Gonadotropin-releasing hormone neurons in the preoptic-hypothalamic region of the rat contain lamprey gonadotropin-releasing hormone III, mammalian luteinizing hormone-releasing hormone, or both peptides.
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This study utilized a newly developed antiserum, specific for lamprey gonadotropin-releasing hormone III (l-GnRH-III), to determine the following: in which regions of the rat hypothalamus the neuronal perikarya producing l-GnRH-III are localized; and whether this peptide, known to selectively induce follicle-stimulating hormone release, is coexpressed in neurons containing mammalian luteinizing hormone-releasing hormone (m-LHRH). Double-label immunocytochemistry was performed by using an l-GnRH-III polyclonal antiserum and an LHRH monoclonal antiserum. Immunopositive neurons for l-GnRH-III, m-LHRH, or neurons coexpressing both peptides were detected within the organum vasculosum lamina terminalis (OVLT) region of the preoptic area (POA). Caudal to the OVLT, l-GnRH-III-positive neurons were also observed dorso-medially, above the third ventricle in the medial POA. The m-LHRH neurons were not observed in this area. The lateral POA region contained neurons positive for both peptides along with single-labeled neurons for each peptide. Importantly, neurons that expressed l-GnRH-III, m-LHRH, or both peptides were also detected in the ventral regions of the rostral hypothalamus, dorsolateral to the borders of the supraoptic nuclei. In both of these latter areas, neurons containing l-GnRH-III were slightly dorsal to neurons containing only m-LHRH. The l-GnRH-III perikarya and fibers were eliminated by absorption of the primary antiserum with l-GnRH-III, but not by l-GnRH-I, chicken-GnRH-II, or m-LHRH. These results indicate that, unlike other isoforms of GnRH found in the mammalian brain, l-GnRH-III neurons not only are observed in regions that control follicle-stimulating hormone release but also are colocalized with m-LHRH neurons in areas primarily controlling LH release. These findings suggest an interrelationship between these two peptides in the control of gonadotropin secretion.
author list (cited authors)
Hiney, J. K., Sower, S. A., Yu, W. H., McCann, S. M., & Dees, W. L.
complete list of authors
Hiney, JK||Sower, SA||Yu, WH||McCann, SM||Dees, WL