Mounting behavior and lordosis behavior in castrated male rats treated with testosterone propionate, or with estradiol benzoate or dihydrotestosterone in combination with testosterone propinonate.

Treatment of prepuberally castrated male rats with testosterone propionate (TP, 50, 200, 500, or 1000 μg for 30 days) in adulthood stimulated the display of both mounting behavior and lordosis behavior. No correlation between mounting and lordosis behavior could be detected at any TP dose level. Treatment of prepuberally castrated male rats with either 1 μg estradiol benzoate (EB) or 500 μg dihydrotestosterone (DHT) for 60 days stimulated the display of mounting behavior in three of eight and four of eight rats, respectively. Treatment with 200 μg TP for the last 30 days of rats receiving either EB or DHT for 60 days resulted in an abrupt onset on mounting behavior as compared to rats treated with oil for 60 days. These results show additive effects of EB or DHT and TP upon mounting behavior by male rats and are interpreted as a support for the suggestion that testosterone to estrogen as well as testosterone to DHT conversion may be involved in the mechanism whereby testosterone activates the mounting behavior of castrated rats.     

Differential effect of testosterone and dihydrotestosterone on the sexual behavior of prepuberally castrated male rabbits

The effect of testosterone propionate (Tp) and dihydrotestosterone propionate (DHTp) at doses of 1, 3 and 9 mg daily for 30 days on the copulatory behavior of prepuberally castrated male New Zealand white rabbits was studied. Tp was significantly more effective than DHTp in eliciting copulatory behavior at each dose level tested. Three milligrams Tp was the minimal dose required to elicit mounting consistently. DHTp at the high dose level (9 mg) only elicited sexual activity comparable to that observed with the low dose of Tp (1 mg). The results suggest that T does not need to be reduced to DHT to stimulate sexual behavior in the male rabbit.     

Effects of dihydrotestosterone and estradiol benzoate pretreatment upon testosterone-induced sexual behavior in the castrated male rat

Three groups of inexperienced castrated male rats were treated daily for 15 days with oil, estradiol benzoate (1 μg), or dihydrotestosterone (1 mg), and thereafter injected daily with testosterone (1 mg) for 21 days. Sexual behavior was tested every third day after the start of the pretreatment until day 36. Estradiol benzoate or dihydrotestosterone failed to elicit sexual behavior. Pretreatment with dihydrotestosterone, but not estradiol benzoate, significantly shortened the intervals to initiation of mounting and intromission in response to testosterone. The results suggest that fully developed genitals (penis and/or sexual accessories) facilitate initiation of copulatory behavior in response to testosterone administration.     

Effects of estrone, estradiol and estriol combined with dihydrotestosterone on mounting and lordosis behavior in castrated male rats

Prepuberally castrated male rats were injected with estrone (1 or 5 μg), estradiol (1 or 5 μg) or estriol (1, 5, or 25 μg) either alone or in combination with dihydrotestosterone, (0.5 mg). Each of these steroids, when given alone, had no or only weak stimulatory effects on male sexual behavior. When combined with dihydrotestosterone all estrogens stimulated full copulatory behavior, the order of potency being estradiol, estrone, and estriol. Lordosis behavior in response to male mounting or manual stimulation was facilitated by all estrogens. All estrogens caused a slight weight increase of the seminal vesicles, ventral prostate and glans penis.     

Serum estradiol, testosterone and dihydrotestosterone in male monkeys treated with testosterone propionate.

Serum estradiol (E2), testosterone (T) and dihydrotestosterone (DHT) were measured in juvenile (pre-pubertal) male rhesus monkeys injected with either 8 mg or 80 mg of testosterone propionate (TP). After one week, the three steroids were elevated and remained essentially unchanged for the duration of the study. There was little difference in serum E2 or DHT when comparing the two groups of steroid-treated monkeys. In contrast, T levels were consistently greater in the animals given the high dosage of TP.     

Influence of progesterone on sexual behavior in castrated male rhesus monkeys treated with testosterone

The effect of progesterone (P) on sexual behavior was tested in five long-term castrated rhesus monkeys treated simultaneously with testosterone (T) and P. A control group consisting of three long-term castrates was treated only with T. Plasma levels of T and P were measured at weekly intervals, and behavioral data were collected for each animal twice a week throughout the study. Progesterone has been reported to inhibit sexual behavior in male guinea pigs and mice, but the levels of behavior in our two groups of monkeys did not differ from each other over 8 weeks of treatment and testing.     

Plasma testosterone and sexual behavior following intracerebral implantation of testosterone propionate in the castrated male rat

Interpretation of behavioral and other effects of intracranial steroid implants depends on knowledge of the rate of release of the implanted hormones into the general circulation. Testosterone propionate implants (200 μg, pellets) in the median eminence and pituitary were found to result in circulating levels of testosterone (T) twice as high as those in the anterior hypothalamus-preoptic area (AHPOA), posterior hypothalamus (PH), and cortex (Ctx). Implants in all cranial areas examined resulted in plasma T levels in the lower range of circulating T found in normal rats for the first 24 hr postoperatively, decreasing thereafter and reaching very low levels by the end of 2 weeks. There were no significant differences in the plasma T levels in rats with implants in the AHPOA, PH, and Ctx, but AHPOA implants were slightly more effective in restoration of sexual behavior than PH implants, and both of these implants were considerably more effective than those in the cortex. There was no apparent correlation between behavioral responses and peripheral levels of T. The major conclusion of this study was that the effects of hypothalamic implants of T on male sexual behavior cannot be explained by the presence of T in the peripheral circulation.     

Role of dihydrotestosterone in the control of sexual behaviour on castrated male sheep

Wethers (at least 2 1/2 years after castration) were implanted with testosterone propionate (TP), oestradiol dipropionate (ODP), dihydrotestosterone, or a combination of dihydrotestosterone and ODP Silastic capsules. Active immunization against both oestradiol and oestrone or oestradiol only was used to negate effects of oestrogens produced by aromatization of TP. On exposure to oestrous ewes, immunization of wethers implanted with TP significantly (P less than 0.01) reduced all components of mating behaviour (except sniffing and Flehmen) to levels seen in untreated controls. The results support the conclusion that dihydrotestosterone potentiates the action of oestrogens, particularly as regards Flehmen, and has no action on its own within the central nervous system, while oestrogens do not restore mating activity to the same level as that following treatment with testosterone.     

Effect of forebrain implants of testosterone or estradiol on scent-marking and sexual behavior in male and female rabbits

Chinning consists of rubbing the chin against an object, thereby depositing secretions from the submandibular glands. As mating, chinning is stimulated in male and female rabbits by testosterone and estradiol, respectively. To investigate the brain sites where steroids act to stimulate chinning and mating we implanted into the ventromedial hypothalamus (VMH) or the medial preoptic area (MPOA) of gonadectomized male and female rabbits testosterone propionate (TP; males) or estradiol benzoate (EB; females) and quantified chinning and sexual behavior. EB implants into the VMH or MPOA reliably stimulated chinning in females. Most of those implanted into the VMH and around half of the ones receiving EB into MPOA or diagonal band of Broca (DBB) showed lordosis. Chinning, but not sexual behavior, was stimulated in males by TP implants into the MPOA or DBB. Neither chinning nor mounting were reliably displayed by males following TP implants into the VMH. Results indicate that, in females, the VMH is an estrogen-sensitive brain area that stimulates both chinning and lordosis while the MPOA seems to contain subpopulations of neurons involved in either behavior. In males, androgen-sensitive neurons of the MPOA, but not the VMH, are involved in chinning stimulation but it is unclear if these areas also participate in the regulation of copulatory behavior.     

Effect of forebrain implants of testosterone or estradiol on scent-marking and sexual behavior in male and female rabbits

Chinning consists of rubbing the chin against an object, thereby depositing secretions from the submandibular glands. As mating, chinning is stimulated in male and female rabbits by testosterone and estradiol, respectively. To investigate the brain sites where steroids act to stimulate chinning and mating we implanted into the ventromedial hypothalamus (VMH) or the medial preoptic area (MPOA) of gonadectomized male and female rabbits testosterone propionate (TP; males) or estradiol benzoate (EB; females) and quantified chinning and sexual behavior. EB implants into the VMH or MPOA reliably stimulated chinning in females. Most of those implanted into the VMH and around half of the ones receiving EB into MPOA or diagonal band of Broca (DBB) showed lordosis. Chinning, but not sexual behavior, was stimulated in males by TP implants into the MPOA or DBB. Neither chinning nor mounting were reliably displayed by males following TP implants into the VMH. Results indicate that, in females, the VMH is an estrogen-sensitive brain area that stimulates both chinning and lordosis while the MPOA seems to contain subpopulations of neurons involved in either behavior. In males, androgen-sensitive neurons of the MPOA, but not the VMH, are involved in chinning stimulation but it is unclear if these areas also participate in the regulation of copulatory behavior.     

The influence of androgenic and estrogenic hormones on sexual behavior in castrated adult male pigs

The objectives of these studies were to evaluate the influence of testosterone propionate (TP), estradiol cypionate (EC), dihydrotestosterone propionate (DHTP), EC + TP, EC + DHTP, and TP + DHTP on traits of masculine sexual behavior in castrated adult male pigs of different breeds. Masculine sexual behavior was restored and maintained by TP, whereas EC initially activated sexual behavior, including copulation and ejaculation, but was unable to sustain copulatory behavior for the 8- to 18-week periods that were evaluated. Treatment with DHTP was ineffective for stimulation of sexual behavior; thus, it is suggested that testosterone promotes some aspects of masculine sexual behavior in male pigs via aromatization to estrogen, but both androgen and estrogen are required for maintenance of the full complement of masculine sexual behavior traits.     

Sustained influence of previous estradiol or testosterone treatments on sexual behaviors of female pigs

Two studies were conducted to determine the consequences of extended treatment with estradiol or testosterone on sexual behavior in postpubertal, female pigs. After ovariectomy, either steroid was administered for 6 weeks at dosages sufficient to maintain serum concentrations similar to those observed in mature male pigs. Behavioral evaluations were initiated 2 months after the last steroid treatment. These treatments reduced receptivity (immobile stance when placed with a mature male) and proceptivity (preference to remain near a mature male) in association with an increase in aggressive behavior. In females treated previously with both estradiol and progesterone, sexual behaviors 2 months later were similar to those of control females. When evaluations were repeated 5 months after extended estradiol treatment had ceased, receptivity and proceptivity had returned to that of control pigs and aggressive behavior had diminished greatly. Interpretation of these changes in behavior is that extended periods of estradiol or testosterone treatment sustain activational influences for a considerable amount of time after treatments cease and progesterone antagonizes estradiol's effect on these behaviors. In a companion study, pubertal and post-pubertal females were similar for receptivity but pubertal females spent less time near a mature male. This difference in proceptivity likely reflects a maturational change associated with sexual development in female pigs. Collectively, these observations in postpubertal, female pigs document that prolonged estrogen treatment will activate aggressive behaviors in association with reduced proceptivity and receptivity. Because these behavioral changes are reversible by 5 months after cessation of treatment, they are not the result of sexual differentiation.     

Effects of intracranial implants of dihydrotestosterone on the reproductive physiology and behavior of male guinea pigs

An experiment was conducted to determine whether the intracranial application of dihydrotestosterone (DHT), a nonaromatizable androgen, would stimulate male guinea pig mating. Of three castrate groups studied, one was a control group in which subjects were implanted both in the medial preoptic area (MPOA) and under the skin with cannulae containing cholesterol (NoDHT). Males in one of the experimental groups received implants of cholesterol in the MPOA plus subcutaneous implants containing DHT (ScDHT). Members of the other experimental group were subcutaneously implanted with cholesterol and simultaneously given intracranial implants of DHT (IcDHT). Compared to either the NoDHT control group of the ScDHT experimental group, greater numbers of males in the IcDHT group displayed mounts (P less than 0.01), intromissions (P less than 0.01), and ejaculations (P less than 0.001). Additionally, the hypothalamic implants of DHT had no significant effects on peripheral target tissues. These data indicate that androgenic stimulation of the guinea pig brain is sufficient to activate masculine sexual behavior in this species.     

Differential effects of testosterone plus dihydrotestosterone on male courtship of castrated newts, Taricha granulosa

Sexually responsive Taricha granulosa males were castrated and implanted with testosterone (T), dihydrotestosterone (DHT), T plus DHT, or no steroid. The incidence of sexual behavior was highest in castrates implanted with T plus DHT. Newts implanted with T or DHT exhibited sexual behavior more frequently than did the untreated castrates, which exhibited none during the last 5 days of testing. A second experiment was conducted using sexually unresponsive males. The occurrence of sexual behavior remained low in castrates implanted with T plus DHT, untreated castrates, and intact control males. These results support the hypothesis that for this species of amphibian the presence of adequate levels of testicular androgen is a necessary, but not sufficient, condition for the manifestation of sexual behavior; the appearance of these behaviors requires, in addition, the presence of some nontesticular hormone.     

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.     

Effects of estradiol benzoate, estrone, and propionates of testosterone or dihydrotestosterone on sexual and related behaviors of ovariectomized rhesus monkeys

Ovariectomized adult rhesus monkeys were injected daily for 10 days with either 1 mg of dihydrotestosterone propionate (DHTP), 1 mg of testosterone propionate (TP), 10 μg of estradiol benzoate (EB), or 500 μg of estrone (El). On the 5th and 10th days of treatment, females received two 24-min behavioral tests with each of two adult males. All females received every hormonal treatment during the course of the study, with the order of treatments counterbalanced. Prior to the initiation of an hormonal treatment, each subject received two tests with no hormone treatment (NORX). Three behaviors related to female proceptivity were recorded. Treatment with DHTP had no influence on any aspect of proceptivity measured, in comparison to the NORX condition, whereas El or TP treatment augmented the frequencies of two of the proceptive behaviors and EB increased all three. The response of the male toward the female was influenced by the female's hormonal condition. Treatment with TP or DHTP did not increase the frequency of male contact or the mount rate in comparison to the NORX condition, whereas EB or El treatment did. In addition, DHTP was the only steroid which failed to increase the percentage of tests with intromission or ejaculation when compared to NORX. Female receptivity, as measured by acceptance or rejection of male contacts, was not different for the NORX-, TP-, EB-, or El-treated conditions. DHTP treatment, however, reduced female receptivity in comparison to all other conditions. Treatment with DHTP or TP resulted in an increase in the frequency of female yawning behavior, whereas neither estrogen treatment showed any effect on this behavior. The influences of TP on female proceptive and male sexual behavior were never duplicated or even approximated by treatment of females with the nonaromatizable DHTP. Nor was there any evidence that TP inhibited female receptivity below the level characteristic of NORX females, as was true for DHTP.     

Steroidal control of sexual behavior in the rough-skinned newt (Taricha granulosa): effects of testosterone, estradiol, and dihydrotestosterone

Adult, sexually mature, male rough-skinned newts (Taricha granulosa) obtained from a wild population were castrated and received Silastic capsules containing testosterone (T), estradiol (E), or 5 alpha-dihydrotestosterone (DHT). The newts received three capsules of T, either one or three capsules of E or DHT, or combined treatments with these two steroids. When tested for sexual responsiveness after 32 and 34 days of steroid treatment, no group differed from the castrated controls (C). After 74 and 75 days of treatment, more T-implanted than C newts were sexually responsive, but the newts treated with E, DHT, or these two steroids in combination did not differ behaviorally from the C group. The diameter of the vas deferens was greater in the T- and DHT-treated males than in the C males, indicating that the implants adequately replaced testicular androgens. Together with other studies on this and other species, these results confirm the participation of testosterone in the regulation of sexual behaviors in male amphibians. Furthermore, these results indicate that in this amphibian, the behavioral effects of T are mediated directly by this steroid, not indirectly by enzymatic conversion to DHT or E.     

Uterine position and the activation of male sexual activity in testosterone propionate-treated female guinea pigs

Fetal female guinea pigs were delivered surgically and their position within a uterine horn relative to male fetuses was noted. When adult they were ovariectomized, injected daily with testosterone propionate, and examined for male copulatory behaviors in response to the presence of a receptive female. Females that developed contiguous to a caudal male were functionally similar to those that had been situated between two males; both exhibited enhanced levels of mounting relative to females that were located contiguous to no males (with and without the presence of a caudal male) and to females contiguous to a cephalic male. Therefore, both contiguity and positioning of the male fetus are necessary conditions for prenatal masculinization of the female guinea pig. Lastly, four animals that had resided singly in the uterus displayed the lowest levels of copulatory behaviors.     

Theophylline, otentiation of testosterone propionate or estradiol bensoate in inducing male but not female sexual behavior in the female rat.

Two experiments were carried out to assess the possible involvement of 3′:5′cyclic adenosine monophosphate (cAMP) in the hormonally mediated activation of masculine and feminine sexual behavior in female rats. In Experiment I, theophylline, a compound shown to be effective in inhibiting the degradation of cAMP, was combined with estradiol benzoate (EB) in an attempt to potentiate the action of estradiol for inducing feminine or masculine sexual behavior. Theophylline, when administered in combination with EB to ovariectomized females, resulted in an increase in masculine sexual behavior but no potentiating action on female receptivity. In Experiment II, theophylline, when given to female rats, potentiated the action of testosterone propionate in stimulating male but not female sexual behavior. These data suggest that estradiol and testosterone may be activating masculine sexual behavior through similar biochemical mechanisms. Likewise, cAMP may be involved in the activation of masculine but not feminine sexual behavior by gonadal steroids.