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Homeostasis of circulating androgens levels in the male three-spined stickleback (Gasterosteus aculeatus)
Stockholm University, Faculty of Science, Department of Zoology, Functional Morphology. (Fish Reproduction)
Stockholm University, Faculty of Science, Department of Zoology, Functional Morphology.ORCID iD: 0000-0003-1248-6987
2012 (English)In: Zoological Studies, ISSN 1021-5506, E-ISSN 1810-522X, Vol. 51, no 8, 1282-1289 p.Article in journal (Refereed) Published
Abstract [en]

In mammals, plasma androgen levels are regulated by homeostatic feedbackmechanisms operating in the brain-pituitary-gonadal axis. However, some earlierstudies suggest that this may not be the case in all teleosts. This study aims atinvestigating to what extent androgens levels are homeostatically regulated in malethree-spined stickleback (Gasterosteus aculeatus), and whether aromatisation ofandrogens plays a role in this. To that end, breeding male sticklebacks were eithercompletely castrated or hemi-castrated or sham-operated, and implanted with differentdoses of 11- ketoandrostenedione (11KA) and testosterone (T) or with the aromataseinhibitor (AI) fadrozole. Hemi-castration alone diminished androgen levels andcomplete castration almost removed them. Low doses of 11KA and T increasedplasma androgen levels in castrated but not in sham-operated fish. Both low and highdoses of 11KA increased plasma 11-ketotestosterone (11KT) in hemi-castrated fish,whereas only the high dose of 11KA did so in sham-operated fish. If aromatizationplays a role in homeostatic mechanisms, androgen levels would be expected to rise insham-operated fish treated with AI. However, this was not the case. The reduction ofplasma androgen levels in fully mature hemi-castrated fish may suggest that theremaining testis is not able to increase its steroidogenesis further. However, both311KA and T treatments increased plasma levels much less in sham-operated fish thanin castrated ones, indicating that homeostatic mechanisms are nevertheless present.

Place, publisher, year, edition, pages
2012. Vol. 51, no 8, 1282-1289 p.
Keyword [en]
steroid, RIA, homeostasis, feedback, stickleback
National Category
Zoology
Research subject
Zoological physiology
Identifiers
URN: urn:nbn:se:su:diva-80875OAI: oai:DiVA.org:su-80875DiVA: diva2:557928
Available from: 2012-10-01 Created: 2012-10-01 Last updated: 2017-12-07Bibliographically 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)
Opponent
Supervisors
Note

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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