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

Abstract

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 dorsomedially, 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 singlelabeled 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.onadotropin-releasing hormones (GnRHs) have been detected in all vertebrate species studied across the phylogenetic scale from tunicates (1, 2) to humans (2, 3). In mammals, the prevailing view is that luteinizing hormone (LH) and folliclestimulating hormone (FSH) release is primarily controlled by mammalian luteinizing hormone-releasing hormone (m-LHRH). However, recent studies have uncovered other isoforms of the GnRH peptide besides m-LHRH in the mammalian brain (3-8). Chicken-GnRH-II (c-GnRH-II) (4-7) and lampreyGnRH (l-GnRH; refs. 3 and 8) have been detected in the mammalian hypothalamus. Specifically, in situ hybridization experiments localized c-GnRH-II mRNA in the supraoptic, paraventricular, and suprachiasmatic nuclei as well as in the medial basal hypothalamus, but this mRNA was not detected within neurons that were immunopositive for m-LHRH (5). With regard to l-GnRH, an antiserum to l-GnRH-I bound to cells and nerve fibers projecting through the arcuate nucleus and terminating in the median eminence (ME) in the human brain (3). Additionally, our recent study using an antibody that recognized both l-GnRH-I and l-GnRH-III allowed u...

Molecular Polymorphism of Native Gonadotropin-Releasing Hormone (GnRH) Is Restricted to Mammalian GnRH and [Hydroxyproline⁹] GnRH in the Developing Rat Brain

“…The present data show that small amounts of materials related to cGnRH-II, lGnRH-III and sGnRH were present in crude brain extracts, but we did not observe any differences between the hypothalamus and the remaining brain, as expected from previous reports [8,24,25,26], or any changes with advancing age in animals of either sex. These materials did not elute during HPLC as native or [hydroxyproline 9 ] forms of GnRH variants, but emerged at an early stage in the RP procedure like unspecific RIA- interfering moieties, giving rise to a false-positive peak with all the antibodies used.…”

“…The hypothalamus and the brain of rat have been reported to contain cGnRH-II [5], sGnRH [7] and lGnRH-III [8], whereas other studies showed no evidence of any additional isoforms [3, 6,9,10,11,12]. sGnRH was reported to occur in the brain of an ancestral rodent [13, 14], but this finding was not subsequently confirmed [6].…”

“…In addition, no other endogenous lGnRH-like peptide was recognized by the antibody used in the characterization of lGnRH-III from the lamprey brain [32]. A recent study showed the presence of lGnRH-III in the rat hypothalamus [8]. However, lGnRH-III and mHypGnRH were found to coelute during RP-HPLC, while the GnRH-like IR from the rat brain eluted like both decapeptides and was identified as mHypGnRH after determining the primary structure [12].…”

Contribution of Chicken GnRH-II and Lamprey GnRH-III on Gonadotropin Secretion

“…Although lGnRH-III is not a natural ligand of the type I or type II GnRHR, the lGnRH-III receptor shares different characteristics of both type I and type II GnRHRs (Silver et al, 2005;Silver and Sower, 2006). The presence of lGnRH-III (or a related analog) have been reported in brain extracts from humans, sheep, cows and rats (Dees et al, 1999;Hiney et al, 2002;Yahalom et al, 1999;Yu et al, 2000), suggesting a biological activity of this GnRH isoform in several species. However, to date, the gene expression of lGnRH-III has not been reported in mammalian species.…”

“…The presence of lGnRH-III in the brain of rats was identified by immunocytochemistry (Dees et al, 1999), and subsequently localized in the dorsomedial preoptic area (POA) of the brain and colocalized with mGnRH (Hiney et al, 2002). However, lGnRH-III was not d e t e c t e d i n r a t s a n d o t h e r r o d e n t s b y r e v e r s e -p h a s e -H P L C f o l l o w e d b y R I A , o r b y performing two successive HPLC steps to prevent the coelution of GnRH peptides (Gautron et al, 2005;Montaner et al, 1999;Montaner et al, 2001).…”