Partner preference: Assessing the role of the female goat

For domestic ruminants, the male is thought to have the control over mate choice. The aim of this study was to assess the potential role the female goat plays in choosing a sexual partner. Approach frequency and proximity time to various social or sexual stimuli in a Y-maze apparatus were used as partner preference assessment parameters. Ovariectomized females were either induced into estrus (n = 8) or induced into anestrus (n = 8) and exposed to various goal stimuli — intact unfamiliar females (estrous and diestrous), intact males, and neutral (empty) in six separate trials. Total arm entries and time spent within one body length of the goal (proximity time — used to calculate preference scores) were recorded for subjects. With a male present, anestrous subjects had significantly more total arm entries than estrous subjects. Estrous subjects showed a significant preference for the male goal (M) versus the estrous female (ES), diestrous female (DS), and empty goals, respectively. Estrous subjects also showed a preference for the ES and DS goals when one goal was left empty. Anestrous subjects showed a preference for the goal containing ES, DS, and M compared to empty goals. They also showed a preference for ES vs. DS. The Y-maze is a tool that can be used to assess sexual and social partner preferences in female goats. The role the female plays in choosing a partner may be much greater than previously considered.     

"Some guys have all the luck": mate preference influences paced-mating behavior in female rats

In the present study, mating behavior was observed in female rats that were given the opportunity to mate with two males simultaneously. Three groups of females were tested: 1) sexually na?ve, naturally cycling rats in proestrous; 2) sexually na?ve, hormone-primed, ovariectomized (OVX) rats; and 3) hormone-primed, OVX rats tested 1 week after sexual receptivity testing. One male rat was determined to be the preferred male for each female, if she spent more time with him during a mating test. Independent of sexual experience, female rats were less likely to leave their preferred male than their non-preferred male following intromissions. However, when they left their preferred male, they returned to him faster than to their non-preferred male. This effect of preference was slightly more robust in the OVX rats. When female rats from Group 2 were tested with the same pair of males for 3 additional tests, each female's preference for a particular male was stable. That is, a female rat preferred the same male in approximately 3 out of the 4 tests, which is more likely than would be expected by chance. In a final experiment, pairs of male rats were tested with different females once weekly to determine if different females would prefer particular males consistently. Although no male rat was preferred by all females, females consistently preferred the same male from each pair during approximately 70% of the tests. In conclusion, female mate preference may have adaptive significance for the reproductive success of rats.     

Reinforcing effects for female hamsters of non-copulatory exposure to normal male hamsters

Naturally cycling female hamsters were run in a T-maze to determine their preference for exposure to an intact male enclosed in one goal box or a castrated male in the other goal box; physical contact with the goal animals was prevented. All animals preferred the intact male, but only on estrous days, and the preference was maintained even when no differential stimuli reached the choice point from the goal animals. The preference is interpreted as demonstrating that non-copulatory exposure to stimuli emanating from an intact male is reinforcing for an estrous female.     

Sexual motivation in the female rat after testosterone treatment

The effect of testosterone propionate (TP) on sexual motivation in the ovariectomized female rat was studied. The urge to seek sexual contact was measured in terms of location in the male vicinity in an open field, the amount of aversive stimulus (crossing of an electric grid) the animal was willing to take to seek contact with a sexually active male and the preference in a run and choice situation for a sexually active male versus a female. It was a consistent finding in the three different methods used that TP 1 mg/kg induced a significant increase in the willingness of ovariectomized rats to seek contact with a sexually active male. A sexually active male was more incentive than a castrated male or a female. The effect of TP was dose-dependent and the maximal response occurred after 2–4 days.     

Sexual reward induces Fos in the cerebellum of female rats

The cerebellum is generally considered a neural structure specialized in motor control and recent imaging data suggest its role in sexual behavior. Herein, we analyzed the pattern of Fos immunoreactivity (Fos-IR) in the cerebellum of female rats allowed to pace copulation as a model of sexual reward in rodents. Ovariectomized, hormone-primed, sexually naïve females formed three groups: Pacing, Nonpacing and Control. Pacing occurred in arenas bisected by a middle divider that allowed only females to control sexual interaction with stud males. For nonpaced copulation the divider was removed, and control females were allowed to pace in chambers without a male. Fos-IR was analyzed in granule and Purkinje layers of the 10 cerebellar lobules, and in the fastigial deep nucleus (FDN). Results indicated that Pacing females expressed more Fos-IR in the granule layer compared to Nonpacing and Controls, and more Fos-IR in Purkinje compared to Nonpacing. No differences were observed in FDN. Such response cannot be explained with motor activity because Pacing females moved less in general. We discuss the role of the cerebellum and its connections in the sexual reward induced by pacing.     

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.     

Characterization of 50-kHz ultrasonic vocalizations in male and female rats

Male and female rats emit ultrasonic vocalizations in reproductive encounters. While estrous bedding has been used to elicit vocalizations of males, the number of responses is variable. We report a reliable method to assess vocalizations using exposure to a stimulus animal. The stimulus rat is placed behind a wire barrier for 5 min, then removed. Vocalizations are then recorded for 5 min. Experiment 1 validated this method and it was used for subsequent experiments. In Experiment 2, male rats were castrated and tested for the restoration of vocalizations. In one group, males were allowed to copulate freely; in the other, females had vaginal masks to prevent ejaculation, but not mounting. Vocalizations were restored only in males allowed to ejaculate. In Experiment 3, we measured vocalizations in sexually nai;ve and sexually experienced males following exposure to either castrated (CAS) males, testosterone (T)-treated males, ovariectomized (OVX) females, or OVX females receiving estrogen plus progesterone (E+P). Males vocalized most after exposure to E+P females, whether they were sexually experienced or naive. However, the rate of vocalizations was significantly higher after exposure to E+P females when the males were sexually experienced. In Experiment 4, we measured vocalizations in females following exposure to CAS males, T-treated males, OVX females, or E+P females. Females vocalized most after exposure to T-treated males. Our results show that (1) sexual experience facilitates vocalizations in male rats, (2) vocalizations are highest after exposure to hormonally receptive conspecifics, and (3) ultrasonic signaling is a sensitive index for assessing the hormonal disposition of conspecifics.     

Ventromedial hypothalamic damage and sexual proceptivity in female rats

Sexual proceptivity is indicated by behaviors which reflect feminine initiation with respect to the occurrence of mating behavior. In this study we used ovariectomized female rats, and tested for sexual behavior in a relatively large arena with a sexually active male tethered in one corner. This testing situation gave the unrestrained female control over the occurrence of sexual interaction, and the frequency with which a female approaches a sexually active male provides a measure of sexual proceptivity. We find that administration of estrogen and progesterone to neurologically intact female rats induces sexual receptivity and increases the frequency with which they approach a sexually active male. Bilateral destruction of the ventromedial hypothalamus renders females non-receptive and virtually eliminates the tendency for females to approach males. Bilateral sagittal knife cuts which bracket the ventromedial region produce similar effects. Apparently, the ventromedial hypothalamus is importantly involved in the control of both receptive and proceptive components of feminine sexual behavior.     

Midbrain lesions eliminate sexual receptivity but spare sexual motivation in female rats

To measure sexual motivation we have used a preference test paradigm which involves testing a female with a sexually active male and a sexually inactive castrate male at the same time. On the assumption that a sexually motivated female will choose to spend more time with a partner who can provide her with stimulation appropriate to her motivational state, a female can be said to be sexually motivated to the extent that she spends more time with the active male than with the castrate. We find that bilateral destruction of the midbrain peripeduncular region eliminates the lordosis reflex in female rats, and abolishes sexual soliciting darting responses. Lesioned females treated with ovarian hormones continue, however, to show a strong preference for a sexually active male over a castrate. Thus, although peripeduncular destruction eliminates copulatory behavior, such destruction appears to spare hormone dependent systems for sexual motivation.     

Effects of hormonal, sexual, and social history on mating and pair bonding in prairie voles

The interactive effects of hormones, sexual history and cohabitation on sexual and social behaviors were examined in pairs of ovariectomized female and sexually experienced male prairie voles (Microtus ochrogaster). Monitoring with time lapse video tape revealed that females in estradiol benzoate (EB)-induced estrus, and their male partners engaged in high levels of sexual activity which continued intermittently for at least 3 days (until observations were arbitrarily terminated). In conjunction with other studies, these results indicate that the hormonal condition of the female at the time of testing is a major determinant of sexual activity. Prior hormonal, copulatory, or cohabitation experience did not significantly influence sexual responses between females and unfamiliar male partners. However, affiliative behaviors, such as side by side contact, were higher in pairs that were familiar due to prior sexual and cohabitational experience. These results indicate that social and sexual behaviors are independently regulated. Other behaviors, including nasogenital investigation and autogrooming were influenced by the hormonal and sexual history of the female. The implications of these behavioral patterns for reproductive activation, pair bonding, and incest avoidance are discussed.     

Hormonal control of receptivity,proceptivity and sexual motivation

The results of three experiments using ovariectomized female rats are reported. In each experiment, females were individually tested in large arena with a partner (or partners) tethered so as to give the unrestrained female control over the occurrence of social interaction. In the first experiment we show that ovariectomized females will repeatedly approach a sexually active male and allow themselves to be mounted. Other forms of female initiated contact are common. These include “grooming” and “nosing” the male, crawling over or under the male, the “push-past” the male, genital sniffing, and following the male. For convenience we refer to these as feminine social contacts. Treatment with ovarian hormones induces sexual receptivity, increases the frequency with which females approach males, and increases the display of sexual soliciting behaviors such as hopping and darting. In this setting the frequency of feminine social contacts is decreased. In a second experiment we show that hopping/darting is frequently displayed by intensely receptive females when they are tested with sexually active males, but these beahviors are almost never displayed in the presence of either a sexually passive male or a female. The frequency of feminine social contacts varies predictably with the setting: contact frequency is low when receptive females are tested with active males; contact frequency is high when females are tested with a passive male or a female. In the third experiment we used a preference test paradigm to measure sexual motivation. This involved testing a female with a sexually active male and a sexually inactive castrate at the same time. Treatment with ovarian hormones increases a female's preference for the sexually active male over the castrate, and by this criterion hormonal stimulation can be said to increase sexual motivation. The results of this experiment, using a very simple test for sexual motivation, form the basis for a forthcoming series of papers dealing with the effects of brain damage upon reflexive and volitional components of feminine sexual behavior.     

Embryonic exposure to an antiestrogen masculinizes behavior of female quail

Japanese Quail eggs were injected on Day 9 of incubation with the antiestrogen CI-628. When sexually mature, treated and control birds were given exogenous testosterone and tested for sexual behavior. Unlike control females, females treated with CI-628 before hatching displayed the male mating pattern. Males were unaffected by CI-628. Previous research has shown that male quail treated with sex steroids before hatching are permanently feminized behaviorally, and as adults fail to copulate. Normal female quail also fail to show male sexual behavior, even when given exogenous testosterone as adults. These findings suggest that the male quail is the neutral (anhormonal) sex with respect to behavioral sex differentiation, and that estrogen produced by female embryos results in female behavioral differentiation by eliminating the capacity for male sexual behavior.     

The role of vaginal stimulation for the acquisition of conditioned place preference in female Syrian hamsters

This study investigated the importance of vaginal stimulation on conditioned place preference by sexual behavior in female Syrian hamsters. Hormonally primed female hamsters given vaginal masks and topical lidocaine prior to conditioning sessions were no different in their place preference conditioning compared to female controls with no vaginal mask or lidocaine. Control females not provided a sexually active male did not show any preference for either compartment of the conditioning apparatus. These results suggest that stimuli, in addition to vaginal stimulation, are effective in producing a place preference during the mating experience in female hamsters.     

Sexual arousal patterns of bisexual men revisited

Men who identify themselves as bisexual report feeling sexually aroused by both men and women. However, past research has not demonstrated that such men exhibit substantial genital arousal to both male and female erotic stimuli, suggesting that they identify as bisexual for reasons other than their genital arousal pattern. The purpose of the present study was to examine arousal patterns among bisexual men who were recruited using stringent criteria involving sexual and romantic experience with both men and women in order to increase the likelihood of finding a bisexual arousal pattern. Bisexual men in the present study demonstrated bisexual patterns of both subjective and genital arousal. It remains unclear which pattern is most typical of contemporary bisexual men: the present results supporting a bisexual arousal pattern, or previous results not finding one. In either case, understanding men with bisexual arousal patterns could help illuminate the etiology and development of male sexual orientation.     

Effects of Sexual Experience on Sexual Motivation in Copulatory Behavior in Male Rats

The effects of sexual experience on the behavior of one-year-old male Wistar rats in conditions excluding direct interaction and in conditions of direct contact with potential sexual and social partners were studied. Interest in a social partner on the other side of a partition was most strongly demonstrated by sexually experienced males, while sexually naive males showed the greatest interest in conditions of direct contact. All males showed maximum activity levels in the presence of a receptive female. Sexual experience in males had no effect on the motivational component of male sexual behavior, i.e. sexual excitation: the levels of sexual motivation in the presence of a receptive female were identical in sexually naive and experienced male rats. However, sexual experience produced fundamental changes in the nature of the consumatory stage of male sexual behavior on interaction with a receptive female, significantly increasing its expression. There were increases in measures of copulatory behavior such as the numbers of mountings and intromissions while the latent periods of their appearance decreased. There was also an increase in the proportion of males demonstrating elements of copulatory behavior in relation to partners of predominantly social significance.     

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)     

Sexual Aggression in Mice: Effects of Male Strain and of Female Estrous State

We have observed that 50% of FVB/NtacfBR (FVB) males were aggressive toward females in tests of mating behavior. We decided to gather basic evidence for an effect of genotype on this behavior by testing for strain differences between FVB and C57BL/6J (B6) male mice. Also, hypotheses developed from theoretical work on sexually coercive behavior suggest there should be a cycling effect on sexually aggressive behavior (Smuts and Smuts, 1993). We tested for an estrous cycling effect by using stimulus females in a state of either estrus or diestrus. Both strains modulated mating behavior to female cycling state. Cycling state did not modulate B6 aggression. FVB males were more aggressive than B6 males, and cycling state modulated their behavior. We conclude that sexually aggressive male mice modulate aggressive behavior to female social signals and indicate how this data can be used to study the genetics of sexual aggression.     

An active part of female mice in sexual interaction]

Proceptive behavior, according to Beach (1976), maintains and accelerates sexual interactions toward the end goal. Such distinctive type of proceptive behavior as darting or hopping of female rats is not apparent in mice. Nevertheless, it seems more reasonable that females may take an active part as much as their male partners also in this species. Twenty sexually experienced females in estrus were paired with 20 naive males of the same strain (ICR/JCL) and the pairs were observed for 6 hours. Eleven males of the 20 pairs successfully ejaculated. Females exhibited lordosis more frequently when they actively approached the male partners than when they were approached and mounted by males. This indicated that the rate of mating success was higher in the case of female's approach. Female's approaching behavior thus possibly plays a role as a proceptive behavior in mice.     

An NMDA antagonist impairs copulation and the experience-induced enhancement of male sexual behavior in the rat

Sexual experience facilitates subsequent male sexual behavior; activation of the N-methyl-D-aspartate (NMDA) glutamate receptor may play a role in this experience-induced enhancement. In this article, the authors report that systemic injections of MK-801, an NMDA receptor antagonist, impaired male sexual behavior in sexually naive and sexually experienced male rats. Furthermore, saline-treated rats that received 7 daily exposures to an inaccessible estrous female instead of sexual experience displayed enhancement of copulation on the following day. Injections of MK-801 before each of these exposures inhibited the experience-induced enhancement on the drug-free test on Day 8. These data suggest that stimulation of NMDA receptors enhances sexual performance immediately and mediates the experience-induced enhancement of subsequent copulatory behavior.