The development of small primate models for aging research

Nonhuman primate (NHP) aging research has traditionally relied mainly on the rhesus macaque. But the long lifespan, low reproductive rate, and relatively large body size of macaques and related Old World monkeys make them less than ideal models for aging research. Manifold advantages would attend the use of smaller, more rapidly developing, shorter-lived NHP species in aging studies, not the least of which are lower cost and the ability to do shorter research projects. Arbitrarily defining "small" primates as those weighing less than 500 g, we assess small, relatively short-lived species among the prosimians and callitrichids for suitability as models for human aging research. Using the criteria of availability, knowledge about (and ease of) maintenance, the possibility of genetic manipulation (a hallmark of 21st century biology), and similarities to humans in the physiology of age-related changes, we suggest three species--two prosimians (Microcebus murinus and Galago senegalensis) and one New World monkey (Callithrix jacchus)--that deserve scrutiny for development as major NHP models for aging studies. We discuss one other New World monkey group, Cebus spp., that might also be an effective NHP model of aging as these species are longer-lived for their body size than any primate except humans.     

The sexual behavior of the primates]

The article presents the review of modern data of the field and laboratory investigations of primate sexual behavior, cyclicity, reproductive strategies and copulation in different primates taxa: strepsirrhini, platyrrhyni, catarrhini. The specific character, progressiveness and adaptation of some reproductive models are discussed by the authors. A problem of connection between dominance and reproductive success is also discussed, the role of sexual teaching in postnatal ontogenesis, age and hormonal status for expression of sexual behavior are analysed. Some forms of sexual declinations in primates are considered.     

Pregnancy initiation in the rhesus macaque: Towards functional manipulation of the maternal-fetal interface

Nonhuman primates provide an important opportunity to define the mechanisms that contribute to the success of early pregnancy. We have focused for several years now on defining the expression of novel placental major histocompatibility complex (MHC) class I molecules. In parallel, we have used reagents against human immune cell markers to characterize the leukocyte population in the decidua and have demonstrated dynamic changes in these cell populations during the first 5 weeks of gestation. The challenge is to identify the possible role(s) of placental MHC class I in modifying/directing the maternal endometrial or systemic immune system in the post-implantation period. Foremost among the challenges is the difficulty in modifying placental function. In the instance of trophoblast surface proteins, passive immunization studies are feasible, although limitations include the empirical nature of this approach, as well as the inability to modify intracellular function. We have shown that using lentiviral vectors to effect preimplantation gene transfer for transgene expression in the placenta is not only feasible, but of good efficiency. In addition to transgene overexpression, robust approaches for knocking down/knocking out placental gene expression are essential. Recent developments in RNA interference approaches may allow "transient knockout" experiments. While the rhesus monkey has been our model of choice, currently there are limitations in the number of available female rhesus monkeys of reproductive age for research in early pregnancy. It is critical that the technologies for advanced study move forward in other species. The baboon has been used significantly in reproductive tract biology and early pregnancy research and important models have been developed for manipulation of the maternal-fetal interface. Additional characterization of other species, such as the cynomolgus and African green (vervet) monkey is critical. Given the limitations on antigen recognition when using human reagents, we also propose that the development of panels of primate-specific anti-leukocyte antibodies is essential for moving forward nonhuman primate reproductive research.     

Nonhuman primate infections after organ transplantation

Nonhuman primates, primarily rhesus macaques (Macaca mulatta), cynomolgus macaques (Macaca fascicularis), and baboons (Papio spp.), have been used extensively in research models of solid organ transplantation, mainly because the nonhuman primate (NHP) immune system closely resembles that of the human. Nonhuman primates are also frequently the model of choice for preclinical testing of new immunosuppressive strategies. But the management of post-transplant nonhuman primates is complex, because it often involves multiple immunosuppressive agents, many of which are new and have unknown effects. Additionally, the resulting immunosuppression carries a risk of infectious complications, which are challenging to diagnose. Last, because of the natural tendency of animals to hide signs of weakness, infectious complications may not be obvious until the animal becomes severely ill. For these reasons the diagnosis of infectious complications is difficult among post-transplant NHPs. Because most nonhuman primate studies in organ transplantation are quite small, there are only a few published reports concerning infections after transplantation in nonhuman primates. Based on our survey of these reports, the incidence of infection in NHP transplant models is 14%. The majority of reports suggest that many of these infections are due to reactivation of viruses endemic to the primate species, such as cytomegalovirus (CMV), polyomavirus, and Epstein-Barr virus (EBV)-related infections. In this review, we address the epidemiology, pathogenesis, role of prophylaxis, clinical presentation, and treatment of infectious complications after solid organ transplantation in nonhuman primates.     

Hormonal therapies and osteoporosis

Osteoporosis, now defined as a disease characterized by low bone mass and a microarchitectural deterioration of bone tissue leading to enhanced bone fragility and fracture risk, is a major public health problem. Classic hormonal therapies to prevent and treat osteoporosis associated with menopause have recently been questioned due to the risk/benefit ratio of prolonged treatment. There is a critical need for safe and effective alternative therapeutics for this disease. Nonhuman primates have been used as models to assess bone changes associated with estrogen deficiency because their trabecular and cortical bone remodeling processes, monthly menstrual cycles, and reproductive-hormone patterns are similar to those of humans. The ovariectomized nonhuman primate has become the preferred model in which to study effects on bone remodeling, particularly with regard to bone mass, architecture, and strength, in fulfillment of studies required by international guidelines for the development of antiosteoporotic drugs. The nonhuman primate is amenable to several methodologies that assess bone quantity and quality, including dual energy x-ray absorptiometry (DXA), quantitative computed tomography (QCT), histology, static and dynamic histomorphometry, and biomechanical testing, as well as assays developed for clinical use, which serve as biomarkers of bone metabolic processes. The use of the nonhuman primate model in the assessment of osteoporosis therapeutics, both hormonal (sex steroids and their analogues, parathyroid hormone) and nonhormonal (bisphosphonates), has provided valuable information on the safety and efficacy as well as the mechanisms of bone loss associated with estrogen deficiency that is directly applicable to the human situation.     

Primate Behavioral Ecology: From Ethnography to Ethology and Back

Nonhuman primates occupy a special niche in anthropology because of the comparative insights into humans they provide. Initial anthropological interest in primates targeted the apes for their close phylogenetic relationships with humans, and the semiterrestrial Old World monkeys for their ecological similarities with hominids adapting to life on the ground. From the earliest anecdotal reports of tool use and hunting to more contemporary quantitative analyses of local "cultural" traditions, nonhuman primates have challenged deep-rooted concepts of human uniqueness and redefined the boundaries between us and other animals. Yet, despite the long-standing influence of primate studies in anthropology, approaches to studying primates began diverging from those of earlier ethnographers. Advances in primatology, particularly during the 1990s, have included a much deeper understanding of how ecology, phylogeny, and demography affect behavior. Insights into intraspecific, population-level variation represent an important area of convergence between primatology, other areas of anthropology, and conservation biology. [Keywords: primate behavioral ecology, anthropocentrism, evolutionary theory, systematic methods, biology]     

Sex hormones, insulin sensitivity, and diabetes mellitus

Sex differences and the role of gonadal hormones in modulating insulin sensitivity and glucose tolerance are of increasing interest and importance because of the increasing prevalence of type 2 diabetes mellitus and the metabolic abnormalities associated with aging. Body composition is closely associated with insulin sensitivity, and increased body fat, particularly in the visceral compartment, is a risk factor for developing type 2 diabetes mellitus. Sex differences in body composition and/or insulin sensitivity are evident in humans throughout the lifespan. Ovarian hormones influence insulin sensitivity across the menstrual cycle, during pregnancy, and in the menopausal transition. Similarly, estrogens and progestins used for contraception and hormone replacement therapy affect glucoregulation. Nonhuman primates and humans have similar life histories and reproductive characteristics. As a result, nonhuman primates provide a valuable model for investigating factors related to insulin sensitivity. Studies of nonhuman primates have contributed significantly to our understanding of sex differences and the influence of sex steroids in this context. This brief review surveys present knowledge of the sex differences in body composition, insulin sensitivity, and risk for development of type 2 diabetes mellitus derived from studies in humans and nonhuman primates. The influences of endogenous and exogenous gonadal steroids are emphasized.     

Nonhuman primates are relevant models for research in hematology, immunology and virology

Nonhuman primates have been used for biomedical research for several decades. They have proved to be models that are relevant to humans because of the high level of gene homology which underlies physiological and biochemical similarities. The similarity of monkeys to humans has been used to investigate pathophysiological mechanisms in hematology, immunology and virology. New therapeutic procedures can be assessed in primates by using materials, in particular pharmacological reagents, and methods designed for humans. The relevance of these models also relies on the use of species-specific pathogens and the availability of recombinant, homologous cytokines. The introduction of more and more sophisticated cell and gene therapy protocols in hematopoietic cell transplantation and immunotherapy requires the development of preclinical trials similar to clinical settings. For several decades now, baboons and cynomolgus/rhesus monkeys have been the most useful primate models in experimental hematology, and this has contributed to numerous therapeutic advances. Primate models of AIDS have been developed to study the pathogenesis, transmission and immune responses to infection, and to test vaccines and drugs. Primate research should be restricted in quantity, and mainly designed with the aim of removing uncertainty as to the safety and clinical benefit to the patient, of new biomedical protocols.     

Markers of cartilage and bone matrix metabolism differ between the sera of macaque and squirrel monkeys

BACKGROUND: Nonhuman primates develop the characteristic lesions of osteoarthritis, making them attractive biomedical models for the study of environmental factors, such as diet, which may influence the progress of the condition. METHODS AND MATERIALS: We used ELISA assays of potential markers of osteoarthritis which were developed for use in humans to see if we could determined the presence of immunoreactivity in two nonhuman primate genera - Macaca (macaque monkeys) and Saimiri (squirrel monkeys). RESULTS: Inter-generic differences were significant for most markers. Three markers (bone alkaline phosphatase, hyaluronin and YKL-40) were outside the human range and two markers (laminin and C2C) did not yield useful results because they were off-scale high. CONCLUSION: Our results indicate that most of the ELISA assays designed for use with human serum can be used in nonhuman primates. The highly significant differences we observed between the sera of Macaca and Saimiri, suggest that further examination is warranted.     

Models of focal cerebral ischemia in the nonhuman primate

Ischemic stroke is a uniquely human disease syndrome. Models of focal cerebral ischemia developed in nonhuman primates provide clinically relevant platforms for investigating pathophysiological alterations associated with ischemic brain injury, microvascular responses, treatment responses, and clinically relevant outcomes that may be appropriate for ischemic stroke patients. A considerable number of advantages attend the use of nonhuman primate models in cerebral vascular research. Appropriate development of such models requires neurosurgical expertise to produce single or multiple vascular occlusions. A number of experimentally and clinically accessible outcomes can be measured, including neurological deficits, neuron injury, evidence of non-neuronal cell injury, infarction volume, real-time imaging of injury development, vascular responses, regional cerebral blood flow, microvascular events, the relation between neuron and vascular events, and behavioral outcomes. Nonhuman primate models of focal cerebral ischemia provide excellent opportunities for understanding the vascular and cellular pathophysiology of cerebral ischemic injury, which resembles human ischemic stroke, and the appropriate study of pharmacological interventions in a human relevant setting.     

Biology of primate relaxin: A paracrine signal in early pregnancy?

Relaxin is a peptide hormone that exerts numerous effects in a variety of tissues across a broad range of species. Although first identified more than 75 years ago interest in relaxin biology has waxed and waned over the years consistent with peaks and troughs of new experimental data on its wide-ranging biological effects and advances in relaxin enabling technologies. Recent insights into species-dependent differences in relaxin biology during pregnancy have once again stimulated a relative surge of interest in the study of relaxin's reproductive biology. Identification and pharmacological characterization of orphaned relaxin receptors and exploration of its paracrine effects on pregnancy using genomic and proteomic technologies have succeeded in fueling current interest in relaxin research. Primates and non-primate vertebrates exhibit very disparate profiles of relaxin genomics, proteomics and functional biology. Non-human primates appear to exhibit a very close similarity to humans with respect to relaxin reproductive biology but the similarities and subtle differences are only just beginning to be understood. We, and others, have shown that relaxin produces significant changes to the non-human primate endometrium during the peri-implantation period that are consistent with relaxin's long perceived role as a paracrine modulator of pregnancy. The purpose of this review is to summarize the reproductive biology of relaxin in non-human primates with a specific emphasis on the paracrine role of ovarian and endometrial relaxin during embryo implantation and early pregnancy.     

Menopause in nonhuman primates?

A gradual alteration in the mechanisms underlying reproduction and fertility characterizes the aging process in human females. These changes culminate in menopause, conventionally defined as a cessation of menstrual cycles that marks the end of reproductive capacity. In fact, a central and defining event in menopause is the discontinuation of ovulation, which is correlated with a number of structural and functional changes in the reproductive axis. Despite several decades of research, a degree of uncertainty remains as to whether nonhuman primates undergo menopause, and whether they are suitable models of human reproductive senescence. We review some of the controversies that have clouded our understanding of reproductive aging in nonhuman primates, including issues of definition, timing, comparability of data from wild versus captive populations, and cross-species comparisons. The existing data support the view that menopause occurs in a number of primate species and is not unique to humans.     

Retrieval of rhesus monkey (Macaca mulatta) oocytes by ultrasound‐guided needle aspiration: Problems and solutions

Oocytes of nonhuman primates such as rhesus monkeys are excellent models for diverse studies on developmental biology, epigenetics, human reproduction, and assisted reproductive technologies, as well as on transgenics. Such studies require numerous oocytes that can be retrieved after controlled ovarian stimulation. Currently, most primate centers use laparoscopic aspiration or laparotomy followed by aspiration to collect rhesus oocytes, although the ultrasound‐guided needle aspiration is more advantageous due to reduced infection risk, less injury, and a shorter recovery period. Yet, some initial difficulties associated with the ultrasound‐guided needle aspiration limit its broader application. The objective of the present study was to address these obstacles. By presenting practical solutions to the initial difficulties, results from our study show that it is possible to collect a mean number of 38 ± 10 rhesus oocytes per hormonally stimulated female. These results compare favorably to the average number of rhesus oocytes collected using the laparoscopic approach and suggest that when initial obstacles are overcome, the ultrasound‐guided oocyte retrieval represents a good alternative to more invasive approaches. Mol. Reprod. Dev. 76: 890–896, 2009. © 2009 Wiley‐Liss, Inc.     

Sex and context: hormones and primate sexual motivation

Gonadal hormones regulate the ability to copulate in most mammalian species, but not in primates because copulatory ability has been emancipated from hormonal control. Instead, gonadal hormones primarily influence sexual motivation. This separation of mating ability from hormonally modulated mating interest allows social experience and context to powerfully influence the expression of sexual behavior in nonhuman primates, both developmentally and in adulthood. For example, male rhesus monkeys mount males and females equally as juveniles, but mount females almost exclusively as adults. Having ejaculated with a female better predicted this transition to female mounting partners than did increased pubertal testosterone (T). It is proposed that increased pubertal T stimulates male sexual motivation, increasing the male's probability of sexual experience with females, ultimately producing a sexual preference for females. Eliminating T in adulthood reduces male sexual motivation in both humans and rhesus monkeys, but does not eliminate the capacity to engage in sex. In male rhesus monkeys the effects of reduced androgens on sexual behavior vary with social status and sexual experience. Human sexual behavior also varies with hormonal state, social context, and cultural conventions. Ovarian hormones influence female sexual desire, but the specific sexual behaviors engaged in are affected by perceived pregnancy risk, suggesting that cognition plays an important role in human sexual behavior. How the physical capacity to mate became emancipated from hormonal regulation in primates is not understood. This emancipation, however, increases the importance of motivational systems and results in primate sexual behavior being strongly influenced by social context.     

Urinary cyclic AMP excretion is increased in Macaca fascicularis and Macaca mulatta compared to humans

Changes in parathyroid hormone and its second messenger cyclic AMP have been implicated in the pathogenesis of osteoporosis. Nonhuman primate models have been useful in the study of osteoporosis, but the physiology of mineral metabolism in certain species is different than in humans. We investigated parameters of mineral metabolism in 15 normal adult female cynomolgus and 14 normal adult female rhesus monkeys. In both species, urinary cyclic AMP was increased compared with humans, and the nephrogenous cyclic AMP in the cynomolgus monkeys was also elevated. Despite this, there was no evidence for hyperparathyroidism in either species as evaluated by serum or plasma phosphorus and midregion-specific and/or aminoterminal-specific immunoreactive parathyroid hormone. Given the increasing use of nonhuman primates in the study of osteoporosis, understanding basic changes in mineral metabolism is important before pathologic effects of bone loss can be understood.     

关于非人灵长类的公正行为的研究

人类关注公正, 非人灵长类也表现出公正行为。本文先以现有研究资料为基础, 以理毛为例分析后认为, 非人灵长类关注投入—收益的对称性, 说明它们可能具备不公正规避这一心理特质; 关于非人灵长类公正行为的实验也表明, 它们不仅比较自身的投入—收益对称性, 而且能在社会比较过程中与其它个体相比。有实验得出期望假设和挫折效应能更好地解释被试的行为, 本文认为, 这些实验结论不一致的主要原因, 是研究者未充分考虑"投入"对被试行为的影响。文章在最后进行了总结并提出了三点研究展望。     

Zika virus persistence in the male macaque reproductive tract

Zika virus (ZIKV) is unique among mosquito-borne flaviviruses in that it is also vertically and sexually transmitted by humans. The male reproductive tract is thought to be a ZIKV reservoir; however, the reported magnitude and duration of viral persistence in male genital tissues vary widely in humans and non-human primate models. ZIKV tissue and cellular tropism and potential effects on male fertility also remain unclear. The objective of this study was to resolve these questions by analyzing archived genital tissues from 51 ZIKV-inoculated male macaques and correlating data on plasma viral kinetics, tissue tropism, and ZIKV-induced pathological changes in the reproductive tract. We hypothesized that ZIKV would persist in the male macaque genital tract for longer than there was detectable viremia, where it would localize to germ and epithelial cells and associate with lesions. We detected ZIKV RNA and infectious virus in testis, epididymis, seminal vesicle, and prostate gland. In contrast to prepubertal males, sexually mature macaques were significantly more likely to harbor persistent ZIKV RNA or infectious virus somewhere in the genital tract, with detection as late as 60 days post-inoculation. ZIKV RNA localized primarily to testicular stem cells/sperm precursors and epithelial cells, including Sertoli cells, epididymal duct epithelium, and glandular epithelia of the seminal vesicle and prostate gland. ZIKV infection was associated with microscopic evidence of inflammation in the epididymis and prostate gland of sexually mature males, pathologies that were absent in uninfected controls, which could have significant effects on male fertility. The findings from this study increase our understanding of persistent ZIKV infection which can inform risk of sexual transmission during assisted reproductive therapies as well as potential impacts on male fertility.     

Use of primates in research: a global overview

We assessed the use of nonhuman primates and nonhuman primate biological material in research by reviewing studies published in 2001 in peer-reviewed journals. The number and species of primates used, the origin of the animals, the type of study, the area of research of the investigation, and the location at which the research was performed were tabulated. Additionally, factors related to the animals that may have affected the outcome of the experiments were recorded. A total of 2,937 articles involving 4,411 studies that employed nonhuman primates or nonhuman primate biological material were identified and analyzed. More than 41,000 animals were represented in the studies published in 2001. In the 14% of studies for which re-use could be determined, 69% involved animals that had been used in previous experiments. Published studies most commonly used nonhuman primates or nonhuman primate biological material from the species Chlorocebus aethiops (19%), Macaca mulatta (18%), M. fascicularis (9%), and Papio spp. (6%). Of these studies, 54% were classified as in vitro studies, 14% as noninvasive, 30% as chronic, and 1% were considered acute. Nonhuman primates were primarily used in research areas in which they appear to be the most appropriate models for humans. The most common areas of research were microbiology (including HIV/AIDS (26%)), neuroscience (19%), and biochemistry/chemistry (12%). Most (84%) of the primate research published in 2001 was conducted in North America, Europe, and Japan. The animals and conditions under which they were housed and used were rarely described. Although it is estimated that nonhuman primates account for an extremely small fraction of all animals used in research, their special status makes it important to report the many husbandry and environmental factors that influence the research results generated. This analysis has identified that editors rarely require authors to provide comprehensive information concerning the subjects (e.g., their origin), treatment conditions, and experimental procedures utilized in the studies they publish. The present analysis addresses the use of primates for research, including the effects of a shortage of suitable nonhuman primate subjects in many research areas.     

Primate vaginal microbiomes exhibit species specificity without universal Lactobacillus dominance

Bacterial communities colonizing the reproductive tracts of primates (including humans) impact the health, survival and fitness of the host, and thereby the evolution of the host species. Despite their importance, we currently have a poor understanding of primate microbiomes. The composition and structure of microbial communities vary considerably depending on the host and environmental factors. We conducted comparative analyses of the primate vaginal microbiome using pyrosequencing of the 16S rRNA genes of a phylogenetically broad range of primates to test for factors affecting the diversity of primate vaginal ecosystems. The nine primate species included: humans (Homo sapiens), yellow baboons (Papio cynocephalus), olive baboons (Papio anubis), lemurs (Propithecus diadema), howler monkeys (Alouatta pigra), red colobus (Piliocolobus rufomitratus), vervets (Chlorocebus aethiops), mangabeys (Cercocebus atys) and chimpanzees (Pan troglodytes). Our results indicated that all primates exhibited host-specific vaginal microbiota and that humans were distinct from other primates in both microbiome composition and diversity. In contrast to the gut microbiome, the vaginal microbiome showed limited congruence with host phylogeny, and neither captivity nor diet elicited substantial effects on the vaginal microbiomes of primates. Permutational multivariate analysis of variance and Wilcoxon tests revealed correlations among vaginal microbiota and host species-specific socioecological factors, particularly related to sexuality, including: female promiscuity, baculum length, gestation time, mating group size and neonatal birth weight. The proportion of unclassified taxa observed in nonhuman primate samples increased with phylogenetic distance from humans, indicative of the existence of previously unrecognized microbial taxa. These findings contribute to our understanding of host–microbe variation and coevolution, microbial biogeography, and disease risk, and have important implications for the use of animal models in studies of human sexual and reproductive diseases.     

Cognition, mood disorders, and sex hormones

Macaques (Macaca spp.) are useful models to evaluate effects of ovarian sex steroids and selective estrogen receptor modulators (SERMs) on mood and cognitive function due to similarities to women in their reproductive and central nervous systems. The results of nonhuman primate studies support the hypothesis that estrogen mediates specific aspects of attention and memory, yet much work is needed to understand which cognitive processes are affected, whether natural versus surgical menopause effects are different, and the interaction of age and ovarian senescence on cognitive function. This knowledge is necessary to determine whether to support the cognitive function of women in the menopausal phase of life and, if so, to determine efficacious therapeutic interventions. Mood disorders are prevalent in women and are associated with reproductive function in women and macaques. Exogenous steroid therapies, including oral contraceptives and postmenopausal hormone replacement therapies, have behavioral effects in women and appear to affect the behavior and underlying neural substrates of monkeys. Additional research is necessary to confirm and extend these observations. Ovarian steroids have multiple effects on serotonin synthesis, reuptake, and degradation, on neural activity that drives serotonin release, and on receptor activation in primates. This system modulates cognitive function and mood and is the target of a broad class of antidepressant therapies. Understanding the effects of ovarian steroids on the neural serotonergic system is necessary to understand depression in women. These studies are best carried out in primate models, which are more similar to humans in neural serotonergic function than other animal models.