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.     

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.     

Influence of photoperiod on the secretion of testosterone as a response to sexual stimulus in male goats

Monthly sexual behavior tests were carried out for 1 yr in a group of 19 male goats (10 Verata breed and 9 Malague?a breed) 12 mo of age. Simultaneously with the tests, 5 blood samples were collected, 2 before and 3 after contact with females, to determine the influence of sexual stimulus on the secretion of testosterone. By means of radioimmunoassay, it was determined that both breeds showed a significant increase in testosterone secretion as a result of the sexual stimulus during increasing daylength (Verata: P<0.01; Malague?a: P<0.05), when testosterone secretion levels prior to the stimulus were the lowest of the year. Moreover, the level of testosterone secretion was higher in the Verata than in the Malague?a breed (P<0.01). A significant though low correlation (P<0.05) between the rise of testosterone levels as a response to sexual stimulus and the degree of sexual behavior in the males was observed in the Verata breed. However, there was no correlation between these factors in Malague?a male goats.     

Effect of newborn rat testes on the male sexual behavior of the testosterone-treated adult

Neonatal male rats were castrated either at 0, 6 or 24 hrs. after birth. As adults, testosterone was delivered by subcutaneous implantation of a Silastic capsule containing this hormone. The probability to display mounting behavior in presence of an estrous female was lower when the animals were castrated at 0 hr. than at 6 or 24 hrs. or when they received a subcutaneous injection of 1 microgram of testosterone propionate, at the time of castration at 0 hr. These results suggest that in the rat, during the 6 hrs. following birth, neonatal testes influence the sensitivity of the adult central nervous system to testosterone.     

Adrenocorticotropin administration increases testosterone secretion in adult male rats

It appears that the effect of acute administration of pituitary-adrenal hormones on the pituitary-gonadal axis is species-dependent. However, no information is available with regard to the effect of acute adrenocorticotropin (ACTH) administration on testosterone secretion in rats. The present data indicate that acute ACTH administration can increase serum testosterone levels without modifying luteinizing hormone (LH) levels. Since this rise was not observed in castrated rats, it must be assumed that increased serum testosterone was of gonadal origin. The action of ACTH on testosterone secretion was likely an indirect one since there is no evidence at present for a direct, short-term action of the pituitary-adrenal axis on Leydig cell function.     

Effects of increased testosterone secretion on the behavior of adult male rhesus living in a social group.

Selected members of an all-male social group of rhesus monkeys were treated with twice-weekly injections of human chorionic gonadotropin (HCG) to determine the effects of the consequently increased androgen secretion on social behavior. Radioimmunoassay of blood samples confirmed significant increases in serum testosterone levels in each of 4 subject, but only 3 of these showed significant behavioral changes. The basic social structure of the group, including the dominance hierarchy, was not disrupted by the treatment with HCG. Rather, the behavioral changes which did not occur appeared to be intensifications of previously existing social relationship.     

Studies on feminine sexual behavior in the male rat: Influence of olfactory stimuli

The aim of this study was to determine if the display of lordosis behavior in the male rat could be influenced by the olfactory environment. Unexperienced adult male rats were orchidectomized (ORCH). They were primed with 75 μg estradiol benzoate and 1 mg progesterone was injected at an interval of 39 hr following long-term (LT = 3 weeks) or short-term (SHT = 8 hr 30 min) exposure to the odor of male or female urine. For 10 min they were placed in the presence of a “stimulus” male of proven sexual vigor 9 hr 30 min ± 1 hr after progesterone injection. Both LT and SHT exposure to the odor of male urine caused a significant increase in the number of ORCH rats which showed lordosis response to male mounts compared to either the ORCH rats exposed to the odor of female urine or to the controls. Following complete olfactory bulb removal (COBR), no difference was observed in the occurrence of lordosis behavior between the ORCH rats whether or not exposed to the odor of urine. For the ORCH-COBR rats exposed to male urine the proportion of animals responding to mounts did not differ from that of their nonbulbectomized counterparts. In comparing the effects of COBR vs anterior olfactory bulb removal (AOBR) lordosis behavior occurred more frequently in COBR than in AOBR-ORCH rats. The lordosis quotient (LQ) was not affected by exposure to the odor of male urine in the nonbulbectomized ORCH rats. In contrast, it appeared to be higher in both COBR and AOBR animals than in their nonbulbectomized counterparts. The olfactory bulbs were then concluded to inhibit the display of lordosis behavior in the male rat. It was also thought that the olfactory stimuli originating from male urine were capable of releasing the hypothalamic structures involved in the control of lordosis behavior of the male rat from an olfactory inhibitory influence.     

Cell proliferation and survival in the mating circuit of adult male hamsters: Effects of testosterone and sexual behavior

The transient actions of gonadal steroids on the adult brain facilitate social behaviors, including reproduction. In male rodents, testosterone acts in the posterior medial amygdala (MeP) and medial preoptic area (MPOA) to promote mating. Adult neurogenesis occurs in both regions. The current study determined if testosterone and/or sexual behavior promote cell proliferation and survival in MeP and MPOA. Two experiments were conducted using the thymidine analog BrdU. First, gonad-intact and castrated male hamsters (n = 6/group) were compared 24 h or 7 weeks after BrdU. In MeP, testosterone-stimulated cell proliferation 24 h after BrdU (intact: 22.8 ± 3.9 cells/mm², castrate: 13.2 ± 1.4 cells/mm²). Testosterone did not promote cell proliferation in MPOA. Seven weeks after BrdU, cell survival was sparse in both regions (MeP: 2.5 ± 0.6 and MPOA: 1.7 ± 0.2 cells/mm²), and was not enhanced by testosterone. In Experiment 2, gonad-intact sexually-experienced animals were mated weekly to determine if regular neural activation enhances cell survival 7 weeks after BrdU in MeP and MPOA. Weekly mating failed to increase cell survival in MeP (8.1 ± 1.6 vs. 9.9 ± 3.2 cells/mm²) or MPOA (3.9 ± 0.7 vs. 3.4 ± 0.3 cells/mm²). Furthermore, mating at the time of BrdU injection did not stimulate cell proliferation in MeP (8.9 ± 1.7 vs. 8.1 ± 1.6 cells/mm²) or MPOA (3.6 ± 0.5 vs. 3.9 ± 0.7 cells/mm²). Taken together, our results demonstrate a limited capacity for neurogenesis in the mating circuitry. Specifically, cell proliferation in MeP and MPOA are differentially influenced by testosterone, and the birth and survival of new cells in either region are not enhanced by reproductive activity.     

Cell proliferation and survival in the mating circuit of adult male hamsters: effects of testosterone and sexual behavior

The transient actions of gonadal steroids on the adult brain facilitate social behaviors, including reproduction. In male rodents, testosterone acts in the posterior medial amygdala (MeP) and medial preoptic area (MPOA) to promote mating. Adult neurogenesis occurs in both regions. The current study determined if testosterone and/or sexual behavior promote cell proliferation and survival in MeP and MPOA. Two experiments were conducted using the thymidine analog BrdU. First, gonad-intact and castrated male hamsters (n = 6/group) were compared 24 h or 7 weeks after BrdU. In MeP, testosterone-stimulated cell proliferation 24 h after BrdU (intact: 22.8 ± 3.9 cells/mm², castrate: 13.2 ± 1.4 cells/mm²). Testosterone did not promote cell proliferation in MPOA. Seven weeks after BrdU, cell survival was sparse in both regions (MeP: 2.5 ± 0.6 and MPOA: 1.7 ± 0.2 cells/mm²), and was not enhanced by testosterone. In Experiment 2, gonad-intact sexually-experienced animals were mated weekly to determine if regular neural activation enhances cell survival 7 weeks after BrdU in MeP and MPOA. Weekly mating failed to increase cell survival in MeP (8.1 ± 1.6 vs. 9.9 ± 3.2 cells/mm²) or MPOA (3.9 ± 0.7 vs. 3.4 ± 0.3 cells/mm²). Furthermore, mating at the time of BrdU injection did not stimulate cell proliferation in MeP (8.9 ± 1.7 vs. 8.1 ± 1.6 cells/mm²) or MPOA (3.6 ± 0.5 vs. 3.9 ± 0.7 cells/mm²). Taken together, our results demonstrate a limited capacity for neurogenesis in the mating circuitry. Specifically, cell proliferation in MeP and MPOA are differentially influenced by testosterone, and the birth and survival of new cells in either region are not enhanced by reproductive activity.     

Bisexual behavior in the male rat: Influence of masculine sexual activity on the display of lordosis behavior

Sexually inexperienced male Wistar rats (strain WI in our colony) known to very infrequently display spontaneous lordosis behavior (Schaeffer et al., 1990b) were used. A first group was tested four times at 5-day intervals for lordosis with vigorous stimulus males (heterotypic sexual behavior), immediately following testing for masculine sexual activity with highly receptive females (homotypic sexual behavior). A small number of animals displayed lordosis during the first test, but more and more animals displayed this behavior from the first to the fourth test. There was no relationship between the degree of masculine sexual activity--intromission without ejaculation or ejaculation--and the occurrence of lordosis behavior. A second group was tested only once for both masculine sexual activity and lordosis behavior as above and afterwards three times at 5-day intervals for lordosis behavior in the absence of any previous testing for masculine sexual activity. A few animals displayed lordosis during their first test. As compared to the first group, the animals which had not displayed lordosis in the first test never showed lordosis responses in the following tests. It is concluded that both homotypic and heterotypic sexual interactions are required for the display of lordosis behavior in the strain of Wistar rats used in this study.     

Effects of egg testosterone on female mate choice and male sexual behavior in the pheasant

Evidence is accumulating that sex steroids in the eggs, besides affecting progeny phenotype and behavior in the short term, also have enduring effects until adulthood, when they may translate into differences in reproductive strategies and success. Maternal steroids transfer may therefore affect both agonistic behavior and mate choice decisions, either through the promotion of body size and condition or through a priming effect on the neuroendocrine system. However, owing to the prevalence of a short-term perspective, relevance of maternal transfer of sex steroids to sexual selection processes has been seldom studied. Here we investigate the effects of an experimental increase in egg testosterone on male dominance and copulation success in the ring-necked pheasant, Phasianus colchicus, a polygynous galliform with multiple male ornamental traits, in captivity. We found that females from testosterone (T) injected eggs copulated less than control females. Males from T-injected eggs obtained more copulations than control males, specifically with control females. The effect of male ‘ordinary’ and secondary sexual traits on either dominance or copulation frequency did not depend on early exposure to T, nor did T treatment affect male dominance. Present results demonstrate that variation in the early hormonal environment set up by mothers affects sexual behavior of the offspring, which might translate into fitness differences.     

The relationship between circulating testosterone levels and male sexual behavior in rats

The relationships between plasma testosterone (T) and various parameters of male sexual behavior were examined in intact and castrated T-treated male rats. Repeated blood sampling and behavioral testing revealed no correlation between any measure of sexual behavior and plasma T in normal untreated sexually active males. T-Filled Silastic capsules, implanted subcutaneously at the time of castration, were found to produce plasma T levels proportional to capsule size. Plasma T titers less than 10% of normal (0.2 ng/ml) maintained ejaculatory behavior near normal levels for the 58 days of the experiment. Measures of sexual behavior which showed androgen dependence were intromission latency, postejaculatory interval, and intromission frequency. The plasma T concentration required to maintain these parameters within the intact range was 0.7 ng/ml, which is less than one-third of the mean intact level (2.6 ng/ml). No significant improvement in the sex behavior measures was seen with plasma T levels between 0.7 and 3.1 ng/ml. It was concluded that the absence of relationships between circulating T and sexual behavior in the normal rat population is due to the androgen requirement for this behavior being less than the amount normally present. Findings on T levels and T treatment in noncopulator males are also presented.     

Subthalamic lesions eliminate sexual behavior in the male rat

Electrical stimulation of parts of the subthalamus and mesencephalon produces coordinated stepping movements, and for this reason these areas are sometimes referred to as the subthalamic and mesencephalic "locomotor" regions. In this study we contrast the sexual behavioral effect of electrolytic destruction of these two regions in the male rat. Lesions of the mesencephalic locomotor region had no significant effect on male sexual behavior. In contrast, subthalamic lesions centered on the caudal zona incerta just dorsal to the subthalamic nucleus eliminated sexual behavior in 6 of 15 males. The sexual behavior of the remaining males was affected to a lesser degree, for the most part in accord with the extent of destruction to this "critical zone." Subthalamic lesions produced no obvious impairment in locomotion, posture, limb use, muscle tone or sensorimotor orientation. Even so, the fact that electrical stimulation of the subthalamus elicits coordinated stepping suggests that the region is linked with systems directly concerned with movement and locomotion. These links could be particularly important in the process by which sexual motivation is translated into sexual behavior.     

Effects of postnatal microwave exposure on thyrotropin level in the adult male rat

Postnatal exposure of male rats to microwaves modulated the evolution of the thyrotropin level. Indeed, this treatment increased plasma TSH without affecting significantly plasma thyroxine. Moreover, the histological study of the thyroid demonstrated a high activity of this gland in irradiated animals. The modification observed in the thyrotropin level was correlated to an increase in hypothalamic noradrenaline described previously in rats submitted to the same irradiation.     

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.