Future Surgical Leaders: Resident Perception Of Longitudinal Leadership And Non-Technical Skills Curriculum

OBJECTIVE

A paucity of formal leadership training programs exists for residents, and outcomes of those are limited in reporting. Based on a robust needs assessment, our program created a longitudinal cohort curriculum, Future Surgical Leaders, for residents and fellows of all levels to provide training in nontechnical skills. Our objective was to evaluate surgical resident short-term outcomes and satisfaction with the Future Surgical Leaders (FSL) curriculum.

DESIGN

Participants were sent a brief survey after each session of the curriculum from October 2020 to February 2022. The data was compiled after seventeen months of delivery. Likert Scale responses and text comments were analyzed with a 2-sample t-test and 2-way analysis of variance.

SETTING

Academic tertiary institution.

PARTICIPANTS

General surgery residents.

RESULTS

Survey response rate from 54 sessions among all postgraduate year levels was 73%. Overall, 96% of residents/fellows either "agreed" or "strongly agreed" that the topics of the FSL curriculum were important to learn during surgical training. Only 24% of learners knew "a lot" or "a great deal" about the topics prior to the session which rose to 73% afterwards (p < 0.01). Each postgraduate year class showed statistically significant increase in knowledge. About 80% of learners wanted to investigate these topics further. Open comment questions identified themes requesting delivery of specific sessions earlier in residency training and positive overall attitudes toward the FSL curriculum.

CONCLUSIONS

FSL is a satisfactory means of teaching leadership skills to surgical residents. Residents recognize the need to develop leadership skills prior to entering practice and want to learn more. The FSL curriculum may be considered for application at other surgical training programs.

Defining Pathologic Upstaging in cT1b Esophageal Cancer: Should We Consider Neoadjuvant Therapy?

INTRODUCTION

Neoadjuvant chemoradiation therapy (NCRT) for cT1b esophageal cancer is not recommended despite the risk of pathologic upstaging with increased depth of penetration. We aimed to (1) define the rate of and factors associated with pathologic upstaging, (2) describe current trends in treatments, and (3) compare overall survival (OS) with and without NCRT for surgically resected cT1b lesions.

METHODS

We used the 2020 National Cancer Database to identify patients with cT1b N0 esophageal cancer with or without pathologic upstaging who underwent removal of their tumor. We built multivariable logistic regression models to assess factors associated with pathologic upstaging. Survival was compared using log-rank analysis and modeled using multivariable Cox proportional hazards regressions.

RESULTS

Out of 1106 patients with cT1b esophageal cancer, 17.3% (N = 191) had pathologic upstaging. A higher tumor grade (P = 0.002), greater tumor size (P < 0.001), and presence of lympho-vascular invasion (P < 0.001) were associated with pathologic upstaging. 8.0% (N = 114) of patients were treated with NCRT. Five-y OS was 49.4% for patients who received NCRT compared to 67.2% for upfront esophagectomy (P < 0.05). Pathologic upstaging was associated with decreased OS (pathologic upstaging 43.7% versus no pathologic upstaging 67.7%) (hazard ratio 2.12 [95% confidence interval, 1.70-2.65; P < 0.001]). Compared to esophagectomy, endoscopic local tumor excision was associated with a decreased OS (hazard ratio 1.50 [95% confidence interval, 1.19-1.89; P = 0.001]).

CONCLUSIONS

Pathologic upstaging of cT1b lesions is associated with decreased OS. Esophagectomy is associated with a survival benefit over endoscopic local tumor excision for these lesions. NCRT is not associated with an increase in OS in cT1b lesions compared to upfront esophagectomy.

Spatial distributions in disaster risk vulnerability for people with disabilities in the U.S

BACKGROUND

The spread of Coronavirus Disease 2019 (COVID-19) in the United States has centered the role of natural hazards such as pandemics into the public health sphere. The impacts of these hazards disproportionately affect people with disabilities, who are frequently in situations of social, political, or economic disadvantage. Because of these disadvantages, people with disabilities may have less access to necessary resources and services, putting them at risk due to unmet health needs. These disparities in access also highlight important regional, state, and county-level differences with regards to vulnerability and preparedness for natural hazards.

OBJECTIVE

The objective of this paper is to examine the relationship between disability and disaster risk in the United States. We examine the geographic variation in the relationship between risk from natural disasters and the percentage of people with disabilities living in a community. Because emergency management functions in the U.S. are directed and enacted at the county level, we also explore how these relationships change across U.S. counties. In addition to the overall prevalence of people with disabilities, we disaggregate the population of people with disabilities by gender, race, ethnicity, age, and disability impairment type.

METHODS

To measure risk of natural hazards, we use Expected Annual Loss index, a component of the 2020 National Risk Index, developed by Federal Emergency Management Agency, which identifies communities most at risk to18 natural hazards. We measure the percent of people with disabilities per county using the American Community Survey. We estimate the nationwide relationship between the proportion of people with disabilities and risk of natural hazards using ordinary least squares regression. To explore geographic differences in these relationships across the United States, we use a geographically weighted regression model to estimate local relationships for each county in the contiguous United States. We use mapping techniques to display regional differences across different disability demographic groups.

RESULTS

Counties with higher percentages of people with disabilities have a lower risk of natural disasters. Across the United States, a one percent increase in prevalence of people with disabilities in a county is associated with two percent decrease in the natural hazard risk score. Small but statistically significant regional differences exist as well. County-specific estimates range from a five percent decrease to a one percent increase. Stronger associations between risk and the prevalence of people with disabilities are observed in the Midwest and parts of the Southwest and West, whereas the relationship across racial groups is more scattered across the United States.

CONCLUSION

In this study, nationwide results suggest that people with disabilities are more likely to live in communities with lower risk of natural hazards, but this relationship differs across U.S. counties and by demographic subgroups. These findings represent a contribution in further understanding the health and well-being of people with disabilities in the United States and the geographic variation therein.

Bridging the Gap: How to Get Osteopathic Residents Into Fellowships

Introduction

The fellowship match process is convoluted, with each specialty having its match on its timeline- with some programs having a Post Graduate Year (PGY) 4^th-year or 5^th-year match.

This study aims to identify tangible recommendations for osteopathic surgery residents to use to improve their applications and, ultimately, the success rate for matching into post-graduate fellowship training.

Methods

In October 2021, as a part of the American College of Osteopathic Surgeons (ACOS) Strategic Planning efforts, the ACOS Resident Student Section sent a questionnaire to the listed email contact for each surgical fellowship program. Fellowship coordinators and program directors were included in the survey. The programs that were included in the study were vascular, thoracic (which included cardiothoracic), surgical critical care, endocrine, hepatobiliary, transplant, pediatric, surgical oncology, breast, minimally invasive, and colorectal surgery.

Results

Of the 108 programs that answered the survey, 36% of them reported they currently had an osteopathic fellow, and another 29% said they had an osteopathic fellow in the past. 35% of the programs listed that they had never had an osteopathic fellow in their program.

In regards to how residents can improve their application for fellowship matches the most common answer was research in the field, they were trying to match into. They wanted to see high scores on the United States Medical Licensing Examination (USMLE) and American Board of Surgery In-Training Examination (ABSITE) exams. They also noted that they wanted candidates from more well know residency programs, where they knew the residents would have gotten good training.

Conclusion

We recommend that any potential fellowship applicant focus on the following three areas increase competitiveness for matching into fellowship training: publication in the desired field, increased overall scholarly activity, and increased ABSITE scores.

Rare Case of Tracheal Fibromyxoma in Obstructive Tracheal Mass

A 77-year-old male with a history of chronic obstructive pulmonary disease (COPD) who presented with cough, congestion, and stridor and was found to have a near obstructing tracheal mass. He subsequently underwent excision of the mass. On pathologic examination, it was diagnosed as fibromyxoma of the trachea. Primary tumors of the trachea are rare, and fibromyxoma of the trachea is extremely rare. This is the third report of a fibromyxoma on the tracheal wall. In this report the clinical manifestations, and surgical management were compared with the other two reported cases.

Predicting program outcomes for vocational rehabilitation customers: A machine learning approach

BACKGROUND: The Vocational Rehabilitation (VR) program provides support and services to people with disabilities who want to work. OBJECTIVE: Approximately one-third of eligible VR customers are employed when they exit the program. The remainder either exit without ever receiving services or without employment after receiving services. In this study, we explore how customer characteristics and VR services predict these outcomes. METHODS: We examined VR case level data from the RSA-911 files. Machine learning techniques allowed us to explore a large number of potential predictors of VR outcomes while requiring fewer assumptions than traditional regression methods. RESULTS: Consistent with existing literature, customers who are employed at application are more likely to exit with employment, and those with mental health conditions or low socioeconomic status are less likely to exit with employment. Some customers with low or no earnings at application who are not identified in prior studies are more likely than others to have poor program outcomes, including those with developmental disability who are under 18, customers without developmental or learning disabilities, and customers who do not receive employment or restoration services. CONCLUSIONS: VR counselors and administrators should consider implementing early, targeted interventions for newly identified at-risk groups of VR customers.

What happens after high school? A review of independent living practices to support youth with disabilities transitioning to adult life

BACKGROUND: Centers for Independent Living (CILs) can help out-of-school youth with disabilities. CIL services may be particularly important for minority youth with disabilities that face additional transition barriers. OBJECTIVE: This literature review documents existing practices that might aid CILs as they seek to help youth, including minority youth, with disabilities transition to adult life. METHODS: First, we conducted a literature search to identify practices that might help CILs assist youth with disabilities transition to independent living (IL) in early adult life. Then we examined various literature syntheses of postsecondary transition interventions with evidence of promise or efficacy for any IL-related outcome—regardless of whether the intervention targeted youth with disabilities. RESULTS: We discovered a variety of practices CILs might learn from or consider adopting to help youth with disabilities transition to adult life. However, the practices rarely focused on minority youth and usually had limited or no evidence about whether they improved IL outcomes. CONCLUSIONS: The limitations of the evidence we found suggest the need to develop and test interventions that help transition age youth with disabilities—especially minority youth with disabilities—achieve their IL goals.

Correction to: Benefit Duration and Return to Work Outcomes in Short Term Disability Insurance Programs: Evidence from Rhode Island's Temporary Disability Insurance Program

The original version of this article unfortunately contained a mistake in the article title. The text "Rhode Island's" inadvertently omitted in the original publication.

Benefit Duration and Return to Work Outcomes in Short Term Disability Insurance Programs: Evidence from Temporary Disability Insurance Program

Purpose The Workforce Innovation and Opportunity Act strengthens the vocational rehabilitation program's focus on providing early intervention services to keep workers with disabilities in the workforce. At the same time, some have suggested that short-term disability insurance (STDI) programs may hold promise as an early intervention service, helping people with disabilities stay in the labor force and avoid needing longer-term benefits. Rhode Island is one of five states with a mandatory STDI program. We examine the extent to which Rhode Island STDI claimant characteristics are correlated with partial return-to-work (PRTW) benefit receipt and certain STDI benefit receipt duration measures.Methods Our study used administrative data from 2011 to 2014 to explore Rhode Island's STDI program-called the Temporary Disability Insurance program-and regression analysis to estimate the correlations of interest. Results Regression adjusted estimates revealed that claimants opting to receive PRTW benefits earned more and received benefits for fewer weeks than claimants opting to not receive PRTW benefits. We also observed significant correlations between duration of benefit receipt and claimant characteristics such as diagnosis and treating healthcare provider specialty. Conclusions Findings suggest that STDI claimants with certain characteristics are more likely to receive benefits for a long duration or not receive PRTW benefits, signaling that they might benefit from early Vocational Rehabilitation supports and services that would allow them to remain productive members of the workforce and avoid long term benefit receipt.

Personal and Contextual Factors Associated With Successful Vocational Rehabilitation and Employment Outcomes

Some individuals with disabilities have relatively better labor outcomes than others. If vocational rehabilitation (VR) counselors can better understand what factors are correlated with positive outcomes, they could better identify what clients are at risk for poor outcomes and then intervene early to improve chances for success. Unfortunately, until recently VR survey and administrative data have had insufficient information to investigate these questions. We use a survey of 932 Ohio VR clients combined with administrative earnings data to examine the barriers and facilitators associated with employment and earnings outcomes. The survey data are from the 2014 Survey of Disability and Employment, a survey of VR applicants in three states. We compare VR case status and earnings through 2016, by demographics, functional limitation status, employment history and attitudes, and reasons stated for not working in the survey. We find that about 25% of survey respondents exited the program employed or had at least one quarter of average monthly earnings above the Social Security Administration’s substantial gainful activity amount. Pain, depression or anxiety, longer duration of job separation, personal and familial attitudes about work, and not working because of personal and health reasons were associated with poorer outcomes among survey respondents.

Understanding the Disability Dynamics of Youth: Health Condition and Limitation Changes for Youth and Their Influence on Longitudinal Survey Attrition

Disability status-experiencing a functional limitation caused by a health condition-is dynamic throughout the life cycle, even during adolescence and young adulthood. We use data from the 1997 cohort of the National Longitudinal Survey of Youth to better understand these dynamics, examining how health condition and limitation statuses evolve during adolescence and young adulthood as well as how changes in these characteristics are related to survey nonresponse and attrition. Health condition and limitation dynamics are evident in our data: the proportion of sample members who reported having a limitation in their activities for any interview increased from approximately 12 % during the initial interview (when sample members were 12 to 17 years old) to almost 25 % 13 years later. Multivariate analyses revealed that women are more likely than men to report changes in health condition or limitation status. Those with mild limitations were relatively less likely than those without limitations or with severe limitations to experience changes in limitation status. Somewhat surprisingly, a survival analysis of survey participation outcomes found limited correlation among health conditions, limitations, and either missing a survey interview for the first time or permanently leaving the survey sample.

Starting Behind

We estimate the wage offers and employment of young adults with and without disabilities using National Longitudinal Survey of Youth 1997 data. We find evidence that wage offer and employment gaps between adults with and without disabilities emerge early and are largest for those with mental limitations or any type of severe limitation. The wage offer gaps we estimate between people with and without disabilities are almost always larger than the wage gaps between those groups. These employment and wage offer gaps that exist in early adulthood likely help explain some of the differences in human capital, employment, and earnings between older adults with and without disabilities. The results also highlight the need for interventions that improve the employability and wage offers of youth with disabilities.

Is Timing Everything? Disability Onset of Youth and Their Outcomes As Young Adults

The accumulation of human capital during childhood and adolescence greatly influences the value employers place on youth as they transition into the adult labor market. Disabilities acquired prior to adulthood have the potential to disrupt this critical human capital accumulation. This study examines how disability onset among youth affects their education and employment outcomes as young adults. We find that youth with limiting disabilities—especially mental limiting impairments—have poorer labor market and human capital outcomes than their peers without limitations. We also discover some evidence that youth with persistent or later onset disabilities have poorer outcomes than those whose disabilities dissipate as they become adults. These findings suggest that surveys targeting youth and young adults should consider including better measures of disability onset and mental impairment status to understand the disability characteristics of this population.

The role and potential sites of action of thyroid hormone in timing the onset of puberty in male primates

Puberty in primates is first delayed by a neurobiological switch that arrests pulsatile GnRH release during infancy and then triggered, after a protracted period of juvenile development, by resurgence in intermittent release of this hypothalamic peptide. The purpose of this chapter is to review recent studies conducted in our laboratories to begin to examine the role of thyroid hormone (TH) in governing this postnatal development of pulsatile GnRH release in primates and therefore the timing of puberty in these species. The male rhesus monkey was used as the experimental model and TH activity was manipulated by surgical and chemical thyroidectomy on the one hand, and by thyroxine (T(4)) and triiodothyronine (T(3)) replacement on the other. Our results indicate that the resurgence in pulsatile GnRH release at the termination of the juvenile phase of development is dependent on a permissive action of TH. Whether this action of TH is mediated directly on hypothalamic centers regulating the pulsatile release of GnRH, or indirectly by circulating signals reflecting TH action on somatic development remains to be determined.

Leptin-signaling inhibition results in efficient anti-tumor activity in estrogen receptor positive or negative breast cancer

Introduction

We have shown previously that treatment with pegylated leptin peptide receptor antagonist 2 (PEG-LPrA2) reduced the expression of vascular endothelial growth factor (VEGF), vascular endothelial growth factor receptor type 2 (VEGFR2) and growth of 4T1-breast cancer (BC) in syngeneic mice. In this investigation, PEG-LPrA2 was used to evaluate whether the inhibition of leptin signaling has differential impact on the expression of pro-angiogenic and pro-proliferative molecules and growth of human estrogen receptor-positive (ER⁺) and estrogen receptor-negative (ER^-) BC xenografts hosted by immunodeficient mice.

Methods

To test the contribution of leptin signaling to BC growth and expression of leptin-targeted molecules, PEG-LPrA2 treatment was applied to severe immunodeficient mice hosting established ER⁺ (MCF-7 cells; ovariectomized/supplemented with estradiol) and ER^- (MDA-MB231 cells) BC xenografts. To further assess leptin and PEG-LPrA2 effects on ER⁺ and ER^- BC, the expression of VEGF and VEGFR2 (protein and mRNA) was investigated in cell cultures.

Results

PEG-LPrA2 more effectively reduced the growth of ER⁺ (>40-fold) than ER^- BC (twofold) and expression of pro-angiogenic (VEGF/VEGFR2, leptin/leptin receptor OB-R, and IL-1 receptor type I) and pro-proliferative molecules (proliferating cell nuclear antigen and cyclin D₁) in ER⁺ than in ER^- BC. Mouse tumor stroma in ER⁺ BC expressed high levels of VEGF and leptin that was induced by leptin signaling. Leptin upregulated the transcriptional expression of VEGF/VEGFR2 in MCF-7 and MDA-MB231 cells.

Conclusions

These results suggest that leptin signaling plays an important role in the growth of both ER⁺ and ER^- BC that is associated with the leptin regulation of pro-angiogenic and pro-proliferative molecules. These data provide support for the potential use of leptin-signaling inhibition as a novel treatment for ER⁺ and ER^- BC.

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.

Regulation of circulating leptin and its soluble receptor during pubertal development in the male rhesus monkey (Macaca mulatta)

In humans, circulating leptin levels are low in early childhood and rise until puberty, whereas the reverse occurs for the soluble leptin receptor (sOB-R). In women, leptin remains high and sOB-R remains low, but in men leptin declines after adolescence and sOB-R increases. These observations suggest that leptin may regulate the production of sOB-R, and that the increased testosterone in adolescent boys may be responsible for the gender differences in leptin and sOB-R. To test this hypothesis, leptin was administered continuously to agonadal juvenile male monkeys for 16 days. No change in sOB-R was observed. Intact juvenile male monkeys were given pulsatile doses of gonadotropins for a period of 7 weeks to induce precocious puberty and assess the effect on plasma testosterone, leptin, and sOB-R. By 4 weeks testosterone had reached adult levels. No changes were observed in leptin, but by week 4, sOB-R was higher than pretreatment values and remained higher at week 7. These data suggest that leptin may not play a significant role in regulating the production of sOB-R and that gender differences in sOB-R in humans may be driven by the increased production of testosterone at puberty in males.

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.

Influence of a leptin deficiency on testicular morphology, germ cell apoptosis, and expression levels of apoptosis-related genes in the mouse

Leptin-deficient (ob/ob) male mice are morbidly obese and exhibit impaired reproductive function. The objective of this study was to assess the effect of a leptin deficiency on testicular morphology, germ cell development, apoptotic activity within germ cells, and expression levels of apoptosis-related genes in the testis. Sixteen week-old ob/ob male mice (n = 8) and controls (n = 8) were killed, and their reproductive organs were weighed. Testes were processed for either histomorphological analysis (hematoxylin and eosin [H&E] staining), germ cell apoptosis assessment (deoxy-UTP-digoxigenin nick end labeling [TUNEL] method), or apoptosis-related gene expression analysis (microarray). Cross sections of the testes of leptin-deficient animals showed reduced seminiferous tubule area, fewer pachytene spermatocytes, and fewer tubules exhibiting elongated spermatids/mature spermatozoa. Condensation of germ cell nuclei and Sertoli cell vacuolization were evident in the testes of some ob/ob animals. Overall there was an elevation of apoptotic activity in the germ cells of ob/ob mice, particularly within the pachytene spermatocytes. With microarray technology, we identified 9 proapoptosis-related genes that were expressed at a significantly higher level in the testes of ob/ob mice than in the testes of the controls. Among these were members of the tumor necrosis factor receptor super family 1A and 5 (TNFR1 and 5) and peptidoglycan recognition proteins (associated with the extrinsic apoptotic pathway), and granzymes A and B, growth arrest and DNA damage inducible 45 gamma, sphingosine phosphate lyase 1, and caspase 9 (associated with the intrinsic apoptotic pathway). The results of the current study show that a leptin deficiency in mice is associated with impaired spermatogenesis, increased germ cell apoptosis, and up-regulated expression of proapoptotic genes within the testes.

Impact of gonadotropin administration on folliculogenesis in prepubertal ob/ob mice

Female leptin deficient (ob/ob) mice exhibit abnormal ovarian folliculogenesis resulting in an impaired ability to reproduce. This effect may be related to the hypogonadotropic state of these animals, or leptin may directly modulate ovarian follicle development. In the present study we assessed whether exogenous gonadotropin administration would normalize folliculogenesis and induce ovulation in immature ob/ob animals. Eight 26-day-old ob/ob and eight control mice were injected sc with pregnant mare serum gonadotropin followed 48 h later with a sc injection of human chorionic gonadotropin. Animals were killed 24 h later. Gonadotropin (GTH) administration increased both ovarian and uterine weights in control mice, but this effect was attenuated in leptin deficient animals. The number of preantral follicles was greater in ob/ob mice than controls, but in GTH-treated animals the number of antral follicles was subnormal in the ovaries of leptin deficient animals. Ob/ob animals also failed to ovulate in response to GTH, and the protective actions of GTH against granulosa cell apoptosis and follicular atresia were attenuated in these animals. Interestingly, however, serum levels of estradiol and progesterone were higher in ob/ob mice than controls, regardless of whether or not the animals received GTH treatment. We conclude that the ovarian responsiveness to GTH is subnormal in leptin deficient animals suggesting that leptin may modulate the process of folliculogenesis by directly altering the sensitivity of the ovary to GTH.

Relationship between serum concentrations of leptin, soluble leptin receptor, testosterone and IGF-I, and growth during the first year of postnatal life in the male rhesus monkey, Macaca mulatta

OBJECTIVES

Subnormal leptin levels in low birth weight infants may allow for catch-up growth during infancy. Scant data are available that relate growth with circulating leptin during normal infancy in primates. The current study objective was to examine the association between serum leptin, its soluble receptor (sOB-R), testosterone and IGF-I concentrations, and body weight during infancy in male rhesus monkeys.

DESIGN

Hormone levels were assessed longitudinally in animals (n = 7) from birth until 1 year of age.

RESULTS

Body weight increased during the first 6 months of life and was strongly correlated with rising IGF-I levels and, as IGF-I plateaued and then declined during the second half of the year, body weight gain decelerated. In contrast, leptin levels declined gradually with age during the first year of life in conjunction with increasing body weight. There was no association between body weight gain and serum leptin levels or between serum testosterone and leptin values. Since sOB-R levels also declined with leptin values, it does not appear that levels of bioavailable leptin changed during infancy.

CONCLUSIONS

The data do not support the contention that leptin regulates growth during infancy, but the close association between IGF-I levels and body weight suggested that this hormone may regulate growth in infant male monkeys. The failure to observe an association between serum testosterone and leptin concentrations suggested that leptin is not involved in the activation of the hypothalamic-pituitary -testicular axis during this developmental period.

Folliculogenesis Is Impaired and Granulosa Cell Apoptosis Is Increased in Leptin-Deficient Mice1

Leptin purportedly plays an important role in pubertal development in a number of mammalian species. Adult leptin-deficient (ob/ob) female mice are infertile, but the mechanisms responsible for the reproductive failure have not been fully elucidated. The major objective of the current study was to assess the effects of a leptin deficiency on ovarian folliculogenesis and apoptosis. Beginning at 4 wk of age, control (n = 8) and ob/ob (n = 7) mice were weighed and examined daily for vaginal opening. After 3 wk the mice were killed, and the reproductive organs were weighed. Ovaries were paraffin-embedded for hematoxylin and eosin histology, TUNEL assay, and immunohistochemistry for Fas, Fas ligand (FasL), and proliferating cell nuclear antigen (PCNA). Vaginal opening was delayed, uteri were smaller, and the number of primordial follicles and total number of ovarian follicles were subnormal in ob/ob animals. Leptin-deficient animals also had a higher number of atretic follicles than controls. Granulosa cells (predominantly in preantral and early antral follicles) of ob/ob mice exhibited increased apoptotic activity as documented by TUNEL assay and elevated expression of the apoptotic markers Fas and FasL, compared with that in control animals. Ovarian expression of PCNA, a marker of DNA replication, repair, or both, did not differ between ob/ob and control mice. The data suggest that a leptin deficiency in mice is associated with impaired folliculogenesis, which results in increased follicular atresia. This impairment may be one of the causative components of infertility in leptin-deficient animals.

Does leptin mediate the effect of photoperiod on immune function in mice?

Seasonal fluctuations in immune status have been documented for avian and mammalian populations. During the late summer and early fall, immune function is bolstered to help animals cope with the more physiologically demanding winter. The environmental cue for these seasonal changes is apparently decreasing photoperiod. In the present study, we determined the potential role of leptin in mediating the effect of photoperiod on cell-mediated immune responses in male mice. Leptin-deficient (ob/ob) and littermate control mice were housed for 10 wk in either a short (8L:16D) or a long (16L:8D) photoperiod beginning at 6 wk of age. After the mice were killed, immune and reproductive organs were weighed and splenocytes isolated. The proliferative and cytokine responses (interleukin [IL]-2 and IL-4) of splenocytes to the T-cell mitogen, concanavalin A (Con A; 0-40 microg/ml), were determined. Body weights were elevated and both testes and seminal vesicle weights subnormal in ob/ob mice (by ANOVA, main effect of leptin deficiency), but thymuses and spleens were of normal size. Serum leptin levels were at minimum detection limits in ob/ob mice, but leptin levels in control mice housed at 8L:16D were higher than in control mice housed at 16L:8D. The proliferative response of splenocytes from ob/ob mice to Con A was subnormal (by ANOVA, main effect of leptin deficiency), but photoperiod had no effect on this response. Production of IL-2 in splenocytes of ob/ob mice was subnormal (by ANOVA, main effect of leptin deficiency) irrespective of photoperiod, but cells from mice housed at 8L:16D (by ANOVA, main effect of photoperiod) produced more IL-2 than cells from animals housed at 16L:8D. In contrast, a leptin deficiency did not alter IL-4 production, but cells from animals (ob/ob and controls) housed at 16L:8D produced less IL-4 than cells from animals housed at 8L:16D (by ANOVA, main effect of photoperiod). The present study suggests that both photoperiod and leptin have mutually independent effects on the proliferation of lymphocytes and cytokine production profiles. The data do not provide definitive support for the hypothesis that photoperiod-induced changes in leptin secretion mediate the effects of season on immune status.

Changes in circulating leptin, leptin receptor, and gonadal hormones from infancy until advanced age in humans

We determined developmental changes in circulating levels of the soluble leptin receptor (sOB-R), leptin, and gonadal hormones in human subjects. In both sexes the rise in leptin with age was associated with a decline in sOB-R, and age-related changes in both parameters preceded the pubertal rise in gonadal hormones. Leptin levels above 10 ng/ml were a strong predictor of sOB-R concentrations, but this predictive value decreased as leptin declined. In young subjects there were no gender differences in serum leptin, but boys had higher sOB-R levels. In adults neither leptin nor sOB-R changed with age, but serum leptin was higher and sOB-R was lower in women than men. There was a significant negative correlation between sOB-R and leptin in women, but not men. The data suggest that bioavailable leptin in the circulation may be increasing more rapidly during development than indicated by total leptin levels, and that these changes may serve as one of the signals to the central nervous system that metabolic conditions are adequate to support pubertal development. Furthermore, the study provides suggestive evidence that leptin regulates the secretion of its own binding protein, but it also appears that an additional gender-specific, leptin-independent, regulatory mechanism is functional before puberty.

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.

Leptin and pubertal development

Sexual development after birth in rodents, nonhuman primates, and humans is driven by the gonadotropin-releasing hormone (GnRH) pulse generator. During the neonatal period in primates, pulsatile GnRH discharge from the medial basal hypothalamus drives an active period of pituitary gonadotropin and gonadal hormone secretion. During the transition from the neonatal to the juvenile period, however, the activity of the GnRH pulse generator is restrained or arrested and gonadotropin and gonadal hormone secretion enters a quiescent period that continues until the onset of puberty. As puberty approaches the GnRH pulse generator is reactivated, resulting in enhanced gonadotropin secretion, accelerated growth, maturation of the gonads, and the achievement of sexual competence. Rodents do not appear to exhibit a developmental phase analogous to the quiescent juvenile period in primates when the GnRH pulse generator is held in check. Instead, progressive maturational changes in the pattern of GnRH pulsatility appear to drive sexual development in rodents. The role that leptin plays in sexual development has not been fully defined, but the balance of current evidence appears to support the idea that, in both rodents and primates, leptin plays a permissive rather than a causal role in timing this process. When body energy reserves rise above a critical level, blood leptin increases to a threshold concentration signaling to the central nervous system that the body can support sexual function. Puberty can apparently occur over a wide range of concentrations above this critical leptin threshold. Leptin does not appear to act as a trigger to time the initiation of puberty but, instead, once leptin reaches this threshold pubertal development may proceed if, and only if, other critical control mechanisms are operational.

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.

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.

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.

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 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.

A Reinke-like inclusion within Leydig cells of the marmoset monkey (Callithrix jacchus)

The Reinke crystal is a distinctive feature of human Leydig cells of the adult maturation phase. This large subcellular structure, first described in 1896 by Reinke, has been well documented ultrastructurally by numerous investigators during the past few decades (e.g. Fawcett & Burgos, 1960; de Kretser, 1967; Sohval et al. 1973; Christensen, 1975; Kerr, 1991). Although Leydig cells of many mammals contain unusual inclusions, the Reinke crystal has long been considered unique to the human Leydig cell. Its precise molecular composition and significance are unknown. It is, however, known to contain proteins (Janko & Sandberg, 1970) and has been found to increase within the cell with age (Mori et al. 1978). The purpose of the present report is to describe the presence of an inclusion with much similarity to the Reinke crystal within Leydig cells of the marmoset monkey (Callithrix jacchus).

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.

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.

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.

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.

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.

Acute immobilization stress alters LH and ACTH release in response to administration of N-methyl-D,L-aspartic acid in peripubertal and adult male rats

We have evaluated the effects of stress on the pituitary hormone response to N-methyl-D,L aspartic acid (NMA) in peripubertal (43 day old) and adult (80 day old) male rats. Animals were stressed by immobilization for 3 h. Fifteen min prior to the end of the stress period, animals were injected sc with either vehicle or increasing doses of NMA (10, 30 or 60 mg/kg BW). Animals were sacrificed 15 minutes later. A significant rise in plasma LH in response to NMA occurred at a lower dose (10 versus 60 mg/kg BW), and the magnitude of the response was greater overall in peripubertal than in adult unstressed rats. Stress altered the LH response to NMA in both age groups. In peripubertal stressed rats, NMA did not induce a rise in plasma LH levels. In adult rats exposed to stress, the magnitude of the LH response to 60 mg/kg BW of NMA was lower than in unstressed animals. NMA administration triggered a rise in plasma ACTH levels in unstressed rats of both age groups, but the magnitude of the rise was greater in adults than in peripubertal animals. Stress reduced the ACTH response to NMA administration in both age groups. Plasma FSH concentrations were higher in peripubertal animals than in adults. NMA and stress were without major effect on plasma FSH levels in either age group. These data suggest that excitatory amino acids (EAA) form an important component in the regulatory processes governing the release of LH and ACTH, and that the maturational stage of the central nervous system and exposure to stress alter the LH and ACTH response to EAA.

Acute immobilization stress disrupts testicular steroidogenesis in adult male rats by inhibiting the activities of 17 alpha-hydroxylase and 17,20-lyase without affecting the binding of LH/hCG receptors

We have investigated the effect of acute immobilization (3 hours) stress on testicular steroidogenesis in the adult rat. Immobilization did not alter plasma luteizing hormone (LH) levels, but plasma testosterone (T) levels were reduced by 82%. Plasma levels of corticosterone in stressed rats were elevated more than ninefold over control levels. After 3 hours of stress, testicular levels of progesterone were elevated 33%, and levels of 17 alpha-hydroxyprogesterone and T were reduced 47% and 37%, respectively, compared to controls. Immobilization for 3 hours had no effect on the association or dissociation rate constants of LH/human chorionic gonadotropin (hCG) receptors of testicular interstitial cells and did not alter specific hCG binding. The effect of 3 hours of immobilization on testicular 17 alpha-hydroxylase and 17,20-lyase was assessed by incubating testicular microsomes from stressed and control animals in the presence of 21[14C]progesterone and [3H]17 alpha-hydroxyprogesterone. Immobilization of rats reduced the Vmax values of 17 alpha-hydroxylase and 17,20-lyase by 47% and 48%, respectively, but had no effect on the Km values. These results support the hypothesis that stress for 3 hours disrupts rat testicular steroidogenesis via a mechanism that is independent of changes in circulating levels of LH and the binding characteristics of LH/hCG receptors. The effects of immobilization on the content of testicular steroids and on the activities of 17 alpha-hydroxylase and 17,20-lyase suggest that stress inhibits the activities of both 17 alpha-hydroxylase and 17,20-lyase.