Male hamster investigatory and copulatory responses to vaginal discharge: Relationship to the endocrine status of females

The ability of vaginal discharge from ovariectomized (OVEX) or hypophysectomized (HYPOX) female hamsters to elicit intense genital investigation and to facilitate overt copulatory behavior in males was compared with that of estrous vaginal discharge. The discharges were collected by vaginal lavage with water. In order to avoid exposure of experimental males to female stimuli other than vaginal discharge, the behavioral tests employed anesthetized mates (female surrogates) whose hindquarters were scented with the collected vaginal material or with control solvent (water). Both the OVEX and HYPOX discharges elicited intense genital investigation and significantly increased the incidence of intromission attempts toward the scented surrogates. However, both types of discharge had significantly less behavioral activity than estrous vaginal discharge. In a subsequent experiment, a water dilution series of estrous vaginal discharge was tested for the ability to promote genital investigation and copulatory behavior toward scented surrogates. The amount of discharge typically extruded by one estrous female in response to tactile genital stimulation can be diluted one hundred-fold without appreciable reductions in its behavioral activity. These results demonstrate that the behavioral activity of hamster vaginal discharge is related to the endocrine status of females, and suggest that previous failures to demonstrate clear dependence on ovarian function might have been due to ceiling effects in laboratory tests.     

Chemical studies of hamster vaginal discharge: Male behavioral responses to a high molecular weight fraction require physical contact

This report describes the isolation and behavioral testing in normal male hamsters of a high molecular weight fraction (HMF) of vaginal discharge which accounts for much of the aphrodisiac activity in the discharge. The HMF encompasses a group of proteins which elute as a relatively narrow, major peak upon agarose gel filtration of estrous vaginal discharge. The crude fraction from gel filtration retains a variety of volatiles including sulfur-containing compounds which we have previously found to account for much of the initial attraction of males to the female but which do not, themselves, facilitate overt copulatory behavior. Procedures for markedly reducing the presence of such volatiles to yield the HMF are described. In behavioral assays using anesthetized males as surrogate females, scenting the hindquarters of the surrogates with the HMF elicits intense genital investigation by experimental males, although this effect on investigatory behavior is not as dramatic as that of the unfractionated vaginal discharge. Like the unfractionated discharge, the HMF significantly increases the incidence of intromission attempts toward scented surrogates. To assess whether physical contact with the HMF is required for behavioral activity, as would be expected if the active material is proteinaceous, series of preference tests were performed using vanillin as a competing stimulus under conditions in which physical contact with the stimuli either was possible or was prevented. The unfractionated discharge was preferred in both conditions, whereas significant preferences for the HMF were exhibited only if it could be contacted by the snout of experimental males. The active material in the HMF thus appears to be of extremely low volatility, at least prior to physical contact with it by the male.     

Chemical studies of hamster vaginal discharge: effects of endocrine ablation and protein digestion on behaviorally active macromolecular fractions

Our previous studies have demonstrated that macromolecular fractions of hamster vaginal discharge elicit intense genital investigation and facilitate copulatory behavior toward anesthetized males (female surrogates) whose hindquarters have been scented with these fractions, and that the aphrodisiac activity is significantly reduced in the vaginal discharge of ovariectomized (OVEX) or hypophysectomized (HYPOX) females. The present series of studies compared the protein compositions of estrous, diestrous, OVEX, and HYPOX vaginal discharge, and assessed whether protein digestion of estrous vaginal discharge affects its aphrodisiac activity. Polyacrylamide gel electrophoresis of vaginal lavages showed that the endocrine status of females has a profound effect on the protein composition of the vaginal discharge. The concentration of the major proteins dropped by about ten-fold in going from the estrous to the diestrous condition. The concentration of these same proteins appear to be at least another order of magnitude lower in the vaginal discharges of OVEX and HYPOX females. These major proteins had molecular weights greater than 10,000 Daltons. A macromolecular fraction of estrous vaginal discharge isolated by gel filtration at elevated temperature (conditions known to separate some protein-bound steroids) and containing proteins of molecular weight greater than 10,000 Daltons was found to be modestly but significantly less active than estrous discharge in its ability to elicit intense genital investigation, and not significantly different from estrous discharge in its ability to facilitate overt copulatory behavior toward scented surrogates. Pronase digestion of the proteins in this fraction did not alter its effects on investigatory behavior toward scented surrogates but significantly reduced its ability to facilitate copulatory behavior.(ABSTRACT TRUNCATED AT 250 WORDS)     

Methyl thiolbutyrate: A reliable correlate of estrus in the golden hamster

A volatile sulfur-containing compound that is characteristic of estrous (Day 1) hamster vaginal discharge has been identified as methyl thiolbutyrate (MTB). From numerous measurements of MTB concentration on each day of the estrous cycle, it is clear that this compound could well serve as a natural chemical signal of the estrous state of the female. Both the ability of MTB to attract male hamsters and its ability to facilitate copulatory behavior toward female surrogates were evaluated in behavioral experiments. The responses to MTB were compared to those elicited by dimethyl disulfide (DMDS), by a mixture of MTB and DMDS, by a grand mixture of MTB and DMDS with thirteen other known volatile constituents of the vaginal discharge, and by fresh vaginal discharge. In contrast to fresh vaginal discharge, none of the identified compounds or mixtures facilitated male copulatory behavior. Most of the attraction observed in the behavioral experiments could be attributed to the DMDS in the test samples. The MTB is readily converted to DMDS and may serve as a precursor of DMDS in the vaginal discharge.     

Sex responses of the female hamster: Effects on male performance

During copulation the female hamster adjusts the position of the perineal region in response to tactile stimulation from the male. Anaesthetization of the perineal region of the female eliminates these adjustment responses and reduces the probability that the male will ejaculate in a five-minute mating test. Anaesthetization also increases the variability of male performance. However, sexually aroused males were not affected.     

Male hamster copulatory responses to a high molecular weight fraction of vaginal discharge: effects of vomeronasal organ removal

The importance of the vomeronasal (accessory olfactory) system for the copulatory responses of male hamsters to a high molecular weight fraction (HMF) of vaginal discharge was assessed in animals that had their vomeronasal organs (VNO) removed. These organs were extirpated bilaterally using an oral approach through the palate so as to eliminate the peripheral afferents to the accessory olfactory bulb (AOB) with minimal or no damage to the main olfactory system. The selective peripheral deafferentation procedure was verified by applying horseradish peroxidase intranasally following intraperitoneal injections of epinephrine to facilitate the vomeronasal pumping mechanism that draws fluids into the VNO. Heavy, bilateral anterograde labeling was evident in the olfactory nerve afferents within the main olfactory bulb of males that had their VNO removed and of animals that received sham surgery. Sham-operated males also had heavy, bilateral labeling in the vomeronasal nerve afferents within the AOB, whereas no such labeling occurred among animals with bilateral removal of the VNO. In sham-operated animals, both the HMF and the unfractionated discharge significantly increased the incidence of intromission attempts toward anesthetized males (surrogate females) whose hindquarters were scented with these stimuli. The unfractionated discharge also produced a significant elevation of overt copulatory behavior in males with selective peripheral deafferentation of the vomeronasal system, whereas the HMF did not facilitate copulatory behavior in these animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Olfactory and vomeronasal system participation in male hamsters' attraction to female vaginal secretions.

The effects of olfactory (OLF) vomeronasal (VN), or combined deafferentations of male hamsters on their attraction to female hamster vaginal secretions (FHVS) were determined using 2 different attraction tests. In the first, FHVS was placed on one wall of a plastic test chamber, while in the second test, FHVS was rubbed onto 1 of 2 anesthetized castrate hamsters. OLF deafferentation abolished the males' attraction to FHVS in the first test but had no effect in the second. The persistence of FHVS attraction in the anesthetized castrate test depended on the VN system in that its subsequent deafferentation greatly attenuated the attraction. When the VN system was deafferented alone, FHVS attraction was significantly reduced only in males exhibiting severe mating behavior deficits. These results are interpreted to support the hypothesis that the OLF and VN systems may be preferentially responsive to volatile and non-volatile odorants, respectively. Our findings emphasize that both the OLF and VN systems participate in subserving males' attraction to FHVS and their mating with receptive females. Thus each chemosensory system may influence both sexual arousal and copulatory mechanisms.     

An electron microscopic study of the harderian gland of the Syrian hamster with particular reference to the processes of formation and discharge of the secretory vacuoles

The lipid-secreting cells of the Harderian gland of the Syrian hamster were studied using light, transmission, and scanning electron microscopy. Three morphologically different secretory cell types are identified in the gland: type I and II cells of the male gland and, distinct from either, the female gland cell. In all secretory cell types, lipid droplets in the cytoplasm were surrounded by unit membranes. Ultrastructural evidence of the involvement of the Golgi apparatus in the formation of the secretory vacuoles was obtained. The process of secretion involved the fusion of the boundary unit membrane of the vacuole with the plasma membrane and the release of the vacuolar content alone into the lumen. No evidence of holocrine processes was observed in this study. In addition to lipids, vacuoles contained materials whose solubility properties clearly differed from those of lipids. There appear to be variations in the ultrastructural characteristics of the vacuole content of the different types of secretory cell. © 1993 Wiley-Liss, Inc.     

Male hamster sociosexual behaviors: effects of testosterone and its metabolites

Male hamsters were tested for copulatory behavior (CB) with receptive females, for investigatory responses to the females' ano-genital region (A/G), and for attraction to female hamster vaginal secretion (FHVS). After castration, the males received Silastic capsules containing one of two doses of testosterone (T), 5 alpha-dihydrotestosterone (DHT), estradiol (E2) or DHT + E2, and the maintenance of their copulatory and chemoinvestigatory responsiveness was assessed during weekly tests for the next month. The major findings were: (1) T thresholds for the maintenance of CB were lower than they were for the maintenance of A/G behavior and FHVS attraction; (2) DHT + E2 or DHT alone were more effective in maintaining A/G and FHVS attraction than was E2 alone; (3) DHT + E2 or DHT alone maintained ejaculatory behavior in some animals but E2 did not; (4) the posttreatment maintenance of normal ejaculation latencies and intromissions to ejaculation shown by intact and T-treated males was not demonstrated by males receiving DHT or DHT + E2. These results are consistent with the hypothesis that copulatory and chemoinvestigatory behaviors may be subserved by distinct neuroendocrine mechanisms in male hamsters.