Brain transections differentially alter lordosis and ear wiggling of 6-day-old rats.

The involvement of various brain regions in lordosis and ear-wiggling, which resemble components of adult female sexual behavior, was examined by making acute transections along the neuraxis from the olfactory tract to the medulla in 6-day-old rats. Four to 5 hrs after the transection procedure, pups were tested for lordosis and ear wiggling. Lordosis was reduced or eliminated in pups with cuts through the hindbrain or diencephalon (above the level of the mammillary bodies) but was relatively unaffected by cuts through the posterior hypothalamus and rostral tegmentum and by cuts rostral to the anterior hypothalamus. Ear wiggling was disrupted by transections throughout the hindbrain and was facilitated only in females by transections throughout the forebrain (anterior to the mammillary bodies). Data suggest that facilitation from the hypothalamus is required for lordosis in the infant rat and the forebrain inhibitory systems for ear wiggling are functional in female infants by 6 days of age. Similarities and differences between the neural control of lordosis and ear wiggling in infant and adult rats suggest that the infant sex-like behaviors may be precursors of adult female sexual behavior. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of repeated testing on sexual behavior of the female rat.

Investigated effects of stimulation during repeated testing, using 24 female Sprague-Dawley rats in which intromission was prevented by a vaginal mask. Ss were ovariectomized and administered 1 mg of estradiol benzoate (EB) daily for 10 days (Exp I) or 5 mg of EB for 2 days (Exp II). Behavioral indices included lordosis quotient (a measure of sexual receptivity) and rejection quotient (a measure of social rejection of the male). Intensity and duration of lordosis gave additional measures. In Exp I hourly testing increased lordosis quotient and duration, especially in Ss receiving EB for 5 days; no effects of daily testing were shown. Exp II compared the behavior of Ss that were either handled hourly and tested hourly with the male rat or only handled hourly to the behavior of Ss that were tested and handled only once. Repeated testing and/or handling facilitated sexual responsiveness, while Ss that received neither treatment were sluggish in their social response to the male rat when they were tested, and were not sexually receptive. (17 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Heterotypical sexual behavior in male rats: individual difference in lordosis respones

Castrated Wistar male rats were primed with varying amounts of estradiol benzoate (EB) for successive 2 days and progesterone (P) on the third day 6-8 hr prior to the behavioral test. The tests were performed 4 times at 2-3 weeks intervals. As a priming procedure for the first behavioral test, 50 mug EB and 0.5 mg P were given. The quantity of P was kept constant therafter. For the second test, the dose of EB was increased to 100 mug, but decreased again to 50 mug and further to 10 mug for the third and fourth tests, respectively. The inciedence of animals showing lordosis was quite low, and was not significantly changed by increasing or decreasing the dosage of EB during the series of the behavioral tests. Forty-three out of 51 animals never showed lordosis at all 4 behavioral tests. In contrast, 5 out of 8 rats which responded to mountings by the males continued to display lordosis behavior throughout the series of the successive 4 tests. This consistence of individual responeses during the series of the behavioral tests may indicate the possible existence of individual difference in lordosis responde in male rats.     

Differential effects of beta-endorphin and Met- and Leu-enkephalin on steroid hormone-induced lordosis in ovariectomized female rats

The effect of intrathirdventricular (I.T.V.) injections of beta-endorphin, anti-beta-endorphin antiserum, Met-enkephalin, Leu-enkephalin, and naloxone on the initial activation and final development of steroid hormone-mediated induction of female sexual receptivity was studied in ovariectomized female rats. The lordosis response to male mounts in ovariectomized rats after subcutaneous (S.C.) estradiol benzoate (EB) and progesterone (Prog) priming was facilitated by beta-endorphin, and Met-enkephalin (10 microg x 5 microl(-1)), but inhibited by Leu-enkephalin, when the peptides were injected into the third ventricle at the time of S.C. EB priming. A lower dose Met-enkephalin had no effects. Lordosis behavior in steroid hormone-primed rats was significantly facilitated when I.T.V. injections of Met-enkephalin were given 1 h prior to behavioral testing (47 h after EB priming). At 1 h prior to behavioral testing (47 h after EB priming), I.T.V. injection of beta-endorphin significantly inhibited lordosis behavior, especially at the higher dose of beta-endorphin (10 microg x 5 microl(-1)). Under those conditions, Leu-enkephalin had no effect. Lordosis behavior of ovariectomized female rats receiving S.C. steroid hormones and I.T.V. injection of anti-beta-endorphin antiserum was significantly inhibited when anti-beta-endorphin antiserum was injected at the time of EB priming. However, lordosis was significantly facilitated when anti-beta-endorphin antiserum was injected 1 h prior to the behavior testing (47 h after EB priming). In contrast, I.T.V. injection of the opioid antagonist naloxone given either at the time of EB priming or 1 h prior to behavioral testing (47 h after EB priming) decreased lordosis behavior. The present results suggest that 1) beta-endorphin, Met-enkephalin, and Leu-enkephalin have differential effects in the control of lordosis behavior; 2) the opioidergic systems may modulate initial-stage and final-stage estrogen-induced lordosis behavior; and 3) the opioidergic systems could be divided into the endorphinergic modulation-type and enkephalinergic modulation-type, based on their effects on lordosis behavior.     

Hypophysectomy facilitates sexual behavior in female rats

Lordosis was elecited in 49% of 87 hormonally untreated, hypophysectomized-ovariectomized (hypox-ovx) female rats in response to palpation of the flanks and perineum (vaginal stimulation was not applied). By contrast, only 12% of 113 hormonally untreated ovariectomized (ovx) rats showed lordosis in response to such stimulation. Subsequently, hypox-ovx and ovx-only rats were given daily injections of 1 mug/kg estradiol benzoate (EB) and tested for sexual receptivity with males. Teh estrogen-treated hypox-ovx females became sexually receptive significantly earlier, and exhibited higher lordosis quotients and more soliciting behavior, than the estrogen-treated ovx-only rats. The increased sexual responsiveness in the hypox-ovx rats could be due to increased LRH activity. To test this, we treated hypox-ovx rats with dihydrotestosterone propionate (DHT-P), which suppresses plasma LH levels but is relatively ineffective in inducing sexual receptivity, and found a significant depression of lordosis responsiveness. These experiments suggest that hypox-ovx females show a heightened responsiveness to hormonal and/or sensory factors that induce a lordosis response, possibly because of increased LRH activity.     

Localization in the amygdala of the amnestic action of diazepam on emotional memory

Electrical lesions of the medial preoptic area/anterior hypothalamus (MPOA/AH) have been reported to enhance the display of steroid-induced lordosis in castrated male rats. This study employed the cell body-specific neurotoxin, ibotenic acid, to ascertain whether neurons originating in this region (as opposed to axons of passage) tonically inhibit steroid-induced lordosis in adult male rats. Castrated, adult Long-Evans males received bilateral electrical lesions or injections of ibotenic acid or vehicle aimed at the MPOA/AH. Following administration of estradiol benzoate (EB) and progesterone, lordosis quotients (LQs) and lordosis ratings (LRs) were significantly higher in groups of rats with electrical lesions (LQ = 62.2 +/- 15.1; LR = 1.22 +/- 0.34) and ibotenic acid-induced lesions (LQ = 58.1 +/- 12.2; LR = 0.99 +/- 0.24) than in the control group (LQ = 12.8 +/- 7.3; LR = 0.22 +/- 0.13). To determine whether this enhancement of receptive behavior in MPOA/AH-lesioned males was an effect on estradiol-induced, as compared to progesterone-facilitated lordosis, groups of castrated rats in a second experiment received bilateral injections of ibotenic acid or vehicle aimed at the MPOA/AH and were tested for lordosis after administration of EB alone and again after injection of progesterone. Following treatment with EB alone, rats with ibotenic acid-induced MPOA/AH lesions tended to be slightly less receptive than control animals. However, following injections of progesterone, LQs and LRs were higher in the MPOA/AH-lesioned group than in the control animals, as had been observed in the first experiment.(ABSTRACT TRUNCATED AT 250 WORDS)     

Hormonal responses of male gerbils to stimuli from their mate and pups

Following copulation and cohabitation with a pregnant female, male gerbils show high levels of parental behavior toward their pups. The initiation of male parental behavior may be the result of neuroendocrine changes induced by cohabiting with the pregnant female or by pup stimuli. Experiment 1 examines the changes in androgen and prolactin levels in male gerbils cohabiting with females over the reproductive cycle. Gerbils were mated and blood samples taken from males for hormone analysis 1, 10, and 20 days after pairing and 3, 10, and 20 days after pups were born. A group of unmated male gerbils served as controls. Plasma prolactin levels of males were elevated throughout the female's pregnancy and lactation periods, but were only statistically significantly higher than those of unmated males 20 days after pups were born. Androgen levels rose during pregnancy and dropped significantly after the birth of the pups. These hormonal changes are similar to those found in males of monogamous birds and differ from those found in males of polygynous rodents such as the rat. Experiment 2 examined the hormonal responses of male and female gerbils to pup replacement after 4 hr of parent-pup separation. Female gerbils showed a significant elevation of prolactin levels 1 hr after pup replacement, but males did not. Males with pups returned showed no difference in androgen levels from males who did not have pups returned. Thus, male gerbils show neuroendocrine changes following long-term cohabitation with their mate and pups, but do not show acute hormone responses to pup removal and replacement. These results indicate that parental males have neuroendocrine changes associated with parental behavior and these differ from the neuroendocrine changes underlying female parental behavior.     

Induction of female and male mating patterns in female rats by gonadal steroids: Effects of neonatal or adult olfactory bulbectomy.

Three experiments evaluated hormonally mediated sexual response patterns in Long-Evans female rats receiving olfactory bulb ablations neonatally (Day 2) or in adulthood. In a test of Ss' reactivity to a caged male in an open field, estrogen and progesterone treatments increased the number of squares entered and the number of cage contacts, but olfactory bulb removal had no effect on these measures. During mating tests, the feminine sexual behavior of Ss' bulbectomized on Day 2 was similar to that of control-operated Ss, whereas Ss bulbectomized as adults displayed enhanced levels of lordosis, darting, and ear wiggling. Lordosis varied with estrogen dose, whereas darting was progesterone-dependent. In tests of masculine copulatory behavior, the proportion of bulbectomized Ss (Day 2 and adult) that mounted was significantly lower than that of control-operated Ss. The effects of olfactory bulb removal, which vary with the age at ablation and the behavioral system investigated, are not mediated by a single neuroendocrine system and cannot be interpreted in terms of a unitary "arousal" construct. (54 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Gender differences in ethanol preference and ingestion in rats. The role of the gonadal steroid environment

An ethanol oral self administration paradigm showed the existence of gender differences in alcohol preference in rats: whereas males and females initiated alcohol drinking at similar rates, females maintained their preference for ethanol over a longer duration. Neonatal estrogenization of females, which effectively confers a male phenotype on a genetically female brain, resulted in patterns of drinking that were similar to those displayed by intact male rats, indicating that gender differences in alcohol drinking patterns may be, at least partially, accounted for by sexual differentiation of the brain. To test whether gonadal steroids also exert activational effects on ethanol-seeking behavior, we also examined the effects of gonadectomy alone, or in combination with gonadal steroid replacement therapy. Castration did not significantly alter ethanol consumption in males, although treatment of castrated rats with dihydrotestosterone resulted in a significant inhibition of this parameter. As compared with the situation in intact female rats, ethanol ingestion was significantly reduced in ovariectomized female rats receiving estradiol (E2) and in ovariectomized female rats receiving combined E2 and progesterone replacement therapy. However, neither ovariectomy nor progesterone replacement in ovariectomized rats resulted in ethanol drinking patterns that were different compared to those observed in intact female controls. Thus, dihydrotestosterone and E2, respectively, appear to exert modulatory influences on the male and female rats' preference for ethanol, but further investigations are necessary to determine to what extent these effects result from activational actions on the brain.     

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

Analyzed the behavioral responses of 60 female golden hamsters to sexually experienced males as a function of the stage of the female's estrous cycle. Exogenous estradiol or estradiol followed by progesterone was given to ovariectomized Ss to determine the role of these hormones in regulation of cyclic changes in the female's response to the male. Ss were paired daily with sexually active males for 10 min, and behavioral interactions were recorded. Significantly more fighting occurred during early diestrus than later in the cycle. By 8 hrs prior to the onset of sexual receptivity, 86% of Ss exhibited a behavior resembling the onset of lordosis without immobilization. Following ovariectomy, fighting was at a high level. Estradiol replacement over 28 days resulted in a significant decrease in aggression and increase in display of the prelordotic response. Initially, treatment with progesterone following 7 days of estradiol caused lordosis display. After 24 hrs a significant increase in aggression, which continued as long as progesterone was present, was observed. 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 hrs, estrogen/progesterone-treated females become agonistic to the male. (15 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Evaluation of osteocalcin and pyridinium crosslinks of bone collagen as markers of bone turnover in gingival crevicular fluid during different stages of orthodontic treatment

Treatment with serotonin reuptake inhibitors (SRIs) has been shown to cause reduced libido and anorgasmia in women. A large body of evidence suggests that serotonin may influence sexual behavior in estradiol + progesterone primed, gonadectomized female rats; however, the influence of selective SRIs on the estrous behavior of intact female rats has not been described previously. In the present study, the effect of 1 to 3 weeks of fluoxetine administration (10 mg/kg daily) on vaginal and behavioral estrus in intact female rats was studied; in addition, the effect of fluoxetine (same dose, 1-8 weeks) on copulatory behavior and on sexual motivation in hormone-primed gonadectomized rats was investigated. Subchronic administration of fluoxetine did not influence cyclicity as judged by the examination of vaginal smears but significantly reduced the percentage of rats displaying receptive behavior in the estrous phase. In addition, fluoxetine significantly reduced receptive behavior, including lordosis, in ovariectomized female rats primed with estradiol (6.25 micrograms/rat; -48 hr) plus progesterone (1.0 mg/rat, -4 hr); in contrast, sexual motivation--as reflected by the amount of time these rats elected to spend in the vicinity of a male rather than in the vicinity of a female or elsewhere--was little affected by the treatment.     

Hormonal control of behavior in the Japanese quail.

Adult male and female Japanese quail were functionally castrated by exposure to a short photoperiod and then injected with either estradiole benzoate (EB) or testosterone propionate (TP). Females injected with EB (n = 24) exhibited normal sexual receptivity again but displayed no male courtship behavior. Males injected with EB (n = 10) showed both male and female copulatory patterns. Females injected with TP (n = 14) showed little sexual behavior of any sort, while males injected with TP (n = 10) displayed male sexual behavior. The male quail is thus more bisexual than the female. In contrast with mammalian species, the female is more bisexual. The difference is discussed in relation to the differences in the embryology and cytogenetics of birds and mammals. (29 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

In an experiment with 48 male and 48 female golden hamsters, neonatally and adult castrated males as well as neonatally androgenized and nonandrogenized females were tested for both mounting and lordosis behaviors during treatment with either testosterone or ovarian hormones. Neonatal androgenization facilitated mounting behavior in adult Ss administered either testosterone or ovarian hormones and suppressed lordosis behavior in adult ovarian-hormone-treated Ss. 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 are discussed. (29 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effect of ovarian secretions on female behavioral potentiality in the rat.

Measured receptivity in female Sprague-Dawley rats ovariectomized at 5 ages, in neonatally gonadectomized females and males implanted with ovaries, and in neonatally castrated males injected with estradiol benzoate (EB) or oil. Mean receptivity, darting, and lordosis scores were higher during the 1st 4-5 mating tests in females and males having ovaries prepubertally. In amounts greater than .01 mg., EB inhibited female behavior. Even after ovariectomy, body weight was lightest in males and females having ovaries for 60 days. Progesterone and EB decreased weight gain faster in Ss gonadectomized prepubertally. Results indicated that physiological amounts of ovarian hormones, while not necessary for development of female potentiality, permanently influence it by modifying rate of utilization of estrogen circulating during adulthood. (24 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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

The possible interaction between relative amounts of androgen present during specific stages of development and adequate prepuberal social stimulation was evaluated by characterizing the ejaculatory and lordotic behavior potentials of 20 prenatally stressed and 23 control male Sprague-Dawley 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 Ss. 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. Results support and extend the finding by J. L. Dunlap et al (see record 1980-11465-001) 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. (27 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Concurrent inhibition of sexual behavior, but not brain [–3H]estradiol uptake, by progesterone in female rats.

In 7 experiments with ovariectomized female Sprague-Dawley rats, chronic injections of high doses of progesterone (5 mg) and low doses of estradiol benzoate (EB; 2 μg) resulted in less sexual behavior than did low doses of progesterone (.5 mg) and low doses of EB. In a typical procedure for inducing sexual behavior, EB and progesterone were given sequentially, separated by 42 hrs. High levels of progesterone (2.5 and 5 mg) administered concurrently with EB inhibited the induction of sexual receptivity. Increasing the dose of EB from 2 μg to 6 μg or 10 μg offset this inhibition. High doses inhibited the induction of sexual behavior, but the inhibition waned when progesterone was administered 48 hrs prior to EB. A single injection of progesterone (1 mg) that did not inhibit the induction of sexual behavior when administered concurrently with EB did inhibit lordosis when distributed into 5 injections (.2 mg) every 4 hrs. Results of 2 experiments in which progesterone did not inhibit the uptake or retention of [–3H]estradiol by brain cell nuclei suggest that the antiestrogenic action of progesterone in the CNS is not to interfere with the binding of estradiol. (37 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Effects of coital stimulation upon behavior of the female rat.

Tested the importance of vagino-cervical stimulation during coitus in 2 experiments, using 16 intact and 48 ovariectomized Sprague-Dawley female rats, in which intromission was prevented by a vaginal mask. The behavior of Ss was compared to that of unmasked females. Behavioral indices included lordosis quotient, a measure of sexual responsiveness, and rejection quotient, a measure of social response toward the males. The rating of lordosis intensity on a 3-point scale provided a mean lordosis intensity. Exp. I investigated long-term effects of coital stimulation by repeated testing of Ss in natural and hormone-induced heat. Coital stimulation generally decreased the probability of subsequent lordosis and increased display of rejection. Exp. II studied the short-term effects of coital stimulation using single 50-mount tests. Coital stimulation decreased intensity as well as probability of subsequent lordosis. (23 ref.) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

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 along 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. (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Modifications induced by neonatal steroids in reproductive organs and behavior of male rats.

112 3-day-old male Sprague-Dawley rats were injected neonatally with .01, .1, 1, 10, 100, or 1,000 μg of estradiol benzoate (EB), 10,000 μg of testosterone propionate (TP), or sesame oil; they were subsequently examined for testicular, penile, and accessory organ development. Sexual behavior was evaluated during therapy with fluoxymesterone (FM) and then with TP. EB in dosages greater than 1.0 μg delayed testicular descent, reduced the size and hormone responsiveness of reproductive organs, and decreased sexual behavior in a dose-dependent manner. The 10,000 μg dosage of neonatal TP delayed testicular descent and reduced sexual behavior to levels near those of the 10–200 μg EB groups, but it produced no significant penile or accessory organ changes. Neither reduced peripheral organ development nor inhibited neonatal testicular secretions fully explain reductions in male behavior following large dosages of neonatal TP. Neonatal androgen may reduce the responsiveness of CNS neurons governing male sexual behavior after being converted to estrogen or by directly altering steroid receptor systems. (32 ref) (PsycINFO Database Record (c) 2010 APA, all rights reserved)     

Nitric oxide mediates sexual behavior in female rats

Nitric oxide (NO), an active free radical formed during the conversion of arginine to citrulline by the enzyme NO synthase (NOS), mediates vasorelaxation, cytotoxicity, and neurotransmission. Neurons containing NOS (NOergic) are located in the hypothalamus. These NOergic neurons control the release of several hypothalamic peptides. Release of NO from these NOergic neurons stimulates pulsatile release of luteinizing hormone-releasing hormone (LHRH) in vivo and LHRH release in vitro. LHRH not only induces LH release, which induces ovulation, but also facilitates female sexual behavior. Sexual behavior can be induced reliably in estrogen-primed ovariectomized female rats by progesterone (P). This behavior consists of proceptive behavior to attract the male and the assumption of a clear characteristic posture, lordosis, when mounted by the male. To ascertain the role of NO in the control of sexual behavior in female rats, an inhibitor of NOS, NG-monomethyl-L-arginine was microinjected into the third cerebral ventricle (3V) of conscious, ovariectomized, estrogen-primed rats with indwelling cannulae. NG-Monomethyl-L-arginine (10-1000 micrograms) prevented P-facilitated lordosis when administered intracerebroventricularly into the 3V, 20 min prior to the 3V injection of P. NG-Monomethyl-D-arginine, which does not inhibit NOS, did not inhibit lordosis under the same experimental conditions. Microinjection into the 3V of sodium nitroprusside (SNP), which spontaneously releases NO, facilitated lordosis in estrogen-primed rats in the absence of P. The facilitation of lordosis induced by either P or SNP was prevented by intracerebroventricular injection of hemoglobin, which binds NO. Lordosis facilitated by P or SNP was blocked by injection of LHRH antiserum into the 3V. The results are interpreted to mean that the P-facilitated lordosis response is mediated by LHRH release. Furthermore, since NO release from SNP also facilitates lordosis in the absence of P and this response could be blocked by LHRH antiserum, we conclude that P brings about the release of NO, which stimulates LHRH release that facilitates lordosis. Thus, the results indicate that NO induces LHRH release and that LHRH then plays a crucial role in mediation of sexual behavior in the female rats.