Self-agency in rhesus monkeys

Rhesus monkeys (Macaca mulatta) have shown the ability to monitor their own mental states, but fail the mirror self-recognition test. In humans, the sense of self-agency is closely related to self-awareness, and results from monitoring the relationship between intentional, sensorimotor and perceptual information. Humans and rhesus monkeys were trained to move a computer icon with a joystick while a distractor icon partially matched their movements. Both humans and monkeys were able to monitor and identify the icon they were controlling, suggesting they have some understanding of self-agency.     

Endocardiosis in rhesus monkeys

Endocardiosis was diagnosed as an incidental finding in two rhesus monkeys. The gross and histologic appearance of the lesions was described, and the similarity of this lesion to lesions of endocardiosis as found in dogs and man was discussed.The animals used in this study were handled in accordance with the Guide for Laboratory Animal Facilities and Care established by the National Academy of Science, National Research Council.     

Rib biopsy technique for cortical bone evaluation in rhesus monkeys (Macaca mulatta)

Old World primates are often studied to model human skeletal physiology. An important advantage of monkeys over other animal models (i.e., rodents) is the presence of cortical bone Haversian remodeling. Seventy-five female rhesus monkeys (Macaca mulatta) were subjected to bone biopsy. With monkeys in lateral decubitus position, the tenth rib was surgically exposed and freed from periosteum by use of careful sharp and blunt dissection. The rib section was resected, using bone cutters, and the surgical wound was closed. This procedure was repeated for the contralateral rib at a later time point in 65 monkeys. There was no mortality or appreciable morbidity. The bone specimens were (mean +/- SD) 2.50 +/- 0.25 cm long, with 5.5 +/- 1.0 mm2 total cross-sectional area. They were adequate for histologic, immunohistochemical, and quantitative histomorphometric examinations. Prevalence of pneumothorax was approximately 8.0% for the 140 procedures. This complication was immediately and successfully corrected by insertion of a small thoracic tube, evacuation of pneumothorax, and closure of the incision. This well-tolerated, repeatable procedure yields excellent specimens for performance of cortical bone histologic examination without euthanasia, allowing longitudinal evaluation.     

mtDNA diversity in rhesus monkeys reveals overestimates of divergence time and paraphyly with neighboring species

Reconstructions of the human-African great ape phylogeny by using mitochondrial DNA (mtDNA) have been subject to considerable debate. One confounding factor may be the lack of data on intraspecific variation. To test this hypothesis, we examined the effect of intraspecific mtDNA diversity on the phylogenetic reconstruction of another Plio- Pleistocene radiation of higher primates, the fascicularis group of macaque (Macaca) monkey species. Fifteen endonucleases were used to identify 10 haplotypes of 40-47 restriction sites in M. mulatta, which were compared with similar data for the other members of this species group. Interpopulational, intraspecific mtDNA diversity was large (0.5%- 4.5%), and estimates of divergence time and branching order incorporating this variation were substantially different from those based on single representatives of each species. We conclude that intraspecific mtDNA diversity is substantial in at least some primate species. Consequently, without prior information on the extent of genetic diversity within a particular species, intraspecific variation must be assessed and accounted for when reconstructing primate phylogenies. Further, we question the reliability of hominoid mtDNA phylogenies, based as they are on one or a few representatives of each species, in an already depauperate superfamily of primates.      

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.     

Immunogenetic studies of rhesus monkeys

To assay for transplacental immunization in rhesus monkeys, sera from 253 postpartum females, 31 virgin females, and 40 males were tested for erythrocyte agglutinins. Nineteen percent of the mothers exhibited antibodies, but less than three percent of the virgin females or males did so. Antibodies were detected in 26 percent of the mothers who bore blood group-incompatible infants, in contrast to only eight percent of the mothers with compatible offspring. Thus, blood group incompatibility may lead to transplacental alloimmunization of the rhesus female. Unlike the situation in humans, hemolytic disease was not observed, even when the erythrocytes of the newborn rhesus were coated with maternal antibodies.     

Immunogenetic studies of rhesus monkeys

Five alloimmune rhesus monkey blood typing reagents have been produced which define two new blood group loci inMacaca mulatto. Three of these reagents detect blood group factors at theM locus; the other two detect factors at theN locus. By typing over 1900 pedigreed monkeys we have established that these two loci are independent of each other and of any of our previously defined blood group systems.     

Immunogenetic studies of rhesus monkeys

Five alloimmune blood typing reagents have been produced which define five new blood group systems in rhesus monkeys. Each of the five independent blood group loci is comprised of a detectable allele and a null allele. Using these new reagents and those previously described, we can potentially identify close to a million phenotypes in rhesus monkeys.     

Generation of chimeric rhesus monkeys

Totipotent cells in early embryos are progenitors of all stem cells and are capable of developing into a whole organism, including extraembryonic tissues such as placenta. Pluripotent cells in the inner cell mass (ICM) are the descendants of totipotent cells and can differentiate into any cell type of a body except extraembryonic tissues. The ability to contribute to chimeric animals upon reintroduction into host embryos is the key feature of murine totipotent and pluripotent cells. Here, we demonstrate that rhesus monkey embryonic stem cells (ESCs) and isolated ICMs fail to incorporate into host embryos and develop into chimeras. However, chimeric offspring were produced following aggregation of totipotent cells of the four-cell embryos. These results provide insights into the species-specific nature of primate embryos and suggest that a chimera assay using pluripotent cells may not be feasible.     

Anatomic brain asymmetry in vervet monkeys

Asymmetry is a prominent feature of human brains with important functional consequences. Many asymmetric traits show population bias, but little is known about the genetic and environmental sources contributing to inter-individual variance. Anatomic asymmetry has been observed in Old World monkeys, but the evidence for the direction and extent of asymmetry is equivocal and only one study has estimated the genetic contributions to inter-individual variance. In this study we characterize a range of qualitative and quantitative asymmetry measures in structural brain MRIs acquired from an extended pedigree of Old World vervet monkeys (n = 357), and implement variance component methods to estimate the proportion of trait variance attributable to genetic and environmental sources. Four of six asymmetry measures show pedigree-level bias and one of the traits has a significant heritability estimate of about 30%. We also found that environmental variables more significantly influence the width of the right compared to the left prefrontal lobe.     

Postnatal protein deprivation in rhesus monkeys

We studied the growth of 97 rhesus monkeys (M. mulatta) that from birth until 120 days of age were fed a diet containing 13.4%, 6.7%, 3.35% protein or a commercial simulated human-milk formula (SMA) affording 9% protein. After 120 days, all animals were fed SMA. Females fed the diet lowest in protein, but not the other diets, were moderately affected, gaining less weight than their well-fed counterparts did, but they recovered their deficit during the repletion period, so that at 240 days no group differences remained. Males fed the two lowest-protein diets were severely and profoundly affected, in keeping with the depth of their protein deficiency. Moreover, unlike the females, they recovered none of their weight deficit during the repletion period. Food intake during deprivation was lower in the animals eating the low-protein diets. During SMA repletion, intakes followed no simple rule, but they did not converge. Except for the males fed the 3.35% protein diet, relative food intake (ml formula/kg body weight) did not differ substantially between diets or sexes at any time during the deprivation and diminished as the animals got older. Those males' relative intakes did not decline. During repletion, the SMA females ate the most in proportion to weight and the 13.4% group the least. The lowest-protein males, in contrast, ate the most in proportion to their weight during both deprivation and repletion. Males fed the lowest-protein diet gained little for what they ate; those fed the highest-protein diet gained much. Females were more efficient than males were when eating the low-protein diet and less efficient when eating the high-protein diet. When fed SMA during repletion, males' food efficiencies (grams gained/liter of diet) were nearly equal; females still differed: the SMA group was the least efficient and the low-protein group most efficient. Its counterpart, protein efficiency, was greatest (during deprivation) for females eating the low-protein diet and least (among females) for those eating the high-protein diet. Males were least protein efficient if eating the low-protein diet. Evidently, a 4 month bout of protein deprivation had prolonged effects on the amount of food the animals needed to produce a given gain in weight.     

Relative numerical middle in rhesus monkeys

Animals show vast numerical competence in tasks that require both ordinal and cardinal numerical representations, but few studies have addressed whether animals can identify the numerical middle in a sequence. Two rhesus monkeys (Macaca mulatta) learned to select the middle dot in a horizontal sequence of three dots on a touchscreen. When subsequently presented with longer sequences composed of 5, 7 or 9 items, monkeys transferred the middle rule. Accuracy decreased as the length of the sequence increased. In a second test, we presented monkeys with asymmetrical sequences composed of nine items, where the numerical and spatial middle were distinct and both monkeys selected the numerical middle over the spatial middle. Our results demonstrate that rhesus macaques can extract an abstract numerical rule to bisect a discrete set of items.