Effect of transient hypothyroidism during infancy on the postnatal ontogeny of luteinising hormone release in the agonadal male rhesus monkey (Macaca mulatta): implications for the timing of puberty in higher primates.

The present study examined whether a transient thyroid hormone (T(4)) deficit during infancy in male monkeys would compromise the arrest of luteinising hormone (LH) secretion during the infant-juvenile transition, and/or interfere with the pubertal resurgence of LH. Animals were orchidectomized and thyroidectomized (n = 3; Tx) or sham Tx (n = 3) within 5 days of birth. T(4) replacement was initiated in two Tx monkeys at age 19 weeks to reestablish a euthyroid condition. Blood samples were drawn weekly for hormone assay. Body weight, crown-rump length, and bone age were assessed throughout the study. Within a week of Tx, plasma T(4) declined to undetectable levels and, by 6-8 weeks of age, signs of hypothyroidism were evident. Transient hypothyroidism during infancy failed to prevent either arrest of LH secretion during the infant-juvenile transition or the pubertal resurgence of LH secretion, both of which occurred at similar ages to sham Tx animals. Although body weight exhibited complete catch-up with T(4) replacement, crown-rump length and bone age did not. Thus, bone age at the time of the pubertal LH resurgence in Tx animals was less advanced than that in shams. Although Tx did not influence qualitatively the pattern of gonadotrophin secretion, LH levels during infancy and after pubertal LH resurgence were elevated in Tx monkeys. This was not associated with changes in LH pulse frequency and amplitude, but half-life (53 versus 65 min) of the slow second phase of LH clearance was greater in Tx animals. These results indicate that hypothalamic mechanisms dictating the pattern of gonadotrophin-releasing hormone release from birth to puberty are not dependent on T(4) action during infancy, and fail to support the notion that onset of puberty is causally coupled to skeletal maturation. They also indicate that LH renal clearance mechanisms may be programmed in a T(4) dependent manner during infancy.

Induction of a hypothyroid state during juvenile development delays pubertal reactivation of the neuroendocrine system governing luteinising hormone secretion in the male rhesus monkey (Macaca mulatta).

The present study aimed to determine the influence of thyroid status on the timing of the pubertal resurgence in gonadotrophin-releasing hormone pulse generator activity [tracked by circulating luteinising hormone (LH) levels] in male rhesus monkeys. Six juvenile monkeys were orchidectomised and then treated with the antithyroid drug, methimazole, from 15-19 months until 36 months of age, at which time thyroxine (T(4)) replacement was initiated. Four additional agonadal monkeys served as controls. Blood samples were drawn weekly for hormonal assessments. Body weight, crown-rump length and bone age were monitored at regular intervals. By 8 weeks of methimazole treatment, plasma T(4) had fallen sharply, and the decline was associated with a plasma thyroid-stimulating hormone increase. In controls, plasma LH levels remained undetectable until the pubertal rise occurred at 29.3 +/- 0.2 months of age. This developmental event occurred in only half of the methimazole-treated animals before 36 months of age when T(4) replacement was initiated. The hypothyroid state was associated with a profound arrest of growth and bone maturation, but increased body mass indices and plasma leptin levels. T(4) replacement in methimazole-treated monkeys was associated with the pubertal rise in LH in the remaining three animals and accelerated somatic development in all six animals. Although pubertal resurgence in LH secretion occurred at a later chronological age in methimazole-treated animals compared to controls, bone age, crown-rump length and body weight at that time did not differ between groups. There were no long-term differences in plasma prolactin between groups. We conclude that juvenile hypothyroidism in male primates causes a marked delay in the pubertal resurgence of LH secretion, probably occasioned at the hypothalamic level. Whether this effect is meditated by an action of thyroid hormone directly on the hypothalamus or indirectly as a result of the concomitant deficit in somatic development remains to be determined.

Leptin and thyroxine during sexual development in male monkeys: effect of neonatal gonadotropin-releasing hormone antagonist treatment and delayed puberty on the developmental pattern of leptin and thyroxine secretion.

OBJECTIVE: Neonatal treatment of male monkeys with a gonadotropin-releasing hormone antagonist (Ant) increased the incidence of delayed puberty. Using blood samples that had been collected from monkeys with normal or delayed puberty, we assessed the potential involvement of leptin and thyroxine (T4) in sexual development. DESIGN AND METHODS: Monkeys were treated from birth until 4 months of age with vehicle, Ant or Ant/androgen and blood samples were drawn from 10 to 62 months of age. RESULTS: Serum leptin and total T4 concentrations declined in parallel throughout adolescence in all treatment groups. There was no transient rise in leptin before or in association with the onset of puberty. Also, leptin did not differ during the peripubertal period between animals experiencing puberty at that time versus those in which puberty was being delayed. Neonates treated with Ant either alone or with androgen replacement had higher leptin levels than controls throughout development. While leptin exhibited no significant changes during the peripubertal period, T4 values increased and declined in parallel with the peripubertal changes in hypothalamic-pituitary-testicular activity. CONCLUSIONS: These data do not support the concept that a transient rise in leptin triggers the onset of puberty in male monkeys. However, the disruption of neonatal activity of the pituitary-testicular axis alters the developmental pattern of leptin. The changes in T4 levels during the peripubertal period suggest that thyroid status may be a significant contributor to the process of sexual development in the male monkey and that peripubertal changes in secretion of this hormone may serve as an effective physiological response during a critical period of elevated energy expenditure.

Endocrine-immune interaction: alteractions in immune function resulting from neonatal treatment with a GnRH antagonist and seasonality in male primates.

PROBLEM: The effect of neonatal gonadotropin releasing hormone (GnRH) antagonist (Ant) treatment and seasonality on immune system development and function was investigated in male primates. METHOD OF STUDY: Neonatal male rhesus monkeys and marmosets were treated with Ant, and its effect on immune system morphology, circulating lymphocyte subsets, and cell- and humorally-mediated immune responses was assessed during development. In adult rhesus monkeys, we correlated seasonal changes in immune function with circannual fluctuations in immunoactive hormones. RESULTS: In neonatal marmosets, Ant reduced the number of B cells and T cells in the thymic medulla and T cells in the periarterial lymphatic sheaths (PALS) of the spleen. Ant also altered the development of, but did not permanently impair, the proliferative index (PI) of blood lymphocytes to mitogens. In vitro treatment of control lymphocytes with GnRH analogues altered their response to these proliferative agents. In neonatal rhesus monkeys, Ant treatment increased the frequency of clinical problems, lowered circulating levels of lymphocytes, total T cells, CD8+ T cells and B cells, and altered the PI of lymphocytes to mitogens. As adults, the cell- and humorally-mediated immune responses remained impaired. We also documented seasonal fluctuations in the prevalence of diseases, circulating immune cells and immune function in rhesus monkeys. The number of cases of campylobacteriosis and shigellosis was lowest in the winter and highest in the spring. Circulating numbers of white blood cells (WBC) and neutrophils and the PI of lymphocytes to mitogens were higher in the winter than in the summer. Natural killer cell activity also varied with season. Cortisol and leptin secretion exhibited circannual rhythms, rising in concert with decreasing photoperiod and increasing testicular activity in the fall. Conversely, prolactin levels declined with decreasing photoperiod and then rose in the spring. CONCLUSION: Neonatal exposure of male primates to Ant appears to alter early postnatal programming of immune function. In the rhesus monkey, immune function shows seasonal fluctuations that may be driven by circannual changes in the secretion of immunoactive hormones.

Timing of prenatal androgen exposure: anatomical and endocrine effects on juvenile male and female rhesus monkeys.

Prenatal androgen shapes genital differentiation. In humans, genital anatomy determines sex of rearing and subsequent behavioral development. Rhesus monkey genital anatomy and neuroendocrine function are sexually differentiated, and behavioral development occurs in a complex social environment. We investigated prenatal hormonal influences on sexual differentiation by suppressing or increasing androgens in male and female rhesus monkeys. Pregnant multiparous female rhesus monkeys received 35-40 days of testosterone enanthate (TE) treatment, androgen antagonist (flutamide, FL) treatment, or vehicle starting on gestation day (GD) 35 or 40 (early) or GD 110 or 115 (late). Exogenous androgen increased neonatal LH secretion in females when given early and altered female genital differentiation when administered either early or late. TE treatment, early or late in gestation, had no measurable effects on male genital differentiation or neuroendocrine function. Early FL treatment, however, radically altered male genital differentiation, producing in two cases males with a urethral opening separate from the glans. In females, early FL treatment produced detectable alterations in genitalia consistent with a reduced exposure to prenatal androgen, suggesting that female rhesus monkeys are naturally exposed prenatally to meaningful levels of T. Late FL treatment reduced male penis size and increased neonatal T secretion, but had no effect in females. This is the first study to block endogenous prenatal testosterone in rhesus monkeys, thereby altering sexual differentiation. These findings illustrate the complexity of prenatal influences on anatomical and neuroendocrine development. The relationship between the anatomical changes reported here and sex differences in behavior is currently under investigation.

Seasonal variations in cytokine expression and cell-mediated immunity in male rhesus monkeys.

Our objectives in this study were to examine seasonal changes in immune responses including cytokine profiles of male rhesus monkeys housed under natural lighting conditions. We also monitored circannual changes in the secretion of several immunomodulatory hormones as potential mediators of the seasonal shifts in immune status. Retrospectively, the medical records of a large group of rhesus monkeys were examined to determine whether a common disease (campylobacteriosis) in this species shows a seasonal pattern of prevalence. Results of the study showed that there was a seasonal shift in the frequency of cells expressing TH1 cytokines (interleukin-2 and interferon-gamma) versus the TH2 prototype cytokine (interleukin-4) by peripheral blood mononuclear cells (PBMC) collected during the winter and summer. The frequency of TH1-type cytokine synthesis in the summer was markedly greater than in the winter whereas TH2-type cytokine expression did not vary between the two seasons. The proliferative response of PBMC to mitogens and natural killer cell activity of PBMC also varied with the season. Several hormones (testosterone, leptin, and prolactin) that modulate immune function exhibited circannual patterns of secretion. The prevalence of Campylobacter infections was higher in the spring than during the summer, fall, or winter. The data suggest that seasonal fluctuations in immune system status may alter the ability of primates to successfully respond to pathogens, and this may be related to circannual patterns of secretion of immunomodulatory hormones.

A longitudinal study of leptin during development in the male rhesus monkey: the effect of body composition and season on circulating leptin levels.

The objective of this study was to examine longitudinal changes in serum leptin concentrations during development and to correlate those changes with sexual development in male rhesus monkeys housed under natural environmental conditions. Blood samples were drawn from 8 control animals approximately every other month from 10 to 30 mo of age and thereafter monthly through 80 mo of age. Leptin levels declined through the juvenile period until the onset of puberty and were negatively correlated with body weight. Seven of the eight animals became sexually mature during the breeding season of their fourth year of life. Puberty was delayed in the other animal until the subsequent breeding season. There were no significant fluctuations in leptin levels prior to or in association with the pubertal rise in LH and testosterone (T) secretion. During the peripubertal period, levels of leptin varied between 2 and 3 ng/ml. The animal that exhibited delayed puberty had the lowest body weight and highest leptin levels during this period. With the achievement of sexual maturity, leptin levels varied seasonally, with peak levels in the late winter (Jan-Mar) and a nadir in the late summer (Aug-Sept). A late winter rise in leptin was also evident in most of the animals during Years 2 and 3, but not during Year 4. In the fall of Years 5 and 6, the seasonal rise in leptin concentrations lagged 3-4 mo behind the seasonal increase in LH and T. In the fall of Year 5, but not thereafter, leptin levels were positively related to percent body fat and negatively correlated with lean body mass. The data do not support the hypothesis that increasing leptin concentrations trigger the onset of puberty in the male rhesus monkey. During the juvenile period and after sexual maturation, but not during the peripubertal period, leptin secretion varied with season in the animals; but the environmental factors that cue or drive this rhythm remain to be determined.

Effect of neonatal treatment with a GnRH antagonist on development of the cell-mediated immune response in marmosets.

PROBLEM: We examined the effect of neonatal treatment with a gonadotropin-releasing hormone (GnRH) antagonist (antide) on the development of cell-mediated immunity in male marmosets. METHOD OF STUDY: Neonatal marmoset twins were treated with either vehicle or antide, and the proliferative response (PR) of lymphoid tissue to mitogens was assessed during infancy, the peripubertal period, and adulthood. RESULTS: Basal proliferation of peripheral blood mononuclear cells (PBMC) from treated peripubertal twins was elevated above control values, but the PR of the cells to T and B cell mitogens was subnormal. Conversely, PBMC from treated infants exhibited an enhanced PR to some of the mitogens employed. In vitro culturing of thymocytes (control or treated) from the three developmental stages with either antide or a GnRH agonist increased basal proliferation, but decreased the PR to mitogens by 60-80%. CONCLUSION: Neonatal treatment with antide alters development of, but does not permanently impair, cell-mediated immunity in the marmoset. GnRH appears to modulate immune responses throughout development in the primate.

Expression of mRNA and proteins for testicular steroidogenic enzymes and brain and pituitary mRNA for glutamate receptors in rats exposed to immobilization stress.

The objectives of this study were to determine whether stress attenuates the pituitary LH response to excitatory amino acids by altering expression of glutamate receptor 1 (GluR1) and N-methyl-D-aspartic acid (NMDA) receptor mRNA levels in the hypothalamus or pituitary, and assess whether stress influences testicular levels of mRNA or protein for steroidogenic enzymes. Three hours (h) of immobilization stress was associated with a greater than 7-fold increase in serum corticosterone, and a marked reduction in serum testosterone (T) concentrations. Stress did not significantly alter hypothalamic or pituitary GluR1 and NMDA receptor mRNA levels. Although transcript levels for P450SCC and P45017alpha mRNA in the testis were unchanged in stressed rats, western blotting of testicular fractions revealed reduced amounts of P450SCC and 3beta-HSD, but not P45017alpha. The data suggest that immobilization stress reduces T production by suppressing the translation of transcripts for P450SCC and 3beta-HSD, but the attenuated LH response of stressed animals to NMDA is not mediated by altered hypothalamic or pituitary expression of GluR1 and NMDA receptor levels.

Effect of neonatal treatment with a gonadotropin releasing hormone antagonist on developmental changes in circulating lymphocyte subsets: a longitudinal study in male rhesus monkeys.

We have examined changes in circulating lymphocyte subsets from the neonatal period until adulthood (4 months until 5.5 years of age) in male rhesus monkeys, and the impact of neonatal treatment with a GnRH antagonist (Ant) or Ant and androgen (Ant/And) on these parameters. Absolute numbers of lymphocytes, B cells, total T lymphocytes, and CD4+ T cells decreased, neutrophils increased, and CD8+ T cells did not change with age. WBC counts increased between 4 mo and 2 years of age and then fell to neonatal levels over the next two years. The decline of CD4 + T cells in association with stable CD8+ T cell levels resulted in an age-related decrease in the CD4+/CD8+ T cell ratio. At 4 months of age, WBC's, lymphocytes, total T cells, CD8+ T cells and B cells were lower in Ant- and Ant/And-treated animals compared to controls. With the exception of WBC counts, these values had normalized by 2 years of age. Reduced WBC levels in treated animals persisted through adulthood. CD4+ T cell levels tended to be lower in Ant-treated and higher in Ant/And-treated animals than in controls at 4 months of age. CD4+ T cells remained lower in Ant- than in Ant/And-treated animals at most ages. The higher CD4 + T cell counts in Ant/And-treated animals resulted in an elevated CD4 + /CD8 + T cell ratio that persisted until the onset of year 5. During years 5 and 6, seasonal fluctuations in WBC's and neutrophils were observed with counts being higher in the breeding (fall) than in the nonbreeding (summer) season. The data document that developmental changes in circulating immune cells in the rhesus monkey are qualitatively similar to those reported in humans, and provide further evidence that neonatal treatment of male rhesus monkeys with Ant or Ant/And may alter early programming of the immune system.

Sexual maturation in male rhesus monkeys: importance of neonatal testosterone exposure and social rank.

In a 5-year longitudinal study, we examined the effect of disrupting the neonatal activity of the pituitary-testicular axis on the sexual development of male rhesus monkeys. Animals in a social group under natural lighting conditions were treated with a GnRH antagonist (antide), antide and androgen, or both vehicles, from birth until 4 months of age. In antide-treated neonates, serum LH and testosterone were near or below the limits of detection throughout the neonatal period. Antide + androgen-treated neonates had subnormal serum LH, but above normal testosterone concentrations during the treatment period. From 6 to 36 months of age, serum LH and testosterone were near or below the limits of detection. Ten of 12 control animals reached puberty during the breeding season of their 4th year, compared with five of 10 antide- and three of eight antide + androgen-treated animals. Although matriline rank was balanced across treatment groups at birth, a disruption within the social group during year 2 resulted in a marginally lower social ranking of the two treated groups compared with the controls. More high (78%) than low (22%) ranking animals reached puberty during year 4. During the breeding season of that year, serum LH, testosterone and testicular volume were positively correlated with social rank. Thus the lower social rank of treated animals may have contributed to the subnormal numbers of these animals reaching puberty during year 4. However, of those animals achieving puberty during year 4, the pattern of peripubertal changes in serum testosterone and testicular volume differed between control and antide-treated animals. The results appear to suggest that the disruption of normal activity of the neonatal pituitary--testicular axis retarded sexual development, but that social rank is a key regulatory factor in setting the timing of sexual maturation in male rhesus monkeys. The effect of neonatal treatment with antide and low social rank on sexual development could not be reversed by neonatal exposure to greater than normal concentrations of androgen.

Changes in lymphoid tissue after treatment with a gonadotropin releasing hormone antagonist in the neonatal marmoset (Callithrix jacchus).

PROBLEM: The effect of neonatal treatment with a gonadotropin releasing hormone (GnRH) antagonist on the morphology and distribution of lymphocytes in lymphoid tissue of the infant marmoset was examined. METHOD OF STUDY: From a screened panel of antihuman antibodies for specific immune cells, antibodies for the CD20 and CD3 antigens showed excellent reactivity with marmoset tissue. Five sets of marmoset twins were treated with either the GnRH antagonist or a vehicle from birth, and were euthanized at 7 to 9 (3 sets) or 16 to 20 weeks (2 sets) of age. The spleen, thymus, and inguinal lymph nodes from each animal were processed for immunocytochemistry, and the number of cells expressing the CD20 and CD3 antigens were quantified. RESULTS: Control twins exhibited high plasma levels of testosterone, characteristic of the neonatal period, whereas testosterone concentrations were reduced (P = 0.001) to detection limits in the GnRH antagonist-treated twins. Microscopic evaluation suggested that treatment reduced the volume and cellularity of the thymic cortex, resulting in a decrease in the cortical-to-medullary ratio. Treatment reduced (P = 0.046) the number of thymocytes expressing the B-cell antigen (CD20) and marginally lowered (P = 0.067) the number expressing the T-cell antigen (CD3) in the thymic medulla. In the spleens of treated animals, periarterial lymphatic sheaths were less prominent on microscopic examination, and there were marginally fewer (P = 0.064) CD3+ cells. Numbers of CD20+ lymphocytes in the peripheral white pulp of the spleen and in the germinal centers of the lymph nodes, or CD3+ cells in the paracortex and germinal centers of the lymph nodes, were not altered by treatment. CONCLUSION: Neonatal treatment with a GnRH antagonist may alter maturational processes for B and T cells in the thymus and spleen of the marmoset and may deprive the immune system of its normal sensitivity to GnRH at a potentially critical time in development.

Blockade of the hypothalamic-pituitary-testicular axis with a GnRH antagonist in the neonatal marmoset monkey: changes in Leydig cell ultrastructure.

Little is known of the cell biology of Leydig cells during the neonatal activation of the hypothalamic-pituitary-testicular (HPT) axis. The current study examined the effect of blockade of the HPT axis with a GnRH antagonist (antide) on the neonatal population of Leydig cells in the new world primate, the common marmoset. Three sets of twins, age 7 weeks, were studied: in each pair one twin was used as a control, while the other received treatment with GnRH antagonist from the day of birth to suppress pituitary gonadotrophin secretion. Leydig cells of treated animals were dramatically different from those of controls. The cells were atrophic and exhibited very irregular nuclei. The organelles involved in steroid synthesis were reduced to the extent to being barely evident. The smooth endoplasmic reticulum (SER) was greatly diminished in quantity and distribution. The usual form of the SER (anastomosing tubules) was not evident, but, instead, the SER was relatively unbranched. Peroxisomes, organelles involved in transfer of cholesterol to the mitochondria, were greatly reduced in number. Mitochondria were relatively sparse and exhibited a non-typical morphology, as tubular elements of the cristae were rarely evident. Thus, the central apparatus in steroid production, the SER, mitochondria and peroxisomes, was essentially shut down in the GnRH-antagonist-treated animals. Storage of cholesterol, the precursor of steroid biosynthesis, was also not in evidence, as lipid droplets were extremely rare. Two prominent features of control in neonatal marmoset Leydig cells, the membranofibrillar inclusion (MFI) and basal laminae, remain prominent in the Leydig cells of treated animals. Evidence of apoptosis was not observed. These results provide strong support that the gonadotrophic hormones are the primary regulator of neonatal Leydig cell development in primates, and also suggest cell regression, rather than apoptosis, being the mechanism of this inhibition.

Prolonged inhibition of normal ovarian cycles in the rat and cynomolgus monkeys following a single s.c. injection of danazol.

In castrated male rats, a single s.c. injection of danazol has been shown to result in an inordinately prolonged inhibition of serum luteinizing hormone (LH) and follicle stimulating hormone (FSH) concentrations. In the present study, we have examined whether the same and similar routes of administration suppresses ovarian function in normally cycling rats and cynomolgus monkeys. Normally cycling female rats received danazol as a single administration either orally, i.m. or s.c. and a separate group also received danazol in silastic capsules. The duration of the dioestrous interval until the next oestrous smear was followed daily and cycle lengths were compared with vehicle-treated groups. Six normally cycling cynomolgus monkeys were followed by daily observation and blood sampling at 2-3 day intervals. After one normal cycle, danazol (200 mg/kg) was administered as a single s.c. injection. Monkeys were followed until the next menses and one cycle thereafter and blood samples were assayed for oestradiol, progesterone and bioactive LH. Oestrous cycle length in vehicle-treated control rats was 4.7 days. A single administration of danazol s.c. at the higher dose prolonged the dioestrous interval to 31.3 days (P <0.001) and a similar prolongation was observed with this high dose when administered i.m. (27.7 days; P <0.001). In normally cycling monkeys, the menstrual cycle length was 30.2 days, but following a single danazol administration, the mean duration to the next menses was prolonged to 117.5 days (P <0.001). In five out of six monkeys, there was a decrease in LH and an absence of normal oestradiol and progesterone patterns. After this prolonged hiatus, a subsequent menstrual cycle was normal in length and endocrine pattern. A single s.c. administration of danazol resulted in a prolonged suppression of ovarian cyclicity in both normally cycling rats and cynomolgus monkeys.

Inhibin-B in the male rhesus monkey: impact of neonatal gonadotropin-releasing hormone antagonist treatment and sexual development.

We examined the effect of reversibly suppressing pituitary-testicular function during the neonatal period on developmental changes in inhibin-B and FSH secretion in male rhesus monkeys. Infants were treated with either vehicle, a GnRH antagonist (Ant) or the Ant and androgen (Ant/And) for the first 4 postnatal months, and the effects on serum inhibin-B and FSH were monitored during the neonatal and peripubertal periods. In neonates, Ant or Ant/And treatment lowered both serum FSH and inhibin-B levels. By 12 months of age, inhibin-B concentrations no longer differed across treatment groups. A major increase in inhibin-B occurred between 27-36 months of age (late prepubertal period) in all groups, but levels were lower at 33 and 36 months of age in Ant/And-treated animals than in controls. These differences most likely were related to fewer Ant/And-treated animals achieving sexual maturity during their fourth year of life. Regardless of treatment, inhibin-B levels were higher in those that were destined to become mature (in year 4) than in those that were not. During the late prepubertal period, serum inhibin-B was positively correlated with age and testicular volume, but not with serum LH or testosterone. After this period (39-52 months of age), inhibin-B no longer correlated with these parameters. FSH levels were near or below detection limits in most peripubertal animals, but FSH was detectable in fewer samples from control than treated animals. The data suggest that inhibin-B secretion in the neonate is driven by gonadotropin secretion, but during the juvenile hiatus in gonadotropin secretion, the monkey testis continues to produce substantial amounts of this hormone.

The neonatal period: a critical interval in male primate development.

It appears from the evidence documented in this Commentary that the neonatal period is another critical stage in the process of sexual, behavioural and immune system development and maturation in primates. Interference with normal brain-pituitary-gonadal function during this period (e.g. with a GnRH analogue in monkeys) appears to impact adversely on subsequent reproductive, immunological and behavioural function. These data further emphasize the importance of fully understanding the regulatory mechanisms that govern neonatal gonadal function in the primate, if we are to eliminate, control or minimize the potential risk resulting from its disruption in humans. Given the recent evidence that the reproductive potential of the human male has declined rather dramatically over the last 50 years, and that clinical conditions associated with abnormal testicular function are on the rise, continued investigation in this area would appear to be imperative.

Mechanism of stress-induced attenuation of the testicular response to gonadotropin: possible involvement of testicular opioids, a pertussis toxin-sensitive G-protein, and phosphodiesterase.

This study examined the potential role of testicular opioids, a pertussis toxin (PT)-sensitive G-protein, and phosphodiesterase in mediating the inhibitory effect of immobilization stress on testicular steroidogenesis in adult rats. The experiments were initiated with enriched preparations of Leydig cells, but the stress effect was not sustained in vitro either as a result of the disruption of the morphology of the testis and/or the time required for Leydig cell isolation. Consequently, testicular fragments from control and stressed (3-hour immobilization) rats were used in these experiments. When fragments from stressed rats were incubated for 2 hours in the absence and presence of human chorionic gonadotropin (hCG) (0.1,1, or 10 mlU), testosterone (T) production in response to 1 and 10 mlU hCG was lower (P < 0.05 and 0.01, respectively) than that from control fragments. Basal T secretion did not differ between stressed and control fragments. Naloxone (1, 10, or 100 mu M), did not alter basal or hCG-stimulated T secretion from control fragments, but it normalized the T response to hCG from stressed fragments. Control fragments also showed a reduced T response (P < 0.05) to hCG in the presence of beta-endorphin (beta-E; 36 nM). Incubation of control fragments with PT (30 ng) did not alter basal or hCG-stimulated T production. However, PT normalized (P < 0.01) hCG-stimulated T secretion from stressed fragments. Methylisobutylxanthine (MIX; 0.125 mM) elevated (P < 0.01) hCG-stimulated T production from control fragments, but hCG-stimulated T secretion from stressed fragments remained subnormal in the presence of the phosphodiesterase inhibitor. The data suggest that acute immobilization stress inhibits gonadotropin-induced T production in adult male rats via a mechanism involving testicular opioids and a PT sensitive G-protein. We found no evidence to suggest that a stress induced increase in the activity of phosphodiesterase was involved in this mechanism.

Neonatal testosterone and handedness in yearling rhesus monkeys (Macaca mulatta).

This study investigated the relationship between neonatal testosterone (T) and hand bias in young rhesus monkeys (Macaca mulatta). Subjects (n = 8 per group) included: neonatally androgen-suppressed males, using a Nal-Lys gonadotropin releasing hormone (GnRH) antagonist (Antide); androgen-suppressed males receiving T replacement by a long-acting T preparation (CDB); control males; and control females. Antide suppressed T to the female range, whereas CDB replacement produced supranormal levels. Visually guided reaching, in a social context, showed a population-level left-hand bias. Males with elevated T did not show a stronger left-hand bias than males with normal T, but did show a stronger bias for the preferred hand whether left or right. Males with Antide-suppressed T showed an intermediate degree of hand bias. Results suggest that high neonatal T levels affect laterality and raise the possibility that GnRH analogues influence brain development. These data suggest a broad influence of the CNS-pituitary-testicular axis on brain asymmetries and provide support for an early neonatal period of T-influenced brain differentiation.

Effects of neonatal testicular suppression with a GnRH antagonist on social behavior in group-living juvenile rhesus monkeys.

Twenty-four male and eight female 1-year-old rhesus monkeys (Macaca mulatta) were observed for social interaction with other yearlings and with their mothers. The males comprised three groups which differed in the level of neonatal androgen exposure. One group received the GnRH antagonist Antide during their first four neonatal months (Antide n = 8), which suppressed pituitary LH secretion resulting in peak neonatal T levels < 0.7 nmol/liter. A second group received Antide treatment combined with a long-lasting testosterone replacement (Ant/And n = 8), which resulted in peak neonatal T levels of 29.1 +/- 3.8 nmol/liter. The third group (Vehicle n = 8) received the Antide and androgen vehicles and had intermediate peak T levels of 5.2 +/- 1.0 nmol/liter. Behavior of males was compared to that of unmanipulated control females living in the same social group (Control Female n = 8) when androgen levels were uniformly low (< 0.7 nmol/liter) in all male groups. Subjects received 12 weekly 30-min focal observations by an observer blind to the neonatal treatments. Marked sex differences were found in several categories of sociosexual behavior. All three groups of males engaged in significantly more sexual and play behavior than females, with the exception of quiet solitary play, which females exhibited significantly more frequently In addition, females exhibited significantly more interest in infants than did any male group. There were no differences between groups in agonistic behavior or time spent in contact with other individuals, but females spent significantly more time than any male group in proximity to other animals. Both females and Antide males initiated proximity and followed animals significantly more frequently than Ant/And males, but not Vehicle males. Proximity durations with mothers initiated and terminated by yearlings were longer for females than for any male group and for Antide males than for Ant/and males. Antide males were groomed significantly longer than any other group. These results demonstrate effects of neonatal testosterone exposure on social behavior in yearling rhesus. Suppression of neonatal T did not affect sexually dimorphic patterns of play and sexual behavior, but altered the character of interactions with their mothers. Whether this reflects a delay in the development of maternal independence or a fundamental alteration in patterns of social interaction remains to be resolved.