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Early Maturity in the Male Striped Bass, Morone saxatilis: Follicle-Stimulating Hormone and Luteinizing Hormone Gene Expression and Their Regulation by Gonadotropin-Releasing Hormone Analogue and Testosterone¹

^a Center of Marine Biotechnology, University of Maryland Biotechnology Institute, Baltimore, Maryland 21202

ABSTRACT

Striped bass are seasonal breeding fish, spawning once a year during the spring. All 3-yr-old males are sexually mature; however, 60–64% of the fish mature earlier as 1- or 2-yr-old animals. The endocrine basis underlying early maturity in 2-yr-old males was studied at the molecular level by monitoring changes in pituitary ßFSH and ßLH mRNA levels by ribonuclease protection assay, and correlating these changes to stages of testicular development. In maturing males, the mRNA levels of ßFSH were elevated during early spermatogenesis, whereas ßLH mRNA levels peaked during spermiation. The appearance of spermatozoa in the testis was associated with a decrease in ßFSH mRNA and a rise in ßLH mRNA abundance. Immature males had lower levels of ßLH mRNA than maturing males, but there were no differences in ßFSH mRNA levels between immature and maturing males. The regulation of gonadotropin gene expression in 2-yr-old males was studied by the chronic administration of GnRH analogue (GnRHa) and testosterone (T), with or without pimozide (P) supplementation. In immature males, the combination of T and GnRHa stimulated a three- to fivefold increase in ßFSH and ßLH mRNA levels, but the same treatment had no effect on gonadotropin gene expression in maturing males. In addition, the coadministration of P to immature males suppressed the stimulatory effect of GnRHa and T on ßFSH and ßLH mRNA levels, suggesting that dopamine may have a novel role in regulating gonadotropin gene expression.

FOOTNOTES

First decision: 6 June 2000.

¹ This research was supported in part by grants (to Y.Z.) IS-2634-95-C from the U.S.-Israel Binational Agricultural Research and Development Fund (BARD), NA46RG0091 (Amnd. 6) from Maryland Sea Grant College Program, and 58-6420-7-049 from the United States Department of Agriculture. This publication is contribution no. 522 from the Center of Marine Biotechnology, University of Maryland Biotechnology Institute.

² Correspondence: Yonathan Zohar, 701 E. Pratt St., Baltimore, MD 21202. FAX: 410 234 8896; zohar{at}umbi.umd.edu

³ Current address: SARS International Center for Molecular Marine Biology, University of Bergen, Thormøhlensgt. 55, 5008 Bergen, Norway.

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