scholarly journals Norepinephrine Suppresses Gonadotropin-Releasing Hormone Neuron Excitability in the Adult Mouse

Endocrinology ◽  
2007 ◽  
Vol 149 (3) ◽  
pp. 1129-1135 ◽  
Author(s):  
Seong-Kyu Han ◽  
Allan E. Herbison
Keyword(s):  
Adrenergic Receptors ◽  
Adult Mouse ◽  
Fluorescent Protein ◽  
Receptor Activation ◽  
Electrical Excitability ◽  
Gonadotropin Secretion ◽  
Membrane Hyperpolarization ◽  
Gnrh Neurons ◽  
Green Fluorescent ◽  
Β Adrenergic Receptors

Norepinephrine (NE) is considered to exert an important modulatory influence upon the activity of GnRH neurons. In the present study, we used a transgenic GnRH-green fluorescent protein mouse model to examine the effects of NE on the electrical excitability of GnRH neurons in male and female mice. Gramicidin-perforated patch recordings demonstrated that NE (10–100 μm) exerted a robust membrane hyperpolarization, with associated suppression of firing, in more than 85% of male prepubertal and adult GnRH neurons (n = 25). The same hyperpolarizing action was observed in female GnRH neurons from diestrous (91%, n = 11), proestrous (50%, n = 14), estrous (77%, n = 13), and ovariectomized (82%, n = 11) mice. A subpopulation (<10%) of silent GnRH neurons in all groups responded to NE with hyperpolarization followed by the initiation of firing upon NE washout. The hyperpolarizing actions of NE were mimicked by α1-adrenergic (phenylephrine) and β-adrenergic (isoproterenol) receptor agonists, but α2 receptor activation (guanabenz) had no effect. Approximately 75% of the NE-evoked hyperpolarization was blocked by the α1 receptor antagonist prazosin, and 75% of GnRH neurons responded to both phenylephrine and isoproterenol. These findings indicate that NE acts through both α1- and β-adrenergic receptors located on the soma/dendrites of GnRH neurons to directly suppress their excitability throughout the estrous cycle and after ovariectomy. These data force a reanalysis of existing models explaining the effects of NE on gonadotropin secretion.

scholarly journals RFamide-Related Peptide-3, a Mammalian Gonadotropin-Inhibitory Hormone Ortholog, Regulates Gonadotropin-Releasing Hormone Neuron Firing in the Mouse

Endocrinology ◽  
2009 ◽  
Vol 150 (6) ◽  
pp. 2799-2804 ◽  
Author(s):  
Eric Ducret ◽  
Greg M. Anderson ◽  
Allan E. Herbison
Keyword(s):  
Firing Rate ◽  
Fluorescent Protein ◽  
Suppressive Effect ◽  
Small Population ◽  
Neuron Activity ◽  
Gonadotropin Secretion ◽  
Gnrh Neurons ◽  
Gonadotropin Inhibitory Hormone ◽  
Green Fluorescent ◽  
Prolactin Releasing Peptide

The recent discovery that an RFamide termed gonadotropin-inhibitory hormone is likely to be a hypophysiotrophic gonadotropin release-inhibiting hormone in birds has generated interest into the role of LPXRFamide neuropeptides in the control of gonadotropin secretion in mammals. Recent immunocytochemical studies in birds and mammals have suggested that neurons expressing the mammalian LPXRFamides, RFamide-related peptides (RFRPs) 1 and 3, may innervate and regulate GnRH neurons directly. We used cell-attached electrophysiology in adult male and female GnRH-green fluorescent protein-tagged neurons to examine whether RFRP-3 modulated the electrical excitability of GnRH neurons. RFRP-3 was found to exhibit rapid and repeatable inhibitory effects on the firing rate of 41% of GnRH neurons. A small population of GnRH neurons (12%) increased their firing rate in response to RFRP-3, and the remainder was unaffected. No difference was detected in the RFRP-3 responses of GnRH neurons from male, diestrous, or proestrus female mice. The suppressive effect of RFRP-3 was maintained when amino acid transmission was blocked, suggesting a possible direct effect of RFRP-3 upon GnRH neurons. To evaluate the effects of other RFamide neuropeptides on GnRH neurons, we tested the actions of prolactin-releasing peptide-20 and -31. Neither compounds altered the firing rate of GnRH neurons. These studies demonstrate that RFRP-3 has a likely direct suppressive action on the excitability of GnRH neurons, indicating a role for RFRPs in the regulation of gonadotropin secretion in mammals through modulation of GnRH neuron activity.

scholarly journals An inhibitory circuit from brainstem to GnRH neurons in male mice: a new role for the RFRP receptor

Endocrinology ◽  
2021 ◽  
Author(s):  
Stephanie Constantin ◽  
Katherine Pizano ◽  
Kaya Matson ◽  
Yufei Shan ◽  
Daniel Reynolds ◽  
...  
Keyword(s):  
Neuropeptide Y ◽  
Fluorescent Protein ◽  
Nucleus Tractus Solitarius ◽  
Brain Slices ◽  
Adult Brain ◽  
Energy Deficit ◽  
Gonadotropin Secretion ◽  
Gnrh Neurons ◽  
Gonadotropin Inhibitory Hormone ◽  
Green Fluorescent

Abstract RFamide-related peptides (RFRPs, mammalian orthologs of gonadotropin-inhibitory hormone) convey circadian, seasonal and social cues to the reproductive system. They regulate gonadotropin secretion by modulating gonadotropin-releasing hormone (GnRH) neurons via the RFRP receptor. Mice lacking this receptor are fertile but exhibit abnormal gonadotropin responses during metabolic challenges such as acute fasting, when the normal drop in gonadotropin levels is delayed. Although it is known that these food intake signals to the reproductive circuit originate in the nucleus tractus solitarius (NTS) in the brainstem, the phenotype of the neurons conveying the signal remains unknown. Given that neuropeptide FF (NPFF), another RFamide peptide, resides in the NTS and can bind to the RFRP receptor, we hypothesized that NPFF may regulate GnRH neurons. To address this question, we used a combination of techniques: cell-attached electrophysiology on GnRH-driven green fluorescent protein-tagged neurons in acute brain slices; calcium imaging on cultured GnRH neurons; and immunostaining on adult brain tissue. We found 1) NPFF inhibits GnRH neuron excitability via the RFRP receptor and its canonical signaling pathway (Gi/o protein and G protein-coupled inwardly-rectifying potassium channels), 2) NPFF-like fibers in the vicinity of GnRH neurons coexpress neuropeptide Y, 3) the majority of NPFF-like cell bodies in the NTS also coexpress neuropeptide Y, and 4) acute fasting increased NPFF-like immunoreactivity in the NTS. Together these data indicate that NPFF neurons within the NTS inhibit GnRH neurons, and thus reproduction, during fasting but prior to the energy deficit.

scholarly journals Microvascular Sprouting, Extension, and Creation of New Capillary Connections with Adaptation of the Neighboring Astrocytes in Adult Mouse Cortex under Chronic Hypoxia

2013 ◽  
Vol 34 (2) ◽  
pp. 325-331 ◽  
Author(s):  
Kazuto Masamoto ◽  
Hiroyuki Takuwa ◽  
Chie Seki ◽  
Junko Taniguchi ◽  
Yoshiaki Itoh ◽  
...  
Keyword(s):  
Adult Mouse ◽  
Fluorescent Protein ◽  
Vascular Endothelial Cells ◽  
Three Dimensional ◽  
Vascular Endothelial ◽  
Two Photon Microscopy ◽  
Two Photon ◽  
Mouse Cortex ◽  
Hypoxia Adaptation ◽  
Green Fluorescent

The present study aimed to determine the spatiotemporal dynamics of microvascular and astrocytic adaptation during hypoxia-induced cerebral angiogenesis. Adult C57BL/6J and Tie2-green fluorescent protein (GFP) mice with vascular endothelial cells expressing GFP were exposed to normobaric hypoxia for 3 weeks, whereas the three-dimensional microvessels and astrocytes were imaged repeatedly using two-photon microscopy. After 7 to14 days of hypoxia, a vessel sprout appeared from the capillaries with a bump-like head shape (mean diameter 14  μm), and stagnant blood cells were seen inside the sprout. However, no detectable changes in the astrocyte morphology were observed for this early phase of the hypoxia adaptation. More than 50% of the sprouts emerged from capillaries 60  μm away from the center penetrating arteries, which indicates that the capillary distant from the penetrating arteries is a favored site for sprouting. After 14 to 21 days of hypoxia, the sprouting vessels created a new connection with an existing capillary. In this phase, the shape of the new vessel and its blood flow were normalized, and the outside of the vessels were wrapped with numerous processes from the neighboring astrocytes. The findings indicate that hypoxia-induced cerebral angiogenesis provokes the adaptation of neighboring astrocytes, which may stabilize the blood–brain barrier in immature vessels.

scholarly journals Suppression of Basal Spontaneous Gonadotropin-Releasing Hormone Neuronal Activity during Lactation: Role of Inhibitory Effects of Neuropeptide Y

Endocrinology ◽  
2008 ◽  
Vol 150 (1) ◽  
pp. 333-340 ◽  
Author(s):  
Jing Xu ◽  
Melissa A. Kirigiti ◽  
Michael A. Cowley ◽  
Kevin L. Grove ◽  
M. Susan Smith
Keyword(s):  
Neuropeptide Y ◽  
Neuronal Activity ◽  
Fluorescent Protein ◽  
Resting Membrane Potential ◽  
Inhibitory Effects ◽  
Gnrh Neurons ◽  
Cell Current ◽  
Green Fluorescent ◽  
Hypothalamic Slices

Increased neuropeptide Y (NPY) activity drives the chronic hyperphagia of lactation and may contribute to the suppression of GnRH activity. The majority of GnRH neurons are contacted by NPY fibers, and GnRH cells express NPY Y5 receptor (Y5R). Therefore, NPY provides a neurocircuitry for information about food intake/energy balance to be directly transmitted to GnRH neurons. To investigate the effects of lactation on GnRH neuronal activity, hypothalamic slices were prepared from green fluorescent protein-GnRH transgenic rats. Extracellular loose-patch recordings determined basal GnRH neuronal activity from slices of ovariectomized control and lactating rats. Compared with controls, hypothalamic slices from lactating rats had double the number of quiescent GnRH neurons (14.51 ± 2.86 vs. 7.04 ± 2.84%) and significantly lower firing rates of active GnRH neurons (0.25 ± 0.02 vs. 0.37 ± 0.03 Hz). To study the NPY-postsynaptic Y5R system, whole-cell current-clamp recordings were performed in hypothalamic slices from control rats to examine NPY/Y5R antagonist effects on GnRH neuronal resting membrane potential. Under tetrodotoxin treatment, NPY hyperpolarized GnRH neurons from −56.7 ± 1.94 to −62.1 ± 1.83 mV; NPY’s effects were blocked by Y5R antagonist. To determine whether increased endogenous NPY tone contributes to GnRH neuronal suppression during lactation, hypothalamic slices were treated with Y5R antagonist. A significantly greater percentage of GnRH cells were activated in slices from lactating rats (52%) compared with controls (28%). These results suggest that: 1) basal GnRH neuronal activity is suppressed during lactation; 2) NPY can hyperpolarize GnRH neurons via postsynaptic Y5R; and 3) increased inhibitory NPY tone during lactation is a component of the mechanisms responsible for suppression of GnRH neuronal activity. Neuropeptide Y (NPY) directly hyperpolarizes GnRH neurons via postsynaptic NPY Y5 receptor. Increased inhibitory NPY tone during lactation is an important component of the suppression of GnRH neuronal activity.

scholarly journals Retrograde Transport of Transcription Factor NF-κB in Living Neurons

2000 ◽  
Vol 276 (15) ◽  
pp. 11821-11829 ◽  
Author(s):  
Henning Wellmann ◽  
Barbara Kaltschmidt ◽  
Christian Kaltschmidt
Keyword(s):  
Transcription Factor ◽  
Green Fluorescent Protein ◽  
Fluorescent Protein ◽  
Retrograde Transport ◽  
Receptor Activation ◽  
Transcriptional Changes ◽  
Localization Signal ◽  
Green Fluorescent ◽  
Living Neurons

The mechanism by which signals such as those produced by glutamate are transferred to the nucleus may involve direct transport of an activated transcription factor to trigger long-term transcriptional changes. Ionotropic glutamate receptor activation or depolarization activates transcription factor NF-κB and leads to translocation of NF-κB from the cytoplasm to the nucleus. We investigated the dynamics of NF-κB translocation in living neurons by tracing the NF-κB subunit RelA (p65) with jellyfish green fluorescent protein. We found that green fluorescent protein-RelA was located in either the nucleus or cytoplasm and neurites, depending on the coexpression of the cognate inhibitor of NF-κB, IκB-α. Stimulation with glutamate, kainate, or potassium chloride resulted in a redistribution of NF-κB from neurites to the nucleus. This transport depended on an intact nuclear localization signal on RelA. Thus, in addition to its role as a transcription factor, NF-κB may be a signal transducer, transmitting transient glutamatergic signals from distant sites to the nucleus.

scholarly journals Small-Conductance Calcium-Activated Potassium Channels Control Excitability and Firing Dynamics in Gonadotropin-Releasing Hormone (GnRH) Neurons

Endocrinology ◽  
2008 ◽  
Vol 149 (7) ◽  
pp. 3598-3604 ◽  
Author(s):  
Xinhuai Liu ◽  
Allan E. Herbison
Keyword(s):  
Fluorescent Protein ◽  
Current Injection ◽  
Sk Channels ◽  
Cellular Mechanisms ◽  
Burst Frequency ◽  
Single Action ◽  
Sk Channel ◽  
Gnrh Neurons ◽  
Green Fluorescent ◽  
Small Conductance

The cellular mechanisms determining the firing patterns of GnRH neurons are presently under intense investigation. In this study, we used GnRH-green fluorescent protein transgenic mice and perforated-patch electrophysiology to examine the role of small conductance calcium-activated potassium (SK) channels in determining the electrical excitability and burst-firing characteristics of adult GnRH neurons. After establishing an appropriate protocol for examining the afterhyperpolarization potential (AHP) currents in GnRH neurons, the highly selective SK channel blocker apamin was used to demonstrate that all GnRH neurons express functional SK channels (35.7 ± 2.7 pA, mean decay time constant = 2167 msec, apamin IC50 = 9.6 nm) and that this channel underlies approximately 90% of the AHP in these cells. Current-clamp experiments showed that apamin-sensitive SK channels were tonically active in the majority (74%) of GnRH neurons, with apamin (100 nm) administration resulting in a mean 6.9 ± 0.5 mV membrane depolarization. Apamin also elevated the firing rate of GnRH neurons, including increased burst frequency and duration in spontaneously bursting cells as well as the ability of GnRH neurons to fire action potentials in response to current injection. In GnRH neurons activated by current injection, apamin significantly enhanced the amplitude of the afterdepolarization potential after a single action potential and eliminated spike frequency adaptation. Together, these studies show that apamin-sensitive SK channels play a key role in restraining GnRH neuron excitability. Through direct modulation of the AHP and indirect actions on the afterdepolarization potential, the SK channel exerts a powerful tonic influence upon the firing dynamics of GnRH neurons.

scholarly journals Receptor activation and 2 distinct COOH-terminal motifs control G-CSF receptor distribution and internalization kinetics

Blood ◽  
2004 ◽  
Vol 103 (2) ◽  
pp. 571-579 ◽  
Author(s):  
Lambertus H. J. Aarts ◽  
Onno Roovers ◽  
Alister C. Ward ◽  
Ivo P. Touw
Keyword(s):  
Fluorescent Protein ◽  
Surface Expression ◽  
Receptor Activation ◽  
Cell Surface Expression ◽  
Serine Threonine Kinase ◽  
Late Endosomes ◽  
Dileucine Motif ◽  
Internalization Kinetics ◽  
Green Fluorescent ◽  
Kinetics Of

Abstract We have studied the intracellular distribution and internalization kinetics of the granulocyte colony-stimulating factor receptor (G-CSF-R) in living cells using fusion constructs of wild-type or mutant G-CSF-R and enhanced green fluorescent protein (EGFP). Under steady-state conditions the G-CSF-R localized predominantly to the Golgi apparatus, late endosomes, and lysosomes, with only low expression on the plasma membrane, resulting from spontaneous internalization. Internalization of the G-CSF-R was significantly accelerated by addition of G-CSF. This ligand-induced switch from slow to rapid internalization required the presence of G-CSF-R residue Trp650, previously shown to be essential for its signaling ability. Both spontaneous and ligand-induced internalization depended on 2 distinct amino acid stretches in the G-CSF-R COOH-terminus: 749-755, containing a dileucine internalization motif, and 756-769. Mutation of Ser749 at position –4 of the dileucine motif to Ala significantly reduced the rate of ligand-induced internalization. In contrast, mutation of Ser749 did not affect spontaneous G-CSF-R internalization, suggesting the involvement of a serine-threonine kinase specifically in ligand-accelerated internalization of the G-CSF-R. COOH-terminal truncation mutants of G-CSF-R, found in severe congenital neutropenia, lack the internalization motifs and were completely defective in both spontaneous and ligand-induced internalization. As a result, these mutants showed constitutively high cell-surface expression.

scholarly journals Dose-Dependent Switch in Response of Gonadotropin-Releasing Hormone (GnRH) Neurons to GnRH Mediated through the Type I GnRH Receptor

Endocrinology ◽  
2004 ◽  
Vol 145 (2) ◽  
pp. 728-735 ◽  
Author(s):  
Chun Xu ◽  
Xu-Zhi Xu ◽  
Craig S. Nunemaker ◽  
Suzanne M. Moenter
Keyword(s):  
Firing Rate ◽  
Fluorescent Protein ◽  
Brain Slices ◽  
Dose Dependence ◽  
Gnrh Receptor ◽  
Neuron Activity ◽  
Type I ◽  
Pulsatile Release ◽  
Gnrh Neurons ◽  
Green Fluorescent

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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