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GnRH mRNA levels in the brain of male three-spined stickleback, Gasterosteus aculeatus;effects of photoperiod, gonadectomy and breeding-postbreeding condition
Stockholm University, Faculty of Science, Department of Zoology, Functional Morphology.
(English)Article in journal (Other academic) Submitted
Abstract [en]

In vertebrates, reproduction is regulated by the brain-pituitary-gonad (BPG) axis where thegonadotropin- releasing hormone (GnRH) is one of the components. However, very little isknown about the possible role of GnRHs in environmental and feedback control of fishreproduction. To investigate this, GnRH2 (chicken II GnRH) and GnRH3 (salmon GnRH) mRNAlevels in male three-spined stickleback (Gasterosteus aculeatus), where GnRH1 is absent,were measured in different reproductive conditions; breeding or post-breeding, treated withlong (LD: 16:8) or short (LD: 8:16) photoperiod and castrated or sham-operated in thebreeding season. Using in situ hybridization, specific GnRH3 RNA probe labeled cells wereobserved in hypothalamus and pituitary and ventral telecephalon, but barely in other brainareas. GnRH2 expressing cells were mainly located in the mesencephalon and thalamus, butwere found in hypothalamus and pituitary as well. The GnRH3 mRNA levels were always farhigher than GnRH2. Breeding male brains had considerably higher levels of both GnRH2 andGnRH3 mRNA than post-breeding male brains. This suggests that both forms havereproductive functions. Fish kept under long photoperiod, which stimulated breeding, hadhigher mRNA levels of GnRH2, but not of GnRH3 which is probably the hypophysiotropicform, than fish kept under non-stimulatory short photoperiod. Thus, the higher expressionsof gonadotropins under long than under short photoperiod are not likely to be regulated viaGnRHs. Furthermore, castrated males’ brains showed lower GnRH2 and GnRH3 mRNA levelsthan sham-operated ones. This is consistent with that the positive feedback known toregulate lh-β in this phase could be exerted via GnRHs.

Keyword [en]
photoperiod, GnRH2, GnRH3, stickleback, feedback, mRNA
National Category
Zoology
Research subject
Zoological physiology
Identifiers
URN: urn:nbn:se:su:diva-80873OAI: oai:DiVA.org:su-80873DiVA: diva2:557925
Available from: 2012-10-01 Created: 2012-10-01 Last updated: 2012-10-01Bibliographically 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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