Monkeys reared in isolation with pictures as visual input: evidence for an innate releasing mechanism.

Monkeys reared in isolation from birth to 9 months received varied visual input solely from colored slides of monkeys in various activities and from nonmonkey pictures. Exploration, play, vocalization, and disturbance occurred most frequently with pictures of monkeys threatening and pictures of infants. From 2.5 to 4 months threat pictures yielded a high frequency of disturbance.Lever-touching to turn threat pictures on was very low during this period. Pictures of infants and of threat thus appear to have prepotent general activating properties, while pictures of threat appear to release a developmentally determined, inborn fear response.

Selection of social partners as a function of peer contact during rearing.

Three groups of monkeys were raised with different degrees of contact with their peers. The first group was allowed no contact, the second only visual and auditory contact, and the third was allowed complete and normal contact with their peers. Animals of all three groups were allowed to interact socially; they were then tested for their preference for monkeys raised under the same conditions or for monkeys raised under different conditions. Monkeys raised under the same conditions preferred each other, even if the stimulus animals were completely strange to the test monkey.

Selection of social partners as a function of peer contact during rearing.

In the report "Selection of social partners as a function of peer contact during rearing" by C. L. Pratt and G. P. Sackett (3 Mar., p. 1133), the third sentence of the first paragraph should read as follows: "Monkeys reared in isolation tend to withdraw from other animals and huddle by themselves in social situations. If such animals prefer each other over more normal monkeys, they may not be effectively exposed to the stimuli which lead to some degree of social adjustment."

Fetal toxicity of zidovudine (azidothymidine) in Macaca nemestrina: preliminary observations.

The objective of this study was to determine the dam, fetal, and infant toxicity of zidovudine (AZT) administered to pigtailed macaques during pregnancy. Pregnant macaques were administered AZT (1.5 mg/kg/dose every 4 h) or water via gastric catheter throughout pregnancy. AZT concentration and hematological changes were monitored in the dam, and fetal growth was monitored via ultrasound. Infant hematocrit was assessed at birth, and the neurological, perceptual, and motor development of the offspring were assessed for 9 to 10 months. Twelve pregnancies were brought to term. Mean plasma concentrations of AZT were comparable to those in human studies. Hemoglobin dropped significantly in pregnant dams and remained low, whereas platelets increased during treatment but returned to normal before the end of the study. There were no significant differences in any ultrasound measure of fetal growth, and AZT-exposed infants exhibited little behavioral delay or impairment. We predict no significant toxic effects of prenatal AZT exposure at this dosage in humans.

Development of lymphocyte subsets in pigtailed macaques.

The early development of eight lymphocyte subsets was determined for pigtailed macaque infants from 0 to 800 days of age using two-color flow cytometry and fluorescein- and R-phycoerythrin-conjugated monoclonal antibodies specific for human leukocyte antigens. Four major lymphocyte subsets in monkeys (B, CD4+ T, CD8+ T, and NK cells) could be further divided using two-color analysis. In neonates, the frequency of lymphocyte subpopulations having surface phenotypes found principally on dense, resting cells (IgD+ B cells, Lp220+ CD4+ T cells, and CD18dull CD8+ T cells) was much higher than subpopulations having phenotypes present principally on buoyant, activated cells (IgD- B cells, Lp220- CD4+ T cells, CD18bri CD8+ T cells). There was a complete absence of two CD18bri CD8+ subsets (CD8dull and CD8bri) during the first 300 days of life. The relative proportion of lymphocyte subsets with resting phenotype decreased with increasing age, while the subpopulations associated with activation gradually increased with age. These findings suggest that during early development immunocompetent cells gradually differentiate into activated lymphocytes.

Parental MHC antigen sharing and pregnancy wastage in captive pigtailed macaques.

Among some human populations, immunogenetic similarity between mates is associated with increased risk of pregnancy loss. To investigate the relationship between histocompatibility and reproductive performance in non-human primates, 128 pigtailed macaque couples were classified as 'reproductively successful' or 'unsuccessful' according to previous breeding performance. These couples were arranged into 64 triads composed of individual females, and a 'successful' and 'unsuccessful' mate. Individuals were typed for class I MHC antigens using a microcytotoxicity technique and species-specific alloantisera. Matched-pair analysis revealed that significantly more 'unsuccessful' couples shared MnLA-A antigens than did the matched 'successful' couples. Conditional matched-pair logistic regression analysis further revealed that parental sharing of MnLA-A antigens is an even more significant predictor of pregnancy wastage than is advanced maternal age. In our study population, sharing of MnLA-A antigens predicted 72% of pregnancy loss among 'unsuccessful' couples (P < 0.009). Identification of histocompatibility-associated factors influencing pregnancy success could have profound clinical implications for chronic spontaneous abortion, intra-uterine growth retardation and birth defects in humans. Among captive primates, identification of MHC or MHC-linked genes affecting reproductive outcome could lead to more efficient colony management strategies as well as development of a model for understanding human immunologically-mediated reproductive failure.

Methylmercury effects on the social behavior of Macaca fascicularis infants.

Observations of the social behavior of Macaca fascicularis exposed in utero to methylmercury (MeHg) and nonexposed control infants were performed as part of a study of the toxic, reproductive and developmental effects of maternal MeHg intake. Infants were tested twice weekly from 2 weeks to 8 months of age. Data were summarized into 6 categories of social behavior and 7 categories of nonsocial behavior. Analysis of the most prevalent behavior indicated that MeHg-exposed offspring exhibited a decrease in social play behavior and a concomitant increase in nonsocial passive behavior. The MeHg effect on social play behavior tended to decrease with age, while the group differences in nonsocial passive behavior tended to increase. The results indicate that maternal intake of MeHg during pregnancy can affect the social development of infant primates by suppressing social interactions and increasing nonsocial behavior.

Multiple-spell, discrete-time survival analysis of developmental data: object concept in pigtailed macaques.

To measure cognitive development in 123 pigtailed macaques, we calculated medians and quartiles for the milestones of classical (Piagetian) object concept development (plain reach, partial-hide, full-hide, and A-not-B) in both 2-dimensional (screen) and 3-dimensional (well) tasks. Using multiple-spell, discrete-time survival analysis, we examined the influence of 4 independent variables (starting age, sex, birth weight, and task) on the probability of completing the milestones on any given test. The significant predictors for completion of the well sequence were birth weight and task. The best predictors for completion of the screen sequence were birth weight, number of test sessions, and interaction between birth weight and task. Birth weight had a greater predictive relationship in the earlier stages. This analysis provided information that cannot be obtained with traditional parametric methods.

Social preferences by and for pigtailed macaques (Macaca nemestrina) with trisomy 18.

Social choices of trisomic macaques (macaca nemestrina) were compared with those of age-matched controls and of infants and adult females without handicaps. All groups chose social over nonsocial stimuli and showed few differences in their preferences for stimulus animals with and without handicaps. On initial encounter, the trisomic monkeys were socially interesting to age-matched controls and to younger animals and adult females. Thus, avoidance of individuals with handicaps probably is not a general primate trait. Even though the trisomic monkeys showed inappropriate social and motor behavior in play groups, their preference for social stimuli demonstrates that the presence of mental retardation and physical handicaps need not reduce positive social motivation even when prior social experiences have been largely negative.

Effects of weaning age on mortality of colony-born Macaca nemestrina.

In an effort to determine empirically the proper age for separation of pigtailed macaque (Macaca nemestrina) infants from their dams in a large domestic breeding colony, we conducted a retrospective survey of 1,592 infants. Survivorship was highest for infants not separated from their dams at all and for those separated within the first four months of life. Survivorship was poor for animals separated during or after the fifth month. Thus, not weaning or weaning early are the most acceptable management strategies in terms of mortality risk. This result is paradoxical with regard to nutritional considerations, but appears to be related to a sensitive period in social development. The relative advantages and disadvantages of various weaning ages are discussed.

Receiving severe aggression correlates with fetal gender in pregnant pigtailed monkeys.

Pregnant females were severely bitten in 220 of 2,822 conceptions among pigtail macaques living in harem groups. These pregnancies yielded 58.6% female offspring compared with 48.5% for nonbitten pregnant animals. The fetal gender difference occurred only after midterm, reaching a peak of 70% female fetuses in the 4th gestational month. Fetal gender thus appeared to influence maternal behavior, appearance, or physiology in some way detectable to other monkeys with the consequence of altering risk for receiving severe aggression.

A nonhuman primate model of risk for deviant development.

Delayed development and permanent retardation can result from genetic, prenatal, perinatal, and postnatal factors often acting through complex interactions. For human subjects experimental study of such developmental systems is often impossible due to confounding of variables and ethical considerations. One alternative is to study an animal model. A nonhuman primate model for studying genetic, physiological, and psychosocial processes producing delayed development was described in this paper. The model focuses on parental risk for poor reproductive outcomes using pigtailed monkey (Macaca nemestrina) subjects. In initial experiments subjects were offspring from high- and low-risk breeders who were nursery-reared with no postnatal contact with their parents. Results showed that both maternal and paternal factors are associated with delayed development in systems ranging from tooth eruption to concept learning ability.

Behavioral changes in nonambulatory, profoundly mentally retarded individuals.

Nonambulatory, profoundly mentally retarded (NPMR) individuals seldom have been studied as a distinct population. This investigation sought to describe the pshysical, etiological, and behavioral characteristics of NPMR children and adults and to evaluate the effects of intensive physical and social stimulation on their ongoing behavior. Sixteen NPMR subjects were studied for 2 1/2 years. All were PMR, bedridden, abnormally small, and unresponsive to external stimulation. Baseline data concerning developmental status, diurnal patterns of sleep and activity, behavior in a novel situation, ongoing ward behavior, and anthropometric measures were obtained. Subjects were highly variable in their responses to items from the Bayley Scales of Infant Development, with overall performance below that of a normal six month old. Although subjects showed some diurnal pattern of sleep, they frequently fell asleep for short periods at random time during the day. In a novel situation subjects responded minimally to stimulus objects, or not at all. Typically, their ongoing ward behavior consisted of very low level activity, involving small peripheral limb movements, wandering or blinking eyes, mouthing or grimacing, and repetitive, reflexive types of patterns labeled "fixed action sequences." Experimental treatment consisted of three phases of daily stimulation. (1) Subjects were placed in an upright or elevated position in specially constructed "playpens." (2) Subjects were placed in "playpens" and many toys were presented. (3) Subjects were positioned in pairs so that direct physical contact was provided. Each phase resulted in changed behavioral profiles during treatment. Furthermore, all experimental subjects showed beneficial effects of treatment in their ongoing ward behavior, diurnal sleep patterns, Bayley performance, or response to novel situations. Implications of this research extend to understanding environmentally induced changes in neurological maturation and social development in individuals previously thought to be hopelessly devastated. The descriptive data are intended to provide a useful framework for further systematic research with NPMR populations.