The effect of oestradiol, testosterone and dihydrotestosterone on sexual motivation in the ovariectomized female rat

Androgen receptors and sociosexual behaviors in mammals: The limits of generalization

Circulating testosterone is easily aromatized to estradiol and reduced to dihydrotestosterone in target tissues and elsewhere in the body. Thus, the actions of testosterone can be mediated either by the estrogen receptors, the androgen receptor or by simultaneous action at both receptors. To determine the role of androgens acting at the androgen receptor, we need to eliminate actions at the estrogen receptors. Alternatively, actions at the androgen receptor itself can be eliminated. In the present review, I will analyze the specific role of androgen receptors in male and female sexual behavior as well as in aggression. Some comments about androgen receptors and social recognition are also made. It will be shown that there are important differences between species, even between strains within a species, concerning the actions of the androgen receptor on the behaviors mentioned. This fact makes generalizations from one species to another or from one strain to another very risky. The existence of important species differences is often ignored, leading to many misunderstandings and much confusion.

Sexual incentive motivation and male and female copulatory behavior in female rats given androgen from postnatal day 20

Masculinization and feminization of rat sexual behavior has been supposed to occur during a short postnatal period. However, much data have made it evident that these processes may continue until adolescence. In the present study, we evaluated whether androgen treatment of females from postnatal day 20 and onwards could alter sexual motivation and behavior in a male direction. Juveniles were ovariectomized on day 20 and concurrently implanted with Silastic capsules containing either testosterone or dihydrotestosterone. Controls were implanted with an empty capsule. Tests for sexual incentive motivation and male sexual behavior were performed every fifth day when the females were between 50 and 75 days of age. At day 80, a test for female sexual behavior was performed. Females treated with testosterone approached a female sexual incentive far more than a male incentive, showing that sexual motivation had been changed in a male-like direction. Dihydrotestosterone had a similar, albeit smaller, effect. Females implanted with an empty capsule approached both incentives equally. Testosterone produced a high level of mounting behavior, whereas intromission-like behavioral patterns were rare and ejaculation-like behavior was absent. In the test for female sexual behavior, the testosterone-treated animals displayed a relatively high lordosis quotient, far above that displayed in females implanted with dihydrotestosterone or an empty capsule. It is concluded that treatment with an aromatizable androgen during the peripubertal-adolescent period masculinizes sexual motivation and partly sexual behavior. A non-aromatizable androgen weakly masculinize sexual motivation without enhancing male sexual behavior. It appears that simultaneous actions on androgen and estrogen receptors are needed for significant masculinization during the period studied here. Since the testosterone-treated females displayed lordosis, sexual behavior was not defeminized. In sum, these results suggest that sexual differentiation continues well into the peripubertal and adolescent periods.

When do we eat? Ingestive behavior, survival, and reproductive success

The neuroendocrinology of ingestive behavior is a topic central to human health, particularly in light of the prevalence of obesity, eating disorders, and diabetes. The study of food intake in laboratory rats and mice has yielded some useful hypotheses, but there are still many gaps in our knowledge. Ingestive behavior is more complex than the consummatory act of eating, and decisions about when and how much to eat usually take place in the context of potential mating partners, competitors, predators, and environmental fluctuations that are not present in the laboratory. We emphasize appetitive behaviors, actions that bring animals in contact with a goal object, precede consummatory behaviors, and provide a window into motivation. Appetitive ingestive behaviors are under the control of neural circuits and neuropeptide systems that control appetitive sex behaviors and differ from those that control consummatory ingestive behaviors. Decreases in the availability of oxidizable metabolic fuels enhance the stimulatory effects of peripheral hormones on appetitive ingestive behavior and the inhibitory effects on appetitive sex behavior, putting a new twist on the notion of leptin, insulin, and ghrelin "resistance." The ratio of hormone concentrations to the availability of oxidizable metabolic fuels may generate a critical signal that schedules conflicting behaviors, e.g., mate searching vs. foraging, food hoarding vs. courtship, and fat accumulation vs. parental care. In species representing every vertebrate taxa and even in some invertebrates, many putative "satiety" or "hunger" hormones function to schedule ingestive behavior in order to optimize reproductive success in environments where energy availability fluctuates.

Quantitative assessment of female sexual motivation in the rat: Hormonal control of motivation

While a good deal of information has been garnered in the last few decades regarding the neural and hormonal control of female sexual behavior, literature elucidating these mechanisms with respect to female sexual motivation has been scarce. We believe that one reason for this is the lack of a standardized paradigm that will quantify female sexual motivation while allowing for sexual interaction to occur. Here we describe a two-chambered apparatus that utilizes operant responding (nose poking) to quantify female sexual motivation. During the test, the female exhibits nose pokes to gain access to a sexually active male, with whom she is allowed to mate. Therefore, this apparatus allows for examination of sexual behavior as well as quantification of sexual motivation by assessing the number of nose pokes the female will exhibit within a fixed interval to gain access to the male. We report that hormone priming significantly increases sexual motivation in the female as indicated by the number of nose pokes she will exhibit to gain access to the male. Additionally, hormone primed females enter the male compartment after a shorter period and spend more time in direct contact with the male compared to when they are not hormone primed. In contrast, when females are not hormone primed they spend more time in view, but out of reach, of the male. This paradigm will help to advance the study of female sexual motivation, providing a method for quantifiable assessment of female sexual motivation while allowing for sexual activity to occur.

A selective androgen receptor modulator enhances male-directed sexual preference, proceptive behavior, and lordosis behavior in sexually experienced, but not sexually naive, female rats

Androgens influence many aspects of reproductive behavior, including sexual preference of females for males. In oophorectomized women with sexual desire disorder, testosterone patches improve libido, but their use is limited because of adverse side effects. Selective androgen receptor modulators offer an improved safety profile for both sexes: enhancing libido and muscle and bone growth in a manner similar to steroidal androgens but with fewer adverse effects, such as hirsutism, acne, and prostate growth. The current study investigated the action of a novel selective androgen receptor modulator (LGD-3303 [9-chloro-2-ethyl-1-methyl-3-(2,2,2-trifluoroethyl)-3H-pyrrolo-[3,2-f]quinolin-7(6H)-one]) on male-directed sexual preference, proceptivity, and lordosis behavior of female rats. LGD-3303 is a nonsteroidal, nonaromatizable, highly selective ligand for the androgen receptor and effectively crosses the blood-brain barrier. Gonadectomized female rats were treated with LGD-3303 (3-30 mg/kg) or vehicle by daily oral gavage. Results showed that LGD-3303 treatment enhanced sexual preference of females for males but only if females had previous sexual experience. This occurred after 1 or 7 d of treatment. In contrast, preference for males was inhibited by LGD-3303 treatments of sexually naive females. The LGD-3303 increase in male preference was blocked by pretreatment with the androgen receptor antagonist flutamide. LGD-3303 treatment increased lordosis and proceptivity behaviors in ovariectomized females primed with suboptimal doses of estradiol benzoate plus progesterone. These data support the concept that LGD-3303 can stimulate aspects of female sexual behavior and may serve as a potential therapeutic for women with sexual desire disorders.

Effects of steroid hormones on morphology and vascular endothelial growth factor expression in female bladder

OBJECTIVES

To investigate the roles of steroid hormones, including estrogen, progesterone, and testosterone, in the morphology and vascularization of the female bladder.

METHODS

A total of 70 adult, female Sprague-Dawley rats were divided into 7 groups: group 1, sham; group 2, ovariectomized rats without treatment; group 3, low-dose estradiol; group 4, high-dose estradiol; group 5, progesterone; group 6, estradiol combined with progesterone; and group 7, testosterone. All were given for 4 weeks. The serum steroid hormone levels were determined by radioimmunoassay. The total weight and thickness of the bladder were measured. Morphologic changes were observed under light and electron microscopy. The expression of vascular endothelial growth factor (VEGF) in the bladder was evaluated by immmohistochemistry and Western blotting.

RESULTS

The ovariectomized rats had a thinner bladder wall compared with the sham group (0.97 +/- 0.11 mm vs 1.10 +/- 0.10 mm, P < .05) and widened spaces between the detrusor muscle fascicles with collagen deposit. Estrogen reversed these changes, and testosterone increased the thickness of the bladder wall to 1.26 +/- 0.12 mm (P < .05). VEGF staining was mainly located in the urothelium and endothelial cells, with weak staining in the smooth muscles. VEGF was almost absent in the urothelium after ovariectomy. In the estrogen- and androgen-treated groups, although the expression of VEGF was significantly greater than that in the nontreated ovariectomized group, it was still lower than normal.

CONCLUSIONS

Our findings suggest the importance of steroid hormones in maintaining the integrity of the bladder structure and regulating the expression of VEGF in the female urinary tract. Both estrogen and androgen can reverse the bladder muscle atrophy induced by ovariectomy. However, the decline in VEGF expression in the bladder cannot be fully recovered with either estrogen or androgen replacement.

The effect of acute bupropion on sexual motivation and behavior in the female rat

Recent clinical studies have suggested that the atypical antidepressant, bupropion (Wellbutrin), may stimulate sexual desire in women. Two experiments were conducted, testing the effect of acute bupropion administration on the sexual motivation and copulatory behavior of female rats. In the first experiment, 63 sexually-experienced, female Long-Evans rats were tested in a runway for their motivation to approach an empty goalbox, a nonestrous female, and an adult male. Both latency to approach and time spent in close proximity to the targets were used as dependent variables. Subjects were tested in both a nonestrous (OVX) and estrous (OVX+15 microg estradiol+500 microg progesterone) state, and following administration of 0.0, 7.5, or 15 mg/kg bupropion hydrochloride (subcutaneous, 45 min prior to testing). Results indicated that pre-treatment with ovarian hormones significantly increased the sexual motivation of the subjects. Bupropion treatment had no significant effect, either stimulatory or inhibitory, on subjects' socio-sexual motivation. In the second experiment, 60 female subjects were paired with an adult male for a thirty-minute copulatory test. Subjects were tested under one of three hormonal conditions: nonestrous (no hormones), 15 mug estradiol, or 15 microg estradiol+500 microg progesterone. Subjects were also pre-treated with either physiological saline or 15 mg/kg bupropion. Results indicated that while hormonal administration had a strong effect on female sexual behavior, bupropion treatment did not significantly affect either lordosis or the emission of hop-darts. Males paired with bupropion-treated females successfully achieved a greater number of ejaculations and demonstrated significantly shortened post-ejaculatory intervals. It is possible that bupropion treatment enhanced female attractiveness.

Hormonal status and test condition, but not sexual experience, modulate partner preference in female rats

A series of experiments was conducted to determine the contributions of hormonal status, test condition, and sexual experience to the display of partner preference by female rats. Preference for a sexually active male rat over a sexually receptive female rat was assessed in independent groups of female rats tested in a condition limiting physical contact (No Contact) and a condition allowing for sexual interaction (Contact). Although hormonal status and test condition influenced the preference for a sexually active male, repeated testing and sexual experience had no effect. Experiment 1 demonstrated that independent of test condition, preference for the male is stronger in estrogen- and progesterone-primed rats than in rats receiving the vehicle. Moreover, independent of hormone condition, rats tested in the No Contact condition exhibit a stronger preference for the male than rats tested in the Contact condition, reflecting in part the active pacing of mating stimulation by sexually receptive rats tested in the Contact condition. Experiment 2 showed that the overall pattern of partner preference in proestrous and diestrous rats was similar to that observed in ovariectomized, estrogen- and progesterone-primed, and oil-treated rats, respectively. In Experiment 3, rats primed with estrogen alone did not exhibit a preference for the male even though fully receptive. Experiments 4 and 5 demonstrated that sexual experience does not affect the expression of preference for the male in estrogen- and progesterone-primed rats. The present findings demonstrate that the female rat's preference for the male is stable across repeated tests and is not affected by sexual experience. Our results also confirm that gonadal hormones influence the expression of a preference for a sexually active male versus a sexually receptive female and demonstrate that the magnitude of preference is modulated by test conditions.

Effect of sex steroids and coital experience on ferrets' preference for the smell, sight and sound of conspecifics

Previous research showed that ferrets of both sexes recognize potential opposite-sex mates on the basis of volatile body odors. We compared the ability of estrogen and androgen treatments to activate a preference in gonadectomized male and female ferrets for distal cues (volatile body odors alone or volatile odors+sight+sounds) from male versus female stimulus ferrets using an airtight Y-maze and a "stimulus proximity" or a "discrete trials" testing paradigm. Sexually naive, gonadectomized male and female ferrets that received either testosterone propionate (TP) or estradiol benzoate (EB) spent equal time in proximity to goal boxes that provided either volatile odors alone or odors+sight+sounds of male and female stimulus animals. After they received coital experience, male and female subjects (treated with either EB or TP) showed a significant preference for both types of opposite-sex stimuli. When discrete trials tests were given to these ferrets prior to receiving coital experience, EB-treated females preferred to approach odor only cues, as well as odors+sight+sounds of stimulus males, and this preference was further strengthened after coital experience. Sexually naive, TP-treated males preferred to approach volatile odor cues from stimulus females; however, these animals showed an equal preference for odors+sight+sounds of stimulus females and males. Again, after coital experience, males' preference for both sets of cues from stimulus females was significantly enhanced. Thus, in sexually naive ferrets, discrete trials, but not stimulus proximity tests, revealed a preference for distal cues (body odors with or without concurrent sight and sounds) from opposite-sex conspecifics in subjects of both sexes. Coital experience significantly enhanced these preferences for heterosexual distal cues under both testing paradigms.

What do female rats like about sex? Paced mating

The motivational aspects of female sexual behavior have been evaluated by a variety of methodologies including: the increasing barrier method, the runway procedure, partner preference test, operant behavior and conditioned place preference. When female rats are tested for sexual receptivity under traditional laboratory conditions, usually a small open area, both appetitive and aversive components of the sexual interaction are easily observed. For example, after prolonged testing, subsequent lordosis and the intensity of this response are reduced increasing the rejection behavior by the female. However, when female rats are allowed to pace (control) the rate of sexual stimulation they received, as usually occurs under seminatural and natural conditions, the aversive properties of mating are reduced. The conditioned place preference can be use to measure the positive affect elicited by mating. We have combined pacing and conditioned place preference in an attempt to reduced the possible aversive consequences associated with mating and increase the likelihood of detecting the appetitive effects of coital interaction in female rats. Only female rats that regulated (paced) their coital interactions with a stud male through a two-compartment chamber in which only the female could freely move from one compartment to the other developed a clear place preference. As well, females that received ten or 15 paced intromissions (without ejaculation) also developed place preference. The place preference induce by paced mating is blocked by the systemic administration of naloxone suggesting that opioids are involved in the reward processes associated with paced mating. Paced sexual interactions can induce a positive affect of sufficient intensity and duration to induce conditioning.

Sex differences in estrogen and androgen receptors in hamster brain

The present study was conducted to measure the levels of estrogen and androgen receptors (ER and AR, receptively) simultaneously in the anterior pituitary (AP), and various brain regions from adult male and proestrous female hamsters. Medial preoptic area (MPOA), medial basal hypothalamus (MBH), lateral hypothalamus (LH), medial forebrain bundle (MFB), and amygdala (AMG) were identified and removed from 200-microns frozen brain sections by the Palkovits punch-out technique. ER and AR were determined by the in vitro binding assay using [3H]-estradiol and [3H]-methyltrienolone as the binding ligands. In males, high levels of AR were found in the MPOA, MBH, and AP. In females, the MPOA, MBH, LH, and AP contained high levels of ER. The males exhibited significantly higher levels of AR than females in the MPOA, MBH, and LH, whereas the ER levels in these areas were higher in females. In males, ER and AR contents in the AP were higher, but the contents in the AMG were lower as compared to those of females. The calculated ER/AR ratio in MPOA, MBH, and LH were lowest in males. On the contrary, the ratio in these areas were highest in females. These data suggest that sex differences in response to estrogen and androgen may in part be due to sex differences in ER and AR contents in specific brain regions.

Synergistic action of estradiol, progesterone and testosterone on rat proceptive behavior

The role of estradiol (E), progesterone (P) and testosterone (T) in the control of rat feminine sexual behavior (receptivity, proceptivity and sexual orientation) was analyzed. The action of estradiol benzoate (EB, 1.25 micrograms/rat x 3 days) and P (0.5 mg/rat) was compared in ovariectomized (OVX) and ovariectomized-adrenalectomized (OVX + ADX) subjects. Administration of EB alone was followed by maximum levels of lordosis behavior and a male-directed orientation in both OVX and OVX + ADX females. A reduction in the level of proceptivity was observed in EB-treated OVX + ADX animals as compared with EB-treated OVX rats. The administration of P to OVX + ADX females resulted in an increase in proceptive behavior similar to that observed in OVX EB-treated animals. A further study analyzed the effect of combined administration of EB, P and various doses of T (30, 90 and 270 micrograms/rat) in OVX + ADX rats. A synergistic action of all three hormones on proceptivity was observed. Neither a further increase in lordosis nor in male-directed orientation was observed in EB-treated females after additional treatment with P or T independently or together. Finally, we studied the effect of adrenalectomy on the spontaneous onset of estrous behavior. Adrenalectomy did not modify any aspect of normal feminine sexual behavior, suggesting that the adrenals, in the presence of the ovaries, are of no critical importance for this behavior. The possible contribution of adrenal steroids to the expression of proceptivity is discussed.

Role of androgen, estrogen and sexual experience on the female rat's partner preference

Virgin ovariectomized rats were implanted with Silastic tubings containing estradiol (E2, 5 mm), testosterone (T, 30 mm), dihydrotestosterone (DHT, 30 mm), or injected daily SC with the synthetic nonaromatizable androgen, methyltrienelone (R 1881, 5 mg.kg-1) daily for three weeks. Animals were tested for partner preference behavior (staying in the vicinity of a sexually active male, an estrous female or staying elsewhere) before and after they had been tested for feminine and masculine sexual behavior. All naive androgen-treated groups showed a male-oriented preference, while the naive E2-treated females did not show any consistent partner preference. Sexual experience abolished the male-directed orientation of the androgen-treated groups while E2 treatment induced a male-directed orientation. E2-treated females spent significantly longer time elsewhere in both tests compared to the other groups which might be due to insufficient levels of E2. Feminine sexual behavior was seen after treatment with E2 or T but not after treatment with DHT or R 1881. It was concluded, 1) that the effect of treatment with an androgen on the partner preference behavior differs according to whether the females are virgins or sexually experienced, and 2) the effect of the hormone treatment on the partner preference behavior is independent of whether the hormone stimulates feminine sexual behavior.

On the organization of partner preference behavior in female Wistar rats

The possible prenatal organizing effects of testosterone (T) on adult sexual partner preference, i.e., sexual orientation in female rats, were studied through prenatal exposure (days 11-22) of female fetuses to the antiandrogens flutamide (Sch 13521; 4'-nitro-3'-trifluoromethylisobutyranilide; 5 or 10 mg/day; Experiment 1) or anandron [RU 23908; 5,5-dimethyl-3-(4-nitro-3-(trifluoromethyl)phenyl)- 2,4-imidazolidinedione; 35 mg/kg/day; Experiment 2]. The neonatal organizing effects of T were further studied by giving T, dihydrotestosterone (DHT) or oil within 9 h after birth to female pups (Experiment 3). In adulthood sexual orientation was ascertained, after ovariectomy followed by hormone treatment, in an automated open field (AOF), with stimulus animals behind wire mesh, and in a 3-compartment box (3-CB), with stimulus animals tethered. When given the choice between an estrous female and a sexually active male in the AOF, flutamide females, as well as controls, preferred the male partner. After long-term T treatment and 3 weekly pair-tests with an estrous female, flutamide females as well as controls switched their preference to the estrous female partner. In anadron females similar results were obtained. Thus the prenatal antiandrogens had no significant effect on sexual orientation in female rats. This suggests that adult sexual orientation in female rats is not organized prenatally through endogenous T. The change in preference after sexual experience corroborates earlier findings from our laboratory. When given the choice between an estrous female and a sexually active male in the 3-CB (sexual interaction with incentives possible), neonatally DHTP-treated females preferred the male; neonatally TP- or oil-treated females showed no preference.(ABSTRACT TRUNCATED AT 250 WORDS)

Preference for an estrous female over a non-estrous female evinced by female rats requires dihydrotestosterone plus estradiol

The effects were studied of long-term treatment with testosterone metabolites (dihydrotestosterone. DHT, and estradiol, E2, in sc Silastic implants) on preference behavior of ovariectomized female rats for an estrous female over a non-estrous female. For measuring this behavior a residential plus-maze was used which harbored two ovariectomized "stimulus" females on the top of peripheral boxes, one of which was made estrus by injection of estradiol benzoate and progesterone. When both steroids (DHT plus E2) were circulating simultaneously they evoked preference for an estrous female, while neither steroid by itself sufficed. In earlier work with adult male rats castrated on the day of birth, E2 was effective in the absence of DHT. This sex difference, therefore, seems to have arisen before birth. Further, administration of DHT alone caused a profound lack of interest in both "stimulus" females, which cannot be fully explained by the reduced locomotor activity which has been found to be induced by DHT in earlier studies.

Sexual experience and preference for males or females in the female rat

The influence of sexual experience on preference behavior was investigated in adult female rats. In the first experiment, preference behavior for sexually active males versus estrous females was investigated in female rats who were experienced with mounting behavior. Preference of these mount experienced females was compared to preference of females who were naive in this respect. Mount experience with estrous females induced a female-directed preference in ovariectomized female rats, irrespective of whether the females were treated with OIL or with testosterone-propionate (500 micrograms TP, injected once 48 h prior to testing). Sexually naive, OIL-treated females did not show a preference for males or females, but TP induced a preference for a male. Individual differences in mount frequency were not correlated with preference behavior. In the second experiment, the influence of experience with feminine sexual responses on preference behavior was investigated. OIL-treated and TP-treated females oriented equally toward males and females when they had been given the opportunity to copulate with males prior to the preference tests. The results strongly suggest that prior sexual experience is an important determinant of preference behavior. The female's behavior during sexual interactions was, however, not predictive of later preference.

Homosexual and heterosexual partner preference in ovariectomized female rats: effects of testosterone, estradiol and mating experience

Ovariectomized female rats, longterm treated with estradiol benzoate (EB, 20 micrograms, 3 x/week) or testosterone propionate (TP, 0.4 mg, 3 X/week), were tested for homo- or heterosexual partner preference behavior with either tethered animals (sexually active male vs. estrous female) or animals behind a wire mesh. A preference score was calculated by subtracting the time spent in the vicinity of the stimulus female from the time spent in the vicinity of the stimulus male. Thus, a positive score indicates preference for the male (heterosexual preference), a negative score preference for the female (homosexual preference). Two weeks of EB treatment caused a clearcut preference for the male incentive. This heterosexual preference was significantly different from the indistinct preference of the TP-treated females. Sexual interaction with a freely moving active male (with or without a vaginal mask which prevented intromissions) did not alter the preference for the male of the EB-treated females. It did affect, however, the preference behavior of the TP-treated females significantly: it changed in the direction of the sexually active estrous incentive female, i.e., a homosexual preference. This change in preference could not be attributed to the experience of penile intromissions, it occurred despite the presence of a vaginal mask. Apparently, being mounted by a sexually active male had a negative reinforcing value in the TP-treated female rats and provoked a homosexual partner preference.

Androgens are specifically implicated in female rat sexual motivation. The influence of methyltrienelone (R1881) on sexual orientation

The present experiment was designed to investigate whether androgens are specifically involved in the induction of a male-directed orientation in adult female rats. Ovariectomized female rats were either treated with the non-aromatizable androgen methyltrienelone (R1881), with testosterone propionate (TP), with estradiol benzoate (EB) or with an equal volume of the solvent. Sexual orientation of these females towards either sexually active males or estrous females was then investigated and related to levels of receptive and mounting behavior. Compared to the solvent-treated females, females treated with R1881, TP or EB spent more time near sexually active males. Mounting behavior was stimulated in the R1881- and TP-treated females, but EB-treated females mounted as often as females treated with the solvent only. Lordosis behavior was only observed in TP-treated or EB-treated females. Mount frequency of the females of the different treatment groups was positively correlated with time spent near males. These correlations reached statistical significance in the TP-treated and EB-treated females. In the TP-treated females, the lordosis quotient was negatively correlated with time spent near males. The results of the present experiment suggest that androgens need not be converted into estrogens in order to facilitate a male-directed orientation in ovariectomized female rats.

Neonatal exposure of female ferrets to testosterone alters sociosexual preferences in adulthood

Sociosexual preferences in adult female ferrets, as measured in a choice arena, were altered by neonatal exposure to exogenous testosterone. Adult female ferrets showed a preference for males which did not depend on the presence of gonadal steroids, because gonadectomized and gonadectomized estrogen-treated females showed identical preferences for males. Adult castrated males showed no preference for females unless these males were treated with testosterone. A similar no-preference pattern was found in adult females that had received testosterone neonatally. Females exposed neonatally to dihydrotestosterone or estradiol exhibited the normal females' male-oriented preference. These results indicate that testosterone secreted by the testes in the developing male may interrupt the phenotypic female development pattern and hence prevent the emergence of a homosexual preference in adulthood in the male ferret.

On the involvement of progesterone in sexually rewarded choice behavior of the female rat

The present experiment was designed to investigate the role of Progesterone in the regulation of two aspects of the female's appetitive sexual behavior. Ovariectomized females were tested for partner preference using either a test in which sexual interaction was not possible ("sexual orientation") or a test which included the possibility of sexual interaction ("sexually rewarded choice behavior"). The females were either primed with OIL, Estradiol benzoate (EB) or with Testosterone propionate (TP). Additional groups of females which were primed with EB or TP were treated with Progesterone (P) four hours prior to testing. The results indicate that females which are either treated with EB or with TP, show a male-directed orientation, while OIL-treated females do not. Sexually rewarded choice behavior however, was not affected by hormonal treatment with EB or TP. Additional treatment with P did not further increase the female's male-directed sexual orientation. Sexually rewarded choices for males, in contrast, were drastically increased. EB + P- or TP + P-treated females also showed a significant increase in heterosexual interactions with males in the goal box. The present results support the hypothesis that P plays a role in the female's appetitive sexual behavior, only when the possibility for interaction with a male is present.

Effect of environmental lighting on sexual behavior and testosterone levels of female rats

The effects of exposure to two different lighting regimes, constant light (LL) and cyclic light (LD) on the sexual performance and serum testosterone concentrations of intact, virgin, female rats was investigated. During copulatory pairing there were significant changes in the sexual performance of both LL and LD rats. Sexual receptivity in the LL females increased as a result of copulatory stimulation, whereas the sexual performance of LD females declined. Throughout copulatory testing the level of sexual receptivity displayed by the LL females was significantly less than that of the LD females. Testosterone levels in acyclic virgin LL rats were significantly lower than the levels in cycling, virgin, LD rats. The implications of these findings were discussed.

Effect of ACTH 4-10 on copulatory bahavior and on the response for socio-sexual motivation in the female rat

Female copulatory behavior and the urge of a female rat to seek contact with a sexually active male was studied after treatment with the peptide ACTH 4-10. No effects of this peptide were seen on the copulatory response of ovariectomized females treated with estradiol benzoate (EB) alone or EB and progesterone combined. An increasing barrier technique was used to measure how much of an average stimulus (cresssing an electrified grid) a female was willing to endure to gain contact with sexually active male. It has been shown in previous investigations (15) with ovariectomized rats that after a certain time of adaptation and training in this apparatus the response attained remains at a certain basal level from which it is increased by treatment with EB. Animals treated with ACTH 4-10 during the phase of adaptation and training attained a significantly higher basal response level than controls. This effect was only observed when the peptide treatment covered the period of adaptation and was not seen when the treatment was started after this critical period. The EB-induced response was not influenced by ACTH 4-10 given during the period of adaptation or given in connection with the EB treatment. It is concluded that ACTH 4-10 influenced the acquired response level but had no effect on steroid induced responses, which are probably controlled by more innate mechanisms.

Effects of anti-estrogens on testosterone stimulated male sexual behavior and peripheral target tissues in the castrate male rat

In the first experiment castrated male rats were injected daily with either vehicle or 800 mug testosterone together with either 6 hr pretreatment or concurrent treatment with the anti-estrogens CI-628 (4 mg) or MER-25 (20 mg). The only treatment found to significantly reduce male copulatory behavior was concurrent treatment with CI-628. Anti-estrogen treatment was also found to slightly reduce body weights, increase seminal vesicle weights in response to testosterone and to have no significant effects on androgen stimulated increases in penis weight and length. In the second experiment castrated male rats were injected daily with either vehicle or 500 mug testosterone together with 2.5 mg injections of CI-628 given 6 hr before and concurrent with the androgen injections. The anti-estrogen treatment was found to markedly inhibit the desplay of male sexual behavior, to reduce body weights, and to stimulate seminal vesicle weights. Penile weights and lengths were again not effected by the anti-estrogen therapy. These results were interpreted as supporting the theory that testosterone stimulated male sexual behavior in the rat following its aromatization to estradiol in the brain.

Stimulation of male and female sexual behavior in gonadectomized rats with estrogen and androgen therapy and its inhibition with concurrent anti-hormone therapy

In the first experiment gonadectomized male rats were injected daily with various combinations of vehicle (V), estradiol benzoate (E), dihydrotestosterone (D) and/or the anti-androgen cyproterone acetate (CA). The eight treatment combinations consisted of V, E, D, CA, E + D, E + CA, D + CA and E + D + CA. Only those males treated with both E and D were found to display ejaculations. Concurrent treatment with CA completely blocked ejaculatory behavior and it significantly reduced both mount and intromission frequencies. Examination of peripheral androgen target tissues indicated that following stimulation with D, CA effectively reduced seminal vesicle and penile weights, and penile lengths, but it did not reduce penile spines. In the second experiment gonadectomized female rats were treated with two daily injections of E, E + CA or E + the anti-estrogen CI-628. A second set of gonadectomized females received three daily injections of testosterone (T), T + CA or T + CI-628. On the day after completion of these injections all females received progesterone and were tested for sexual receptivity three hours later. Both E and T treated females were found to display the lordotic posture in response to mounting stimulation while both CI-628 and CA were found to block this behavior. In E treated females, CI-628 and CA were also found to reduce uterine weight. Thus, CA was shown to have anti-estrogenic as well as anti-androgenic properties. These results were discussed in terms of the aromatization and 5alpha reduction theories of testosterone action in sexual behavior.