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Gonadotrophin‐Inhibitory Hormone in the Cichlid Fish Cichlasoma dimerus : Structure, Brain Distribution and Differential Effects on the Secretion of Gonadotrophins and Growth Hormone
Author(s) -
Di Yorio M. P.,
Pérez Sirkin D. I.,
Delgadin T. H.,
Shimizu A.,
Tsutsui K.,
Somoza G. M.,
Vissio P. G.
Publication year - 2016
Publication title -
journal of neuroendocrinology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.062
H-Index - 116
eISSN - 1365-2826
pISSN - 0953-8194
DOI - 10.1111/jne.12377
Subject(s) - medicine , endocrinology , cichlid , biology , hypothalamus , context (archaeology) , hormone , immunocytochemistry , gonadotropic cell , preoptic area , pituitary gland , fish <actinopterygii> , paleontology , fishery
The role of gonadotrophin‐inhibitory hormone (Gn IH ) in the inhibition of the reproductive axis has been well‐established in birds and mammals. However, its role in other vertebrates, such as the teleost fish, remains controversial. In this context, the present study aimed to evaluate whether Gn IH modulates the release of gonadotrophins and growth hormone ( GH ) in the cichlid fish Cichlasoma dimerus . First, we partially sequenced the precursor polypeptide for Gn IH and identified three putative Gn IH peptides. Next, we analysed the expression of this precursor polypeptide via a polymerase chain reaction in the reproductive axis of both sexes. We found a high expression of the polypeptide in the hypothalamus and gonads of males. Immunocytochemistry allowed the observation of Gn IH ‐immunoreactive somata in the nucleus posterioris periventricularis and the nucleus olfacto‐retinalis, with no differences between the sexes. Gn IH ‐immunoreactive fibres were present in all brain regions, with a high density in the nucleus lateralis tuberis and at both sides of the third ventricle. Finally, we performed in vitro studies on intact pituitary cultures to evaluate the effect of two doses (10 −6 m and 10 −8 m ) of synthetic C. dimerus (cd‐) LPQRF a‐1 and LPQRF a‐2 on the release of gonadotrophins and GH . We observed that cd‐ LPQRF a‐1 decreased β‐luteinising hormone ( LH ) and β‐follicle‐stimulating hormone ( FSH ) and also increased GH release to the culture medium. The release of β‐ FSH was increased only when it was stimulated with the higher cd‐ LPQRF a‐2 dose. The results of the present study indicate that cd‐ LPQRF a‐1, the cichlid fish Gn IH , inhibits β‐LH and β‐ FSH release and stimulates GH release in intact pituitary cultures of C. dimerus . The results also show that cd‐ LPQRF ‐2 could act as an β‐ FSH ‐releasing factor in this fish species.