Prevalence and correlates of 30-day suicidal ideation and intent: Results of the South African National Student Mental Health Survey

Background. Although suicide prevention is recognised as a priority among university students in South Africa (SA), it is unclear whatproportion of students require urgent indicated interventions and what the characteristics are of these students.Objective. To assess the prevalence and sociodemographic correlates of 30-day suicidal ideation, frequency of ideation and self-reported intention to act on ideation in the next year among a national sample of SA university students.Methods. Self-report cross-sectional data were collected online from students (N=28 268) at 17 universities across SA as part of the national student mental health survey. Students reported suicidal ideation in the past 30 days, frequency of ideation and intention to act on ideation in the next year. Data were weighted within institutions by gender and population group, and across the four main types of universities (historically white, historically disadvantaged, technical and distance learning) to correct for response rate discrepancies. Prevalence was estimated with these weighted in the total sample and across types of universities. Poisson regression with robust error variances was used to investigate associations of sociodemographic characteristics with ideation and intention to act on suicidal ideation. Results are reported as relative risks (RRs) with design-based 95% confidence intervals (CIs).Results. Thirty-day prevalence of suicidal ideation was 24.4% (standard error (SE) 0.3), with 2.1% (SE 0.1) and 4.1% (SE 0.1), respectively,reporting suicidal ideation all/almost all the time, or most of the time. A total of 1.5% (SE 0.1) of respondents reported being very likely to act on their suicidal ideation, while 3.9% (SE 0.2) were somewhat likely, 8.7% (SE 0.2) were not very likely and 85.8 (SE 0.5) either reported no suicidal ideation or that they were not at all likely to act on this ideation. Risk of suicidal ideation with high intent in the total sample was elevated among females (RR 1.9, 95% CI 1.3 - 2.7) and gender non-conforming students (RR 4.3, 95% CI 1.4 - 13.0) relative to males, black African students compared with white students (RR 3.6, 95% CI 1.9 - 7.1), students whose parents did not progress to secondary school compared with students whose parents had a university education (RR 1.6, 95% CI 1.0 - 2.5) and sexual minority students compared with heterosexual students (RR 1.9, 95% CI 1.3 - 2.6). Among students with 30-day ideation (controlling for frequency of ideation), only two of these predictors of high intent remained significant: identifying as black African (RR 2.7, 95% CI 1.4 - 5.1), and having parents with less than secondary education (RR 1.5, 95% CI 1.0 - 2.1).Conclusion. Scalable suicide prevention interventions are needed to reach the large number of SA students who report suicidal ideation with intent.

Consequences of group fission for the patterns of relatedness among rhesus macaques

When mammalian social groups exceed their optimal size, they often tend to split. In view of the potential evolutionary benefits, it should be more advantageous for animals to stay with kin, rather than nonkin, during such fission events. In the present study, the spontaneous fission of two social groups, R and S, of rhesus macaques living on Cayo Santiago, Puerto Rico, provided the opportunity to compare the kinship structure of the corresponding parent and daughter groups, using information on both maternal and paternal relatedness. In both instances, maternal half-siblings and pairs of animals from the same family were significantly more prevalent in the fission products than in the parent group. During the split of group R, significantly more paternal half-siblings stayed in the remnants of the parent group than joined the seceding group. Our findings are compatible with previous behavioural studies demonstrating that female primates bias their social behaviour more to maternal than to paternal kin, but that both types of half-siblings prefer each other more than unrelated animals. It remains to be clarified by future research, however, whether the observed co-segregation of paternal half-sibs in our study reflects active choice or is a by-product of the group-specific kin structures, prior to fission.

A longitudinal study of age-specific reproductive output and body condition among male rhesus macaques, Macaca mulatta

In many mammalian species, male reproductive success appears to climb sharply at young adulthood, form a brief plateau during prime ages, and decline among older animals, a pattern often attributed to reduced physical condition with ageing. However, solid evidence to either substantiate or refute this profile among nonhuman primates is lacking. Here, we combine a decade of genetic analysis of paternity among free-ranging rhesus macaques, Macaca mulatta, with information about body condition in order to evaluate how changes in morphology might govern age-specific reproduction among males. We show that age-specific reproductive success traverses the same life history profile as found in other mammals, but reductions in reproductive output with advanced age were associated with reduced chances of survivorship rather than accompanied by diminished body condition. We demonstrate that variance in male age at onset of reproduction is three times greater than variance in female age at onset of reproduction. We provide the first evidence from primates that age-specific reproductive output among males is not a consequence of age-related changes in body condition, but reflects social and demographic factors.

Multiple sirehood in free-ranging twin rhesus macaques (Macaca mulatta)

Rhesus macaque females regularly copulate with a number of partners, and produce a single offspring per reproductive cycle in over 99% of cases. We used genotyping of 10 STR markers to determine paternity in the Cayo Santiago population of rhesus macaques. About 1,500 monkeys have been analyzed to date, with their marker genotypes entered into a computerized database. These data enable us to report the first documented case in any cercopithecine nonhuman primate species of the production of twin offspring sired by different males.

Primigravidity, body weight, and costs of rearing first offspring in rhesus macaques

Body size is associated with menarche and ovarian function, but the relationship to first conception is rarely examined. We conducted a longitudinal investigation of rhesus macaques, Macaca mulatta, to determine the effect of differences in body weight on both the age at first conception and survivorship of first progeny. Young females who became pregnant weighed significantly more than peers who remained barren, with weight changes for females who successfully raised offspring no different than those for females who did not produce offspring. Infant mortality among primiparae was not significantly greater than that among multiparae, although nearly twice as high. First-born males tended to have lower survivorship than first-born female offspring. We suggest that reproductive costs encountered by primiparous females are more likely to be modulated by immature neuroendocrine function than by inexperience, small body size, or infant suckling patterns. We conclude that body size influences probability of first conception, socioendocrine factors mediate the likelihood of infant survival, and primiparous production of male progeny seems to exert a greater reproductive cost than does production of female progeny.

Signs of glaucoma in rhesus monkeys from a restricted gene pool

PURPOSE

To investigate the distribution of intraocular pressure (IOP) and cup properties in a colony of rhesus monkeys that has had no outside genetic input since 1938 (approximately 12 generations). This sample of sequestered monkeys is significantly larger than any previously reported. Comparisons are made with a sample of random-source monkeys to develop population estimates defining the limits of normalcy.

METHODS

The IOP and cup/disc ratio estimates were collected from 701 eyes of 354 adult rhesus monkeys from the closed colony on Cayo Santiago, Puerto Rico. Results for IOP were compared with the normal rhesus IOP population distribution function calculated from an earlier sample of genetically heterogeneous rhesus.

RESULTS

The mean +/- standard deviation IOP in the Cayo Santiago monkeys (15.8+/-3 mmHg) related well to the calculated "normal" rhesus distribution (14.5+/-2 mmHg) below and around the mean IOP only. Above the mean rhesus IOP, the samples from the Cayo monkeys were strongly skewed: 129 eyes had IOP more than two standard deviations above the normal mean IOP, and 54 eyes had IOP more than three standard deviations above the normal mean IOP. Cup/disc ratio estimations tended to cluster as higher values in the higher IOP quartiles. Some eyes with IOP below the mean had cup/disc ratios > 0.5. Values for IOP that were more than two standard deviations above the mean and cup/disc ratios > 0.4 were not uniformly distributed across social groupings, although incidence of high IOP was more than 25% in one group.

CONCLUSION

After 12 generations with the same genetic pool, expression of ocular hypertension and large optic disc cups is high but not uniform.

Osteoarthritis of the hand in nonhuman primates: a clinical, radiographic, and skeletal survey of Cayo Santiago rhesus macaques

We describe the relative prevalence and pattern of distribution of osteoarthritis (OA) in the hands of elderly (> 15 years) rhesus macaques using clinical, radiographic, and skeletal examinations. In the clinical study the prevalence of nodes was 72% and 16% in the distal inter-phalangeal joints (DIPJ) and proximal inter-phalangeal joints (PIPJ), respectively, 31% of all monkeys had polyarticular nodes. Radiographic OA was present in 55%, 9.1%, and 0% of the DIPJs, PIPJs, and thumb base, respectively. Skeletal OA as defined by joint surface eburnation for the DIPJ, PIPJ, and thumb base were 16%, 8%, and 2%, respectively. A similar pattern of hand OA with humans is described except for the thumb base OA. This may be due to the relatively rudimentary manipulative role of the macaque thumb. The finding of polyarticular nodal OA raises the possibility of a common pathogenensis for IPJ OA amongst primates.

Subcutaneous rabies vaccination of pigtail macaques

Nonhuman primates housed in outside cages in rabies enzootic areas should be vaccinated against rabies because of the risk of exposure to rabid wildlife. This article reports that vaccination with an inactivated rabies vaccine for domestic animals induced levels of neutralizing antibodies against rabies in pigtail macaques (Macaca nemestrina) without causing adverse reactions.

Osteoarthritis staging: comparison between magnetic resonance imaging, gross pathology and histopathology in the rhesus macaque

Although osteoarthritis (OA) is the most common cause of articular skeletal disability in humans, assessing progression (staging) with noninvasive methods remains a major clinical problem. Using the rhesus macaque animal model, the objective of this study was to compare OA staging by noninvasive magnetic resonance imaging (MRI) against gross pathology and histopathology. Right knee joints from 18 rhesus macaques were used in this study. Using a four-point ordinal scale for each of the above-mentioned modalities, the lateral and medial femoral condyle and tibial plateau of each knee joint was independently scored for OA severity, i.e. normal, mild OA, moderate OA and severe OA. Correlation between each staging system was performed using Stuart's Tau-c correlation coefficient. By our criteria, MRI staging correlated as well with gross pathology (tau = 0.75) and histopathology (tau = 0.80) as did gross pathology with histopathology (tau = 0.78). Our study shows that MRI is a promising noninvasive modality to evaluate the severity of OA. MRI appears to be sensitive for demarcating the presence and extent of focal OA cartilage lesions. However, at this time, while MRI is sensitive for detecting OA change it cannot distinguish between certain lesions such as superficial cartilage matrix fibrillation and hypertrophy both of which show elevated signal intensity.

Osteoarthritis in rhesus macaque knee joint: quantitative magnetic resonance imaging tissue characterization of articular cartilage

OBJECTIVE

To assess cartilage matrix quality variation by anatomical location and extent of osteoarthritis (OA) using quantitative magnetic resonance imaging (MRI) and to compare the anatomic MR morphologic features with corresponding histological findings.

METHODS

We studied 18 fully encapsulated right knee joints from a population of rhesus monkeys with a high incidence of degenerative arthritis resembling human OA. Relaxation times (T1 and T2) spin density, and cartilage thickness were determined along 8 contiguous anteroposterior segments of articular cartilage. Histological slides, prepared in the same plane as the MR image, were assessed for OA severity. Using a modification of Mankin's OA classification, each quadrant was grouped into normal (0), mild (1), moderate (2), or severe OA (3). Histopathological scores served as the standard and corresponding MR quadrants were classified accordingly.

RESULTS

Cumulative results revealed a significant decrease in T1 relaxation time (p = 0.04) and an increase in T2 relaxation time (p = 0.03) in the mild and severe OA groups, respectively. Statistically significant changes in spin density and cartilage thickness measurements were not observed. MR signal intensity abnormalities in selected regions of interest were demarcated and studied histologically. Regions with histological proliferating chondrocytes or fibrillated cartilage showed bright signal intensity on MR images (TR = 3000 ms; TE = 10 ms) and corresponded with elevated T1 and T2 values. Histological regions of collagen condensation showed low signal intensity on MR images (TR = 3000 ms; TE = 10 ms) and corresponded with decreased T1 and T2 relaxation times.

CONCLUSION

Topological quantitative MRI relaxation time assessment demonstrates increasing cartilage matrix quality variation with OA progression.

Effect of age and osteoarthritis on bone mineral in rhesus monkey vertebrae

We have used vertebrae of free-ranging rhesus macaques to study the effect of age and osteoarthritis on bone mineralization and bone density and to relate these findings to weight, sex, parity, and mineral chemistry. Bone mineralization was determined using the density fractionation technique and bone density using dual-photon absorptiometry. Arthritis was determined osteologically. We found a relationship between mineralization, age, and osteophytes, such that mineralization rose with age in nonarthritics and decreased with age in arthritics. This could also be seen when the females were examined separately. In males, only an increase in mineralization with age could be seen. In females mineralization decreases with parity. Also in females, DPA density decreases with age and increases with parity. No relationships with DPA density could be seen using males and females together or males alone. In conclusion, we have shown that normal skeletal aging in rhesus monkeys is accompanied by an increase in mineralization similar to that in other species, but this is not true in the presence of osteoarthritis. In the females parity has an important effect because it seems to build up bone mass even though the bone present may be undermineralized.

Primary open angle glaucomas in the rhesus monkey

Rhesus monkeys from the closed Cayo Santiago colony of the University of Puerto Rico demonstrate elevated (> or = 22 mm Hg) intraocular pressure in a pattern which significantly favours certain maternal lineage groupings. The colony had remained genetically pure since 1938. Of nine matriarchal lineages (matrilines) examined, two had an incidence of ocular hypertension of more than 40% and six of more than 10%. Information on 18 matrilines is currently located in the colony data base which identifies each individual and its vital statistics. In 1990, six animals were moved to the laboratory in Florida. Among those from a low incidence matriline, we found abnormal optic nerve cups, pallor, reduced function of (mainly peripheral) fields, progression and loss of optic nerve axons in the presence of ocular hypertension. In another individual where the cup/disc ratio for the right eye was 0.7 and left eye 0.4 and outflow facility was normal, we excluded all other causes of optic nerve atrophy, and low tension glaucoma was diagnosed. This female was from a matriline with a low incidence of ocular hypertension. Relatively rapid aging (3-4 years/human year) monkeys with ocular hypertension and familial clustering produce a near ideal glaucoma research model.

The effects of diet, age, and sex on the mineral content of primate bones

The effect of diet, age, and sex on the mineral content of primate bones was determined for free-ranging rhesus monkeys (Macaca mulatta) from the Caribbean Primate Research Center. Monkeys in this study were of known age and sex and had been provided with either a low protein (15%) or a high protein (25%) diet for most of their lives. Instrumental neutron activation analysis was used to assess bone mineral content. Results showed that diet had no significant effect on the bulk mineral composition of Ca, Mg, Br, and Cl in the bones. Of the minerals analyzed, only Na and Mn showed significant diet-related effects. The bone Ca content was found to be lower in females than in males when controlled for age. Finally, Ca content was found to be higher in young adults, lower at middle age, and higher in old age in both male and female monkeys. In conclusion, this study has shown that increasing protein content in the diet does not change the bulk mineral content of primate bones. The nondietary effect that Ca content of monkey bones is lower during middle age has not been previously reported.

The combined assessment of cellular apoptosis, mitochondrial function and proliferative response to pokeweed mitogen has prognostic value in SIV infection

Using the assessment of the mitochondrial metabolic activity of freshly isolated blood mononuclear cells, the flow cytometric detection of apoptosis and of the proliferative responses to PWM, SIV-infected macaques were classified in: stage 0, which included all animals with unaffected parameters, and stages 1, 2, and 3, which included animals having one, two, or all three parameters affected, respectively. This novel three-parametric staging system (ISS) provides a new prognostic tool in the longitudinal study of SIV infection.

Osteoarthritis in rhesus macaques: assessment of cartilage matrix quality by quantitative magnetic resonance imaging

To assess cartilage quality with anatomical location and extent of osteoarthritis (OA), magnetic resonance imaging (MRI) of the knee joint from rhesus monkeys was performed. MRI measurements--T1 and T2 relaxation times, proton density and cartilage thickness were taken from 8 equal segments of articular cartilage volumes extending from anterior to posterior edge of 1 mm sagittal slices. To grade the severity of OA in each quadrant of the knee joint a modified Mankin score was applied on the histological sections. Our results suggest that MR relaxation times and proton density values vary with the severity of osteoarthritis.

A non-invasive technique for the control of intestinal parasites in rhesus macaques (Macaca mulatta)

Control of intestinal parasites is a major concern in maintaining the health and well-being of captive primates. This study established that percutaneous application of ivermectin was as effective as subcutaneous administration for the control of nematodes in captive rhesus macaques. The method is less intrusive than the standard subcutaneous or oral delivery routes and did not adversely affect the health of any of the study subjects.

A primate model for age related macular drusen

A closed colony of semi-free-ranging rhesus monkeys maintained in isolation since 1938 by the Caribbean Primate Research Center (CPRC) is being studied as a model for age related macular drusen. Of examined colony animals 57.7% of the monkeys and 47.3% of their eyes have drusen. The prevalence and severity of drusen are linearly related to increasing age and are significantly higher in specific maternal lineages (matrilines). An electrophysiological estimate indicates loss of function associated with drusen. Prevalence of drusen in CPRC females is almost twice that of males, while the prevalence among CPRC animals in general appears to be several times that of monkeys from continental US facilities. Evidence suggests that the frequency of endstage lesions is also similar to that in human populations. The CPRC matriline monkeys appear to provide the best model yet reported for human age related macular drusen.

Species differences in the binding kinetics of 25-hydroxyvitamin D3 to vitamin D binding protein

The specific binding of 25-hydroxyvitamin D3 to its binding protein was studied in serum of the human, rhesus monkey, cow, horse, and rat. The free fraction of 25-hydroxyvitamin D3 in the rat was 0.34 +/- 0.15 pmol free/nmol total (+/- SD) and this was lower than in any of the other species (p less than 0.01). In the human, the free fraction was 1.5 +/- 0.32 pmol free/nmol total, which was higher than in any of the other species (p less than 0.001). The differences in the free fraction were mainly due to differences in dissociation constant. The relative levels of free 25-hydroxyvitamin D should be taken into account when extrapolating findings about vitamin D metabolism in animals to the human. A technical outcome of this study is that of the species tested, vitamin D binding protein from rat serum is the most suitable as a reagent component for methods used to measure total 25-hydroxyvitamin D by competitive protein binding assay.

In vitro HIV infection of primate lymphocytes

Peripheral blood mononuclear cells (PBMC) obtained from four different primate species were tested for their respective ability to support the "in vitro" replication of the human immunodeficiency viruses, HIV-1, and HIV-2. PBMC of Cebus apella, patas (Erythrocebus patas), green (cercopithecus aethiops sabaeus) and rhesus monkeys (Macaca mulatta) were infected "in vitro" with either HIV-1 or HIV-2. Cultures were assayed weekly for particle-associated reverse transcriptase activity. Both viruses were found to be cytolytic for all these monkey's PBMC. Low levels of HIV-1 and HIV-2 infection were observed in Cebus cells. However, productive infection was only detected in HIV-2 infected rhesus PBMC. The capacity of HIV-2 to replicate in rhesus cells may provide a useful model for evaluating antiviral drugs and vaccines.

Spontaneous osteoarthritis in rhesus macaques. II. Characterization of disease and morphometric studies

From examination of the articular tissue of 35 animals from the Caribbean Primate Research Centre, we identified the epidemiological and histomorphometric features of the spontaneous osteoarthritis (OA) that affects the free-ranging rhesus macaques. The frequency of this disease increases with aging, and in females, with increased parity. Histological and morphological studies demonstrate that as in humans, the disease is characterized by persistence of the chondrocyte density typified by the cartilage of young animals. Owing to its epidemiologic and histologic resemblance to the disease in man, we conclude that degenerative arthritis affecting rhesus macaques provides a useful model for the study of factors contributing to the pathogenesis of OA.

Spontaneous osteoarthritis in rhesus macaques. I. Chemical and biochemical studies

We analyzed the articular cartilage of 41 rhesus macaques for elemental concentrations including [Ca] calcium, [P] phosphorus, [Mg] magnesium, [S] sulfur, [K] potassium and glycosaminoglycan (GAG) and collagen content. Our findings revealed an increase in all elements with aging. Within the osteoarthritic (OA) groups, young OA had higher levels of all elements than old OA, and significantly greater levels compared to young normals. In addition, GAG content was dramatically increased in young OA. Old OA did not differ from old normals for any elements although GAG levels decreased. Collagen was shown to be stable with increasing age in both normal and OA cartilage, but decreased in OA cartilage. This macaque model of spontaneous OA is valuable because it demonstrates early OA changes typical of experimental models and late changes similar to human OA.

A brief description of the Cayo Santiago rhesus monkey colony

A description of the Cayo Santiago rhesus monkey (Macaca mulatta) colony is provided including an aerial photograph and map.

Serological survey for viral diseases in the Cayo Santiago rhesus macaque population

The free-ranging population of rhesus monkeys (Macaca mulatta) on Cayo Santiago was sero-surveyed for human measles, simian virus 40, B virus (Herpes simiae), rhesus cytomegalovirus, human and simian retroviruses and encephalomyocarditis virus to determine the prevalence of these viruses in the colony. The results of this study indicate that the colony is free of SV40, HTLVIII (HIV-1), STLVIII (SIV) and SRV1; has a low prevalence of measles and EMCV; and high prevalence rates for B virus, CMV and HTLVI.

Adult-onset macular degeneration in the Cayo Santiago macaques

Since 1985 a group from the University of Florida has examined 136 rhesus monkeys from the Cayo Santiago colony. From the sample, 97 are older than nine years (approximately 30 human years) and 39 are younger. Drusen were found in 17% of the younger eyes and in 46% of the older eyes. All animals over 25 years of age had drusen in the central fundus. The incidence of drusen varied from 19-77% between five social groups. Incidence reported in random-source colonies in the continental U.S.A. is about six percent. Compared to near-age matched controls without drusen, selected rhesus exhibited visual resolution losses amounting to two Snellen-lines or more. The end-stage disciform changes and ultrastructural similarities are comparable with human macular disease. Future prospective studies may include therapies, surgical intervention, environmental manipulation and genetic research.

Rhesus macaques as an experimental model for degenerative arthritis

To understand the pathogenesis of degenerative arthritis, an experimental model of the disease in which systemic factors can be investigated is required. This study reviews the evidence that the spontaneous degenerative arthritis in free ranging rhesus macaques at the Caribbean Primate Research Center meets the criteria for such a model. Two forms of degenerative arthritis in rhesus macaques have been identified: osteoarthritis and calcium pyrophosphate dihydrate crystal deposition disease. These diseases resemble spontaneous human arthritis with respect to age, sex, joint histology and cartilage composition. The availability of large numbers of affected primates as well as the availability of age/sex matched controls free of disease are additional factors that make spontaneous degenerative arthritis in rhesus macaques a suitable experimental model for the study of the human disease.

Abnormalities in insulin secretion and glucose clearance among Macaca mulatta examined on Cayo Santiago

Macaca mulatta on Cayo Santiago (CS) were examined with intravenous glucose tolerance tests (IV-GTT) for evidence of abnormalities in glucose clearance and insulin secretion. About 10% of the 98 monkeys had impaired glucose clearance associated with impaired insulin secretion. Another 6% had either fasting or secretory hyperinsulinemia with slightly increased rates of glucose clearance, and 20% had low insulin secretion, but no significant changes in glucose clearance. Results were compared to those obtained with CS-derived monkeys tested at Sabana Seca (SS). Glucose clearance per amount of insulin secreted was 40% more effective among CS macaques than among those at SS. There were no differences in weight between impaired and control macaques on CS. Effects of genetics, physical activity, and food consumption can be studied among these macaques and results related to similar metabolic abnormalities in prediabetic and diabetic human beings.

Bone mineral and osteoporosis in aging rhesus monkeys

55 femora of free ranging rhesus monkeys from the Caribbean Primate Research Center ranging in age from 2-25 years were analyzed using histology, density fractionation and chemical analysis and correlated with morphometric data. The vertebral density was determined by photon absorptiometry. 119 caudal vertebrae from the skeletal collection were analyzed chemically. Cortical mineral density and porosity increased with age, and vertebral density and cortical area increased with weight. There was significant sexual dimorphism in many histological variables reflecting size differences and cortical porosity was greater in males. The chemical analysis showed no influence of the diet on bone mineral but that Ca increase with age in females but not in males. Finally a subgroup of aged, animals had hypermineralized, and more porous bone. This subpopulation may prove to be a valuable model for senile osteoporosis.

Macular disease in related rhesus monkeys

During (January) 1986-(May) 1988, we examined 272 eyes in 136 rhesus monkeys in the closed Cayo Santiago colony of the Caribbean Primate Research Center of the University of Puerto Rico. Seventy-eight eyes were less than 10 years of age. One hundred and ninety-four were aged 10-28 years. The fundi were examined and photographed. Fluorescein angiography was performed in some eyes. Selected cases were evaluated for 'acuity' loss by recording of pattern-evoked retinal and cortical signals. Light and electron microscopy were used to evaluate the pigment epithelium of some animals. Thirty-eight percent of all eyes had posterior pole drusen. Incidence was highly age-related. When late-stage lesions were found, we did not see neovascularization, but late hyperfluorescence was consistent with degenerative scarring and atrophy. Electrophysiology demonstrated moderately reduced acuity in the presence of numerous macular drusen. Electrooculograms were low normal. Histopathology showed changes identical to those reported in human age-related macular degeneration. No eyes less than 10 years of age had confluent drusen or disciform-like lesions. The incidence of drusen in samples of some social groups was much higher than others.

Degenerative changes in maculas of rhesus monkeys

In the hope of identifying an animal model for age-related macular degeneration (AMD) we undertook a pilot investigation of aged rhesus monkeys. Twenty-nine monkeys from a seminatural colony were examined at the Caribbean Primate Research Center. Macular drusen were found in 74% of the monkey eyes. Alterations of the retinal pigment epithelium within the macula were noted in 45% of the eyes. Fluorescein angiography in selected animals revealed window defects consistent with drusen. None of this sample showed the exudative form of AMD or disciform scarring. One typical monkey underwent special studies including measurement of visual resolution by electrophysiological study of the retinal and visual cortex. Application of human criteria to this animal supported the diagnosis of early AMD. Histopathologic study of one eye by transmission electron microscopy confirmed the presence of drusen with nearly identical ultrastructural features to those found in the human pigment epithelium in AMD.

Cholesterol and dominance rank in the Cayo Santiago macaques

The relationship between serum total cholesterol (STC) and social dominance rank was investigated in adult (greater than or equal to 5 year old) males of a single, naturally-formed free-ranging troop of rhesus monkeys (Macaca mulatta) on Cayo Santiago, Puerto Rico. Dominance rank, age and body weight were not correlated with STC, nor was rank correlated with age or body weight. The mean (+/- 1 SD) STC was 154.0 +/- 27.0 mg/dl. Seven of the 34 males sampled had STC levels (189.1 +/- 4.3 mg/dl) greater than 1 SD above the mean for all males. These monkeys did not differ significantly in age or body weight from each other or the remaining males in the study, but 5 of the 7 monkeys with high STC were high-ranking in the group and 7 of 8 monkeys with STC (115.6 +/- 5.8 mg/dl) 1 SD or more below the mean for all males were low-ranking. The difference was significant (p less than .05, Fisher's Exact Test).

Macular degeneration in a community of rhesus monkeys. Ultrastructural observations

The eyes of 29 aged adult, (mean age, 20 years) rhesus monkeys were examined for the presence of age-related macular degeneration (AMD). This sample represented approximately 25% of the aged population in the seminatural colony at the Caribbean Primate Research Center (CPRC) of the University of Puerto Rico. Approximately 75% of the animals examined had drusen in the posterior pole. Ultrastructural analysis was used to determine whether the pathologic alteration of Bruch's membrane and drusen in the colony resembled those noted in aged or AMD-afflicted human retinas. There were abnormalities in all layers of Bruch's membrane. Deposits of heterogeneous material, comprised of membranous, granular, and cellular components, were seen in both the inner collagenous zone (ICZ) and the outer collagenous zone (OCZ). Accumulation of this drusenoid material in the ICZ produced a scalloping of the basal border of the retinal pigment epithelium (RPE). Dense bodies were seen in both Bruch's membrane and RPE cytoplasm near the basal infoldings. Cytoplasmic processes, as well as whole cells, were seen with regularity within the drusenoid material. In one case there was a cell with a basement membrane crossing the middle elastic layer of Bruch's membrane. These changes are consistent with those reported in human aging and AMD. Aged individuals in this colony appear to be predisposed to macular degenerative changes and may prove to be an invaluable animal model for studying AMD in humans.

Treatment of endometriosis in monkeys: effectiveness of continuous infusion of a gonadotropin-releasing hormone agonist compared to treatment with a progestational steroid

The use of a GnRH agonist or a progestational steroid (levonorgestrel) for the treatment of endometriosis in monkeys was compared. Four monkeys with spontaneous endometriosis were treated for 6 months with a continuous infusion of a GnRH agonist (25 micrograms/day). Five animals with surgically induced endometriosis were treated with the same agonist for 3 months. An additional group of five monkeys with surgically induced endometriosis was treated orally with levonorgestrel (1 mg/kg X day), while a final group of four monkeys served as untreated controls. During agonist treatment, the four monkeys with spontaneous endometriosis gained body weight and had a greater than 80% decline in cyst size (representing a decline in secretory activity). Monkeys with surgically induced endometriosis had almost total resolution of endometrial lesions during agonist treatment, which was maintained throughout a 4-month posttreatment period. After initial stimulation at the onset of the GnRH agonist infusion, serum LH, FSH, estradiol, and progesterone levels decreased to near the levels of detection, where they remained until treatment was terminated. In comparison, levonorgestrel reduced endometrial lesion size, but the monkeys did not resume normal cycles as early as those treated with the agonist. Levonorgestrel-treated monkeys had normal serum LH and FSH levels, but low serum estradiol and progesterone levels. The results of this study indicate that either continuous infusion of a GnRH agonist or administration of levonorgestrel is effective for treating endometriosis in monkeys. The hormonal data suggest that the GnRH agonist acts at the level of the hypothalamus and pituitary, whereas levonorgestrel acts at the ovarian level.

Tissue responses of the monkey retina: tuning and dependence on inner layer integrity

Recent technical and conceptual advances have made it possible to experiment with models of local human inner retinal disease and changes in very small, tissue-specific signals. Local retrograde degeneration of the ganglion cells was induced in four rhesus monkeys by 160 degrees microdiathermy fiber layer burns at the nasal or temporal edges of the optic disc. There were no abnormalities of the classical electroretinograms (ERGs) during the following 210 days. With nasal lesions, pattern-evoked retinal (PERR) and cortical responses over a range of grating contrasts and spatial frequencies were largely normal. The authors found a cortical spatial tuning peak near 0.5 cycles/deg (cpd) and a retinal peak at 0.25-0.3 cpd. With temporal lesions, the retinal signals to high frequency stimuli (greater than 1.0 cpd) approached zero between 20-60 days. The cortical evoked signal declined with a course similar to the retinal components. Histological evidence was found for extensive loss of ganglion cells and fibers in a central 30-40 degrees temporal area, including the macula, 210 days after the temporal lesions. This is strong evidence that local ganglion cell-dependent electrical potentials, bearing little relation to the ERG, can be measured in response to selected stimuli.

Induction of experimental myasthenia gravis in rhesus monkeys: a model for the study of the human disease

Experimental autoimmune myasthenia gravis (EAMG) was induced in rhesus monkeys using purified acetylcholine receptor (AChR) from Torpedo california. A single dose of 80 micrograms induced antibody formation two weeks after injection. Two subsequent doses at two-week intervals caused clinical signs (anorexia, fatigability, weight loss, ptosis and dysphagia) which initially responded to treatment with neostigmine. Histologic examination of post-mortem tissues revealed lesions characteristic of myasthenia gravis in man: muscular atrophy, fibrous degeneration and lymphocytic infiltration. Antibodies were quantitated in the sera of three other monkeys which received only 60 micrograms of purified AChR. Abnormally high titers persisted for two years (60-200 micrograms /ml versus 0-10 micrograms/ml for controls). A monkey injected with 60 micrograms AChR as part of reconstituted membrane vesicles had lower titers (30-50 micrograms/ml) than those which received purified receptor. Only those monkeys with antibody titers exceeding 800 micrograms/ml developed overt disease. These titers were 4-100 times higher than those reported for myasthenic humans. The antibody-antigen molar ratios were higher for monkeys with disease than for asymptomatic animals. These data suggest that the diversity of antibody molecules synthesized by the sensitized monkeys determined the appearance of clinical signs, and that the cross reaction of anti-torpedo antibodies with monkey receptor was primarily responsible for the development of EAMG.