Progesterone facilitation of lordosis in male and female Sprague-Dawley rats following priming with estradiol pulses

Adult male Sprague-Dawley rats rarely exhibit progesterone-facilitated lordosis following steroid treatments which are effective in females. In contrast, progesterone-facilitated lordosis has been observed following priming with estradiol pulses in another strain. The aim of this study was to compare progesterone-facilitated feminine sexual behavior in adult male and female Sprague-Dawley rats following priming with estradiol benzoate (EB) or estradiol pulses. Female sexual behavior was measured in adult, gonadectomized males and females treated as follows: Two pulses of estradiol followed by progesterone or oil the next day; EB (two doses) for 3 days, and progesterone or oil the next day. These protocols were repeated at 4- or 6-day intervals, respectively. Progesterone-facilitated lordosis was observed consistently in both sexes treated with estradiol pulses. By the fifth test, lordosis quotients did not differ between the sexes, but the lordosis ratings in progesterone-treated males remained lower than those observed in females. Proceptivity (hop-darting) was facilitated by progesterone in females, but was never observed in males. Lordosis was induced in both sexes by 15 micrograms EB, but was not reliably facilitated by progesterone. Treatment with the lower dose of EB (1.5 micrograms) induced high levels of receptivity in females (occasionally facilitated by progesterone), but not in males regardless of subsequent treatment (i.e, progesterone or oil). These data suggest that progesterone-facilitated lordosis can be induced in male Sprague-Dawley rats, if a regimen of estradiol pulses is used. Thus, the brain of the adult male is not inflexibly differentiated with regard to progesterone facilitation of feminine receptive behavior.     

Estrogen and progesterone interactions influencing sexual and social behavior in the brown lemming, Lemmus trimucronatus.

The effects of estrogen and progesterone on the social and sexual behavior of brown lemmings, Lemmus trimucronatus, were investigated. The behavior of hormone-treated and untreated ovariectomized females and sexually vigorous males was observed in six consecutive daily 5-min dyadic encounters. Sexual receptivity, as measured by lordosis, and other social behaviors including nasonasal contact, boxing postures, allogrooming, perineal investigation, and male mounting increased following 48 hr of exposure to daily injections of 0.5 μg estradiol benzoate (EB). Lordosis in EB-primed females was not facilitated or inhibited by short-term (4 hr) exposure to 0.5 mg progesterone (P). Long-term (greater than 24 hr) exposure to P apparently inhibited lordosis and other social behaviors in EB-treated females, although males continued to attempt to mount these females. In EB-treated females a dramatic increase in threat-leaps, directed by the female toward the male, was observed within 4 hr of P injection. Threat-leaps declined when P was withdrawn. Threat-leaps were also observed in ovariectomized females after prolonged exposure to P only (0.5 mg/day). Vaginal perforation and cornification were first apparent 48 hr after EB injection. P-alone treated ovariectomized females also showed vaginal perforation but cornified cells were infrequent and these animals did not show lordosis.     

Mu-, delta-, and kappa-opioid receptor agonists selectively modulate sexual behaviors in the female rat: differential dependence on progesterone.

Previous studies suggested that opioid receptor agonists infused into the lateral ventricles can inhibit (through mu receptors) or facilitate (through delta receptors) the lordosis behavior of ovariectomized (OVX) rats treated with estrogen and a low dose of progesterone. The present study investigated the behavioral and hormonal specificity of those effects using more selective opioid receptor agonists. Sexually experienced OVX rats were implanted stereotaxically with guide cannulae aimed at the right lateral ventricle. One group of rats was treated with estradiol benzoate (EB, 10 micrograms) 48 hr and progesterone (P, 250 micrograms) 4 hr before testing, whereas the other group was treated with EB alone. Rats were infused with different doses of the selective mu-receptor agonist DAMGO, the selective delta-receptor agonist DPDPE, or the selective kappa-receptor agonist U50-488. The females were placed with a sexually vigorous male in a bilevel chamber (Mendelson and Gorzalka, 1987) for three tests of sexual behavior, beginning 15, 30, and 60 min after each infusion. DAMGO reduced lordosis quotients and magnitudes significantly in rats treated with EB and P, but not in rats treated with EB alone. In contrast, DPDPE and U50-488H increased lordosis quotients and magnitudes significantly in both steroid-treatment groups. Surprisingly, measures of proceptivity, rejection responses, and level changes were not affected significantly by mu or kappa agonists, although proceptivity and rejection responses were affected by DPDPE treatment. These results suggest that the effects of lateral ventricular infusions of opioid receptor agonists on the sexual behavior of female rats are relatively specific to lordosis behavior. Moreover, the facilitation of lordosis behavior by delta- or kappa-receptor agonists is independent of progesterone treatment, whereas the inhibitory effect of mu-receptor agonists on lordosis behavior may require the presence of progesterone.     

The reversible inhibition of steroid-induced sexual behavior by intracranial cycloheximide

Cycloheximide(Cyclo), an inhibitor of protein synthesis by a direct action on protein synthesis at the ribosomal level, was used to reversibly inhibit estrogen-induced sexual receptivity. Cyclo (100 μg per rat) was infused into the preoptic area(POA) of ovariectomized rats at varying times before, simultaneously with, and after 3 μg of subcutaneous estradiol benzoate (EB). All animals received 0.5 mg progesterone (P) 36 hr after EB, and were tested for sexual receptivity 4–6 hr after P. The females were placed with stud males and a lordosis quotient was computed for each female (lordosis quotient = number of lordosis responses/20 mounts by the male × 100). Females receiving Cyclo 6 hr before, simultaneously with, or 12 hr after EB showed significantly lower levels of sexual receptivity when compared to females receiving Cyclo 36 hr before and 18 and 24 hr after EB. When those animals that showed low levels of sexual behavior after Cyclo infusion were reprimed with EB and P 7 days later and presented with a male they showed high levels of sexual receptivity. Thus, the effect of Cyclo was reversible. Only Cyclo infusions into the POA (bilateral) and third ventricle were effective in suppressing sexual behavior. Caudate nucleus, lateral ventricle, and unilateral POA infusions were without effect.The data presented are in agreement with earlier work that utilized actinomycin D to inhibit steroid-induced sexual behavior. Cyclo was found to be less toxic than actinomycin D. All of the available evidence is consistent with the hypothesis that estrogen stimulates RNA and/or protein synthesis in its facilitation of sexual behavior in the female rat.     

Independence of progesterone-induced facilitation and inhibition of lordosis behavior in ovariectomized guinea pigs

In ovariectomized Hartley guinea pigs, 15 μg progesterone was shown to facilitate lordosis in 48% of animals when administered 36 hr after a 3.3 μg injection of estradiol benzoate. This dose of progesterone also inhibited lordosis behavior in 65% of animals administered an additional 0.6 mg progesterone at 60 hr. Significant inhibition of lordosis response to the 0.6 mg progesterone existed among animals in which lordosis was not facilitated by the initial 15 μg dose of progesterone. These results show that progesterone-induced inhibition can occur without prior facilitation of lordosis as tested by the manual stimulation technique.     

Different doses of estradiol benzoate induce conditioned place preference after paced mating

The ovarian hormones estrogen and progesterone are required for the complete display of sexual behavior in female rats. Paced mating produces a reward state in intact cycling and ovariectomized (OVX), hormonally primed females as evaluated by the conditioned place preference (CPP) paradigm. Most of the studies that have evaluated CPP induced by paced mating in OVX females have used relatively high doses of estradiol benzoate (EB). In the present study we determined if different doses of EB, combined with progesterone (P), could induce CPP after paced mating. For this purpose OVX female rats were divided in five groups that received one of different doses of estradiol benzoate (5, 2.5, 1.25 or 0.625 μg estradiol + 0.5 mg of progesterone) before being allowed to pace the sexual interaction and conditioned in a CPP paradigm. We found that the lowest dose of EB used (0.625 μg) significantly reduced the lordosis quotient and the lordosis coefficient. Even though these females paced the sexual interaction, they didn't change its original preference, suggesting that sexual interaction did not induce a positive affective, reward state. Females allowed to pace the sexual interaction with higher doses of EB developed CPP after paced mating. These results indicate that a threshold of estradiol is required for paced mating to induce CPP.     

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.     

Duration of hormonal deprivation: influences on physiological and behavioral responsiveness to estradiol

A total of 54 ovariectomized female guinea pigs were divided into three groups and tested six times at 2-week intervals for their responsiveness to exogenous ovarian hormones (3 days of 4 micrograms/kg estradiol benzoate plus 1 day of 0.4 mg/kg progesterone) or control injections (0.2 ml oil vehicle). Two weeks after ovariectomy, treatment with estradiol significantly reduced food intake and body weight, and also produced vaginal membrane rupture in 98.1% of the females. When tested for sexual behavior at 4, 6, and 8 hr after the progesterone injection, 29 of the subjects (53.7%) displayed lordosis in response to manual stimulation. Twelve weeks after ovariectomy, the effects of estradiol on food intake, body weight, and vaginal membrane condition had not diminished. However, the overall proportion of females from which lordosis could be elicited declined to 27.8%. Biweekly injections of estradiol benzoate plus progesterone to one of the groups of females did not prevent this decline in the sexual response. Based on these results, it was concluded that the observed reduction in behavioral lordosis does not represent a general decline in the responsiveness of ovariectomized guinea pigs to estrogenic stimulation, but may involve changes in their responsiveness to progesterone or in other mechanisms more specifically associated with sexual behavior.     

Musculinization and defeminization induced in female hamsters by neonatal treatment with estradiol, RU-2858, and nafoxidine

Newborn female hamsters were treated with 0.1 or 1.0 ng of estradiol benzoate (EB), with 1.0 ng–2.0 μg of the synthetic estrogen RU-2858, or with 0.1 or 0.5 μg of the antiestrogen nafoxidine. When adult the animals were treated with EB and progesterone and tested for the display of lordosis and with testosterone propionate and tested for the display of mounting behavior. The EB doses used failed to alter sexual differentiation. RU-2858 masculinized and defeminized in a dose-dependent manner being most effective when given neonatally as two divided doses. Nafoxidine inhibited lordosis without enhancing mounting behavior. The findings support the hypothesis that estrogens may be involved in the normal sexual differentiation process.     

Effects of septal lesions on behavioral sensitivity of female rats to gonadal hormones

Spayed female rats were given bilateral septal lesions or a sham operation and 3 wk later tested for hormone-induced female sexual behavior. When primed with 0.5, 1.0, or 2.0 μg of estradiol benzoate (EB) per day for 3 days and tested for lordosis behavior on the fourth day, animals with septal lesions showed a positive dose-related increase in mean lordosis quotient (LQ), whereas control animals showed a low mean LQ for all doses of EB. After priming with a low dose of EB (0.5 μg/day for 3 days), progesterone administration prior to behavior testing on day 4 produced a comparable facilitation in LQ for both septal-lesioned and sham-operated animals. When treated for 3 days with either 50 or 150 μg of testosterone propionate (TP) and given progesterone prior to behavior testing on day 4, female rats with septal lesions showed a higher mean LQ than sham-operated rats. Thus, septal lesions increase the behavioral sensitivity of female rats to both EB and TP as measured by female sexual behavior, but do not appear to alter the responsiveness of animals to progesterone.     

Ovarian hormones and the duration of sexual receptivity in the female golden hamster

The induction of sexual receptivity and its maintenance after copulation in ovariectomized female golden hamsters (Mesocricetus auratus) was found to be a function of the levels of ovarian hormones administered. Various combinations of estradiol benzoate (between 0.6 and 666 μg) and progesterone (between 0.05 and 5.0 mg) were administered in two experiments. Although some animals responded at 0.6 μg, higher levels of estradiol benzoate (1–6 μg or more) were more effective in inducing levels of lordosis equivalent to those seen in intact females in natural estrus. After mating, a depression in lordosis was observed in both ovariectomized and intact females. However, in ovariectomized females (excluding animals that did not respond initially) the duration of postcopulatory receptivity was a function of the level of progesterone administered. High levels of progesterone tended to prolong slightly the duration of postcopulatory receptivity.     

Natural or hormone-induced sexual and social behaviors in the female brown lemming (Lemmus trimucronatus)

The behaviors of intact or ovariectomized, estradiol benzoate-treated or estradiol benzoate followed by progesterone-treated female brown lemmings were compared. Intact, diestrous females engaged in more social interactions with a male than did ovariectomized females (Experiment 1). In the first 5 min of a 1-hr mating exposure (Experiment 2, Test A) intact females in natural estrus engaged in more social and sexual behaviors than did ovariectomized females in estrogen-induced estrus. However, during the last 5 min of the 1-hr exposure (Test B) ovariectomized females receiving estrogen alone continued to show high levels of sexual activity with a male partner, while intact estrous females or females receiving estrogen followed by progesterone showed an apparent drop in sexual receptivity and an increase in aggressivity. Aggressive behaviors, as indexed by threat-leap behaviors on the part of the female may increase in the presence of progesterone. Declines in sexual activity, occurring within 1 hr of progesterone injection, were apparently dependent on the interaction of progesterone and copulatory events which may affect both the male and female.     

Progesterone-Facilitated Lordosis in Medial Preoptic Area-Lesioned, Juvenile Guinea Pigs

Juvenile female guinea pigs rarely display lordosis in response to estradiol and progesterone treatments that elicit sexual receptivity in adults. To test the hypothesis that the medial preoptic area (MPOA) tonically inhibits the display of steroid-induced lordosis in juveniles, 11-day-old guinea pigs were ovariectomized (OVX) and received bilateral, sham, or electrolytic lesions aimed at the MPOA 3–4 days later. At 20–22 days of age, these females were tested for the expression of sexual receptivity following injections of estradiol benzoate (EB, 10 μg sc) and progesterone (0.5 mg sc, 40 h after EB). The lesions damaged portions of the MPOA, the nucleus of the diagonal band of Broca, the lateral aspect of the medial preoptic nucleus, the medial part of the preventricular portion of the periventricular nucleus, and the anterior commissure. The lesions did not alter the display of estradiol-induced lordosis. However, after treatment with EB plus progesterone, 20% of the sham-lesioned females displayed lordosis, as compared to 80% of the MPOA-lesioned animals. These data are consistent with the hypothesis that neurons originating in and/or traversing the MPOA tonically suppress the display of progesterone-facilitated lordosis in juvenile guinea pigs. Removal of this inhibitory input allows prepubertal females to respond behaviorally to estradiol and progesterone in an adult-typical fashion.     

Differential hormonal control of aggression and sexual behavior in female Syrian hamsters

These experiments were designed to test the effects of chronic estradiol treatment on aggression and sexual behavior in female hamsters. Isolated female hamsters were ovariectomized and tested for their behavioral responses to a group-housed, ovariectomized female hamster (aggression test) and a group-housed, intact male hamster (sexual behavior test). Following these baseline tests, the experimental females were implanted sc with Silastic capsules containing different concentrations of estradiol (100, 25, 10, or 0%) diluted with cholesterol and retested 3, 7, 10, and 14 days after implantation. High levels of aggression were observed on the baseline test, with no changes in aggression toward an intruder female observed for any implant group on subsequent tests. Despite these high levels of aggression toward another female, most of the estradiol-treated females (80% at 14 days) were sexually responsive in the presence of a male. There was no effect of Silastic estradiol concentration on sexual behavior, even though a range of serum estradiol levels (39–105 pg/ml) resulted. Lordosis latencies decreased and lordosis durations increased over the extent of estradiol treatment. Seventeen days after Silastic implantation, all females were injected with progesterone and retested. Estradiol-treated females showed an extreme reduction in aggression toward a stimulus female, as well as a further stimulation of sexual behavior after progesterone treatment. High levels of aggression in cholesterol-treated females (0% estradiol) were maintained even after progesterone injection, and these females never displayed any sexual responsivity. These results suggest that sexual behavior in the female hamster is sensitive to estradiol alone, whereas the inhibition of aggression requires the combination of estradiol plus progesterone.     

The effect of estrogen treatment on scopolamine inhibition of lordosis.

Previous evidence indicates that the cholinergic muscarinic antagonist, scopolamine, inhibits lordosis in female rats. In the experiments reported here, the effects of various doses and repeated administrations of estrogen on the scopolamine inhibition of lordosis were examined. In the first experiment, intraperitoneal injections of scopolamine (1 mg/rat) completely inhibited lordosis in ovariectomized rats primed with low doses of estradiol benzoate (0.25 or 0.5 micrograms for 3 days) and progesterone (500 micrograms). However, scopolamine was significantly less effective in inhibiting lordosis in females primed with a higher dose of estradiol benzoate (25 micrograms for 3 days) and progesterone (500 micrograms). When hormone priming was repeated on subsequent weeks, scopolamine continued to inhibit lordosis in females that received 0.25 micrograms estradiol benzoate but was less effective in females primed with 0.5 micrograms. Scopolamine failed to inhibit lordosis in females treated with 25 micrograms estradiol benzoate on these later tests. In the second experiment, various doses of scopolamine (1, 2, or 4 mg/rat) were administered intraperitoneally to females primed with the highest dose of estradiol benzoate (25 micrograms) and progesterone (500 micrograms). Lordosis was inhibited equally by all scopolamine doses during the first week. As in the first experiment, scopolamine failed to inhibit lordosis at all doses on subsequent weeks of testing. These results indicate that the ability of scopolamine to inhibit lordosis is reduced by increasing the dose or the number of estrogen exposures. Because higher doses of scopolamine failed to restore its inhibitory effect on lordosis an upregulation of muscarinic receptors by estrogen cannot account for the reduced effectiveness of scopolamine.     

Estrogenic effects of zearalenone on the expression of progestin receptors and sexual behavior in female rats

Zearalenone is a resorcylic acid lactone compound that is produced by fungal infection of edible grains and is believed to influence reproduction by binding to estrogen receptors. In order to study the potential estrogenic effects of this compound in the brain, we examined the effects of zearalenone on the expression of neuronal progestin receptors and feminine sexual behavior in female rats. Ovariectomized rats were treated with zearalenone (0.2, 1.0, or 2.0 mg), estradiol benzoate, or vehicle daily for 3 days. They were then either perfused, and progestin receptors visualized by immunocytochemistry, or injected with progesterone and tested for sexual receptivity with male rats. Progestin receptor-containing cells were counted in the medial preoptic area and ventromedial hypothalamus. The two highest doses of zearalenone increased the concentration of neuronal progestin receptors, as did 10 microg of estradiol. The highest dose of zearalenone (2 mg) also induced progestin receptor staining density comparable to that of 10 microg of estradiol benzoate. In behavioral tests, ovariectomized animals treated with 2 mg of zearalenone followed by progesterone showed levels of sexual receptivity comparable to females treated daily with estradiol benzoate (2 microg) followed by progesterone. These studies suggest that, although structurally distinct and less potent than estradiol, zearalenone can act as an estrogen agonist in the rat brain.     

Effects of ovarian hormones on the behavior of captive Macaca fascicularis

To examine the effects of ovarian hormones on the behavior of female Macaca fascicularis and their male partners, daily 1-hr behavior tests were conducted while ovariectomized females were (1) untreated, (2) given estradiol benzoate (EB) (5 μg subcutaneously [s.c.]/day), (3) given estradiol benzoate together with increasing doses of progesterone (P) (5 mg, 10 mg, and 20 mg. s.c./day), and (4) given testosterone propionate (TP) (0.25 mg s.c./day) (six pairs, 540 tests). Weekly blood samples were analyzed by radioimmunoassay for plasma hormone levels (81 samples). Estrogen treatment produced plasma estradiol levels similar to those of intact females during the late follicular phase of the menstrual cycle. Additional progesterone at the lowest dose produced plasma progesterone levels similar to or somewhat higher than those during the midluteal phase, while higher doses produced supraphysiological levels. Androgen treatment resulted in plasma levels well above the physiological range. Hormone treatments produced highly significant effects on the sexual, social, and aggressive interactions of the pairs. As in rhesus monkeys, estrogen increased male and female sexual activity, and increasing doses of additional progesterone reversed these effects. Unlike in rhesus monkeys, testosterone propionate increased both female sexual motivation (invitations) and also male sexual activity and ejaculatory performance. The direction of the hormone-dependent changes in grooming and aggressive interactions confirmed earlier results with intact females and indicated that aggressive interactions and male grooming times were highest, and female grooming times were lowest, when copulatory activity was at its height.     

Paced mating behavior in female rats in response to different hormone priming regimens

A female rat will display a repertoire of behaviors during a sexual encounter with a male rat including sexually receptive (the lordosis response) and proceptive (hopping, darting) behaviors. In addition, when given the opportunity, a sexually receptive female rat will approach and withdraw from the male rat, controlling the timing of the receipt of mounts, intromissions, and ejaculations, a behavior known as paced mating behavior. The present experiments tested the hypotheses (1) that progesterone regulates paced mating behavior, and (2) that multiple hormone regimens used previously to induce sexual receptivity have the same effect on paced mating behavior. Paced mating behavior was assessed in sexually receptive ovariectomized female rats after treatment with: (1) estradiol benzoate (EB; 30.0 mg/kg) followed by a range of doses of progesterone (P; 1.0-8.0 mg/kg), (2) two pulses of unesterified estradiol (E2; 2.0 microg/rat) followed by 1.0 mg/rat of P, and (3) EB alone (5.0 microg/rat) for 6 days. No differences in sexual receptivity or in paced mating behavior were observed across doses of P (1.0-8.0 mg/kg). In contrast, the number of hops and darts per min increased with the dose of P administered. E2 + P administration resulted in slightly, but significantly, lower levels of sexual receptivity along with significantly longer contact-return latencies following an intromission in relation to the other treatment conditions. In addition, female rats exhibited fewer hops and darts per min in response to E2 + P than in response to EB + 8.0 mg/kg of P. The administration of EB alone for 6 days induced levels of receptivity and paced mating behavior indistinguishable from EB + P, while eliciting significantly fewer hops and darts per min than the EB + 8.0 mg/kg P treatment condition. Hormone priming regimen had no effect on the percentage of exits displayed during the paced mating tests in any experimental phase. Dose of P had no effect on paced mating behavior in sexually receptive rats. In addition, P does not appear to be necessary for the display of paced mating behavior following long-term treatment with EB. In contrast, the pulsatile administration of E2 + P induced a different pattern of paced mating behavior in sexually receptive rats.     

Estrogen-progesterone induction of mating in female rats

Ovariectomized female rats were administered 1, 2, 4, and 8 μg of estradiol benzoate and either 10, 25, 50, 100, or 200 μg of progesterone and were tested for sexual receptivity. The probability of lordosis was related directly to the dose of both steroids. Individual differences in hormone response were marked. Ear wiggling and hopping were primarily related to the dose of progesterone.     

Lordosis behavior in castrated male rats treated with estradiol benzoate or testosterone propionate in combination with an estrogen antagonist, MER-25, and in intact male rats

Lordosis behavior could be elicited by manual stimulation in castrated male rats after treatment with estradiol benzoate (15 μg for 10 days) or testosterone propionate (1 or 3 mg for 10 days). The effect was antagonized by treatment with the estrogen antagonist MER-25 (10mg for 10 days). Prolonged treatment with testosterone propionate (1 mg for 26 days) resulted in display of male (nine of ten rats) as well as female (seven of ten rats) sexual behavior. Eleven of 32 intact male rats (age 120 days) and 22 of 37 other intact males (age 75 days) displayed lordosis in response to manual stimulation without hormonal treatment. Seven intact males which showed lordosis without hormone treatment were injected with MER-25 (10 mg/day × 10 days) and lordosis was abolished in six cases. The results suggest that estrogen is involved in the regulation of lordosis behavior in TP-treated and intact male rats.