Interactions among paternal behavior, steroid hormones, and parental experience in male marmosets (Callithrix kuhlii)

Male black tufted-ear marmosets (Callithrix kuhlii) contribute to the rearing of their offspring. Here we evaluated predictions of hypotheses suggesting that (1) T and E2 influence infant-care behavior in male marmosets, (2) levels of T and E2 are modulated by paternal experience, and (3) paternal behavior and levels of T and E2 in male marmosets covary with stress. We observed the behavior of marmosets in their family groups following the birth of infants and evaluated urinary concentrations of T, E2, and the stress hormone cortisol (CORT) among fathers before and after the birth of young. Urinary levels of T, E2, and CORT were lower among males who carried infants at high rates than males who carried at low rates, and T and CORT levels were negatively correlated with carrying rates across all males. Males had significantly lower T levels while carrying the second compared to the first litter and slightly lower rates of infant-carrying, possibly due to assistance provided by offspring of the first litter. There were increases in CORT levels of fathers after the birth of the first litter, but decreases in CORT after the birth of the second. Our results suggest a relationship in C. kuhlii between paternal behavior, hormones, and paternal experience. Rates of infant-carrying appear to be linked to hormone levels, and hormone levels in turn are affected by experience caring for young. Our data also suggest that T, E2, and CORT have synergistic influences on infant-carrying behavior or alternatively that associations between T and E2 and rates of infant-carrying are influenced by stress or other glucocorticoid-related variables. Finally, we propose a hypothesis suggesting that experience-related changes in hormones reinforce the commitment of males to successful breeding partnerships.     

Testosterone selectively increases serum follicle-stimulating hormonal (FSH) but not luteinizing hormone (LH) in gonadotropin-releasing hormone antagonist-treated male rats: evidence for differential regulation of LH and FSH secretion

Both testosterone (T) and gonadotropin-releasing hormone (GnRH)-antagonist (GnRH-A) when given alone lower serum luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in intact and castrated rats. However, when graded doses of testosterone enanthate (T.E.) were given to GnRH-A-treated intact male rats, a paradoxical dose-dependent increase in serum FSH occurred; whereas serum LH remained suppressed. This surprising finding led us to ask whether the paradoxical increase in serum FSH in GnRH-A-suppressed animals was a direct stimulatory effect of T on the hypothalamic-pituitary axis or the result of a T effect on a testicular regulator of FSH. To test these hypotheses, we treated adult male castrated rats with GnRH-A and graded doses of T.E. In both intact and castrated rats, serum LH remained undetectable in GnRH-A-treated rats with or without T.E. However, addition of T.E. to GnRH-A led to a dose-dependent increase in serum FSH in castrated animals as well, thus pointing against mediation by a selective testicular regulator of FSH. These data provide evidence that pituitary LH and FSH responses may be differentially regulated under certain conditions. When the action of GnRH is blocked (such as in GnRH-A-treated animals), T directly and selectively increases pituitary FSH secretion.     

Behavioral and Endocrine Responses in Male Marmosets to the Establishment of Multimale Breeding Groups: Evidence for Non-monopolizing Facultative Polyandry

Studies of wild callitrichids provide conflicting evidence regarding polyandrous groups. One perspective supports a monopolizing breeding strategy on the part of one male, while the alternative perspective suggests that polyandry does not lead to a breeding monopoly. We tested the hypotheses in male marmosets (Callithrix kuhlii) with 5 polyandrous groups composed of related/familiar males as our attempts to establish polyandrous groups of unrelated/familiar males failed. We monitored male social and sexual behavior and urinary testosterone (T) and cortisol (CORT) across the first 80 days of group formation and contrasted them with similar measures in males housed in monogamous groups. We also examined the same measures across the females' ovulatory cycles for polyandrous males. We found little evidence that males in polyandrous groups exercised a mating monopoly over the female and no evidence for overt competition between polyandrous males. We found 2 behavioral differences: polyandrous males were less often in proximity and copulated more often with the female than monogamous males did. Our findings suggest that the males in newly-formed groups of marmosets do not monopolize breeding and social behavior with the female. This appears to be the case for 3 reasons. First, males may use sperm competition rather than overt competition. Secondly, it may take longer for relationships to develop between the female and the males in polyandrous groups versus in monogamous groups. Thirdly, the cost of infant care is sufficiently high to demand that group members get along when groups are small and reproductive benefits are shared.     

Effects of gonadotropin-releasing hormone administration on the pituitary-gonadal axis in male and female dogs before and after gonadectomy

GnRH-stimulation tests were performed in 14 female and 14 male client-owned dogs of several breeds, before and 4 to 5 mo after gonadectomy. The aim of the study was to obtain more insight into the pituitary-gonadal axis in intact and neutered dogs and to establish reference values. Basal plasma luteinizing hormone (LH) and follicle-stimulating hormone (FSH) concentrations were increased significantly after gonadectomy in both bitches and male dogs. In both males and females ranges of the basal plasma FSH concentrations, before and after gonadectomy, did not overlap as opposed to the overlap in ranges of the basal plasma LH concentrations. Before gonadectomy basal plasma LH concentrations were lower and basal plasma FSH concentrations were higher in bitches than in male dogs. After gonadectomy these basal values did not differ significantly. GnRH administration before gonadectomy resulted in an increase in plasma LH and FSH concentrations in both genders. GnRH administration after gonadectomy produced an increase only in plasma LH concentrations in both genders, and a just significant increase in plasma FSH in castrated male dogs. GnRH administration before gonadectomy resulted in a significant increase in plasma testosterone concentration in both genders. In males ranges of basal and GnRH-stimulated plasma testosterone concentrations before and after gonadectomy did not overlap. Basal plasma estradiol concentrations were significantly higher in intact males than in castrated males and their ranges did not overlap. The basal estradiol concentrations in bitches before and after ovariectomy were not significantly different. At 120 min after GnRH administration, ranges of plasma estradiol concentration of intact and ovariectomized bitches no longer overlapped. In conclusion, basal plasma FSH concentration appears to be more reliable than basal plasma LH concentration for verification of neuter status in both male and female dogs. The basal plasma testosterone concentration appears to be reliable for verification of neuter status in male dogs. The plasma estradiol concentration at 120 min after GnRH administration can be used to discriminate between bitches with and without functional ovarian tissue.     

The postnatal demasculinization of sexual behavior in the Japanese quail (Coturnix coturnix japonica)

Three experiments were performed to analyze the time course of demasculinization in the Japanese quail and to test the activating and organizing effects of estradiol (E2) in adult sexually active birds. In Experiment 1, males and females were castrated at the age of 1 day or 1, 2, 4, and 6 weeks and treated as adults with testosterone (T). The age of castration had no effect on behavior and morphology in males. Plasma gonadotrophins (LH and FSH) were, however, higher in males castrated at or before than in those castrated after 2 weeks of age. This suggests that postnatal testicular secretions have organizing effects on the pituitary activity. Females which were castrated before 1 week of age were less sensitive to the activating effects of T than males, but were not fully demasculinized. The demasculinization of different reproductive characteristics such as male sexual behavior, cloacal gland size, and weight of the syringeal muscles is achieved in females at different times posthatching. In Experiment 2, castration of male and female quail at the ages of 4 days or 4 weeks confirmed that postnatal ovarian secretions contribute to the full behavioral and morphological demasculinization of females. It is easier to elicit mounting in T-treated females when they are tested in their home cage instead of a test arena. This difference was not observed in males. During Experiment 3, it was impossible to demasculinize sexually active adult males or females by treatment with Silastic implants of E2. E2 did not maintain sexual behavior in ovariectomized females showing male sexual behavior when treated with T but maintained the behavior in males.     

Effect of steroid milieu on gonadotropin-releasing hormone-1 neuron firing pattern and luteinizing hormone levels in male mice

GnRH neuronal function is regulated by gonadal hormone feedback. In males, testosterone can act directly or be converted to either dihydrotestosterone (DHT) or estradiol (E2). We examined central steroid feedback by recording firing of green fluorescent protein (GFP)-identified GnRH neurons in brain slices from male mice that were intact, castrated, or castrated and treated with implants containing DHT, E2, or E2 + DHT. Castration increased LH levels. DHT or E2 alone partially suppressed LH, whereas E2 + DHT reduced LH to intact levels. Despite the inhibitory actions on LH, the combination of E2 + DHT increased GnRH neuron activity relative to other treatments, reflected in mean firing rate, amplitude of peaks in firing rate, and area under the curve of firing rate vs. time. Cluster8 was used to identify peaks in firing activity that may be correlated with hormone release. Castration increased the frequency of peaks in firing rate. Treatment with DHT failed to reduce frequency of these peaks. In contrast, treatment with E2 reduced peak frequency to intact levels. The frequency of peaks in firing rate was intermediate in animals treated with E2 + DHT, perhaps suggesting the activating effects of this combination partially counteracts the inhibitory actions of E2. These data indicate that E2 mediates central negative feedback in males primarily by affecting the pattern of GnRH neuron activity, and that androgens combined with estrogens have a central activating effect on GnRH neurons. The negative feedback induced by E2 + DHT to restore LH to intact levels may mask an excitatory central effect of this combination.     

Hypertrophy of gonadotropin releasing hormone-containing neurons after castration in the teleost, Haplochromis burtoni.

In the African cichlid fish, Haplochromis burtoni, males are either territorial or nonterritorial. Territorial males suppress reproductive function in the nonterritorial males, and have larger gonads and larger gonadotropin-releasing hormone- (GnRH) containing neurons in the preoptic area (POA). We describe an experiment designed to establish the causal relationship between large GnRH neurons and large testes in these males by determining the feedback effects of gonadal sex steroids on the GnRH neurons. Territorial males were either castrated or sham-operated, 4 weeks after which they were sacrificed. Circulating steroid levels were measured, and the GnRH-containing neurons were visualized by staining sagittal sections of the brains with an antibody to salmon GnRH. The soma areas of antibody-stained neurons were measured with a computer-aided imaging system. Completely castrated males had markedly reduced levels of circulating sex steroids [11-ketotestosterone (11KT) and testosterone (T)], as well as 17 beta-estradiol (E2). POA GnRH neurons in castrates showed a significant increase in mean soma size relative to the intact territorial males. Hence, in mature animals, gonadal steroids act as a brake on the growth of GnRH-containing neurons, and gonadal products are not responsible for the large GnRH neurons characteristic of territorial males.     

Review on testicular development, structure, function, and regulation in common marmoset

BACKGROUND: The common marmoset (Callithrix jacchus) is a New World primate that has been used increasingly in toxicological evaluations including testing for testicular toxicity of pharmaceutical and environmental chemicals. Information on structural and functional characteristics of the testis in common marmosets ("marmoset" in this review) is critical for designing experiments, interpreting data collected, and determining relevance to humans in risk assessment. METHODS: This study provides a comprehensive review on testicular development, structure, function, and regulation in common marmosets. RESULTS: There is little information regarding testicular formation and development during gestation. Based on the overall pattern of embryonic development in marmosets, it is postulated that gonadal formation and testicular differentiation most likely takes place during gestational Week 6-12. After birth, the neonatal period of the first 2-3 weeks and the pubertal period from Months 6-12 are critical for establishment of spermatogenesis in the adult. In the adult, a nine-stage model has been used to describe the organization of seminiferous epithelium and multiple stages per tubular cross-section have been observed. Seminiferous epithelium is organized in a wave or partial-wave manner. There are on average two stages per cross-section of seminiferous tubules in adult marmoset testis. Sertoli cells in the marmoset have a uniform morphology. Marmoset spermatogenesis has a high efficiency. The prime determinant of germ cell production is proliferation and survival of spermatogonia. Sertoli cell proliferation during the neonatal period is regulated by follicle-stimulating hormone (FSH), but chorionic gonadotropin (CG), instead of luteinizing hormone (LH), is the only gonadotropin with luteinizing function in marmoset. The receptor gene for CG in marmoset is unique in that it does not have exon 10. Marmosets have a "generalized steroid hormone resistance," i.e., relatively high levels of steroid hormones in circulation and relatively low response to exogenous steroids. Blockage of FSH, CG, and testosterone production during the first 3 months after birth does not cause permanent damage to the male reproductive system. Initiation of spermatogenesis in the marmoset requires unique factors that are probably not present in other mammals. Normal male marmosets respond to estradiol injection positively (increased LH or CG levels), a pattern seen in normal females or castrated males, but not usually in normal males of other mammalian species. CONCLUSIONS: It seems that the endocrine system including the testis in marmosets has some unique features that have not been observed in rodents, Old World primates, and humans, but detailed comparison in these features among these species will be presented in another review. Based on the data available, marmoset seems to be an interesting model for comparative studies. However, interpretation of experimental findings on the testicular effects in marmosets should be made with serious caution. Depending on potential mode of testicular actions of the chemical under investigation, marmoset may have very limited value in predicting potential testicular or steroid hormone-related endocrine effects of test chemicals in humans.     

Cues that Elicit Ultrasounds from Adult Male Mice

Adult male mice (Mus musculus) which have a prior history ofexperience with other adult male and adult female mice readilyproduce 70 kHz ultrasonic vocalizations in the presence of urinefrom adult females but not in the presence of urine from adultmales. Urine from immatures of either sex does not elicit ultrasoundsfrom socially experienced adult males. The ultrasound elicitingpotency of adult male urine was not improved substantially followingcastration of adult males, injection of testosterone propionateto castrated adult males, administration of estradiol benzoateto castrated adult males, or neonatal castration. Ovarian hormonesdo not appear to be necessary for either the appearance at puberty,or the maintenance during adulthood, of the ultrasound elicitingcues of female urine. Stage of estrus did not have a major modulatingeffect on urinary cues eliciling male ultrasounds. Treatmentsthat did not substantially reduce the signal value of adultfemale urine include ovariectomy before or after puberty, ovariectomywith adrenalectomy, and neonatal administration of testosterone.The administration of testosterone to ovariectomized adult females,and hypophyseclomy, virtually eliminated the ability of urinefrom adult females to elicit ultrasounds from socially experiencedadult males. The implication of pituitary hormones in the modulationof female urinary cues thai elicit ultrasounds is particularlyinteresting since pituitary factors are also implicated in theproximal causation of postparturient maternal aggression, whichadult male ultrasounds may function to moderate.     

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

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

Hormonal stimulation and paternal experience influence responsiveness to infant distress vocalizations by adult male common marmosets,Callithrix jacchus

Parental experience and hormones play a large role in the common marmoset (Callithrix jacchus) father's care of their offspring. We tested the effect of exogenous estradiol or testosterone on the responsiveness of common marmosets to respond to infant distress vocalizations and whether males who haven't become fathers yet (paired males) would have increased responsiveness to infant distress calls with either steroid or whether parental experience is the most important component for the onset of paternal care. Sixteen male marmosets (8 fathers, 8 paired males) received a vehicle, low dose or high dose of estradiol and additional 16 males were tested with testosterone at three doses for their response either to a vocal control or a recording of an infant distress call for 10 min. Without steroid stimulation fathers were significantly more likely to respond to the infant distress stimulus than paired males. Low dose estradiol stimulation resulted in a significant increase in fathers' behavioral response towards the infant distress stimulus but not in paired males. Fathers also showed a significant increase in infant responsiveness from the vehicle dose to the estradiol low dose treatment, but not to the estradiol high dose treatment. Testosterone treatment did not show significant differences between infant responsiveness at either dose and between fathers and paired males. We suggest that neither steroid is involved in the onset of paternal care behaviors in the marmoset but that estradiol may be involved in facilitating paternal motivation in experienced fathers.     

Differential maintenance of penile responses and copulatory behavior by gonadal hormones in castrated male rats

Sexually experienced male rats were castrated and immediately received implants of Silastic tubing containing either testosterone (T), dihydrotestosterone (DHT), estradiol (E), or nothing (blank). The ability of these hormone treatments to maintain precastration levels of copulatory behavior and ex copula penile responses was assessed for 40 days after castration. Throughout the study T- and E-treated males, but not males with DHT or blank implants, maintained normal copulatory behavior. In contrast males treated with T and DHT, but not E or blanks, maintained penile responses ex copula. In blank-treated males, penile-response latencies increased more rapidly than did intromission latencies. These results, together with those of previous studies, appear to rule out a role for estradiol and reinforce the role of androgens in the activation of rats' penile-response potential ex copula. Similarly, the results support the conclusion that in castrated male rats estradiol treatment is sufficient for the activation of masculine copulatory behavior, and that the penile actions necessary for intromission are not dependent on androgen. Thus, the evocability of penile actions and their relative androgen dependence are context sensitive.     

Effect of infusion of gonadotropin releasing hormone upon plasma concentrations of sex hormones in prepubertal and pubertal males.

Plasma testosterone (T), dihydrotestosterone (DHT), 17-hydroxyprogesterone (17OHP), androstenedione (A), estradiol (E2), and dehydroepiandrosterone sulfate (DHAS) were measured by radioimmunoassay after celite chromatography prior to and after a 3-hour infusion of the synthetic gonadotropin releasing factor, GnRH, in normal prepubertal and pubertal boys. Plasma T levels rose (p less than 0.001) in the pubertal but not prepubertal boys. 17OHP concentrations increased in those boys who had an increment of T. A, DHT, E2 or DHAS levels did not increase after GnRH. Basal levels of T, DHT, A and DHAS correlated with the peak and mean serum LH levels attained during the GnRH infusion. These data confirm the greater Leydig cell responsivity to transient rises of endogenous gonadotropin in pubertal males and also suggest that there may be a relationship between adrenal androgen production and maturation of the hypothalamic-pituitary-gonadal system.     

Stress reactivity in young marmosets (Callithrix geoffroyi): ontogeny, stability, and lack of concordance among co-twins

Variation in response styles in the hypothalamic-pituitary-adrenal (HPA) axis are known to be predictors of short- and long-term health outcomes. The nature of HPA responses to stressors changes with developmental stage, and some components of the stress response exhibit long-term individual consistency (i.e., are trait-like) while others are transient or variable (i.e., state-like). Here we evaluated the response of marmoset monkeys (Callithrix geoffroyi) to a standardized social stressor (social separation and exposure to a novel environment) at three different stages of development: juvenile, subadult, and young adult. We monitored levels of urinary cortisol (CORT), and derived multiple measures of HPA activity: Baseline CORT, CORT reactivity, CORT Area Under the Curve (AUC), and CORT regulation. Juvenile marmosets exhibited the most dramatic stress response, had higher AUCs, and tended to show poorer regulation. While baseline CORT and CORT regulation were not consistent within an individual across age, CORT reactivity and measures of AUC were highly correlated across time; i.e., individuals with high stress reactivity and AUC as juveniles also had high measures as subadults and adults, and vice-versa. Marmoset co-twins did not exhibit similar patterns of stress reactivity. These data suggest that regardless of the source of variation in stress response styles in marmosets, individually-distinctive patterns are established by six months of age, and persist for at least a year throughout different phases of marmoset life history.     

Elevated urinary testosterone excretion and decreased maternal caregiving effort in marmosets when conception occurs during the period of infant dependence

The proximate mechanisms that regulate transitions in mammalian female reproductive effort have not been widely studied. However, variation in circulating levels of the androgenic steroid hormone testosterone (T) appears to mediate a trade-off between investment in current and future offspring in males [Ketterson, E.D., Nolan, V., Jr., 1992. Hormones and life histories: an integrative approach. Am. Nat. 140, S33-S62; Ketterson, E.D., Nolan, V., Jr., 1994. Hormones and life histories: an integrative approach. In: L.A. Real (Ed.), Behavioral Mechanisms in Evolutionary Ecology, University of Chicago Press, Chicago, pp. 327-353; Ketterson, E. D., Nolan, V., Jr., 1999. Adaptation, exaptation, and constraint: A hormonal perspective. Am. Nat. 154S, S4-S25]. The purpose of this study was to investigate the possibility that T is also associated with transitions in the reproductive effort of females, by examining the relationship between urinary T excretion, maternal caregiving behavior, and the timing of the postpartum conception in female Wied's black tufted-ear marmosets (Callithrix kuhlii). We examined the maternal carrying effort and peripartum T profiles of six females across two conditions: (1) when they conceived during the period of infant dependence (DPID), such that gestation was coupled with lactation; and (2) when the same females conceived after the period of infant dependence (APID). We also assessed the relationship between postpartum T levels and caregiving effort. When female marmosets conceived DPID, they dramatically reduced their caregiving effort, and had higher levels of urinary T, relative to when they conceived APID. Further, the litter-to-litter changes in maternal caregiving effort that we observed were related to variation in urinary T excretion; as weekly levels of urinary T excretion increased, concurrent caregiving effort declined. Our results suggest that variation in T secretion may regulate transitions in female reproductive behavior, and that the regulation of male and female parental behavior may be mediated by homologous neuroendocrine mechanisms.     

Variation in steroid hormones associated with infant care behaviour and experience in male marmosets (Callithrix kuhlii)

We describe temporal patterns of change in paternal behaviour and urinary concentrations of the steroid hormones testosterone (T) and oestradiol (E(2)) in male black tufted-ear marmosets, Callithrix kuhlii, relative to the birth of their young, and test predictions of the hypotheses that (1) high levels of T are incompatible with paternal care and (2) levels of T and E(2)vary with a father's prior experience in his family group. After young were born, levels of urinary T and E(2)remained near prepartum concentrations and rates at which fathers carried infants were below peak levels until the approximate time that postpartum mating ordinarily occurs, suggesting a possible trade-off between readiness to mate and paternal behaviour in C. kuhlii. Infant-carrying behaviour of fathers occurred at its highest rate 3-4 weeks after parturition and coincided with significant declines in urinary levels of T and E(2), providing preliminary support for the hypothesis that these hormones are antagonistic to paternal behaviour. Urinary T and E(2)declined among fathers regardless of whether their young survived to weaning or died at birth, indicating that variation in these hormones after parturition occurs even in the absence of continued stimuli from infants. When adjusted for declines ordinarily associated with aging, urinary T tended to be lower among fathers with a great deal of prior experience caring for young compared with fathers having little or no experience, suggesting that either experience affects T levels of fathers, or that T levels influence fathers' chances of successfully rearing infants. Overall, our results suggest that in male C. kuhlii, T, and possibly E(2), play an important role in balancing the expression of paternal care with that of other reproductive behaviours. Copyright 2000 The Association for the Study of Animal Behaviour.     

Estradiol is responsible for reduced renal prostaglandin dehydrogenase activity in female rats

The contribution of sex steroids to sex-related differences in renal prostaglandin dehydrogenase activity and urinary prostaglandin excretion was examined in 7-8-week-old male and female rats subjected to sham-operation or gonadectomy at 3 weeks of age. Rats were injected subcutaneously twice over a 6-day interval with vehicle (peanut oil, 0.5 mg/kg) or with depot forms of testosterone (10 mg/kg), estradiol (0.1 mg/kg), progesterone (5 mg/kg), or with estradiol and progesterone combined (0.1 and 5 mg/kg). After the second injection, 24-h urine samples were collected for prostaglandin measurement by radioimmunoassay; the rats were killed, and renal and pulmonary prostaglandin dehydrogenase activities were determined by radiochemical assay. Renal prostaglandin dehydrogenase activity was 10-times higher in intact male rats than in intact females. Gonadectomy increased renal prostaglandin dehydrogenase activity 4-fold in females, but had no effect in males; estradiol, alone or combined with progesterone, markedly suppressed renal prostaglandin dehydrogenase activity in both sexes, while testosterone or progesterone alone had no effect. Pulmonary prostaglandin dehydrogenase did not differ between the sexes and was unaffected by gonadectomy or sex-steroid treatment. Intact female sham-operated rats excreted 70-100% more prostaglandin E2, prostaglandin F2 alpha, and 6-keto-prostaglandin F1 alpha in urine than did males; gonadectomy abolished the difference in urinary prostaglandin E2 excretion. Estradiol decreased urinary prostaglandin E2 in females but not in males; treatment with other sex steroids did not alter urinary prostaglandin excretion.     

Hormonal regulation of male reproductive behavior in the lizard Anolis sagrei: a test of the aromatization hypothesis

This study examined the hypothesis that aromatization of testosterone (T) to estradiol (E) is required to activate reproductive behavior in castrated male lizards (Anolis sagrei). Adult, reproductively active males were assigned to an intact control group or to one of four treatment groups. Treatment males were castrated and 1 week later three of the four castrated groups were implanted with subcutaneous pellets containing either 0.05 mg of E, 0.5 mg of T, or 0.5 mg of dihydrotestosterone (DHT). Two weeks after pellet implantation, males were tested with stimulus males, and 2 days later were tested with stimulus females. Behavioral tests were of 15-min duration and were videotaped. Significantly fewer E-treated castrates erected a crest in tests with stimulus males than did intact males. In tests with stimulus females, significantly fewer E-treated castrates displayed, neck-gripped, and intromitted than did intact males. Estradiol-treated castrates also showed significantly less display behavior than did intact males. However, aggressive and sexual behavior of DHT-treated castrates was not significantly different from that of intact males. The same was true for T-treated castrates with the exception that display behavior in tests with stimulus females was reduced compared to that of intact males. The results suggest that aromatization of T to E is not required for induction of androgen-dependent reproductive behavior in this lizard.     

Testosterone modulates the differential release of luteinizing hormone and follicle-stimulating hormone that occurs in response to changing gonadotropin-releasing hormone pulse frequency in the male monkey, Macaca fascicularis

Selective elevations of plasma follicle-stimulating hormone (FSH) levels are characteristic of some physiological conditions, such as the early stages of human puberty, and in some disorders of testicular function, such as idiopathic oligospermia. We tested the hypotheses that a slow gonadotropin-releasing hormone (GnRH) pulse frequency favors a selective elevation of plasma FSH and that this is influenced by the circulating steroidal milieu. We administered exogenous GnRH at frequencies of once every 90 min (q 90 min) and once every 240 min (q 240 min) to castrated prepubertal male monkeys who had received either empty (sham) or testosterone (T)-filled Silastic capsules at the time of castration. At the end of each experimental frequency period, mean plasma levels of luteinizing hormone (LH) and FSH were measured. Plasma T levels were also measured. Animals with T implants had plasma levels of this hormone that were in the adult range (approximately equal to 8 ng/ml), whereas those with sham implants had plasma T levels in the prepubertal range (less than or equal to 4 ng/ml). In animals with sham implants, mean plasma FSH levels were markedly elevated at the slower GnRH pulse frequency (39.5 +/- 3.6 ng/ml following GnRH q 240 min compared with 23.7 +/- 2.8 ng/ml following GnRH q 90 min). This selective FSH elevation was not apparent in animals with T implants. Mean plasma LH levels were similar (approximately equal to 8 micrograms/ml) at the two GnRH pulse frequencies, in both T-treated and sham-implanted animals.(ABSTRACT TRUNCATED AT 250 WORDS)     

Testosterone production in mice lacking inducible nitric oxide synthase expression is sensitive to restraint stress

Immobilization stress (IMO) induces a rapid increase in glucocorticoid secretion [in rodents, corticosterone CORT)] and this is associated with decreased circulating testosterone (T) levels. Nitric oxide (NO), a reactive free radical and neurotransmitter, has been reported to be produced at higher rates in tissues such as brain during stress. The biosynthesis of T is also known to be dramatically suppressed by NO. Specifically, the inducible isoform of nitric oxide synthase (iNOS) was directly implicated in this suppression. To assess the respective roles of CORT and NO in stress-mediated inhibition of T production, adult wild-type (WT) and inducible nitric oxide synthase knockout (iNOS(-/-)) male mice were evaluated. Animals of each genotype were assigned to either basal control or 3-h IMO groups. Basal plasma and testicular T levels were equivalent in both genotypes, whereas testicular weights of mutant mice were significantly higher compared with WT animals. Exposure to 3-h IMO increased plasma CORT and decreased T concentrations in mice of both genotypes. Testicular T levels were also affected by stress in WT and mutant males, being sharply reduced in both genotypes. However, the concentrations of nitrite and nitrate, the stable metabolites of NO measured in testicular extracts, did not differ between control and stressed WT and iNOS(-/-) mice. These results support the hypothesis that CORT, but not NO, is a plausible candidate to mediate rapid stress-induced suppression of Leydig cell steroidogenesis.