Ovarian hormones influence odor stimulated flank marking behavior in the hamster (Mesocricetus auratus)

The effect of ovarian hormones on the frequency of female flank marking in response to the odors of male hamsters was examined. The amount of flank marking differed significantly (p less than 0.01) among the days of the estrous cycle, with the lowest levels of flank marking occurring on estrus. Ovariectomy (OVX) eliminated the 4 day rhythm, and significantly (p less than 0.01) reduced the total amount of flank marking. Implantation of Silastic capsules containing estradiol benzoate (EB) in OVX hamsters increased flank marking by approximately two-fold when compared to hamsters implanted with blank Silastic capsules. In a second series of experiments, OVX hamsters given EB flank marked significantly (p less than 0.01) more than those with blank capsules. Subcutaneous injection of progesterone (P) into OVX-EB treated hamsters 6 hr prior to testing significantly reduced flank marking when compared to OVX-EB treated hamsters given oil. No differences were observed in flank marking between groups of OVX hamsters with blank capsules and injected with P or oil. In summary, these data indicate that the four day rhythm of odor stimulated flank marking in intact female hamsters may be the result of the 4 day fluctuations of estrogen and progesterone that occur during the estrous cycle.     

The role of estrogen and progesterone in the control of preputial gland sex attractant odors in the female rat

Sexually experienced male rats were used to test the attractiveness of body odors of female rats. The attractiveness of these odors varied with the estrous cycle. Odors from female rats in proestrus were the most attractive to male rats and those from female rats during the darkness hours of diestrus the least attractive. The preputial glands appeared to be the source of these odors for the male rats showed no preference for the odors of proestrous female rats that had been preputialectomized. Administration of 1 μg estrdiol benzoate (EB) for 5 days increased the attractiveness of body odors of ovariectomized rats. A higher dose of EB (5 μg) had the same effect when administered for 1 or 5 days although the increase that occurred after 3 days was not significant. A single dose of progesterone (P) (500 μg) on the other hand, decreased the attractiveness of ovariectomized female odors although no change was seen after 3 days of treatment. A single injection of P also decreased the attractiveness of odors of ovariectomized females that had received EB for 3 days. However, P failed to decrease the attractiveness of odors in ovariectomized females after preputialectomy. We conclude that the preputial glands are an important source of sex attractant odors in the female rat and that the changes in the release of these odors that occur throughout the estrous cycle and pregnancy are controlled by ovarian steroids. While estrogen acts to stimulate the production and release of these odors P appears to inhibit their release.     

Effects of fluprazine hydrochloride on conspecific odor preferences in rats

The effect of Fluprazine Hydrochloride (DU 27716) on preference for conspecific male, estrous female and food odors was examined in male rats utilizing a two-compartment choice apparatus. Treatment with 8.0 mg/kg Fluprazine enhanced the preference of males for male odors but had no effect on preference for either estrous female or food odors. The drug-induced enhancement of male odor preference is consistent with the suggestion that Fluprazine interferes in some way with the processing of olfactory stimuli which normally precede offensive attack. The failure of the drug to alter the preference of males for estrous female odors suggests that the increased sniffing of estrous females noted during social testing may be secondary to other sources of conspecific stimulation or may reflect a highly transitory effect on olfactory processes. These results suggest that the suppressive effects of Fluprazine on intermale aggression and copulation are mediated by somewhat distinct mechanisms.     

Olfactory experience and the development of odor preference and vaginal marking in female Syrian hamsters

Rodent reproductive behavior relies heavily on odor processing, and evidence suggests that many odor-guided sexual behaviors are shaped by prior experience. We sought to determine if exposure to male odors during development is required for the adult expression of proceptive sexual behavior toward male odors in female Syrian hamsters. Exposure to male odors was restricted in na?ve subjects by removing all male siblings from the litter at three to five days of age. Control litters were also culled, but included equal numbers of male and female pups. As adults, na?ve females displayed investigatory preferences toward male odors in a Y-maze that were comparable to control females; this preference was observed whether contact with the odor stimuli was prevented of allowed. In contrast, na?ve females vaginal scent-marked equally toward male and female volatile odors, suggesting an inability to target behavior toward sexually relevant odors. However, na?ve females marked preferentially toward male odors when allowed to contact the odor stimuli. These results provide evidence for the experience-dependent development of vaginal marking behavior toward volatile components of sexual odors. Furthermore, they suggest that distinct mechanisms regulate the development of odor preferences and vaginal marking behavior in this species.     

A competitive effect of androgen signaling on male mouse attraction to volatile female mouse odors

Olfaction plays an important role in animal communication. We hypothesized that males recognize the attractive volatile odors attributed to female reproductive ability. We measured the period during which a male mouse spent sniffing volatile odors from a sham-operated female mouse or an ovariectomized mouse without visual or tactile contact. Intact male mice spent more time sniffing volatile odors from proestrous, estrous or metestrous females than from ovariectomized females. There was no difference in castrated male mice. To investigate the involvement of sexual hormone in this behavior, castrated male mice were treated with 17 alpha-estradiol (E), dihydrotestosterone (DHT), or both. E-treatment did not affect sniffing behavior. Regardless of the estrous stages, DHT-treated castrated males spent less time sniffing the volatile odors from sham-operated than from ovariectomized female mice. Both E- and DHT-treated castrated males spent less time sniffing the volatile odors from proestrous or estrous females than from ovariectomized females. These results suggest that neither androgen nor estrogen is sufficient for reproducing male attraction to volatile female mouse odors, and that androgen signaling has a competitive effect against the attraction.     

Estrous correlated modulations of circadian and ultradian wheel-running activity rhythms in LEW/Ztm rats

Estrogen treatment alters the expression of ultradian activity rhythms in male and female LEW/Ztm rats. This finding raises the possibility that the expression of ultradian rhythms may vary on different days of the estrous cycle. To test this hypothesis, we recorded the circadian and ultradian wheel-running activity rhythms of entrained (LD 12:12) and free-running sexually mature LEW/Ztm females during their 4- or 5-day estrous cycle. The mean daily activity, the duration of activity, the circadian period of activity, and the occurrence of ultradian rhythms differed significantly among the days of the estrous cycle. In LD 12:12, the phase angle difference between the beginning of activity and light offset varied reliably in 5-day cycling animals. The highest daily mean of activity, the longest duration, and the shortest circadian period length were observed on the day of estrus in both entrained and free-running animals. The day of estrus was characterized by a constant high level of activity throughout the activity phase, while the days following ovulation showed a bi- or trimodal activity pattern. Power spectrum analysis revealed significant ultradian components for the days of metestrus and diestrus, but only circadian components for the days of proestrus and estrus. These results were interpreted as indicating that endogenous changes in circulating hormone levels can induce changes in the ultradian and circadian patterns of wheel-running activity in LEW/Ztm rats.     

Estrus cycle stage modifies the presentation of stress-induced startle suppression in female Sprague-Dawley rats

Tailshock stress causes transient reductions in startle reactivity, associative learning and open field activity in female rats in an ovarian hormone dependent manner. Others have shown estrogen modulation of associative learning by testing across the estrus cycle and pharmacological manipulations. Here we tested whether stress-induced suppression of startle reactivity can be attributed to circulating ovarian hormones. Female rats were tracked across the estrus cycle and subjected to the stressor (2 h periodic tailshock) the morning of diestrus, proestrus, estrus, or metestrus. Startle reactivity was tested 2 h following the cessation of the tailshock. Using a multi-stimulus protocol, we determined there were differences in startle sensitivity and responsivity. Following stressor exposure, estrus females exhibited reduced startle responsivity. In contrast, diestrus females exhibited increased sensitivity to the lowest acoustic stimulus. The results are discussed with respect to ovarian hormone regulation of the immune system and sensory reactivity during and following trauma that may lead to different abnormal behaviors in females in the wake of traumatic stress.     

Effect of sex steroids and coital experience on ferrets' preference for the smell,sight and sound of conspecifics

Previous research showed that ferrets of both sexes recognize potential opposite-sex mates on the basis of volatile body odors. We compared the ability of estrogen and androgen treatments to activate a preference in gonadectomized male and female ferrets for distal cues (volatile body odors alone or volatile odors+sight+sounds) from male versus female stimulus ferrets using an airtight Y-maze and a "stimulus proximity" or a "discrete trials" testing paradigm. Sexually naive, gonadectomized male and female ferrets that received either testosterone propionate (TP) or estradiol benzoate (EB) spent equal time in proximity to goal boxes that provided either volatile odors alone or odors+sight+sounds of male and female stimulus animals. After they received coital experience, male and female subjects (treated with either EB or TP) showed a significant preference for both types of opposite-sex stimuli. When discrete trials tests were given to these ferrets prior to receiving coital experience, EB-treated females preferred to approach odor only cues, as well as odors+sight+sounds of stimulus males, and this preference was further strengthened after coital experience. Sexually naive, TP-treated males preferred to approach volatile odor cues from stimulus females; however, these animals showed an equal preference for odors+sight+sounds of stimulus females and males. Again, after coital experience, males' preference for both sets of cues from stimulus females was significantly enhanced. Thus, in sexually naive ferrets, discrete trials, but not stimulus proximity tests, revealed a preference for distal cues (body odors with or without concurrent sight and sounds) from opposite-sex conspecifics in subjects of both sexes. Coital experience significantly enhanced these preferences for heterosexual distal cues under both testing paradigms.     

Female behavior is affected by male ultrasonic vocalizations in house mice

The effects of male-mouse ultrasonic vocalizations on female preference behavior were investigated using Swiss-Webster mice. Intact females spent more time with an intact tethered male than with a devocalized tethered male during 3-min preference tests. Female preference behavior was similar during estrus and diestrus; but, a preference for the vocalizing male was absent after ovariectomy, and returned following replacement treatment with ovarian hormones. Similar effects on female behavior were obtained using synthetic 70 kHz ultrasounds presented behind one of two devocalized tethered males during preference tests. The results indicate that ultrasounds maintain the female close to the vocalizing male and may facilitate copulation.     

Organization and expression of agonistic and socio-sexual behavior in golden hamsters over the estrous cycle and after ovariectomy

Paris of hamsters were housed in large enclosures that contained separate male and female living areas and observed over the 4-day estrous cycle and after ovariectomy. Agonistic elements exhibited frequently by females included on-back, boxing, lateral posturing, and biting, whereas males engaged frequently in boxing and on-back patterns of behavior. Furthermore, on-back and boxing by females were significantly higher on estrus than on any other day of the estrous cycle. Agonistic acts performed after ovariectomy did not differ in occurrence from those shown by animals on diestrus and proestrus. Vaginal marking increased during diestrus and attained a peak 24 hr prior to sexual receptivity. Both vaginal marking and mating occurred more frequently in the female's than male's home area suggesting that vaginal marks on days preceding behavioral estrus serve to attract males to the nest of females. Males also organized their marking patterns by location as shown by more flank marking in their own than their partner's area, albeit the significance for this difference in location is not known. The results demonstrate that when heterosexual paris of hamsters are tested in large and partially familiar habitats, a wide range of behavior is exhibited and organized in a manner that is not observed in small and unfamiliar cages.     

Disruption of urinary odor preference and lordosis behavior in female mice given lesions of the medial amygdala

Previous research showed that axonal inputs to both anterior and posterior subdivisions of the medial amygdala from the main and accessory olfactory bulbs of female mice, respectively, process volatile and non-volatile pheromonal signals from male conspecifics. In the present study we found that bilateral electrolytic lesions that included posterior portions, but not the anterior subdivision alone of the medial amygdala (Me) blocked the preference of estrous female mice to investigate volatile urinary odors from testes-intact vs. castrated males. Similar results were obtained in separate tests in which nasal contact with urinary stimuli was permitted. In addition, total time investigating volatile urinary stimuli was reduced in subjects with posterior Me lesions. Subjects were able to discriminate volatile urinary odors from testes-intact vs. castrated male mice, suggesting that this disruption of odor preference did not result from the inability of females given amygdaloid lesions to discriminate these male urinary odors. Bilateral lesions of the Me that were either restricted to the anterior or posterior subdivisions, or included areas of both regions, caused significant reductions in the display of lordosis behavior in estrous female mice. Our results suggest that the Me is a critical segment of the olfactory circuit that controls both mate recognition and mating behavior in the female mouse.     

Volatile female odors activate the accessory olfactory system of male mice without physical contact

We previously reported that male mice are more attracted to volatile odors from intact female mice than from ovariectomized female mice. In the present study, we investigated male attraction to volatile odors from soiled bedding collected from the cages of estrous or ovariectomized female mice. There was no difference in the total time spent sniffing volatile odors from estrous and ovariectomized female mice, suggesting that female mice emit volatile odors which are not excreted into bedding. To test this possibility, we investigated c-Fos expression in the mitral cell layer and granule cell layer of the accessory olfactory bulb 60 min after exposure of male mice to volatile odors without physical contact. Volatile odors from an estrous female mouse significantly increased the total number of c-Fos positive cells in each of the rostral and caudal granule cell layer, but not in the mitral cell layer. After exposure to volatile odors from estrous bedding, the total number of c-Fos positive cells did not increase. Volatile odors from a male mouse did not increase the total number of c-Fos positive cells. Volatile odors from an ovariectomized female mouse increased c-Fos expression only in the caudal granule cell layer. These results suggest that female mice emit specific volatile odors which are not excreted into bedding, and that the volatile odors activate the accessory olfactory system of male mice without physical contact. To characterize the female-specific volatile odors, we conducted habituation-dishabituation tests. Whereas sham-operated male mice discriminated between volatile odors of estrous and ovariectomized female mice, vomeronasal organ-removed male mice did not. These results suggest that male mice discriminated whether or not female mice were ovariectomized, by volatile odors via the accessory olfactory system, and that the female-specific volatile odors are involved in reproduction.     

On the organization of partner preference behavior in female Wistar rats

The possible prenatal organizing effects of testosterone (T) on adult sexual partner preference, i.e., sexual orientation in female rats, were studied through prenatal exposure (days 11-22) of female fetuses to the antiandrogens flutamide (Sch 13521; 4'-nitro-3'-trifluoromethylisobutyranilide; 5 or 10 mg/day; Experiment 1) or anandron [RU 23908; 5,5-dimethyl-3-(4-nitro-3-(trifluoromethyl)phenyl)- 2,4-imidazolidinedione; 35 mg/kg/day; Experiment 2]. The neonatal organizing effects of T were further studied by giving T, dihydrotestosterone (DHT) or oil within 9 h after birth to female pups (Experiment 3). In adulthood sexual orientation was ascertained, after ovariectomy followed by hormone treatment, in an automated open field (AOF), with stimulus animals behind wire mesh, and in a 3-compartment box (3-CB), with stimulus animals tethered. When given the choice between an estrous female and a sexually active male in the AOF, flutamide females, as well as controls, preferred the male partner. After long-term T treatment and 3 weekly pair-tests with an estrous female, flutamide females as well as controls switched their preference to the estrous female partner. In anadron females similar results were obtained. Thus the prenatal antiandrogens had no significant effect on sexual orientation in female rats. This suggests that adult sexual orientation in female rats is not organized prenatally through endogenous T. The change in preference after sexual experience corroborates earlier findings from our laboratory. When given the choice between an estrous female and a sexually active male in the 3-CB (sexual interaction with incentives possible), neonatally DHTP-treated females preferred the male; neonatally TP- or oil-treated females showed no preference.(ABSTRACT TRUNCATED AT 250 WORDS)     

Neurokinin A in the hypothalamus and anterior pituitary during the estrous cycle in the golden hamster

The fluctuations in the neurokinin A concentrations in the hypothalamus and anterior pituitary of female golden hamsters were studied in the different stages of the estrous cycle, and they were correlated with the changes in serum estradiol levels. Neurokinin A levels in the hypothalamus were lowest at day 4 of the cycle (proestrus), when serum estradiol levels were highest. Neurokinin A levels in the hypothalamus of hamsters in day 1 (estrus), day 2 (diestrus I), and day 3 (diestrus II) were not significantly different from each other. In the anterior pituitary, the highest neurokinin A concentrations were found during day 1 of the cycle (estrus), the levels in day 2 (diestrus I), day 3 (diestrus II), and day 4 (proestrus) were significantly lower than at estrus, again showing the lowest levels during proestrus, when estradiol levels were maximal. These results show that neurokinin A levels in the hypothalamus and anterior pituitary of the female hamster undergo significant changes during the estrous cycle.     

Cellular proliferation in the anterior pituitary gland of normal adult rats: Influences of sex,estrous cycle,and circadian change

Proliferative activity of the anterior pituitary gland in 10 week-old male and female rats under normal conditions was investigated by counting mitotic figures and using single and double immunostaining of 5-bromo-2′-deoxyuridine (BrdU), proliferating cell nuclear antigen (PCNA), and six pituitary hormones. To determine which proliferative changes depend on the estrous cycle and circadian changes, respectively, six groups of female and two groups of male rats were studied at various times of day. Additionally, BrdU-incorporated cells were further classified by the six types of hormones they contained, or as immunonegative cells. Cell proliferative activity in the females fluctuated drastically with the highest activity in estrus and the lowest in diestrus. In the males, proliferative activity was at a relatively low level, and was similar to that in females in proestrus or early estrus, with the greater activity at night. Identified by their pituitary hormones, the distribution of the proliferating cells was almost the same in each sex, with prolactin (PRL) cells accounting for the highest proportion, followed by growth hormone (GH) cells, and adrenocorticotropic hormone (ACTH), luteinizing hormone (LH), follicle stimulating hormone (FSH), and thyroid stimulating hormone (TSH) cells. These percentages agreed well with previously reported levels of cell types among all pituitary cells of the rat. It is therefore suggested that the life span and cycle of rat pituitary cells does not differ among cell types. In another test, male and female rats were given BrdU continuously via an osmotic pump for 8 days to compare cell proliferative activity between sexes, exclusive of the influence of estrous cycle and circadian changes. In this way, we were able to demonstrate that the cumulative incorporation of BrdU in females was consistently twice as high as in males over a constant period of time, and to conclude that cell renewal occurs at a doubled rate in the pituitary of female rat. © Wiley-Lis, Inc.     

Sexual and olfactory preference in noncopulating male rats

In some species including rats, mice, gerbils, and rams, apparently normal males fail to copulate when repeatedly tested with receptive females. These animals are called "noncopulators (NC)," and the cause of this behavioral deficit is unknown. It has been shown that NC rats do not have hormonal alterations or deficits in the mechanisms that control penile function. The present study was designed to examine (Experiment 1) whether NC male rats prefer receptive females to sexually active males. In addition, the olfactory preference for bedding soiled from estrous or for anestrous bedding was investigated. These tests were performed in NC and copulating (C) male rats when the subjects were intact, gonadectomized (GDX), or GDX and treated with high doses of testosterone propionate (TP). Our results demonstrate that NC rats do not display sexual behavior even after high TP treatment. While C male rats have a clear preference for receptive females as opposed to a sexually active male, NC rats do not. In all hormonal conditions, the preference shown by NC rats for estrous bedding was significantly reduced in comparison to that seen in C rats. TP treatment in NC rats did not modify either partner or odor preference. In Experiment 2, we evaluated if NC rats are feminized and if it could be easier to induce feminine-like behavior by hormone treatment with estradiol benzoate (EB) or with EB plus progesterone (P) (EB+P). Odor preference for estrous or male bedding under these hormonal conditions was also compared. No differences between NC and C rats were found in feminine sexual behavior. In the olfactory test, we found that NC rats prefer odors from receptive females as opposed to male odors, but this preference is reduced compared to that of C rats. Males treated with EB or EB+P show no preference for female odors. These results demonstrate that treatment with EB or EB+P does not increase feminine sexual behavior in NC rats.     

Effects of vomeronasal organ removal on individual odor discrimination, sex-odor preference, and scent marking by female hamsters

Removal of the vomeronasal organ (VNX) did not eliminate the ability of female hamsters to discriminate between individual male's flank gland or urine odors in a habituation/discrimination task nor did it impair preference for male odors over female odors from a distance. Vomeronasal organ removal did reduce overall levels of investigation of flank gland odor in the habituation/discrimination task. Although VNX females did not show severe impairments in the frequency of either flank or vaginal marking in response to odors, they did show an abnormal pattern of marking. VNX females, unlike shams, did not flank mark more to female odors than to male odors, nor did they vaginal mark more to male odors than to female odors. Thus, the vomeronasal organ in female hamsters appears to be important for differences in scent marking toward male and female odors, but is not essential for discrimination of individual odors or for preferences for male over female odors.     

Early olfactory learning is influenced by sex in hamsters but not rats

The odor of cedar shavings repels infant and juvenile rats and hamsters reared in pine shavings when animals are tested in a two-choice situation. Housing male and female infants of either species in cedar shavings for 3 days before testing increases preference for both cedar odor and for a mixture of cedar and conspecific odors. Similar exposure of juvenile male and female rats and male hamsters, has little or no significant impact on odor preferences. However, housing female hamsters in cedar at either developmental stage equally influences odor preferences. The data imply that sex differences influence the development of early odor-guided behavior in hamsters but not rats. These species differences may have adaptive significance in that the birth of a litter produces a greater environmental change demanding a larger preference adjustment of solitary female hamsters than colonial female rats.     

Sexual preference in female rats during estrous cycle, pregnancy and lactation.

Choice of a male or female social contact was studied in intact female rats in a runway-choice apparatus during estrous cycle, pregnancy, and lactation. The male was chosen significantly more often during proestrus/estrus than during the diestrous days of the cycle. During pregnancy this preference in choice declined only to reappear gradually during the lactation period. The shifts in the level of motivation to seek out the male support previous studies and point to the significance of estrogen in producing the preference for the male.     

Role of urine in coordinating reproduction in a desert rodent (Dipodomys merriami)

Detection of reproductive status from chemical signals in the urine of a desert rodent was examined. Intact and castrated male and estrous (induced) and nonestrous (ovariectomized) female Dipodomys merriami were tested for their preferences for various combinations of water and urine from intact males, estrous females, castrated males, and nonestrous females. Intact and castrated males were also tested for their responses to urine from females at different stages of the reproductive cycle: proestrus, estrus, and diestrus. Neither intact nor castrated males exhibited a preference for urine from females in any stage of the estrous cycle. Urine from intact males, however, was preferred by both intact males and estrous females. Urine from reproductively active males, rather than from estrous females, seems to contain information for coordinating reproduction in D. merriami.