Sexual behavior in response to testosterone in old long-term-castrated rhesus males

The sexual behavior of 20-year-old long-term-castrated and intact male rhesus macaques (Macaca mulatta) was observed. In the first experiment we compared the sexual behavior of males tested in 1980 with their performance in 1970 (before castration and sham castration) and in 1971 (1 year after the operation). In 1971 and 1980, the castrated males were tested while under testosterone propionate treatment. The castrated and intact males did not differ in any measures of sexual behavior over the 10-year period, but both groups showed a decline in the percentage of tests with intromissions and ejaculations; a decline in the rates of contacting, mounting, and intromitting; and an increase in the latencies to contact, intromit, and ejaculate. In a second experiment, the sexual performances of old castrated and intact males were compared to those of young intact males (8 to 12 years). The intromission rate and the percentage of tests with intromissions were significantly greater in young males than in old intact males, but did not differ from values for old castrated males. The old castrated and old intact males did not differ from each other in these measures. Young males had a higher percentage of tests with ejaculation than either group of old males. We have concluded that old long-term-castrated rhesus males retain the potential to display sexual behavior at levels comparable to those observed in old intact males.     

Sexual behavior of castrated male rhesus monkeys treated with 19-hydroxytestosterone

The sexual behavior of 10 adult long-term castrated rhesus monkeys before and after treatment with 19-hydroxytestosterone (19-OH-T) was compared. Only the rate at which males contacted females increased significantly after treatment. The sexual behavior of these castrates was also compared with that of 8 untreated intact controls. Levels of estradiol-17β (E₂) and luteinizing hormone (LH) in peripheral plasma were determined by radioimmunoassay both before and after 19-OH-T treatment. After treatment, there was a significant increase in E₂ levels and a significant decrease in LH levels. Only the 5 males that had showed the ejaculatory response before treatment displayed it while undergoing treatment. These males had the lowest E₂ level during treatment whereas the 5 males that had failed to achieve intromission and ejaculation had the highest levels of E₂. The mounting rate correlated negatively with the level of E₂ in the blood.     

Naltrexone effects on male sexual behavior, corticosterone, and testosterone in stressed male rats

Chronic physical or psychological stress disrupts male reproductive function. Studies in our laboratory have shown that stress by immersion in cold water (ICW) and by electrical foot shocks (EFS) has inhibitory effects on male sexual behavior; these effects do not seem to be mediated by an increase in corticosterone, nor by a decrease in testosterone. On the other hand, it is known that endogenous opioids are released in the brain in response to these same stressors; consequently, they could be participating in the impairment of sexual behavior, as well as in the changes in corticosterone and testosterone caused by stress. The aim of this study was to analyze the effects of the opioid antagonist naltrexone (NTX) on male sexual behavior, corticosterone, and testosterone in both stressed sexually experienced and naive male rats. Sexually experienced adult male rats were assigned to one of the following groups (n = 10 each): 1) control group, males without sexual evaluation; 2) control group, rats injected ip with saline, non-stressed; 3) control group, rats injected with NTX (3 mg/kg) non-stressed; 4) rats injected ip with saline, and stressed by EFS; 5) rats injected ip with NTX (1.5 mg/kg) and stressed by EFS; 6) rats injected ip with saline and stressed by ICW; 7) rats injected ip with NTX (1.5 mg/kg) and stressed by ICW; 8) rats injected ip with NTX (3 mg/kg) and stressed by ICW. Naive males were assigned to the same control groups but only stressed by ICW and the NTX dose used was 3 mg/kg. Injections were given 30 min before stress sessions. Stress was applied on 20 consecutive days. Male sexual behavior was assessed 15 min after EFS or 30 min after ICW, on days 1, 4, 8, 12, 15, and 20. Trunk blood was collected at the end of the experiments on day 20 of stress. Corticosterone and testosterone were evaluated by HPLC.Mount, intromission and ejaculation latencies were longer in control saline naive males compared to control saline sexually experienced males on the first day. NTX administration to control naive males caused a decrease in mount, intromission, and ejaculation latencies, as well as an increase in ejaculatory frequency/30 min, compared to control-saline only on day 1. Stressed naive males showed higher mount, intromission and ejaculation latencies, compared to control and stressed sexually experienced males, as well as comparable increase in corticosterone and decrease in testosterone plasma levels. NTX administration before exposure to stress prevented the modifications caused by stress in sexual parameters. Sexual behavior in control sexually-active males injected with saline or NTX was not modified. Saline stressed males showed the previously reported alterations in sexual behavior, as well as an increase in corticosterone and a decrease in testosterone plasma levels. Stressed males injected with NTX before exposure to stress showed no alterations in male sexual behavior. NTX in control non-stressed males did not modify corticosterone plasma levels, but did cause a significant increase in plasma testosterone. The increase in corticosterone and the decrease in testosterone due to stress, were attenuated with the opioid antagonist, both in naive and sexually experienced males. Prevention of ICW stress effects was more effective with higher doses of NTX (3 mg/kg). These data suggest that endogenous opioids could be participating in the effects caused by stress on male sexual behavior, corticosterone, and testosterone.     

Hyperprolactinemia and male sexual behavior: effects of steroid replacement with estrogen plus dihydrotestosterone

To determine if alterations in the availability of the active metabolites of testosterone (T) are involved in the inhibition of sexual activity in hyperprolactinemic animals, the effects of four ectopic pituitary grafts on copulatory behavior were examined in castrated male rats given subcutaneous implants of T or estradiol-17 beta (E2) plus 5 alpha-dihydrotestosterone (DHT). Two weeks after implantation of the steroid-filled capsules, half the animals of each group were given pituitary grafts and the remainder were sham-operated. Tests of copulatory behavior were performed prior to, and one, two, and three months following pituitary transplantation. Pituitary grafting caused significant inhibition of copulatory behavior in both T and E2 + DHT treated animals. PRL levels were significantly higher in E2 + DHT treated grafted males than in T treated grafted animals (2000 +/- 140 vs. 395 +/- 26 ng/ml), but did not differ between the corresponding control groups (61 +/- 8 vs. 73 +/- 6 ng/ml). The results of these experiments preclude the possible involvement of alterations in steroid secretion by the testes or modifications of the conversion of T to its active metabolites in the effects of hyperprolactinemia on copulatory behavior.     

Relationship of free and bound testosterone to sexual behavior in old rhesus males

Total serum testosterone concentrations, percentage of total serum testosterone bound to testosterone-binding globulin (TeBG), and estimates of free testosterone concentrations were determined in old and young male rhesus macaques. Also the sexual performance of the old (20 years and older) males was studied. The two groups did not differ in either the mean level of total testosterone or the index of free testosterone but the old males had a significantly higher percentage of testosterone bound to TeBG than did the young (10 years old) ones. We found significant negative correlations between the percentage of testosterone binding and sexual behavior in the old males. The percentage of bound testosterone was negatively correlated with the rates of contacting females, mounting, and intromission, and with the percentages of tests during which intromission and ejaculation occurred. Neither the total serum testosterone level nor the index of free testosterone correlated with the level of sexual performance.     

Effects of bilateral amygdaloid lesions on gonadal and pituitary hormones in serum and on sexual behavior in female rhesus monkeys

Bilateral lesions that destroyed the amygdaloid nuclear complex failed to alter either serum concentrations of luteinizing hormone (LH), estradiol (E2), progesterone, and testosterone or sexual behavior in female rhesus monkeys. In 3 of 5 females ovulation occurred in the postoperative cycle, and in 4 of 5 females exogenous E2 treatment released a surge of LH whose pattern was indistinguishable from the normal preovulatory surge. A postcastration rise in serum LH also occurred in the 5 lesioned monkeys, and E2 again induced an LH release. The data suggest that the amygdala does not play a major role in regulation of LH or ovarian steroid secretion during the menstrual cycle. Moreover amygdaloid lesions in female monkeys do not alter their sexual behavior.     

Neonatal bonadal hormones: effect on maternal and sexual behavior in the male rat

Neonatal exposure of rats to androgen results in alteration of adult sex behavior and gonadotropin release. Other sexually dimorphic adult behaviors have also been shown to be dependent, either in part or in full, upon exposure to androgen neonatally. The present study was conducted to determine the effect of neonatal androgens in organizing the brain of the male rat (Long-Evans strain) with regard to maternal behavior. The results indicate that males neonatally exposed to androgen exhibit poor maternal behavior as adults when compared to males castrated at birth and males receiving gonadotropin antiserum in infancy. The males castrated at birth and males receiving gonadotropin antiserum in infancy, when primed with estrogen and progesterone, showed high levels of female sexual behavior when compared to controls. In terms of male sex behavior, the control groups performed slightly better than the males castrated at birth and males receiving antisera in infancy. The results suggest that the neonatal pituitary gland has an indirect role in the process of sexual differentiation.     

The effects of testosterone and its metabolites on sexual behavior and morphology in male and female Japanese quail

Adult Japanese quail are sexually dimorphic. Even when implanted with testosterone (T), ovariectomized females fail to copulate and their cloacal glands are smaller than those of males. This may be due to a reduced capacity of the females to transform testosterone into active metabolites (estradiol-17β and 5α-dihydrotestosterone). Indeed, in the male quail, estradiol-17β (E₂) activates copulation whereas 5α-dihydrotestosterone (5α-DHT) activates crowing, strutting and the development of the cloacal gland. To test this hypothesis, we studied the effects of in vivo treatments of male and female quail with the different T-metabolites. Forty-one castrated male and female quail were implanted with subcutaneous silastic implants of T, 5α-DHT, E₂ and E₂ in combination with 5α-DHT. When implanted with these metabolites, females failed to copulate and their cloacal glands remained less developed than those of males. Sexual differences in behavior and morphology thus cannot be entirely explained by sexual dimorphism of the metabolism.     

Old age and sexual exhaustion in male rhesus macaques

The capacity for multiple ejaculations was measured in three groups of rhesus macaques whose ages ranged from 9 to 30 years. Each male was given a test of sexual exhaustion with each of five ovariectomized, estrogen treated females. Sexual exhaustion was defined as a 45-min period without a mount when the males were paired with a female. None of the very old males (25-30 years, N = 4) achieved more than two ejaculations before reaching sexual exhaustion. Old males (19-20 years, N = 5) displayed as many as six ejaculations and fully adult (9-15 years, N = 5) males achieved a maximum of five ejaculations before meeting the criterion of sexual exhaustion. Although very old males mounted as often as younger males they achieved fewer intromissions and the latency to intromission and ejaculation was longer. Mean mount and ejaculation latencies and the postejaculatory interval increased after ejaculation in all age groups. The females were not equally attractive sexually to the males and very old males were especially selective, copulating with only three of the females.     

Ejaculation is important for mating-induced testosterone increases in male rhesus monkeys

Sexual behavior of male and estrogen-treated female rhesus monkeys was observed at 1000 and 1400 hr within and outside the breeding season. Blood samples for analysis of testosterone were taken before and after these 1 hr behavioral tests. Group testosterone levels increased significantly only during the one condition in which over half of the males ejaculated (in season afternoon), and only in those males actually ejaculating. In other time and seasonal conditions, increases in testosterone were observed when tests without ejaculation were eliminated from analysis. Furthermore, males in which testosterone levels increased following ejaculation displayed no increase when caged alone for an equivalent time period, or when tested with an untreated, ovariectomized female. These results suggest that ejaculation (rather than other aspects of the test setting) may be critical for the occurrence of androgen increases.     

Social and seasonal influences on testosterone secretion in the male rhesus monkey.

Adult male rhesus monkeys, maintained in all-male social groups housed such that only distal contact with female rhesus was possible, exhibited a seasonal testosterone rhythm indistinguishable from the pattern previously reported for male rhesus housed with females. In contrast, males maintained in social groups isolated from all contact with females failed to exhibit the typical seasonal pattern. In the latter instance, testosterone levels during the mating season were intermediate between the typical birth season low and mating season peak. These data suggest that the annual testosterone rhythm in male rhesus monkeys is mediated by stimuli from females, and confirm that these stimuli may be distal in nature, since sexual access to the females is not required. The intermediate increase exhibited by males isolated from females suggests that two different factors may play a role in regulating the annual testosterone cycle.     

Effects of dihydrotestosterone on sexual behavior of castrated male rhesus monkeys

The sexual and sex-related behavior of 10 adult male rhesus monkeys castrated three years earlier was studied in pair tests with receptive females. Their performance before and during treatment with 1 mg/kg dihydrotestosterone propionate (DHTP) was compared. Nine unoperated adult males served as controls. DHTP effectively rendered the performance level of the castrates comparable to that of the intact controls.     

Role of testosterone secretion and penile reflexes in sexual behavior and sperm competition in male rats: a theoretical contribution

A number of experiments have documented that when male rats are exposed to female rats they undergo a marked increase in the secretion of luteinizing hormone and testosterone. This response can be conditioned to other, previously neutral, stimuli associated with mating. Recent work has highlighted the remarkable sensitivity of penile reflexes to fluctuations in blood concentration of testosterone. Other work has pointed to the function of penile reflexes in seminal plug removal and deposition. It is hypothesized that penile reflexes are potentiated by the increase in testosterone that occurs in response to sexually relevant cues and that the potentiated reflexes play a role in sperm competition during multi-male mating encounters. The sperm competition centers around a male rat's ability to dislodge seminal plugs left in the vagina by other males and to deposit his own plug as tightly as possible to resist dislodgement by another.     

Development of olfactory-guided behavior in the golden hamster.

Hamster pups were tested for an odor preference every day from 1-16 days of age with shavings from their home cage and with clean wood shavings. The hamster pups showed a clear preference for their home cage shavings by 8 days of age. They were then tested for preferences with other odor combinations. Tests for preference with other odor pairs indicate that this preference is due to a change in the hamsters rather than a change in the stimulus. In these tests the hamster pups did not demonstrate a preference for their home shavings over shavings in which a nonlactating female had lived. Further tests will have to be done to determine how specific the hamster pup's olfactory preferences are.     

Stress and sexual behavior in male rats

The relationship between sexual behavior and stress in male rats was investigated. Stress induction by psychophysical immobilization fo 3 hours along three days caused significant alterations of the different parameters which make up the sexual behavior of male rats. An extension of the stressing situation from 3 to 6 hours under the same experimental conditions produced very similar sexual disturbances. Our experimental results suggest that effects of acute stress on sexuality may be independent of time.     

The relation between sexual behavior and seminal fructose in intact and castrated rabbits

Seminal fructose and sexual behavior were studied in intact and castrated, testosterone treated rabbits. Both seminal fructose and the intensity of sexual behavior increased after testosterone treatment. The dose-response relations were quite different for the two variables. A dose of 7.5 mg testosterone propionate injected every third day during the experiment restored the sexual behavior to precastrational levels, whereas a dose of 30 mg TP was insufficient to give seminal fructose concentrations comparable to those in the intact animals. There were no correlations between sexual behavior and seminal fructose in individual animals. Neither were any such correlations found in the intact animals. The data seem to support the idea of different hormonal mechanisms controlling sexual behavior and activity in the accessory sexual glands.     

Interaction of androgens and estrogens in the control of sexual behavior in male Japanese quail

A series of 4 experiments was performed to study the relative contribution of androgens and estrogens in the activation of sexual behavior in castrated male quail. The synthetic androgen methyltrienolone (R 1881) which is not metabolized in androgen target tissues activated sexual behavior in castrated birds and at the dose level of 0.5-1 mg/day/animal had the same potency as testosterone (T). However R 1881 was much more active than T in the induction of cloacal gland growth and activation of crowing, two typically androgen-dependent responses. This suggests that sexual behavior is not controlled by exactly the same mechanism as crowing or cloacal gland growth. In another experiment, estradiol (E2) alone activated sexual behavior but it is only at very high doses which had clear toxic effects that a significant behavioral activation could be observed. This questions the role of E2 as the physiological agent stimulating copulation in intact birds unless it is assumed that centrally administered E2 would be much more active compared to peripheral E2 which is exposed to a very intense peripheral catabolism. In the last two experiments, a clear synergism could be detected between 5 alpha-dihydrotestosterone (5 alpha-DHT) and E2 in the activation of sexual activity and doses of hormones could be defined which had almost no activity by themselves but significantly stimulated sexual behavior when given simultaneously. It was however impossible to define a hormonal treatment with T metabolites which restored behavior to its precastration level, a result very easily achieved with T treatments. Taken together, these data suggest that activation of sexual behavior in quail does not depend only on E2, nor 5 alpha-DHT nor even on their combined action. Considering that specific T receptors which probably do not bind 5 alpha-DHT are present in the brain, it would seem justified to reconsider the possible role played by T itself in the activation of behavior.     

Estradiol facilitates mounting behavior in male green anole lizards

Steroid hormones activate sexual behaviors across vertebrate species. In green anole lizards, testosterone is particularly important for the display of courtship and copulation by adult males. However, unlike a variety of other species, the role of its metabolite, estradiol, has been unclear. To evaluate its function and potential interaction with testosterone in the facilitation of reproductive behaviors, adult males were gonadectomized and given two treatments. The first consisted of either estradiol or its vehicle, and the second testosterone or a blank control. Parallel manipulations were done in the breeding and non-breeding seasons. Courtship and copulatory behaviors were more readily facilitated during the breeding than non-breeding season. As predicted based on previous experiments, testosterone increased the display of sexual behaviors. In addition, estradiol increased mount attempts. While this hormone did not influence the effects of subsequent testosterone exposure, the present data are consistent with the idea that it facilitates a component of reproduction in the green anole, as in species from other taxa.     

Increasing dosages of estradiol benzoate activate equivalent degrees of sexual receptivity in gonadectomized male and female ferrets

Daily SC injections of increasing dosages (0, 2, 4, 6, 8, or 10 μg/kg) of estradiol benzoate (EB) dissolved in sesame oil caused equivalent increments in acceptance quotients displayed by adult, gonadectomized male and female ferrets in response to a stimulus male. This finding provides further evidence that in the ferret behavioral defeminization normally is not a consequence of perinatal exposure to testicular androgen.     

Self-injurious behavior in male rhesus macaques does not reflect externally directed aggression

Self-injurious behaviors (SIB), such as self-biting and self-wounding, have been observed in a small percentage of captive nonhuman primates. Because rhesus monkeys that exhibit SIB also tend to be more aggressive, it was hypothesized that SIB is related to externally directed aggression and is associated with contexts in which physical contact between participants is prevented. The purpose of this study was to test the hypothesized relationship between SIB and outward aggression. Subjects were first presented with videotapes of conspecifics, scenery and a blank screen, and their behavior was recorded. Levels of salivary cortisol, an indicator of stress, were also measured before and after presentation of the videos. Although aggression increased when subjects viewed tapes containing conspecifics, neither cortisol levels nor self-biting behavior varied as a function of tape content. The subjects were then placed in two additional test situations: an empty room and the same room containing an unfamiliar conspecific. Aggression was significantly higher in the stranger condition compared to the empty room condition. The two situations yielded parallel increases in cortisol, suggesting that being alone was just as stressful as being paired with an unfamiliar conspecific. Self-biting rates were also similar in these two conditions. Thus, contrary to our prediction, increases in aggression did not correlate with increases in SIB. These results suggest that under similarly stressful conditions, SIB and externally directed aggression are unrelated.