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.     

Orexin A (hypocretin-1) application at the medial preoptic area potentiates male sexual behavior in rats

The medial preoptic area plays an important role in the regulation of male sexual behavior in rats, and this area receives orexinergic inputs. The role of orexinergic inputs in the medial preoptic area in sexual behavior has not been studied, though they have been shown to play a role in some other physiological functions. In this study, the changes in male sexual behavior in rats were studied after local injection of orexin A (Hypocretin-1) at the medial preoptic area. The results of the study showed that orexin A application at the medial preoptic area increased sexual arousal as well as the copulatory performance. Sexual arousal is one of the physiological stimuli, which influences wakefulness. It is possible that the earlier reports showing increased wakefulness, on application of orexin A at the medial preoptic area/basal forebrain, has a contribution from sexual arousal.     

Does sexual coercion play a role in the high-risk sexual behavior of adolescent and young adult women?

Sexual coercion and its relationship to high-risk sexual behavior were examined in five samples of young women. Sample 1 (N=22) consisted of sexually active adolescents aged 15 to 19. Samples 2 (N=206) and 3 (N=70) were recruited from among patients at three sexually transmitted disease clinics. Sample 4 (N=51) consisted of young homeless women living on the street in a large city. Sample 5 (N=51) was recruited from among young women on a college campus. Across all samples, 44.4% of women indicated that they had been forced into some form of sexual activity against their will. Self-reports of sexually coercive experiences were consistently related to risky sexual behavior. It appears that many young women are coerced into engaging in high-risk sexual behavior. This implies the need for greater attention to male coercive sexual behavior and women's skills for coping with such behavior.Support for this paper was provided by Grant HD 26249 from the National Institute of Child Health and Human Development and Grant MH45651 from the National Institute of Mental Health.     

Risk recognition and trauma-related symptoms among sexually revictimized women.

This study used experimental methodology to investigate the differential impact of various levels of sexual victimization on women's perceptions of risk and evaluative judgments of sexual assault within a dating interaction. Single- and multiple-incident victims were compared with nonvictims. Results supported the hypothesis that revictimized women would exhibit longer latencies than either single-incident victims or nonvictims in signaling that an audiotaped date rape should be halted. Revictimized women with greater posttraumatic stress disorder (PTSD) symptoms, arousal symptoms in particular, exhibited latencies similar to those of nonvictims, whereas revictimized women with lower levels of PTSD symptoms had significantly longer latencies. Dissociative symptoms were not related to latency. These findings suggest that PTSD-related arousal symptoms may serve a buffering effect, increasing sensitivity to threat cues that portend a sexually coercive interaction.     

Initiation, desistance, and persistence of men's sexual coercion

Patterns of sexually coercive behavior were examined among 266 Asian American and 299 European American men over 1 year. Noncoercer (n = 358), desister (n = 120), initiator (n = 39), and persistent (n = 48) sexually coercive groups were identified. The strongest predictor of sexual coercion was past sexual coercion. Persistent sexual coercers were higher than the other groups in delinquency and hostile masculinity and were nearly twice as likely to engage in laboratory sexual harassment. Loss of face attenuated self-reported sexual coercion and laboratory sexual harassment risk among Asian Americans and attenuated only laboratory sexual harassment risk among European Americans. These findings suggest that the heterogeneity of sexually coercive behavior and ethnicity are important research and clinical considerations.     

Copulatory behavior of sexually naive and sexually experienced male rats following removal of the vomeronasal organ

The question addressed was whether removal of the vomeronasal organ (VNO) of the male rat would produce observable deficits in sexual behavior. Both sexually naive and sexually experienced males were used and each animal was given more than 12 hours to mate with a receptive female. Although sexual arousal was depressed in both groups, and depressed more among naive than experienced animals, every male was eventually aroused by the receptive female and eventually ejaculated. We conclude that while the VNO contributes to arousal it is not indispensable for arousal.     

Opinions concerning criminality among mental patients

Estimations of the arrest rates for various offense categories of civilly admitted male mental patients were made by mental health center professionals, state hospital professionals and aides, law enforcement officers, college students, legislators, and community residents. Mental health personnel and legislators tended to judge patients as having lower arrest rates than was actually the case. Community residents overestimated patient arrest rates for rape and “other sexual offenses”, while police overestimated the patient rate for “other sexual offenses”.     

Learning about sex: conditioning of partner preference: theoretical comment on Coria-Avila et Al. (2005)

Sexual partner preference in female rats has been difficult to establish experimentally because the vaginocervical stimulation the female receives during the preference test can be rewarding or aversive depending on the context. G. A. Coria-Avila, A. J. Ouimet, P. Pacheco, J. Manzo, and J. G. Pfaus (2005) reported that female rats can be conditioned to show partner preference for a male that is scented with a sexually neutral odor if they are mated repeatedly with that male in a paced mating test. These results suggest that establishment of a partner preference depends on rewarding characteristics of the vaginocervical stimulation the female receives during an initial mating and that selection of a sexual partner can be determined by olfactory stimuli associated with that stimulation. These results are discussed within the context of the appetitive-consummatory construct of sexual behavior and the evolutionary significance of conditioned partner preference.     

Changes in male copulatory behavior after sexual exciting stimuli: effects of medial amygdala lesions.

A paradigm was developed to investigate how precoital sexual arousal affects parameters of sexual behavior in male rats. Estrous females in a wire mesh cage were used to induce sexual arousal before the sexual interaction test. In control procedures, males were presented in a wire mesh cage or else there was no stimuli at all. The results indicate that ejaculation latency is consistently reduced after preexposure to a female, but not after preexposure to a male, showing that the effect is specific for precoital sexual arousal. Other parameters were affected by precoital sexual arousal in some, but not in all experiments. Reductions in intromission latency moreover, were observed after both preexposure to a male and preexposure to a female, indicating that general social excitement affects this parameter. Preexposure to females for 10 minutes or 3 hours produced similar results. It was subsequently found that medial amygdala-lesioned (AME) animals differed from sham-lesioned (SHAM) controls with respect to their reaction to precoital sexual arousal. The results show that AME-lesioned animals, in contrast to SHAM-animals, do not show reduced ejaculation latencies after preexposure to an estrous female. The results are in line with the idea that AME-lesioned animals are deficient in the assimilation of information on sexual exciting stimuli.     

Men and women differ in amygdala response to visual sexual stimuli

Men are generally more interested in and responsive to visual sexually arousing stimuli than are women. Here we used functional magnetic resonance imaging (fMRI) to show that the amygdala and hypothalamus are more strongly activated in men than in women when viewing identical sexual stimuli. This was true even when women reported greater arousal. Sex differences were specific to the sexual nature of the stimuli, were restricted primarily to limbic regions, and were larger in the left amygdala than the right amygdala. Men and women showed similar activation patterns across multiple brain regions, including ventral striatal regions involved in reward. Our findings indicate that the amygdala mediates sex differences in responsiveness to appetitive and biologically salient stimuli; the human amygdala may also mediate the reportedly greater role of visual stimuli in male sexual behavior, paralleling prior animal findings.     

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.     

Fluctuations in brain temperature during sexual interaction in male rats: an approach for evaluating neural activity underlying motivated behavior

Since metabolic activity is accompanied by heat release, measurement of brain temperatures offers a method for assessing behavior-associated changes in neural activity. To explore this possibility, we monitored local brain (nucleus accumbens, medial-preoptic hypothalamus, and hippocampus) and body (temporal muscle) temperature in an experienced male rat during sexual behavior with a sexually receptive female. Placement of the female into a neighboring compartment increased the male's temperature and additional increases occurred when rats were allowed to see and partially interact with the female through a Plexiglas barrier with dime-size holes. The temperature increase was robust (1.5-2.0 degrees C), faster in all brain areas than in muscle, and peaked (38-39 degrees C) when the barrier was removed and full interaction was allowed. As the male repeatedly mounted and achieved intromission with the female, temperature further increased, peaking at ejaculation (+0.2-0.4 degrees C). Following ejaculation, the temperature abruptly dropped, until sexual interest and interaction resumed. These biphasic temperature fluctuations were generally similar in each recording location, but all brain sites (particularly, nucleus accumbens and medial-preoptic hypothalamus) showed more profound changes than the muscle.These data generally match single-unit and other physiological findings, suggesting that male sexual behavior is accompanied by sustained and generalized neural activation. This activation is triggered by sexually relevant stimuli (arousal), maintained during repeated mounts and intromissions, and peaked at ejaculation. These findings suggest brain temperature fluctuations not only as a sensitive index of functional neural activation, but as a powerful factor affecting various neural functions and an important part of brain mechanisms underlying motivated behavior.     

Male bisexual arousal: A matter of curiosity?

Conflicting evidence exists regarding whether bisexual-identified men are sexually aroused to both men and women. We hypothesized that a distinct characteristic, level of curiosity about sexually diverse acts, distinguishes bisexual-identified men with and without bisexual arousal. Study 1 assessed men's (n = 277) sexual arousal via pupil dilation to male and female sexual stimuli. Bisexual men were, on average, higher in their sexual curiosity than other men. Despite this general difference, only bisexual-identified men with elevated sexual curiosity showed bisexual arousal. Those lower in curiosity had responses resembling those of homosexual men. Study 2 assessed men's (n = 72) sexual arousal via genital responses and replicated findings of Study 1. Study 3 provided information on the validity on our measure of sexual curiosity by relating it to general curiosity and sexual sensation seeking (n = 83). Based on their sexual arousal and personality, at least two groups of men identify as bisexual.     

Cerebrospinal fluid from patients with multiple system atrophy promotes in vitro α-synuclein fibril formation

The presence of a sexually receptive female behind perforated transparent partition induced sexual arousal and specific behavior in male mice so they spent more time near partition in an attempt to make their way to the female. Three-chambered free-choice model was used to evaluate sexual partner preference. The main pattern of sexual preference was the time spent by a male mouse at the partition dividing female (F-partition time) versus a partition dividing male (M-partition time). Pregnant mice were given ethanol (11vol.%) for 1-21 gestational days, and were exposed to restraint stress (2h daily for 15-21 day of the gestation). Control pregnant mice had free access to water and food and were not stressed. Adult male offspring of ethanol and stress exposed dams (E+S) showed decreased F-partition time and increased M-partition time. Whereas F-partition time in all control mice prevailed over M-partition time, 78% E+S mice demonstrated prevailed M-partition time. E+S mice were more active in social interaction with juvenile male. No significant differences between E+S and control mice in the open field and novelty tests were revealed. Therefore, E+S exposure during dam gestation inverted sexual partner preference in male offspring, suggesting that stress and alcohol in pregnancy produces predisposition to homosexuality.     

"Nice guys finish last": influence of mate choice on reproductive success in Long-Evans rats

The present study was designed to determine if male physiology and male reproductive behavior predict reproductive success in Long–Evans rats. Mating behavior was observed in sexually naïve, naturally cycling female rats during behavioral estrous that were given the opportunity to mate with two males simultaneously. DNA analysis of offspring born following these mating encounters was used to identify the paternity of each pup. In order to assess the effect of mate choice during these mating encounters on reproductive success, one male rat in each pair was categorized as the preferred mate if the female spent more time (> 50%) with him during the mating test of the present study. Furthermore, each male in the pairs was categorized as “attractive” or “non-attractive” by computing the number of females that preferred each male across many mating tests. Similar to results reported in Lovell et al. (2007), during 76% of these mating tests the same male rat in each pair was preferred by different female rats. Overall attractiveness of individual male rats predicted reproductive success in the present study. Interestingly, “attractive” males sired significantly FEWER pups than “non-attractive” males. Neither behavioral (e.g., latency to first sexual stimulation, number of sexual stimulations) nor physiological measures (e.g., body weight, urinary testosterone levels) of male rats predicted their reproductive success. In conclusion, the present results indicate that certain features of some males are more attractive to females, but attractive males are at a reproductive disadvantage (as measured by the number of pups sired). Although basal urinary testosterone levels did not differ between males that sired the majority of pups in a litter and males that sired few or none of the pups in a litter, aggression and/or other physiological measures of fertility (e.g., penile reflexes) may differ between males that are attractive to females and those that have a reproductive advantage.     

Effects of prenatal stress on sexual partner preference in mice

Three-month old, male Swiss Webster mice were born to either control dams or dams who had been prenatally stressed with light, heat, noise and handling during the last week of gestation. As adults, male offspring were tested on sexual partner preference and sexual behavior (mounting, intromissions and lordosis) with a sexually experienced male stimulus animal and a stimulus estrous female. In comparison to males born to control dams, prenatally stressed males showed a sexual partner preference for the sexually active male as demonstrated by a negative partner preference score, more and longer visits to the male's compartment, fewer and shorter visits to the female's compartment and longer latencies to and lower frequencies of mounts and intromissions of females. In addition, stressed males showed a greater frequency of lordosis and a higher lordosis quotient than did control males. This study is the first to investigate the effects of prenatal stress alone, without hormonal manipulation, on sexual partner preference using both a partner preference paradigm and measures of sexual behavior such as mounting, intromissions and lordosis. These findings support the suggestion that prenatal stress alone is enough to significantly affect sexual partner preference in male mice.     

Role of androgen, estrogen and sexual experience on the female rat's partner preference

Virgin ovariectomized rats were implanted with Silastic tubings containing estradiol (E2, 5 mm), testosterone (T, 30 mm), dihydrotestosterone (DHT, 30 mm), or injected daily SC with the synthetic nonaromatizable androgen, methyltrienelone (R 1881, 5 mg.kg-1) daily for three weeks. Animals were tested for partner preference behavior (staying in the vicinity of a sexually active male, an estrous female or staying elsewhere) before and after they had been tested for feminine and masculine sexual behavior. All naive androgen-treated groups showed a male-oriented preference, while the naive E2-treated females did not show any consistent partner preference. Sexual experience abolished the male-directed orientation of the androgen-treated groups while E2 treatment induced a male-directed orientation. E2-treated females spent significantly longer time elsewhere in both tests compared to the other groups which might be due to insufficient levels of E2. Feminine sexual behavior was seen after treatment with E2 or T but not after treatment with DHT or R 1881. It was concluded, 1) that the effect of treatment with an androgen on the partner preference behavior differs according to whether the females are virgins or sexually experienced, and 2) the effect of the hormone treatment on the partner preference behavior is independent of whether the hormone stimulates feminine sexual behavior.     

Exposure to PCB 77 affects partner preference but not sexual behavior in the female rat

In rats, exposure to the polychlorinated biphenyl congener 3, 4, 3′, 4′-tetrachlorobiphenyl (PCB 77) affects the brain and behavior of the offspring as well as the maternal behavior of the dams. In the present study, a cross-fostering design was used to examine the effects of pre- and/or postnatal exposure to PCB 77 on sexual behavior and partner preference in female rats, and to determine the role of altered maternal behavior in the mediation of these effects. Pregnant rats were treated with oil or PCB dissolved in oil (2 mg/kg b.w.) on gestation days 6-18 and then given pups that had been exposed to either the oil vehicle or PCB during gestation. As adults, the female offspring were tested for partner preference (that is, whether they preferred to spend time with a sexually receptive female or a sexually active male) and sexual behavior. None of the treatments affected female sexual behavior. However, both double exposure and postnatal exposure diminished the animals' preference for a male over a female stimulus, but partner preference was not affected by prenatal exposure alone. There were no significant correlations between the changes in partner preferences due to PCB exposure and the amount of maternal grooming and licking received by the treated litters. Thus, female partner preference is affected by early PCB exposure, and the effects depend upon whether the exposure is in utero or via lactation and may be independent of any effects of the PCB on maternal care.