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Androgen feedback effects on LH and FSH, and photoperiodic control of reproduction in male three-spined sticklebacks, Gasterosteus aculeatus
Stockholm University, Faculty of Science, Department of Zoology.
Stockholm University, Faculty of Science, Department of Zoology.
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2013 (English)In: General and Comparative Endocrinology, ISSN 0016-6480, E-ISSN 1095-6840, Vol. 182, 16-23 p.Article in journal (Refereed) Published
Abstract [en]

Sexual maturation in the stickleback is controlled by photoperiod. The aim of this study was to find out whether changes in feedback effects exerted by sex steroids could mediate the photoperiodic effect, which is regarded to be of an all-or-nothing character. To that end, males were castrated and treated with different doses of testosterone (T) and in one experiment also with the aromatase inhibitor fadrozole (AI) and kept under different photoperiods. In control fish, long day (LD 16:8) stimulated maturation, associated with more hypertrophied kidneys (a secondary sexual character) and higher levels of pituitary lhb and fshb mRNA than under short day conditions (LD 8:16). Under LD 8:16, low doses of T suppressed both lhb and fshb mRNA levels. However, with the use of high doses of T and/or longer photoperiods the inhibitory effects on lhb and fshb mRNA levels became less clear or instead positive effects were observed. Under intermediate photoperiod conditions, the negative feedback effect of a low dose of T on fshb was more prominent with shorter photoperiods, whereas no such shift was observed for lhb mRNA. The inhibitory effect of the low dose of T on lhb mRNA levels under LD 8:16 was abolished by AI, whereas the stimulatory effect of the high dose of T was not. The negative feedback effects were more marked under short days than under long days, whereas positive feedback effects were more marked under long days. The suppression of both fshb and lhb mRNA levels by low androgen levels, especially under short days, may inhibit maturation completely unless a rise of androgens above threshold levels would allow complete maturation.

Place, publisher, year, edition, pages
2013. Vol. 182, 16-23 p.
Keyword [en]
lhb, fshb, mRNA, Feedback, Reproduction, Stickleback, Photoperiod
National Category
Zoology
Research subject
Zoological physiology
Identifiers
URN: urn:nbn:se:su:diva-88677DOI: 10.1016/j.ygcen.2012.10.017ISI: 000315013100003OAI: oai:DiVA.org:su-88677DiVA: diva2:613023
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AuthorCount:6;

Available from: 2013-03-26 Created: 2013-03-25 Last updated: 2017-12-06Bibliographically approved
In thesis
1. The brain-pituitary-gonadal axis of the three-spined stickleback, Gasterosteus aculeatus
Open this publication in new window or tab >>The brain-pituitary-gonadal axis of the three-spined stickleback, Gasterosteus aculeatus
2012 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The seasonal reproduction of the three-spined stickleback is stimulated by long day photoperiod. As in other vertebrates, the reproductive system of stickleback is regulated by the brain-pituitary-gonadal (BPG) axis which is largely controlled by feedback effects. Both negative and positive feedback effects on the BPG axis have been found in fish. So far, the roles feedback effects on the BPG axis play in the photoperiodic regulation of seasonal reproduction are still unclear. This thesis focused on the photoperiodic regulation and gonadal feedback effects on the gene expressions of gonadotropin (GtH) and gonadotropin-releasing hormones (GnRH) in the brain and pituitary, and how gonadal feedback regulated the steroid homeostasis in stickleback.Both GnRH2 and GnRH3 mRNA was found in the hypothalamus. Higher expression levels of both GnRH2 and 3 in breeding than in post-breeding males suggested that they are both involved in seasonal reproduction. There was no evidence for a role of GnRH3, which may be the dominating form, in the photoperiodic control of reproduction. However, the polarity of the feedback effect on gnrh3 gene expression may turn from positive to be negative when the males went into post-breeding state. Tapeworm, Schistocephalus solidus, infection inhibited the reproduction of sticklebacks. However, the infection caused higher expression levels of both GnRHs and GtHs genes, which may be due to feedback effect on the BPG axis.Under short day, both lh-β and fsh-β were suppressed by low androgen levels. This negative feedback may inhibit maturation completely, unless a rise of androgens triggers positive feedback under long day. The change in feedback polarity may result in all or nothing maturation. Furthermore, the androgen inhibitory effect on lh-β and fsh-β under short day could be abolished by aromatase inhibitor, which means the estrogen may cause negative feedback in males under short day.There was no compensation effect on plasma androgen level in fully mature hemi-castrated fish. However, both testosterone and 11-ketoandrostenedione treatments increased plasma levels much less in sham-operated fish than in castrated ones, indicating that homeostatic mechanisms are nevertheless present.

Place, publisher, year, edition, pages
Stockholm: Department of Zoology, Stockholm University, 2012. 39 p.
Keyword
BPG axis, GnRH, lh-β, fsh-β, three-spined stickleback, Gasterosteus aculeatus, homeostasis, feedback
National Category
Zoology
Research subject
Functional Zoomorphology
Identifiers
urn:nbn:se:su:diva-80473 (URN)978-91-7447-568-5 (ISBN)
Public defence
2012-10-19, William-Olssonsalen, Geovetenskapens hus, Svante Arrhenius väg 14, Stockholm, 10:00 (English)
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At the time of the doctoral defense, the following papers were unpublished and had a status as followsPaper 1: Submitted. Paper 3: Submitted. Paper 4: Submitted.

Available from: 2012-09-28 Created: 2012-09-20 Last updated: 2013-05-08Bibliographically approved

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