Sexual motivation is demasculinized, but not feminized, in prenatally stressed male rats

Sexual motivation and copulation in male rats are associated with dopamine release in the nucleus accumbens. Demasculinized copulatory behavior has been demonstrated in prenatally stressed adult male rats. We have previously reported that approximately 80% of prenatally stressed male rats do not exhibit copulation and that no significant changes in nucleus accumbens dopamine release are seen during exposure to estrous females. In the present study, we investigated whether prenatal stress affects sexual motivation in these animals as adults. Pregnant Wistar rats were subjected to immobilization stress for two hours daily from day 15-19 of gestation. The prenatally stressed male offspring at the age of 3 months were allowed contact with receptive female rats for a 30 min period per week for 10 weeks; then, between the age of 5 and 6 months, their sexual motivation and copulatory activity were measured. Sexual motivation was measured in terms of sexual partner preference. The number of visits and the duration of each visit to an estrous female (stimulus female) or to a sexually active male rat (stimulus male) were recorded. Compared with control males, prenatally stressed male rats showed a significantly lower number of visits and a shorter duration of each visit to stimulus females. Prenatally stressed males showed no preference for male or female stimulus rats in terms of the number of visits and the duration of each visit, whereas control rats showed a significantly higher number of visits and duration of visits to female stimulus rats than male stimulus rats. A significant decrease in copulatory activity was observed in the prenatally stressed male offspring compared with control male rats, with most of the prenatally stressed males failing to show copulation. In vivo microdialysis experiments were performed on the nucleus accumbens with concurrent observation of sexual behavior. The prenatally stressed rats that did not exhibit copulation showed no significant changes in nucleus accumbens dopamine release during exposure to a stimulus male behind a wire-mesh barrier and the amount of dopamine release remained at the basal levels during actual physical contact. These results, combined with those of our previous report, indicate that sexual motivation in prenatally stressed male rats is demasculinized, but not feminized.     

Prenatal stress and prepuberal social rearing conditions interact to determine sexual behavior in male rats

The two major categories of factors known to influence adult sexual behavior potentials are the relative amounts of androgen present during specific stages of perinatal ontogeny and adequate social stimulation during prepuberal development. The possible interaction between these two was evaluated by characterizing the ejaculatory and lordotic behavior potentials of prenatally stressed and control male rats that had been weaned at 16 days of age and raised either in total social isolation or with a same-age female, a control male, or a prenatally stressed male. The decrement in male sexual behavior produced by prenatal stress was attenuated by raising the male with either a female or a control male. Social isolation alone or in combination with stress resulted in severely deficient male behavior. Peripheral skin shock promoted ejaculatory behavior in many previously noncopulating prenatally stressed males raised with other stressed males, but it was ineffective in most isolated animals. The high lordosis potential characteristic of prenatally stressed male rats was slightly lower in the group with a female cagemate and was markedly decreased by social isolation. These results support and extend the finding by Dunlap, Zadina, and Gougis (1978) that prenatal hormonal events and prepuberal rearing conditions can interact to attenuate or accentuate the effects that either treatment alone has on the development of adult sexual behavior potentials.     

Effects of prenatal antiandrogen treatment on masculinization and defeminization of guinea pigs.

Gonadectomized (gdx) guinea pigs which had received the antiandrogen flutamide prenatally were tested for female-typical and male-typical sexual behavior in adulthood. In tests for lordosis behavior, gdx males and females were injected with estradiol benzoate and progesterone. Prenatally flutamide-treated females showed a longer mean lordosis response than control females. This was true whether they were given either a high or a low dose of EB. No male ever showed a lordosis response. In tests for male-typical sexual behavior, gdx adult males were treated with testosterone propionate and tested with stimulus females. The prenatally flutamide-treated males showed significantly decreased levels of ejaculation, a lower intromission rate and a decreased percentage of mounts which included pelvic thrusts, when compared to control males. Mount rate and rate of pericopulatory behavior did not differ between the flutamide and control males. The fact that prenatal administration of flutamide increased female-typical behavior in adult females suggests that the female guinea pig is normally partially defeminized by androgens in utero. The male guinea pig appears to be resilient to attempts to block defeminization with prenatal antiandrogens. However, some aspects of masculinization can be blocked.     

Effects of malnutrition,maternal stress,or ACTH injections during pregnancy on sexual behavior of male offspring

Pregnant rats were subjected to nutritional stress, environmental stress (immobilization-illumination-heat), or injections of adrenocorticotropic hormone (ACTH) during the third trimester of gestation. Masculine and feminine behavior potentials of the male offspring were determined in adulthood. Compared to control males, male copulatory behavior was severely impaired in all three experimental groups. The prenatally stressed animals showed a significant reduction in the cumulative percent ejaculating and an increase in the number of intromissions prior to the first ejaculation compared to control animals. When tested for female behavior, all three treatment groups displayed a significantly greater lordosis quotient than the control males. Gestation length was increased in the mothers exposed to environmental stress and ACTH injections but not in the nutritional stress animals. At birth, offspring from all experimental groups showed a significant reduction in body weight when compared with control offspring. These results confirm and extend earlier data which indicate that exposure of the mother to stress during the period of fetal sexual differentiation may impair masculine and feminine sexual behavior of the male offspring.     

Prenatal stress eliminates differential maternal attention to male offspring in Norway rats

Maternal licking behavior was observed in 20 Long-Evans rat dams on two consecutive days. Stimulus pups were male and female foster pups from dams that were either housed with 5 adult males during the last trimester of pregnancy (stressed) or housed alone (unstressed). Unstressed male pups received significantly more maternal licking than their female siblings, but prenatally stressed males and females received similar levels of maternal licking, comparable to that directed to unstressed females. In a second study, urine collected from prenatally stressed male pups elicited significantly less investigation from dams in a choice test than urine from age-matched unstressed males. It is concluded that the chemosignals which stimulate dams normally to provide more maternal attention to male than female neonates are deficient in prenatally stressed males. The results raise the possibility that differential maternal care may mediate some effects of prenatal stress on behavioral development in males.     

Prenatal stress affects the rate of sexual maturation and attractiveness in bank voles

Field studies reveal that bank vole females' mobility and aggression increase during pregnancy. Here we investigated the reaction of pregnant females to social stress evoked by short but frequent meetings with another female at the same stage of pregnancy. The stress neither evoked pregnancy termination nor affected pregnancy duration but had a long-term effect on the reproductive activity of the offspring. Prenatal stress reduced the rate of sexual maturation of voles as estimated at the age of 20 days. Uterine weights of prenatally stressed females and testes weights of prenatally stressed males were significantly lower than in offspring born to nonstressed mothers. Olfactory signals are known to be important in the sexual preferences of bank voles. Adult prenatally stressed females were more attractive to other adult females than were nonstressed animals. For bank vole males, however, prenatal stress decreased the attractiveness of females; adult males selected nonstressed females over stressed partners, by odor. This study shows that prenatal conditions evoked by short but frequent encounters with another pregnant female lead to delayed puberty in females and males, and decrease sexual attractiveness in adult offspring. These two negative effects may significantly limit the reproduction of prenatally stressed offspring.     

Reward value of intromissions and morphine in male rats evaluated by conditioned place preference

The present experiment was designed to determine if intromissions alone could induce a reward state as evaluated by conditioned place preference (CPP). We also compared the rewarding properties of one ejaculation and a morphine injection. We evaluated if intromissions alone could induce CPP in males with one or three ejaculations as previous sexual experience. Different groups of males were allowed to display 5, 10, and 15 intromissions or an ejaculation with a sexually receptive female before being placed in the originally non-preferred compartment of a CPP cage. On alternate days they were placed in the preferred compartment. The groups that displayed 5 or 10 intromissions did not modify their original preference, regardless of whether they had experienced 1 or 3 ejaculations before the conditioning procedure. The groups that had experienced 1 ejaculations that were allowed to display 15 intromissions or one ejaculation modified their original preference indicating the induction of a reward state. These results suggest that male rats displaying sexual behavior require a minimum amount of stimulation, 15 intromissions or an ejaculation, in order for sex to be sufficiently rewarding to induce CPP. In a separate experiment we evaluated if a morphine injection (1 mg/kg) has the same reward value that one ejaculation in male rats has. Two groups of sexually active males were used, in one group ejaculation was paired with the initially non-preferred compartment and morphine administration was paired with the initially preferred compartment. In the other group morphine injection was paired with the non-preferred compartment and ejaculation with the preferred compartment. None of the groups changed their originally preferred compartment suggesting that morphine and one ejaculation have the same reward value in male rats.     

Masculinization diminished by disruption of prenatal estrogen biosynthesis in male rats

Male rats were exposed to the aromatization inhibitor 1,4,6-androstatriene-3, 17-dione (ATD) in utero via prenatal injections to the mother on days 10 through 22 of gestation. At birth anogenital distance (AGD) and body weight (BW) were measured to assess effects of ATD on the development of genital morphology and body weight. Animals were castrated in adulthood and tested for the display of masculine sexual behavior in response to daily injections of 100 μg testosterone propionate replacement therapy. Prenatal exposure to ATD resulted in males with significantly decreased copulatory rates (MIPM) and slightly diminished probabilities of ejaculating when compared to control animals. Overall mounting, and intromission frequencies as well as percentages of animals displaying mounts and intromissions did not differ significantly across groups. These data lend support to the idea of a prenatal androgen-sensitive phase of neural sexual differentiation in which masculinization occurs, and further suggests that androgen aromatized to estrogen may be important for masculinization prenatally.     

Effects of progesterone on lordotic responses to specific mating stimuli in hamsters

Mating-induced inhibition of sexual receptivity was examined in ovariectomized, estrogen (E) treated and estrogen plus progesterone (E + P) treated hamsters given 10 min of exposure to male mounting stimulation alone or to mounts, intromissions, and ejaculations at eight hourly intervals. In E + P treated females, no differential effects of exposure to full mating stimulation vs. mounting stimulation alone were observed. In contrast, females given E treatment alone showed a marked differential response. Fully mated, E-treated females showed more lordosis than E-treated females exposed to mounts alone during the initial test. However, total lordosis duration declined precipitiously in the fully mated group by 2 hr and remained significantly below that in other groups during subsequent tests. Levels of receptivity in E-treated females mounted-only remained relatively constant until 8 hr. These results suggest that P reduces the inhibitory effects of vaginocervical cues received during mating without affecting the response to mounting stimulation alone. In addition, vaginocervical stimulation may initially facilitate lordosis in E-treated females.     

Juvenile play conditions sexual partner preference in adult female rats

Rats can display a conditioned partner preference for individuals that bear an odor previously associated with sexual reward. Herein we tested the possibility that odors associated with the reward induced by social play in prepubescent rats would induce a conditioned partner preference in adulthood. Two groups of 31-day-old, single-housed female rats were formed, and were given daily 30-min periods of social play with scented females. In one group, almond scent was paired with juvenile play during conditioning trials, whereas lemon scent functioned as a novel odor in the final test. The counterbalanced group received the opposite association. At age 42, females were tested for play partner preference with two males, one almond-scented and one lemon-scented. In both groups females displayed a play partner preference only for males scented with the paired odor. They were ovariectomized, hormone-primed, and at age 55 were tested for sexual partner preference with two scented stud males. Females displayed a sexual preference towards males scented with the paired odor as observed with more visits, solicitations, hops and darts, intromissions and ejaculations. These results indicate that olfactory stimuli paired with juvenile play affects later partner choice for play as well as for sex in female rats.     

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.     

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)     

Partner preference in male hamsters: steroids, sexual experience and chemosensory cues

This study investigated the effects of gonadal steroids on sexual motivation in male Syrian hamsters, using partner preference as a model. Male hamsters were assigned to 5 groups: control (n=4), Intact-->Orchx (n=8), Orchx-->Orchx+T (n=7), olfactory bulbectomy (BulbX, n=5), and vomeronasal organ lesion (VnoX, n=8). Each male was tested for partner preference before and after sexual experience. Unlike rats, sexually-inexperienced gonad-intact male hamsters preferred the receptive female to a stimulus male. However, sexual experience did not enhance preference for the stimulus female. Castration (Orchx) reduced sexual motivation: Orchx males showed no significant preference for the stimulus female. Subsequently, intact males were castrated (Intact-->Orchx) and Orchx males received a testosterone implant (Orchx-->Orchx+T) to determine the time course of gonadal hormones on partner preference and mating behavior. Partner preference changed significantly in both groups within 6 weeks. In Intact-->Orchx males, preference for the stimulus female decreased while Orchx-->Orchx+T males increased their preference for the stimulus female. However, significant changes in mating behavior preceded the alterations in partner preference. Chemosensory cues are also important for partner preference. After BulbX, preference for the stimulus female significantly decreased. However, VnoX failed to block partner preference. These results show that partner preference may be even more dependent on testosterone than is sexual behavior. Furthermore, while chemosensory cues are essential for sexual motivation, the vomeronasal organ is not required for partner preference.     

Tickling in juvenile but not adult female rats conditions sexual partner preference

Female rats display a conditioned partner preference for males that bear odors paired with different types of rewarding unconditioned stimuli (UCS). Here we examined whether tickling constitutes a rewarding UCS that supports the development of partner preferences. In Experiment 1, we tested the possibility that odors associated with a tickling UCS in prepubescent rats would induce a conditioned partner preference in adulthood. Two groups were formed with 31-day-old, single-housed females, tickled for 6 min daily for 10 days, by a hand that wore a scented glove (almond or lemon). At 47 days of age, females were ovariectomized (OVX), hormone-primed (EB+P), and tested for sexual partner preference with two scented stud males (one almond and one lemon). In each group, females displayed a sexual preference toward males bearing the odor paired with tickling, as observed with longer visits, more solicitations, hops & darts, and receiving more intromissions and ejaculations from the preferred male. In Experiment 2, we used 3-month old, OVX, hormone-primed rats conditioned every 4 days for 10 trials. In contrast to juvenile females, adult females failed to prefer males that bore the odor paired with tickling but instead preferred the novel male. These results suggest that tickling has opposite age-dependent effects in the conditioning of partner preference. Tickling in juvenile females appears to act as a rewarding UCS, whereas in adult females it may act as an aversive UCS. Further research is needed to understand brain mechanisms that might account for such differences.     

Development of feminine sexual behavior in the rat: Androgenic and temporal influences

The contributions of prenatal and postnatal androgen exposure upon the development of sexual behavior in rats were examined by prenatal treatment of pups with an androgen antagonist (flutamide) and postnatal androgenization or castration. Male and female rats were exposed to the androgen receptor-blocker flutamide (FLU) in utero via prenatal injections to the mother on Days 10 through 22 of gestation. At birth (Day 1) males were castrated. Both males and females were injected with either 100 μg testosterone propionate (TP) or oil on Day 1. In adulthood all gonadectomized animals were tested for the display of feminine sexual behavior (lordosis) in response to a range of estrogen dosages. Prenatal exposure to FLU enhanced lordosis in both sexes when compared to vehicle-treated controls. Postnatal TP treatment decreased lordotic potential as expected. However, in animals given TP postnatally, those receiving prenatal flutamide had higher lordosis quotients than animals receiving vehicle treatment. These data confirm (1) that the development of feminine sexual behavior is inhibited by androgen exposure, (2) that such exposure occurs prenatally, (3) that the potential for feminine behavioral differentiation occurs prenatally as well as postnatally, and (4) that androgen acts perinatally to affect estrogen sensitivity in adulthood.     

Prenatal stress feminizes juvenile play patterns in male rats.

Sexually dimorphic rough-and-tumble play patterns were compared in male and female rats derived from control mothers and mothers stressed from days 14-21 of pregnancy. Animals were weaned into groups of 8 consisting of 2 males and 2 females from each treatment. Play in the home cage was recorded at 25, 28, 31, 34, 37 and 45 days of age and was most intense on day 31. The overall level of play was significantly higher in control males than in females or stressed males. Control males showed higher levels of the pinning component of rough-and-tumble play than females or stressed males. No play partner preferences were detected in any group. In adulthood, a higher percentage of stressed than control males displayed the female lordotic pattern. No deficits in ejaculatory behavior occurred in the stressed males. Since maternal stress alters patterns of plasma testosterone in male fetuses, the data suggest that the sexual differentiation of social play begins during prenatal ontogeny in the rat. The present results show that sexually dimorphic behaviors displayed before puberty are incompletely masculinized in prenatally stressed males, a finding similar to that reported for a number of adult behaviors.     

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.     

Interactional effects of pudendal nerve section and social restriction on male rat sexual behavior

Transection of the pudendal nerve causing desensitization of the glans penis impaired the sexual behavior of male rats. Compared to intact males, fewer animals performed intromissions and ejaculations while no decrease in mounting frequency was observed. The total sexual activity as measured by number of mounts and intromissions was decreased and the copulatory efficiency as measured by the ratio of intromissions and total sexual activity was lowered. The impairment of the sexual activity following penile desensitization was more marked in inexperienced rats than in experienced ones. It was concluded that penile stimulation, although not a prerequisite for any specific component of the mating pattern, still is necessary for maintaining the behavior at a normal performance level.     

Stimulus animal characteristics do not modulate the expression of partner preference by female rats

The stimulus animals used in tests of partner preference in female rats vary. To test the hypothesis that the alternative stimulus animal modulates the preference for an intact male, gonadectomized (GDX) female rats received estradiol benzoate plus progesterone or the oil vehicle and were tested for partner preference with either an intact male paired with a GDX hormone-primed female or an intact male paired with a GDX male. Rats were tested under conditions that limited physical contact (No Contact) or allowed sexual interaction (Contact). Stimulus animal condition was not a primary determinant of partner preference. In contrast, contact condition and hormone treatment modulated preference, as well as activity levels and the display of proceptive behaviors. Our findings demonstrate that the characteristics of the alternative stimulus animals tested here do not play a significant role in modulating partner preference in female rats.     

Effect of prenatal androgen receptor antagonist or aromatase inhibitor on sexual behavior, partner preference and neuronal Fos responses to estrous female odors in the rat accessory olfactory system

Many socially relevant odors are detected in rodent species by the vomeronasal organ and subsequently processed by the accessory olfactory system (AOS). We previously found that gonadectomized male and female rats treated in adulthood with testosterone propionate (TP) showed equivalent Fos responses in the AOS to odors derived from estrous females. Likewise, in contrast with numerous other mammalian species, gonadectomized female rats show surprisingly high levels of male-typical mounting behavior in response to adult TP. We tested the hypothesis that prenatal testosterone (T) exposure, acting via androgen receptors (ARs) or via estrogen receptors, masculinizes the AOS in rats of both sexes. Pregnant dams were treated with either the AR blocker, Flutamide, the aromatase inhibitor, 1,4,6-androstatriene-3,17-dione (ATD), or nothing (control) to assess the role of prenatal androgen and estradiol receptor activation, respectively, in this masculinization. Beginning at birth, male and female offspring were injected subcutaneously (sc) every other day with either ATD (pre- and neonatal ATD group) or oil vehicle (Flutamide and control groups) until postnatal Day 12. Subjects were gonadectomized as adults, hormonally treated and tested for different behaviors before having their AOS Fos responses to estrous female odors assessed. Prenatal treatment with Flutamide (but not ATD) significantly decreased anogenital distance and severely impaired intromissive and ejaculatory behaviors in males tested after TP replacement without disrupting mounting capacity in either sex. Pre- and neonatal treatment with ATD (but not Flutamide) enhanced lordosis responsiveness in males tested after sc injections of estradiol and progesterone, whereas these perinatal treatments had no effect on any aspect of masculine coital performance in either sex. After TP treatment, male and female control subjects preferred to approach a tethered stimulus female as opposed to a male, and prenatal Flutamide or perinatal ATD treatments did not modify this pattern of partner preference. Neuronal Fos responses to estrous odors were (as in previous studies) identical in the AOS of gonadectomized TP-treated control males and females. Prenatal Flutamide or perinatal ATD treatments failed to disrupt consistently this profile of Fos responses to estrous odors in the AOS of rats of either sex. These behavioral and neuroanatomical findings raise the possibility that the similar level of male-typical responsiveness to social odors that occurs in male and female rats after adult TP treatment results from nonsteroid-hormone-dependent, species-specific factors that act perinatally in the brains of rats of both sexes.