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Blanco W, Tabak J, Bertram R. Population bursts in a modular neural network as a mechanism for synchronized activity in KNDy neurons. PLoS Comput Biol 2024; 20:e1011820. [PMID: 39083544 PMCID: PMC11318907 DOI: 10.1371/journal.pcbi.1011820] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2024] [Revised: 08/12/2024] [Accepted: 07/16/2024] [Indexed: 08/02/2024] Open
Abstract
The pulsatile activity of gonadotropin-releasing hormone neurons (GnRH neurons) is a key factor in the regulation of reproductive hormones. This pulsatility is orchestrated by a network of neurons that release the neurotransmitters kisspeptin, neurokinin B, and dynorphin (KNDy neurons), and produce episodic bursts of activity driving the GnRH neurons. We show in this computational study that the features of coordinated KNDy neuron activity can be explained by a neural network in which connectivity among neurons is modular. That is, a network structure consisting of clusters of highly-connected neurons with sparse coupling among the clusters. This modular structure, with distinct parameters for intracluster and intercluster coupling, also yields predictions for the differential effects on synchronization of changes in the coupling strength within clusters versus between clusters.
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Affiliation(s)
- Wilfredo Blanco
- Department of Computer Science, State University of Rio Grande do Norte, Natal, Brazil
- Graduate Program in Bioinformatics, Federal University of Rio Grande do Norte, Natal, Rio Grande do Norte, Brazil
| | - Joel Tabak
- Department of Clinical and Biomedical Sciences, University of Exeter Medical School, Exeter, United Kingdom
| | - Richard Bertram
- Department of Mathematics and Programs in Molecular Biophysics and Neuroscience, Florida State University, Tallahassee, Florida, United States of America
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Chen X, Moenter SM. Gonadal Feedback Alters the Relationship between Action Potentials and Hormone Release in Gonadotropin-Releasing Hormone Neurons in Male Mice. J Neurosci 2023; 43:6717-6730. [PMID: 37536982 PMCID: PMC10552940 DOI: 10.1523/jneurosci.2355-22.2023] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2022] [Revised: 07/14/2023] [Accepted: 07/20/2023] [Indexed: 08/05/2023] Open
Abstract
In vertebrates, the pulsatile release of gonadotropin-releasing hormone (GnRH) from neurons in the hypothalamus triggers secretion of anterior pituitary gonadotropins, which activate steroidogenesis, and steroids in turn exert typically homeostatic negative feedback on GnRH release. Although long-term episodic firing patterns of GnRH neurons in brain slices resemble the pulsatile release of GnRH and LH in vivo, neither the relationship between GnRH neuron firing and release nor whether this relationship is influenced by gonadal feedback are known. We combined fast-scan cyclic voltammetry and patch-clamp to perform simultaneous measurements of neuropeptide release with either spontaneous action potential firing or in response to neuromodulator or action-potential-spike templates in brain slice preparations from male mice. GnRH release increased with higher frequency spontaneous firing to a point; release reached a plateau after which further increases in firing rate did not elicit further increased release. Kisspeptin, a potent GnRH neuron activator via a Gq-coupled signaling pathway, triggered GnRH release before increasing firing rate, whether globally perfused or locally applied. Increasing the number of spikes in an applied burst template increased release; orchidectomized mice had higher sensitivity to the increased action potential number than sham-operated mice. Similarly, Ca2+ currents triggered by these burst templates were increased in GnRH neurons of orchidectomized mice. These results suggest removal of gonadal feedback increases the efficacy of the stimulus-secretion coupling mechanisms, a phenomenon that may extend to other steroid-sensitive regions of the brain.SIGNIFICANCE STATEMENT Pulsatile secretion of GnRH plays a critical role in fertility. The temporal relationship between GnRH neuron action potential firing and GnRH release remains unknown as does whether this relationship is influenced by gonadal feedback. By combining techniques of fast-scan cyclic voltammetry and patch-clamp we, for the first time, monitored GnRH concentration changes during spontaneous and neuromodulator-induced GnRH neuron firing. We also made the novel observation that gonadal factors exert negative feedback on excitation-secretion coupling to reduce release in response to the same stimulus. This has implications for the control of normal fertility, central causes of infertility, and more broadly for the effects of sex steroids in the brain.
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Affiliation(s)
- Xi Chen
- Departments of Molecular and Integrative Physiology
| | - Suzanne M Moenter
- Departments of Molecular and Integrative Physiology
- Internal Medicine
- Obstetrics and Gynecology, University of Michigan, Ann Arbor, Michigan 48109-5622
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3
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SiO 2 nanoparticles modulate the electrical activity of neuroendocrine cells without exerting genomic effects. Sci Rep 2018; 8:2760. [PMID: 29426889 PMCID: PMC5807366 DOI: 10.1038/s41598-018-21157-8] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2017] [Accepted: 01/15/2018] [Indexed: 01/21/2023] Open
Abstract
Engineered silica nanoparticles (NPs) have attracted increasing interest in several applications, and particularly in the field of nanomedicine, thanks to the high biocompatibility of this material. For their optimal and controlled use, the understanding of the mechanisms elicited by their interaction with the biological target is a prerequisite, especially when dealing with cells particularly vulnerable to environmental stimuli like neurons. Here we have combined different electrophysiological approaches (both at the single cell and at the population level) with a genomic screening in order to analyze, in GT1-7 neuroendocrine cells, the impact of SiO2 NPs (50 ± 3 nm in diameter) on electrical activity and gene expression, providing a detailed analysis of the impact of a nanoparticle on neuronal excitability. We find that 20 µg mL−1 NPs induce depolarization of the membrane potential, with a modulation of the firing of action potentials. Recordings of electrical activity with multielectrode arrays provide further evidence that the NPs evoke a temporary increase in firing frequency, without affecting the functional behavior on a time scale of hours. Finally, NPs incubation up to 24 hours does not induce any change in gene expression.
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Vanacker C, Moya MR, DeFazio RA, Johnson ML, Moenter SM. Long-Term Recordings of Arcuate Nucleus Kisspeptin Neurons Reveal Patterned Activity That Is Modulated by Gonadal Steroids in Male Mice. Endocrinology 2017; 158:3553-3564. [PMID: 28938398 PMCID: PMC5659697 DOI: 10.1210/en.2017-00382] [Citation(s) in RCA: 30] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/19/2017] [Accepted: 07/25/2017] [Indexed: 11/19/2022]
Abstract
Pulsatile release of gonadotropin-releasing hormone (GnRH) is key to fertility. Pulse frequency is modulated by gonadal steroids and likely arises subsequent to coordination of GnRH neuron firing activity. The source of rhythm generation and the site of steroid feedback remain critical unanswered questions. Arcuate neurons that synthesize kisspeptin, neurokinin B, and dynorphin (KNDy) may be involved in both of these processes. We tested the hypotheses that action potential firing in KNDy neurons is episodic and that gonadal steroids regulate this pattern. Targeted extracellular recordings were made of green fluorescent protein-identified KNDy neurons in brain slices from adult male mice that were intact, castrated, or castrated and treated with estradiol or dihydrotestosterone (DHT). KNDy neurons exhibited marked peaks and nadirs in action potential firing activity during recordings lasting 1 to 3.5 hours. Peaks, identified by Cluster analysis, occurred more frequently in castrated than intact mice, and either estradiol or DHT in vivo or blocking neurokinin type 3 receptor in vitro restored peak frequency to intact levels. The frequency of peaks in firing rate and estradiol regulation of this frequency is similar to that observed for GnRH neurons, whereas DHT suppressed firing in KNDy but not GnRH neurons. We further examined the patterning of action potentials to identify bursts that may be associated with increased neuromodulator release. Burst frequency and duration are increased in castrated compared with intact and steroid-treated mice. The observation that KNDy neurons fire in an episodic manner that is regulated by steroid feedback is consistent with a role for these neurons in GnRH pulse generation and regulation.
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Affiliation(s)
- Charlotte Vanacker
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan 48109
| | - Manuel Ricu Moya
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan 48109
| | - R. Anthony DeFazio
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan 48109
| | - Michael L. Johnson
- Department of Pharmacology, University of Virginia, Charlottesville, Virginia 22908
| | - Suzanne M. Moenter
- Department of Molecular and Integrative Physiology, University of Michigan, Ann Arbor, Michigan 48109
- Department of Internal Medicine, University of Michigan, Ann Arbor, Michigan 48109
- Department of Obstetrics and Gynecology, University of Michigan, Ann Arbor, Michigan 48109
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5
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Woller MJ, Meyer S, Ada-Nguema A, Waechter-Brulla D. Dissecting Autocrine Effects on Pulsatile Release of Gonadotropin-Releasing Hormone in Cultured Rat Hypothalamic Tissue. Exp Biol Med (Maywood) 2016; 229:56-64. [PMID: 14709777 DOI: 10.1177/153537020422900107] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The control of reproductive function is manifested centrally through the control of hypothalamic release of gonadotropin-releasing hormone (GnRH) in episodic events or pulses. For GnRH release to occur in pulses, GnRH neurons must coordinate release events periodically to elicit a bolus of GnRH. We used a perifusion culture system to examine the release of GnRH from both intact hypothalami and enzymatically dispersed hypothalamic cells after challenge with GnRH analogs to evaluate the role of anatomical neuronal connections on autocrine/paracrine signals by GnRH on GnRH neurons. The potent GnRH agonist des-Gly10-D-Ala6-GnRH N-ethylamide, potent GnRH antagonists D-Phe2-D-Ala6-GnRH and D-Phe2,6-Pro3-GnRH or vehicle were infused, whereas GnRH release from hypothalamic tissue and cells were measured. PULSAR analysis of GnRH release profiles was conducted to evaluate parameters of pulsatile GnRH release. Infusion of the GnRH agonist resulted in a decrease in mean GnRH (P < 0.001), pulse nadir (P < 0.01), and pulse frequency (P < 0.05) but no effect on pulse amplitude. Infusion of GnRH antagonists resulted in an increase in mean GnRH (P < 0.001), pulse nadir (P < 0.05), and pulse frequency (P < 0.05) and in GnRH pulse amplitude only in dispersed cells (P < 0.05). These results are consistent with the hypothesis that GnRH inhibits endogenous GnRH release by an ultrashort-loop feedback mechanism and that treatment of hypothalamic tissue or cells with GnRH agonist inhibits ultrashort-loop feedback, whereas treatment with antagonists disrupts normal feedback to GnRH neurons and elicits an increased GnRH signal.
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Affiliation(s)
- Michael J Woller
- Biological Sciences, University of Wisconsin-Whitewater, Whitewater, Wisconsin 53190, USA.
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Ezzat A, Pereira A, Clarke IJ. Kisspeptin is a component of the pulse generator for GnRH secretion in female sheep but not the pulse generator. Endocrinology 2015; 156:1828-37. [PMID: 25710282 DOI: 10.1210/en.2014-1756] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We tested the hypothesis that kisspeptin cells constitute the "pulse generator" for GnRH secretion. In ewes, we determined whether iv administered kisspeptin elicits a secretory pulse of LH in anaesthetized, sex-steroid suppressed ovariectomized ewes. A response was seen in both anaesthetized and conscious animals, which was not associated with induction of c-Fos labeling in GnRH cells, supporting the notion that kisspeptin acts on the neurosecretory GnRH terminals. Response was lower in the anaesthetized animals, suggesting that some nonkisspeptin elements may be involved in GnRH responses. Microinjection of kisspeptin (100 nmol) into the median eminence of conscious ewes elicited a pulse of LH, indicating that kisspeptin acts at this level to cause GnRH secretion. To determine which cells are activated at the time of GnRH secretion, we blood sampled 18 ewes during the luteal phase of the estrous cycle and harvested brains after 3 hours. Three of these ewes displayed a pulse of LH within 30 minutes of euthanasia. An increase in c-Fos labeling was seen in kisspeptin and glutamate cells of the arcuate nucleus but not in GnRH neurons, preoptic kisspeptin neurons, or preoptic glutamate neurons. Immunohistochemistry in 4 hypothalami showed that 72% of arcuate kisspeptin cells receive glutamatergic input. These data support the concept that the kisspeptin cells of the arcuate nucleus drive pulsatile secretion of GnRH at the level of the median eminence, but this may involve "upstream" input from glutamate cells. We conclude that the pulse generator for GnRH secretion involves more than 1 element.
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Affiliation(s)
- Ahmed Ezzat
- Department of Physiology, Monash University, Clayton, Victoria 3800, Australia
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7
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Abstract
Acquisition of a mature pattern of gonadotropin-releasing hormone (GnRH) secretion from the CNS is a hallmark of the pubertal process. Little is known about GnRH release during sexual maturation, but it is assumed to be minimal before later stages of puberty. We studied spontaneous GnRH secretion in brain slices from male mice during perinatal and postnatal development using fast-scan cyclic voltammetry (FSCV) to detect directly the oxidation of secreted GnRH. There was good correspondence between the frequency of GnRH release detected by FSCV in the median eminence of slices from adults with previous reports of in vivo luteinizing hormone (LH) pulse frequency. The frequency of GnRH release in the late embryonic stage was surprisingly high, reaching a maximum in newborns and remaining elevated in 1-week-old animals despite low LH levels. Early high-frequency GnRH release was similar in wild-type and kisspeptin knock-out mice indicating that this release is independent of kisspeptin-mediated excitation. In vivo treatment with testosterone or in vitro treatment with gonadotropin-inhibitory hormone (GnIH) reduced GnRH release frequency in slices from 1-week-old mice. RF9, a putative GnIH antagonist, restored GnRH release in slices from testosterone-treated mice, suggesting that testosterone inhibition may be GnIH-dependent. At 2-3 weeks, GnRH release is suppressed before attaining adult patterns. Reduction in early life spontaneous GnRH release frequency coincides with the onset of the ability of exogenous GnRH to induce pituitary LH secretion. These findings suggest that lack of pituitary secretory response, not lack of GnRH release, initially blocks downstream activation of the reproductive system.
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Li Y, Shi X, Song J, Lü C, Kim TI, McCall JG, Bruchas MR, Rogers JA, Huang Y. Thermal analysis of injectable, cellular-scale optoelectronics with pulsed power. Proc Math Phys Eng Sci 2013. [DOI: 10.1098/rspa.2013.0142] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
An ability to insert electronic/optoelectronic systems into precise locations of biological tissues provides powerful capabilities, especially in neuroscience such as optogenetics where light can activate/deactivate critical cellular signalling and neural systems. In such cases, engineered thermal management is essential, to avoid adverse effects of heating on normal biological processes. Here, an analytic model of heat conduction is developed for microscale, inorganic light-emitting diodes (μ-ILEDs) in a pulsed operation in biological tissues. The analytic solutions agree well with both three-dimensional finite-element analysis and experiments. A simple scaling law for the maximum temperature increase is presented in terms of material (e.g. thermal diffusivity), geometric (e.g. μ-ILED size) and loading parameters (e.g. pulsed peak power, duty cycle and frequency). These results provide useful design guidelines not only for injectable μ-ILED systems, but also for other similar classes of electronic and optoelectronic components.
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Affiliation(s)
- Yuhang Li
- Department of Civil and Environmental Engineering, Institute for Public Health and Medicine, Northwestern University, Evanston, IL 60208, USA
- Department of Mechanical Engineering, Institute for Public Health and Medicine, Northwestern University, Evanston, IL 60208, USA
- Department of Engineering Mechanics, Zhejiang University, Hangzhou 310027, People’s Republic of China
| | - Xiaoting Shi
- Department of Mechanical Engineering, Institute for Public Health and Medicine, Northwestern University, Evanston, IL 60208, USA
- Shanghai Key Laboratory of Materials Laser Processing and Modification, School of Materials Science and Engineering, Shanghai Jiaotong University, Shanghai 200240, People's Republic of China
| | - Jizhou Song
- Department of Mechanical and Aerospace Engineering, University of Miami, Coral Gables, FL 33146, USA
| | - Chaofeng Lü
- Department of Civil Engineering and Soft Matter Research Center, Zhejiang University, Hangzhou 310058, People's Republic of China
| | - Tae-il Kim
- Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
- School of Chemical Engineering, Sungkyunkwan University (SKKU), Suwon 440-746, Korea
| | - Jordan G. McCall
- Department of Anesthesiology, Division of Basic Research, Washington University Pain Center; Department of Anatomy and Neurobiology; Division of Biological and Biomedical Sciences, Washington University School of Medicine, St Louis, MO 63110, USA
| | - Michael R. Bruchas
- Department of Anesthesiology, Division of Basic Research, Washington University Pain Center; Department of Anatomy and Neurobiology; Division of Biological and Biomedical Sciences, Washington University School of Medicine, St Louis, MO 63110, USA
| | - John A. Rogers
- Frederick Seitz Materials Research Laboratory, Department of Materials Science and Engineering, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA
| | - Yonggang Huang
- Department of Civil and Environmental Engineering, Institute for Public Health and Medicine, Northwestern University, Evanston, IL 60208, USA
- Department of Mechanical Engineering, Institute for Public Health and Medicine, Northwestern University, Evanston, IL 60208, USA
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9
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Lehman MN, Hileman SM, Goodman RL. Neuroanatomy of the kisspeptin signaling system in mammals: comparative and developmental aspects. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2013; 784:27-62. [PMID: 23550001 DOI: 10.1007/978-1-4614-6199-9_3] [Citation(s) in RCA: 112] [Impact Index Per Article: 10.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/24/2022]
Abstract
Our understanding of kisspeptin and its actions depends, in part, on a detailed knowledge of the neuroanatomy of the kisspeptin signaling system in the brain. In this chapter, we will review our current knowledge of the distribution of kisspeptin cells, fibers, and receptors in the mammalian brain, including the development, phenotype, and projections of different kisspeptin subpopulations. A fairly consistent picture emerges from this analysis. There are two major groups of kisspeptin cell bodies: a large number in the arcuate nucleus (ARC) and a smaller collection in the rostral periventricular area of the third ventricle (RP3V) of rodents and preoptic area (POA) of non-rodents. Both sets of neurons project to GnRH cell bodies, which contain Kiss1r, and the ARC kisspeptin population also projects to GnRH axons in the median eminence. ARC kisspeptin neurons contain neurokinin B and dynorphin, while a variable percentage of those cells in the RP3V of rodents contain galanin and/or dopamine. Neurokinin B and dynorphin have been postulated to contribute to the control of GnRH pulses and sex steroid negative feedback, while the role of galanin and dopamine in rostral kisspeptin neurons is not entirely clear. Kisspeptin neurons, fibers, and Kiss1r are found in other areas, including widespread areas outside the hypothalamus, but their physiological role(s) in these regions remains to be determined.
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Affiliation(s)
- Michael N Lehman
- Department of Neurobiology and Anatomical Sciences, University of Mississippi Medical Center, Jackson, MS, USA.
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10
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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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Hyperpolarization-activated currents in gonadotropin-releasing hormone (GnRH) neurons contribute to intrinsic excitability and are regulated by gonadal steroid feedback. J Neurosci 2010; 30:13373-83. [PMID: 20926664 DOI: 10.1523/jneurosci.1687-10.2010] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Pulsatile release of gonadotropin-releasing hormone (GnRH) is required for fertility and is regulated by steroid feedback. Hyperpolarization-activated currents (I(h)) play a critical role in many rhythmic neurons. We examined the contribution of I(h) to the membrane and firing properties of GnRH neurons and the modulation of this current by steroid milieu. Whole-cell voltage- and current-clamp recordings were made of GFP-identified GnRH neurons in brain slices from male mice that were gonad-intact, castrated, or castrated and treated with estradiol implants. APV, CNQX, and bicuculline were included to block fast synaptic transmission. GnRH neurons (47%) expressed a hyperpolarization-activated current with pharmacological and biophysical characteristics of I(h). The I(h)-specific blocker ZD7288 reduced hyperpolarization-induced sag and rebound potential, decreased GnRH neuron excitability and action potential firing, and hyperpolarized membrane potential in some cells. ZD7288 also altered the pattern of burst firing and reduced the slope of recovery from the after-hyperpolarization potential. Activation of I(h) by hyperpolarization increased spike frequency, whereas inactivation of I(h) by depolarization reduced spike frequency. Castration increased I(h) compared with that in gonad-intact males. This effect was reversed by in vivo estradiol replacement. Together, these data indicate I(h) provides an excitatory drive in GnRH neurons that contributes to action potential burst firing and that estradiol regulates I(h) in these cells. As estradiol is the primary central negative feedback hormone on GnRH neuron firing in males, this provides insight into the mechanisms by which steroid hormones potentially alter the intrinsic properties of GnRH neurons to change their activity.
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Arroyo A, Kim BS, Biehl A, Yeh J, Bett GCL. Expression of kv4.3 voltage-gated potassium channels in rat gonadotrophin-releasing hormone (GnRH) neurons during the estrous cycle. Reprod Sci 2010; 18:136-44. [PMID: 20861393 DOI: 10.1177/1933719110382306] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
Regular and timely electrical activity of gonadotrophin-releasing hormone (GnRH) neurons accompanies the pulsatile release of GnRH that plays a central role in regulating fertility. Although transient outward A-type currents (I(A)) have been electrophysiologically identified in GnRH neurons, the molecular identity of the channels that underlie these currents are unknown. Several families of voltage-gated potassium channels can underlie I(A). However, the biophysical properties of I(A) described in previous electrophysiological studies are strongly characteristic of members of the Kv4 family of voltage-gated channels. We, therefore, sought to determine the presence of Kv4 channels in GnRH neurons. We used reverse transcriptase-polymerase chain reaction (RT-PCR) and Western blot analysis to determine whether Kv4 messenger RNA (mRNA) and protein are present in the rat medial preoptic area (MPOA) and median eminence (ME). We used double-label immunohistochemistry to determine whether Kv4 colocalized with GnRH cell bodies in the MPOA and GnRH axons in the ME. Kv4.3 channels co-localized with GnRH in the MPOA but not in the ME. Neither Kv4.2 nor Kv4.1 co-localized with GnRH in either the MPOA or the ME. The electrical activity of GnRH neurons changes dramatically during the estrous cycle. We, therefore, studied the change in Kv4.3 expression in GnRH neurons during the estrous cycle. In the estrus phase, 58.05% of GnRH neurons expressed Kv4.3 compared to 74.48% in diestrus-proestrus rats (P < .05). Our data suggest that Kv4.3 is the major molecular component of I(A) in GnRH neurons, and furthermore that the expression of Kv4.3 changes significantly during the rat estrous cycle.
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Affiliation(s)
- Armando Arroyo
- Department of Gynecology-Obstetrics, State University of New York, University at Buffalo, School of Medicine and Biomedical Sciences, Buffalo, NY, USA.
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Christian CA, Moenter SM. The neurobiology of preovulatory and estradiol-induced gonadotropin-releasing hormone surges. Endocr Rev 2010; 31:544-77. [PMID: 20237240 PMCID: PMC3365847 DOI: 10.1210/er.2009-0023] [Citation(s) in RCA: 199] [Impact Index Per Article: 14.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/01/2009] [Accepted: 02/18/2010] [Indexed: 12/14/2022]
Abstract
Ovarian steroids normally exert homeostatic negative feedback on GnRH release. During sustained exposure to elevated estradiol in the late follicular phase of the reproductive cycle, however, the feedback action of estradiol switches to positive, inducing a surge of GnRH release from the brain, which signals the pituitary LH surge that triggers ovulation. In rodents, this switch appears dependent on a circadian signal that times the surge to a specific time of day (e.g., late afternoon in nocturnal species). Although the precise nature of this daily signal and the mechanism of the switch from negative to positive feedback have remained elusive, work in the past decade has provided much insight into the role of circadian/diurnal and estradiol-dependent signals in GnRH/LH surge regulation and timing. Here we review the current knowledge of the neurobiology of the GnRH surge, in particular the actions of estradiol on GnRH neurons and their synaptic afferents, the regulation of GnRH neurons by fast synaptic transmission mediated by the neurotransmitters gamma-aminobutyric acid and glutamate, and the host of excitatory and inhibitory neuromodulators including kisspeptin, vasoactive intestinal polypeptide, catecholamines, neurokinin B, and RFamide-related peptides, that appear essential for GnRH surge regulation, and ultimately ovulation and fertility.
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Affiliation(s)
- Catherine A Christian
- Departments of Medicine and Cell Biology, University of Virginia, Charlottesville, 22908, USA.
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Ichikawa T. Partial synchronization dynamics of coupled ultradian oscillators comprising an insect neurosecretory cell system. Zoolog Sci 2009; 26:861-9. [PMID: 19968474 DOI: 10.2108/zsj.26.861] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
An insulin-related peptide, bombyxin, in the silkmoth Bombyx mori is secreted by four pairs of cerebral neurosecretory cells that form a weakly coupled oscillator system to produce a pulsatile pattern of hormone secretion. The activity of individual bombyxin-producing (BP) cells oscillated with different periods (20-70 min). The population of BP cells exhibited complex phase dynamics, including spontaneous synchronization and desynchronization of different combinations of cells. Statistical cross-correlation analyses of oscillation patterns between BP cells revealed that one cell usually correlated closely with a few particular cells of similar periodicity. Close investigation of the phase differences between individual active phases of the related cell pairs revealed that an inphase synchronous state was usually maintained for many cycles, whereas an antiphase state was transient, lasting for a few cycles. In contrast, antiphase synchronous states often occurred between several cell pairs when the brain containing the cerebral neurosecretory cell system was disconnected from the ventral nerve cord containing the neuronal mechanism that induced periodic heartbeat reversals at intervals of 80-110 min and exerted a periodic suppressive or phase-resetting effect on individual BP cells. These results suggest that the internal coupling mechanism in the BP cell system is not sufficient to maintain an in-phase synchronous state in the heterogeneous cell population, and that the external phase resetting mechanism may assist in-phase synchronization of many neurosecretory cells to generate an overall pulsatile pattern of bombyxin secretion.
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Affiliation(s)
- Toshio Ichikawa
- Department of Biology, Faculty of Sciences, Kyushu University, 6-10 Hakozaki, Higashi-ku, Fukuoka 812-8581, Japan.
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An integrated model of electrical spiking, bursting, and calcium oscillations in GnRH neurons. Biophys J 2009; 96:4514-24. [PMID: 19486674 DOI: 10.1016/j.bpj.2009.03.037] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2008] [Revised: 02/28/2009] [Accepted: 03/11/2009] [Indexed: 11/22/2022] Open
Abstract
The plasma membrane electrical activities of neurons that secrete gonadotropin-releasing hormone (GnRH) have been studied extensively. A couple of mathematical models have been developed previously to explain different aspects of these activities. The goal of this article is to develop a single model that accounts for the previously modeled experimental results and some more recent results that have not been accounted for. The latter includes two types of membrane potential bursting mechanisms and their associated cytosolic calcium oscillations. One bursting mechanism has not been reported in experiments and is thus regarded as a model prediction. Although the model is mainly based on data collected in immortalized GnRH cell lines, it is capable of explaining some properties of GnRH neurons observed in several other preparations including mature GnRH neurons in hypothalamic slices. We present a spatial model that incorporates a detailed description of calcium dynamics in a three-dimensional cell body with the ion channels evenly distributed on the cell surface. A phenomenological reduction of the spatial model into a simplified form is also presented. The simplified model will facilitate the study of the roles of plasma membrane electrical activities in the pulsatile release of GnRH.
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Ariano P, Lo Giudice A, Marcantoni A, Vittone E, Carbone E, Lovisolo D. A diamond-based biosensor for the recording of neuronal activity. Biosens Bioelectron 2009; 24:2046-50. [DOI: 10.1016/j.bios.2008.10.017] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2008] [Revised: 10/01/2008] [Accepted: 10/21/2008] [Indexed: 10/21/2022]
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Christian CA, Glidewell-Kenney C, Jameson JL, Moenter SM. Classical estrogen receptor alpha signaling mediates negative and positive feedback on gonadotropin-releasing hormone neuron firing. Endocrinology 2008; 149:5328-34. [PMID: 18635656 PMCID: PMC2584581 DOI: 10.1210/en.2008-0520] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/14/2008] [Accepted: 07/09/2008] [Indexed: 01/22/2023]
Abstract
During the female reproductive cycle, the neuroendocrine action of estradiol switches from negative feedback to positive feedback to initiate the preovulatory GnRH and subsequent LH surges. Estrogen receptor-alpha (ERalpha) is required for both estradiol negative and positive feedback regulation of LH. ERalpha may signal through estrogen response elements (EREs) in DNA and/or via ERE-independent pathways. Previously, a knock-in mutant allele (ERalpha-/AA) that selectively restores ERE-independent signaling onto the ERalpha-/- background was shown to confer partial negative but not positive estradiol feedback on serum LH. The current study investigated the roles of the ERE-dependent and ERE-independent ERalpha pathways for estradiol feedback at the level of GnRH neuron firing activity. The above ERalpha genetic models were crossed with GnRH-green fluorescent protein mice to enable identification of GnRH neurons in brain slices. Targeted extracellular recordings were used to monitor GnRH neuron firing activity using an ovariectomized, estradiol-treated mouse model that exhibits diurnal switches between negative and positive feedback. In wild-type mice, GnRH neuron firing decreased in response to estradiol during negative feedback and increased during positive feedback. In contrast, both positive and negative responses to estradiol were absent in GnRH neurons from ERalpha-/- and ERalpha-/AA mice. ERE-dependent signaling is thus required to increase GnRH neuron firing to generate a GnRH/LH surge. Furthermore, ERE-dependent and -independent ERalpha signaling pathways both appear necessary to mediate estradiol negative feedback on serum LH levels, suggesting central and pituitary estradiol feedback may use different combinations of ERalpha signaling pathways.
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Affiliation(s)
- Catherine A Christian
- Neuroscience Graduate Program, Department of Medicine, University of Virginia, Charlottesville, Virginia 22908, USA
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Wang Y, Garro M, Dantzler HA, Taylor JA, Kline DD, Kuehl-Kovarik MC. Age affects spontaneous activity and depolarizing afterpotentials in isolated gonadotropin-releasing hormone neurons. Endocrinology 2008; 149:4938-47. [PMID: 18583421 PMCID: PMC2582911 DOI: 10.1210/en.2008-0308] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Neuronal activity underlying the pulsatile secretion of GnRH remains poorly understood, as does the endogenous generation of such activity. It is clear that changes at the level of the hypothalamus are taking place during reproductive aging, yet virtually nothing is known about GnRH neuronal physiology in aging and postreproductive animals. In these studies, we performed cell-attached and whole-cell recordings in GnRH-enhanced green fluorescent protein neurons dissociated from young (3 months), middle-aged (10 months), and old (15-18 months) female mice. All mice were ovariectomized; half were estradiol replaced. Neurons from all ages fired spontaneously, most in a short-burst pattern that is characteristic of GnRH neuronal firing. Membrane characteristics were not affected by age. However, firing frequency was significantly reduced in neurons from old animals, as was spike patterning. The amplitude of the depolarizing afterpotential, evoked by a 200-msec current pulse, was significantly smaller in aged animals. In addition, inward whole-cell currents were reduced in estradiol-treated animals, although they were not significantly affected by age. Because depolarizing afterpotentials have been shown to contribute to prolonged discharges of activity after a very brief excitatory input, a decreased depolarizing afterpotential could lead to attenuated pulses in older animals. In addition, decreases in frequency and pattern generation could lead to improper information coding. Therefore, changes in the GnRH neuron during aging could lead to dysregulated activity, potentially resulting in the attenuated LH pulses observed in the transition to reproductive senescence.
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Affiliation(s)
- Yong Wang
- Department of Biomedical Sciences, E102 Vet Med, 1600 East Rollins, University of Missouri, Columbia, Missouri 65211, USA
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Robust synchrony and rhythmogenesis in endocrine neurons via autocrine regulations in vitro and in vivo. Bull Math Biol 2008; 70:2103-25. [PMID: 18797973 DOI: 10.1007/s11538-008-9328-z] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2007] [Accepted: 04/29/2008] [Indexed: 10/21/2022]
Abstract
Episodic pulses of gonadotropin-releasing hormone (GnRH) are essential for maintaining reproductive functions in mammals. An explanation for the origin of this rhythm remains an ultimate goal for researchers in this field. Some plausible mechanisms have been proposed among which the autocrine-regulation mechanism has been implicated by numerous experiments. GnRH binding to its receptors in cultured GnRH neurons activates three types of G-proteins that selectively promote or inhibit GnRH secretion (Krsmanovic et al. in Proc. Natl. Acad. Sci. 100:2969-2974, 2003). This mechanism appears to be consistent with most data collected so far from both in vitro and in vivo experiments. Based on this mechanism, a mathematical model has been developed (Khadra and Li in Biophys. J. 91:74-83, 2006) in which GnRH in the extracellular space plays the roles of a feedback regulator and a synchronizing agent. In the present study, we show that synchrony between different neurons through sharing a common pool of GnRH is extremely robust. In a diversely heterogeneous population of neurons, the pulsatile rhythm is often maintained when only a small fraction of the neurons are active oscillators (AOs). These AOs are capable of recruiting nonoscillatory neurons into a group of recruited oscillators while forcing the nonrecruitable neurons to oscillate along. By pointing out the existence of the key elements of this model in vivo, we predict that the same mechanism revealed by experiments in vitro may also operate in vivo. This model provides one plausible explanation for the apparently controversial conclusions based on experiments on the effects of the ultra-short feedback loop of GnRH on its own release in vivo.
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Kononenko NI, Honma S, Dudek FE, Honma KI. On the role of calcium and potassium currents in circadian modulation of firing rate in rat suprachiasmatic nucleus neurons: multielectrode dish analysis. Neurosci Res 2008; 62:51-7. [PMID: 18602427 DOI: 10.1016/j.neures.2008.06.001] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/23/2008] [Revised: 05/19/2008] [Accepted: 06/10/2008] [Indexed: 10/21/2022]
Abstract
The master circadian clock of mammals in the suprachiasmatic nucleus (SCN) of the hypothalamus entrains to a 24-h daily light-dark cycle and regulates circadian rhythms. The SCN is composed of multiple neurons with cell autonomous clocks exhibiting robust firing rhythms with a high firing rate during the subjective day. The membrane target(s) of the cellular clock responsible for circadian modulation of the firing rate in SCN neurons still remain unclear. Previously, L-type Ca(2+) currents and fast delayed rectifier (FDR) K(+) currents have been suggested to contribute directly to circadian modulation of electrical activity. Using long-term continuous recording of activity from dispersed rat SCN neurons in multielectrode dish and ionic channel blockers, we tested these hypotheses. Neither an L-type Ca(2+) current blocker (20 microM of nifedipine for 2 days) nor an FDR current blocker (500 microM of 4-aminopyridine (4-AP) for 4 days) suppressed the circadian modulation of firing rate. A specific blocker of Na(+) persistent current (5 microM of riluzole for 1 day followed by 10 microM during the next day) reversibly suppressed firing activity in a dose-dependent manner. These data indicate that neither nifedipine-sensitive Ca(2+) current(s) nor 4-AP-sensitive K(+) current(s) are key membrane targets for circadian modulation of electrical firing rate in SCN neurons.
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Affiliation(s)
- Nikolai I Kononenko
- Department of Physiology, Hokkaido University Graduate School of Medicine, Sapporo, Japan.
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Turi GF, Liposits Z, Hrabovszky E. Cholinergic afferents to gonadotropin-releasing hormone neurons of the rat. Neurochem Int 2008; 52:723-8. [DOI: 10.1016/j.neuint.2007.09.001] [Citation(s) in RCA: 23] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2007] [Revised: 08/31/2007] [Accepted: 09/03/2007] [Indexed: 11/29/2022]
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Zhang C, Bosch MA, Levine JE, Rønnekleiv OK, Kelly MJ. Gonadotropin-releasing hormone neurons express K(ATP) channels that are regulated by estrogen and responsive to glucose and metabolic inhibition. J Neurosci 2007; 27:10153-64. [PMID: 17881521 PMCID: PMC6672659 DOI: 10.1523/jneurosci.1657-07.2007] [Citation(s) in RCA: 100] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2006] [Revised: 08/01/2007] [Accepted: 08/02/2007] [Indexed: 11/21/2022] Open
Abstract
Gonadotropin-releasing hormone (GnRH) is released in a pulsatile manner that is dependent on circulating 17beta-estradiol (E2) and glucose concentrations. However, the intrinsic conductances responsible for the episodic firing pattern underlying pulsatile release and the effects of E2 and glucose on these conductances are primarily unknown. Whole-cell recordings from mouse enhanced green fluorescent protein-GnRH neurons revealed that the K(ATP) channel opener diazoxide induced an outward current that was antagonized by the sulfonylurea receptor 1 (SUR1) channel blocker tolbutamide. Single-cell reverse transcription (RT)-PCR revealed that the majority of GnRH neurons expressed Kir6.2 and SUR1 subunits, which correlated with the diazoxide/tolbutamide sensitivity. Also, a subpopulation of GnRH neurons expressed glucokinase mRNA, a marker for glucose sensitivity. Indeed, GnRH neurons decreased their firing in response to low glucose concentrations and metabolic inhibition. The maximum diazoxide-induced current was approximately twofold greater in E2-treated compared with oil-treated ovariectomized females. In current clamp, estrogen enhanced the diazoxide-induced hyperpolarization to a similar degree. However, based on quantitative RT-PCR, estrogen did not increase the expression of Kir6.2 or SUR1 transcripts in GnRH neurons. In the presence of ionotropic glutamate and GABA(A) receptor antagonists, tolbutamide depolarized and significantly increased the firing rate of GnRH neurons to a greater extent in E2-treated females. Finally, tolbutamide significantly increased GnRH secretion from the preoptic-mediobasal hypothalamus. Therefore, it appears that K(ATP) channels and glucokinase are expressed in GnRH neurons, which renders them directly responsive to glucose. In addition, K(ATP) channels are involved in modulating the excitability of GnRH neurons in an estrogen-sensitive manner that ultimately regulates peptide release.
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Affiliation(s)
| | | | - Jon E. Levine
- Department of Neurobiology and Physiology, Northwestern University, Evanston, Illinois 60208
| | - Oline K. Rønnekleiv
- Department of Physiology and Pharmacology
- Department of Anesthesiology and Perioperative Medicine, and
- Division of Neuroscience, Oregon National Primate Research Center, Oregon Health and Science University, Portland, Oregon 97239, and
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Chu Z, Moenter SM. Endogenous activation of metabotropic glutamate receptors modulates GABAergic transmission to gonadotropin-releasing hormone neurons and alters their firing rate: a possible local feedback circuit. J Neurosci 2006; 25:5740-9. [PMID: 15958740 PMCID: PMC1201448 DOI: 10.1523/jneurosci.0913-05.2005] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Gonadotropin-releasing hormone (GnRH) neurons are the primary central regulators of fertility, receiving input from GABAergic afferents via GABA(A) receptors. We tested whether metabotropic glutamate receptors (mGluRs) regulate GABA transmission to GnRH neurons and GnRH neuronal firing pattern. Whole-cell recordings were performed under conditions isolating ionotropic GABA postsynaptic currents (PSCs) in brain slices. The broad-spectrum mGluR agonist 1-aminocyclopentane-1,3-dicarboxylic acid (ACPD) decreased the frequency of GABA(A)-mediated spontaneous PSCs in a reversible manner. Amplitude and kinetics were not altered, suggesting that afferent GABA neurons are the primary targets. TTX eliminated the effects of ACPD in most tested neurons. Group II [2-(2,3-dicarboxycyclopropyl) glycine] and III (L-AP-4) mGluR agonists mediated this response; a group I agonist (3,5-dihydroxyphenylglycine) was not effective. The broad-spectrum antagonist alpha-methyl-4-carboxyphenylglycine (MCPG) and/or (RS)-alpha-cyclopropyl-4-phosphonophenylglycine (CPPG) (group III antagonist) enhanced spontaneous PSC frequency, particularly when initial frequency was low, suggesting that endogenous activation of mGluRs regulates GABA transmission to GnRH neurons. Extracellular recordings were used to evaluate GnRH neuron firing rate within the network. ACPD reduced firing rate, and MCPG plus CPPG had an opposite effect, indicating that mGluRs help control excitability of the GnRH network. GnRH neurons express vesicular glutamate transporters, suggesting they may corelease this transmitter. Simulation of firing activity in a GnRH neuron decreased PSC frequency in that cell, an effect blocked by antagonism of mGluRs but not GnRH receptors. These results demonstrate an inhibition of GABAergic inputs to GnRH neurons by mGluRs via a presynaptic mechanism. Through this mechanism, local glutamate milieu, possibly contributed by GnRH neurons themselves, plays an important role in modulating GnRH release and the central regulation of fertility.
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Affiliation(s)
- Zhiguo Chu
- Department of Internal Medicine, University of Virginia, Charlottesville, Virginia 22908, USA
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24
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Neuromodulatory Functions of Terminal Nerve‐GnRH Neurons. ACTA ACUST UNITED AC 2006. [DOI: 10.1016/s1546-5098(06)25011-8] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/17/2023]
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Christian CA, Mobley JL, Moenter SM. Diurnal and estradiol-dependent changes in gonadotropin-releasing hormone neuron firing activity. Proc Natl Acad Sci U S A 2005; 102:15682-7. [PMID: 16230634 PMCID: PMC1257388 DOI: 10.1073/pnas.0504270102] [Citation(s) in RCA: 170] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
A robust gonadotropin-releasing hormone (GnRH) surge is a prerequisite signal for the luteinizing hormone (LH) surge that triggers ovulation. In rodents, the GnRH surge is initiated by elevated estradiol and a diurnal switch in estrogen action from negative to positive feedback. The ability of constant estradiol treatment to induce daily LH surges was tested in adult mice that were ovariectomized (OVX) or OVX and treated with estradiol implants (OVX+E). LH in OVX mice showed no time-of-day difference. In contrast, OVX+E mice showed a large LH surge (8- to 124-fold relative to the a.m.) in p.m. samples on d 2-5 post-OVX+E. Targeted extracellular recordings were used to examine changes in firing activity of GnRH neurons in brain slices. There was no time-of-day difference in cells from OVX mice. In contrast, OVX+E cells recorded in the p.m. showed an increased mean firing rate and instantaneous firing frequency, which could increase GnRH release, and decreased duration of quiescence between bouts of firing, possibly reflecting increased pulse frequency, compared with cells recorded in the a.m. In the a.m., OVX+E cells showed changes in GnRH neuron firing reflecting negative feedback compared with OVX cells, whereas in the p.m., OVX+E cells exhibited changes suggesting positive feedback. These data indicate that differences in pattern and level of individual GnRH neuron firing may reflect the switch in estradiol action and underlie GnRH surge generation. The persistence of altered GnRH neuron activity in slices indicates that this approach can be used to study the neurobiological mechanisms of surge generation.
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Affiliation(s)
- Catherine A Christian
- Departments of Internal Medicine and Cell Biology and Neuroscience Graduate Program, University of Virginia, Charlottesville, VA 22908, USA
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Abe H, Terasawa E. Firing pattern and rapid modulation of activity by estrogen in primate luteinizing hormone releasing hormone-1 neurons. Endocrinology 2005; 146:4312-20. [PMID: 15976055 PMCID: PMC1479770 DOI: 10.1210/en.2005-0435] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
We have shown previously that cultured LHRH-1 neurons, derived from monkey olfactory placode region, exhibit pulsatile LHRH-1 release at hourly intervals and spontaneous intracellular calcium oscillations, which synchronize at a frequency similar to LHRH-1 release. Brief application of estrogen induced a rapid increase in the frequency of intracellular calcium oscillations and the frequency of synchronizations. The estrogen-induced frequency of intracellular calcium oscillations was mediated by estrogen receptors (ER), whereas the frequency of synchronizations was not mediated by ER. In the present study, we further examined the rapid action of estrogen using patch-clamp recording in primate LHRH-1 neurons. Cell-attached patch-clamp recording showed that LHRH-1 neurons exhibited monophasic or biphasic action currents that were sensitive to an increase in extracellular K+ and the sodium channel blocker tetrodotoxin. The majority (90%) of LHRH-1 neurons showed irregular firing patterns composed of bursts and irregular beatings of action currents, which further formed a "cluster" firing pattern. Brief application of 17beta-estradiol (1 nM) increased the firing frequency and burst duration of LHRH-1 neurons with a latency of 60-120 sec for up to 25 min. ICI182,780, an ER antagonist, blocked the 17beta-estradiol-induced increase in the firing activity of LHRH-1 neurons. These results suggest that 1) primate LHRH-1 neurons exhibit complex firing patterns composed of activities with different time domains, 2) estrogen causes rapid stimulatory action of firing activity, and 3) this estrogen action is mediated by ER in primate LHRH-1 neurons.
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Affiliation(s)
- Hideki Abe
- Wisconsin National Primate Research Center and
| | - Ei Terasawa
- Wisconsin National Primate Research Center and
- Department of Pediatrics, University of Wisconsin, Madison, Wisconsin 53715-1261
- * Correspondence: Ei Terasawa, Wisconsin National Primate Research Center, University of Wisconsin, 1223 Capitol Court, Madison, WI 53715-1299, E-mail:
, Phone: (608) 263-3579, Fax: (608) 263-3524
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Ashworth AJ, Banks JR, Brierley MJ, Balment RJ, McCrohan CR. Electrical activity of caudal neurosecretory neurons in seawater and freshwater-adapted Platichthys flesus, in vivo. J Exp Biol 2005; 208:267-75. [PMID: 15634846 DOI: 10.1242/jeb.01372] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
SUMMARY
This study examined the electrical firing activity of neuroendocrine Dahlgren cells in the caudal neurosecretory system (CNSS) of the euryhaline flounder in vivo. Intracellular recordings revealed generally similar activity patterns and membrane properties to those previously reported in vitro. To investigate the potential role of the CNSS in osmoregulatory adaptation, extracellular, multiunit, recordings compared the activity patterns of Dahlgren cells in fully seawater- and freshwater-adapted fish. The proportion of cells showing bursting (as opposed to phasic or tonic) activity was greater in seawater-than in freshwater-adapted fish, as was the Correlation Index, a measure of the degree of correlation between firing activities of cells recorded simultaneously from the same preparation. Acute transfer of fish from seawater to freshwater gill perfusion led to recruitment of previously silent Dahlgren cells and a reduction in Correlation Index;freshwater to seawater transfer increased the Correlation Index. Severing the spinal cord anterior to the CNSS led to an increase in overall Dahlgren cell activity. Electrical stimulation of branchial nerve branches providing input to the brainstem, or tactile (pinch) stimulation of lips or fins, led to a reduction in CNSS activity lasting up to 500 s, indicating the presence of descending modulatory pathways from the brain. These results are consistent with a role for CNSS neuropeptides, urotensins, in supporting survival in a hypertonic, seawater, environment.
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Affiliation(s)
- A J Ashworth
- Faculty of Life Sciences, The University of Manchester, Manchester M13 9PT, UK
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Suyama K, Daikoku S, Funabashi T, Kimura F. Effects of GABA and bicuculline on the electrical activity of rat olfactory placode neurons derived at E13.5 and cultured for 1 week on multi-electrode dishes. Endocr J 2004; 51:171-6. [PMID: 15118267 DOI: 10.1507/endocrj.51.171] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/23/2022] Open
Abstract
The present study was performed to record the electrical activity of olfactory placode neurons and to check the effect of GABA and bicuculline on it. Olfactory placodes obtained at day 13.5 of gestation were cultured for 1 week on multi-electrode dishes. Olfactory placode neurons showed spontaneous firing, with firing rates of 0.77 +/- 0.05 Hz (0.03-3.82 Hz, n = 12), but there was no bursting activity. Perfusion with 10 microM GABA almost immediately inhibited 8 of 11 firing activities (we could not test it in 1 activity). In contrast, perfusion with 10 microM bicuculline induced facilitation in 5 of 12 activities and did not induce any change in 7 other activities. Statistical analysis by chi(2)-test showed a significant difference in the response of neurons to the two drugs. Fisher's exact probability test showed that the inhibitory effect of GABA was significant (p<0.05) whereas neither the facilitatory effect nor the lack of effect of bicuculline was significant (p>0.1). These results suggest that cultured olfactory placode neurons, even in a probably immature stage, respond to GABA with inhibition, as generally observed at mature stages.
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Affiliation(s)
- Kumiko Suyama
- Department of Neuroendocrinology, Yokohama City University Graduate School of Medicine, Japan
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Xu C, Xu XZ, Nunemaker CS, Moenter SM. Dose-dependent switch in response of gonadotropin-releasing hormone (GnRH) neurons to GnRH mediated through the type I GnRH receptor. Endocrinology 2004; 145:728-35. [PMID: 14576189 DOI: 10.1210/en.2003-0562] [Citation(s) in RCA: 52] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
Pulsatile release of GnRH provides central control of reproduction. GnRH neuron activity is likely synchronized to produce hormone pulses, but the mechanisms are largely unknown. One candidate for communication among these neurons is GnRH itself. Cultured embryonic and immortalized GnRH neurons express GnRH receptor type I (GnRHR-1), but expression has not been shown in adult GnRH neurons. Using mice that express green fluorescent protein (GFP) in GnRH neurons, we tested whether adult GnRH neurons express GnRHR-1. GFP-positive (n = 42) and -negative neurons (n = 22) were harvested from brain slices, and single-cell RT-PCR was performed with cell contents. Fifty-two percent of the GnRH neurons tested expressed GnRHR-1, but only 9% of non-GnRH hypothalamic neurons expressed GnRHR-1; no false harvest controls (n = 13) were positive. GnRHR-1 expression within GnRH neurons suggested a physiological ultrashort loop feedback role for GnRH. Thus, we examined the effect of GnRH on the firing rate of GnRH neurons. Low-dose GnRH (20 nm) significantly decreased firing rate in 12 of 22 neurons (by 42 +/- 4%, P < 0.05), whereas higher doses increased firing rate (200 nm, five of 10 neurons, 72 +/- 26%; 2000 nm, nine of 13 neurons, 53 +/- 8%). Interestingly, the fraction of GnRH neurons responding was similar to the fraction in which GnRHR-1 was detected. Together, these data demonstrate that a subpopulation of GnRH neurons express GnRHR-1 and respond to GnRH with altered firing. The dose dependence suggests that this autocrine control of GnRH neurons may be not only a mechanism for generating and modulating pulsatile release, but it may also be involved in the switch between pulse and surge modes of release.
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Affiliation(s)
- Chun Xu
- Department of Internal Medicine, P.O. Box 800578, University of Virginia, Charlottesville, VA 22908, USA
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Circadian gene expression regulates pulsatile gonadotropin-releasing hormone (GnRH) secretory patterns in the hypothalamic GnRH-secreting GT1-7 cell line. J Neurosci 2003. [PMID: 14657179 DOI: 10.1523/jneurosci.23-35-11202.2003] [Citation(s) in RCA: 124] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
Although it has long been established that episodic secretion of gonadotropin-releasing hormone (GnRH) from the hypothalamus is required for normal gonadotropin release, the molecular and cellular mechanisms underlying the synchronous release of GnRH are primarily unknown. We used the GT1-7 mouse hypothalamic cell line as a model for GnRH secretion, because these cells release GnRH in a pulsatile pattern similar to that observed in vivo. To explore possible molecular mechanisms governing secretory timing, we investigated the role of the molecular circadian clock in regulation of GnRH secretion. GT1-7 cells express many known core circadian clock genes, and we demonstrate that oscillations of these components can be induced by stimuli such as serum and the adenylyl cyclase activator forskolin, similar to effects observed in fibroblasts. Strikingly, perturbation of circadian clock function in GT1-7 cells by transient expression of the dominant-negative Clock-Delta19 gene disrupts normal ultradian patterns of GnRH secretion, significantly decreasing mean pulse frequency. Additionally, overexpression of the negative limb clock gene mCry1 in GT1-7 cells substantially increases GnRH pulse amplitude without a commensurate change in pulse frequency, demonstrating that an endogenous biological clock is coupled to the mechanism of neurosecretion in these cells and can regulate multiple secretory parameters. Finally, mice harboring a somatic mutation in the Clock gene are subfertile and exhibit a substantial increase in estrous cycle duration as revealed by examination of vaginal cytology. This effect persists in normal light/dark (LD) cycles, suggesting that a suprachiasmatic nucleus-independent endogenous clock in GnRH neurons is required for eliciting normal pulsatile patterns of GnRH secretion.
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Moenter SM, DeFazio AR, Pitts GR, Nunemaker CS. Mechanisms underlying episodic gonadotropin-releasing hormone secretion. Front Neuroendocrinol 2003; 24:79-93. [PMID: 12762999 DOI: 10.1016/s0091-3022(03)00013-x] [Citation(s) in RCA: 122] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The episodic secretion of gonadotropin-releasing hormone (GnRH) is crucial for fertility, but the cellular mechanisms and network properties generating GnRH pulses are not well understood. We will explore three primary aspects of this intermittent hormonal signal: the source of rhythm(s), the possible mechanisms comprising oscillator(s), and how GnRH neurons are synchronized to produce a pulse of hormone release into the pituitary portal blood. Current knowledge will be reviewed, and hypotheses and working models proposed for future studies.
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Affiliation(s)
- Suzanne M Moenter
- Departments of Internal Medicine and Cell Biology, University of Virginia, PO BOX 800578, Charlottesville, VA 22908, USA.
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Nunemaker CS, DeFazio RA, Moenter SM. A targeted extracellular approach for recording long-term firing patterns of excitable cells: a practical guide. Biol Proced Online 2003; 5:53-62. [PMID: 12734556 PMCID: PMC150391 DOI: 10.1251/bpo46] [Citation(s) in RCA: 84] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/17/2002] [Revised: 01/23/2003] [Accepted: 02/05/2003] [Indexed: 11/29/2022] Open
Abstract
Excitable cells in many endocrine and neuronal systems display rhythms with periodicities on the order of many minutes. To observe firing patterns that represent the output of these rhythms requires a recording technique that can monitor electrophysiological activity for several hours without affecting cell behavior. A targeted extracellular approach (also known as loose-patch) accomplishes this objective. Because low resistance seals (<20 MOmega) do not influence the cell membrane and because the normal intracellular milieu is maintained, this approach is the least invasive method for monitoring the endogenous electrical activity of single cells. In this report, we detail our use of this technique to record the firing patterns of gonadotropin-releasing hormone (GnRH) neurons in brain slices continuously for several hours.
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Affiliation(s)
- Craig S. Nunemaker
- Departments of Internal Medicine and Cell Biology, and the NSF Center for Biological Timing, University of Virginia. P.O. Box 800578, Jefferson Park Avenue, University of Virginia, Charlottesville, VA 22908. USA
| | - R. Anthony DeFazio
- Departments of Internal Medicine and Cell Biology, and the NSF Center for Biological Timing, University of Virginia. P.O. Box 800578, Jefferson Park Avenue, University of Virginia, Charlottesville, VA 22908. USA
| | - Suzanne M. Moenter
- Departments of Internal Medicine and Cell Biology, and the NSF Center for Biological Timing, University of Virginia. P.O. Box 800578, Jefferson Park Avenue, University of Virginia, Charlottesville, VA 22908. USA
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Terasawa E, Richter TA, Keen KL. A role for non-neuronal cells in synchronization of intracellular calcium oscillations in primate LHRH neurons. PROGRESS IN BRAIN RESEARCH 2003; 141:283-91. [PMID: 12508575 DOI: 10.1016/s0079-6123(02)41099-0] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/28/2023]
Affiliation(s)
- Ei Terasawa
- Wisconsin National Primate Research Center, 1223 Capitol Court, Madison, WI 53715-1299, USA.
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Richter TA, Keen KL, Terasawa E. Synchronization of Ca(2+) oscillations among primate LHRH neurons and nonneuronal cells in vitro. J Neurophysiol 2002; 88:1559-67. [PMID: 12205175 DOI: 10.1152/jn.2002.88.3.1559] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Periodic release of luteinizing hormone-releasing hormone (LHRH) from the hypothalamus is essential for normal reproductive function. Pulsatile LHRH release appears to result from the synchronous activity of LHRH neurons. However, how the activity of these neurons is synchronized to release LHRH peptide in a pulsatile manner is unclear. Because there is little evidence of physical coupling among LHRH neurons in the hypothalamus, we hypothesized that the activity of LHRH neurons might be coordinated by indirect intercellular communication via intermediary (nonneural) cells rather than direct interneural coupling. In this study, we used an in vitro preparation of LHRH neurons derived from the olfactory placode of monkey embryos to assess whether nonneuronal cells, play a role in coordinating LHRH neuronal activity. We found that cultured LHRH neurons and nonneuronal cells both exhibit spontaneous oscillations in the concentration of intracellular Ca(2+) ([Ca(2+)](i)) at similar frequencies. Moreover, [Ca(2+)](i) oscillations in both types of cell were periodically synchronized. Synchronized [Ca(2+)](i) oscillations spread as intercellular Ca(2+) waves across fields of cells that included LHRH neurons and nonneuronal cells, although waves spread at a higher velocity among LHRH neurons. These results suggest that LHRH neurons and nonneuronal cells are functionally integrated and that nonneuronal cells could be involved in synchronizing the activity of the LHRH neurosecretory network.
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Affiliation(s)
- T A Richter
- Wisconsin National Primate Research Center, University of Wisconsin, Madison, Wisconsin 53715-1261, USA
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Nunemaker CS, DeFazio RA, Moenter SM. Estradiol-sensitive afferents modulate long-term episodic firing patterns of GnRH neurons. Endocrinology 2002; 143:2284-92. [PMID: 12021193 DOI: 10.1210/endo.143.6.8869] [Citation(s) in RCA: 78] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/19/2022]
Abstract
GnRH neurons comprise the final common pathway of an estrogen-sensitive pattern generator controlling fertility. To determine estradiol effects on GnRH neuron firing patterns, adult transgenic mice were ovariectomized (OVX), and half were treated with estradiol (OVX+E). One week later targeted single-unit extracellular recordings were made from GnRH neurons identified by green fluorescent protein expression. Estradiol markedly affected GnRH neuron firing patterns, increasing the percentage and duration of time these cells were quiescent (< or = 1 action current/min). Estradiol increased the interval between episodes of increased firing rate determined by Cluster analysis of recordings more than 45 min (OVX+E 38.8 +/- 7.2 min, OVX 16.7 +/- 2.1 min, n = 6 each). Possible mechanisms of estradiol modulation were examined by simultaneously blocking ionotropic secretion of gamma-aminobutyric acid and glutamatergic receptors. This treatment had no effect on cells from OVX mice (n = 10), indicating episodic firing of GnRH neurons is not driven by activation of these receptors. Receptor blockade eliminated estradiol effects on GnRH neurons in the midventral preoptic area (n = 7) but not elsewhere (n = 7). Individual GnRH neurons thus display episodic firing patterns at intervals previously reported for secretory pulses. Estradiol modulates episode frequency to exert feedback control; in a substantial subset of GnRH neurons, estradiol feedback is enforced via GABAergic and/or glutamatergic afferents.
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Affiliation(s)
- Craig S Nunemaker
- Department of Internal Medicine and National Science Foundation Center for Biological Timing, University of Virginia, Charlottesville, Virginia 22908, USA
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Episodic bursting activity and response to excitatory amino acids in acutely dissociated gonadotropin-releasing hormone neurons genetically targeted with green fluorescent protein. J Neurosci 2002. [PMID: 11896170 DOI: 10.1523/jneurosci.22-06-02313.2002] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022] Open
Abstract
The gonadotropin-releasing hormone (GnRH) system, considered to be the final common pathway for the control of reproduction, has been difficult to study because of a lack of distinguishing characteristics and the scattered distribution of neurons. The development of a transgenic mouse in which the GnRH promoter drives expression of enhanced green fluorescent protein (EGFP) has provided the opportunity to perform electrophysiological studies of GnRH neurons. In this study, neurons were dissociated from brain slices prepared from prepubertal female GnRH-EGFP mice. Both current- and voltage-clamp recordings were obtained from acutely dissociated GnRH neurons identified on the basis of EGFP expression. Most isolated GnRH-EGFP neurons fired spontaneous action potentials (recorded in cell-attached or whole-cell mode) that typically consisted of brief bursts (2-20 Hz) separated by 1-10 sec. At more negative resting potentials, GnRH-EGFP neurons exhibited oscillations in membrane potential, which could lead to bursting episodes lasting from seconds to minutes. These bursting episodes were often separated by minutes of inactivity. Rapid application of glutamate or NMDA increased firing activity in all neurons and usually generated small inward currents (<15 pA), although larger currents were evoked in the remaining neurons. Both AMPA and NMDA receptors mediated the glutamate-evoked inward currents. These results suggest that isolated GnRH-EGFP neurons from juvenile mice can generate episodes of repetitive burst discharges that may underlie the pulsatile secretion of GnRH, and glutamatergic inputs may contribute to the activation of endogenous bursts.
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