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Does kisspeptin participate in GABA-mediated modulation of GnRH and GnRH receptor biosynthesis in the hypothalamic-pituitary unit of follicular-phase ewes? Pharmacol Rep 2019; 71:636-643. [PMID: 31176893 DOI: 10.1016/j.pharep.2019.02.019] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/26/2018] [Revised: 02/25/2019] [Accepted: 02/28/2019] [Indexed: 11/24/2022]
Abstract
BACKGROUND The inverse relationship between GnRH transcript level and GABA neurons activity has suggested that GABA at the hypothalamic level may exert a suppressive effect on subsequent steps of the GnRH biosynthesis. In the present study, we analyzed the effects of GABA type A receptor agonist (muscimol) or antagonist (bicuculline) on molecular mechanisms governing GnRH/LH secretion in follicular-phase sheep. METHODS ELISA technique was used to investigate the effects of muscimol and/or bicuculline on levels of post-translational products of genes encoding GnRH ligand and GnRH receptor (GnRHR) in the preoptic area (POA), anterior (AH) and ventromedial (VMH) hypothalamus, stalk/median eminence (SME), and GnRHR in the anterior pituitary (AP). Real-time PCR was chosen for determination of the effect of drugs on kisspeptin (Kiss 1) mRNA level in POA and VMH including arcuate nucleus (VMH/ARC), and on Kiss1 receptor (Kiss1r) mRNA abundance in POA-hypothalamic structures. These analyses were supplemented by RIA method for measurement of plasma LH concentration. RESULTS The study demonstrated that muscimol and bicuculline significantly decreased or increased GnRH biosynthesis in all analyzed structures, respectively, and led to analogous changes in plasma LH concentration. Similar muscimol- and bicuculline-related alterations were observed in levels of GnRHR. However, the expression of Kiss 1 and Kiss1r mRNAs in selected POA-hypothalamic areas of either muscimol- and bicuculline-treated animals remained unaltered. CONCLUSIONS Our data suggest that GABAergic neurotransmission is involved in the regulatory pathways of GnRH/GnRHR biosynthesis and then GnRH/LH release in follicular-phase sheep conceivably via indirect mechanisms that exclude involvement of Kiss 1 neurons.
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Kanasaki H, Tumurbaatar T, Oride A, Hara T, Okada H, Kyo S. Gamma-aminobutyric acid A receptor agonist, muscimol, increases KiSS-1 gene expression in hypothalamic cell models. Reprod Med Biol 2017; 16:386-391. [PMID: 29259493 PMCID: PMC5715903 DOI: 10.1002/rmb2.12061] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2017] [Accepted: 08/20/2017] [Indexed: 01/03/2023] Open
Abstract
Purpose Accumulating evidence indicates that hypothalamic kisspeptin plays a pivotal role in the regulation of the hypothalamic-pituitary-gonadal (HPG) axis. In this study, the direct action of the gamma-aminobutyric acid (GABA)A receptor agonist on kisspeptin-expressing neuronal cells was examined. Methods A hypothalamic cell model of rat hypothalamic cell line R8 (rHypoE8) cells and primary cultures of neuronal cells from fetal rat brains were stimulated with a potent and selective GABAA receptor agonist, muscimol, to determine the expression of the KiSS-1 gene. Results Stimulation of the rHypoE8 cells with muscimol significantly increased the level of KiSS-1 messenger (m)RNA expression. The ability of muscimol to increase the level of KiSS-1 mRNA also was observed in the primary cultures of the neuronal cells from the fetal rat brains. The muscimol-induced increase in KiSS-1 mRNA expression was completely inhibited in the presence of the GABAA receptor antagonist. Although muscimol increased the expression of KiSS-1, the natural compound, GABA, failed to induce the expression of KiSS-1 in the rHypoE8 cells. Muscimol did not modulate gonadotropin-releasing hormone expression in either the rHypoE8 cells or the primary cultures of the fetal rat brains. Conclusions This study's observations suggest that the activation of the GABAA receptor modulates the HPG axis by increasing kisspeptin expression in the hypothalamic neurons.
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Affiliation(s)
- Haruhiko Kanasaki
- Department of Obstetrics and Gynecology Shimane University School of Medicine Izumo Japan
| | | | - Aki Oride
- Department of Obstetrics and Gynecology Shimane University School of Medicine Izumo Japan
| | - Tomomi Hara
- Department of Obstetrics and Gynecology Shimane University School of Medicine Izumo Japan
| | - Hiroe Okada
- Department of Obstetrics and Gynecology Shimane University School of Medicine Izumo Japan
| | - Satoru Kyo
- Department of Obstetrics and Gynecology Shimane University School of Medicine Izumo Japan
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Kanasaki H, Oride A, Mijiddorj T, Sukhbaatar U, Kyo S. How is GnRH regulated in GnRH-producing neurons? Studies using GT1-7 cells as a GnRH-producing cell model. Gen Comp Endocrinol 2017; 247:138-142. [PMID: 28131616 DOI: 10.1016/j.ygcen.2017.01.025] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2016] [Revised: 01/05/2017] [Accepted: 01/23/2017] [Indexed: 12/24/2022]
Abstract
Hypothalamic secretion of gonadotropin-releasing hormone (GnRH) has been established as a principle pathway for initiating and integrating female reproductive function. GnRH stimulates the release of two gonadotropins-luteinizing hormone and follicle-stimulating hormone-from the anterior pituitary, which eventually stimulate the synthesis of sex steroids in association with follicular growth and ovulation. This reproductive control of the hypothalamic-pituitary-gonadal (HPG) axis also mediates gonadal feedback mechanisms. Although GnRH neurons certainly play a pivotal role in the HPG axis, the detailed mechanisms of their functional network, including regulatory systems, remain unknown. After the discovery of the indispensable role of kisspeptin in the development of human reproductive functions, our understanding of the neuroendocrine regulation of the HPG axis was revolutionized, and it is now recognized that kisspeptin acts upstream of GnRH and is responsible for sex steroid feedback mechanisms. Kisspeptin can stimulate gonadotropin release from the pituitary gland by stimulating GnRH release and GnRH antagonists prevent kisspeptin-induced gonadotropin release. Furthermore, it has been shown that GnRH neurons express kisspeptin receptors. Nevertheless, the detailed mechanisms underlying the regulation of homogeneous populations of GnRH neurons are still largely unknown because of the limitations of experimental models used for investigation. The hypothalamus consists of a complex network of distinct neuronal cells, and it is difficult to isolate single-cell populations of GnRH neurons. The establishment of GnRH-expressing cell lines has allowed us to examine the events happening at the single-cell level. In this review, we describe in vitro studies using a GnRH-producing cell model, GT1-7 cells, which have been used to examine how GnRH-producing cells respond to hypothalamic factors and how they are involved in GnRH synthesis.
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Affiliation(s)
- Haruhiko Kanasaki
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan.
| | - Aki Oride
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan
| | - Tselmeg Mijiddorj
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan
| | - Unurjargal Sukhbaatar
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan
| | - Satoru Kyo
- Department of Obstetrics and Gynecology, Shimane University Faculty of Medicine, Izumo 693-8501, Japan
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Li X, Shao B, Lin C, O'Byrne KT, Lin Y. Stress-induced inhibition of LH pulses in female rats: role of GABA in arcuate nucleus. J Mol Endocrinol 2015; 55:9-19. [PMID: 25999179 DOI: 10.1530/jme-15-0084] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Accepted: 05/21/2015] [Indexed: 12/21/2022]
Abstract
Stress exerts profound inhibitory effects on reproductive function by suppression of the pulsatile release of GnRH and therefore LH. Besides the corticotrophin-releasing factor (CRF), this effect also might be mediated via GABAergic signaling within the arcuate nucleus (ARC) since its inhibitory effects on LH pulses and increased activity during stress. In the present study, we investigated the role of endogenous GABAergic signaling within the ARC in stress-induced suppression of LH pulses. Ovariectomised oestradiol-replaced rats were implanted with bilateral and unilateral cannulae targeting toward the ARC and lateral cerebral ventricle respectively. Blood samples (25 μl) were taken via chronically implanted cardiac catheters every 5 min for 6 h for measurement of LH pulses. Intra-ARC infusion of GABAA receptor antagonist, bicuculline (0.2 pmol in 200 nl artificial cerebrospinal fluid (aCSF) each side, three times at 20-min intervals) markedly attenuated the inhibitory effect of lipopolysaccharide (LPS; 25 μg/kg i.v.) but not restraint (1 h) stress on pulsatile LH secretion. In contrast, restraint but not LPS stress-induced suppression of LH pulse frequency was reversed by intra-ARC administration of GABABR antagonist, CGP-35348 (1.5 nmol in 200 nl aCSF each side, three times at 20-min intervals). Moreover, intra-ARC application of either bicuculline or CGP-35348 attenuated the inhibitory effect of CRF (1 nmol in 4 μl aCSF, i.c.v.) on the LH pulses. These data indicate a pivotal and differential role of endogenous GABAA and GABAB signaling mechanisms in the ARC with respect to mediating immunological and psychological stress-induced suppression of the GnRH pulse generator respectively.
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Affiliation(s)
- XiaoFeng Li
- First Department of NeurologyFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, ChinaDivision of Women's HealthSchool of Medicine, King's College London, Guy's Campus, London, UKDepartment of Surgery LaboratoryFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, China First Department of NeurologyFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, ChinaDivision of Women's HealthSchool of Medicine, King's College London, Guy's Campus, London, UKDepartment of Surgery LaboratoryFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, China
| | - Bei Shao
- First Department of NeurologyFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, ChinaDivision of Women's HealthSchool of Medicine, King's College London, Guy's Campus, London, UKDepartment of Surgery LaboratoryFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, China
| | - ChengCheng Lin
- First Department of NeurologyFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, ChinaDivision of Women's HealthSchool of Medicine, King's College London, Guy's Campus, London, UKDepartment of Surgery LaboratoryFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, China
| | - Kevin T O'Byrne
- First Department of NeurologyFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, ChinaDivision of Women's HealthSchool of Medicine, King's College London, Guy's Campus, London, UKDepartment of Surgery LaboratoryFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, China
| | - YuanShao Lin
- First Department of NeurologyFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, ChinaDivision of Women's HealthSchool of Medicine, King's College London, Guy's Campus, London, UKDepartment of Surgery LaboratoryFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, China First Department of NeurologyFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, ChinaDivision of Women's HealthSchool of Medicine, King's College London, Guy's Campus, London, UKDepartment of Surgery LaboratoryFirst Affiliated Hospital of Wenzhou Medical University, Wenzhou 325000, China
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Sukhbaatar U, Mijiddorj T, Oride A, Kanasaki H. Stimulation of δ subunit-containing GABAA receptor by DS1 increases GnRH receptor expression but reduces GnRH mRNA expression in GnRH-producing GT1-7 cells. Endocrine 2015; 49:222-30. [PMID: 25355308 DOI: 10.1007/s12020-014-0464-y] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/10/2014] [Accepted: 10/23/2014] [Indexed: 12/23/2022]
Abstract
Acting via ionotropic GABAA receptors, the neurotransmitter γ-aminobutyric acid (GABA) is an important modulator of gonadotropin-releasing hormone (GnRH) neurons. In the present study, we examined the effect of DS1, a GABAA α4β3δ receptor agonist, on a strain of mouse hypothalamic immortalized GnRH neuronal cells, the GT1-7 cell line. DS1 increased the activities of serum-response element (SRE) and cAMP-response element (CRE) promoters, which reflect the activities of extracellular signal-regulated kinase and cAMP/protein kinase A (PKA) pathways, respectively. In G protein-coupled receptor 54 (GPR54)-overexpressing GT1-7 cells, both DS1 and kisspeptin-10 stimulated SRE promoter activity, and combined treatment with DS1 and kisspeptin further increased SRE promoter activity compared with DS1 or kisspeptin alone. Pituitary adenylate cyclase-activating polypeptide (PACAP) increased CRE promoter activity in PACAP type I receptor-overexpressing GT1-7 cells, with an effect similar to that of DS1 alone, and combined stimulation with PACAP and DS1 potentiated their individual effects. DS1 stimulated the transcriptional activity of GnRH receptor, and DS1 induced GnRH receptor mRNA and protein expression. PACAP-increased GnRH receptor expression was enhanced in the presence of DS1. However, DS1 significantly inhibited the basal expression of GnRH mRNA in GT1-7 cells. Our current observations suggest that DS1 exerts its stimulatory effect on the intracellular signal transduction system via GABAA α4β3δ receptors in GnRH-producing neurons. Stimulation with DS1 increased the expression of GnRH receptor but decreased the basal expression of GnRH mRNA.
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Affiliation(s)
- Unurjargal Sukhbaatar
- Department of Obstetrics and Gynecology, Shimane University School of Medicine, 89-1 Enya, Izumo City, Shimane Prefecture, 693-8501, Japan
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Mijiddorj T, Kanasaki H, Sukhbaatar U, Oride A, Kyo S. DS1, a delta subunit-containing GABA(A) receptor agonist, increases gonadotropin subunit gene expression in mouse pituitary gonadotrophs. Biol Reprod 2014; 92:45. [PMID: 25519184 DOI: 10.1095/biolreprod.114.123893] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
4-Chloro-N-[6,8-dibromo-2-(2-thienyl)imidazo[1,2-alpyridine-3-yl] (DS1) is a GABA(A) receptor agonist that selectively binds to delta subunit-containing GABA(A) alpha4beta3delta receptors. In the present study, we examined the effect of DS1 on pituitary gonadotropin subunit gene expression using the mouse pituitary gonadotroph cell line LbetaT2. DS1 increased the promoter activity of the gonadotropin subunits luteinizing hormone beta (LHbeta), follicle-stimulating hormone beta (FSHbeta), and alpha. Gonadotropin-releasing hormone (GnRH) receptor promoters were also activated by DS1. The effects of DS1 on gonadotropin subunit promoters were obvious, but they were less than those induced by stimulation with GnRH. GnRH-stimulated gonadotropin subunit promoters were enhanced in the presence of DS1. A prototypic specific agonist for GABAA receptors, muscimol, failed to increase LHbeta and FSHbeta subunit promoter activity and had no effect on GnRH-increased LHbeta and FSHbeta promoter activity. In addition, SKF97541, a specific agonist for GABAB receptors, did not modulate basal or GnRH-induced LHbeta and FSHbeta promoter activity. A natural GABA compound failed to increase gonadotropin promoter activity and potentiated the effect of GnRH on the FSHbeta promoter. DS1 increased the activity of serum response element (SRE) and cAMP response element (CRE) promoters, which reflect the activity of the extracellular signal-regulated kinase and cAMP/protein kinase A (PKA) pathways, and GnRH-increased SRE and CRE promoter activity was enhanced in the presence of DS1. A specific inhibitor of the ERK signaling pathway, U0126, prevented DS1-induced LHbeta and FSHbeta promoter activity almost completely; however, H89, a PKA inhibitor, did not modulate the effect of DS1. Our current observations demonstrate that the GABAA alpha4beta3delta receptor agonist DS1 can stimulate gonadotropin subunit gene expression in association with the ERK signaling pathway.
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Affiliation(s)
- Tselmeg Mijiddorj
- Department of Obstetrics and Gynecology, Shimane University School of Medicine, Izumo, Japan
| | - Haruhiko Kanasaki
- Department of Obstetrics and Gynecology, Shimane University School of Medicine, Izumo, Japan
| | - Unurjargal Sukhbaatar
- Department of Obstetrics and Gynecology, Shimane University School of Medicine, Izumo, Japan
| | - Aki Oride
- Department of Obstetrics and Gynecology, Shimane University School of Medicine, Izumo, Japan
| | - Satoru Kyo
- Department of Obstetrics and Gynecology, Shimane University School of Medicine, Izumo, Japan
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Lin YS, Li XF, Shao B, Hu MH, Goundry ALR, Jeyaram A, Lightman SL, O'Byrne KT. The role of GABAergic signalling in stress-induced suppression of gonadotrophin-releasing hormone pulse generator frequency in female rats. J Neuroendocrinol 2012; 24:477-88. [PMID: 22172044 DOI: 10.1111/j.1365-2826.2011.02270.x] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/25/2023]
Abstract
Stress exerts profound inhibitory effects on reproductive function by suppressing the pulsatile release of gonadotrophin-releasing hormone (GnRH) and therefore luteinising hormone (LH). This effect is mediated in part via the corticotrophin-releasing factor (CRF) system, although another potential mechanism is via GABAergic signalling within the medial preoptic area (mPOA) because this has known inhibitory influences on the GnRH pulse generator and shows increased activity during stress. In the present study, we investigated the role of the preoptic endogenous GABAergic system in stress-induced suppression of the GnRH pulse generator. Ovariectomised oestradiol-replaced rats were implanted with bilateral and unilateral cannulae targeting toward the mPOA and lateral cerebral ventricle, respectively; blood samples (25 μl) were taken via chronically implanted cardiac catheters every 5 min for 6 h for the measurement of LH pulses. Intra-mPOA administration of the specific GABA(A) receptor antagonist, bicuculline (0.2 pmol each side, three times at 20-min intervals) markedly attenuated the inhibitory effect of lipopolysaccharide (LPS; 25 μg/kg i.v.) but not restraint (1 h) stress on pulsatile LH secretion. By contrast, restraint but not LPS stress-induced suppression of LH pulse frequency was reversed by application of the selective GABA(B) receptor antagonist, CGP-35348, into the mPOA (1.5 nmol each side, three times at 20-min intervals). However, intra-mPOA application of either bicuculline or CGP-35348 attenuated the inhibitory effect of CRF (1 nmol i.c.v.) on the pulsatile LH secretion. These data indicate a pivotal and differential role of endogenous GABAergic signalling in the mPOA with respect to mediating psychological and immunological stress-induced suppression of the GnRH pulse generator.
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Affiliation(s)
- Y S Lin
- Division of Women's Health, School of Medicine, King's College London, Guy's Campus, London, UK
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Neuroendocrine regulation of GnRH release and expression of GnRH and GnRH receptor genes in the hypothalamus-pituitary unit in different physiological states. Reprod Biol 2010; 10:85-124. [PMID: 20668503 DOI: 10.1016/s1642-431x(12)60054-0] [Citation(s) in RCA: 32] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
This review is focused on the relationship between neuroendocrine regulation of GnRH/LH secretion and the expression of GnRH and GnRH receptor (GnRHR) genes in the hypothalamic-pituitary unit during different physiological states of animals and under stress. Moreover, the involvement of hypothalamic GABA-ergic, Beta-endorphinergic, CRH-ergic, noradrenergic, dopaminergic and GnRH-ergic systems in the regulation of expression of the GnRH and GnRHR genes as well as secretion of GnRH/LH is analyzed. It appears that the neural mechanisms controlling GnRH gene expression in different physiological states may be distinct from those regulating GnRH/LH release. The hypothalamic GnRHR gene is probably located in different neural systems and may act in a specific way on GnRH gene expression and GnRH release.
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Ghuman SPS, Jones DN, Prabhakar S, Smith RF, Dobson H. GABA Control of GnRH Release from the Ewe HypothalamusIn Vitro: Sensitivity to Oestradiol. Reprod Domest Anim 2008; 43:531-41. [DOI: 10.1111/j.1439-0531.2007.00948.x] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
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Bogusz AL, Hardy SL, Lehman MN, Connors JM, Hileman SM, Sliwowska JH, Billings HJ, McManus CJ, Valent M, Singh SR, Nestor CC, Coolen LM, Goodman RL. Evidence that gamma-aminobutyric acid is part of the neural circuit mediating estradiol negative feedback in anestrous ewes. Endocrinology 2008; 149:2762-72. [PMID: 18325998 PMCID: PMC2408799 DOI: 10.1210/en.2007-1362] [Citation(s) in RCA: 12] [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
Seasonal anestrus in ewes is driven by an increase in response to estradiol (E2) negative feedback. Compelling evidence indicates that inhibitory A15 dopaminergic (DA) neurons mediate the increased inhibitory actions of E2 in anestrus, but these neurons do not contain estrogen receptors. Therefore, we have proposed that estrogen-responsive afferents to A15 neurons are part of the neural circuit mediating E2 negative feedback in anestrus. This study examined the possible role of afferents containing gamma-aminobutyric acid (GABA) and nitric oxide (NO) in modulating the activity of A15 neurons. Local administration of NO synthase inhibitors to the A15 had no effect on LH, but GABA receptor ligands produced dramatic changes. Administration of either a GABA A or GABA B receptor agonist to the A15 increased LH secretion in ovary-intact ewes, suggesting that GABA inhibits A15 neural activity. In ovariectomized anestrous ewes, the same doses of GABA receptor agonist had no effect, but combined administration of a GABA A and GABA B receptor antagonist to the A15 inhibited LH secretion. These data are consistent with the hypothesis that endogenous GABA release within the A15 is low in ovary-intact anestrous ewes and elevated after ovariectomy. Using dual immunocytochemistry, we observed that GABAergic varicosities make close contacts on to A15 neurons and that A15 neurons contain both the GABA A-alpha1 and the GABA B-R1 receptor subunits. Based on these data, we propose that in anestrous ewes, E2 inhibits release of GABA from afferents to A15 DA neurons, increasing the activity of these DA neurons and thus suppressing episodic secretion of GnRH and LH.
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Affiliation(s)
- Adrienne L Bogusz
- Department of Physiology and Pharmacology, West Virginia University, Morgantown, West Virginia 26506-9229, USA
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Ciechanowska M, Lapot M, Malewski T, Mateusiak K, Misztal T, Przekop F. Effects of GABA(A) receptor modulation on the expression of GnRH gene and GnRH receptor (GnRH-R) gene in the hypothalamus and GnRH-R gene in the anterior pituitary gland of follicular-phase ewes. Anim Reprod Sci 2008; 111:235-48. [PMID: 18434046 DOI: 10.1016/j.anireprosci.2008.03.006] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2007] [Revised: 02/18/2008] [Accepted: 03/14/2008] [Indexed: 11/19/2022]
Abstract
The effect of prolonged, intermittent infusion of GABA(A) receptor agonist (muscimol) or GABA(A) receptor antagonist (bicuculline) into the third cerebral ventricle on the expression of GnRH gene and GnRH-R gene in the hypothalamus and GnRH-R gene in the anterior pituitary gland was examined in follicular-phase ewes by real-time PCR. The activation or inhibition of GABA(A) receptors in the hypothalamus decreased or increased the expression of GnRH and GnRH-R genes and LH secretion, respectively. The present results indicate that the GABAergic system in the hypothalamus of follicular-phase ewes may suppress, via hypothalamic GABA(A) receptors, the expression of GnRH and GnRH-R genes in this structure. The decrease or increase of GnRH-R mRNA in the anterior pituitary gland and LH secretion in the muscimol- or bicuculline-treated ewes, respectively, is probably a consequence of parallel changes in the release of GnRH from the hypothalamus activating GnRH-R gene expression. It is suggested that GABA acting through the GABA(A) receptor mechanism on the expression of GnRH gene and GnRH-R gene in the hypothalamus may be involved in two processes: the biosynthesis of GnRH and the release of this neurohormone in the hypothalamus.
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Affiliation(s)
- Magdalena Ciechanowska
- The Kielanowski Institute of Animal Physiology and Nutrition, Polish Academy of Sciences, Warsaw, Poland.
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Martin C, Jacobi JS, Nava G, Jeziorski MC, Clapp C, Martínez de la Escalera G. GABA inhibition of cyclic AMP production in immortalized GnRH neurons is mediated by calcineurin-dependent dephosphorylation of adenylyl cyclase 9. Neuroendocrinology 2007; 85:257-66. [PMID: 17551263 DOI: 10.1159/000103557] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/09/2007] [Accepted: 04/24/2007] [Indexed: 11/19/2022]
Abstract
The neurotransmitter gamma-aminobutyric acid (GABA) is an important modulator of gonadotropin-releasing hormone (GnRH), and consequently of reproduction. GABA, acting via ionotropic GABAA receptors, exerts a biphasic effect on GnRH secretion in immortalized GnRH cells. The initial increase in GnRH secretion is triggered by a sharp rise in [Ca2+]i, while the progressive decline of GnRH levels that follows is paralleled by reduced levels of intracellular cAMP. The experiments described here were designed to explore the potential signaling pathways involved in this novel GABAA ionotropic inhibition of cAMP synthesis in GT1-7 cells. Using RT-PCR and real-time PCR, we found that GT1-7 cells express 8 of 9 known membrane adenylyl cyclase (AC) isoforms, including a large proportion of AC3 and AC9, as well as AC5 and AC6, all of which are negatively regulated by increases in [Ca2+]i. In contrast, isoforms of AC that are positively regulated by [Ca2+]i were barely detectable (AC1) or undetectable (AC8). Pharmacological activation of L-type voltage-operated calcium channels with BayK 8644 produced a decrease in [cAMP]i similar to that induced by GABA, while blocking these calcium channels with verapamil reversed the effect of GABA on cAMP synthesis. Furthermore, blocking calcineurin with deltamethrin, FK-506 or cyclosporin A blocked the inhibitory effect of GABA on [cAMP]i, supporting the involvement of AC9 in this effect. In addition, blocking Ca2+/calmodulin-dependent protein kinase II (CamKII) with KN-62 partially reversed the action of GABA, suggesting that AC3 may also be involved in this effect. Finally, GABA increased phosphatase activity in a calcium-dependent manner, an effect blocked by calcineurin inhibitors. Collectively, our results show that the ionotropic action of GABA via the activation of GABAA receptors can decrease AC activity in immortalized GnRH neurons, and that the effect of GABA appears to be mediated by a transient increase in [Ca2+]i followed by activation of calcineurin and CamKII, leading to dephosphorylation of AC9 and phosphorylation of AC3, respectively, and subsequently reducing the synthesis of cAMP.
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Affiliation(s)
- Cecilia Martin
- Departamento de Neurobiología Celular y Molecular, Instituto de Neurobiología, Universidad Nacional Autónoma de México (UNAM), Querétaro, México
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Sliwowska JH, Billings HJ, Goodman RL, Lehman MN. Immunocytochemical colocalization of GABA-B receptor subunits in gonadotropin-releasing hormone neurons of the sheep. Neuroscience 2006; 141:311-9. [PMID: 16713120 DOI: 10.1016/j.neuroscience.2006.03.039] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2005] [Revised: 03/07/2006] [Accepted: 03/18/2006] [Indexed: 11/28/2022]
Abstract
GABA has been shown to play an important role in the control of gonadotropin-releasing hormone (GnRH) and luteinizing hormone secretion in many mammals. In sheep, seasonal differences in the ability of GABA-B receptor antagonists to alter pulsatile luteinizing hormone secretion have led to the hypothesis that this receptor subtype mediates the increased inhibitory effects of estradiol on GnRH and luteinizing hormone pulse frequency seen during the non-breeding season (anestrus). The aim of the present study was to use multiple-label immunocytochemistry to determine if ovine GnRH neurons contain the GABA-B receptor subunits R1 and/or R2, and to determine whether there are seasonal differences in the colocalization of these subunits in GnRH neurons. A majority of GnRH cells in the preoptic area, anterior hypothalamic area, and medial basal hypothalamus of both breeding season and anestrous ewes contained either GABA-B R1 or R2 subunits; a subset of GnRH neurons in breeding season (42%) and anestrous ewes (60%) contained both subunits. In contrast to colocalization within cell bodies, GnRH fibers in the median eminence did not colocalize GABA-B receptor subunits. Although the percentage of GnRH neurons expressing GABA-B receptor subunits tended to be higher in anestrus than in the breeding season, there were no significant seasonal differences in R1 and R2 subunit colocalization in GnRH cell bodies. Thus, while GABA may act directly on GnRH cell bodies via GABA-B receptors in the sheep, any role that GABA-B receptors may play in seasonal reproductive changes is likely mediated by other neurons afferent to GnRH cells.
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Affiliation(s)
- J H Sliwowska
- Department of Cell Biology, Neurobiology and Anatomy, University of Cincinnati College of Medicine, Cincinnati, OH 45267-0521, USA
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Jackson GL, Kuehl D. The GABA(B) antagonist CGP 52432 attenuates the stimulatory effect of the GABA(B) agonist SKF 97541 on luteinizing hormone secretion in the male sheep. Exp Biol Med (Maywood) 2002; 227:315-20. [PMID: 11976401 DOI: 10.1177/153537020222700503] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/16/2022] Open
Abstract
The objectives of this study were to determine if the gamma-aminobutyric acid (GABA)(B) agonist, 3-aminopropyl (methyl) phosphinic acid (SKF97541), would increase luteinizing hormone (LH) secretion when infused by microdialysis into the medial basal hypothalamus (MBH) of the castrated ram, and to determine if the action of SKF97541 would be attenuated by co-infusion of the GABA(B) antagonist CGP52432. Initial experiments established that infusion of SKF alone, at concentrations as low as 5 microM, increased mean LH, LH pulse amplitude, and in some cases, pulse interval. In the last experiment, animals were treated with artificial cerebrospinal fluid (CSF) alone, SKF alone (30 microM), 3-[[(3, 4-dichlorophenol) methyl] amino] propyl] diethoxymethyl) phosphinic acid (CGP) alone (500 microM), or SKF plus CGP. SKF increased both mean LH and LH pulse amplitude as compared with CSF. CGP alone had no significant effect on LH, but it attenuated the effect of SKF on mean LH. These observations indicate that the stimulatory effects of GABA(B) agonists on LH pulse patterns are mediated through GABA(B) receptors and provide further evidence that GABA(B) receptors located in the MBH can regulate pulsatile GnRH-LH release.
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Affiliation(s)
- Gary L Jackson
- Department of Veterinary Biosciences, University of Illinois, 2001 West Lincoln Avenue, 3838 VMBSB, Urbana, IL 61802, USA.
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Tilbrook AJ, Clarke IJ. Negative feedback regulation of the secretion and actions of gonadotropin-releasing hormone in males. Biol Reprod 2001; 64:735-42. [PMID: 11207186 DOI: 10.1095/biolreprod64.3.735] [Citation(s) in RCA: 92] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/01/2022] Open
Abstract
This minireview considers the state of knowledge regarding the interactions of testicular hormones to regulate the secretion and actions of GnRH in males, with special focus on research conducted in rams and male rhesus monkeys. In these two species, LH secretion is under the negative feedback regulation of testicular steroids that act predominantly within the central nervous system to suppress GnRH secretion. The extent to which these actions of testicular steroids result from the direct actions of testosterone or its primary metabolites, estradiol or dihydrotestosterone, is unclear. Because GnRH neurons do not contain steroid receptors, the testicular steroids must influence GnRH neurons via afferent neurons, which are largely undefined. The feedback regulation of FSH is controlled by inhibin acting directly at the pituitary gland. In male rhesus monkeys, the feedback regulation of FSH secretion is accounted for totally by the physiologically relevant form of inhibin, which appears to be inhibin B. In rams, the feedback regulation of FSH secretion involves the actions of inhibin and testosterone and interactions between these hormones, but the physiologically relevant form of inhibin has not been determined. The mechanisms of action for inhibin are not known.
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Affiliation(s)
- A J Tilbrook
- Department of Physiology, Monash University, Victoria 3800, Australia. Prince Henry's Institute of Medical Research, Clayton, Victoria 3168, Australia.
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