The hormonal control of scent marking and precopulatory behavior in male gray short-tailed opossums (Monodelphis domestica)

Little is known about the hormonal control of behavior in marsupials. In the present study, the effects of castration and of testosterone or estradiol replacement therapy on scent marking and precopulatory behavior in male gray short-tailed oppossums (Monodelphis domestica) were examined. It was found that castration resulted in decreases in chest and flank/hip marking displayed by male gray opossums. Testosterone but not estradiol stimulated chest marking in castrates. Males treated with either estradiol or testosterone displayed more flank/hip marking than control males. Highest levels of female aggression toward males were seen when the males had received testosterone treatment. These findings are discussed with respect to similarities and differences between marsupials and eutherians in the neural metabolism of testosterone and the hormonal control of scent marking behavior.     

Sex steroid hormones enhance immune function in male and female Siberian hamsters

Immune function is better in females than in males of many vertebrate species, and this dimorphism has been attributed to the presence of immunosuppressive androgens in males. We investigated the influence of sex steroid hormones on immune function in male and female Siberian hamsters. Previous studies indicated that immune function was impaired in male and female hamsters housed under short-day photoperiods when androgen and estrogen concentrations were virtually undetectable. In experiment 1, animals were gonadally intact, gonadectomized (gx), or gx with hormone replacement. Females exhibited the expected increase in antibody production over males, independent of hormone treatment condition, whereas male and female gx animals exhibited decreased lymphocyte proliferation to the T cell mitogen, phytohemagglutinin (PHA) compared with intact animals, and this effect was reversed in gx hamsters following testosterone and estradiol treatment, respectively. In experiment 2, testosterone, dihydrotestosterone, and estradiol all enhanced cell-mediated immunity in vitro, suggesting that sex steroid hormones may be enhancing immune function through direct actions on immune cells. In experiment 3, an acute mitogen challenge of lipopolysaccharide significantly suppressed lymphocyte proliferation to PHA in intact males but not females, suggesting that males may be less reactive to a subsequent mitogenic challenge than females. Contrary to evidence in many species such as rats, mice, and humans, these data suggest that sex steroid hormones enhance immunity in both male and female Siberian hamsters.     

Sex-influenced population kinetics of Leishmania donovani in hamsters

Susceptibility of animals to infections depends upon various factors including sex of the host which plays a pivotal role. The intake of L. donovani was investigated in male and female hamsters as also in gonadectomized and hormone (sex) treated animals. Male hamsters developed more parasites (55/100 cell nuclei) than their female counterparts (22/100 cell nuclei). The hamsters receiving testosterone (250 micrograms/animal for 7 days) exogenously (im) had enhanced parasitic count (1.1-fold in male and 1.5-fold in females with respect to their respective controls). Administration of estradiol (3 micrograms/animal for 3 days) suppressed the infection in males by 2.5-fold and in female by 1.94-fold. Castration lowered the parasite 'in take' while ovarectomy promoted infection. In these (gonadectomized) animals the administration of testosterone in males restored parasite load while the estradiol therapy in females suppressed the infection. The results suggest a definite modulatory role of sex hormone, in the susceptibility of hamsters to L. donovani infection.     

Fetal testosterone and empathy

BACKGROUND: In animals, fetal testosterone (fT) plays a central role in organizing the brain and in later social behavior. In humans, exposure to atypical levels of prenatal androgens may result in masculine behavior and ability patterns. Normal inter-individual variation in fT levels has also been correlated with later sex-typed behavior. METHODS: In the current study, 38 children (24 male, 14 female), whose fT was analyzed in amniotic fluid, were followed up at age 4. They were asked to describe cartoons with 2 moving triangles whose interactions with each other suggested social relationships and psychological motivations. RESULTS: Females used more mental and affective state terms to describe the cartoons than males. fT was not associated with the frequency of mental or affective state terms. Females also used more intentional propositions than males. fT was negatively correlated with the frequency of intentional propositions, taking sex differences into account. fT was also negatively correlated with the frequency of intentional propositions when males were examined separately. Males used more neutral propositions than females. fT was directly correlated with the frequency of neutral propositions, taking sex differences into account. This relationship was not seen when males and females were examined separately. CONCLUSIONS: These findings implicate fT in human social development. The relevance of our findings to the 'extreme male brain' theory of autism is also discussed.     

Hormonal regulation of organic cation transporter OCT2 expression in rat kidney

Rat (r) OCT2 was identified as the second member of the organic cation transporter (OCT) family, and is predominantly expressed in the kidney. We reported previously that rOCT2 was responsible for the gender differences in renal basolateral membrane organic cation transport activity. As renal rOCT2 expression in males is much higher than that in females, we hypothesized that rOCT2 expression may be under the control of sex hormones. Treatment of male and female rats with testosterone significantly increased the expression levels of rOCT2 mRNA and protein in the kidney, whereas estradiol treatment moderately decreased the expression levels of rOCT2. There was no regulation of renal rOCT1 mRNA expression by testosterone or estradiol. Treatment of male and female rats with testosterone significantly stimulated the tetraethylammonium (TEA) accumulation by renal slices, whereas estradiol treatment caused a decrease in the TEA accumulation by slices from male but not female rats. The present findings suggested that testosterone up-regulates renal rOCT2 expression and estradiol moderately down-regulates rOCT2.     

Differential effects of testosterone metabolites in the neonatal period on open-field behavior and lordosis in the rat

Two experiments were done to compare the effects of neonatal exposure to testosterone and its major metabolites, dihydrotestosterone (DHT) and estradiol (E₂), on the development of sex differences in open-field behavior in the rat. In Experiment 1 female rats administered either testosterone propionate (TP), DHT, or estradiol benzoate (EB) were found as adults to have low activity scores, more typical of adult males, when compared to the high scores of oil-treated females. In Experiment 2 the adult open-field behavior of female rats treated neonatally with testosterone or the metabolites was compared to that of male rats treated from Day 1 to 10 of life with the aromatizing enzyme inhibitor, androst-1,4,6-triene-3,17-dione (ATD). These same animals were later tested for lordotic behavior after gonadectomy and priming with EB and progesterone. All male animals and female animals exposed neonatally to testosterone or to either of the metabolites had suppressed open-field activity scores compared to oil-treated females. However, the lordotic behavior of females exposed to DHT and of males exposed to ATD was not defeminized and was comparable to that of oil-treated females. These observations were discussed in terms of a role for the androgenic actions of testosterone in establishing sex differences in nonreproductive behavior in the rat.     

Hormonal correlates of dominance in meerkats (Suricata suricatta)

In cooperatively breeding meerkats (Suricata suricatta), individuals typically live in extended family groups in which the dominant male and female are the primary reproductives, while their offspring delay dispersal, seldom breed, and contribute to the care of subsequent litters. Here we investigate hormonal differences between dominants and subordinates by comparing plasma levels of luteinizing hormone (LH), estradiol and cortisol in females, and testosterone and cortisol in males, while controlling for potential confounding factors. In both sexes, hormone levels are correlated with age. In females, levels of sex hormone also vary with body weight and access to unrelated breeding partners in the same group: subordinates in groups containing unrelated males have higher levels of LH and estradiol than those in groups containing related males only. When these effects are controlled, there are no rank-related differences in circulating levels of LH among females or testosterone among males. However, dominant females show higher levels of circulating estradiol than subordinates. Dominant males and females also have significantly higher cortisol levels than subordinates. Hence, we found no evidence that the lower levels of plasma estradiol in subordinate females were associated with high levels of glucocorticoids. These results indicate that future studies need to control for the potentially confounding effects of age, body weight, and access to unrelated breeding partners before concluding that there are fundamental physiological differences between dominant and subordinate group members.     

The effects of gonadal hormones on scent marking and related behavior and morphology in female gray short-tailed opossums (Monodelphis domestica)

The hormonal control of scent marking and related behavior and morphology was examined in female gray short-tailed opossums. Females rarely scent marked when intact or following ovariectomy. Testosterone (T) but not estradiol (E) treatment stimulated chest marking while either hormone stimulated head marking in ovariectomized females tested alone. When the same females were tested with males, T-treated females showed little scent marking of any type; E-treated females showed hip marking in significantly more tests than females in the other treatment groups. Suprasternal scent glands (absent in intact females) and phalluses of females that received T were significantly larger than those of animals that received E or control animals. These findings are discussed with respect to similarities and differences between marsupial and eutherian females and between male and female gray opossums in the hormonal control of sexually dimorphic behavior and morphology.     

Antiphonal duetting and sex hormones in the tropical bush shrike Laniarius funebris (HARTLAUB).

We investigated changes in antiphonal duetting with phases of reproduction and circulating levels of luteinizing hormone, testosterone, and estradiol in slate-colored boubous (Laniarius funebris) breeding in aviaries. Frequency of overall male singing did not vary with reproductive phase while frequencies of female singing and female vocal responses to male song were reduced during incubation and feeding of nestlings. This resulted in significant changes in frequency of duetting. Males sang the sexual song type M1 more often during courtship and nest building than during the nestlings phase. Their territorial song types M2 and M4 did not vary with breeding phase. Females were less responsive to M1 during incubation and to M2 during the nest building and nestlings than during the courtship phase. Plasma levels of luteinizing hormone and testosterone increased in males from the prebreeding to the courtship phase. While testosterone decreased already during nest building and remained low during subsequent phases of reproduction, luteinizing hormone decreased during incubation and feeding of nestlings. Female luteinizing hormone levels were highest during nest building. Female estradiol levels decreased from nest building to incubation and increased again during subsequent nest building. Female testosterone levels were low but not basal and did not vary with phase. Neither the overall male and female singing frequencies nor the frequencies of male song types were correlated with hormonal state. However, female participation in territorial duets M4 correlated positively with their testosterone levels. It is suggested that in this monogamous, duetting species with prolonged pairbonds behavioral cues between the mates are more important than the hormonal state in control of male and female singing.     

Gonadal hormones modulate the display of submissive behavior in socially defeated female Syrian hamsters

There are striking differences in the behavioral response to social defeat between male and female Syrian hamsters. Whereas males exhibit a prolonged behavioral response to defeat (i.e., conditioned defeat), many females remain aggressive or show only a transient submissive response following defeat. The current study tested the hypothesis that sex steroids underlie this differential behavioral responsivity to social defeat. Female hamsters were ovariectomized and implanted with Silastic capsules containing estradiol (E(2)), testosterone (T), progesterone (P), dihydrotestosterone (DHT), or a blank capsule (no hormone replacement). After a 3-week recovery period, each subject was placed inside the home cage of a larger, more aggressive female for four 5-min defeat trials. The following day, each animal was tested for conditioned defeat by testing it in its own home cage in the presence of a smaller, non-aggressive intruder. Submissive, aggressive, social, and nonsocial behaviors were subsequently scored. Hamsters receiving E(2) or T displayed significantly lower levels of submissive behavior than did animals receiving P, DHT, or no hormone replacement. There were no significant differences in aggressive behavior among groups. These data suggest that gonadal hormones can influence submissive behavior in female hamsters. Collectively, these results suggest that the sex differences observed in conditioned defeat may, in part, be explained by sex differences in circulating gonadal hormones.     

Central and peripheral action of testosterone propionate on scent gland morphology and marking behaviour in the Mongolian gerbil

Scent gland size and activity and frequency of marking under standard conditions were compared in five groups of male and female gerbils: (1) intact, sham-operated controls, (2) intact with scent glands excised, (3) gonadectomized, (4) gonadectomized injected with 1000 μg testosterone propionate (TP) on alternate days, and (5) gonadectomized with a low dose (25 μg) TP applied topically to the ventral scent gland on alternate days. The animals were housed in individual cages and tested for marking in an open field arena with plastic pegs.The scent gland is not required in either sex for the behavioural act of marking. Topical application of a dose of TP too low to exert a systematic effect restored the scent gland but not marking. Injection of sufficient TP to restore seminal vesicle weight restored marking, as well as the scent glands.It was concluded that in the male, both marking behaviour and scent gland size are controlled by the testes. The effect of androgens on marking is mediated directly through the central nervous system, and not through peripheral stimulation of the glands.Females have smaller glands and mark less than males. The ovaries appear to have little control over marking frequency, and some control over scent gland size. It is possible to stimulate marking behaviour to supernormal levels by TP injection, but not by topical application.     

Social stress decreases marking behavior independently of testosterone in Mongolian gerbils

This study examined the endogenous androgen regulation of the marking behavior in Mongolian gerbils (Meriones unguiculatus). In the first experiment, developmental changes of fecal testosterone levels, ventral gland growth, and the marking frequency of male gerbils were investigated. From 9 weeks of age, marking frequency increased with increases in fecal testosterone levels and ventral gland size. The ventral gland size and marking frequency were significantly correlated to the fecal testosterone level. In the second experiment, we hypothesized that reduction in the marking frequency of subordinate males after social confrontations was controlled by a decrease in the circulating testosterone level, and we followed changes in marking frequency, endocrine status, and ventral gland size after social confrontations in which two adult male gerbils established their social ranks by fighting. As expected, marking frequency and ventral gland size were significantly related to social rank, that is, marking frequency was higher among dominant gerbils and lower among subordinates. In addition, fecal corticosterone levels among subordinates were higher than those of dominant animals. However, neither the fecal and plasma testosterone levels, nor testis size, differed between dominant and subordinate gerbils. These results revealed that endogenous androgen played a role in regulating marking behavior and ventral gland size during the developmental stage and that the reductions in marking frequency and ventral gland size occurring in subordinate males after social confrontations were not directly regulated by androgen changes.     

Sex differences in the analgesic effects of ICI 182,780 and Flutamide on ureteral calculosis in rats

To better define the involvement of gonadal hormones in the sex differences observed in experimental visceral pain, we administered antagonists of estrogen receptors (ICI 182,780 [ICI]) or androgen receptors (Flutamide [FLU]) to adult male and female rats suffering from artificial ureteral calculosis. Subjects were divided into groups and treated with one of the substances (ICI, FLU) or sweet almond oil (OIL, vehicle) for 5 days, starting 2 days before surgery. On day 3, animals underwent surgery, with half receiving an artificial calculosis (Stone) and half only a sham procedure. The animals' behavior (number and duration of ureteral crises) and blood hormone levels (estradiol and testosterone) were determined in all groups. In OIL-treated rats the number and duration of crises were higher in females than in males. The administration of ICI or FLU resulted in hormonal effects in males and behavioral effects in females. In males ICI treatment increased estradiol plasma levels and FLU increased testosterone plasma levels; in females ICI and FLU treatments both decreased the number and duration of the ureteral crises. These results, confirming previous findings of higher sensitivity of females than males to urinary tract pain, showed the modulatory effects of estrogen and androgen antagonists on the behavioral responses induced by pain but only in females.     

Regulation of urine marking in male and female mice: effects of sex steroids

Effects of sex steroids on urine-marking activity were studied in male, female, and neonatally androgenized female mice. Urine marking was estimated by suspending ceramic tubes that were connected in a horizontal row with a steel rod into the home cage of an isolated mouse. Intact males showed high marking activity, which was diminished after castration. Both testosterone propionate (TP) and estradiol benzoate (EB) were effective in restoring the marking activity of castrated males, while 5-alpha-dihydrotesterone (DHT) did not have any stimulative effects. Intact normal females showed quite low marking activity and ovariectomy further depressed it. TP and DHT enhanced the marking of ovariectomized females, but EB restored the activity only to the preovariectomy level. In intact females which were neonatally androgenized, the marking activity was much higher than that of normal females. The pattern of the change induced by gonadectomy and hormone treatment in these females resembled that in males. Thus, ovariectomy reduced the activity and both TP and EB restored the level. These results indicate that the sexual dimorphism in the urine marking in mice is primarily determined by hormonal environment during early postnatal age. Hormonal control of scent marking is discussed in relation to the studies in other rodents.     

Scent-marking in the tamarin, Saguinus oedipus: Sex differences and ontogeny

Many mammalian species which exhibit scent-marking behaviour show a pronounced sexual dimorphism in marking behaviour and scent gland morphology. However, several species of marmosets and tamarins do not show dimorphism in these traits. We examined sex differences in scent-marking structures and behaviour in cotton-top tamarins (Saguinus o. oedipus; Primates: Callitrichidae). While body size and weight were virtually identical in adult males and females, there were pronounced sex differences in scent gland size and in rates of marking behaviour. Females possessed larger anogenital and suprapubic glands and showed 10-fold higher rates of anogenital marking and slightly higher rates of suprapubic marking than males. Observations on the development of anogenital marking revealed a lack of dimorphism during the first 2 years. Adult rates of anogenital marking in females were only observed in females housed separately from their natal family group. The onset of adult levels of marking behaviour corresponds with the adoption of the role of a breeding adult female, suggesting that anogenital marking plays a role in sexual communication.     

Hormones and social behavior in the lizard, Anolis carolinensis

The purpose of this experiment was to study the effects of homologous and heterologous gonadal hormones on sexual and aggressive behavior in a reptilian species. Thirty adult male and thirty adult female lizards (Anolis carolinensis) were divided into 10 groups of six each (five groups per sex) and each group was given one of five treatments: either left intact, sham-castrated and injected with the hormone vehicle, castrated and injected with the hormone vehicle, castrated and injected with estradiol benzoate, or castrated and injected with testosterone propionate. After a week of visual isolation and daily hormone injection, animals were tested four times, twice with a stimulus animal of each sex. Females treated with estrogen were receptive, but did not court. Females treated with androgen were receptive and also courted and pursued stimulus females as frequently as males given androgen. No males in any group were receptive, and thus the female appears to be more capable of heterotypical sexual behavior than the male. Castrated males failed to court. Courtship and pursuit of stimulus females was readily stimulated in males with testosterone, and weakly stimulated by estrogen. Intact males were very aggressive, but lower levels of aggression were independent of gonadal hormones, as was subordination (head-nodding). The results for aggression and subordination are interpreted with reference to naturally-occurring Anolis behavior, and the results for sexual behavior are compared with similar experiments with mammals and birds.     

Sexual differences in 5′-deiodinase activity in the harderian gland of Syrian hamsters and the effect of pinealectomy: Regulation by androgens

Sexual differences on thyroxine 5′-deiodinase (5′-D) in the Harderian gland of Syrian hamsters were investigated. We compared the 24-h profile of 5′-D activity in male and female hamsters, observing a clear rhythm in males but not in females. Female values were always significantly higher than male ones. After pinealectomy day/night variations in male 5′-D activity at the time points studies were abolished, results that are in correlation with serum thyroid hormones. We also studied the regulation by androgen of the enzyme activity. Basal 5′-D activity increased in castrated males and levels fell when animals were implanted with testosterone or its product 5α-dihydrotestosterone (DHT). Female 5′-D activity was also inhibited by androgens. As only the addition of DHT in the presence of epitestosterone, an inhibitor of the conversion of testosterone on DHT, in castrated males was able to decrease 5′-D activity to control animal levels, we suggest a probable direct effect of DHT by itself. © 1996 Wiley-Liss, Inc.     

大仓鼠胁腺的发育及性别差异

通过对繁殖期雌雄大仓鼠胁腺重的比较研究发展雌雄鼠的胁腺重和体重分别存在正相关关系,非成年雌雄大仓鼠的胁腺重无显著性别差异,成年雄性大仓鼠的胁腺显著重于成年雌鼠,通过石蜡切片发现,雄鼠胁腺的皮脂细胞显著于雌鼠,对胁腺分泌物进行了气相色谱分析发现,雌雄胁腺分泌物的化学成分的种类和数量存在明显差异,本文从胁腺的形态,组织结构和化学成分三个方面初步揭示了胁腺在繁殖期具有性别别功能的机制。     

Brain and plasma levels of testosterone, dihydrotestosterone and estradiol in the one-day-old rat.

Current evidence indicates that the secretion of testosterone during perinatal life is essential in organizing the male brain which subsequently directs the male pattern of gonadotrophin (GTH) secretion and adult male sexual behavior in the rat. It has been hypothesized that testosterone is converted into estradiol enzymatically in the brain prior to its action. In the absence of testosterone and with the resultant low levels of estradiol, female patterns of gonadotrophin secretion and behavior result. In order to investigate this hypothesis further, the endogenous levels of gonadal steroids in the plasmas and brains of 24–48 hr old male and female rats were determined. Pooled samples were analyzed for testosterone, dihydrotestosterone and estradiol by radioimmunoassay. Testosterone levels in male brain and plasma samples were significantly (10-fold) higher than those in the female brain and plasma samples. Brain levels of estradiol were significantly higher in the male than in the female neonate, while plasma levels were identical. Whether the higher level of estradiol in the male brain is due to enzymatic conversion from testosterone within the brain differences in permeability or some other mechanism cannot be stated at this point. The significantly higher brain levels of both testosterone and estradiol in male neonates do fit the pattern predicted by the present concept of sexual differentiation. Dihydrotestosterone levels in brain and plasma of male rats were about 25% of those of testosterone. However in females the brain levels of dihydrotestosterone were significantly higher than testosterone even though the plasma levels of these hormones were identical. This may reflect a protective mechanism through which permeability of testosterone is lowered in the neonatal female brain during the critical period or simply a functional conversion of testosterone to dihydrotestosterone in the female during this period.     

Androgen and estradiol levels in plasma and amniotic fluid of late gestational male and female hamsters: uterine position effects

Using radioimmunoassay we have measured the plasma and amniotic fluid levels of androgen and estradiol in male and female hamster fetuses nearing parturition. On Days 14 and 15 of gestation (day of birth = Day 16), plasma levels of androgen are higher in males than females while estradiol levels are equal. Amniotic fluid levels of these hormones, while lower than plasma, reflect the difference in androgen and the similarity in estradiol between sexes. Uterine position analysis on Day 14 suggests that female siblings located caudally suppress amniotic fluid androgen and elevate estradiol levels of male siblings. Comparison of Day 18 gestation male and female rat amniotic fluid androgen to Day 14 hamsters reveals that male rats are bathed in high levels of androgen. Female rats have lower levels which are not different from those of male hamsters. Female hamsters are exposed to little androgen. Relevance to behavioral sexual differentiation and the display of adult behavior is discussed.