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Majumdar G, Yadav G, Singh NS. Photoperiodic physiology of summer breeding birds and a search for the role of eye. Photochem Photobiol Sci 2024; 23:197-212. [PMID: 38038950 DOI: 10.1007/s43630-023-00505-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2023] [Accepted: 11/06/2023] [Indexed: 12/02/2023]
Abstract
Photoperiod regulation of gonadal cycles is well studied and documented in both birds and mammals. Change in photoperiod is considered as the most effective and important cue to time the initiation of the annual physiological cycles in birds. Approaching of long days (as observed in summer months), signal long-day breeding birds to initiation reproduction and other related functions. Birds and other non-mammalian vertebrates use the extraocular photoreceptors which may be present in the mediobasal hypothalamus (MBH) or associated regions to measure the photoperiodic time and so are different from mammals where only the eyes are lone photoreceptive organs. The downstream signaling involves thyroid responsive genes playing a crucial role in mediating photoperiodic signals in both birds and mammals. Role of eyes in the avian seasonal cycle has been a questionable issue with evidences both favoring and negating any role. We propose that morphological as well as physiological data argue that retinal photoreceptors can participate in gonadal cycle, at least in the quail and duck. The present review details the studies of photoneuroendocrine control of gonadal axis in birds and review evidences to decipher the role eyes in photoperiodic mediated physiologies in birds.
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Affiliation(s)
- Gaurav Majumdar
- Department of Zoology, University of Allahabad, Prayagraj, Uttar Pradesh, 211002, India
| | - Garima Yadav
- Department of Biochemistry, University of Allahabad, Prayagraj, Uttar Pradesh, 211002, India
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2
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Renthlei Z, Hmar L, Kumar Trivedi A. High temperature attenuates testicular responses in tree sparrow (Passer montanus). Gen Comp Endocrinol 2021; 301:113654. [PMID: 33129830 DOI: 10.1016/j.ygcen.2020.113654] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/30/2020] [Revised: 10/23/2020] [Accepted: 10/25/2020] [Indexed: 10/23/2022]
Abstract
The majority of birds use environmental cues to time their reproduction. Photoperiod is the most dominant cue, but other environmental factors may play a critical role in successful reproduction. Some previous studies show the effect of temperature on the timing of nest building and reproduction. Here we tested if the temperature can modulate the reproductive responses of tree sparrows. Three experiments were performed on adult male birds. In experiment 1, birds (n = 5/group) were exposed to either high (30 ± 2 °C) or low temperature (20 ± 2 °C). Change in body mass, bill color, and testes volume was recorded every 30 days. In experiment 2, a similar temperature protocol was followed, but birds were euthanized after 30 days. In experiment 3, birds were first exposed to SD (8L:16D) for 30 days but either with high (30 ± 2 °C) or low temperature (20 ± 2 °C). After 30 days, birds were exposed to LD (14L:10D), but half of the high-temperature birds were moved to low temperature, and half of the low-temperature birds were moved to high temperature. After 30 days, all birds were euthanized. In experiment 2 and 3 immediately after euthanization birds, blood samples were collected, serum was used for hormone assay. mRNA levels of thyroid-stimulating hormone-β (Tshβ), type 2 deiodinase (Dio2), type 3 deiodinase (Dio3), gonadotropin-releasing hormone (GnRH) and gonadotropin inhibitory hormone (GnIH) were measured in hypothalamic tissue. Results from experiment 1 show that high temperature attenuates the testicular responses and accelerates the timing of regression. Experiment 2 shows that on day 30, testicular responses are similar, but reproductive genes express differentially in two groups. Experiment 3 shows that exposure to high temperatures during the photosensitive stage affects the testicular response at the poststimulatory state. Together, these findings suggest that high temperature modulates reproductive responses of tree sparrow.
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Affiliation(s)
| | - Lalruatthara Hmar
- Department of Zoology, Mizoram University, Aizawl, Mizoram, 976004, India
| | - Amit Kumar Trivedi
- Department of Zoology, Mizoram University, Aizawl, Mizoram, 976004, India.
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Nabi G, Hao Y, Liu X, Sun Y, Wang Y, Jiang C, Li J, Wu Y, Li D. Hypothalamic-Pituitary-Thyroid Axis Crosstalk With the Hypothalamic-Pituitary-Gonadal Axis and Metabolic Regulation in the Eurasian Tree Sparrow During Mating and Non-mating Periods. Front Endocrinol (Lausanne) 2020; 11:303. [PMID: 32547486 PMCID: PMC7272604 DOI: 10.3389/fendo.2020.00303] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/24/2020] [Accepted: 04/21/2020] [Indexed: 12/13/2022] Open
Abstract
Reproduction is an energetically costly phenomenon. Therefore, to optimize reproductive success, male birds invest enough energetic resources for maintaining well-developed testes. The hypothalamic-pituitary-thyroid (HPT) axis in birds can crosstalk with the hypothalamic-pituitary-gonadal (HPG) axis, thus orchestrating both the reproduction and metabolism. However, until now, how the free-living birds timely optimize both the energy metabolism and reproduction via HPT-axis is not understood. To uncover this physiological mechanism, we investigated the relationships among body mass, testis size, plasma hormones including thyroid-stimulating hormone (TSH), thyroxine (T4), triiodothyronine (T3), metabolites including glucose (Glu), triglyceride (TG), total cholesterol (TC), uric acid (UA), diencephalon mRNA expressions of type 2 (Dio2) and 3 (Dio3) iodothyronine deiodinase enzymes, thyrotropin-releasing hormone (TRH), thyroid-stimulating hormone (TSH), gonadotropin-releasing hormone I (GnRH-I), and gonadotropin-inhibitory hormone (GnIH) in a male Eurasian tree sparrow (ETS, Passer montanus). We found significantly larger testis size; elevated diencephalon Dio2 and TRH mRNA expressions, plasma T3, and UA levels; and significantly lowered Glu, TG, and TC levels during mating relative to the non-mating stages in male ETSs. However, Dio3, TSH, GnRH-I, and GnIH mRNA expression did not vary with the stage. Furthermore, life-history stage dependent variation in plasma T3 had both direct effects on the available energy substrates and indirect effects on body mass and testis size, indicating a complex regulation of metabolic pathways through the HPT- and HPG-axes. The identified differences and relationships in mRNA expression, plasma T3 and metabolites, and testis size in male ETSs contribute to our understanding how free-living birds adjust their molecular, endocrinal, and biochemical features to orchestrate their reproductive physiology and metabolism for the maintenance of well-developed testes.
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Affiliation(s)
- Ghulam Nabi
- Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, China
| | - Yinchao Hao
- Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, China
- Functional Laboratory, Experimental Center for Teaching, Hebei Medical University, Shijiazhuang, China
| | - Xuelu Liu
- Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, China
| | - Yanfeng Sun
- Ocean College, Hebei Agricultural University, Qinhuangdao, China
| | - Yang Wang
- Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, China
| | - Chuan Jiang
- Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, China
| | - Juyong Li
- Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, China
| | - Yuefeng Wu
- Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, China
| | - Dongming Li
- Key Laboratory of Animal Physiology, Biochemistry and Molecular Biology of Hebei Province, College of Life Sciences, Hebei Normal University, Shijiazhuang, China
- *Correspondence: Dongming Li
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Abstract
Organisms use changes in photoperiod for seasonal reproduction to maximize the survival of their offspring. Birds have sophisticated seasonal mechanisms and are therefore excellent models for studying these phenomena. Birds perceive light via deep-brain photoreceptors and long day–induced thyroid-stimulating hormone (TSH, thyrotropin) in the pars tuberalis of the pituitary gland (PT), which cause local thyroid hormone activation within the mediobasal hypothalamus. The local bioactive thyroid hormone controls seasonal gonadotropin-releasing hormone secretion and subsequent gonadotropin secretion. In mammals, the eyes are believed to be the only photoreceptor organ, and nocturnal melatonin secretion triggers an endocrine signal that communicates information about the photoperiod to the PT to regulate TSH. In contrast, in Salmonidae fish the input pathway to the neuroendocrine output pathway appears to be localized in the saccus vasculosus. Thus, comparative analysis is an effective way to uncover the universality and diversity of fundamental traits in various organisms.
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Affiliation(s)
- Yusuke Nakane
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
- Laboratory of Animal Integrative Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
| | - Takashi Yoshimura
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
- Laboratory of Animal Integrative Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
- Avian Bioscience Research Center, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan
- Division of Seasonal Biology, National Institute for Basic Biology, Myodaiji, Okazaki 444-8585, Japan
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GUH YJ, TAMAI TK, YOSHIMURA T. The underlying mechanisms of vertebrate seasonal reproduction. PROCEEDINGS OF THE JAPAN ACADEMY. SERIES B, PHYSICAL AND BIOLOGICAL SCIENCES 2019; 95:343-357. [PMID: 31406058 PMCID: PMC6766453 DOI: 10.2183/pjab.95.025] [Citation(s) in RCA: 20] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/25/2019] [Accepted: 04/24/2019] [Indexed: 06/01/2023]
Abstract
Animals make use of changes in photoperiod to adapt their physiology to the forthcoming breeding season. Comparative studies have contributed to our understanding of the mechanisms of seasonal reproduction in vertebrates. Birds are excellent models for studying these phenomena because of their rapid and dramatic responses to changes in photoperiod. Deep brain photoreceptors in birds perceive and transmit light information to the pars tuberalis (PT) in the pituitary gland, where the thyroid-stimulating hormone (TSH) is produced. This PT-TSH locally increases the level of the bioactive thyroid hormone T3 via the induction of type 2 deiodinase production in the mediobasal hypothalamus, and an increased T3 level, in turn, controls seasonal gonadotropin-releasing hormone secretion. In mammals, the eyes are the only photoreceptive structure, and nocturnal melatonin secretion encodes day-length information and regulates the PT-TSH signaling cascade. In Salmonidae, the saccus vasculosus plays a pivotal role as a photoperiodic sensor. Together, these studies have uncovered the universality and diversity of fundamental traits in vertebrates.
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Affiliation(s)
- Ying-Jey GUH
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, Aichi, Japan
- Division of Seasonal Biology, National Institute for Basic Biology, Okazaki, Aichi, Japan
| | - Takako K TAMAI
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, Aichi, Japan
| | - Takashi YOSHIMURA
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, Aichi, Japan
- Division of Seasonal Biology, National Institute for Basic Biology, Okazaki, Aichi, Japan
- Laboratory of Integrative Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Aichi, Japan
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Pérez JH, Tolla E, Dunn IC, Meddle SL, Stevenson TJ. A Comparative Perspective on Extra-retinal Photoreception. Trends Endocrinol Metab 2019; 30:39-53. [PMID: 30522810 DOI: 10.1016/j.tem.2018.10.005] [Citation(s) in RCA: 33] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 08/28/2018] [Revised: 10/25/2018] [Accepted: 10/26/2018] [Indexed: 12/20/2022]
Abstract
Ubiquitous in non-mammalian vertebrates, extra-retinal photoreceptors (ERPs) have been linked to an array of physiological, metabolic, behavioral, and morphological changes. However, the mechanisms and functional roles of ERPs remain one of the enduring questions of modern biology. In this review article, we use a comparative framework to identify conserved roles and distributions of ERPs, highlighting knowledge gaps. We conclude that ERP research can be divided into two largely unconnected categories: (i) identification and localization of photoreceptors and (ii) linkage of non-retinal light reception to behavioral and physiological processes, particularly endocrine systems. However, the emergence of novel gene editing and silencing techniques is enabling the unification of ERP research by allowing the bridging of this divide.
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Affiliation(s)
- Jonathan H Pérez
- Institute for Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 3FX, Scotland; The Roslin Institute, The Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian EH25 9RG, Scotland.
| | - Elisabetta Tolla
- Institute for Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 3FX, Scotland
| | - Ian C Dunn
- The Roslin Institute, The Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian EH25 9RG, Scotland
| | - Simone L Meddle
- The Roslin Institute, The Royal (Dick) School of Veterinary Studies, University of Edinburgh, Midlothian EH25 9RG, Scotland
| | - Tyler J Stevenson
- Institute for Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 3FX, Scotland
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Liu L, Chen Y, Wang D, Li N, Guo C, Liu X. Cloning and expression characterization in hypothalamic Dio2/3 under a natural photoperiod in the domesticated Brandt's vole (Lasiopodomys brandtii). Gen Comp Endocrinol 2018; 259:45-53. [PMID: 29154946 DOI: 10.1016/j.ygcen.2017.11.002] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2017] [Revised: 10/18/2017] [Accepted: 11/02/2017] [Indexed: 12/11/2022]
Abstract
The Dio2/3 gene is related to the photoperiodic response in mammals and plays an important role in the development of gonadal organs and seasonal breeding. Our previous studies have reported synchronous variations in the gonadal mass and photoperiodical transition around the summer solstice in a wild Brandt's vole population, a species with striking seasonal breeding. To investigate the role of the Dio2/3 gene in the control of seasonal breeding in this species, we cloned and characterized its expression levels by high-throughput Real-Time PCR during the period around the summer solstice. We selected a domesticated strain to ensure similar development of samples. The synchronous variation pattern between the Dio2/3 expression levels and gonadal mass around the summer solstice supports the prediction that the Dio2/3 gene plays an important role in the seasonal transition in this species. We suggest that the observed photoperiod response may be triggered by differences in the day length rather than the absolute daylength in this species. However, the similar Dio2/3 gene expression patterns but inconsistent gonadal mass patterns between the domesticated strain and the wild strain in the samples collected on Sep 8th, an absolute nonbreeding stage in the wild, lead us to speculate that the core function of the Dio2/3 gene should be restricted in response to the photoperiod rather than factors directly regulating gonadal development, and this laboratory strain could be used as an animal model to test the mechanism of environmental adaptation.
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Affiliation(s)
- Lan Liu
- College of Life Science, Sichuan University, Sichuan, China; Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Yan Chen
- College of Life Science, Sichuan University, Sichuan, China; Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Dawei Wang
- Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Ning Li
- Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China
| | - Cong Guo
- College of Life Science, Sichuan University, Sichuan, China.
| | - Xiaohui Liu
- Institute of Plant Protection, Chinese Academy of Agricultural Sciences, Beijing, China.
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Kuenzel WJ. Mapping the brain of the chicken (Gallus gallus), with emphasis on the septal-hypothalamic region. Gen Comp Endocrinol 2018; 256:4-15. [PMID: 28923430 DOI: 10.1016/j.ygcen.2017.09.003] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/15/2017] [Revised: 07/14/2017] [Accepted: 09/13/2017] [Indexed: 01/28/2023]
Abstract
There has been remarkable progress in discoveries made in the avian brain, particularly over the past two decades. This review first highlights some of the discoveries made in the forebrain and credits the Avian Brain Nomenclature Forum, responsible for changing many of the terms found in the cerebrum and for stimulating collaborative research thereafter. The Forum facilitated communication among comparative neurobiologists by eliminating confusing and inaccurate names. The result over the past 15yearshas been a standardized use of avian forebrain terms. Nonetheless, additional changes are needed. The goal of the paper is to encourage a continuing effort to unify the nomenclature throughout the entire avian brain. To emphasize the need for consensus for a single name for each neural structure, I have selected specific structures in the septum and hypothalamus that our laboratory has been investigating, to demonstrate a lack of uniformity in names applied to conservative brain regions compared to the forebrain. The specific areas reviewed include the distributions of gonadotropin-releasing hormone neurons and their terminal fields in circumventricular organs, deep-brain photoreceptors, gonadotropin inhibitory neurons and a complex structure and function of the nucleus of the hippocampal commissure.
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Affiliation(s)
- Wayne J Kuenzel
- Poultry Science Center, University of Arkansas, Fayetteville, AR 72701, USA.
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9
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Pérez JH, Meddle SL, Wingfield JC, Ramenofsky M. Effects of thyroid hormone manipulation on pre-nuptial molt, luteinizing hormone and testicular growth in male white-crowned sparrows (Zonotrichia leuchophrys gambelii). Gen Comp Endocrinol 2018; 255:12-18. [PMID: 28964732 PMCID: PMC5693035 DOI: 10.1016/j.ygcen.2017.09.025] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 04/18/2017] [Revised: 09/25/2017] [Accepted: 09/26/2017] [Indexed: 12/01/2022]
Abstract
Most seasonal species rely on the annual change in day length as the primary cue to appropriately time major spring events such as pre-nuptial molt and breeding. Thyroid hormones are thought to be involved in the regulation of both of these spring life history stages. Here we investigated the effects of chemical inhibition of thyroid hormone production using methimazole, subsequently coupled with either triiodothyronine (T3) or thyroxine (T4) replacement, on the photostimulation of pre-nuptial molt and breeding in Gambel's white-crowned sparrows (Zonotrichia leuchophrys gambelii). Suppression of thyroid hormones completely prevented pre-nuptial molt, while both T3 and T4 treatment restored normal patterns of molt in thyroid hormone-suppressed birds. Testicular recrudescence was blocked by methimazole, and restored by T4 but not T3, in contrast to previous findings demonstrating central action of T3 in the photostimulation of breeding. Methimazole and replacement treatments elevated plasma luteinizing hormone levels compared to controls. These data are partially consistent with existing theories on the role of thyroid hormones in the photostimulation of breeding, while highlighting the possibility of additional feedback pathways. Thus we suggest that regulation of the hypothalamic pituitary gonad axis that controls breeding may be more complex than previously considered.
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Affiliation(s)
- Jonathan H Pérez
- Department of Neurobiology, Physiology and Behavior, University of California, One Shields Avenue, Davis, CA 95616, USA.
| | - Simone L Meddle
- The Roslin Institute, The Royal (Dick) School of Veterinary Studies, The University of Edinburgh, Easter Bush, Midlothian, EH25 9RG Scotland, UK
| | - John C Wingfield
- Department of Neurobiology, Physiology and Behavior, University of California, One Shields Avenue, Davis, CA 95616, USA
| | - Marilyn Ramenofsky
- Department of Neurobiology, Physiology and Behavior, University of California, One Shields Avenue, Davis, CA 95616, USA
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Dixit AS, Jain Gupta N, Dwivedi V, Bhardwaj SK. Control of annual gonadal cycles in Indian songbirds. BIOL RHYTHM RES 2017. [DOI: 10.1080/09291016.2017.1345437] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
Affiliation(s)
- Anand S. Dixit
- Department of Zoology, North-Eastern Hill University, Shillong, India
| | | | - Vatsala Dwivedi
- Department of Zoology, Dyal Singh College, University of Delhi, Delhi, India
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Mishra I, Bhardwaj SK, Malik S, Kumar V. Concurrent hypothalamic gene expression under acute and chronic long days: Implications for initiation and maintenance of photoperiodic response in migratory songbirds. Mol Cell Endocrinol 2017; 439:81-94. [PMID: 27789391 DOI: 10.1016/j.mce.2016.10.023] [Citation(s) in RCA: 24] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 06/12/2016] [Revised: 10/19/2016] [Accepted: 10/22/2016] [Indexed: 01/22/2023]
Abstract
Hypothalamic expression of the thyroid hormone (TH) responsive gonadostimulatory (eya3, cga, tshβ, dio2, dio3, gnrh, gnih) and neurosteroid pathway genes (androgen receptor [ar], aromatase [cyp19], estrogen receptor [er] α and β) was examined in photosensitive redheaded buntings exposed to 2 (acute, experiment 1) or 12 (chronic, experiment 2) long days (16L:8D). Experiment 2 also included a photorefractory group. Acute long days caused a significant increase in eya3, cga, tshβ, dio2 and gnrh and decrease in dio3 mRNA levels. eya3, cga and tshβ expressions were unchanged after the chronic long days. We also found increased cyp19, erα and erβ mRNA levels after acute, and increased cyp19 and decreased erβ levels after the chronic long-day exposure. Photorefractory buntings showed expression patterns similar to that in the photosensitive state, except for high gnrh and gnih and low dio3 mRNA levels. Consistent with gene expression patterns, there were changes in fat deposition, body mass, testis size, and plasma levels of testosterone, tri-iodothyronine and thyroxine. These results show concurrent photostimulation of the TH-signalling and neurosteroid pathways, and extend the idea, based on differences in gene expression, that transitions in seasonal photoperiodic states are accomplished at the transcriptional levels in absolute photorefractory species.
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Affiliation(s)
- Ila Mishra
- IndoUS Center for Biological Timing, Department of Zoology, University of Delhi, Delhi 110 007, India
| | | | - Shalie Malik
- Department of Zoology, University of Lucknow, Lucknow 226 007, India
| | - Vinod Kumar
- IndoUS Center for Biological Timing, Department of Zoology, University of Delhi, Delhi 110 007, India.
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12
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Nishiwaki-Ohkawa T, Yoshimura T. Molecular basis for regulating seasonal reproduction in vertebrates. J Endocrinol 2016; 229:R117-27. [PMID: 27068698 DOI: 10.1530/joe-16-0066] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/24/2016] [Accepted: 04/11/2016] [Indexed: 12/31/2022]
Abstract
Animals that inhabit mid- to high-latitude regions exhibit various adaptive behaviors, such as migration, reproduction, molting and hibernation in response to seasonal cues. These adaptive behaviors are tightly regulated by seasonal changes in photoperiod, the relative day length vs night length. Recently, the regulatory pathway of seasonal reproduction has been elucidated using quail. In birds, deep brain photoreceptors receive and transmit light information to the pars tuberalis in the pituitary gland, which induces the secretion of thyroid-stimulating hormone. Thyroid-stimulating hormone locally activates thyroid hormone via induction of type 2 deiodinase in the mediobasal hypothalamus. Thyroid hormone then induces morphological changes in the terminals of neurons that express gonadotropin-releasing hormone and facilitates gonadotropin secretion from the pituitary gland. In mammals, light information is received by photoreceptors in the retina and neurally transmitted to the pineal gland, where it inhibits the synthesis and secretion of melatonin, which is crucial for seasonal reproduction. Importantly, the signaling pathway downstream of light detection and signaling is fully conserved between mammals and birds. In fish, the regulatory components of seasonal reproduction are integrated, from light detection to neuroendocrine output, in a fish-specific organ called the saccus vasculosus. Various physiological processes in humans are also influenced by seasonal environmental changes. The findings discussed herein may provide clues to addressing human diseases, such as seasonal affective disorder.
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Affiliation(s)
- Taeko Nishiwaki-Ohkawa
- Laboratory of Animal PhysiologyGraduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan Institute of Transformative Bio-Molecules (WPI-ITbM)Nagoya University, Nagoya, Japan
| | - Takashi Yoshimura
- Laboratory of Animal PhysiologyGraduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan Institute of Transformative Bio-Molecules (WPI-ITbM)Nagoya University, Nagoya, Japan Division of Seasonal BiologyNational Institute for Basic Biology, Okazaki, Japan Avian Bioscience Research CenterGraduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
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Kuenzel WJ, Kang SW, Zhou ZJ. Exploring avian deep-brain photoreceptors and their role in activating the neuroendocrine regulation of gonadal development. Poult Sci 2015. [PMID: 25828571 DOI: 10.3382/ps.2014-04370] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the eyes of mammals, specialized photoreceptors called intrinsically photosensitive retinal ganglion cells (ipRGC) have been identified that sense photoperiodic or daylight exposure, providing them over time with seasonal information. Detectors of photoperiods are critical in vertebrates, particularly for timing the onset of reproduction each year. In birds, the eyes do not appear to monitor photoperiodic information; rather, neurons within at least 4 different brain structures have been proposed to function in this capacity. Specialized neurons, called deep brain photoreceptors (DBP), have been found in the septum and 3 hypothalamic areas. Within each of the 4 brain loci, one or more of 3 unique photopigments, including melanopsin, neuropsin, and vertebrate ancient opsin, have been identified. An experiment was designed to characterize electrophysiological responses of neurons proposed to be avian DBP following light stimulation. A second study used immature chicks raised under short-day photoperiods and transferred to long day lengths. Gene expression of photopigments was then determined in 3 septal-hypothalamic regions. Preliminary electrophysiological data obtained from patch-clamping neurons in brain slices have shown that bipolar neurons in the lateral septal organ responded to photostimulation comparable with mammalian ipRGC, particularly by showing depolarization and a delayed, slow response to directed light stimulation. Utilizing real-time reverse-transcription PCR, it was found that all 3 photopigments showed significantly increased gene expression in the septal-hypothalamic regions in chicks on the third day after being transferred to long-day photoperiods. Each dissected region contained structures previously proposed to have DBP. The highly significant increased gene expression for all 3 photopigments on the third, long-day photoperiod in brain regions proposed to contain 4 structures with DBP suggests that all 3 types of DBP (melanopsin, neuropsin, and vertebrate ancient opsin) in more than one neural site in the septal-hypothalamic area are involved in reproductive function. The neural response to light of at least 2 of the proposed DBP in the septal/hypothalamic region resembles the primitive, functional, sensory ipRGC well characterized in mammals.
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Affiliation(s)
- Wayne J Kuenzel
- Department of Poultry Science, University of Arkansas, Fayetteville 72701
| | - Seong W Kang
- Department of Poultry Science, University of Arkansas, Fayetteville 72701
| | - Z Jimmy Zhou
- Department of Ophthalmology and Visual Science, Yale University School of Medicine, New Haven, CT 06510
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Stevenson TJ, Prendergast BJ. Photoperiodic time measurement and seasonal immunological plasticity. Front Neuroendocrinol 2015; 37:76-88. [PMID: 25456046 PMCID: PMC4405432 DOI: 10.1016/j.yfrne.2014.10.002] [Citation(s) in RCA: 32] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 07/08/2014] [Revised: 09/04/2014] [Accepted: 10/09/2014] [Indexed: 12/16/2022]
Abstract
Seasonal variations in immunity are common in nature, and changes in day length are sufficient to trigger enhancement and suppression of immune function in many vertebrates. Drawing primarily on data from Siberian hamsters, this review describes formal and physiological aspects of the neuroendocrine regulation of seasonal changes in mammalian immunity. Photoperiod regulates immunity in a trait-specific manner, and seasonal changes in gonadal hormone secretion and thyroid hormone signaling all participate in seasonal immunomodulation. Photoperiod-driven changes in the hamster reproductive and immune systems are associated with changes in iodothyronine deiodinase-mediated thyroid hormone signaling, but photoperiod exerts opposite effects on select aspects of the epigenetic regulation of reproductive neuroendocrine and lymphoid tissues. Photoperiodic changes in immunocompetence may explain a proportion of the annual variance in disease incidence and severity in nature, and provide a useful framework to help understand brain-immune interactions.
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Affiliation(s)
- Tyler J Stevenson
- Institute of Biological and Environmental Sciences, University of Aberdeen, Aberdeen AB24 2TZ, UK.
| | - Brian J Prendergast
- Department of Psychology and Institute for Mind and Biology, University of Chicago, Chicago, IL 60637, USA
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15
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Kuenzel WJ, Kang SW, Zhou ZJ. Exploring avian deep-brain photoreceptors and their role in activating the neuroendocrine regulation of gonadal development. Poult Sci 2015; 94:786-98. [DOI: 10.3382/ps.2014-4370] [Citation(s) in RCA: 27] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/06/2023] Open
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16
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Kang SW, Kuenzel WJ. Deep-brain photoreceptors (DBPs) involved in the photoperiodic gonadal response in an avian species, Gallus gallus. Gen Comp Endocrinol 2015; 211:106-13. [PMID: 25486342 DOI: 10.1016/j.ygcen.2014.11.020] [Citation(s) in RCA: 29] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/10/2014] [Revised: 11/26/2014] [Accepted: 11/28/2014] [Indexed: 11/30/2022]
Abstract
Three primitive photoreceptors [melanopsin (Opn4), neuropsin/opsin5 (Opn5) and vertebrate ancient opsin (VAOpn)] were reported as possible avian deep-brain photoreceptors (DBPs) involved in the perception of photoperiodic information affecting the onset and development of reproduction. The objective of this study was to determine the effect of long-day photostimulation and/or sulfamethazine treatment (SMZ, a compound known to advance light-induced testes development) on gene expression of DBPs and key hypothalamic and pituitary genes involved in avian reproductive function. Two-week old chicks were randomly selected into four experimental groups: short-day control (SC, LD8:16), short-day+SMZ (SS, LD8:16, 0.2% diet SMZ), long-day control (LC, LD16:8), and long-day+SMZ (LS, LD16:8, 0.2% diet SMZ). Birds were sampled on days 3, 7, and 28 after initiation of a long-day photoperiod and/or SMZ dietary treatments. Three brain regions [septal-preoptic, anterior hypothalamic (SepPre/Ant-Hypo) region, mid-hypothalamic (Mid-Hypo) region, posterior-hypothalamic (Post-Hypo) region], and anterior pituitary gland were dissected. Using quantitative real-time RT-PCR, we determined changes of expression levels of genes in distinct brain regions; Opn4 and Opn5 in SepPre/Ant-Hypo and Post-Hypo regions and, VAOpn in the Mid-Hypo region. Long-day treatment resulted in a significantly elevated testes weight on days 7 and 28 compared to controls, and SMZ augmented testes weight in both short- and long-day treatment after day 7 (P<0.05). Long-day photoperiodic treatment on the third day unexpectedly induced a large 8.4-fold increase of VAOpn expression in the Mid-Hypo region, a 15.4-fold increase of Opn4 and a 97.8-fold increase of Opn5 gene expression in the Post-Hypo region compared to SC birds (P<0.01). In contrast, on days 7 and 28, gene expression of the three DBPs was barely detectable. LC group showed a significant increase in GnRH-1 and TRH mRNA in the Mid-Hypo compared to SC on day 3. Pituitary LHβ and FSHβ mRNA were significantly elevated in LC and LS groups compared to SC on days 3 and 7 (P<0.05). On days 3 and 7, TSHβ mRNA level was significantly elevated by long-day treatment compared to the SC groups (P<0.05). Results suggest that long-day photoperiodic activation of DBPs is robust, transient, and temporally related with neuroendocrine genes involved in reproductive function. Additionally, results indicate that two subsets of GnRH-1 neurons exist based upon significantly different gene expression from long-day photostimulation and long-day plus SMZ administration. Taken together, the data indicate that within 3 days of a long-day photoperiod, an eminent activation of all three types of DBPs might be involved in priming the neuroendocrine system to activate reproductive function in birds.
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Affiliation(s)
- Seong W Kang
- Department of Poultry Science, Center of Excellence for Poultry Science, University of Arkansas, Fayetteville, AR, United States.
| | - Wayne J Kuenzel
- Department of Poultry Science, Center of Excellence for Poultry Science, University of Arkansas, Fayetteville, AR, United States.
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Shinomiya A, Shimmura T, Nishiwaki-Ohkawa T, Yoshimura T. Regulation of seasonal reproduction by hypothalamic activation of thyroid hormone. Front Endocrinol (Lausanne) 2014; 5:12. [PMID: 24600435 PMCID: PMC3930870 DOI: 10.3389/fendo.2014.00012] [Citation(s) in RCA: 48] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 12/25/2013] [Accepted: 01/31/2014] [Indexed: 12/15/2022] Open
Abstract
Organisms living outside the tropics measure the changes in the length of the day to adapt to seasonal changes in the environment. Animals that breed during spring and summer are called long-day breeders, while those that breed during fall are called short-day breeders. Although the influence of thyroid hormone in the regulation of seasonal reproduction has been known for several decades, its precise mechanism remained unknown. Recent studies revealed that the activation of thyroid hormone within the mediobasal hypothalamus plays a key role in this phenomenon. This localized activation of the thyroid hormone is controlled by thyrotropin (thyroid-stimulating hormone) secreted from the pars tuberalis of the pituitary gland. Although seasonal reproduction is a rate-limiting factor in animal production, genes involved in photoperiodic signal transduction pathway could emerge as potential targets to facilitate domestication.
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Affiliation(s)
- Ai Shinomiya
- Division of Seasonal Biology, National Institute for Basic Biology, Okazaki, Japan
| | - Tsuyoshi Shimmura
- Division of Seasonal Biology, National Institute for Basic Biology, Okazaki, Japan
- Laboratory of Animal Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Taeko Nishiwaki-Ohkawa
- Laboratory of Animal Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, Japan
- Avian Bioscience Research Center, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
| | - Takashi Yoshimura
- Division of Seasonal Biology, National Institute for Basic Biology, Okazaki, Japan
- Laboratory of Animal Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
- Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Nagoya, Japan
- Avian Bioscience Research Center, Graduate School of Bioagricultural Sciences, Nagoya University, Nagoya, Japan
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18
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Sechman A. The role of thyroid hormones in regulation of chicken ovarian steroidogenesis. Gen Comp Endocrinol 2013; 190:68-75. [PMID: 23631902 DOI: 10.1016/j.ygcen.2013.04.012] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/13/2012] [Revised: 04/01/2013] [Accepted: 04/04/2013] [Indexed: 10/26/2022]
Abstract
In all vertebrates, including birds, the normal development of the ovary and ovarian follicles is under the regulatory influence of hormones produced by the reproductive axis. In recent years, it has become clear that in birds an adequate level of thyroid hormones (THs), i.e. thyroxine (T4) and triiodothyronine (T3), in blood circulation is of primary importance for normal female reproductive functions. In avian species, characterized by seasonal reproduction, THs are involved in the photoperiodic regulation of reproduction acting at the mediobasal hypothalamus. In domestic fowl, where the seasonality of reproduction has been eliminated, the role of THs in ovarian function is not fully elucidated. Recent studies have revealed that ovarian follicles of the laying hen express mRNAs of TH nuclear receptors (TRα and TRβ0) as well as integrin (αVβ3) plasma membrane receptors, indicating genomic and nongenomic action of THs in the chicken ovary. In vivo experiments carried out on laying hens have showed that the bolus injection of T3 decreases levels of luteinizing hormone (LH) and estradiol (E2) in blood, and a hyperthyroid state evoked by administration of T3 for few days diminishes LH, E2 and progesterone (P4) levels, reduces the weight of the ovary, induces atresia of preovulatory follicles and eventually causes stoppage of egg laying. In vitro studies have demonstrated that T3 decreases E2 secretion from white nonhierarchical follicles and the theca layer of yellow preovulatory follicles, while on the other hand, it elevates P4 production from the granulosa layer of these follicles. These effects have been associated with steroidogenic enzyme expression and cyclic AMP synthesis. This review summarizes the current knowledge concerning the role of THs in regulation of steroidogenesis in chicken ovarian follicles.
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Affiliation(s)
- Andrzej Sechman
- Department of Animal Physiology and Endocrinology, University of Agriculture in Krakow, Al. Mickiewicza 24/28, 30-059 Krakow, Poland.
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Yoshimura T. Thyroid hormone and seasonal regulation of reproduction. Front Neuroendocrinol 2013; 34:157-66. [PMID: 23660390 DOI: 10.1016/j.yfrne.2013.04.002] [Citation(s) in RCA: 85] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 03/14/2013] [Revised: 04/21/2013] [Accepted: 04/23/2013] [Indexed: 12/15/2022]
Abstract
Organisms living outside the tropics use changes in photoperiod to adapt to seasonal changes in the environment. Several models have contributed to an understanding of this mechanism at the molecular and endocrine levels. Subtropical birds are excellent models for the study of these mechanisms because of their rapid and dramatic response to changes in photoperiod. Studies of birds have demonstrated that light is perceived by a deep brain photoreceptor and long day-induced thyrotropin (TSH) from the pars tuberalis (PT) of the pituitary gland causes local thyroid hormone activation within the mediobasal hypothalamus (MBH). The locally generated bioactive thyroid hormone, T₃, regulates seasonal gonadotropin-releasing hormone (GnRH) secretion, and hence gonadotropin secretion. In mammals, the eyes are the only photoreceptor involved in photoperiodic time perception and nocturnal melatonin secretion provides an endocrine signal of photoperiod to the PT to regulate TSH. Here, I review the current understanding of the hypothalamic mechanisms controlling seasonal reproduction in mammals and birds.
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Affiliation(s)
- Takashi Yoshimura
- Laboratory of Animal Physiology, Graduate School of Bioagricultural Sciences, Nagoya University, Furo-cho, Chikusa-ku, Nagoya 464-8601, Japan.
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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: 51] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [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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Kampf-Lassin A, Prendergast BJ. Photoperiod history-dependent responses to intermediate day lengths engage hypothalamic iodothyronine deiodinase type III mRNA expression. Am J Physiol Regul Integr Comp Physiol 2013; 304:R628-35. [PMID: 23408031 DOI: 10.1152/ajpregu.00577.2012] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Perihypothalamic thyroid hormone signaling features prominently in the seasonal control of reproductive physiology. Triiodothyronine (T(3)) signaling stimulates gonadal development, and decrements in T(3) signaling are associated with gonadal regression. Type 3 iodothyronine deiodinase (DIO3) converts the prohormone thyroxine (T(4)) into biologically inactive 3,3',5'-triiodothyronine, and in long-day breeding Siberian hamsters exposure to long (LD) and short (SD) photoperiods, respectively, inhibit and stimulate hypothalamic dio3 mRNA expression. Reproductive responses to intermediate-duration photoperiods (IntD) occur in a history-dependent manner; IntDs are interpreted as inhibitory only when preceded by longer photoperiods. Because dio3 expression has only been evaluated under LD or SD photoperiods, it is not known whether hypothalamic dio3 encodes absolute photoperiod duration or the reproductive interpretation of photoperiod. Male Siberian hamsters with and without a prior history of LD were exposed to IntD photoperiods, and hypothalamic dio3 mRNA expression was measured 6 wk later. Hamsters with a LD photoperiod history exhibited gonadal regression in IntD and a marked upregulation of hypothalamic dio3 expression, whereas in hamsters without prior exposure to LD, gonadal responses to IntD were absent, and dio3 expression remained low. Patterns of deiodinase expression in hamsters maintained in chronic IntD photoperiods did not appear to reflect feedback effects of gonadal status. Hypothalamic expression of dio3 does not exclusively reflect ambient photoperiod, but rather the context-dependent reproductive interpretation of photoperiod. Neuroendocrine mechanisms that compare current and prior photoperiods, which permit detection of directional changes in day length, occur either upstream, or at the level, of hypothalamic dio3 expression.
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Prendergast BJ, Pyter LM, Kampf-Lassin A, Patel PN, Stevenson TJ. Rapid induction of hypothalamic iodothyronine deiodinase expression by photoperiod and melatonin in juvenile Siberian hamsters (Phodopus sungorus). Endocrinology 2013; 154:831-41. [PMID: 23295738 PMCID: PMC3548179 DOI: 10.1210/en.2012-1990] [Citation(s) in RCA: 38] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/02/2023]
Abstract
Production of T(3) in the mediobasal hypothalamus is critical for regulation of seasonal reproductive physiology. Type 2 iodothyronine deiodinase (DIO2) and DIO3 enzymes catalyze the prohormone T(4) into biologically-active T(3) and biologically-inactive rT(3), respectively. In several seasonally-breeding vertebrates, DIO2 and DIO3 expression is implicated in photoperiod signal transduction in adulthood. These experiments tested the hypothesis that juvenile Siberian hamsters, which are highly responsive to photoperiod at weaning (postnatal day [PND]18), exhibit rapid and sustained changes in hypothalamic dio3 mRNA expression during photoperiod-induced and photoperiod-inhibited puberty. Hypothalamic dio2 and dio3 expression was measured via quantitative PCR in hamsters born and reared in a long-day photoperiod (15L:9D) and weaned on PND18 into short-day photoperiods (9L:15D). In SD males, hypothalamic dio3 mRNA was elevated 2.5-fold within 3 days (PND21) and continued to increase (>20-fold) through PND32; changes in dio3 mRNA preceded inhibition of gonadotropin (FSH) secretion and gonadal regression in SD. Females exhibited comparable dio3 responses to SD. In LD males, dio3 remained low and invariant from PND18-PND32. In contrast, dio2 mRNA rose conspicuously on PND21, independent of photoperiod, returning to basal levels thereafter. In LD, a single afternoon melatonin (MEL) injection on PND18 or PND20 was sufficient to increase hypothalamic dio3 mRNA, and dio3 increased in proportion to the number of successive days of MEL treatment. SD photoperiods and MEL exert rapid, sustained, and additive effects on hypothalamic dio3 mRNA, which may play a central role in inhibiting maturation of the peripubertal hypothalamo-pituitary-gonadal axis.
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23
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Siopes T, Millam J, Steinman M. Initiating egg production in turkey breeder hens: Thyroid hormone involvement. Poult Sci 2010; 89:2265-72. [DOI: 10.3382/ps.2010-00642] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
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Yasuo S, Yoshimura T. Comparative analysis of the molecular basis of photoperiodic signal transduction in vertebrates. Integr Comp Biol 2009; 49:507-18. [DOI: 10.1093/icb/icp011] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
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McNabb FMA. The Hypothalamic-Pituitary-Thyroid (HPT) Axis in Birds and Its Role in Bird Development and Reproduction. Crit Rev Toxicol 2008; 37:163-93. [PMID: 17364708 DOI: 10.1080/10408440601123552] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022]
Abstract
This article reviews thyroid function and its hypothalamic-pituitary-thyroid (HPT) axis control in birds with emphasis on the similarities and differences in thyroid function compared to mammals and other vertebrate classes. Thyroid hormones are important in metabolism and the thermogenesis required for homeothermy in birds, as in mammals, the other homeothermic class of vertebrates. Thyroid hormones play important roles in development and growth in birds, as is the case for all vertebrate classes. The developmental effects of thyroid hormones in birds are presented in the context of differences in precocial and altricial patterns of development and growth with emphasis on oviparous development. The sections on thyroid hormone actions include discussion of effects on the development of a number of tissue types as well as on seasonal organismal processes and interactions of the thyroid axis with reproduction. The current picture of how environmental chemicals may disrupt avian thyroid function is relatively limited and is presented in the context of the assessment endpoints that have been used to date. These endpoints are categorized as thyroid and HPT axis endpoints versus target organ endpoints. The final section discusses two recommended assay protocols, the avian two-generation toxicity assay and the avian one-generation assay, and whether these protocols can evaluate thyroid disruption in birds.
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Affiliation(s)
- F M Anne McNabb
- Department of Biological Sciences, Virginia Tech, Blacksburg, Virginia 24061-0406, USA.
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26
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Paul MJ, Zucker I, Schwartz WJ. Tracking the seasons: the internal calendars of vertebrates. Philos Trans R Soc Lond B Biol Sci 2008; 363:341-61. [PMID: 17686736 PMCID: PMC2606754 DOI: 10.1098/rstb.2007.2143] [Citation(s) in RCA: 155] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Animals have evolved many season-specific behavioural and physiological adaptations that allow them to both cope with and exploit the cyclic annual environment. Two classes of endogenous annual timekeeping mechanisms enable animals to track, anticipate and prepare for the seasons: a timer that measures an interval of several months and a clock that oscillates with a period of approximately a year. Here, we discuss the basic properties and biological substrates of these timekeeping mechanisms, as well as their reliance on, and encoding of environmental cues to accurately time seasonal events. While the separate classification of interval timers and circannual clocks has elucidated important differences in their underlying properties, comparative physiological investigations, especially those regarding seasonal prolactin secretions, hint at the possibility of common substrates.
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Affiliation(s)
- Matthew J Paul
- Department of Neurology, University of Massachusetts Medical School, 55 Lake Avenue North, Worcester, MA 01655, USA.
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Proudman JA, Siopes TD. Potential role of thyroid hormones and prolactin in the programming of photorefractoriness in turkey hens. Poult Sci 2006; 85:1457-61. [PMID: 16903478 DOI: 10.1093/ps/85.8.1457] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/12/2022] Open
Abstract
The domestic turkey hen is a seasonal breeder, requiring a period of short days to establish photosensitivity and a long day length to initiate egg production. The reproductive season is then limited by the onset of photorefractoriness (PR), which causes a decline, and then termination, of egg laying. In passerine birds, PR is programmed early in the reproductive season by the presence of thyroid hormones and a long photoperiod. High circulating prolactin (PRL) is thought to hasten the onset of PR. In a prior study, we reported that hens destined to have PR exhibited lower levels of thyroxine (T4) and PRL at certain points (weeks) following photostimulation than did hens destined to remain photosensitive (PS), a result opposite to what might be expected. The present study was conducted to further explore the possible relationship between circulating hormone levels and subsequent PR in the commercial turkey hen at times (days) closer to photostimulation than our previous study. Plasma levels of triiodothyronine (T3), T4, and PRL were compared in 2 subpopulations of hens identified retrospectively after 50 wk of egg production: A group of 17 hens that exhibited PR (mean onset = 27 wk of photostimulation) and a group of "good" layers that remained PS (mean production = 210 eggs/50 wk). Results showed no differences between groups in plasma T3 or T4 levels or in the T3:T4 ratio at -6, 0, 1, 3, and 7 d from photostimulation. Plasma PRL levels were significantly higher at 8 and 9 wk after photostimulation in hens that remained PS vs. those that became PR. We conclude that thyroid hormone levels around the time of photostimulation either are not actively related to programming of subsequent PR in turkeys or programming for PR in the turkey hen occurs later in the reproductive cycle than in passerine birds. We further conclude that hens that exhibit PR tend to have lower circulating PRL levels early in the reproductive season than hens that remain PS and lay at a relatively high rate.
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Affiliation(s)
- J A Proudman
- Biotechnology and Germplasm Laboratory Building 200, USDA-ARS, BARC-East, Beltsville, MD 20705, USA.
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Kang SW, Thayananuphat A, Rozenboim I, Millam JR, Proudman JA, El Halawani ME. Expression of hypothalamic GnRH-I mRNA in the female turkey at different reproductive states and following photostimulation. Gen Comp Endocrinol 2006; 146:91-9. [PMID: 16427052 DOI: 10.1016/j.ygcen.2005.10.017] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/04/2005] [Revised: 09/07/2005] [Accepted: 10/09/2005] [Indexed: 11/30/2022]
Abstract
In birds, changes in hypothalamic gonadotropin-releasing hormone-I (GnRH-I) content and release are correlated with reproductive stages. This study examined the distribution and expression level of GnRH-I mRNA in anatomically discrete hypothalamic nuclei throughout the turkey reproductive cycle and following photostimulation. GnRH-I mRNA expression was determined using in situ hybridization in non-photostimulated (NPS), egg-laying (LAY), incubating (INC) and photorefractory (REF) hens. Overall, GnRH-I mRNA expression was greatest in the nucleus commissurae pallii (nCPa) and around the organum vasculosum lamina terminalis (OVLT), with less expression observed in the nucleus septalis lateralis (SL), cortico-habenula cortico-septum area, and within the nucleus preopticus medialis. GnRH-I mRNA expression was significantly increased in nCPa, OVLT, and SL after NPS hens (6L:18D) were exposed to a 30 or 90 min pulse of light beginning 14 h after first light (dawn). GnRH-I mRNA abundance within nCPa, OVLT and SL was greater in LAY than in NPS and INC hens, while mRNA expression was least in REF hens. These results indicate that GnRH-I mRNA expression in birds is sensitive to light stimulation during the photosensitive period and can be used to more precisely characterize their different reproductive stages.
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Affiliation(s)
- Seong W Kang
- Department of Animal Science, University of Minnesota, 495 AnSci/Vet Med Bldg., 1988 Fitch Ave., St. Paul, MN 55108 ,USA
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Yamamura T, Yasuo S, Hirunagi K, Ebihara S, Yoshimura T. T3 implantation mimics photoperiodically reduced encasement of nerve terminals by glial processes in the median eminence of Japanese quail. Cell Tissue Res 2006; 324:175-9. [PMID: 16432711 DOI: 10.1007/s00441-005-0126-8] [Citation(s) in RCA: 81] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/17/2005] [Accepted: 11/09/2005] [Indexed: 10/25/2022]
Abstract
Photoperiodically generated triiodothyronin (T(3)) in the mediobasal hypothalamus (MBH) has critical roles in the photoperiodic response of the gonads in Japanese quail. In a previous study, we demonstrated seasonal morphological changes in the neuro-glial interaction between gonadotrophin-releasing hormone (GnRH) nerve terminals and glial endfeet in the median eminence (ME). However, a direct relationship between photoperiodically generated T(3) and seasonal neuro-glial plasticity in the ME remained unclear. In the present study, we examined the effect of T(3) implantation into the MBH on the neuro-glial interaction in the ME. T(3) implantation caused testicular growth and reduced encasement of nerve terminals in the external zone of the ME. In contrast, no morphological changes were observed in birds given an excessive dose of T(3), which did not cause testicular growth. These results support the hypothesis that thyroid hormone regulates photoperiodic GnRH secretion via neuro-glial plasticity in the ME.
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Affiliation(s)
- Takashi Yamamura
- Division of Biomodeling, Graduate School of Bioagricultural Sciences, Nagoya University, 464-8601, Nagoya, Japan
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Goodson JL, Saldanha CJ, Hahn TP, Soma KK. Recent advances in behavioral neuroendocrinology: insights from studies on birds. Horm Behav 2005; 48:461-73. [PMID: 15896792 PMCID: PMC2570788 DOI: 10.1016/j.yhbeh.2005.04.005] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/02/2005] [Revised: 04/05/2005] [Accepted: 04/07/2005] [Indexed: 01/16/2023]
Abstract
Ever since investigations in the field of behavioral endocrinology were hatched with experiments on roosters, birds have provided original insights into issues of fundamental importance for all vertebrate groups. Here we focus on more recent advances that continue this tradition, including (1) environmental regulation of neuroendocrine and behavioral systems, (2) steroidogenic enzyme functions that are related to intracrine processes and de novo production of neurosteroids, and (3) hormonal regulation of neuroplasticity. We also review recent findings on the anatomical and functional organization of steroid-sensitive circuits in the basal forebrain and midbrain. A burgeoning body of data now demonstrates that these circuits comprise an evolutionarily conserved network, thus numerous novel insights obtained from birds can be used (in a relatively straightforward manner) to generate predictions for other taxa as well. We close by using birdsong as an example that links these areas together, thereby highlighting the exceptional opportunities that birds offer for integrative studies of behavioral neuroendocrinology and behavioral biology in general.
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Affiliation(s)
- James L Goodson
- Psychology Department, University of California, 5212 McGill Hall, San Diego, La Jolla, CA 92093-0109, USA.
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YASUO S, EBIHARA S, YOSHIMURA T. Oral thyroxine administration mimics photoperiodically induced gonadal growth in Japanese quail. Anim Sci J 2004. [DOI: 10.1111/j.1740-0929.2004.00205.x] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
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Mishra MK, Wilson FE, Scanlan TS, Chiellini G. Thyroid hormone-dependent seasonality in American tree sparrows (Spizella arborea): effects of GC-1, a thyroid receptor beta-selective agonist, and of iopanoic acid, a deiodinase inhibitor. J Comp Physiol B 2004; 174:471-9. [PMID: 15235810 DOI: 10.1007/s00360-004-0433-5] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 05/13/2004] [Indexed: 10/26/2022]
Abstract
To explore the role of TH in the control of seasonality [i.e., photoperiodic testicular growth, photorefractoriness, and postnuptial (prebasic) molt] in American tree sparrows (Spizella arborea), we performed experiments in which THX males were simultaneously photostimulated and given TH replacement therapy. In the first experiment, equimolar concentrations (1X = 1.3 nmol) of T4, T3, or GC-1, an iodine-free TRbeta agonist, were administered s.c. daily during the first 21 days of photostimulation. Two additional THX groups received GC-1 at 0.1X or 10X, and THX and THI control groups received vehicle. In the second experiment, T4 or T3, alone or in combination with the deiodinase inhibitor IOP, was injected i.m. twice daily during the first 14 days of photostimulation. In both experiments, end points were testis length and molt score. In the first experiment, THI birds given vehicle and THX birds given T4 replacement therapy exhibited all three components of seasonality. THX birds given T3 or GC-1 (1X or 10X) showed a subdued photoperiodic testicular response, but they did not become photorefractory or initiate molt. THX birds that received 0.1X GC-1 or vehicle exhibited none of the components of seasonality. These data are consistent with the hypothesis that photoperiodic testicular growth, a vernal component of seasonality, is a TRbeta-mediated response and suggest that T4 may activate TRbeta more efficiently than does T3 or GC-1. By contrast, the failure both of T3 and of GC-1, but not of T4, to program photostimulated THX males for photorefractoriness and postnuptial molt suggests that autumnal components of seasonality may be TRalpha-mediated responses solely to T4. In the second experiment, IOP administered alone had no significant impact on seasonality. THX birds that received T4 with or without IOP showed all components of seasonality, whereas birds that received T3 with or without IOP showed only photoperiodic testicular growth. These results challenge the widely held view that T4 is merely a prohormone for T3 and support the emerging view that T4 has intrinsic hormonal activity. Because IOP augmented the photoperiodic testicular response in T3-treated THX birds, T3 may act either independently or co-dependently with T4 in programming vernal seasonal events.
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Affiliation(s)
- M K Mishra
- Division of Biology, Kansas State University, Manhattan, KS 66506, USA.
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Vasudevan N, Ogawa S, Pfaff D. Estrogen and thyroid hormone receptor interactions: physiological flexibility by molecular specificity. Physiol Rev 2002; 82:923-44. [PMID: 12270948 DOI: 10.1152/physrev.00014.2002] [Citation(s) in RCA: 83] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
The influence of thyroid hormone on estrogen actions has been demonstrated both in vivo and in vitro. In transient transfection assays, the effects of liganded thyroid hormone receptors (TR) on transcriptional facilitation by estrogens bound to estrogen receptors (ER) display specificity according to the following: 1) ER isoform, 2) TR isoform, 3) the promoter through which transcriptional facilitation occurs, and 4) cell type. Some of these molecular phenomena may be related to thyroid hormone signaling of seasonal limitations upon reproduction. The various combinations of these molecular interactions provide multiple and flexible opportunities for relations between two major hormonal systems important for neuroendocrine feedbacks and reproductive behaviors.
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Affiliation(s)
- Nandini Vasudevan
- Laboratory of Neurobiology and Behavior, The Rockefeller University, New York, New York 10021, USA
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Siopes TD. Circulating thyroid hormone levels in recycled turkey breeder hens during a short day prelighting period and renewal of photosensitivity for egg production. Poult Sci 2002; 81:1342-6. [PMID: 12269614 DOI: 10.1093/ps/81.9.1342] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Two experiments were conducted with yearling turkey hens at the end of their first season of egg laying. The purpose was to examine changes in plasma thyroid hormone levels during recycling and renewal of photosensitivity for egg production. Plasma concentrations of thyroid hormones were determined weekly or biweekly for 8 wk following a change from existing photoperiods of long days (LD) to short days (SD) and during the associated complete renewal (recycling) of photosensitivity for egg production. In both experiments, neither thyroxine (T4) nor triiodothyronine (T3) declined from starting values during the SD exposure but plasma T3 increased significantly from LD controls. There were no significant treatment effects (SD vs. LD) for T4 in either experiment. The increase in T3 was 101 and 145% in Experiments 1 and 2, respectively, and extended over the 8-wk SD treatment period in a parabolic fashion. The T3/T4 ratio was also significantly increased in the SD treatments of both experiments as compared to LD controls. Plasma concentrations of T3, but not T4, clearly changed during recycling and renewal of photosensitivity for egg production in breeder hens. These results were consistent with a participation of plasma T3 in promoting photosensitivity and diminishing photorefractoriness in turkey hens during SD-induced recycling.
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Affiliation(s)
- T D Siopes
- Department of Poultry Science, College of Agriculture and Life Sciences, North Carolina State University, Raleigh, 27695-7608, USA.
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Proudman JA, Siopes TD. Relative and absolute photorefractoriness in turkey hens: profiles of prolactin, thyroxine, and triiodothyronine early in the reproductive cycle. Poult Sci 2002; 81:1218-23. [PMID: 12211315 DOI: 10.1093/ps/81.8.1218] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
An experiment was conducted to determine whether a commercial strain of turkey hens exhibits relative photorefractoriness (rPR) during a reproductive cycle and to ascertain whether plasma levels of certain hormones early in the reproductive cycle might be associated with subsequent expression of rPR or absolute photorefractoriness (aPR). Twenty-seven percent of hens maintained on a stimulatory photoperiod of 18L:6D for 19 wk and then given a shorter, but still stimulatory, photoperiod (13L:11D) ceased to lay and their ovaries regressed within 4 wk. These hens were considered rPR. Subsequent exposure to the 18L:6D photoperiod resulted in ovarian recrudescence in 41.7% of these PR individuals, confirming the presence of rPR at 19 wk after photostimulation. Absolute PR was observed in 15.1% of hens during a 27-wk reproductive season. Hens that became rPR or aPR exhibited significantly lower plasma prolactin levels at 8 and 14 wk after photostimulation than did hens that remained photosensitive (PS). Plasma levels of thyroxine were lower at 1 and 2 wk following photostimulation in hens that subsequently became PR than in hens that remained PS. We conclude that turkey hens may exhibit rPR and aPR during a reproductive cycle, whereas flockmates may remain PS for at least 27 wk. The presence of long daylengths, thyroid hormones, and PRL did not assure expression of PR. The expression of PR appears to be associated with reduced plasma throxine levels during a period when programming of PR is thought to occur and with reduced levels of prolactin following peak egg production.
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Affiliation(s)
- J A Proudman
- Agricultural Research Service, US Department of Agriculture, Beltsville, Maryland 20705, USA.
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Abstract
This review examines how birds use the annual cycle in photoperiod to ensure that seasonal events--breeding, molt, and song production--happen at the appropriate time of year. Differences in breeding strategies between birds and mammals reflect basic differences in biology. Avian breeding seasons tend to be of shorter duration and more asymmetric with respect to changes in photoperiod. Breeding seasons can occur at the same time each year (predictable) or at different times (opportunistic), depending on the food resource. In all cases, there is evidence for involvement of photoperiodic control, nonphotoperiodic control, and endogenous circannual rhythmicity. In predictable breeders (most nontropical species), photoperiod is the predominant proximate factor. Increasing photoperiods of spring stimulate secretion of gonadotropin-releasing hormone (GnRH) and consequent gonadal maturation. However, breeding ends before the return of short photoperiods. This is the consequence of a second effect of long photoperiods--the induction of photorefractoriness. This dual role of long photoperiods is required to impart the asymmetry in breeding seasons. Typically, gonadal regression through photorefractoriness is associated with a massive decrease in hypothalamic GnRH, essentially a reversal to a pre-pubertal condition. Although breeding seasons are primarily determined by photoperiodic control of GnRH neurons, prolactin may be important in determining the exact timing of gonadal regression. In tropical and opportunistic breeders, endogenous circannual rhythmicity may be more important. In such species, the reproductive system remains in a state of "readiness to breed" for a large part of the year, with nonphotic cues acting as proximate cues to time breeding. Circannual rhythmicity may result from a temporal sequence of different physiological states rather than a molecular or cellular mechanism as in circadian rhythmicity. Avian homologues of mammalian clock genes Per2, Per3, Clock, bmal1, and MOP4 have been cloned. At the molecular level, avian circadian clocks appear to function in a similar manner to those of mammals. Photoperiodic time measurement involves interaction between a circadian rhythm of photoinducibility and, unlike mammals, deep brain photoreceptors. The exact location of these remains unclear. Although the eyes and pineal generate a daily cycle in melatonin, this photoperiodic signal is not used to time seasonal breeding. Instead, photoperiodic responses appear to involve direct interaction between photoreceptors and GnRH neurons. Thyroid hormones are required in some way for this system to function. In addition to gonadal function, song production is also affected by photoperiod. Several of the nuclei involved in the song system show seasonal changes in volume, greater in spring than in the fall. The increase in volume is, in part, due to an increase in cell number as a result of neurogenesis. There is no seasonal change in the birth of neurons but rather in their survival. Testosterone and melatonin appear to work antagonistically in regulating volume.
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Affiliation(s)
- A Dawson
- Centre for Ecology and Hydrology, Huntingdon, Cambridgeshire, UK
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Bentley GE. Unraveling the enigma: the role of melatonin in seasonal processes in birds. Microsc Res Tech 2001; 53:63-71. [PMID: 11279671 DOI: 10.1002/jemt.1069] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023]
Abstract
Birds, unlike mammals, do not use the annual profile of pineal melatonin secretion to coordinate their reproductive efforts with a favorable time of year. Melatonin in birds mediates the entrainment of circadian activity rhythms, and thus helps to time hatching of eggs and facilitate migration. However, the role of melatonin as a reliable indicator of day length for seasonal processes has remained equivocal for many years. Recently, the influence of melatonin on two physiological processes involved in aspects of seasonal reproduction has been identified in European starlings: 1) the regulation of seasonal changes in immune function, and 2) neuroplasticity in the song control system. Melatonin can enhance cell-mediated immune function and acts as an inhibitory hormone on the song control system. Melatonin receptor (MelR) density in a forebrain song control nucleus, Area X, is regulated as a function of reproductive state; there is marked downregulation of MelR in Area X during the breeding season in starlings. Seasonal regulation of immune function and neural plasticity within the song control system, and the efficacy of the action of melatonin on these two processes, appears to be modified by the same central, thyroid-dependent mechanism that controls the reproductive state of birds. These data indicate that the interaction of day length and hormones of different classes affects the ability of melatonin to affect seasonal processes in birds. The downstream consequences of MelR regulation within the song control system are discussed with regard to the cellular action of melatonin and its possible interaction with immediate-early genes and transcription factors.
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Affiliation(s)
- G E Bentley
- Department of Psychology, Behavioral Neuroendocrinology Group, The Johns Hopkins University, Baltimore, Maryland, USA.
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