This Article Full Text Full Text (PDF) Purchase Article View Shopping Cart Alert me when this article is cited Alert me if a correction is posted Citation Map Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Request Copyright Permission Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by Parhar, I. S. Articles by Sakuma, Y. Search for Related Content PubMed PubMed Citation Articles by Parhar, I. S. Articles by Sakuma, Y.

Thyroid Hormone and Estrogen Regulate Brain Region-Specific Messenger Ribonucleic Acids Encoding Three Gonadotropin-Releasing Hormone Genes in Sexually Immature Male Fish, Oreochromis niloticus¹

Department of Physiology, Nippon Medical School, Tokyo 113-8602, Japan

Address all correspondence and requests for reprints to: Dr. Ishwar S. Parhar, Department of Physiology, Nippon Medical School, Sendagi-1–1-5, Bunkyo-ku, Tokyo 113-8602, Japan. E-mail: ishwar{at}nms.ac.jp

The present study was undertaken to determine whether T₃, estrogen, and 11-ketotestosterone could alter a specific population of GnRH-containing neurons, as indicated by a change in messenger RNA (mRNA) levels in sexually immature male tilapia, Oreochromis niloticus. Two weeks after castration, fish were assigned to four treatment groups. One group served as the control (sesame oil); a single ip injection of (T₃; 5 µg/g), estradiol benzoate (EB; 5 µg/g), or 11-ketotestosterone (KT; 5 µg/g) was administered to the remaining three groups. Twenty-four hours after the injection, brains were collected and processed for in situ hybridization histochemistry using ³⁵S-labeled 30-mer antisense oligonucleotide probes complementary to the GnRH-coding region of chicken II, salmon, and seabream GnRH. Computerized image analysis was performed to quantify mRNA concentrations, neuronal numbers, and neuronal size of the terminal nerve-nucleus olfactoretinalis, preoptic, and midbrain GnRH neurons. KT had no effect on any of the above neuronal parameters examined for salmon or seabream GnRH. Neither T₃, EB, nor KT was effective to induce changes in midbrain chicken GnRH II mRNA concentrations, neuronal numbers, and neuronal size, indicating that an as yet unknown regulatory mechanism may operate midbrain GnRH neurons. T₃ specifically suppressed the concentration of terminal nerve salmon GnRH mRNA, and EB significantly increased preoptic seabream GnRH neuronal numbers. These results are consistent with the hypothesis that thyroid hormone, by suppressing terminal nerve GnRH expression, promotes inhibition of sexual maturation. Furthermore, the failure of KT, a nonaromatizable androgen, to influence preoptic GnRH neurons emphasizes that an estrogenic pathway, at the onset of sexual maturation, is responsible for the recruitment of additional preoptic GnRH neurons that are fundamental to reproduction and behavior.

This article has been cited by other articles:

				L. N. Moens, K. van der Ven, P. Van Remortel, J. Del-Favero, and W. M. De Coen Expression Profiling of Endocrine-Disrupting Compounds Using a Customized Cyprinus carpio cDNA Microarray Toxicol. Sci., October 1, 2006; 93(2): 298 - 310. [Abstract] [Full Text] [PDF]

				I. S. Parhar, S. Ogawa, and Y. Sakuma Three GnRH receptor types in laser-captured single cells of the cichlid pituitary display cellular and functional heterogeneity PNAS, February 8, 2005; 102(6): 2204 - 2209. [Abstract] [Full Text] [PDF]

				I. S. Parhar, S. Ogawa, and Y. Sakuma Laser-Captured Single Digoxigenin-Labeled Neurons of Gonadotropin-Releasing Hormone Types Reveal a Novel G Protein-Coupled Receptor (Gpr54) during Maturation in Cichlid Fish Endocrinology, August 1, 2004; 145(8): 3613 - 3618. [Abstract] [Full Text] [PDF]

				I. S. Parhar, S. Ogawa, T. Hamada, and Y. Sakuma Single-Cell Real-Time Quantitative Polymerase Chain Reaction of Immunofluorescently Identified Neurons of Gonadotropin-Releasing Hormone Subtypes in Cichlid Fish Endocrinology, August 1, 2003; 144(8): 3297 - 3300. [Abstract] [Full Text] [PDF]

				S. Khosravi and P. C. K. Leung Differential Regulation of Gonadotropin-Releasing Hormone (GnRH)I and GnRHII Messenger Ribonucleic Acid by Gonadal Steroids in Human Granulosa Luteal Cells J. Clin. Endocrinol. Metab., February 1, 2003; 88(2): 663 - 672. [Abstract] [Full Text] [PDF]

				N. Vasudevan, S. Ogawa, and D. Pfaff Estrogen and Thyroid Hormone Receptor Interactions: Physiological Flexibility by Molecular Specificity Physiol Rev, October 1, 2002; 82(4): 923 - 944. [Abstract] [Full Text] [PDF]