amplitude, but prolonged the sodium current inactivation time constant. Estradiol decreased the persistent sodium current amplitude, and induced a significant negative shift in peak current potential. In contrast to results obtained from cells from young reproductive animals, estradiol did not significantly attenuate the sodium current underlying the action potential in cells isolated from middle-aged or old mice. Sodium channels can modulate cell threshold, latency of firing, and action potential characteristics. The reduction of sodium current amplitude by estradiol suggests a negative feedback on GnRH neurons, which could lead to a downregulation of cell excitability and hormone release. The attenuation of estradiol regulation in peripostreproductive and postreproductive animals could lead to dysregulated hormone release with advancing age.
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Age- and sex-specific changes in naloxone-induced luteinizing hormone secretion and Fos expression in gonadotropin-releasing hormone neurons of gonadectomized rats. Neurosci Lett 2010; 471:157-61. [DOI: 10.1016/j.neulet.2010.01.032] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/14/2009] [Revised: 12/29/2009] [Accepted: 01/15/2010] [Indexed: 11/23/2022]
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