Bare-Part Color in Female Budgerigars Changes from Brown to Structural Blue following Testosterone Treatment but Is Not Strongly Masculinized

Whereas several studies have shown that experimentally increased levels of the androgenic steroid testosterone can affect female behavior, fewer studies have focused on the activational effects of exogenous testosterone on female morphology. With respect to colorful displays in birds, almost exclusively the effects of testosterone manipulation on female carotenoid-based colorations have been studied. Other color types such as structural colors (i.e. UV, blue and violet colors that result from differential light reflection in the nanostructures of the tissue) remain largely unstudied. Here, we investigated the short- and long-term effects of exogenous testosterone on the expression of structural bare-part coloration in female budgerigars, Melopsittacus undulatus. In this parrot species, bare-part coloration is expressed in the cere, a structure over the beak which is brown in females and structural blue in males. We experimentally increased plasma testosterone levels in testosterone-treated females (T-females) compared to controls (C-females) and we performed weekly spectrophotometric measurements of the cere for five weeks after implantation and one measurement after ten weeks. We also estimated the extent to which testosterone masculinized female cere color by comparing the experimental females with untreated males. We found significant effects of testosterone on cere color from week four after implantation onwards. T-females expressed significantly bluer ceres than C-females with higher values for brightness and UV reflectance. T-female cere color, however, remained significantly less blue than in males, while values for brightness and UV reflectance were significantly higher in T-females than in males. Our quantitative results show that exogenous testosterone induces the expression of structural blue color in females but does not strongly masculinize female cere coloration. We provide several potential pathways for the action of testosterone on structural color.     

Inter-species variation in yolk steroid levels and a cowbird-host comparison

We examined variability in yolk hormone levels among songbird species and the role of yolk steroids as a mechanism for enhanced exploitation of hosts by the parasitic brown-headed cowbird Molothrus ater . Within-clutch variation in yolk steroids has been found in several avian species in single species studies, but few comparisons have been made among species. We found a large range of differences in yolk testosterone among the seven passerine species examined, with significant differences between those at the high end (song sparrow Melospiza melodia , red-winged blackbird Agelaius phoeniceus , and house sparrow, Passer domesticus ) and those at the low end (eastern phoebe Sayornis phoebe , and house finch Carpodacus mexicanus ). We also found that the testosterone level in cowbird eggs was intermediate in relation to host species levels and was significantly lower than that in three common cowbird hosts (song sparrow, red-winged blackbird, and house sparrow), but not significantly different from three others. Geographical comparisons of yolk testosterone levels in all cowbird subspecies and populations from several regions showed no significant differences, though a trend that deserves further exploration was the pattern of lowest level in the ancestral population of cowbirds in the central prairies and of highest level in the northwestern population where range invasion occurred approximately 40 years ago. The levels of 17 beta-estradiol were similar in the seven songbird species examined, which is consistent with current hypotheses that this hormone plays a role in embryonic sexual differentiation. Further investigation is needed to determine whether the large differences observed among species in absolute level of yolk testosterone are the relevant focal point or whether target tissue sensitivity differences mediate the effects of this yolk steroid, particularly between parasitic and non-parasitic species.     

Male sex hormones promote vagally mediated reflex airway responsiveness to cholinergic stimulation

A sex disparity in airway responsiveness to cholinergic stimulation has been observed in laboratory mice in that males are considerably more responsive than females, but the basis for this difference is unclear. In this report, we demonstrate that male sex hormones promote murine airway responsiveness to cholinergic stimulation via vagus nerve-mediated reflex mechanisms. In tissue bath preparations, no sex-based differences were observed in the contractile responses of isolated tracheal and bronchial ring segments to carbachol, indicating that the mechanism(s) responsible for the in vivo sex difference is (are) absent ex vivo. Bilateral cervical vagotomy was found to abolish in vivo airway responsiveness to methacholine in male mice, whereas it did not alter the responses of females, suggesting a regulatory role for male sex hormones in promoting reflex airway constriction. To test this possibility, we next studied mice with altered circulating male sex hormone levels. Castrated male mice displayed airway responsiveness equivalent to that observed in intact females, whereas administration of exogenous testosterone to castrated males restored responsiveness, albeit not to the level observed in intact males. Administration of exogenous testosterone to intact female mice similarly enhanced responsiveness. Importantly, the promotive effects of exogenous testosterone in castrated male and intact female mice were absent when bilateral vagotomy was performed. Together, these data indicate that male sex hormones promote cholinergic airway responsiveness via a vagally mediated reflex mechanism that may be important in the regulation of airway tone in the normal and diseased lung.     

Effect of antiandrogen cyproterone acetate on the action of testosterone on mouse kidney.

The loss of endogenous testosterone in castrated male mice leads to a marked decrease in seminal vesicle and kidney tissue weight. 21 days' administration of exogenous testosterone abolished the effect of castration on the seminal vesicles and kidney tissue. The antiandrogen cyproterone acetate produced significant changes in the target tissue for androgens, i.e. in the seminal vesicles. In every case it blocked the action of both exogenous and endogenous testosterone on the seminal vesicles, but failed to block the "renotropic" action of testosterone, expressed as relative kidney weight. Contrary to its effect on the seminal vesicles, it did not influence relative kidney weight in normal animals. It likewise did not block the effect of exogenous testosterone on kidney tissue. The mechanism of the action of cyproterone acetate in androgen-dependent tissues is known to consist in inhibition of androgen binding to specific cell receptors in the target tissues. Some of the specific androgen receptors in mouse kidney are evidently different in character from those in the accessary sex glands, that being the reason why cyproterone acetate has an antiandrogenic, but not an antirenotropic effect. In agreement with experiments on rats, adrenal weight also decreases in mice after the administration of cyproterone acetate.     

Helminth-modified pulmonary immune response protects mice from allergen-induced airway hyperresponsiveness

It has been shown that the presence of certain helminth infections in humans, including schistosomes, may reduce the propensity to develop allergies in infected populations. Using a mouse model of schistosome worm vs worm + egg infection, our objective was to dissect the mechanisms underlying the inverse relationship between helminth infections and allergies. We have demonstrated that conventional Schistosoma mansoni egg-laying male and female worm infection of mice exacerbates airway hyperresponsiveness. In contrast, mice infected with only schistosome male worms, precluding egg production, were protected from OVA-induced airway hyperresponsiveness. Worm-infected mice developed a novel modified type 2 cytokine response in the lungs, with elevated allergen-specific IL-4 and IL-13 but reduced IL-5, and increased IL-10. Although schistosome worm-only infection is a laboratory model, these data illustrate the complexity of schistosome modulation of host immunity by the worm vs egg stages of this helminth, with the potential of infections to aggravate or suppress allergic pulmonary inflammation. Thus, infection of mice with a human parasitic worm can result in reduced airway inflammation in response to a model allergen.     

Decrease of mu opioid receptors in the brain and in the hypothalamus of the aged male rat

Experiments have been designed in order to analyze whether the binding capability of mu opioid receptors in the brain of the male rat is modified by age. In a first experiment, the number of receptors (Bmax) and the constant of affinity (Ka) for the mu ligand 3H-dihydromorphine (3H-DHM) have been measured in the whole brain of male rats of 2, 15 and 22 months of age. In a second experiment the Bmax and the Ka for 3H-DHM have been evaluated in the hypothalamus of male rats of 2 and 22 months of age. In this experiment it was also investigated whether the administration of exogenous testosterone modifies the number and/or the affinity of the hypothalamic mu receptors. Serum levels of LH, FSH, prolactin and testosterone have been measured by specific RIAs. The results obtained show that: serum testosterone levels are significantly decreased in aged rats, while serum LH and FSH show only a small decline; serum prolactin is higher in old than in young animals; the number of mu receptors in the whole brain of 15 and 22 month old animals and in the hypothalamus of 22 month old rats is significantly lower than in the same tissues of young animals; the administration to old animals of testosterone, in doses able to bring back towards normal serum levels of testosterone, induces a decrease of LH and FSH, but has no effect on serum prolactin titers. Testosterone administration does not modify the number of hypothalamic mu opioid receptors, indicating that the decline of brain mu receptors in old animals is not the consequence of the physiological decline of testosterone secretion; in no instance the Ka for the mu ligand is significantly affected.     

Parastrongyloides trichosuri, a nematode parasite of mammals that is uniquely suited to genetic analysis

Commonly studied nematode parasites have not proven amenable to simple genetic analyses and this has significantly reduced the available research options. We introduce here a nematode parasite of mammals, Parastrongyloides trichosuri, which has features uniquely suited for genetic analysis. This parasite has the capacity to undergo multiple reproductive cycles as a free-living worm and thereby amplify the numbers of its infective L3s in faeces. Culture conditions are presented that permit facile laboratory maintenance of this worm for >90 free-living life cycles (to date) without the need for re-entry into a permissive host. Even after long maintenance as a free-living worm, culture conditions can be manipulated to favour development of infective L3 worms, which remain able to successfully infect their marsupial hosts. The switch to infective L3 development is triggered by a secreted factor contained in culture medium conditioned by multiple generations of free-living worm culture. It is simple to perform single pair crosses with P. trichosuri to carry out Mendelian genetics in the laboratory and this has been done multiple times with sibling pairs to generate highly inbred lines. Lines of worms can readily be cryopreserved and recovered. Over 7000 expressed sequence tags have been produced from cDNAs at different life cycle stages and used to identify single nucleotide polymorphisms and microsatellites as genetic markers. Free-living worms live only a few days on average while the patency of parasitic infections can last for several months. Since we show this is not the result of re-infection, we conclude that parasitic worms have a lifespan capacity at least 20-30 times longer than their free-living counterparts. We discuss how it should be possible to exploit these unique features of P. trichosuri as a model for future studies that explore the genetic basis of longevity and parasitism.     

Infection with a helminth parasite prevents experimental colitis via a macrophage-mediated mechanism

The propensity of a range of parasitic helminths to stimulate a Th2 or regulatory cell-biased response has been proposed to reduce the severity of experimental inflammatory bowel disease. We examined whether infection with Schistosoma mansoni, a trematode parasite, altered the susceptibility of mice to colitis induced by dextran sodium sulfate (DSS). Mice infected with schistosome worms were refractory to DSS-induced colitis. Egg-laying schistosome infections or injection of eggs did not render mice resistant to colitis induced by DSS. Schistosome worm infections prevent colitis by a novel mechanism dependent on macrophages, and not by simple modulation of Th2 responses, or via induction of regulatory CD4+ or CD25+ cells, IL-10, or TGF-beta. Infected mice had marked infiltration of macrophages (F4/80+CD11b+CD11c(-)) into the colon lamina propria and protection from DSS-induced colitis was shown to be macrophage dependent. Resistance from colitis was not due to alternatively activated macrophages. Transfer of colon lamina propria F4/80+ macrophages isolated from worm-infected mice induced significant protection from colitis in recipient mice treated with DSS. Therefore, we propose a new mechanism whereby a parasitic worm suppresses DSS-induced colitis via a novel colon-infiltrating macrophage population.     

Intra-sexual competition alters the relationship between testosterone and ornament expression in a wild territorial bird

In a reliable signalling system, individual quality is expected to mediate the costs associated with ornamental displays, with relatively lower costs being paid by individuals of higher quality. These relative costs should depend not only on individual quality, but also on levels of intra-sexual competition. We explored the current and delayed effects that testosterone implants have on bird ornamentation in populations with contrasted population densities, as a proxy for intra-sexual competition. In a replicated experiment, we manipulated testosterone in 196 yearling male red grouse Lagopus lagopus scoticus in autumn in populations of high and low levels of intra-sexual competition. Males were assigned to one of three exogenous testosterone (T) treatments: empty implants (T0), small T implants (T1) or larger T implants (T2). We monitored subsequent changes in testosterone levels, ornament size and carotenoid-based colouration, carotenoid levels and body condition from autumn to spring. Testosterone implants increased testosterone levels, comb redness and comb size, and decreased body condition but these effects depended on levels of intra-sexual competition. Specifically, T2-implanted birds increased testosterone levels and comb size more, and reduced body condition more, in populations where intra-sexual competition was low. In the following spring, testosterone levels of T2-treated birds kept increasing in populations where intra-sexual competition was high but not in populations where intra-sexual competition was low. Our results highlight that levels of intra-sexual competition alter the relationship between testosterone levels and ornament expression, influencing their condition-dependence; they also indicate that the outcome of standard hormone manipulation conducted in free-living animals vary depending on the population context.     

A single injection of 17 beta-estradiol facilitates sexual behavior in castrated male mice

Sexual behavior was assessed in castrated adult CD-1 male mice given exogenous steroids under various treatment regimens. Castrated mice maintained on 20 μg testosterone (T) daily for 1 week, but given 250 μg testosterone propionate (TP) on the day of testing showed higher levels of copulatory activity than intact mice or the males receiving an additional dose of 20 μg T on the test day, although plasma testosterone levels were not different at the time of behavioral testing. Castrated males given 50, 125, or 250 μg TP for 1 week including the day of testing showed higher levels of sexual behavior than males receiving the same doses of TP only once, on the test day. A single injection of 17β-estradiol (E₂) completely restored the male copulatory pattern, including ejaculation, in castrated mice under every condition examined. Testosterone and dihydrotestosterone (DHT) were less effective than E₂, as was the combination of E₂ and DHT. The relative efficacy of a single dose of T, DHT, and E₂ plus DHT was dependent upon factors such as the delay between steroid administration and testing, as well as whether or not the castrated mice received androgen replacement prior to testing. Estradiol benzoate (E₂B) was not capable of restoring sexual behavior in castrated mice in this study. The comparison of results obtained with TP, T, E₂, and E₂B suggests that an appreciable, but not necessarily sustained, elevation of E₂ levels in the brain may be critical in the facilitation of male copulatory behavior in mice.     

Gender differences in murine airway responsiveness and lipopolysaccharide-induced inflammation

The roles of gender and sex hormones in lung function and disease are complex and not completely understood. The present study examined the influence of gender on lung function and respiratory mechanics in naive mice and on acute airway inflammation and hyperresponsiveness induced by intratracheal LPS administration. Basal lung function characteristics did not differ between naive males and females, but males demonstrated significantly greater airway responsiveness than females following aerosolized methacholine challenge as evidenced by increased respiratory system resistance and elastance (p < 0.05). Following LPS administration, males developed more severe hypothermia and greater airway hyperresponsiveness than females (p < 0.05). Inflammatory indices including bronchoalveolar lavage fluid total cells, neutrophils, and TNF-alpha content were greater in males than in females 6 h following LPS administration (p < 0.05), whereas whole-lung TLR-4 protein levels did not differ among treatment groups, suggesting that differential expression of TLR-4 before or after LPS exposure did not underlie the observed inflammatory outcomes. Gonadectomy decreased airway inflammation in males but did not alter inflammation in females, whereas administration of exogenous testosterone to intact females increased their inflammatory responses to levels observed in intact males. LPS-induced airway hyperresponsiveness was also decreased in castrated males and was increased in females administered exogenous testosterone. Collectively, these data indicate that airway responsiveness in naive mice is influenced by gender, and that male mice have exaggerated airway inflammatory and functional responses to LPS compared with females. These gender differences are mediated, at least in part, by effects of androgens.     

Cografting of hamster (Phodopus sungorus) and marmoset (Callithrix jacchus) testicular tissues into nude mice does not overcome blockade of early spermatogenic differentiation in primate grafts

The ectopic xenotransplantation of testicular tissues into nude mice is a tool to generate sperm from immature testes. Immunodeficient mice as recipients of xenografts offered an appropriate microenvironment for differentiation of testicular tissue from hamsters, goats, pigs, and macaques. One exception is the neotropical primate Callithrix jacchus. Spermatogenesis in testicular grafts from marmosets does not proceed beyond the spermatogonial stage. The most likely cause for the poor graft development of marmosets is a deletion of exon 10 in the luteinizing hormone-receptor (LHR) gene, which renders this species insensitive to LH but responsive to chorionic gonadotropin (CG). We investigated whether cografting of testicular tissue from Djungarian hamsters would overcome the blockade in marmoset graft development. We also tested if exogenous administration of human CG (hCG) to the recipient would stimulate development of the marmoset tissue. No difference in graft survival was noted between hamster and monkey tissue. Seminiferous lumina were present in marmoset and hamster grafts but were significantly larger in hamster grafts. In the hamster grafts, a high proportion of the tubules contained meiotic and postmeiotic germ cells. In contrast, the marmoset tubules were populated with gonocytes and premeiotic spermatogonia. These results indicate that neither normal serum androgen levels nor the high local testosterone levels were sufficient to initiate marmoset spermatogenesis, nor was administration of hCG successful in overcoming the developmental blockade in marmoset tissue. Our results indicate that the conditions needed for initiation of spermatogenesis in the marmoset are remarkably different from those present in most other mammals.     

Mice lacking the proton channel Hv1 exhibit sex-specific differences in glucose homeostasis

Sex as a physiologic factor has a strong association with the features of metabolic syndrome. Our previous study showed that loss of the voltage-gated proton channel Hv1 inhibits insulin secretion and leads to hyperglycemia and glucose intolerance in male mice. However, there are significant differences in blood glucose between male and female Hv1-knockout (KO) mice. Here, we investigated the differences in glucose metabolism and insulin sensitivity between male and female KO mice and how sex steroids contribute to these differences. We found that the fasting blood glucose in female KO mice was visibly lower than that in male KO mice, which was accompanied by hypotestosteronemia. KO mice in both sexes exhibited higher expression of gluconeogenesis-related genes in liver compared with WT mice. Also, the livers from KO males displayed a decrease in glycolysis-related gene expression and an increase in gluconeogenesis-related gene expression compared with KO females. Furthermore, exogenous testosterone supplementation decreased blood glucose levels in male KO mice, as well as enhancing insulin signaling. Taken together, our data demonstrate that knockout of Hv1 results in higher blood glucose levels in male than female mice, despite a decreased insulin secretion in both sexes. This sex-related difference in glucose homeostasis is associated with the glucose metabolism in liver tissue, likely due to the physiological levels of testosterone in KO male mice.     

Social modulation of testosterone levels in male black howlers (Alouatta pigra)

The influence of social factors on the modulation of male testosterone levels has been demonstrated among several vertebrate species. In addition to sexual activity, parental care and reproductive competition affect testosterone secretion. We examined variations in testosterone levels among male black howlers (Alouatta pigra) in various social contexts. Fecal samples were collected from nine males living in five different groups in the Mexican state of Campeche. The potential for intragroup and extragroup competition varied among the groups. The number of resident males living in the groups was the only variable that significantly explained variations in testosterone levels. Males living in unimale groups had higher testosterone levels; the highest testosterone levels were recorded for males that had experienced a shift from multimale to unimale group compositions. In this species, the probability of being challenged by extragroup males and evicted from the group during immigration events increases when males live in unimale groups. Therefore, our results suggest that male black howlers respond to competition for group membership by increasing their testosterone levels. In this context, testosterone secretion represents an anticipatory response to reproductive conflicts. Therefore, although males living in unimale groups have exclusive access to females, they face higher physiological costs associated with sustaining high testosterone levels for extended time periods.     

A transgenic mouse model for investigating the response of the upstream region of whey acidic protein (WAP) gene to various steroid hormones.

The limitations of studies of clarification of response elements of whey acidic protein (WAP) gene to hormones using mammary cell lines has been shown. We studied the response of the upstream region (2.6 kb) of WAP to various steroid hormones using gonadectomized mWAP/hGH transgenic mice. Ovariectomy or castration for transgenic mice was performed at 10 days or 30 days post partum. Various steroid hormones were administered daily for 10 days to the gonadectomized transgenic mice after they reached 2 months of age. Prior to the hormonal administration and 24 hr after the final administration, blood was collected and the hGH levels in the plasma was measured by RIA. Daily doses of estradiol-17 beta were significantly more effective at increasing hGH levels in transgenic females ovariectomized at 10 days post partum than progesterone of an equal dose. A combined dose of progesterone and of estradiol-17 beta significantly amplified the increase of hGH levels accompanied by the great development of mammary glands, compared to a dose of progesterone alone. Corticosterone induced only a slight increase of hGH, while testosterone had no effect. The doses of gonadal steroid hormones did not induce an increase in hGH levels and development of mammary glands in the castrated transgenic males. The results showed that the response of 5' region of WAP requires at least some extended development of the mammary gland and that the 2.6 kb upstream region of the exogenous WAP gene contained the element responsive to ovarian hormones.     

Down-regulation of testicular aromatization in the horse

A single i.m. injection of testosterone (750 mg of testosterone bexahydrobenzoate) or i.v. injection of human chorionic gonadotrophin (hCG) (10,000 IU) was given to geldings and stallions. Levels of unconjugated and conjugated (after solvolysis) androgens and estrogens were measured in blood and urine samples taken daily from the day of injection (D0) to the tenth day post-injection (D10). In the stallion, both treatments resulted in a sharp increase of plasma estrogens, which peaked one day before the androgen levels. Our results confirmed the testicular localization of a potent aromatase, which is able to aromatize androgens from endogenous as well as exogenous origin into conjugated estrogens. The very similar patterns of estrogen increase following testosterone or hCG administration suggest that the estrogen rise induced by hCG results at least partly from increased availability of testosterone. The abrupt drop in plasma estrogen levels cannot be explained by a lack of substrate, since two successive androgen injections did not succeed in maintaining the high estrogen levels. Since estrogens were unable to inhibit the aromatase activity in vitro, the drop in estrogen levels suggests a down-regulation of the aromatase synthesis.     

Stimulation of cholesterol side-chain cleavage by a luteinizing-hormone-releasing hormone (luliberin) agonist (ICI 118630) in rat Leydig cells.

The action of a luliberin (luteinizing-hormone-releasing hormone) agonist (ICI 118630) and lutropin (luteinizing hormone) on the activity of the cytochrome P-450 cholesterol side-chain cleavage enzyme in rat Leydig cells has been investigated. This has been carried out by studying the metabolism of exogenous (22R)-22- and 25-hydroxycholesterol to testosterone. It was found that both hydroxycholesterols increased testosterone production to higher levels than achieved by lutropin alone. Addition of luliberin agonist but not lutropin was found to increase further the metabolism of the hydroxycholesterol to testosterone; this occurred in the presence of saturating and subsaturating levels of the hydroxycholesterols. This effect of luliberin agonist was potentiated in the presence of lutropin. The protein synthesis inhibitor, cycloheximide, inhibited the luliberin agonist-induced stimulation of the hydroxycholesterol metabolism. At low calcium levels (1.1 microM), testosterone production was increased by addition of (22R)-22-hydroxycholesterol but the luliberin agonist effect was negated. The calmodulin inhibitor trifluoperazine inhibited (22R)-22-hydroxycholesterol-stimulated steroidogenesis and negated the luliberin agonist effect. These results indicate that luliberin agonist specifically increases the synthesis of the cytochrome P-450 cholesterol side-chain cleavage enzyme in rat testis Leydig cells.     

Differential, multihormonal regulation of the mouse major urinary protein gene family in the liver.

The hormonal requirements for the regulation of the major urinary protein (MUP) mRNA levels in mouse liver have been examined. Previous experiments have shown that administration of testosterone to female or castrated male mice increases MUP mRNA levels approximately fivefold to normal male levels. We have found that thyroxine and the peptide hormone, growth hormone, each had a pronounced effect on MUP mRNA levels. MUP mRNA was reduced 150-fold in growth-hormone-deficient mutant mice (little). The administration of growth hormone and thyroxine induced MUP mRNA approximately 150-fold, and when administered together, they induced MUP mRNA approximately 1,000-fold. testosterone administration. When administered separately to these mice, growth hormone and thyroxine induced with MUP mRNA approximately 150-fold, and when administered together, they induced MUP mRNA approximately 1,000-fold. Testicular feminized mice, which lack a functional major testosterone receptor protein, can also be induced to male levels by treatment with both growth hormone and thyroxine. In addition, we present evidence which indicates that growth hormone, thyroxine, and testosterone differentially regulate the levels of distinct MUP mRNA species.     

Diethylstilbestrol-induced cervical and vaginal adenosis using the neonatal mouse model

The relevance of diethylstilbestrol (DES) administration to neonatal mice as a model for human pathology attributed to the use of DES in high-risk pregnancies has been investigated, particularly with respect to cervical and vaginal changes in female offspring. Neonatal DES treatment of mice results in tonic pituitary gonadotropin release and continuous estrogen secretion by the ovary. Studies were designed to determine the effect of this altered ovarian endocrine activity on cervical and vaginal histopathology. Ovariectomy of DES-treated mice, with or without estradiol replacement, did not eliminate the lesions, nor did estrogen and progesterone administered in a regimen intended to mimic estrous cycle changes. Induction of the constant estrus state by neonatal estradiol benzoate or testosterone propionate administration or by exposure to constant light did not produce the type of vaginal or cervical changes seen in DES mice. Thus, altered ovarian function is apparently not required for the vaginal and cervical changes appearing in later life. A role for endogenous (or exogenous) ovarian hormones in the developmental progression toward normality is suggested.     

A single injection of 17β-estradiol facilitates sexual behavior in castrated male mice

Sexual behavior was assessed in castrated adult CD-1 male mice given exogenous steroids under various treatment regimens. Castrated mice maintained on 20 μg testosterone (T) daily for 1 week, but given 250 μg testosterone propionate (TP) on the day of testing showed higher levels of copulatory activity than intact mice or the males receiving an additional dose of 20 μg T on the test day, although plasma testosterone levels were not different at the time of behavioral testing. Castrated males given 50, 125, or 250 μg TP for 1 week including the day of testing showed higher levels of sexual behavior than males receiving the same doses of TP only once, on the test day. A single injection of 17β-estradiol (E₂) completely restored the male copulatory pattern, including ejaculation, in castrated mice under every condition examined. Testosterone and dihydrotestosterone (DHT) were less effective than E₂, as was the combination of E₂ and DHT. The relative efficacy of a single dose of T, DHT, and E₂ plus DHT was dependent upon factors such as the delay between steroid administration and testing, as well as whether or not the castrated mice received androgen replacement prior to testing. Estradiol benzoate (E₂B) was not capable of restoring sexual behavior in castrated mice in this study. The comparison of results obtained with TP, T, E₂, and E₂B suggests that an appreciable, but not necessarily sustained, elevation of E₂ levels in the brain may be critical in the facilitation of male copulatory behavior in mice.