Central progesterone induces female sexual behavior in estrogen-primed intact males rats

Progesterone induced high levels of female lordotic behavior in 10 of 17 intact, estrogen-primed male rats when it was applied directly to the medial preoptic-anterior hypothalamic area. All 17 males previously had shown lordosis when the serotonergic antagonist methysergide was applied to the same central sites. Few males responded to systemic progesterone and none to intracralial cholesterol. Intradiencephalic Metycaine, a local anesthetic, induced lordosis in eight male that previously had responded to central progesterone. These data indicate that estrogen and progesterone act synergistically to induce lordosis in male rats when progesterone is administered directly to sensitive brain sites.     

Receptivity of the female rat (Rattus norvegicus) after male devocalization: a ventral perspective

Male rats (Rattus norvegicus) emit at least two patterns of vocalization during copulation, the mating call and the pre-ejaculatory call. Both calls promote immobility of the female during lordosis, but the pre-ejaculatory calls are more effective. We undertook, through ventral observations of the mating pair, to determine if the female failed to assume or maintain the lordosis posture when mounted by a devocalized male and also to determine if the devocalized male was providing adequate stimulation to induce receptive behavior. Females were more likely to move away from the devocalized males before assuming the full lordosis posture. Furthermore, they were more likely to move away before the males had a chance to engage in intromissive behavior. However, when the females remained immobile long enough for the males to achieve a mount or intromission, there was little difference in the behavior of either animal that resulted from the devocalization of the male.     

Perinatal bromopride treatment: effects on sexual behavior of male and female rats

Effects of different perinatal bromopride treatments on sexual behavior were examined in adult male and female rats of Wistar origin. Female rats of mothers treated with bromopride (BRO) during lactation (VB group) and during pregnancy and lactation (BB group) showed lower lordosis quotients than those of controls (VV group). Females of mothers treated with BRO only during pregnancy (BV group) showed no differences in lordosis quotient when compared to the VV group. There were no significant differences in male sexual behavior between experimental and control groups. The effect of bromopride on the control of sexual behavior is discussed.     

Habenular lesions and feminine sexual behavior of ovariectomized rats: diminished responsiveness to the synergistic effects of estrogen and progesterone.

Bilateral electrolytic lesions in the habenula resulted in disruption of estrogen-progesterone-evoked feminine sexual behaviors of ovariectomized female rats. There were no difference between lesioned and sham-operated animals in tests conducted after the administration of estrogen alone. Animals with lesions were characterized by an increased proportion of mounts not followed by lordosis, a decreased proportion of mounts followed by pronounced lordosis, and a decreased proportion of mounts preceded by soliciting behaviors. Lesions had a negligible effect upon the tendency to hold lordotic postures after the male dismounted. The results suggested that the habenula is involved in modulating responsiveness to the synergistic effects of estrogen and progesterone.     

Neonatal androgenic stimulation and adult sexual behavior in male and female golden hamsters.

Neonatally and adult castrated male hamsters as well as neonatally androgenized and nonandrogenized female hamsters were tested for both mounting and lordosis behaviors during treatment with either testosterone or ovarian hormones. Neonatal androgenization facilitated mounting behavior in adult animals administered either testosterone or ovarian hormones and suppressed lordosis behavior in adult ovarian-hormone-treated animals. Early androgen effects on the display of lordosis behavior during adult testosterone treatment were complex and varied with the exact timing of perinatal endogenous or exogenous androgenization. Species differences in hormone-behavior relationships and the possible role of perinatal androgenization in the development of rodents' ability to aromatize androgens were discussed.     

Vaginal stimulation in rats induces prolonged lordosis responsiveness and sexual receptivity.

Sexual receptivity to males resulted from stimulation of the vagina with a glass rod in previously unreceptive ovariectomized, estrogen-treated rats. Several minutes of rejection behavior preceded the receptivity. In a second study, manual palpation was used to determine the duration of the lordosis response facilitation. Initially, all females were unresponsive to manual flank-perineum stimulation (palpation). Vaginal stimulation plus palpation, which together elicit lordosis, facilitated subsequent lordosis responses to palpation. This effect persisted for several hours after the vaginal stimulation was applied. Vaginal stimulation alone, which was ineffective in eliciting lordosis, also facilitated lordosis in response to subsequent palpation. Repeated palpation did not facilitate lordosis. These prolonged effects were independent of hormone treatment.     

Monoaminergic mediation of female sexual behavior.

Lordotic behavior was facilitated in estrogen-primed female rats by direct application of progesterone or serotonergic or beta-adrenergic receptor blockers to specific telencephalic, anterior hypothalamic-medial preoptic, or posterior hypothalamic sites. Blockade of the alpha-adrenergic system was ineffective in facilitating lordosis, as was the application of the active drugs to control sites in the thalamus or basal ganglia. Female soliciting behavior was not evoked by any of the treatments. It is concluded that the lordotic behavior component of the female rat's estrous behavior pattern is inhibited by a specific central monoaminergic system that also responds to progesterone. Soliciting behavior appears to be mediated by systems that are anatomically, and possibly neurochemically, separable from those regulating lordosis.     

Effect of novel and familiar mating partners on the duration of sexual receptivity in the female hamster

The lordosis duration of the female golden hamster (Mesocricetus auratus) in response to novel and familiar mating partners was examined. In Experiment 1, females mated to the point of sexual satiation with one male hamster, and following its removal, showed renewed receptivity in response to the introduction of a second male. Upon sexual satiation with the second male, females either received a novel third male or were reexposed to the original male. Total lordosis duration in the third bout in the group receiving a novel male was significantly greater than in the group reexposed to the original male. In Experiment 2, the insertion of a 1-h delay between the second and the third mating partner had no effect on the female's responsiveness, regardless of whether the third male was the original male or a novel male. In Experiment 3, removal of the ovaries followed by hormone replacement treatment (40 micrograms estradiol benzoate, 72 h prior to testing, and 500 micrograms progesterone, 4 h prior to testing) failed to alter the females' ability to discriminate between novel and familiar mating partners. These results demonstrate that females make clear discriminations among individual mating partners, that this can affect sexual receptivity and will continue to do so following a delay of at least 1 h, and that the effect is not mediated by the release of ovarian steroids.     

Hippocampal and cortical activity during sexual behavior in the female rat.

Hippocampal and cortical activity were studied during sexual behavior in the female rat. Hippocampal theta appeared during her soliciting behavior. High-frequency theta accompanying the male's pursuit slowed when the male mounted the female and then increased in frequency during the brief continuation of lordosis following mounts without vaginal penetration. During prolonged lordosis after intromissions and ejaculations, slow theta continued. No changes in cortical frequencies were observed during mounts, intromissions, or ejaculations. During immobility (standing, sitting, and lying down) hippocampal activity became slow and irregular. High-amplitude hippocampal and, eventually, cortical spindles developed during immobility as sexual exhaustion was approached. Immobility and its accompanying electroencephalographic spindling are interpreted as indicative of a sexual satiety or inhibitory process.     

Prelordotic behavior in the hamster: a hormonally modulated transition from aggression to sexual receptivity

The behavioral responses of the female golden hamster to a sexually experienced male were analyzed as a function of the stage of the female's estrous cycle. Exogenous estradiol or estradiol followed by progesterone was given to ovariectomized females to determine the role of these hormones in the regulation of cyclic changes in the female's response to the male. Females were paired on a daily basis with sexually active males for 10 min, and behavioral interactions were recorded. Significantly more fighting occurred during early diestrus than later in the cycle. During the 24 hr preceding sexual receptivity, fighting was infrequent. BY 8 HR PRIOR TO THE ONSET OF SEXUAL RECEPTIVITY, 86% OF THE POPULATION EXHIBITED A BEHAVIOR RESEMBLING THE ONSET OF LORDOSIS WITHOUT IMMOBILIZATION (PRELORDOSIS). Following ovariectomy fighting was at a high level (80%--90%). Estradiol replacement, over a 28-day test period, resulted in a significant decrease in aggression and a significant increase in the display of the prelordotic response without inducing lordosis. Initially, the treatment with progesterone following 7 days of estradiol treatment caused the female to display lordosis. After 24 hr a significant increase in aggression, which continued as long as progesterone was present, was observed. After removal of progesterone a significant decrease in aggression occurred. Thus, estradiol causes the female to become tolerant of the male's approach, the female exhibiting prelordosis in response to the male's investigation. Estradiol and progesterone are necessary for normal sexual receptivity; however, after 24 hr, estrogen-progesterone-treated females become agonistic to the male.     

Evidence that a factor besides progesterone, prolactin, or plasma-estradiol-binding protein inhibits estrogen-induced sexual receptivity in pregnant rats.

Daily administration of estradiol benzoate stimulated significantly less lordotic behavior in rats during the second half of pregnancy than in ovariectomized females that received subcutaneous progesterone implants, pituitary grafts that raised plasma prolactin, or both treatments combined. Following an initial facilitation of receptivity, females with progesterone implants showed only moderate reductions in lordosis quotients over 3 test days. The capacity of plasma from pregnant rats to bind estradiol was found to increase significantly during the second half of pregnancy. However, daily administration to pregnant rats of a synthetic estrogen, R 2858, which is not bound by plasma protein, was no more effective than estradiol benzoate in stimulating receptive behavior. Administration of estradiol benzoate also stimulated significantly lower levels of sexual behavior in pregnant females than in females in which pseudopregnancy had been prolonged by previous hysterectomy or induction of uterine decidualization. These findings suggest that some endocrine factor other than progesterone, prolactin, or estradiol-binding protein is primarily responsible for the potent suppression of behavioral responsiveness to estrogen which occurs in pregnant rats. It is suggested that 5 alpha-reduced androgens may cause these behavioral effects.     

Selective approach to a male and subsequent receptivity to mounting comprise mate‐choice behavior of female mice1

Abstract: To ensure the effectiveness of the mate‐choice behavior of female house mice (Mus domesticus), we observed them in two different situations that involved restriction of the area of movement of the male mice. In Experiment 1, we observed 12 trios consisting of two male mice and an estrous female placed in a chamber in which none of the animals was restricted during the 6‐h test. It was found that the female was more receptive to the male that had ejaculated with it first. Additionally, when the female initiated the mating event by approaching the male, the lordosis quotient was higher than that when the male initiated the mating event. In Experiment 2, a female was able to visit two males that were prevented from getting out of small boxes. As a result of the 3‐h observation of 10 cases, it was found that the females were more receptive to the dominant male. The intromission ratio of the dominant male was also higher than that of the subordinate male. The behavioral roles of female mice in mating interactions and their adaptive validity are discussed.     

Postnatal anoxia from CO2 for one minute produces sex-specific changes in contextual fear conditioning in adult rats.

In a split-litter design, equal numbers of male and female rats were exposed either to carbon dioxide for 1 min, or to the control condition on either postnatal Days 9-10 or 17-18. At 120 days of age half the numbers of rats in each condition were given subclinical dosages of lithium (1.5 mEq/kg) and pilocarpine (15 mg/kg) or saline. 40 days later all rats were tested in a conditioned fear paradigm. A four-way analysis of variance as a function of the variables anoxia, age at the time of anoxia sex, and subclinical seizure induction indicated a significant interaction between sex and anoxic history. Post hoc analysis showed that performance of male rats exposed to the anoxic condition did not differ from normal or anoxic female rats. The results suggest that only 1 min. of preweaning anoxia may produce permanent changes in contextual fear conditioning for male but not female rats.     

Effect of the interintromission interval on lordotic response and attack latency in golden hamsters (Mesocricetus auratus)

After 12-15 ejaculatory series, each consisting of several short intromissions (2- to 3-s vaginal penetration) and an ejaculation, male golden hamsters adopt an altered copulatory pattern consisting of long intromissions (5- to 25-s penetration with intravaginal thrusting). Receptivity declines and the tendency for the female to attack the male increases at about the time of this shift in copulatory pattern. Because the mean interintromission interval (III) between short intromissions is about 8 s compared to 100 s between long intromissions, it is possible that females detect this difference and adjust their mating accordingly. When the III between short intromissions from a rested male was experimentally increased to 100 s by use of a halter and lead device, the duration of lordosis was significantly less than that displayed by females paired with control males (8-s III) and virtually the same as that displayed by females paired with males that produced only long intromissions. This suggests that the female uses the temporal patterning of intravaginal stimulation as one criterion for terminating mating with a particular male.     

Mesencephalic participation in the control of sexual behavior in the female rat

Electric stimuli applied to both pudendal nerves evoked field potentials, unit responses, and multiunit responses in the ventrolateral midbrain, in and around the peripeduncular nucleus. Bilateral lesions placed in this region suppressed sexual behavioral responses (lordosis and courting behavior) of ovariectomized rats primed with 5, 10, 100, and 1,000 microgram of estradiol benzoate and 2 mg of progesterone per kilogram of body weight. It is proposed that the region in question represents a relay station for the integration of sensory and endocrine information concerned in the control of receptive sexual behavior in the female rat.     

Sensory cues that elicit ultrasonic vocalizations in female rats (Rattus norvegicus)

Female rats emit ultrasonic vocalizations during copulation. Female vocalizations are associated with darting and other proceptive behavior. In addition, females frequently call while approaching the male. A series of experiments was undertaken to determine whether female rats emit ultrasonic vocalizations in response to other rats or to their odors. Females were exposed either to bedding soiled by males or females or to devocalized conspecifics separated from the subject by a barrier. Females vocalized more to male cues than to female cues, regardless of whether the odor cues were from soiled bedding or from a devocalized conspecific. In addition, subjects vocalized more when presented with a devocalized female rather than a neutral stimulus. Furthermore, devocalized adult males, separated by a barrier, were more effective than either devocalized castrated or juvenile males in eliciting vocalizations; in turn, castrates and juveniles were more effective than neutral stimuli. Female calling was likely induced by odors from the male. In one experiment, the female subject was positioned in such a way that she could neither see or touch the stimulus male. Presentation of tape-recorded male vocalizations did not affect calling by the female. Vocalizations emitted by females in response to male odors may attract males or may facilitate subsequent copulatory behavior by the male.     

Gender differences in acute and chronic stress in Wistar Kyoto (WKY) rats

While females are considered more susceptible to depressive behavior, this assertion is not strongly supported by the experimental literature. Since stress contributes to depressive behavior, male and female Wistar Kyoto (WKY) rats were exposed to either one session (acute stress) or 5 sessions (chronic stress) of restraint plus cold in order to study depressive behavior in male and female rats. After their respective treatment exposure, rats were tested in the open field test (OFT) and for retention of a passive-avoidance (P-A) task. One stress session resulted in significant immobility in the OFT for males, whereas 5 sessions were required to produce similar immobility in female rats. Acute stress interfered with the retention of the P-A response for males, while both acute and chronic stress produced poor P-A responses in female rats. Food consumption decresed, progressively, as a function of stress sessions, in female rats, whereas feeding in males returned to control levels after five stress days. Both acute and chronic stress exacerbated the stress ulcer response in male rats, but not in female rats. Chronic, but not acute, stress resulted in an increase in serotonin transporter mRNA levels in the dorsal raphe nucleus of both male and, female rats. The general consensus from these data suggested that female rats were more vulnerable to chronic stress and consequently supported the notion that females may be more susceptible to stress induced behavioral depression.     

The effects of neonatal gonadectomy and prenatal stress on cortical thickness and asymmetry in rats

In Study I measures of cortical thickness were taken in 90-day-old male and female Sprague-Dawley, Wistar, and Long-Evans rats that were born to pregnant females shipped to the laboratory in late pregnancy and that were either gonadectomized at birth or left intact. No evidence for hemispheric differences in cortical thickness was found in any of the groups. Gonadectomy resulted in increased cortical thickness in male Sprague-Dawley and Wistar rats and in small increases in thickness of the left hemisphere in Long-Evans rats, especially males. No effects of gonadectomy were found in females of any strain. The lack of the expected right-over-left difference in cortical thickness in intact males may have been due to prenatal stress caused by housing, handling, and shipping. In Study 2 measures of cortical thickness were taken in 90-day-old male and female Sprague-Dawley rats that were bred in our laboratory, but otherwise similarly treated at birth. In this second study, the expected right-over-left hemispheric difference in cortical thickness was found in intact male rats; none was found in gonadectomized males or in either of the female groups. The lack of asymmetry in gonadectomized males appeared to be due to an increase in thickness in the left hemisphere. Taken together these studies provide support for the idea that hormones of testicular origin suppress cortical enlargement in the perinatal period, particularly in the left hemisphere.     

Social factors influence haloperidol-induced catalepsy in rat

This study employed manipulations which presumably influence social interactions in rats: (1) paired housing with a heavier conspecific and (2) exposure to the odors of other rats. The dependent variable was the akinetic state induced by haloperidol, a neuroleptic and dopamine antagonist. In Experiment 1, adult male Long-Evans hooded rats were matched by weight and caged alone or in pairs with one rat 30 g heavier than its cagemate. All rats received haloperidol (1.5 mg/kg) and catalepsy testing. Heavy rats showed more catalepsy than the lighter member of pairs or weight-matched, singly housed controls. In Experiment 2, adult male rats were left unrecaged or were recaged into cages with bedding recently soiled by females or other adult males. After haloperidol (1.0 mg/kg), the rats exposed to bedding soiled by other adult males showed more catalepsy than did the control groups. Thus, the results of both experiments indicated that social factors can influence the akinesia induced by dopamine antagonists.     

Sex differences in urinary odors produced by young laboratory rats (Rattus norvegicus)

Responses of adult female rats to male and female pup urine were examined in three experiments. Investigatory sniffing of male and female pup urine deposits by maternal rats was compared in a series of simultaneous choice tests given at 3-day intervals between Day 2 and Day 17 postpartum. Male urine was consistently preferred. Introduction of male, but not female, pup urine to the nest was also found to significantly elevate maternal licking of anogenital regions of pups. Thus, urine from pups of various ages contains sex-identifying odors that differentially elicit spontaneous maternal interest. The odor of male urine may provide a sufficient stimulus to account for the greater anogenital licking that males of this species normally receive. Nonmaternal, naive, adult females behaved like maternal rats, preferring male urine in the choice test. This indicates that the maternal condition of a dam is not necessary either for the olfactory discrimination or for the male odor preference.