Egg-oviduct interaction initiates reproductive behavior

The experiments reported in this paper provide evidence that eggs must pass through the oviducts in order for receptivity to occur after ovulation in the female frog, Rana pipiens. In one experiment, oviductectomized frogs remained unreceptive after ovulation was induced by administration of exogenous pituitary glands, while sham-operates became receptive within 48 hr. Another experiment had four groups of subjects: ovariectomized females, females with oviducts ligated at the ostial end, females with openings in the uteri that prevented eggs from accumulating there, and sham-operated females. Only the last two groups, groups in which eggs could pass through the oviducts, became receptive. In these experiments, receptivity was indicated by absence of the release call during manual clasping of the trunk. Earlier experiments have shown that eggs have to pass through the oviducts in order to become fertilizable. Thus, the passage of eggs through the oviducts provides a mechanism which links the onset of reproductive behavior to the availability of fertilizable gametes.     

Female sex behaviors in the South African clawed frog, Xenopus laevis: gonadotropin-releasing, gonadotropic, and steroid hormones

The goals of this study were to characterize sex behaviors of female South African clawed frogs, Xenopus laevis, and to explore the behavioral effects of endocrine manipulation. The responses of females to clasp assaults by sexually active males were observed. Two patterns of female responses predominated. In one, females exhibited extreme leg extension and ticking vocalizations when clasped (unreceptive behaviors). In the other, females responded to being clasped by adduction of the thighs and increased flexion at the knee; ticking vocalizations were absent (receptive behaviors). When the female was unreceptive, clasps by males generally lasted less than 1 min. With a receptive female, on the other hand, amplexus could last up to 2 days. In intact females, injection of human chorionic gonadotropin (HCG) or of luteinizing hormone-releasing hormone (LHRH) into the dorsal lymph sac results in significant increases in receptivity. These hormones do not promote receptivity in ovariectomized females. Neither estradiol (E) nor progesterone (P) when administered alone was effective in restoring receptivity to ovariectomized females. In combination, E + P increased sexual receptivity. The releasing hormone, LHRH, when given to ovariectomized, E + P-treated females, further increased receptivity and led to the prolonged amplexus otherwise observed with an HCG-injected intact female. The behavioral effects of LHRH may be independent of action on the pituitary since they are not mimicked by gonadotropin.     

Persistence of sexual behavior in ovariectomized stumptail macaques following dexamethasone treatment or adrenalectomy

Daily administration over a period of 6 weeks of increasing doses of dexamethasone sodium phosphate (DEX) to seven long-term ovariectomized female stumptail monkeys significantly lowered circulating levels of testosterone without reducing any aspect of the females' sexual behavior or that of their male partners. Since treatment with DEX failed to suppress serum testosterone levels completely an additional experiment was performed in which the sexual behavior of five ovariectomized stumptails was compared before and after bilateral adrenalectomy, combined with chronic administration of both gluco- and mineralocorticoids. Serum levels of both testosterone and estradiol were reduced to very low levels in females after ovariectomy and adrenalectomy, yet no significant depression of females' sexual performance or that of their male partners occurred. Subsequent sc administration of estradiol or estradiol + testosterone in Silastic capsules to ovariectomized, adrenalectomized stumptails had little effect on sexual interaction. In a third experiment five ovariectomized stumptails which initially were relatively unreceptive and unattractive to males were given first testosterone and then testosterone + estradiol sc in Silastic capsules. One of the three indexes of females' receptivity increased significantly after testosterone; however, no other essential aspect of sexual interaction was affected. These findings suggest that sex steroids are normally not required in the female stumptail macaque for activation of preceptive and receptive sexual behaviors or for maintenance of sexual attractivity.     

Effects of ovariectomy and estradiol replacement therapy upon the sexual and aggressive behavior of the greater galago (Galago crassicaudatus crassicaudatus)

The effects of ovariectomy and estradiol treatment upon sexual and aggressive behavior were studied in a prosimian primate, the greater galago. Ovariectomized galagos were sexually unreceptive and frequently aggressive, but retained their sexual attractiveness to males. When females were treated with estradiol monobenzoate, however, their aggression and refusals of males' mounting attempts decreased markedly. Although males mounted these females, they usually failed to copulate, possibly because the females did not perform certain postural adjustments which assist males to intromit. Estradiol benzoate alone, even in large doses, does not fully restore patterns of mating behavior in ovariectomized female greater galagos. These observations on a prosimian primate are in striking contrast to the results of similar work on Old World monkeys and chimpanzees.     

Mounting behavior in pregnant and pseudopregnant female rats

Mounting behavior by female rats with regular 4-day estrous cycles was significantly reduced after the induction of pregnancy, pseudopregnancy, or treatment with progesterone. The mounting behavior shown by pseudopregnant female rats was comparable to that shown by ovariectomized females. Pseudopregnant and unmated females showed mounts with pelvic thrusting with the same frequency after treatment with estradiol benzoate (EB). EB stimulated the display of mounts with pelvic thrusting in ovariectomized females, and this behavior was not affected by concurrent progesterone treatment. It is suggested that the reduction of mounting in pregnant and pseudopregnant female rats is due to decreased ovarian estrogen secretion.     

Sex and estrous cycle differences in the behavioral effects of high-strength static magnetic fields: role of ovarian steroids

Advances in magnetic resonance imaging are driving the development of higher-resolution machines equipped with high-strength static magnetic fields (MFs). The behavioral effects of high-strength MFs are largely uncharacterized, although in male rats, exposure to 7 T or above induces locomotor circling and leads to a conditioned taste avoidance (CTA) if paired with a novel taste. Here, the effects of MFs on male and female rats were compared to determine whether there are sex differences in behavioral responses and whether these can be explained by ovarian steroid status. Rats were given 10-min access to a novel saccharin solution and then restrained within a 14-T magnet for 30 min. Locomotor activity after exposure was scored for circling and rearing. CTA extinction was measured with two-bottle preference tests. In experiment 1, males were compared with females across the estrous cycle after a single MF exposure. Females circled more and acquired a more persistent CTA than males; circling was highest on the day of estrus. In experiment 2, the effects of three MF exposures were compared among intact rats, ovariectomized females, and ovariectomized females with steroid replacement. Compared with intact rats, ovariectomy increased circling; estrogen replacement blocked the increase. Males acquired a stronger initial CTA but extinguished faster than intact or ovariectomized females. Thus the locomotor circling induced by MF exposure was increased in females and modulated by ovarian steroids across the estrous cycle and by hormone replacement. Furthermore, female rats acquired a more persistent CTA than male rats, which was not dependent on estrous phase or endogenous ovarian steroids.     

Ovarian steroids and hypothalamic norepinephrine release: studies using in vivo brain microdialysis

This study employed microdialysis in urethane-anesthetized female rats to monitor ovarian steroid-dependent changes in KCl-evoked levels of extracellular norepinephrine (NE) in the ventromedial hypothalamus. An initial KCl stimulus (Sl) increased NE from low or undetectable levels in all animals. A second KCl stimulus (S2) given several hr later evoked 40% less NE release than did Sl in ovariectomized (OVX) females or OVX females given only estrogen or progestin. In contrast, the two KCl-evoked NE releases were equivalent in OVX females administered both estrogen and progestin. These results suggest that ovarian steroids may act as presynaptic modulators of NE release in the ventromedial hypothalamus.     

Oxytocin inhibits infanticide in female house mice (Mus domesticus)

Between 60 and 90% of female house mice spontaneously kill unrelated young. A previous report indicated that subcutaneous administration of oxytocin significantly reduced the frequency of infanticide by virgin and pregnant females. However, in this study a distinction could not be made between an action of oxytocin on the CNS versus a secondary effect such as an enhanced release of prolactin by oxytocin. In the current experiment, oxytocin administered intracerebroventricularly was equally as effective at inhibiting infanticide as sc oxytocin. There was no difference in the effectiveness of oxytocin between groups of infanticidal females that were gonadally intact, ovariectomized, or estrogen treated. Pretreatment of infanticidal females with the prolactin inhibitors, bromocriptine and cysteamine, was also without effect on the ability of oxytocin to inhibit infanticide. Last, prolactin-inhibiting drugs had no significant effect on spontaneous parenting behavior by female mice. These data suggest that oxytocin acts directly on the CNS to alter behavior toward pups and that prolactin may not play a role in the maternal behavior of the house mouse.     

Physiological approach to the onset of receptivity in female Acheta domesticus : I. Role of the corpora allata and ovaries

During the 32 hr following the imaginal moult, all female Acheta domesticus actively or passively refuse male courtship; they are unreceptive. As of 32 hr, the most precocious females become receptive and accept mating. At this time, juvenile hormone (JH III) synthesized by corpora allata (CA) is already detectable in hemolymph, while ecdysteroids (synthesized by ovaries) begin increasing at 48 hr. JH III and ecdysteroid levels in hemolymph were measured by RIA. After allatectomy and/or ovariectomy, all females became receptive, thus showing that CA and/or ovaries are not essential to the onset of receptivity. However, male courtship is longer for allatectomized females; in ovariectomized females, mating is delayed.     

Prostaglandin E2 induces receptive behaviors in female Xenopus laevis

The object of this study was to examine the effects of exogenous and endogenous prostaglandin E2 (PGE2) on the sexual behavior of female South African clawed frogs, Xenopus laevis. Ticking and leg extension, which communicate sexual unreceptivity to males, were studied in intact, ovariectomized, and ovariectomized-oviductectomized females. The onset of the PGE2 behavioral effect occurs within 30 sec to 3 min of injection for intact and ovariectomized females; for ovariectomized-oviductectomized females, the latency period for the effect ranges from 10-20 min. PGE2 induced receptivity in doses as low as 0.03 microgram/frog. Injection of the prostaglandin synthesis inhibitors, indomethacin and flurbiprofen (FBP), blocked chorionic gonadotropin- (HCG-) induced behavioral receptivity, suggesting that endogenous prostaglandin synthesis may have a role in regulating female sexual behavior. Flurbiprofen blockade of HCG-induced receptivity was reversed by PGE2 administration, suggesting that FBP's effects are PG synthesis-specific.     

Effect of conspecifics on sexual maturation in female European pine voles (Pitymys subterraneus)

Using the number of large ovarian follicles (Type 8) as an indicator of sexual maturation we found that urinary compounds released by adult males accelerated puberty while urine from females suppressed hormonal activity in juvenile female European pine voles. The release of chemosignals that delayed puberty of juvenile females was not influenced by ovarian hormones; urine from ovariectomized females was as effective as urine from unoperated animals.     

Androgen-induced alterations in vocalizations of femaleXenopus laevis: modifiability and constraints

Summary We examined effects of exogenous androgen (testosterone and dihydrotestosterone) on vocalizations of ovariectomized, adult female South African clawed frogs,Xenopus laevis. When paired with sexually active males, all ovariectomized females exhibited ticking, the unreceptive or release call. Ticking consists of low amplitude, regularly spaced clicks with a mean interclick interval of 154 ms. When androgen-treated and paired with sexually active males, these ovariectomized females also exhibited an aberrant call (atypical ticking) in which click multiples replaced the single clicks of ticking. Mean ICI's for atypical ticking were 37 ms for click doublets and 22 ms for click quadruplets. Androgen treatment decreased the total time spent vocalizing (typical and atypical ticking) by ovariectomized females.All androgen-treated females were then tested repeatedly with sexually receptive females in an attempt to elicit the male-typical vocalization, mate calling. Six of 17 females did not vocalize at all, even when gonadotropin injected. Eight females gave rapid (mean ICI, 36 ms) trains of clicks in an irregular temporal pattern (tick-like calls). Three females gave brief trills with alternating fast and slow components. Comparison of mate calllike vocalizations of androgen-treated females to mate calling of males reveals that calls in females are considerably shorter in duration (female: 0.32 min versus male: 45 min) and slower in tempo (ICI's; fast trill, female: 21 ms, male: 14 ms; slow trill, female: 36 ms, male: 28 ms). Incomplete masculinization of the vocal pattern of females by androgen treatment in adulthood may be due to developmental constraints on the modifiability of the neurons and muscles responsible for calling.Abbreviations C cholesterol - DHT dihydrotestosterone - HCG human chorionic gonadotropin - IBI interburst interval - ICI interclick interval - ovx ovariectomized - T testosterone     

Effects of ovariectomy and estrogen replacement on attractivity and receptivity in the red-sided garter snake (Thamnophis sirtalis parietalis)

Activation of courtship behavior in male red-sided garter snakes, Thamnophis sirtalis parietalis, is independent of the presence of sex steroids. The only consistent treatment that stimulates courtship behavior in males is prolonged exposure to low temperature followed by subsequent warming, mimicking the emergence from hibernation. We investigated whether attractivity and receptivity in female red-sided garter snakes is similarly steroid independent.Female red-sided garter snakes are attractive when they emerge from hibernation and are courted by males; most mate within an hour of emergence. In a series of experiments, groups of females were either ovariectomized (OVEX) in the late spring, fall or while in hibernation. They were tested for attractivity and receptivity upon emergence from hibernation. Females OVEX in the spring were unattractive whereas those OVEX in fall or while in hibernation were attractive. Thus, attractivity appears determined the year before emergence and is dependent on the presence of the ovaries. All OVEX females were unreceptive upon emergence. OVEX females were also given replacement estradiol (E) treatment (either in Silastic capsules or single injections) at various points of their annual cycle. The only treatment that resulted in reinstating receptivity in OVEX females was the injection of E (20 g) one hour prior to emergence. The effectiveness of E in reinstating receptivity was time dependent: the longer the period between emergence and injection, the less effective the same dosage was in stimulating receptive behavior.These experiments suggest that sexual behavior in female red-sided garter snakes is, unlike males, dependent on the presence sex steroid hormones. Although E is naturally at its lowest seasonal level upon emergence, the concentration is sufficient to stimulate receptivity. However, it appears that temperature regulates a time-limited window of sensitivity to E.     

Hormonal regulation of aggression toward juveniles in female house mice

Adult female house mice that had been living in groups inflicted more wounds upon juvenile opponents than did females that had been housed in isolation. Ovariectomy blocked this enhancement of aggression by grouping. Aggression in ovariectomized females was augmented by treatment with testosterone propionate, but not by treatment with estradiol benzoate or progesterone. Preputial gland size was greater in group-housed females than in isolates; this difference was abolished by ovariectomy. Testosterone proprionate, but not estradiol benzoate or progesterone stimulated preputial gland growth in ovariectomized mice. These results are interpreted as supporting the hypothesis that the groupinginduced enhancement of juvenile-directed aggression in female mice is mediated by an increased secretion of ovarian androgens.     

Intracranial dialysis and microinfusion studies suggest that morphine may act in the ventromedial hypothalamus to inhibit female rat sexual behavior.

The present investigation examined the neural sites and mechanisms of opiate inhibition of female sexual behavior. Systemic administration of morphine (10 mg/kg) significantly reduced ovarian steroid-induced estrous behavior in female rats. This behavioral inhibition was prevented when the opiate receptor antagonist naloxone (5 mg/kg) was administered 30 min prior to morphine. Bilateral infusion of morphine directly into the ventromedial hypothalamus (VMH) also inhibited hormone-dependent estrous behavior for at least 2 hr. Furthermore, naloxone infusion into the VMH 20 min before behavior testing reduced the inhibitory effects of systemically administered morphine on lordosis. These results suggest that morphine may inhibit female sexual behavior by acting directly on the VMH, the primary site at which ovarian steroids facilitate this behavior. In a separate experiment we used in vivo brain microdialysis to test the hypothesis that morphine inhibits lordosis by interfering with norepinephrine (NE) neurotransmission in the VMH. In control rats, the onset of mating was associated with increased NE release in the VMH. Morphine-treated animals displayed neither behavioral estrus nor elevated NE release from the VMH when tested with stimulus males. These data are consistent with the hypothesis that morphine suppresses NE release in the VMH. Nevertheless, mechanisms other than or in addition to attenuation of hypothalamic NE release may contribute to the inhibitory effects of morphine on lordosis.     

Sexual receptivity in aged female rats : Behavioral evidence for increased sensitivity to estrogen

Lordosis behavior and behavioral patterns indicative of sexual receptivity or nonreceptivity were evaluated in 3- and 25-month-old female rats. Intact, 25-month-old females revealing a pattern of prolonged vaginal cornification (PVC) were highly receptive, whereas 25-month-old pseudopregnant (PL) females were nonreceptive. These measures did not differ as a result of previous sexual experience (i.e., sexually naive vs retired breeders). Following ovariectomy, sexual behavior persisted significantly longer in 25-month-old PVC females than in 3-month-old females ovariectomized during vaginal proestrus. No difference was observed in the rate at which the vaginal smears of 25-month-old PVC and young ovariectomized females became leukocytic. When tested 5, 19, and 20 days after ovariectomy, sexual behavior was absent in all females. Following treatment with estradiol benzoate (0.5 or 1.0 μg/kg), the latency for the reappearance of sexual behavior in 25-month-old females was significantly shorter than that in similarly treated 3-month-old females. This was the case regardless of prior ovarian condition (PVC or PL) and breeding experience. In addition, the mean lordosis quotient (LQ) of 25-month-old females receiving either dose of EB was significantly greater than that of similarly treated 3-month-old females on at least 5 days of a 10-day treatment period. These results are discussed in terms of possible age-related changes in central and peripheral estrogen metabolism.     

Reproductive Signals of Female Lizards: Pattern of Trait Expression and Male Response

Relative to the volume of studies concerning the function and evolution of male‐biased sexually dimorphic traits, instances of female‐biased sexual dimorphisms remain largely unstudied, especially in species with conventional sex roles. I investigated the signal function of a female‐specific ornamental trait using the striped plateau lizard (Sceloporus virgatus, Phrynosomatidae) as a model system. During the reproductive season, female S. virgatus develop orange color on their throats that is absent in conspecific males. I established the relationship between color expression and female reproductive state, and determined male response to female color. I show that dynamic changes occurring within the color patch can potentially identify each stage of the female reproductive cycle, largely because of a lag in patch growth relative to color intensification. Sexual receptivity is associated with intense patches rapidly growing in size; ovulation occurs near peak color expression; and the unreceptive period is associated with large patches fading in intensity. Because females express orange color during both the receptive and unreceptive periods, the pattern of color expression is consistent with the courtship‐stimulation and courtship‐rejection hypotheses of signal function. Males may preferentially associate with females that have more highly developed color patches during the courtship season, and/or ignore such females when they are unreceptive. An examination of male behavior towards unfamiliar females indicates that female color has a role in courtship stimulation but has little, if any, role in courtship rejection. During the pre‐mating season, males maintained significantly closer affiliation with, and tended to perform more social behavior towards females with more intense color. During the post‐mating season, female color had no apparent effect on male behavior. The evolution and current function of female ornaments may vary among taxonomically‐related species as a result of differences in ecology, social system, and life‐history.     

Gender mediated cardiac protection from adverse ventricular remodeling is abolished by ovariectomy

Gender differences in the prevalence of cardiovascular disease have been observed both clinically and experimentally. These cardioprotective effects have frequently been attributed to female hormones, however, the underlying mechanisms responsible for this cardioprotection are still poorly understood. Accordingly, this study sought to determine the contribution of ovarian hormones to the prevention of adverse ventricular remodeling and congestive heart failure in chronic volume overload (i.e. aortocaval fistula in intact or ovariectomized female rats). Ovariectomized rats developed more extensive cardiac remodeling than intact females at 21 weeks post-fistula, characterized by significantly greater left ventricular (LV) hypertrophy (167 vs. 86%, respectively, p < 0.05) and a substantial increase in LV dilatation (71%, p < 0.05) relative to control. In contrast to the eccentric hypertrophy in ovariectomized females post-fistula, the hypertrophic response in the intact female hearts was essentially concentric. While neither fistula group suffered significant mortality, there was a marked increase in the lung weight of ovariectomized rats (87%, p < 0.05) consistent with the development of pulmonary edema. Overall, the extent of myocardial remodeling and decrease in LV function in the ovariectomized females was comparable to those changes reported for males with symptomatic heart failure, while intact females maintained chronic compensated ventricular function similar to that of controls. The marked ventricular dilatation and symptoms of congestive heart failure seen at 21 weeks post-fistula in the ovariectomized females clearly demonstrate the influence of circulating ovarian hormones on the pattern of myocardial remodeling resulting from a chronic volume overload.     

Age-related changes in plasma oestrogen concentration, behavioural responsiveness to oestrogen, and reproductive success in female gray-tailed voles, Microtus canicaudus

Age-related increases in the incidence of vaginal cornification were associated with increases in the reproductive success of female gray-tailed voles previously isolated from males. The pregnancy rate of females first paired with males at 30-50 days of age was significantly lower than that of females first paired at 90-120 or 150-200 days of age. The improvement was due to increases in propensities to display receptive behaviours and decreases in the incidence of sterile matings. Although plasma oestrogen concentrations increased with age and were higher in receptive than unreceptive females, plasma oestrogen values alone did not account completely for differences in receptive behaviours amongst females of different ages. Females ovariectomized at 30-50 days of age rarely displayed receptive behaviours when treated with large doses of oestradiol benzoate, whereas nearly all females similarly treated were receptive if ovariectomies were performed between 150 and 200 days of age. The receptivity rate of females ovariectomized between 90 and 150 days was intermediate between the rates of the other two groups.     

Acute effects of 2-methoxyestradiol on endothelial aortic No release in male and ovariectomized female rats

The endogenous metabolites of 17β-estradiol are thought to have protective vascular effects, especially in males and estrogen-deprived females. The present study evaluated the acute in vitro effects of the active metabolite 2-methoxyestradiol on endothelial NO release from ovariectomized female and intact male and female rat aortas.NO was measured electrochemically by differential normal pulse amperometry using carbon fiber microsensors, and also by fluorescence microscopy using 4,5-diaminofluorescein diacetate.2-Methoxyestradiol alone induced a maintained increase in endothelial NO release in male and ovariectomized rats that was reduced by pretreatment with L-NAME. NO release induced by calcium ionophore alone (A23187) was lower in aortas from ovariectomized rats than from intact females, indicating that estrogen deprivation induces endothelial dysfunction. Pretreatment of aortas with 2-methoxyestradiol potentiated significantly the A23187-induced-NO release in ovariectomized as well as in males, but not in intact females. This potentiation was reduced or abolished by L-NAME. 2-Methoxyestradiol potentiated the vasodilatory effect of A23187 on intestinal arterioles, and also increased intestinal tissular laser-Doppler blood flow signal.These results demonstrate that 17β-estradiol and its active metabolite 2-methoxyestradiol increase basal aortic endothelial NO production and also cause a potentiation of the calcium ionophore-stimulated NO release in male and ovariectomized, while it has no effects on intact females. 2-Methoxyestradiol appears to be a promising pharmacological agent capable of improving endothelial function in men and postmenopausal women.