Modeling Women's Health with Nonhuman Primates and Other Animals

Effects of Age and Multiple Vaginal Births on Lower Urinary Tract Structure and Function in Nonhuman Primates

Purpose: The relative roles of urinary sphincter damage, aging, and childbirth in stress urinary incontinence (SUI), have not been established. This study was performed to elucidate the roles of these factors.Methods: The study included: (1) 8 female cynomolgus monkeys (17–19 years of age and 7–8 vaginal births each); (2) six 5-yearold nulliparous monkeys with surgically created chronic urinary sphincter dysfunction; and (3) six 5-year-old, nulliparous, nosurgery controls. Sedated abdominal leak point pressure (ALPP) and maximum urethral sphincter pressures (MUP) were measured. Sphincters, bladders, and pelvic support muscles were quantified for collagen content. Additionally, bladders were analyzed for collagen fiber thickness, length, and angle using CT-FIRE analysis of Picrosirius red-stained tissues.Results: Resting MUP values were similar in the controls and older multiparous monkeys (P>0.05). However, aging and multiple births reduced pudendal nerve-stimulated increases in MUP (P<0.05 vs. controls). ALPP values were lower in the older multiparous versus younger groups of monkeys (P<0.05). Sphincter collagen content was greater, and muscle content less, in the injury model (P<0.05 vs. controls). However, these measures were not affected by age and childbirth (P>0.05 vs. young groups). Bladder collagen content was greater, and muscle content less, in the old multiparous monkeys (P<0.05 vs. younger groups). Additionally, collagen fibers were thicker and more angular in the bladders of the older multiparous monkeys than in the other nonhuman primate groups (P<0.05). Pelvic support muscles had higher collagen and lower muscle content in the older multiparous monkeys than in the younger groups of monkeys (P<0.05).Conclusions: SUI, associated with aging and multiple childbirths, appeared to be more strongly associated with bladder dysfunction, reduced pelvic muscle support, and the compensatory response to neural stimulation than with selective urinary sphincter dysfunction.

Nonhuman Primates: A Vital Model for Basic and Applied Research on Female Reproduction, Prenatal Development, and Women's Health

The comparative biology of reproduction and development in mammalian species is remarkable. Hence, because of similarities in environmental and neuroendocrine control of the reproductive axis, the cyclic function of the ovary and reproductive tract, establishment and control of the maternal-fetal-placental unit during pregnancy, and reproductive aging from puberty through menopause, nonhuman primates (NHPs) are valuable models for research related to women's reproductive health and its disorders. This chapter provides examples of research over the past 10+ years using Old World monkeys (notably macaque species), baboons, and to a lesser extent New World monkeys (especially marmosets) that contributed to our understanding of the etiology and therapies or prevention of: (1) ovarian disorders, e.g., polycystic ovary syndrome, mitochondrial DNA-based diseases from the oocyte; (2) uterine disorders, for example, endometriosis and uterine transplantation; and (3) pregnancy disorders, for example, preterm labor and delivery, environmental factors. Also, emerging opportunities such as viral (e.g., Zika) induced fetal defects and germline genomic editing to generate valuable primate models of human diseases (e.g., Huntington and muscular dystrophy) are addressed. Although the high costs, specialized resources, and ethical debate challenge the use of primates in biomedical research, their inclusion in fertility and infertility research is vital for continued improvements in women's reproductive health.

G-protein coupled estrogen receptor, estrogen receptor α, and progesterone receptor immunohistochemistry in the hypothalamus of aging female rhesus macaques given long-term estradiol treatment

Steroid hormone receptors are widely and heterogeneously expressed in the brain, and are regulated by age and gonadal hormones. Our goal was to quantify effects of aging, long-term estradiol (E2 ) treatment, and their interactions, on expression of G protein-coupled estrogen receptor (GPER), estrogen receptor α (ERα) and progesterone receptor (PR) immunoreactivity in two hypothalamic regions, the arcuate (ARC) and the periventricular area (PERI) of rhesus monkeys as a model of menopause and hormone replacement. Ovariectomized (OVX) rhesus macaques were young (∼ 11 years) or aged (∼ 25 years), given oil (vehicle) or E2 every 3 weeks for 2 years. Immunohistochemistry and stereologic analysis of ERα, PR, and GPER was performed. More effects were detected for GPER than the other two receptors. Specifically, GPER cell density in the ARC and PERI, and the percent of GPER-immunoreactive cells in the PERI, were greater in aged than in young monkeys. In addition, we mapped the qualitative distribution of GPER in the monkey hypothalamus and nearby regions. For ERα, E2 treated monkeys tended to have higher cell density than vehicle monkeys in the ARC. The percent of PR density in the PERI tended to be higher in E2 than vehicle monkeys of both ages. This study shows that the aged hypothalamus maintains expression of hormone receptors with age, and that long-term cyclic E2 treatment has few effects on their expression, although GPER was affected more than ERα or PR. This result is surprising in light of evidence for E2 regulation of the receptors studied here, and differences may be due to the selected regions, long-term nature of E2 treatment, among other possibilities.

Assessment of reproductive behavior and hormonal cycles in geriatric western Lowland gorillas

The population of western lowland gorillas in North American zoos is aging and, as is the case with the aging human population, may have unique physical and social needs. We have documented previously that 25% of aging females (5/22) ceased to show reproductive cycles entirely, and could be defined as menopausal. Approximately 32% of females showed somewhat irregular cycling patterns. We review our hormonal and behavioral findings on reproductive aging in gorillas; describe the range of cycling patterns that we see and how we interpret these; and discuss the implications of these findings for captive management and husbandry of aging gorillas. We monitored fecal hormone metabolites (progestogens) in 30 gorillas and collected simultaneous behavioral data to evaluate the relationship between cyclicity and sexual behavior. We identified and described several discrete patterns of irregular cycling. These included extreme variability of cycle length, cyclic patterns with unusually low progestogen peak concentrations that possibly may not support luteal activity, and large variability in maximum progestogen peak height among cycles. All of these changes are consistent with age-related hormonal changes observed in humans and may be signs of changes in fertility as well. Behaviorally, nearly all cycling females exhibited signs of estrus. Affiliative behavior between male silverbacks and estrous females was observed in the control females, but not the geriatric females. These findings suggest that pre-menopausal females are exhibiting signs of perimenopause. As is the case in humans, such changes in hormone patterns may occur years before the onset of menopause. As enhancements in nutrition, husbandry, and veterinary medicine have led to increased longevity in our zoo populations of apes, it has become imperative that we investigate and better understand associated physiological and behavioral changes in geriatric animals to ensure appropriate management of this increasing demographic sub-population. Zoo Biol 0:1-23, 2007. (c) 2007 Wiley-Liss, Inc.

Behavioral and neurobiological characteristics influencing social hierarchy formation in female cynomolgus monkeys

Socially housed monkeys have been used as a model to study human diseases. The present study examined behavioral, physiological and neurochemical measures as predictors of social rank in 16 experimentally naïve, individually housed female cynomolgus monkeys (Macaca fascicularis). The two behavioral measures examined were novel object reactivity (NOR), as determined by latency to touch an opaque acrylic box placed in the home cage, and locomotor activity assessed in a novel open-field apparatus. Serum cortisol concentrations were evaluated three times per week for four consecutive weeks, and stress reactivity was assessed on one occasion by evaluating the cortisol response to adrenocorticotropic hormone (ACTH) following dexamethasone suppression. Measures of serotonin (5-HT) function included whole blood 5-HT (WBS) concentrations, cerebrospinal fluid (CSF) concentrations of the 5-HT metabolite 5-hydroxyindoleacetic acid (5-HIAA) and brain 5-HT transporter (SERT) availability obtained using positron emission tomography (PET). After baseline measures were obtained, monkeys were assigned to four social groups of four monkeys per group. The two measures that correlated with eventual social rank were CSF 5-HIAA concentrations, which were significantly higher in the animals who eventually became subordinate, and latency to touch the novel object, which was significantly lower in eventual subordinate monkeys. Measures of 5-HT function did not change as a consequence of social rank. These data suggest that levels of central 5-HIAA and measures of novel object reactivity may be trait markers that influence eventual social rank in female macaques.

Physiology and Endocrinology of the Ovarian Cycle in Macaques

Macaques provide excellent models for preclinical testing and safety assessment of female reproductive toxicants. Currently, cynomolgus monkeys are the predominant species for (reproductive) toxicity testing. Marmosets and rhesus monkeys are being used occasionally. The authors provide a brief review on physiology and endocrinology of the cynomolgus monkey ovarian cycle, practical guidance on assessment and monitoring of ovarian cyclicity, and new data on effects of social housing on ovarian cyclicity in toxicological studies. In macaques, cycle monitoring is achieved using daily vaginal smears for menstruation combined with cycle-timed frequent sampling for steroid and peptide hormone analysis. Owing to requirements of frequent and timed blood sampling, it is not recommended to incorporate these special evaluations into a general toxicity study design. Marmosets lack external signs of ovarian cyclicity, and cycle monitoring is done by regular determinations of progesterone. Cynomolgus and marmoset monkeys do not exhibit seasonal variations in ovarian activity, whereas such annual rhythm is pronounced in rhesus monkeys. Studies on pair- and group-housed cynomolgus monkeys revealed transient alterations in the duration and endocrinology of the ovarian cycle followed by return to normal cyclicity after approximately six months. This effect is avoided if the animals had contact with each other prior to mingling. These experiments also demonstrated that synchronization of ovarian cycles did not occur.

Controversies about HRT--lessons from monkey models

Lessons from monkey models contribute significantly to a better understanding of the controversies in reconciling the differences in postmenopausal hormone treatment outcomes between observational and randomized trial data. Monkey studies brought attention to premenopausal estrogen deficiency with resulting premature coronary artery atherosclerosis. Recently, those monkey studies were confirmed for premenopausal women in the NHLBI-sponsored Women's Ischemia Syndrome Evaluation (WISE) Study. Monkey studies have provided convincing evidence for the primary prevention of coronary artery atherosclerosis when estrogens are administered soon after the development of estrogen deficiency. Equally convincing are the data from monkey studies indicating the total loss of these estrogens beneficial effects if treatment is delayed for a period equal to six postmenopausal years for women. An attempt has been made using the monkey model to identify the hormone treatment regimen most effective in preventing the progression of coronary artery atherosclerosis. By a substantial margin, the most effective approach is that of using estrogen containing oral contraceptive during the perimenopausal transition, followed directly by hormone replacement therapy postmenopausally. Because of similarities between human and nonhuman breast, monkeys have had a major role in clarifying controversies surrounding the breast cancer risk of estrogen only versus estrogen plus progestin therapies. The results of monkey studies suggest little or no effects of estrogen only treatment; whereas, estrogen+progestin clearly increases breast cancer risk.

Osmotic tolerance and membrane permeability characteristics of rhesus monkey (Macaca mulatta) spermatozoa

Biophysical characteristics of the plasma membrane, such as osmotic sensitivity and water and cryoprotectant permeability are important determinants of the function of spermatozoa after cryopreservation. A series of experiments was conducted with rhesus macaque spermatozoa at 23 degrees C to determine their: (1) cell volume and osmotically inactive fraction of the cell volume; (2) permeability coefficients for water and the cryoprotectants dimethyl sulfoxide, glycerol, propylene glycol, and ethylene glycol; (3) tolerance to anisosmotic conditions; and (4) motility after a one step addition and removal of the four cryoprotectants. An electronic particle counter and computer aided semen analysis were used to determine the cell volume and permeability coefficients, and motility, respectively. Rhesus spermatozoa isosmotic cell volume was 27.7+/-3.0 microm3 (mean+/-SEM) with an osmotically inactive cell fraction of 51%. Hydraulic conductivity in the presence of dimethyl sulfoxide, glycerol, propylene glycol, and ethylene glycol was 1.09+/-0.30, 0.912+/-0.27, 1.53+/-0.53, and 1.94+/-0.47 microm/min/atm, respectively. Cryoprotectant permeability was 1.39+/-0.31, 2.21+/-0.32, 3.38+/-0.63, and 6.07+/-1.1 (x10(-3)cm/min), respectively. Rhesus sperm tolerated all hyposmotic exposures. However, greater than 70% motility loss was observed after exposure to solutions of 600 mOsm and higher. A one step addition and removal of all four cryoprotectants did not cause significant motility loss. These data suggest that rhesus sperm are tolerant to hyposmotic conditions, and ethylene glycol may be the most appropriate cryoprotectant for rhesus sperm cryopreservation, as it has the highest permeability coefficient of the tested cryoprotectants.