Influence of Male Rats on the Luteinizing Hormone-Releasing Hormone Neuronal System in Female Rats: Role of the Vomeronasal Organ

Abstract

Olfactory information processed by the vomeronasal system is reported to influence reproductive functions in a variety of mammals. The present studies were designed to determine if male-associated cues affect the luteinizing hormone-releasing hormone (LHRH) neuronal system, and, if so, to determine the extent to which these cues are processed by the vomeronasal organ (VNO). Ovariectomized rats underwent VNO removal (VNX) or sham surgery (VN-Sham). Forty-eight hours after estrogen priming (5 µg), they were subjected to one of the following treatments: repeated mating, repeated exposure to male-soiled bedding or repeated exposure to clean bedding. In animals treated for 180 min, coronal brain sections were double labelled for Fos protein and LHRH. An intense Fos immunoreactivity was induced following mating in the majority of LHRH neurons in the VN-Sham females, whereas removal of the VNO significantly suppressed the mating-induced Fos staining. Exposure of female rats to male-soiled bedding or clean bedding did not induce appreciable Fos immunoreactivity in LHRH neurons. Following 90 min of mating or exposure to bedding, blood samples were assayed for luteinizing hormone (LH). Mating stimulated the release of LH in VN-Sham females, while the removal of the VNO significantly suppressed the mating-induced LH release. Exposure of the females to male-soiled bedding or clean bedding did not induce an LH surge. The present results demonstrate that male-originating sensory cues (i.e. repeated mating) can influence the LHRH neuronal system, as evidenced by the presence of Fos immunoreactivity in LHRH cell bodies, and indicate that this effect is mediated through the VNO to a certain extent. The lack of Fos immunoreactivity in the LHRH neurons of females exposed to male-soiled bedding and the inability of male-soiled bedding to induce LH release suggest that male-soiled bedding is not as effective as mating in activating the vomeronasal system in rats.

Sexual Stimulation Induces Fos Immunoreactivity within GnRH Neurons of the Female Rat Preoptic Area: Interaction with Steroid Hormones

“…In contrast to the present results, Rajendren et al [26] reported much higher percentages of GnRH neurons that coexpressed Fos following 180 min of COP in ovariectomized, estrogen-primed rats as compared with unmated controls. Differences in the amount of stimulation that the females received, the time course of Fos induction (180 vs. 60 min), and the type of primary antibody used could explain the differences in the results.…”

“…Again, differences in the amount of stimulation, type of antibody, time course of Fos induction, and species may account for these incon sistencies. Interestingly, Rajendren et al [26] reported a lower proportion of double-labelled cells in mated females that had their vomeronasal organs removed as compared with sham-treated females. In our study, females that received manual VCS also had a lower proportion of dou ble-labelled cells as compared with females that received intromissions and ejaculations by the stimulus males.…”

“…Inter estingly, systemic or central administration of GnRH facilitates lordosis behavior [13][14][15][16], Recently, we and others have shown that sexual stimu lation (either COP with intromission or manual VCS) induces c-fos mRNA and Fos-like immunoreactivity (IR) within estrogen-concentrating and nonconcentrating re gions of the female rat brain, including regions known to contain GnRH cells in the septum and above the organum vasculosum (OVLT) in the anterior POA [17][18][19][20][21][22][23], Al though the overall expression of Fos-like IR within these regions did not appear to require treatment with estrogen and progesterone (P), we cannot rule out the possibility that either of these steroids could enhance Fos-like IR within neurochemically defined subgroups of cells. Pre vious work has established that Fos-like IR is found with in GnRH-containing neurons of the anterior POA in the intact female rat during and immediately following the proestrous LH surge [24,25], Moreover, Fos-like IR has been reported within GnRH cells of female mice and rats following COP [26,27], The present study compared the ability of COP or VCS, with or without hormone replace ment, to induce Fos-like IR within GnRH neurons of the female rat brain.…”

Functional Internal Complexity of Amygdala: Focus on Gene Activity Mapping After Behavioral Training and Drugs of Abuse

“…35,367,487). Such a view is supported by the effects of lesions of the medial amygdala that were shown to impair sexual reactions (238,239,294,306,386). The specific role of the medial amygdala in sexual activities is consistent also with the results obtained with pharmacological approach.…”

A Confocal Microscopic Study of Synaptic Inputs to Gonadotropin-Releasing Hormone Cells in Mouse Brain: Regional Differences and Enhancement by Estrogen

“…In female rats, activation of approximately 40% of the GnRH cells located primarily in the OVLT-POA occurs during the steroid-induced [13]and proestrous [14]LH surges, as revealed by the induction of immunoreactivity for Fos. However, in OVX estrogen-primed rats subjected to mating, a larger proportion of the GnRH cells including those located in the anterior septal area expresses Fos immunoreactivity [15]. During the steroid-induced LH surge in mice, a large number of GnRH cells in the OVLT region express Fos [16].…”