Indirect suppression of pulsatile LH secretion by CRH neurons in the female mouse

Endocrinology ◽  
2020 ◽  
Author(s):  
Siew Hoong Yip ◽  
Xinhuai Liu ◽  
Sabine Hessler ◽  
Isaiah Cheong ◽  
Robert Porteous ◽  
...  
Keyword(s):  
Female Mouse ◽  
Pulse Generator ◽  
Acute Stress ◽  
Brain Slices ◽  
Gnrh Neuron ◽  
Ovariectomized Mice ◽  
Electrophysiological Recordings ◽  
Gnrh Neurons ◽  
Gnrh Release ◽  
Lh Secretion

Abstract Acute stress is a potent suppressor of pulsatile LH secretion but the mechanisms through which corticotrophin-releasing hormone (CRH) neurons inhibit GnRH release remain unclear. The activation of paraventricular nucleus (PVN) CRH neurons with Cre-dependent hM3Dq in Crh-Cre female mice resulted in the robust suppression of pulsatile LH secretion. Channelrhodopsin (ChR2)-assisted circuit mapping revealed that PVN CRH neuron projections existed around kisspeptin neurons in the arcuate nucleus (ARN) although many more fibers made close appositions with GnRH neuron distal dendrons in the ventral ARN. Acutely-prepared brain slice electrophysiology experiments in GnRH-GFP mice showed a dose-dependent (30 and 300 nM CRH) activation of firing in ~20% of GnRH neurons in both intact diestrous and ovariectomized mice with inhibitory effects being uncommon (<8%). Confocal GCaMP6 imaging of GnRH neuron distal dendrons in acute para-horizontal brain slices from GnRH-Cre mice injected with Cre-dependent GCaMP6s AAVs demonstrated no effects of 30-300 nM CRH on GnRH neuron dendron calcium concentrations. Electrophysiological recordings of ARN kisspeptin neurons in Crh-Cre,Kiss1-GFP mice revealed no effects of 30 -300 nM CRH on basal or neurokinin B-stimulated firing rate. Similarly, the optogenetic activation (2-20 Hz) of CRH nerve terminals in the ARN of Crh-Cre,Kiss1-GFP mice injected with Cre-dependent ChR2 had no effect on kisspeptin neuron firing. Together, these studies demonstrate that PVN CRH neurons potently suppress LH pulsatility but do not exert direct inhibitory control over GnRH neurons, at their cell body or dendron, or the ARN kisspeptin neuron pulse generator in the female mouse.

Innervation of GnRH Neuron Distal Projections and Activation by Kisspeptin in a New GnRH-Cre Rat Model

Endocrinology ◽  
2020 ◽  
Vol 162 (1) ◽  
Author(s):  
Siew Hoong Yip ◽  
Pauline Campos ◽  
Xinhuai Liu ◽  
Robert Porteous ◽  
Allan E Herbison
Keyword(s):  
Median Eminence ◽  
Pulse Generator ◽  
Ectopic Expression ◽  
Brain Slices ◽  
Gnrh Neuron ◽  
External Zone ◽  
Pulsatile Gnrh ◽  
Gnrh Neurons ◽  
Gnrh Release ◽  
Presynaptic Nerve Terminals

Abstract The neural mechanisms generating pulsatile GnRH release from the median eminence (ME) remain unclear. Studies undertaken in the mouse demonstrate that GnRH neurons extend projections to the ME that have properties of both dendrites and axons, termed “dendrons,” and that the kisspeptin neuron pulse generator targets these distal dendrons to drive pulsatile GnRH secretion. It presently remains unknown whether the GnRH neuron dendron exists in other species. We report here the generation of a knock-in Gnrh1-Ires-Cre rat line with near-perfect targeting of Cre recombinase to the GnRH neuronal phenotype. More than 90% of adult male and female GnRH neurons express Cre with no ectopic expression. Adeno-associated viruses were used in adult female Gnrh1-Ires-Cre rats to target mCherry or GCAMP6 to rostral preoptic area GnRH neurons. The mCherry tracer revealed the known unipolar and bipolar morphology of GnRH neurons and their principal projection pathways to the external zone of the ME. Synaptophysin-labeling of presynaptic nerve terminals revealed that GnRH neuron distal projections received numerous close appositions as they passed through the arcuate nucleus and into the median eminence. Confocal GCaMP6 imaging in acute horizontal brain slices demonstrated that GnRH neuron distal projections lateral to the median eminence were activated by kisspeptin. These studies indicate the presence of a dendron-like arrangement in the rat with GnRH neuron distal projections receiving synaptic input and responding to kisspeptin.

scholarly journals Vasoactive Intestinal Polypeptide Can Excite Gonadotropin-Releasing Hormone Neurons in a Manner Dependent on Estradiol and Gated by Time of Day

Endocrinology ◽  
2008 ◽  
Vol 149 (6) ◽  
pp. 3130-3136 ◽  
Author(s):  
Catherine A. Christian ◽  
Suzanne M. Moenter
Keyword(s):  
Vasoactive Intestinal Polypeptide ◽  
Brain Slices ◽  
Time Of Day ◽  
Gnrh Neuron ◽  
Suprachiasmatic Nuclei ◽  
Neuron Firing ◽  
Neuron Response ◽  
Gnrh Neurons ◽  
Gnrh Release ◽  
Intestinal Polypeptide

A surge of GnRH release signals the LH surge that triggers ovulation. The GnRH surge is dependent on a switch in estradiol feedback from negative to positive and, in rodents, a daily neural signal, likely from the suprachiasmatic nuclei. Vasoactive intestinal polypeptide (VIP) may be involved in suprachiasmatic nuclei-GnRH neuron communication. Here we assessed the effects of acute VIP (5 min treatment) on GnRH neuron function using targeted extracellular recordings of firing activity of GnRH neurons in brain slices. We examined the effect of VIP on firing rate at different times of day using an established ovariectomized, estradiol-treated (OVX+E) mouse model that exhibits daily LH surges timed to the late afternoon. Cells from OVX animals (no estradiol) did not respond to VIP, regardless of time of day. With estradiol, the effect of VIP on GnRH neurons was dependent on the time of recording. During negative feedback, OVX+E cells did not respond. VIP increased firing in cells recorded during surge onset, but this excitatory response was reduced at surge peak. Acute treatment of OVX+E cells during surge peak with a VIP receptor antagonist decreased GnRH neuron firing. This suggests endogenous VIP may both increase GnRH neuron firing during the surge and occlude response to exogenous VIP. These data provide functional evidence for VIP effects on GnRH neurons and indicate that both estradiol and time of day gate the GnRH neuron response to this peptide. VIP may provide an excitatory signal from the circadian clock that helps time the GnRH surge.

scholarly journals Both Estrogen and Androgen Modify the Response to Activation of Neurokinin-3 and κ-Opioid Receptors in Arcuate Kisspeptin Neurons From Male Mice

Endocrinology ◽  
2015 ◽  
Vol 157 (2) ◽  
pp. 752-763 ◽  
Author(s):  
Kristen A. Ruka ◽  
Laura L. Burger ◽  
Suzanne M. Moenter
Keyword(s):  
Estrogen Receptor ◽  
Firing Pattern ◽  
Pulse Generator ◽  
Brain Slices ◽  
Gonadal Steroids ◽  
Gnrh Neuron ◽  
Male Mice ◽  
Neurokinin B ◽  
Neuron Firing ◽  
Kndy Neurons

Abstract Gonadal steroids regulate the pattern of GnRH secretion. Arcuate kisspeptin (kisspeptin, neurokinin B, and dynorphin [KNDy]) neurons may convey steroid feedback to GnRH neurons. KNDy neurons increase action potential firing upon the activation of neurokinin B receptors (neurokinin-3 receptor [NK3R]) and decrease firing upon the activation of dynorphin receptors (κ-opioid receptor [KOR]). In KNDy neurons from intact vs castrated male mice, NK3R-mediated stimulation is attenuated and KOR-mediated inhibition enhanced, suggesting gonadal secretions are involved. Estradiol suppresses spontaneous GnRH neuron firing in male mice, but the mediators of the effects on firing in KNDy neurons are unknown. We hypothesized the same gonadal steroids affecting GnRH firing pattern would regulate KNDy neuron response to NK3R and KOR agonists. To test this possibility, extracellular recordings were made from KNDy neurons in brain slices from intact, untreated castrated or castrated adult male mice treated in vivo with steroid receptor agonists. As observed previously, the stimulation of KNDy neurons by the NK3R agonist senktide was attenuated in intact vs castrated mice and suppression by dynorphin was enhanced. In contrast to observations of steroid effects on the GnRH neuron firing pattern, both estradiol and DHT suppressed senktide-induced KNDy neuron firing and enhanced the inhibition caused by dynorphin. An estrogen receptor-α agonist but not an estrogen receptor-β agonist mimicked the effects of estradiol on NK3R activation. These observations suggest the steroid modulation of responses to activation of NK3R and KOR as mechanisms for negative feedback in KNDy neurons and support the contribution of these neurons to steroid-sensitive elements of a GnRH pulse generator.

scholarly journals Kisspeptin Increases γ-Aminobutyric Acidergic and Glutamatergic Transmission Directly to Gonadotropin-Releasing Hormone Neurons in an Estradiol-Dependent Manner

Endocrinology ◽  
2010 ◽  
Vol 151 (1) ◽  
pp. 291-300 ◽  
Author(s):  
Justyna Pielecka-Fortuna ◽  
Suzanne M. Moenter
Keyword(s):  
Negative Feedback ◽  
Positive Feedback ◽  
Brain Slices ◽  
Cell Voltage ◽  
Dependent Manner ◽  
Glutamatergic Transmission ◽  
Neuron Response ◽  
Gnrh Neurons ◽  
Gnrh Release ◽  
In Cells

Abstract GnRH neurons are the final central pathway controlling fertility. Kisspeptin potently activates GnRH release via G protein-coupled receptor 54 (GPR54). GnRH neurons express GPR54, and kisspeptin can act directly; however, GPR54 is broadly expressed, suggesting indirect actions are possible. Transsynaptic mechanisms are involved in estradiol-induced potentiation of GnRH neuron response to kisspeptin. To investigate these mechanisms, separate whole-cell voltage-clamp recordings were performed of γ-aminobutyric acid (GABA)-ergic and glutamatergic transmission to GnRH neurons in brain slices before and during kisspeptin treatment. To determine whether estradiol alters the effect of kisspeptin on synaptic transmission, mice were ovariectomized and either left with no further treatment (OVX) or treated with estradiol implants (OVX+E). Cells were first studied in the morning when estradiol exerts negative feedback. Kisspeptin increased frequency and amplitude of GABAergic postsynaptic currents (PSCs) in GnRH neurons from OVX+E mice. Blocking action potentials eliminated the effect on frequency, indicating presynaptic actions. Amplitude changes were due to postsynaptic actions. Kisspeptin also increased frequency of glutamatergic excitatory PSCs in cells from OVX+E animals. Kisspeptin did not affect either GABAergic or glutamatergic transmission to GnRH neurons in cells from OVX mice, indicating effects on transmission are estradiol dependent. In contrast to stimulatory effects on GABAergic PSC frequency during negative feedback, kisspeptin had no effect during positive feedback. These data suggest estradiol enables kisspeptin-mediated increases in GABA and glutamate transmission to GnRH neurons. Furthermore, the occlusion of the response during positive feedback implies one consequence of estradiol positive feedback is an increase in transmission to GnRH neurons mediated by endogenous kisspeptin.

Can obestatin modulate the GnRH neurons activity?

2016 ◽  
Vol 62 (5) ◽  
pp. 49-50 ◽  
Author(s):  
Michal Szlis ◽  
Jolanta Polkowska ◽  
Anna Wójcik-Gładysz
Keyword(s):  
Gene Expression ◽  
Central Nervous System ◽  
Nervous System ◽  
Pulse Generator ◽  
Receptor Gene ◽  
Secretory Activity ◽  
Gnrh Neurons ◽  
Gnrh Release ◽  
The Central Nervous System ◽  
Anorexigenic Peptide

Obestatin, an anorexigenic peptide acting at the central nervous system and on the periperial level, can co-create neuroendocrine network, which modulate the gonadotrophic axis activity. The aim of this study was to investigate the role of intracerebroventricular obestatin infusion on the activity of the gonadoliberine (GnRH) neurons activity.The experiment was performed on peripubertal Polish Merino sheep (n=24). Animals were divided into 2 groups: control (Ringer-Lock solution infusions; n=12) and experimental (obestatin infusion, 25μl/120μl/h; n=12). Infusions were performed over three consecutive days; blood samples were collected on day 0 and day 3. After the experiment, the animals were slaughtered, and the chosen brain tissue was preserved for IHC and Real Time RT-qPCR analysis.It was also shown that exogenous obestatin changes the selected gene expression of GnRH pulse generator, decreases the secretory activity of GnRH neurons, resulting from the inhibition of GnRH release from median eminence terminal nerves, and also decreases the GnRH receptor gene expression in pituitary. On the basis of the obtained results it can be concluded that obestatin may be involved in the modulation of reproduction processes in animals at the level of the central nervous system. However, the mechanism of its action requires further research, especially identifying the obestatin receptor itself.

scholarly journals The Gonadotropin-Releasing Hormone Pulse Generator

Endocrinology ◽  
2018 ◽  
Vol 159 (11) ◽  
pp. 3723-3736 ◽  
Author(s):  
Allan E Herbison
Keyword(s):  
Arcuate Nucleus ◽  
Pulse Generator ◽  
Pulse Generation ◽  
Sufficient Evidence ◽  
Gnrh Neuron ◽  
Lh Pulsatility ◽  
Intrinsic Mechanism ◽  
Lh Release ◽  
Lh Secretion ◽  
Present Understanding

Abstract The pulsatile release of GnRH and LH secretion is essential for fertility in all mammals. Pulses of LH occur approximately every hour in follicular-phase females and every 2 to 3 hours in luteal-phase females and males. Many studies over the last 50 years have sought to identify the nature and mechanism of the “GnRH pulse generator” responsible for pulsatile LH release. This review examines the characteristics of pulsatile hormone release and summarizes investigations that have led to our present understanding of the GnRH pulse generator. There is presently little compelling evidence for an intrinsic mechanism of pulse generation involving interactions between GnRH neuron cell bodies. Rather, data support the presence of an extrinsic pulse generator located within the arcuate nucleus, and attention has focused on the kisspeptin neurons and their projections to GnRH neuron dendrons concentrated around the median eminence. Sufficient evidence has been gathered in rodents to conclude that a subpopulation of arcuate kisspeptin neurons is, indeed, the GnRH pulse generator. Findings in other species are generally compatible with this view and suggest that arcuate/infundibular kisspeptin neurons represent the mammalian GnRH pulse generator. With hindsight, it is likely that past arcuate nucleus multiunit activity recordings have been from kisspeptin neurons. Despite advances in identifying the cells forming the pulse generator, almost nothing is known about their mechanisms of synchronicity and the afferent hormonal and transmitter modulation required to establish the normal patterns of LH pulsatility in mammals.

scholarly journals Dendritic Processing of Excitatory Synaptic Input in Hypothalamic Gonadotropin Releasing-Hormone Neurons

Endocrinology ◽  
2006 ◽  
Vol 147 (3) ◽  
pp. 1545-1555 ◽  
Author(s):  
C. B. Roberts ◽  
J. A. Best ◽  
K. J. Suter
Keyword(s):  
Synaptic Input ◽  
Dendritic Structure ◽  
Brain Slices ◽  
Low Frequency ◽  
Reproductive Function ◽  
Synaptic Inputs ◽  
Morphological Findings ◽  
Electrophysiological Recordings ◽  
Excitatory Synaptic Input ◽  
Gnrh Neurons

The activity of hypothalamic GnRH neurons results in the intermittent release of GnRH required for reproductive function. This intermittent neurosecretory activity has been proposed to reflect integration of intrinsic properties of and synaptic input to GnRH neurons. Determining the relative impact of synaptic inputs at different locations on the GnRH neuron is difficult, if not impossible, using only experimental approaches. Thus, we used electrophysiological recordings and neuronal reconstructions to generate computer models of GnRH neurons to examine the effects of synaptic inputs at varying distances from the soma along dendrites. The parameters of the models were adjusted to duplicate measured passive and active electrophysiology of cells from mouse brain slices. Our morphological findings reinforce the emerging picture of a complex dendritic structure of GnRH neurons. Furthermore, analysis of reduced morphology models indicated that this population of cells is unlikely to exhibit low-frequency tonic spiking in the absence of synaptic input. Finally, applying realistic patterns of synaptic input to modeled GnRH neurons indicates that synapses located more than about 30% of the average dendrite length from the soma cannot drive firing at frequencies consistent with neuropeptide release. Thus, processing of synaptic input to dendrites of GnRH neurons is probably more complex than simple summation.

scholarly journals Morphological Characterization of the Action Potential Initiation Segment in GnRH Neuron Dendrites and Axons of Male Mice

Endocrinology ◽  
2015 ◽  
Vol 156 (11) ◽  
pp. 4174-4186 ◽  
Author(s):  
Michel K. Herde ◽  
Allan E. Herbison
Keyword(s):  
Action Potential ◽  
Cell Body ◽  
Brain Slices ◽  
Gnrh Neuron ◽  
Male Mice ◽  
Single Action ◽  
Ankyrin G ◽  
Gnrh Neurons ◽  
Action Potential Initiation ◽  
Potential Initiation

GnRH neurons are the final output neurons of the hypothalamic network controlling fertility in mammals. In the present study, we used ankyrin G immunohistochemistry and neurobiotin filling of live GnRH neurons in brain slices from GnRH-green fluorescent protein transgenic male mice to examine in detail the location of action potential initiation in GnRH neurons with somata residing at different locations in the basal forebrain. We found that the vast majority of GnRH neurons are bipolar in morphology, elaborating a thick (primary) and thinner (secondary) dendrite from opposite poles of the soma. In addition, an axon-like process arising predominantly from a proximal dendrite was observed in a subpopulation of GnRH neurons. Ankyrin G immunohistochemistry revealed the presence of a single action potential initiation zone ∼27 μm in length primarily in the secondary dendrite of GnRH neurons and located 30 to 140 μm distant from the cell soma, depending on the type of process and location of the cell body. In addition to dendrites, the GnRH neurons with cell bodies located close to hypothalamic circumventricular organs often elaborated ankyrin G–positive axon-like structures. Almost all GnRH neurons (>90%) had their action potential initiation site in a process that initially, or ultimately after a hairpin loop, was coursing in the direction of the median eminence. These studies indicate that action potentials are initiated in different dendritic and axonal compartments of the GnRH neuron in a manner that is dependent partly on the neuroanatomical location of the cell body.

scholarly journals Projections of Arcuate Nucleus and Rostral Periventricular Kisspeptin Neurons in the Adult Female Mouse Brain

Endocrinology ◽  
2011 ◽  
Vol 152 (6) ◽  
pp. 2387-2399 ◽  
Author(s):  
Shel-Hwa Yeo ◽  
Allan E. Herbison
Keyword(s):  
Mouse Brain ◽  
Female Mouse ◽  
Arcuate Nucleus ◽  
Third Ventricle ◽  
Retrograde Tracing ◽  
Neuron Activity ◽  
Neuronal System ◽  
Gnrh Neuron ◽  
Gnrh Neurons ◽  
Tracing Techniques

The important role of kisspeptin neurons in the regulation of GnRH neuron activity is now well accepted. However, the ways in which kisspeptin neurons located in the arcuate nucleus (ARN) and rostral periventricular area of the third ventricle (RP3V) control GnRH neurons are poorly understood. The present study used anterograde and retrograde tracing techniques to establish the neuronal projection patterns of kisspeptin cell populations in the female mouse brain. Anterograde tracing studies revealed that kisspeptin neurons in the ARN innervated a wide number of hypothalamic and associated limbic region nuclei, whereas RP3V kisspeptin neurons projected to a smaller number of mostly medially located hypothalamic nuclei. Retrograde tracing confirmed a major projection of RP3V kisspeptin neurons to the ARN and showed that kisspeptin neurons located in the rostral half of the ARN projected to the rostral preoptic area. Peripheral administration of Fluorogold was found to label the majority of GnRH neurons but no kisspeptin neurons. Together, these studies highlight the complexity of the brain kisspeptin neuronal system and indicate that both ARN and RP3V kisspeptin neurons participate in a variety of limbic functions. In relation to the GnRH neuronal network, these investigations demonstrate that, alongside the RP3V kisspeptin cells, rostral ARN kisspeptin neurons may also project to GnRH neuron cell bodies. However, no kisspeptin neurons innervate GnRH nerve terminals in the external layer of the median eminence. These studies provide a neuroanatomical framework for the further elucidation of the functions of the ARN and RP3V kisspeptin neuron populations.

scholarly journals Interactions between neurotensin and GnRH neurons in the positive feedback control of GnRH/LH secretion in the mouse

2010 ◽  
Vol 298 (1) ◽  
pp. E80-E88 ◽  
Author(s):  
Heather M. Dungan Lemko ◽  
Roxana Naderi ◽  
Valeriya Adjan ◽  
Lothar H. Jennes ◽  
Victor M. Navarro ◽  
...  
Keyword(s):  
Basal Forebrain ◽  
Neural Circuits ◽  
Direct Role ◽  
Lh Surge ◽  
Periventricular Nucleus ◽  
Gnrh Neurons ◽  
Gnrh Release ◽  
Double Label ◽  
Lh Secretion

In female mammals, increased ovarian estradiol (E2) secretion triggers GnRH release from neurons in the basal forebrain, which drives LH secretion from the pituitary and subsequently induces ovulation. However, the neural circuits that activate this preovulatory GnRH/LH surge remain unidentified. Neurotensin is expressed in neurons of the anteroventral periventricular nucleus (AVPV), a region thought to be critical for generating the preovulatory GnRH/LH surge. E2 induces neurotensin ( Nts) gene expression in this region, and blockade of neurotensin signaling reduces the LH surge in the rat. We postulated that neurotensin signaling plays a similar role in generating the E2-induced GnRH/LH surge in mice. We used in situ hybridization (ISH) to determine whether E2 induces Nts expression in the mouse and found evidence to support this proposition. Next, we determined that the neurotensin receptor (Ntsr2) is present in many GnRH-expressing neurons. Since the kisspeptin gene ( Kiss1) is expressed in the AVPV and is responsive to E2, we predicted that some neurons in this region express both Kiss1 and Nts; however, by double-label ISH, we observed no coexpression of the two mRNAs. We also postulated that Nts mRNA expression would increase in parallel with the E2-induced LH surge and that the central (icv) administration of neurotensin would stimulate LH secretion and activation of GnRH neurons but found no evidence to support either of these hypotheses. Together, these findings suggest that, although neurotensin neurons in the AVPV are targets for regulation by E2, neurotensin does not appear to play a direct role in generating the GnRH/LH surge in the mouse.

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