A re-examination of the lordosis response in female rats given high doses of testosterone propionate or estradiol benzoate in the neonatal period

High lordosis quotients (LQ) were observed when female Wistar rats injected with 1.25 mgm of testosterone propionate (TP) on Day 4 of postnatal life were tested as intact adults. The high LQ was not due to testing during the lights-on period, the age at which the females were tested, the use of a strain that was insensitive to the masculinizing action of TP or estradiol benzoate (EB), the age at which the females were injected with TP or EB, or an abnormal response to estrogen. High LQ values were found in similar tests on adult female rats of two other strains injected with 1.25 mgm TP on Day 4 of life. A marked reduction of the facilitatory action of progesterone on receptivity in estrogen-primed animals was demonstrated in the females of all three strains treated with TP or EB during the neonatal period and for males after castration as adults.Analysis of the experimental records of the mating tests showed that females anovulatory following TP or EB administration during the neonatal period and tested either intact and under the influence of endogenous hormones or under the influence of exogenous estrogen showed a rapid and highly significant increase in receptivity during the course of prolonged (20 min) tests with two or three active stimulus males. This effect was very much reduced if the treated females were under the influence of exogenous estrogen plus progesterone. The effect was not seen in males castrated as adults and treated with estrogen, or in females not treated with steroids in the neonatal period and tested intact at proestrus alone or under the influence of exogenous steroids after ovariectomy. A significant increase in LQ during the test period was observed in females of the Wistar strain which were anovulatory as a result of exposure to constant light and were tested intact without any exogenous hormone being administered.It is suggested that although tests involving a limited number of mounts or attempts to mount at low rates over a short period of time may be adequate to determine the degree of receptivity of normal female rats they are not adequate to establish the capacity of female rats treated with steroid hormones during the neonatal period to display the lordosis response.     

Influence of androgen on the development of sexual behavior in the rat. II. Time and dosage of androgen administration during the neonatal period and masculine and feminine copulatory behavior in females

The objective of the present study was to delineate the period of sensitivity to a single androgen exposure during the initial neonatal hours on the development of masculine and feminine copulatory behavior in female rats. Female rats were injected once with either 500, 50, or 5 micrograms testosterone propionate (TP) at either 1 or 24 hr after birth. Following castration in adulthood and TP replacement, the females were tested four times at weekly intervals in prolonged sessions for masculine copulatory behavior. One month following the masculine copulatory tests the females were tested for 3 weeks for feminine copulatory behavior with weekly increasing levels of estradiol benzoate (2.5, 10, and 25 micrograms) and progesterone (200 micrograms). The results demonstrate that a single injection of TP administered at either 1 or 24 hr after birth can significantly increase the capacity of female rats to exhibit ejaculation patterns and that the amount of androgen that is administered is critical in determining the levels of ejaculatory responding. Similarly, the females given high doses (50 and 500 micrograms) of TP at either 1 or 24 hr neonatally were almost completely defeminized. In contrast, however, the females treated with 5 micrograms TP at 1 and 24 hr showed different levels of lordotic performance indicating a greater sensitivity to androgen immediately after birth than at 24 hr in female rats as has been shown in male rats.     

Neonatal Androgen Affects Copulatory Behavior in the Female Musk Shrew

The role of neonatal testosterone in the development of copulatory behavior was examined in an insectivore, the musk shrew (Suncus murinus). Female musk shrews were treated with testosterone propionate (TP) for the first 5 days of life and then tested in adulthood for either female or male-like copulatory behavior. Early TP had a masculinizing effect; neonatally treated animals mounted a stimulus female more frequently, and with shorter latencies, in response to adult testosterone treatment than did control females. Neonatally androgenized females also showed deficits in female sexual behavior; few received ejaculations from stud males. This difference was likely caused by increased aggression exhibited by the neonatally TP-treated females toward males. In turn, female aggression decreased efficiency of male partners' intromission attempts. Early TP treatments also caused structural abnormalities in the ovaries, but did not effect their capacity to ovulate in response to either gonadotropin-releasing hormone or human chorionic gonadotropin injection. In sum, exposure to TP during development augmented display of male-like behavior in females and had subtle deleterious effects on expression of feminine behavior.     

Anxiety and fear behaviors in adult male and female C57BL/6 mice are modulated by maternal separation

This study investigated the effects of maternal separation in C57BL/6 male and female mice during infancy on later adult fear and anxiety behaviors. Additionally, we observed the maternal behavior of the dams to examine aspects of maternal care that may be modulated by daily bouts of separation. In males, mice that experienced maternal separation during the neonatal period displayed significantly higher levels of anxiety and fear behavior, as measured by the open field test and elevated plus maze, compared to control, standard facility reared males. In females, however, maternal separation reduced anxiety and fear behavior in the open field test, but only when the females were in the diestrous phase of their estrous cycle. The 30-min daily observation of the dams revealed that the separation did not significantly alter the frequency of the maternal care provided by the dam at the time point measured. These results indicate that the emotionality of adult male and female mice can be modulated by maternal separation. However, this effect is dependent on the sex of the offspring and the phase of the estrous cycle of the female.     

Effects of neonatal testosterone treatment on pacing behaviors and development of a conditioned place preference

Two experiments assessed the effects of neonatal testosterone treatment on paced mating behavior and conditioned place preference in female rats. In both experiments, females received s.c. injections of 5.0 microg testosterone propionate or oil vehicle at three days postpartum. As adults, females were ovariectomized and given s.c. injections of 10 microg estradiol benzoate and 500 microg progesterone, 48 and 4 h before mating, respectively. In Experiment 1, TP- and Oil-treated females exhibited similar high levels of lordosis responsiveness, but TP-treated females showed increased intervals between mounts and between intromissions in paced and non-paced mating conditions compared to control females. The effect was particularly pronounced during paced mating, when contact return latencies were increased approximately 2-fold by TP treatment. TP-treated females showed exaggerated pacing behavior, showing significantly greater return latencies after intromissions than Oil-treated females. In Experiment 2, TP- and Oil-treated groups were tested in a conditioned place preference paradigm to determine if the behavioral changes observed in Experiment 1 were in part a result of changes in the perceived reward produced by paced mating. TP treated and control females developed equivalent preferences for places associated with paced but not non-paced mating, indicating that neonatal TP treatment at this dosage does not disrupt or enhance the conditioned place preference induced by paced mating. The results of the two experiments demonstrate that neonatal TP treatment alters the display of pacing behavior but not the reward state induced by paced mating, and suggest that TP affects neural substrates involved in performance of paced mating without effects on those controlling lordosis or place preference conditioning.     

Intraphypothalamic implants of testosterone or dihydrotestosterone in neonatal female rats with reference to induction of sterility

Implants of paraffin micropellets containing about 5 microgram 5 alpha-dihydrotestosterone (DHT) into the hypothalamus of 5-day-old female rats were without effect on the sexual differentiation of the brain. By contrast, approximately the same amount of testosterone propionate (TP) given as subcutaneous or intrahypothalamic micropellets masculinized the female brain. In the light of these results as well as the author's previous findings that an antiestrogen implanted into the hypothalamus of neonatal female rats failed to block masculinization by subcutaneous injection of TP, the possibility cannot be excluded that testosterone is capable of masculinizing the brain of neonatal females without being converted into estrogens.     

Influence of fetal position on neonatal androgen-induced sterility and sexual behavior in female rats

Two aspects of reproductive function were examined in relation to female fetus' contiguity to intrauterine male littermates. Following injection of 3.5 μg testosterone propionate (TP) on Day 3, females that had been positioned in utero between two males became sterile earlier in life than those located in utero between two females. Anogenital distances on Days 1 and 3 prior to neonatal treatment with TP were greater in females located in utero between two males than in females residing between two females in utero, suggesting that females developing between two males may have been exposed prenatally to a masculinizing substance, presumably an androgen. No reliable contribution of litter composition was apparent with respect to differentiation of female sexual behavior. Results indicate that littermate hormonal influence is present or effective and can be detected in a neonatally androgenized preparation.     

Effects of neonatal handling on social memory, social interaction, and number of oxytocin and vasopressin neurons in rats

Early-life environmental events can induce profound long-lasting changes in several behavioral and neuroendocrine systems. The neonatal handling procedure, which involves repeated brief maternal separations followed by experimental manipulations, reduces stress responses and sexual behavior in adult rats. The purpose of this study was to analyze the effects of neonatal handling on social behaviors of male and female rats in adulthood, as manifest by the results of social memory and social interaction tests. The number of oxytocin (OT) and vasopressin (VP) neurons in the paraventricular (PVN) and supraoptic (SON) nuclei of hypothalamus were also analyzed. The results did not demonstrate impairment of social memory. Notwithstanding, handling did reduce social investigative interaction and increase aggressive behavior in males, but did not do so in females. Furthermore, in both males and females, handling was linked with reduced number of OT-neurons in the parvocellular region of the PVN, while no differences were detected in the magnocellular PVN or the SON. On the other hand, handled males exhibited increased number of VP-neurons in the magnocellular zone of the PVN. We may conclude that the repeated brief maternal separations can reduce affiliative social behavior in adult male rats. Moreover, the disruption of the mother-infant relationship caused by the handling procedure induced long-lasting morphological changes in critical neuroendocrine areas that are involved in social bonding in mammals.     

Influence of androgen on the development of sexual behavior in rats : I. Time of administration and masculine copulatory responses, penile reflexes, and androgen receptors in females

The objective of the present study was to investigate the effect of the time of administration of androgen, during the neonatal period, on the development of masculine copulatory behavior in female rats. In addition, the influence of androgen, administered neonatally, on the development of penile reflexes and cytoplasmic androgen receptor levels in the hypothalamic-preoptic area (HPOA) was examined. Female rats were injected with 0.5 mg testosterone propionate (TP) at either 1, 8, or 24 hr after birth and again 24 hr after the first injection. Fifty percent of the females treated with TP at 1 and 8 hr after birth displayed the ejaculatory response when tested in adulthood. In contrast, 93 and 87.5% of oil-treated males and females, respectively, which were androgenized at 24 hr after birth exhibited this response. The results indicate that a considerable amount of masculinization occurs postnatally in the rat. However, none of the androgenized females displayed any penile reflexes even when tested following the display of an ejaculatory response. HPOA androgen receptor levels were somewhat higher in the oil-treated females than in males but were not correlated with the ability to exhibit ejaculation patterns.     

Differential sensitivity of mounting and lordosis control systems to early androgen treatment in male and female hamsters.

The effects of early testosterone propionate (TP) treatment on the adult sexual behavior of hamsters were investigated in two experiments. In Expt. I, male and female pups were injected with oil vehicle or 1, 5, 10, 50, 100, or 250 μg of TP 24 hr after birth. In Expt. II, males and females received either oil or 10 μg of TP on the day of birth (Day 1), Day 3, Day 5, Day 7, or Day 9. At 70 days of age all animals were gonadectomized and 10 days later tested for lordosis behavior after estrogen and progesterone priming. One week after the test for female behavior all females began receiving 500 μg of TP each day and were tested for mounting and intromission behavior three times at 10 day intervals. Lordosis behavior was inhibited by as little as 5 μg of TP given 24 hr after birth. In males this dose produced the maximal effect, but in females increasing dosages resulted in a proportional decrease in lordosis duration. One μg of TP neonatally facilitated later mounting and intromission behavior in females and 250 μg of TP was no more effective than 1 μg. Lordosis duration was inhibited in females by 10 μg of TP on either Day 1 or 3, however, mounts and intromissions were facilitated by TP treatment on Day 1, 3, 5 or 7. These experiments demonstrate that the mechanisms mediating masculine behavior are more sensitive to neonatal TP treatment than are the mechanisms mediating lordosis behavior.     

Early androgen treatment and male and female sexual behavior in mice

To investigate the role of neonatal androgen stimulation in the development of the potential for masculine and feminine sexual behavior in the mouse, different groups of mice were hormonally manipulated early in life. One group of female mice was administered testosterone propionate (TP) within 24 hr of birth; a second group of females was given a control injection of oil on the day of birth; a third group of females received an injection of TP on the 10th day after birth. A group of males received a control injection of oil on the day of birth. All mice were gonadectomized at about 30 days of age. At 60 days of age, mice were injected with estrogen and progesterone and tested for sexual receptivity; several weeks later all mice were injected with TP and tested for male sexual behavior. Female behavior: Females given oil at birth and females given TP on the 10th day after birth showed high levels of sexual receptivity as adults following estrogen-progesterone treatment. Females given TP on the day of birth, and male mice, rarely exhibited lordosis following estrogen-progesterone treatment. Male behavior: Most mice, regardless of genetic sex or neonatal treatment, mounted in adulthood following administration of exogenous androgen. There was little difference in mounting frequency between groups, suggesting that exogenous or endogenous androgen stimulation of the neonatal mouse does not facilitate adult mounting behavior. These data for the mouse are in essential agreement with existing data for the rat, and indicate that sexual behavioral differentiation induced by androgen stimulation in infancy is best characterized as an inhibition of the potential to display feminine sexual behavior in adulthood.     

Effects of neonatal septal lesions on reproductive behavior of male and female rats

The purpose of this study was to examine the effects of neonatally placed septal lesions (SL) in male, female, and androgenized female rats on reproductive behavior. Animals were castrated as adults and tested for both feminine and masculine sexual behavior. After treatment with estradiol benzoate (EB) alone (2 μg daily for 3 days), only the females with SL which had not been given testosterone propionate (TP) neonatally showed a facilitation of lordosis behavior. Following EB (2 μg for 3 days) plus 0.5 mg progesterone (P), both the lesioned and the sham-operated female groups showed an increase in the display of lordosis in either hormonal condition. All animals were given a pretest for masculine sexual behavior and tested on Days 4, 7, 11, and 15 of daily TP treatment (150 μg/day). There was no effect of the neonatally placed SL on masculine sexual behavior in female rats or in female rats androgenized with 30 μg TP. However, lesioned females treated neonatally with 1 mg TP showed a marginal enhancement of masculine sexual behavior. Male rats given SL neonatally showed a marked enhancement of masculine sexual behavior compared to that of controls. These results suggest that, depending on the neonatal hormone environment, SL selectively increase behavioral sensitivity to hormones. Although neonatally lesioned females show behavioral responses similar to females given SL as adults, male rats given SL neonatally are unique in that they show enhanced masculine sexual behavior whereas males lesioned as adults do not.     

The estrogenic arousal of aggressive behavior in female mice

Experiments were conducted to determine the conditions under which estrogen would promote male-like aggressive behavior in female mice. The results of the first experiment showed that most females chronically exposed to testosterone propionate (TP) in adulthood fought, whereas females similarly treated with estradiol benzoate (EB) did not display aggression. Another experiment found that, when either TP or EB was administered on the day of birth, adult females displayed aggression in response to daily EB injections during adult life. Also, the potentiating effect of neonatal hormone exposure declined over the first 12 days postpartum, as 100% of the Day 0, 75% of the Day 6, and 0% of the Day 12 and 18 TP-treated females fought in response to daily injections of 40 μg of EB in adulthood. The final study showed that, under the test conditions employed, the failure of a chronic adult EB regimen to promote aggression was not due to a competing tendency to display female sexual behavior.     

Reproductive success,postpartum maternal behavior,and masculine sexual behavior of neonatally androgenized female hamsters

Sex differences in maternal behavior induced by pup stimulation (sensitization) have been reported for rats and hamsters and may be affected by the presence or absence of perinatal androgen treatment. Postpartum maternal behavior and litter survival in golden hamsters treated with testosterone propionate (TP) as neonates were studied. A high dose of TP (300 μg) eliminated feminine reproductive capacity when given on Day 2 or 4 postpartum and had no discernible effect on Day 12. Treatment on Days 6, 8, or 10 resulted in treatment day-dependent deficiencies in reproductive success which fell short of sterility in most females. These deficiencies included low birth weight, weight gain, and higher litter losses than controls. However, the maternal behavior of TP dams, as measured by retrieval and crouching, appeared to be normal. The disparity between delivery and successful rearing of normal-weight young may include uterine incompetence, lactation deficiency, and hypercannibalism. Behavioral masculinization was a more sensitive index of neonatal androgen action than any aspect of defeminization, but the two phenomena were dissociated in individuals.     

Hormonal differentiation of sexual behavior in Japanese quail

The effect of hormones on the development of Japanese quail during the postembryonic period was examined. First, subcutaneous implants of estradiol monobenzoate (EB) and testosterone propionate (TP) were implanted 6–12 hr after hatching. EB and TP had no effect on the differentiation of sexual behavior in genetic males or females. However, EB had marked feminizing effects on plumage in genetic males. Second, the role of gonadal hormones during development was examined by gonadectomizing males and females 6–12 hr after hatching and treating them intramuscularly with EB or TP as adults. EB-treated adult females displayed sexual behavior typical of the genetic female and developed female plumage. A significant proportion of TP-treated females (57%) displayed male sexual behavior patterns. Cloacal gland development and male-type vocalizations were induced. EB-treated males displayed either male or female sexual patterns depending on the stimulus conditions. Third, to test whether bisexuality in gonadectomized males and females is maintained despite steroid treatment and expression of sexual behavior in adulthood, gonadectomized quail which were originally treated with EB received TP and vice versa. The results indicate that in the absence of gonadal hormones after hatching female quail remain bisexual until exposed to estrogen, whereas gonadectomized male quail retain behavioral bisexuality irrespective of prior estrogen or androgen exposure.     

Mounting behavior of female guinea pigs after prenatal and adult administration of the propionates of testosterone, dihydrotestosterone, and androstanediol.

Female guinea pigs were exposed prenatally (Day 28–58) to the propionates of testosterone (TP), dihydrotestosterone (DHTP), or androstanediol (ADP). Only TP females failed to display lordosis in adulthood after estrogen and progesterone treatment. When given TP in adulthood, females in all groups mounted, but TP and DHTP females showed augmented intromission frequencies and higher percentages of correctly oriented mounts relative to controls. Moreover, TP females responded more quickly to TP injections in adulthood and had higher over-all mounting frequencies than other groups, while DHTP females displayed mounting frequencies intermediate to controls and TP females. ADP females were not different from controls for any measure of mounting behavior.No female in any group mounted when given DHTP in adulthood, even after 7 wk of daily injections. Since male guinea pigs do mount in response to DHTP given in adulthood, the results raise the possibility that mechanisms determining sensitivity to specific steroids may not be mediated exclusively by steroids during critical periods of embryological differentiation.     

Aromatization: Important for sexual differentiation of the neonatal rat brain

This paper examines the hypothesis that testosterone (T) produces its differ-entiative effect on the neonatal rat brain after undergoing conversion in situ to estradiol-17β (E₂). We examined the abilities of an aromatizing enzyme inhibitor, (1,4,6-androstatriene-3,17-dione) (ATD), and an anti-estrogen, CI628, to inhibit sexual differentiation. Male and female rats were treated during the first few days of postnatal life with ATD or CI628, and females were treated on the following day with T in Silastic capsules or its propionate (TP) in oil. ATD and ATD+T females were normal with respect to time of vaginal opening, ovarian weight, ability to demonstrate an LH surge, and lordosis behavior. T and TP females were masculinized with respect to all these measures. CI628 and CI628+TP females had impaired ovarian function and intermediate lordosis quotients (LQs) compared to controls, though they were higher in both measures than T females. ATD males demonstrated high LQs in response to estradiol benzoate (EB) + progesterone, comparable to those of control females. CI628 males had intermediate LQs, which were significantly higher than those of control males. These results indicate that ATD can substantially protect the neonatal rat brain from the differentiative effects of exogenous or endogenous T, probably by blocking aromatization. CI628 affords only partial protection against T and produces a weak differentiative effect due to its own weak estrogenicity. Thus, aromatization of T in newborn rat brains appears to be essential if sexual differentiation is to occur.     

A hormonal basis for sex differences in the self-grooming of rats

The self-grooming behavior of prepubescent male and female rats is described. Sex differences were observed in components of grooming addressed to the genitals, but not in other aspects of grooming. A hormonal basis for the sex difference was examined in two experiments. When females were injected with testosterone propionate (TP) on the day of birth, their subsequent grooming was found to be no different from that of control-treated females. However, males and females gonadectomized at weaning and treated daily with TP each performed significantly more genital self-grooming than oil-treated controls. There were no sex differences in gonadectomized, oil-treated rats, and sex differences in response to TP were limited to greater responsiveness of females to a 50-micrograms, but not 200-micrograms, TP dose. These results lead to the conclusion that sex differences in self-grooming can be accounted for primarily by differences in testosterone availability during the peripubertal period.     

Oxytocin receptors in the nucleus accumbens shell are involved in the consolidation of maternal memory in postpartum rats

Female rats with maternal experience display a shorter onset of maternal responsiveness compared to those with no prior experience. This phenomenon called ‘maternal memory’ is critically dependent on the nucleus accumbens (NA) shell. We hypothesized that activation of OT receptors in the NA shell facilitates maternal memory. In Experiment 1, postpartum female rats given 1 hour of maternal experience were infused following the experience with either a high or low dose of an OT antagonist into the NA shell and tested for maternal behavior after a 10-day pup isolation period. Females receiving a high dose of the antagonist showed a significantly longer latency to exhibit full maternal behavior after the pup isolation period compared to females that received vehicle or a high dose of antagonist in a control region. In Experiment 2, postpartum female rats were infused with either a high or low dose of OT into the NA shell after a 15-minute maternal experience and tested for maternal behavior after a 10-day pup isolation period. There were no significant differences between the females infused with OT and females treated with a vehicle infused into the NA shell or with OT infused into the control region. One possible reason for a lack of facilitation is a floor effect, since females in the control groups displayed a rapid maternal response after the pup isolation period. These findings suggest that OT receptors, likely in combination with other neurotransmitters, in the NA shell play a role in the consolidation of maternal memory.     

A Comparison of Female Mating Strategies in <Emphasis Type="Italic">Pan troglodytes</Emphasis> and <Emphasis Type="Italic">Pongo</Emphasis> spp.

Orangutans and chimpanzees differ in many aspects of their mating and social systems. Nevertheless, because both great apes require enormous maternal investment in offspring and because female reproductive potential is limited, female orangutans and chimpanzees should be selective of their mates, yet expected to exhibit anti-infanticide strategies such as mating with multiple males. We review and compare mating patterns in orangutans and chimpanzees to understand how these critical pressures are filtered through the different demands of the socioecology of each species. We highlight the variation in female mating behavior as a function of the proximity of ovulation. We conclude that both genera pursue tactics for paternity confusion by mating with multiple males and by mating cooperatively or even proceptively with nonpreferred partners when conception is unlikely. Mating selectivity is suggested by variation in proceptive behavior toward particular partners and by increased resistance of nonpreferred partners during the periovulatory period. Thus, data for both species support a mixed mating strategy whereby females shift their mating behavior in accordance with ovulatory status to accommodate the competing demands of mate selectivity and paternity confusion.