1
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Sun J, Wang W, Xiao Y, Cao NN, Wang YF, Zhang HR, Jiang SQ. Correlation between serum vitamin D level and uterine volume in girls with idiopathic central precocious puberty. J Pediatr Endocrinol Metab 2024; 37:144-149. [PMID: 38114464 DOI: 10.1515/jpem-2023-0381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/15/2023] [Accepted: 12/04/2023] [Indexed: 12/21/2023]
Abstract
OBJECTIVES Investigate serum vitamin D (vit D) levels' relation to uterine volume in idiopathic central precocious puberty (ICPP) girls and compare findings with normal peers. METHODS Analyzed 278 ICPP cases from January 2017 to September 2022 alongside 239 normally developing girls. Collected clinical data and lab markers and performed subgroup analysis based on vit D levels. Correlation and regression analyses were conducted. RESULTS The ICPP group exhibited elevated uterine volume and lower serum vit D compared to controls (p<0.05). A weak negative correlation was noted between vit D and uterine volume in ICPP (r=-0.193, p=0.004), and no such correlation in controls (r=-0.073, p=0.319). The ICPP vit D deficiency subgroup displayed higher uterine volume than the insufficiency and sufficiency subgroups (p<0.05). Uterine volume in the insufficiency subgroup exceeded the sufficiency subgroup (p<0.05). After adjusting for confounders, lower vit D is linked to increased ICPP uterine volume (non-standardized regression coefficient β=-25.55, 95 % CI= -46.23, -4.87, p=0.016). A Limited correlation between vit D and uterine volume was seen in girls with normal pubertal timing. CONCLUSIONS We demonstrated a correlation between vit D and uterine volume in ICPP girls, absent in normal peers. ICPP girls often exhibit lower vit D levels and increased uterine volume. Further research is vital for understanding vit D's role in ICPP pathogenesis and guiding prevention and treatment strategies.
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Affiliation(s)
- Jun Sun
- The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan Province, P.R. China
| | - Wei Wang
- The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan Province, P.R. China
| | - Ya Xiao
- The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan Province, P.R. China
| | - Niu-Niu Cao
- The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan Province, P.R. China
| | - Yi-Fan Wang
- The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan Province, P.R. China
| | - Hong-Ru Zhang
- The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan Province, P.R. China
| | - Shu-Qin Jiang
- The Third Affiliated Hospital of Zhengzhou University, Zhengzhou, Henan Province, P.R. China
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2
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Abedini F, Ghiassi R, Rahbarghazi R, Hamidian G, Keyhanmanesh R. Using Stem Cells to Treat Diabetes-induced Infertility. Curr Diabetes Rev 2022; 19:28-34. [PMID: 36330635 DOI: 10.2174/1573399819666221103143710] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/20/2022] [Revised: 09/02/2022] [Accepted: 09/13/2022] [Indexed: 11/06/2022]
Abstract
Diabetes is one of the main causes of infertility which impacts the quality of life of couples. These reproductive complications are the important issue for all clinicians. The strategies for treatment of diabetes induced infertility are limited with the high cost and unsatisfied results. Due to the multi-directional differentiation potential and self-renewal ability of stem cells, these cells have emerged as an attractive therapeutic agent in many diseases including diabetes mellitus. We reviewed here the current knowledge on all the best available evidence regarding the role of stem cell transplantation in reproductive complications of diabetes.
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Affiliation(s)
- Fatemeh Abedini
- Department of Physiology, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Rafighe Ghiassi
- Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
- Department of Physiology, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Reza Rahbarghazi
- Stem Cell Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
- Department of Applied Cell Sciences, Faculty of Advanced Medical Sciences, Tabriz University of Medical Sciences, Tabriz, Iran
| | - Gholamreza Hamidian
- Department of Basic Sciences, Faculty of Veterinary Medicine, University of Tabriz, Tabriz, Iran
| | - Rana Keyhanmanesh
- Drug Applied Research Center, Tabriz University of Medical Sciences, Tabriz, Iran
- Department of Physiology, Faculty of Medicine, Tabriz University of Medical Sciences, Tabriz, Iran
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3
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Bechmann N, Maccio U, Kotb R, Dweik RA, Cherfane M, Moch H, Bornstein SR, Varga Z. COVID-19 Infections in Gonads: Consequences on Fertility? Horm Metab Res 2022; 54:549-555. [PMID: 35853464 PMCID: PMC9363149 DOI: 10.1055/a-1891-6621] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2022] [Accepted: 05/12/2022] [Indexed: 01/01/2023]
Abstract
COVID-19 may influence human fertility and sexuality in several ways. Different cell types in gonads show a constitutive expression of angiotensin-converting enzyme 2 (ACE2) and transmembrane protease serine subtype 2 (TMPRSS2), which provide potential entry pathways for SARS-CoV-2. In addition to the biological effects of a COVID-19 infection on the gonads, the impact of the ongoing COVID-19 pandemic on mental health issues and sexual behavior may affect reproduction. This review summarizes the current knowledge on the influence of COVID-19 on the gonads and discusses possible consequences on human fertility. In this context, the close interaction between the hypothalamic-pituitary-adrenal axis and the hypothalamic-pituitary-gonadal axis in response to COVID-19-related stress is discussed. Some women noticed changes in their menstrual cycle during the COVID-19 pandemic, which could be due to psychological stress, for example. In addition, occasional cases of reduced oocyte quality and ovarian function are described after COVID-19 infection. In men, COVID-19 may cause a short-term decrease in fertility by damaging testicular tissue and/or impairing spermatogenesis. Moreover, decreased ratio testosterone/LH and FSH/LH in COVID-19 compared to aged-matched healthy men has been reported. Available data do not suggest any effect of the available SARS-CoV-2 vaccines on fertility. The effects of long COVID on human fertility have been reported and include cases with premature ovarian failure and oligomenorrhoea in women and erectile dysfunction in men. Despite the increasing knowledge about the effects of COVID-19 infections on human gonads and fertility, the long-term consequences of the COVID-19 pandemic cannot yet be assessed in this context.
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Affiliation(s)
- Nicole Bechmann
- Institute of Clinical Chemistry and Laboratory Medicine, University
Hospital Carl Gustav Carus Dresden, Technische Universität Dresden,
Dresden, Germany
| | - Umberto Maccio
- Department of Pathology and Molecular Pathology, University Hospital
Zurich, Zurich, Switzerland
| | - Reham Kotb
- Department of Environmental and Public Health, College of Health
Science, Abu Dhabi University, Abu Dhabi, United Arab Emirates
| | - Rania Al Dweik
- Department of Environmental and Public Health, College of Health
Science, Abu Dhabi University, Abu Dhabi, United Arab Emirates
| | - Michele Cherfane
- Department of Environmental and Public Health, College of Health
Science, Abu Dhabi University, Abu Dhabi, United Arab Emirates
| | - Holger Moch
- Department of Pathology and Molecular Pathology, University Hospital
Zurich, Zurich, Switzerland
| | - Stefan R. Bornstein
- Department of Medicine III, University Hospital Carl Gustav Carus,
Medical Faculty Carl Gustav Carus, Technische Universität Dresden,
Dresden, Germany
- Department of Diabetes, School of Life Course Science and Medicine,
King's College London, London, UK
| | - Zsuzsanna Varga
- Department of Pathology and Molecular Pathology, University Hospital
Zurich, Zurich, Switzerland
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4
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Nicola AC, Ferreira LB, Mata MM, Vilhena-Franco T, Leite CM, Martins AB, Antunes-Rodrigues J, Poletini MO, Dornelles RCM. Vasopressinergic Activity of the Suprachiasmatic Nucleus and mRNA Expression of Clock Genes in the Hypothalamus-Pituitary-Gonadal Axis in Female Aging. Front Endocrinol (Lausanne) 2021; 12:652733. [PMID: 34504470 PMCID: PMC8421860 DOI: 10.3389/fendo.2021.652733] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 01/13/2021] [Accepted: 07/06/2021] [Indexed: 11/13/2022] Open
Abstract
The important involvement of the suprachiasmatic nucleus (SCN) and the activity of vasopressinergic neurons in maintaining the rhythmicity of the female reproductive system depends on the mRNA transcription-translation feedback loops. Therefore, circadian clock function, like most physiological processes, is involved in the events that determine reproductive aging. This study describes the change of mRNA expression of clock genes, Per2, Bmal1, and Rev-erbα, in the hypothalamus-pituitary-gonadal axis (HPG) of female rats with regular cycle (RC) and irregular cycle (IC), and the vasopressinergic neurons activity in the SCN and kisspeptin neurons in the arcuate nucleus (ARC) of these animals. Results for gonadotropins and the cFos/AVP-ir neurons in the SCN of IC were higher, but kisspeptin-ir was minor. Change in the temporal synchrony of the clock system in the HPG axis, during the period prior to the cessation of ovulatory cycles, was identified. The analysis of mRNA for Per2, Bmal1, and Rev-erbα in the reproductive axis of adult female rodents shows that the regularity of the estrous cycle is guaranteed by alternation in the amount of expression of Bmal1 and Per2, and Rev-erbα and Bmal1 between light and dark phases, which ceases to occur and contributes to determining reproductive senescence. These results showed that the desynchronization between the central and peripheral circadian clocks contributes to the irregularity of reproductive events. We suggest that the feedback loops of clock genes on the HPG axis modulate the spontaneous transition from regular to irregular cycle and to acyclicity in female rodents.
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Affiliation(s)
- Angela Cristina Nicola
- Programa de Pós-Graduação Multicêntrico em Ciências Fisiológicas—SBFis/UNESP, Department of Basic Sciences, Araçatuba, Brazil
- *Correspondence: Angela Cristina Nicola, ; Rita Cássia Menegati Dornelles,
| | - Larissa Brazoloto Ferreira
- Programa de Pós-Graduação Multicêntrico em Ciências Fisiológicas—SBFis/UNESP, Department of Basic Sciences, Araçatuba, Brazil
| | - Milene Mantovani Mata
- University of Sao Paulo (USP), School of Medicine of Ribeirão Preto, Department of Physiology, Ribeirão Preto, Brazil
| | - Tatiane Vilhena-Franco
- University of Sao Paulo (USP), School of Medicine of Ribeirão Preto, Department of Physiology, Ribeirão Preto, Brazil
| | | | - Andressa Busetti Martins
- Programa de Pós-Graduação Multicêntrico em Ciências Fisiológicas—SBFis/UEL, Department of Physiological Sciences, Londrina, Brazil
| | - José Antunes-Rodrigues
- University of Sao Paulo (USP), School of Medicine of Ribeirão Preto, Department of Physiology, Ribeirão Preto, Brazil
| | - Maristela Oliveira Poletini
- Federal University of Minas Gerais (UFMG), Institute of Biological Sciences, Department of Physiology and Biophysics, Belo Horizonte, Brazil
| | - Rita Cássia Menegati Dornelles
- Programa de Pós-Graduação Multicêntrico em Ciências Fisiológicas—SBFis/UNESP, Department of Basic Sciences, Araçatuba, Brazil
- São Paulo State University (UNESP), School of Dentistry, Department of Basic Sciences, Araçatuba, Brazil
- *Correspondence: Angela Cristina Nicola, ; Rita Cássia Menegati Dornelles,
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5
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Plunk EC, Richards SM. Endocrine-Disrupting Air Pollutants and Their Effects on the Hypothalamus-Pituitary-Gonadal Axis. Int J Mol Sci 2020; 21:ijms21239191. [PMID: 33276521 PMCID: PMC7731392 DOI: 10.3390/ijms21239191] [Citation(s) in RCA: 32] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/15/2020] [Revised: 11/28/2020] [Accepted: 11/30/2020] [Indexed: 12/19/2022] Open
Abstract
Anthropogenic endocrine-disrupting chemicals (EDCs) can contaminate air, soil, and water. Human exposures to EDCs occur through inhalation, absorption, and ingestion. EDCs act by disrupting various pathways in the endocrine system. When the hypothalamic–pituitary–gonadal (HPG) axis is disrupted by EDCs, there can be effects on fertility in both men and women. Not only can fertility be indirectly affected by EDC disruptions of the HPG axis, but EDCs can also directly affect the menstrual cycle and sperm morphology. In this review, we will discuss the current findings on EDCs that can be inhaled. This review examines effects of exposure to prominent EDCs: brominated and organophosphate flame retardants, diesel exhaust, polycyclic aromatic hydrocarbons, cadmium and lead, TCDD, and polychlorinated biphenyls on fertility through alterations that disrupt the HPG axis and fertility through inhalation. Although the studies included herein include multiple exposure routes, all the studies indicate receptor interactions that can occur from inhalation and the associated effects of all compounds on the HPG axis and subsequent fertility.
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Affiliation(s)
- Elizabeth C. Plunk
- Department of Environmental Medicine, University of Rochester Medical School, Rochester, NY 14642, USA
- Correspondence:
| | - Sean M. Richards
- Department of Biological, Geological and Environmental Sciences, University of Tennessee-Chattanooga, Chattanooga, TN 37403, USA;
- Department of Obstetrics and Gynecology, College of Medicine, University of Tennessee Health Science Center, Chattanooga, TN 37403, USA
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6
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Trova S, Bovetti S, Pellegrino G, Bonzano S, Giacobini P, Peretto P. HPG-Dependent Peri-Pubertal Regulation of Adult Neurogenesis in Mice. Front Neuroanat 2020; 14:584493. [PMID: 33328903 PMCID: PMC7732626 DOI: 10.3389/fnana.2020.584493] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/17/2020] [Accepted: 10/29/2020] [Indexed: 11/13/2022] Open
Abstract
Adult neurogenesis, a striking form of neural plasticity, is involved in the modulation of social stimuli driving reproduction. Previous studies on adult neurogenesis have shown that this process is significantly modulated around puberty in female mice. Puberty is a critical developmental period triggered by increased secretion of the gonadotropin releasing hormone (GnRH), which controls the activity of the hypothalamic-pituitary-gonadal axis (HPG). Secretion of HPG-axis factors at puberty participates to the refinement of neural circuits that govern reproduction. Here, by exploiting a transgenic GnRH deficient mouse model, that progressively loses GnRH expression during postnatal development (GnRH::Cre;Dicer loxP/loxP mice), we found that a postnatally-acquired dysfunction in the GnRH system affects adult neurogenesis selectively in the subventricular-zone neurogenic niche in a sexually dimorphic way. Moreover, by examining adult females ovariectomized before the onset of puberty, we provide important evidence that, among the HPG-axis secreting factors, the circulating levels of gonadal hormones during pre-/peri-pubertal life contribute to set-up the proper adult subventricular zone-olfactory bulb neurogenic system.
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Affiliation(s)
- Sara Trova
- Department of Life Sciences and Systems Biology, Neuroscience Institute Cavalieri Ottolenghi, University of Torino, Orbassano, Italy.,Univ.Lille, Inserm, CHU Lille, U1172 - LilNCog - Lille Neuroscience and Cognition, Laboratory of the Development and Plasticity of Neuroendocrine Brain, Lille, France
| | - Serena Bovetti
- Department of Life Sciences and Systems Biology, Neuroscience Institute Cavalieri Ottolenghi, University of Torino, Orbassano, Italy
| | - Giuliana Pellegrino
- Univ.Lille, Inserm, CHU Lille, U1172 - LilNCog - Lille Neuroscience and Cognition, Laboratory of the Development and Plasticity of Neuroendocrine Brain, Lille, France
| | - Sara Bonzano
- Department of Life Sciences and Systems Biology, Neuroscience Institute Cavalieri Ottolenghi, University of Torino, Orbassano, Italy
| | - Paolo Giacobini
- Univ.Lille, Inserm, CHU Lille, U1172 - LilNCog - Lille Neuroscience and Cognition, Laboratory of the Development and Plasticity of Neuroendocrine Brain, Lille, France
| | - Paolo Peretto
- Department of Life Sciences and Systems Biology, Neuroscience Institute Cavalieri Ottolenghi, University of Torino, Orbassano, Italy
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Abstract
The fetal hypothalamus-pituitary gonadal (HPG) axis begins to function during mid-gestation but its activity decreases during late pregnancy due to the suppressive effects of placental estrogens. Placental hormones drop immediately after birth, FSH and LH surge at around 1 week and peak between 1 and 3 months of life. The HPG axis is activated in both sexes, but a sexual dimorphism is evident with higher LH values in boys, while FSH prevails in girls. Both gonadotrophins decline in boys by around 6 months of age. In girls, LH declines at the same time as in boys, while FSH persists elevated up to 3 or 4 years of age. As a result of gonadotropin activation, testicular testosterone increases in males and ovarian estradiol rises in females. These events clinically translate into testicular and penile growth in boys, enlargement of uterus and breasts in girls. The functional impact of HPG axis activity in infancy on later reproductive function is uncertain. According to the perinatal programming theory, this period may represent an essential programming process. In boys, long-term testicular hormonal function and spermatogenesis seem to be, at least in part, regulated by minipuberty. On the contrary, the role of minipuberty in girls is still uncertain. Recently, androgen exposure during minipuberty has been correlated with later sex-typed behavior. Premature and/or SGA infants show significant differences in postnatal HPG axis activity in comparison to full-term infants and the consequences of these differences on later health and disease require further research. The sex-dimorphic HPG activation during mid-gestation is probably responsible for the body composition differences observed ad birth between boys and girls, with boys showing greater total body mass and lean mass, and a lower proportion of fat mass. Testosterone exposure during minipuberty further contributes to these differences and seems to be responsible for the significantly higher growth velocity observed in male infants. Lastly, minipuberty is a valuable "window of opportunity" for differential diagnosis of disorders of sex development and it represents the only time window before puberty when congenital hypogonadism can be diagnosed by the simple analysis of basal gonadotropin and gonadal hormone levels.
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Abstract
Endocrine disrupting chemicals (EDC) are exogenous agents that alter endogenous hormone signaling pathways. These chemicals target the neuroendocrine system which is composed of organs throughout the body that work alongside the central nervous system to regulate biological processes. Of primary importance is the hypothalamic-pituitary-gonadal (HPG) axis which is vital for maintaining proper reproductive function. Atrazine (2-chloro-4-ethylamino-6-isopropylamino-1,3,5-triazine) is a pre-emergent herbicide used to prevent the growth of weeds on various crops. This herbicide is reported to widely contaminate potable water supplies everywhere it is applied. As such, the European Union banned the use of atrazine in 2004. Currently the United States Environmental Protection Agency regulates atrazine at 3 parts per billion (ppb; μg/L) in drinking water, while the World Health Organization recently changed their drinking water guideline to 100 ppb. Atrazine is implicated to be an EDC that alters reproductive dysfunction by targeting the HPG axis. However, questions remain as to the human health risks associated with atrazine exposure with studies reporting mixed results on the ability of atrazine to alter the HPG axis. In this review, the current findings for atrazine’s effects on the HPG axis are examined in mammalian, anuran, and fish models and in epidemiological studies.
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9
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Piomboni P, Governini L, Gori M, Puggioni E, Costantino-Ceccarini E, Luddi A. New players in the infertility of a mouse model of lysosomal storage disease: the hypothalamus-pituitary-gonadal axis. Front Endocrinol (Lausanne) 2014; 4:204. [PMID: 24432014 PMCID: PMC3880942 DOI: 10.3389/fendo.2013.00204] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 11/21/2013] [Accepted: 12/21/2013] [Indexed: 11/13/2022] Open
Abstract
Mammalian spermatogenesis is a complex hormone-dependent developmental program where interactions between different cell types are finely regulated. Mouse models in which any of the sperm maturation steps are perturbed provide major insights into the molecular control of spermatogenesis. The Twitcher mouse is a model for the Krabbe disease, characterized by the deficiency of galactosylceramidase (GALC), a lysosomal enzyme that hydrolyzes the terminal galactose from galactosylceramide, a typical component of the myelin membrane. In addition, GALC catalyzes the hydrolysis of the terminal galactose from galactosyl-alkyl-acyl-glycerol, precursor of seminolipids, specifically expressed on the membrane of germ cells. Previous data reported by our group demonstrated that glycolipids play an important role in sperm maturation and differentiation. Moreover, we hypothesized that the severe impairment of the central nervous system that affects the Twitcher mouse could interfere with the hypothalamus-pituitary-gonadal axis function, contributing to infertility. To highlight this hypothesis we have determined, at molecular level, the potential variation in expression pattern of brain hormones involved in spermatogenesis regulation.
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Affiliation(s)
- Paola Piomboni
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
| | - Laura Governini
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
| | - Martina Gori
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
| | - Erica Puggioni
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
| | | | - Alice Luddi
- Department of Molecular and Developmental Medicine, University of Siena, Siena, Italy
- *Correspondence: Alice Luddi, Department of Molecular and Developmental Medicine, University of Siena, Policlinico Le Scotte, viale Bracci, Siena 53100, Italy e-mail:
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10
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Ubuka T, Bentley GE, Tsutsui K. Neuroendocrine regulation of gonadotropin secretion in seasonally breeding birds. Front Neurosci 2013; 7:38. [PMID: 23531789 PMCID: PMC3607074 DOI: 10.3389/fnins.2013.00038] [Citation(s) in RCA: 52] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2013] [Accepted: 03/05/2013] [Indexed: 01/17/2023] Open
Abstract
Seasonally breeding birds detect environmental signals, such as light, temperature, food availability, and presence of mates to time reproduction. Hypothalamic neurons integrate external and internal signals, and regulate reproduction by releasing neurohormones to the pituitary gland. The pituitary gland synthesizes and releases gonadotropins which in turn act on the gonads to stimulate gametogenesis and sex steroid secretion. Accordingly, how gonadotropin secretion is controlled by the hypothalamus is key to our understanding of the mechanisms of seasonal reproduction. A hypothalamic neuropeptide, gonadotropin-releasing hormone (GnRH), activates reproduction by stimulating gonadotropin synthesis and release. Another hypothalamic neuropeptide, gonadotropin-inhibitory hormone (GnIH), inhibits gonadotropin synthesis and release directly by acting on the pituitary gland or indirectly by decreasing the activity of GnRH neurons. Therefore, the next step to understand seasonal reproduction is to investigate how the activities of GnRH and GnIH neurons in the hypothalamus and their receptors in the pituitary gland are regulated by external and internal signals. It is possible that locally-produced triiodothyronine resulting from the action of type 2 iodothyronine deiodinase on thyroxine stimulates the release of gonadotropins, perhaps by action on GnRH neurons. The function of GnRH neurons is also regulated by transcription of the GnRH gene. Melatonin, a nocturnal hormone, stimulates the synthesis and release of GnIH and GnIH may therefore regulate a daily rhythm of gonadotropin secretion. GnIH may also temporally suppress gonadotropin secretion when environmental conditions are unfavorable. Environmental and social milieus fluctuate seasonally in the wild. Accordingly, complex interactions of various neuronal and hormonal systems need to be considered if we are to understand the mechanisms underlying seasonal reproduction.
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Affiliation(s)
- Takayoshi Ubuka
- Department of Biology, Center for Medical Life Science, Waseda University Shinjuku, Tokyo, Japan ; Department of Biology, College of Liberal Arts and Sciences, Tokyo Medical and Dental University Ichikawa, Japan
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