Aging in the musculoskeletal system of rhesus monkeys: I. Passive joint excursion

In order to describe ontogenetic change in the musculoskeletal system of rhesus monkeys, 126 Macaca mulatta from Cayo Santiago, ranging in age from 7 months to 21 years, were examined under anesthesia. Passive joint excursions were measured at the wrist, elbow, shoulder, hip, and knee. Mean ranges of excursion at these joints differed significantly between age groups and by sex. The potential for most movements appeared to decrease approximately 25 degrees over the first two decades of the macaque life span, and males generally showed less potential for movement than females in all age groups. These results are similar to those obtained for humans and are consistent with patterns of positional behavior, trauma, and osteoarthritis observed in this rhesus monkey population. Thus, to fully describe the locomotor strategy of rhesus monkeys, age- and sex-related variation in locomotor anatomy and functional capacity must be considered.     

Aging in the musculoskeletal system of rhesus monkeys: III. Bone loss

It is well established that aging of the human skeleton includes the loss of bone mass or density, but little comparative information on age-related osteopenia in other primates is available. In order to determine whether bone loss occurs in normally locomoting nonhuman primates, radiographs of 139 rhesus monkey skeletons from the Cayo Santiago collection were examined, and measures of percent cortical bone (PCT) at the midshaft of second metacarpals, humeri, and femora were calculated. An age-related osteopenia was observed in the metacarpal of adult female macaques, although much individual variation was present. This variability could not be explained by reproductive history (number of offspring), matrilineal affiliation, or degree of osteoarthrosis. However, in a subsample of 15 animals, females who had given birth in the three months prior to death showed lower PCTs than those who had not conceived in the previous mating season. In adult males, PCT did not vary significantly with age, but males that weighed less and those with no/little osteoarthrosis showed lower PCTs than heavier or more arthritic animals, respectively. The multifactorial nature of the variation in PCT observed here suggests that similar processes of bone behavior are involved in the skeletal aging of both humans and rhesus monkeys.     

Menopause in female rhesus monkeys

Fifteen female rhesus monkeys (Macaca mulatto), ranging in age from 8 to 34 years, were studied for one year to characterize the endocrine and menstrual changes associated with menopause in this species. Five monkeys were premenopausal; these younger monkeys, ages 8–11 years, menstruated and showed cyclic ovarian activity during the 12–month study period, as evidenced by menses and periodic elevations of serum estradiol (E₂) and luteinizing hormone (LH) concentrations. Four females, ages 24–26 years, were in transition to menopause. Two of these perimenopausal females menstruated and secreted E₂ and LH in a periodic fashion; the other two females showed elevated LH concentrations, consistently low E₂ levels, and no evidence of menstruation. Six females, ages 27–34 years, were clearly postmenopausal; LH concentrations were high, whereas E₂ concentrations were uniformly low. There was a significant inverse correlation between basal E₂ concentrations and age, and a significant positive correlation between age and LH concentrations across all 15 animals. Hormonal changes indicative of ovulation, when they occurred, were generally restricted to the winter and early spring months. Histological analysis of ovaries from four postmenopausal females revealed little or no evidence of active folliculogenesis. These data indicate that menopause in female rhesus monkeys does not occur until the second half of thethird decade of life. © 1995 Wiley-Liss, Inc.     

Colon cancer in aged captive rhesus monkeys (Macaca mulatta)

The age-related incidence of malignant neoplasia was surveyed from a total of 301 necropsy cases of rhesus monkeys ranging in age from 13–37 years performed in the Pathology Service Unit of the Wisconsin Regional Primate Research Center during the past 15 years. All our aged monkeys lived in indoor cages and were fed with monkey chow and supplemental fruits during the past decades. In this survey, we found a total of 51 malignant neoplasms, and among them 25 cases were colon cancer. The incidence of colon cancer increased with advancing age: 3.2% at 13–19 years, 9.2% at 20–25 years, 13.5% at 26–29 years, and 20.7% at 30–37 years. Most cancers were located in the cecum and transverse regions with a unicentric origin. Two multicentric cases were associated with chronic hypertrophic colitis. Precancerous polypous lesions were not found in all cases. Histologically, all cases were mucinous adenocarcinoma and had local invasion to the muscular wall. Metastasis to the mesenteric lymph nodes was found in only two cases. As in humans, colon cancer is a common outcome of aging in nonhuman primates. Am. J. Primatol. 44:19–27, 1998. © 1998 Wiley-Liss, Inc.     

Survival rate and life span of rhesus monkeys at the Yerkes regional primate research center

This paper describes the survival rates of 763 rhesus monkeys maintained at the Yerkes Regional Primate Research Center (YRPRC). The survival rates were determined by methods used to calculate survival rates of human populations. The monkeys were divided into 3 groups based on their specific life histories. Group I monkeys were wild-born and were housed singly from the time they came into captivity at about 2 years of age. Group II monkeys were born either in the wild or in captivity and were housed in social groups since their acquisition at ages 2 to 8 years. Group III monkeys were born at the YRPRC and housed in social groups. Due to these differences in life histories, direct comparisons among survival curves of the 3 groups are, at best, tenuous, as are comparisons with populations maintained at other facilities. In the present study the highest mortality rate occurred during the first month of life. The maximum life span attained in our group I was 35 years, with only 6.2% of monkeys in this group attaining an age beyond 30 years.     

Inbreeding in three captive groups of rhesus monkeys

Using electrophoretic and serological genetic markers each of 17 potentially inbred matings in three groups of rhesus monkeys could be classified as either inbred or noninbred matings. Although nine of these 17 matings involved either father-daughter or paternal half-sib matings, only 7.4 were expected by chance alone. At least two, and possibly as many as three, of the nine cases of inbreeding involved father-daughter matings. Thus, no evidence of avoidance of inbreeding was observed in the closed captive groups of rhesus monkeys studied. Colony management policies must be developed to minimize the opportunity for or the deleterious effects of both father-daughter and half-sib matings. Furthermore, kin selection theory should consider why kin recognition, if it occurs, does not lead to avoidance of inbreeding.     

Glucose disappearance rate in rhesus monkeys: Some technical considerations

The intravenous glucose tolerance test (IVGTT) has been widely used as a tool to assist in the diagnosis of diabetes mellitus. Glucose disappearance rate (K_G) is calculated as an indicator of relative glucose tolerance; however, a standardized dose, consistent sampling times, and a consistent formula for the calculation of K_G have not yet been established for rhesus monkeys. Interpretation of results reported by different laboratories has, therefore, been rendered difficult. In the present study, 48 IVGTTs obtained from 33 male rhesus monkeys ranging widely in glucose tolerance have been analyzed. Various formulas for calculating K_G values have been tested in all experiments including a range of different pairs of time points, as well as the t_1/2. Regression analysis revealed that the log_e transformation of the plasma glucose levels obtained after an intravenous glucose load were best fitted with a straight line during the period between five and 20 minutes (R² = 0.97 ± 0.005). The use of time points prior to the five-minute value tended to produce spuriously larger K_G values, while sampling points that were later than 30 min occasionally produced an invalid K_G because in some monkeys the plasma glucose levels had already returned to basal levels. The advantages of using the five- and 20-minute glucose levels in calculating the K_G include (1) the optimal reflection of tissue uptake of glucose; (2) the relatively short sampling time required to obtain an accurate, consistent, and meaningful value for K_G; and (3) the relative ease in the calculation of K_G.     

Atretogenic action of estrogen in rhesus monkeys: Effects of repeated treatment

The effects of 17β-estradiol (E₂), administered in Silastic capsules for 24 hours at intervals of 10 or 14 days, on follicular development and menstrual cycle characteristics were studied in 13 rhesus monkeys. In seven monkeys receiving E₂ at l0-day intervals for 50 treatment periods, new follicles frequently developed between treatments but usually regressed. In seven instances, the follicles persisted longer than expected but were steroidogenically suppressed and regressed spontaneously. Ovulation occurred in only two instances. In six monkeys receiving E₂ at 14-day intervals, new follicles developed regularly, with seven ovulations occurring in 37 treatment periods. A persistent anovulatory follicle was noted in only one instance. Menstruation occurred with equal frequency, and the interval from treatment to onset of menstruation was not significantly different regardless of treatment or the occurrence of ovulation; the intervals between menstruation approximated those of normal menstrual cycles. In general, following termination of treatment, menstrual cycles returned to normal quickly. These data indicate that E₂ administered intermittently at 10-day intervals effectively suppresses ovulation, and they provide new insight into the actions of E₂ on folliculogenesis in primates.     

Growth of rhesus monkeys during the first 54 months of life

As part of a study of the long-term effects of environmental conditions on the health and development of non-human primates, the growth of 60 rhesus monkeys (Macaca mulatta, 34 males and 26 females) was determined longitudinally with biweekly or triweekly measurements of eight body dimensions from one to 54 months of age. Our data showed similar growth to previous studies and provide additional data defining normal rhesus monkey growth under more precisely defined living conditions than were reported in previously published studies on this species.     

Carbon monoxide excretion as an index of bilirubin production in rhesus monkeys

The role of increased heme catabolism in neonatal hyperbilirubinemia was investigated in rhesus (Macaca mulatta) neonates through the measurement of carbon monoxide excretion rates (VECO), blood carboxyhemoglobin content (HbCO), and plasma bilirubin concentrations. Neonatal values were compared to those of adult rhesus monkeys. These indices of bilirubin production responded appropriately to administration of NEM-damaged erythrocytes and tin protoporphyrin. Our results indicate that VECO measurements are a valid index of changes in bilirubin production in the newborn rhesus monkey.     

Atresia of the dominant ovarian follicle in rhesus monkeys is detected within 24 hours of estradiol treatment

Following treatment with estradiol-17β (E₂) on day 6 of the menstrual cycle, degenerative alterations in the microenvironment of the dominant follicle (DF) (follicular fluid [FF], granulosa cells [GC], and oocyte) are readily apparent on day 10, or 96 h after E₂ administration. The present study was designed to determine how early such changes could be detected and which indices of atresia were observed first. The DF was identified during laparoscopy on day 5 or 6 of the cycle, and four capsules containing crystalline E₂ were inserted s.c. for 24 h. Contents of the DF were aspirated at 24, 48, and 72 h following initiation of E₂ treatment. General size and appearance of the DF did not change distinctly with E₂ treatment; however, by 48 h FF viscosity was increased markedly. GC viability was not altered with treatment. FF concentrations of estrogen (E) were dramatically reduced at 24 h. These differences were maintained at 48 h and at 72 h. E accumulation by cultured GC was significantly reduced by > eightfold. There appeared a similar trend for reduced progesterone (P) in FF and decreased P production by GC in vitro. These results demonstrate that degenerative alterations in the DF indicative of atresia can be detected as early as 24 h after initiation of E₂ treatment; the index of atresia appearing earliest is a reduction in FF concentrations of E, and the first morphological changes in the DF can be observed 24 h later. This study indicates that biochemical alterations precede morphologic changes with E₂-induced atresia, and should allow us to begin to determine the earliest events and putative initiation sites of atresia.     

Growth of the masseter muscle in rhesus monkeys (Macaca mulatta)

The growth of the masseter muscle in eight infant, juvenile, and adolescent female rhesus monkeys (M. mulatta) was examined over a 2.5 year period using serial radiographic cephalometric techniques with the aid of radiopaque muscle markers. The radiopaque markers, which are composed of small pieces of root canal broach inserted into the muscle belly, make it possible to determine longitudinal masseter muscle growth as well as migration of the masseter muscle relative to the mandible. It was found that the masseter muscle increased in length by 64% during the total growth period, most of which occurred between 6 and 18 months of age. Relative to the cranium, the masseter muscle grew markedly inferiorly and only slightly posteriorly. Relative to the mandible, the masseter migrated in a posterior and slightly superior direction, keeping pace with the ramus and condyle as they grew posteriorly and posterosuperiorly throughout the study period. It was concluded that: 1) radiopaque muscle markers are a valuable tool for analysis of muscle growth and alteration of muscle location; 2) the masseter muscle in the rhesus monkey undergoes elongation, probably due to addition of sarcomeres at the fiber-tendon junctions; and 3) posterior migration of the masseter muscle relative to the corpus of the mandible, probably due to the nature of its periosteal attachment, results in a stability of the anteroposterior position of the masseter muscle despite the anterior displacement of the mandible.     

Segregation distortion and differential fitness at the albumin locus in rhesus monkeys (Macaca mulatta)

The observed patterns of segregation of two co-dominant alleles at the macaque albumin locus in 400 rhesus monkey offspring were compared with those expected for five segregating mating phenotypes. Rates of reproductive loss and conception were also compared among females of each albumin phenotype. The common albumin allele in macaques, Al^A_mac, segregated more frequently than expected when the mother was heterozygous but less frequently than expected when she was homozygous for Al^B_mac. In both cases, the phenotype identical to that of the mother appeared to be favored. Mothers who were either homozygous for Al^A_mac or heterozygous were also found to experience higher conception rates than mothers homozygous for Al^B_mac. It is hypothesized that phenotypic differences in bilirubin binding, and in competitive binding by dietary constituents, by albumin influences both these results and the nonrandom distribution of Al^B_mac in Asian macaques.     

Behavioral responses of unrelated adult male rhesus monkeys familiarized and paired for the purpose of environmental enrichment

An attempt was made to pair ten unrelated, adult male rhesus monkeys that had been kept in single cages for several years. Potential companions were first given the opportunity to establish clear-cut rank relationships (unidirectional fear-grinning and/or withdrawing) during a 5-day period of noncontact familiarization. Only then were they paired in a different double cage. Rank relationships were confirmed within the first 6 minutes after pairing without the occurrence of any biting and fighting. A total of four physical aggressions (slapping) were observed in all five dyads during 5 hours of observations on the first 5 days after pairing. It was concluded that the establishment of clear-cut rank relationships prior to pairing was instrumental in this extremely low incidence of aggression.     

Effect of testosterone on epididymal proteins in castrated rhesus monkeys

The effect of testosterone on regulation of epididymal protein synthesis has been investigated in castrated rhesus monkeys (Macaca mulatta). The proteins in the treated monkeys were characterized using polyacrylamide gel electrophoresis (under nondenaturing and denaturing conditions) and electrofocusing. At least four distinct proteins have been shown to be synthesized by the monkey epididymis under testosterone influence. Two of these proteins were detected following two days of testosterone treatment while the other two proteins were detected after a six-day treatment period. None of these proteins was detectable in monkeys treated with estradiol for six days. Electrofocusing of epididymal cytosol proteins from untreated and testosterone-treated and castrated monkeys also confirmed the presence of four androgen-dependent proteins in this species. The isoelectric points of these proteins were shown to range between 5.8 and 6.4. The molecular weights of these proteins were found to vary between 47,500 and 66,000. The in vitro incorporation of ³H-labeled amino acids was markedly greater in the androgen-primed epididymis as compared with the control tissue.     

Temporal and endocrine sequelae of aspirating follicular contents in rhesus monkeys

Aspiration of ovarian follicular contents in humans is a well-established procedure used to obtain oocytes for fertilization in vitro (IVF). However, the effects of aspiration on the menstrual cycle and resulting luteal function have been incompletely characterized. The present study was designed to investigate alterations in the temporal and endocrine characteristics of menstrual cycles following aspiration of contents of the dominant preovulatory follicle (DF) on day 10 of the cycle in normal rhesus monkeys. When aspiration was performed prior to the preovulatory surge of luteinizing hormone (LH), cycle length was extended to 38.6 ± 8.6 [15] (x days ± SD, [n]), as compared to 29.5 ± 5.7 [8] days when the surge occurred before the time of aspiration. Mean and maximal amounts of progesterone (P) in the luteal phase and the number of days in which P-values were > 1 ng/ml were significantly greater when aspiration was performed prior to the surge of LH than for aspiration after this event. Laparoscopic observations made in the midluteal phase in animals of the former group demonstrated that the corpus luteum (CL was derived from a follicle other than the original DF which had been aspirated on day 10 of the menstrual cycle; observations in the latter group of animals indicated that the CL was derived from the DF.     

Quantitative evaluation of Enterocytozoon bieneusi infection in simian immunodeficiency virus-infected rhesus monkeys

The association of the microsporidia Enterocytozoon bieneusi with chronic diarrhea and wasting in individuals with acquired immunodeficiency syndrome (AIDS) has been demonstrated. The disease caused by E. bieneusi has been linked to decreased levels of circulating CD4+ T lymphocytes. In this study, we investigated the relationship between the extent of excretion of E. bieneusi in feces of simian immunodeficiency virus (SIV)-infected juvenile macaques and the CD4+ T lymphocyte counts in the peripheral blood. Twelve juvenile rhesus monkeys (Macaca mulatta) were intravenously inoculated with the pathogenic molecular clone SIVmac239. Numbers of CD4+ T lymphocytes were assessed by three-color flow cytometry. The presence of E. bieneusi DNA in feces was assessed by nested PCR. In addition, selected samples of feces were examined by competitive quantitative PCR to assess the level of E. bieneusi infection. Low (n = 5) to undetectable (n = 7) quantities of E. bieneusi were present in feces of the twelve animals in prior to inoculation with SIV. After SIV inoculation the number of animals shedding E. bieneusi increased (n = 10) as did the quantity of E. bieneusi shedding in the feces. Of the twelve juvenile animals, five animals died within 8 months post-SIV inoculation with symptoms of AIDS. Four of the five deceased animals showed shedding of E. bieneusi DNA in feces (> or =100 spores/g) for at least three consecutive months. Increased number of E. bieneusi in feces was accompanied by decreased counts of circulating CD4+ T lymphocytes and increased SIV plasma viral load.     

Metric characteristics of the canine dental complex in prenatally androgenized female rhesus monkeys (Macaca mulatta).

Permanent maxillary canine teeth (C1) are appreciably larger in males than in females in most nonhominid Anthropoidea. Mandibular canines (C1) and mandibular first premolars (P3), against which C1 are sharpened in honing behavior, reflect commensurate sexual dimorphism. These three teeth constitute the canine dental complex. The canine complex crown metrics of seven mature genetically female rhesus Macaques, androgenized by prenatal exposure to testosterone propionate, were compared with a control sample (N = 12) for evidence of masculinization. The C1 and C1 were measured for clinical crown lengths (L) and mesiodistal and buccolingual widths. The functionally significant and highly dimorphic honing dimensions (HD), which approximate the honing surfaces of P3, were noted. In t-test comparisons, the C1 L and P3 HD in androgenized monkeys were significantly larger than those of the control group (P less than 0.05). Identical results were obtained with White's nonparametric ranking technique. Standardized lateral skull radiographs showing earlier dental formative stages were available for five of the seven animals, and these were compared with radiographs of control skulls. The developing C1 were longer and wider than in the controls. This was not reflected in the crown metrics of mature animals because of marked dental attrition. We concluded that androgens can masculinize the female rhesus canine complex, if given during critical periods of prenatal development. We hypothesize that genes encoding the male canine complex are normally activated by endogenous fetal androgens during such critical periods.