Distribution of Variant Forms of Immunoreactive Gonadotropin-Releasing Hormone and β-Gonadotropins I and II in the Platyfish, Xiphophorus maculatus, from Birth to Sexual Maturity

Abstract

Immunoreactive (ir) lamprey (l), mammalian (m), chicken II (chII), and salmon (s) gonadotropin-releasing hormone (GnRH) and ir-coho salmon β-gonadotropins I and II (GTH I and GTH II) have been localized in the brain and pituitary gland of Xiphophorus maculatus, the platyfish, at various stages of development from birth to sexual maturity. Ir-GTH I was found in the pituitary gland at all stages examined; ir-GTH II was found only in animals in the pubertal and mature stages. Ir-sGnRH was seen only in the pituitary gland of neonatal and immature animals. In pubertal fish, it was found in the nucleus olfactoretinalis (NOR) of the brain as well as in the pituitary gland. In older animals it was found in the nucleus preopticus periventricularis (NPP) and the nucleus lateralis tuberis (NLT), as well as in the NOR and the pituitary gland. Ir-mGnRH was seen in the pituitary of neonatal and immature fish. It was restricted to the NOR and pituitary gland of pubertal animals. In mature animals, it had a similar, but not identical, distribution as that of ir-sGnRH. Antisera to mGnRH and sGnRH appeared to stain the same cells in the brain and pituitary gland. Ir-lGnRH was found only in the pituitary gland of animals of all ages where it stained the same cells as ir-mGnRH and ir-sGnRH. Ir-chIIGnRH was absent in all immature stages. In animals that were sexually mature it was seen in tracts in the NPP, nucleus preopticus (NPO), NLT, and pituitary gland. Ir-chIIGnRH seemed to colocalize with ir-sGnRH in the pituitary but there was no apparent colocalization with any other form of ir-GnRH in the brain. These results demonstrate that variant forms of GnRH and GTH are present at defined stages of development in specific regions of the brain and pituitary gland and suggest that different forms of GnRH and GTH regulate different aspects of reproductive system development and physiology.