GnRH mRNA levels in the brain of male three-spined stickleback, Gasterosteus aculeatus;effects of photoperiod, gonadectomy and breeding-postbreeding condition
(English)Article in journal (Other academic) Submitted
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.
photoperiod, GnRH2, GnRH3, stickleback, feedback, mRNA
Research subject Zoological physiology
IdentifiersURN: urn:nbn:se:su:diva-80873OAI: oai:DiVA.org:su-80873DiVA: diva2:557925