Date of Degree
Martin P. Schreibman
The use of cytometric, immunocytochemical and radioimmunological methods has allowed the investigation of the ontogeny and functional significance of LHRH containing centers in sibling platyfish (Xiphophorus maculatus) genetically determined to reach sexual maturity at different ages and in adult fish which were hypophysectomized and given replacement therapy with gonadotropin.
There is a sequential development of three immunoreactive (ir-) LHRH centers in the brain that is directly related to stage, not age of sexual maturation. The first region to contain ir-LHRH is the nucleus olfactoretinalis (NOR). Ir-LHRH then appears in the nucleus preopticus periventricularis (NPP), followed by the nucleus lateralis tuberis (NLT). This anterior to posterior sequence has been termed as the "cascade effect" and is essentially similar to both early and late maturing genotypes, except that in late maturers, specific steps of the "cascade effect" take place at similar developmental stages, but in older animals, and require more time to be completed.
The appearance of these LHRH producing centers in the brain precede and are presumably essential for the completion of gonadotrop development and the subsequent maturation of the gonads. A direct correlation is found between the number of ir-LHRH containing perikarya in the brain and number of ir-GTH cells in the pituitary of both early and late maturers. In both genotypes, the number of ir-cells are similar in the NOR and PI, but in late maturers, the number of ir-cells in the NPP, NLT and CPD are significantly less.
The dynamics of the interaction between LHRH and GTH are further illustrated by the effect of hypophysectomy and hormone replacement. ICC and RIA results demonstrate that hypophysical removal produces distinct changes in the distribution and quantity of LHRH in the brain. A decrease in the total LHRH content occurs in the brains of hypophysectomized animals, which is partially restored by the administration of gonadotropin.
The different responses of these ir-LHRH containing centers to hypophysectomy and the sequential accumulation of ir-LHRH in the NOR, NPP and NLT between birth and puberty against that they differ in their roles in regulating BPG axis function.
The results of this study also indicate that the site(s) and mechanism(s) of the P gene are highly complex phenomena and that the P gene may express itself, either directly or indirectly, at various levels of the nervous and endocrine systems.
Halpern-Sebold, Leslie R., "The Ontogeny and Functional Significance of Luteinizing Hormone Releasing Hormone (LHRH) Containing Centers of the Brain of the Freshwater Teleost, Xiphophorus maculatus" (1984). CUNY Academic Works.