Changes in cortical dendritic branching subsequent to partial social isolation in stumptailed monkeys

The effects of breastfeeding versus formula-feeding on cerebral cortex maturation in infant rhesus macaques

Breastfeeding is positively associated with several outcomes reflecting early brain development and cognitive functioning. Brain neuroimaging studies have shown that exclusively breastfed children have increased white matter and subcortical gray matter volume compared to formula-fed children. However, it is difficult to disentangle the effects of nutrition in breast milk from other confounding factors that affect brain development, particularly in studies of human subjects. Among the nutrients provided by human breast milk are the carotenoid lutein and the natural form of tocopherol, both of which are selectively deposited in brain. Lutein is the predominant carotenoid in breast milk but not in most infant formulas, whereas infant formulas are supplemented with the synthetic form of tocopherol. In this study, a non-human primate model was used to investigate the effects of breastfeeding versus formula-feeding, as well as lutein and natural RRR-α-tocopherol supplementation of infant formula, on brain maturation under controlled experimental conditions. Infant rhesus macaques (Macaca mulatta) were exclusively breastfed, or were fed infant formulas with different levels and sources of lutein and α-tocopherol. Of note, the breastfed group were mother-reared whereas the formula-fed infants were nursery-reared. Brain structural and diffusion MR images were collected, and brain T₂ was measured, at two, four and six months of age. The mother-reared breastfed group was observed to differ from the formula-fed groups by possessing higher diffusion fractional anisotropy (FA) in the corpus callosum, and lower FA in the cerebral cortex at four and six months of age. Cortical regions exhibiting the largest differences include primary motor, premotor, lateral prefrontal, and inferior temporal cortices. No differences were found between the formula groups. Although this study did not identify a nutritional component of breast milk that could be provided to infant formula to facilitate brain maturation consistent with that observed in breastfed animals, our findings indicate that breastfeeding promoted maturation of the corpus callosum and cerebral cortical gray matter in the absence of several confounding factors that affect studies in human infants. However, differences in rearing experience remain as a potential contributor to brain structural differences between breastfed and formula fed infants.

Using diffusion anisotropy to study cerebral cortical gray matter development

Diffusion-weighted magnetic resonance imaging (diffusion MRI) is being used to characterize morphological development of cells within developing cerebral cortical gray matter. Abnormal morphology is a shared characteristic of cerebral cortical neurons for many neurodevelopmental disorders, and therefore diffusion MRI is potentially of high value for monitoring growth-related anatomical changes of relevance to brain function. Here, the theoretical framework for analyzing diffusion MRI data is summarized. An overview of quantitative methods for validating the interpretations of diffusion MRI data using light microscopy is then presented. These theoretical modeling and validation methods have been used to precisely characterize changes in water diffusion anisotropy with development in the context of several animal model systems. Further, in diffusion MRI studies of several preclinical models of neurodevelopmental disorders, the ability is demonstrated of diffusion MRI to detect abnormal morphological neural development. These animal model studies are reviewed along with recent initial efforts to translate the findings into an approach for studies of human subjects. This body of data indicates that diffusion MRI has the requisite sensitivity to detect abnormal cellular development in the context of several models of neurodevelopmental disorders, and therefore may provide a new strategy for detecting abnormalities in early stages of brain development in humans.

Attachment in medical care: A review of the interpersonal model in chronic disease management

Objective Patient-physician interaction is continually examined in an era prioritizing patient-centered approaches, yet elaboration beyond aspects of communication and empathy is lacking. Major chronic conditions would benefit tremendously from understanding interpersonal aspects of patient-physician encounters. This review intends to provide a concise introduction to the interpersonal model of attachment theory and how it informs both the patient-physician interaction and medical outcomes in chronic care. Methods A narrative review of the theoretical, neurobiological, epidemiological, investigational, and clinical literature on attachment theory and its impact on medical outcomes was conducted, utilizing a variety of key words as searched on PubMed database. Studies and reviews included were of a variety of sources, including textbooks and peer-reviewed journals. Reports in languages other than English were excluded. Results Measurable, discrete attachment styles and behavioral patterns correlate with poor medical outcomes, including nonadherence in insecure dismissing attachment and care overutilization in insecure preoccupied attachment. Furthermore, insecure dismissing attachment is associated with significant mortality. These variables can be easily assessed, and their effects are reversible, as evidenced by collaborative care outcome data. Discussion Attachment theory is useful a model with application in clinical and investigational aspects of chronic illness care. Implications and guidelines are explored.

Consequences of early adverse rearing experience(EARE) on development: insights from non-human primate studies

Early rearing experiences are important in one's whole life, whereas early adverse rearing experience(EARE) is usually related to various physical and mental disorders in later life. Although there were many studies on human and animals, regarding the effect of EARE on brain development, neuroendocrine systems, as well as the consequential mental disorders and behavioral abnormalities, the underlying mechanisms remain unclear. Due to the close genetic relationship and similarity in social organizations with humans, non-human primate(NHP) studies were performed for over 60 years. Various EARE models were developed to disrupt the early normal interactions between infants and mothers or peers. Those studies provided important insights of EARE induced effects on the physiological and behavioral systems of NHPs across life span, such as social behaviors(including disturbance behavior, social deficiency, sexual behavior, etc), learning and memory ability, brain structural and functional developments(including influences on neurons and glia cells, neuroendocrine systems, e.g., hypothalamic-pituitary-adrenal(HPA) axis, etc). In this review, the effects of EARE and the underlying epigenetic mechanisms were comprehensively summarized and the possibility of rehabilitation was discussed.

High order neural correlates of social behavior in the honeybee brain

BACKGROUND

Honeybees are well established models of neural correlates of sensory function, learning and memory formation. Here we report a novel approach allowing to record high-order mushroom body-extrinsic interneurons in the brain of worker bees within a functional colony. New method The use of two 100 cm long twisted copper electrodes allowed recording of up to four units of mushroom body-extrinsic neurons simultaneously for up to 24h in animals moving freely between members of the colony. Every worker, including the recorded bee, hatched in the experimental environment. The group consisted of 200 animals in average.

RESULTS

Animals explored different regions of the comb and interacted with other colony members. The activities of the units were not selective for locations on the comb, body directions with respect to gravity and olfactory signals on the comb, or different social interactions. However, combinations of these parameters defined neural activity in a unit-specific way. In addition, units recorded from the same animal co-varied according to unknown factors. Comparison with existing method(s): All electrophysiological studies with honey bees were performed so far on constrained animals outside their natural behavioral contexts. Yet no neuronal correlates were measured in a social context. Free mobility of recoded insects over a range of a quarter square meter allows addressing questions concerning neural correlates of social communication, planning of tasks within the colony and attention-like processes.

CONCLUSIONS

The method makes it possible to study neural correlates of social behavior in a near-natural setting within the honeybee colony.

Larval Population Density Alters Adult Sleep in Wild-Type Drosophila melanogaster but Not in Amnesiac Mutant Flies

Sleep has many important biological functions, but how sleep is regulated remains poorly understood. In humans, social isolation and other stressors early in life can disrupt adult sleep. In fruit flies housed at different population densities during early adulthood, social enrichment was shown to increase subsequent sleep, but it is unknown if population density during early development can also influence adult sleep. To answer this question, we maintained Drosophila larvae at a range of population densities throughout larval development, kept them isolated during early adulthood, and then tested their sleep patterns. Our findings reveal that flies that had been isolated as larvae had more fragmented sleep than those that had been raised at higher population densities. This effect was more prominent in females than in males. Larval population density did not affect sleep in female flies that were mutant for amnesiac, which has been shown to be required for normal memory consolidation, adult sleep regulation, and brain development. In contrast, larval population density effects on sleep persisted in female flies lacking the olfactory receptor or83b, suggesting that olfactory signals are not required for the effects of larval population density on adult sleep. These findings show that population density during early development can alter sleep behavior in adulthood, suggesting that genetic and/or structural changes are induced by this developmental manipulation that persist through metamorphosis.

The prefrontal-limbic system: development, neuroanatomy, function, and implications for socioemotional development

The knowledge that neonatal emotional experience and associated learning processes are critical in the maturation of prefronto-limbic circuits emphasizes the importance of preterm and neonatal care. The further improvement of care and intervention strategies requires a deeper understanding of epigenetic mechanisms mediating experience-induced synaptic reorganization underlying the emergence of emotional and cognitive behavioral traits. Interdisciplinary research efforts are needed in which pediatricians and developmental biologists and psychologists merge their knowledge, concepts, and methodology. The hope is that the translational relevance of research efforts can be improved through a greater interaction between basic and clinical scientists.

Long-term effects of differential early rearing in rhesus macaques: behavioral reactivity in adulthood

Adverse early experiences are associated with a range of deleterious health outcomes in humans, including higher risk for affective disorders. Studies using a long-standing model of nonhuman primate model of early adversity have demonstrated that nursery-reared (NR) monkeys exhibit alterations in multiple aspects of biobehavioral development; however, few studies have evaluated the persistence of socioaffective behavioral changes through adulthood. We evaluated the effects of early rearing experience on adult animals' response to a well-validated assessment of anxiety-like behavior, the human intruder paradigm (HIP). We tested 22 rhesus monkeys who were either nursery-reared (NR) or reared with their mothers (mother-reared; MR). NR monkeys were inhibited in their behavior compared to MR monkeys, with reduced locomotion and exploratory behaviors. NR animals showed a marginal increase in freezing. Together these findings demonstrate that the consequences of differential infant rearing experience on socioaffective behavior persist into adulthood, with evidence of greater inhibition in NR monkeys.

The experience-dependent maturation of prefronto-limbic circuits and the origin of developmental psychopathology: implications for the pathogenesis and therapy of behavioural disorders

The maturation of prefronto-limbic neuronal pathways that mediate essential affective and social regulatory functions is experience dependent. Immediately after birth the infant's affective experiences, especially those embedded in the relationship with the primary caregiver, trigger the reorganization and adaptive fine-tuning of synaptic circuits. Research in humans and in animal models supports the hypothesis that socio-emotional deprivation and emotional trauma during early childhood may leave 'scars' in prefronto-limbic function, brain regions that are essential for emotional behaviour, learning, and memory. The focus of this review is to point out that mechanisms involved in structuring and optimizing neural circuits during brain development might also be used in moulding personality and behaviour during psychotherapy in the adult brain.

Identifying key features of early stressful experiences that produce stress vulnerability and resilience in primates

This article examines the complex role of early stressful experiences in producing both vulnerability and resilience to later stress-related psychopathology in a variety of primate models of human development. Two types of models are reviewed: Parental Separation Models (e.g., isolate-rearing, peer-rearing, parental separations, and stress inoculation) and Maternal Behavior Models (e.g., foraging demands, variation in maternal style, and maternal abuse). Based on empirical evidence, it is argued that early life stress exposure does not increase adult vulnerability to stress-related psychopathology as a linear function, as is generally believed, but instead reflects a quadratic function. Features of early stress exposure including the type, duration, frequency, ecological validity, sensory modality, and developmental timing, within and between species, are identified to better understand how early stressful experiences alter neurobiological systems to produce such diverse developmental outcomes. This article concludes by identifying gaps in our current knowledge, providing directions for future research, and discussing the translational implications of these primate models for human development and psychopathology.

A psychobiological theory of attachment

This article describes a neurobiological basis for the “first attachment” of the primate infant to its caretaker. The infant normally internalizes a neurobiological “image” of the behavioral and emotional characteristics of its caregiver that later regulates important features of its brain function. Current models of sensorimotor analysis and its relation to emotion suggest that sensorimotor systems are also habit and memory systems, their functional status and lability regulated in part by biogenic amine systems. The intertwined development of neural and social functions can sometimes go awry. If the attachment process fails or the caregiver is incompetent, the infant may become socially dysfunctional. This helps explain the developmental psychopathology and later vulnerability to adult psychopathology that result from disruptions of social attachment.

The impact of perinatal stress on the functional maturation of prefronto-cortical synaptic circuits: implications for the pathophysiology of ADHD?

Enriched as well as impoverished or adverse perinatal environment plays an essential role in the development and refinement of neuronal pathways, which are the neural substrate of intellectual capacity and socioemotional competence. Perinatal experience and learning events continuously interact with the adaptive shaping of excitatory, inhibitory, and neuromodulatory synaptic as well as the endocrine stress systems, including the neuronal corticotropin-releasing factor (CRF) pathways. Adverse environments, such as stress and emotional deprivation can not only delay experience-dependent maturation of these pathways, but also induce permanent changes in prefronto-cortical wiring patterns. We assume that such dysfunctional connections are the neuronal basis for the development of psychosocially induced mental disorders during later life. The aim of this review is to focus on the impact of perinatal stress on the neuronal and synaptic reorganization during brain development and possible implications for the etiology and therapy of mental disorders such as ADHD.

Amphetamine sensitization alters dendritic morphology in prefrontal cortical pyramidal neurons in the non-human primate

Amphetamine (AMPH) sensitization in the nonhuman primate induces persistent aberrant behaviors reminiscent of the hallmark symptoms of schizophrenia, including hallucinatory-like behaviors, psychomotor depression, and profound cognitive impairment. The present study examined whether AMPH sensitization induces similarly long-lasting morphologic alterations in prefrontal cortical pyramidal neurons. Three to 3(1/2) years postsensitization, sensitized, and AMPH-naïve control monkeys were killed. Blocks of prefrontal cortex were Golgi-impregnated for elucidation of pyramidal dendritic morphology in layers II/superficial III (II/IIIs), deep III, and V/VI. In AMPH-sensitized animals as compared to AMPH-naïve controls, pyramidal dendrites in layer II/IIIs exhibited reduced overall dendritic branching and reduced peak spine density (22%) on the apical trunk. Across all layers, the distance from soma to peak spine density along the apical trunk was decreased (126.38+/-7.65 mum in AMPH-sensitized compared to 162.98+/-7.26 microm in AMPH-naïve controls), and basilar dendritic length was reduced (32%). These findings indicate that chronic dopamine dysregulation, consequent to AMPH sensitization, results in enduring, atrophic changes in prefrontal pyramidal dendrites that resemble the pathologic alterations described in patients with schizophrenia and may contribute to the persistence of schizophrenia-like behavioral changes and cognitive dysfunction associated with sensitization. These findings may also provide key insights into the etiologic origin of the pronounced behavioral disturbances and cognitive dysfunction associated with schizophrenia.

Experience induces structural and biochemical changes in the adult primate brain

Primates exhibit complex social and cognitive behavior in the wild. In the laboratory, however, the expression of their behavior is usually limited. A large body of literature shows that living in an enriched environment alters dendrites and synapses in the brains of adult rodents. To date, no studies have investigated the influence of living in a complex environment on brain structure in adult primates. We assessed dendritic architecture, dendritic spines, and synaptic proteins in adult marmosets housed in either a standard laboratory cage or in one of two differentially complex habitats. A month-long stay in either complex environment enhanced the length and complexity of the dendritic tree and increased dendritic spine density and synaptic protein levels in the hippocampus and prefrontal cortex. No differences were detected between the brains of marmosets living in the two differentially complex environments. Our results show that the structure of the adult primate brain remains highly sensitive even to modest levels of experiential complexity. For adult primates, living in standard laboratory housing may induce reversible dendritic spine and synapse decreases in brain regions important for cognition.

Recognition of partially concealed leopards by wild bonnet macaques (Macaca radiata). The role of the spotted coat

Wild bonnet macaques (Macaca radiata) have been shown to recognize models of leopards (Panthera pardus), based on their configuration and spotted yellow coat. This study examined whether bonnet macaques could recognize the spotted and dark melanic morph when partially concealed by vegetation. Seven troops were studied at two sites in southern India, the Mudumalai Wildlife Sanctuary and the Kalakad-Mundanthurai Tiger Reserve. The forequarters and hindquarters of the two leopard morphs were presented from behind thick vegetation to individuals at feeding stations 25 m away. Flight reaction times and frequency of flight were obtained from video for only those individuals who oriented towards the models prior to hearing alarm calls. Bonnet macaques exhibited faster reaction times and greater frequency of flight after looking at the spotted morph's forequarter than after looking at either its spotted hindquarter or the dark morph's forequarter. The hindquarter of the dark morph was ignored completely. Artificial neural network modeling examined the perceptual aspects of leopard face recognition and the role of spots as camouflage. When spots were integrated into the pattern recognition process via network training, these spots contributed to leopard face recognition. When networks were not trained with spots, spots did not act as camouflage by disrupting facial features.

Gastroesophageal reflux disease: attachment style and parental bonding

The attachment styles and parental bonding of 72 patients (M age= 45.3 yr., SD=13.5) suffering from Gastroesophageal Reflux Disease were compared with those of 105 healthy subjects (M age =44.9 yr., SD = 5.8). A clinical interview and two questionnaires, the Attachment Style Questionnaire and the Parental Bonding Instrument, showed that the scores on the ASQ Confidence subscale were significantly lower in the clinical group. Similar results were obtained for the Discomfort with Closeness subscale in the subsample with Pure Gastroesophageal Reflux Disease. The results indicate Insecure Attachment in the clinical sample. The results obtained from the Parental Bonding Instrument indicate that scores on the Protection Mother scale were significantly higher in the clinical subjects, suggesting a Low Care-High Protection combination (Affectiveless Control), at least for patients with pure Gastroesophageal Reflux Disease. These characteristics can be considered important factors in the tendency to somatization. The symptoms may have a paradoxically normalising function while the patient shows an emotional detachment towards intimate relationships. The illness appears to act as a bond through which the relationship with the caregivers is maintained.

Early experience and depressive disorders: human and non-human primate studies

This paper reviews evidence from both human and non-human primate studies concerning the role of early adverse experiences in the onset and course of adult depressive disorders. Despite accumulating evidence that stressful life events can play a major role in precipitating the onset of depressive episodes in humans, the mechanisms by which early experiences mediate and moderate the risk for later affective illnesses are not fully understood. Experimental paradigms in primates have documented the important role of undeveloped (social deprivation) or disrupted attachment systems (social separation). Effects of early social deprivation can be seen in many domains. Behavioral effects include repetitive idiosyncratic behaviors, increased self-directed behaviors, inappropriate expression of aggressive behaviors, non-modulated patterns of consumption, and inappropriate sexual and maternal behaviors. Cognitively, such animals require longer habituation time for any task and demonstrate increased perseverance on tasks following non-reward. Physiological effects include an altered hypothalamic-pituitary-adrenal response to stress, changes in diurnal temperature regulation, and alterations in immune function. Neurochemical effects include abnormalities in noradrenergic, serotonergic, and dopaminergic systems. Even neuroanatomical changes following early social deprivation have been reported. Studies with primates have also confirmed that early maternal and peer separations are major behavioral and neurobiological events with both short- and long-term consequences that parallel human depression. Future utilization of experimental paradigms in non-human primates may assist in better understanding the role of early experiences in predisposing to the development of affective illnesses in humans. This review concludes by presenting a model for understanding a developmentally based vulnerability to adult depressions.

Local brain functional activity following early deprivation: a study of postinstitutionalized Romanian orphans

Early global deprivation of institutionalized children may result in persistent specific cognitive and behavioral deficits. In order to examine brain dysfunction underlying these deficits, we have applied positron emission tomography using 2-deoxy-2-[(18)F]fluoro-D-glucose in 10 children (6 males, 4 females, mean age 8.8 years) adopted from Romanian orphanages. Using statistical parametric mapping (SPM), the pattern of brain glucose metabolism in the orphans was compared to the patterns obtained from two control groups: (i) a group of 17 normal adults (9 males, 8 females, mean age 27.6 years) and (ii) a group of 7 children (5 males and 2 females, mean age 10.7 years) with medically refractory focal epilepsy, but normal glucose metabolism pattern in the contralateral hemisphere. Consistent with previous studies of children adopted from Romanian orphanages, neuropsychological assessment of Romanian orphans in the present study showed mild neurocognitive impairment, impulsivity, and attention and social deficits. Comparing the normalized glucose metabolic rates to those of normal adults, the Romanian orphans showed significantly decreased metabolism bilaterally in the orbital frontal gyrus, the infralimbic prefrontal cortex, the medial temporal structures (amygdala and head of hippocampus), the lateral temporal cortex, and the brain stem. These findings were confirmed using a region-of-interest approach. SPM analysis showed significantly decreased glucose metabolism in the same brain regions comparing the orphans to the nonepileptic hemisphere of the childhood epilepsy controls. Dysfunction of these brain regions may result from the stress of early global deprivation and may be involved in the long-term cognitive and behavioral deficits displayed by some Romanian orphans.

Attachment and psychosomatic medicine: developmental contributions to stress and disease

OBJECTIVE

The object of this study was to evaluate the evidence linking attachment insecurity to illness. Attachment theory describes lifelong patterns of response to threat that are learned in the interaction between an infant and his or her primary caregiver. Despite its biopsychosocial domain, attachment theory has only recently been applied to psychosomatic medicine.

METHOD

MEDLINE and PsychInfo databases were searched from 1966 to 2000 for English language papers with key words "attachment" and "object relations." Papers and their cited references were reviewed if they were directly related to physical illness, symptoms, or physiology. A hypothetical causal model was developed.

RESULTS

Direct and indirect evidence from survey studies supports an association between attachment insecurity and disease. Animal studies and human experiments suggest that attachment contributes to individual differences in physiological stress response. There is also less robust support for insecure attachment leading to symptom reporting and to more frequent health risk behaviors, especially substance use and treatment nonadherence. Evidence supports the prediction from attachment theory that the benefits of social support derive more from attachment relationships than nonattachment relationships.

CONCLUSIONS

Although the available data are suggestive rather than conclusive, the data can be organized into a model that describe attachment insecurity leading to disease risk through three mechanisms. These are increased susceptibility to stress, increased use of external regulators of affect, and altered help-seeking behavior. This model warrants further prospective investigation.

Physiological correlates of self-injurious behavior in captive, socially-reared rhesus monkeys

This study examined the relationship between self-injurious behavior (SIB) in rhesus monkeys and several biological variables, including monoamine metabolites in cerebrospinal fluid (CSF) and circulating levels of ACTH, cortisol, and testosterone. Cisternal CSF and blood plasma samples were obtained from 23 individually housed male rhesus macaques, 14 of which had a veterinary record of self-inflicted wounding. CSF samples were analyzed for 5-hydroxyindole-3-acetic acid (5-HIAA), homovanillic acid (HVA) and 3-methoxy-4-hydroxyphenylglycol (MHPG) using isocratic high-performance liquid chromatography with electrochemical detection (HPLC-EC). Plasma samples were analyzed for ACTH, cortisol, and testosterone using commercially available radioimmunoassays (RIAs). Rates of self-directed biting were determined by systematic observation of all monkeys. Monkeys with SIB did not differ from controls in their basal monoamine or gonadal activity. However, the SIB group showed consistently lower mean plasma cortisol levels than the control group. Plasma cortisol was negatively correlated with rates of self-directed biting. These results suggest a persistent dysregulation of the hypothalamic-pituitary-adrenal (HPA) axis in monkeys with SIB. It is not yet clear whether this phenomenon of low cortisol represents chronically reduced adrenocortical secretion under basal conditions or a difference in response to the mild stress of capture and chemical restraint. The implications of these findings will be discussed with respect to SIB in humans as well as post-traumatic stress disorder (PTSD), a condition characterized by pituitary-adrenocortical hypoactivity.

Early environmental regulation of glucocorticoid feedback sensitivity in young adult monkeys

Variations in maternal care induce in neonatal rodents life-long changes in glucocorticoid feedback regulation of the hypothalamic-pituitary-adrenal axis. This aspect of plasticity in neuroendocrine development has not been established in primates. We assessed, in young adult squirrel monkeys, postnatal rearing effects on cortisol-induced suppression of corticotropin-releasing factor (CRF) stimulated secretion of adrenocorticotropic hormone (ACTH). Offspring of randomly bred monkeys were periodically removed from natal groups between 13 and 21 weeks of age. In two other postnatal rearing conditions, systematic differences in maternal availability were produced by manipulating the effort required of lactating mothers to successfully find food. All offspring were subsequently administered, 3-5 years later on two occasions, an intravenous ovine CRF injection preceded 60 min earlier by placebo or cortisol pretreatment. The difference between CRF-stimulated time-integrated secretion of ACTH following placebo vs cortisol pretreatment served as an index of glucocorticoid negative feedback. Difference scores were greatest in monkeys previously separated from natal groups. This finding was not attributable to significant rearing condition differences in plasma cortisol levels achieved following pretreatment with exogenous cortisol, nor plasma ACTH levels produced when the CRF injection was preceded by pretreatment with placebo. The results suggest that postnatal experiences altered glucocorticoid feedback in monkeys at least through early adulthood. This conclusion supports retrospective reports indicating that, for humans with major mood and anxiety disorders, systematic differences in glucocorticoid feedback may reflect neural mechanisms in development linking early life stress with psychopathology in adulthood.

Early social deprivation in nonhuman primates: long-term effects on survival and cell-mediated immunity

BACKGROUND

Early differential social experience of non-human primates has resulted in long-term alterations in behavior and neurobiology. Although brief maternal separation has been associated with changes in immune status, the long-term effects on survival and immune function of prolonged early social deprivation are unknown.

METHODS

Survival rates were examined in rhesus monkeys, half of which had been socially deprived during their first year of life. Repeated measures of immune status were tested in surviving monkeys (18-24 years old). Peripheral blood T, B, and natural killer lymphocytes, macrophages, and monocytes were measured by flow cytometry. Functional cellular immune activity measures included T-cell proliferative responses to mitogens (concanavalin and phytohemagglutinin), T-cell memory response to tetanus toxoid antigen, T-cell-dependent B-cell proliferative responses to mitogen (PWM) and natural killer cell cytotoxic activity.

RESULTS

Despite identical environments following isolation, early social deprivation resulted in a significantly decreased survival rate, males being particularly vulnerable to early death. Early social deprivation was associated with a decrease in the ratio of helper to suppressor T cells, and a significant increase in natural killer cell number and in natural killer cell activity in the surviving monkeys. No differences in T- or B-lymphocyte proliferation following mitogen or tetanus toxoid antigen stimulation were observed.

CONCLUSIONS

Prolonged early social deprivation of non-human primates profoundly affected mortality and resulted in lifelong effects on cell-mediated immune status.

Postnatal experiences and genetic effects on squirrel monkey social affinities and emotional distress

Most nonhuman primate research on risk factors underlying vulnerability to stress has focused on early psychosocial experiences in various species of macaques. To test for genetic and experiential effects on emotional vulnerability in randomly bred squirrel monkeys, here we combined a paternal half-sibling analysis with three postnatal rearing protocols that altered aspects of maternal availability. In one condition offspring were periodically removed from natal groups, whereas differences in maternal availability were produced in two other conditions by manipulating the effort required of lactating mothers to successfully locate food. After completion of these protocols at 21 weeks of age, social affinities, maternal separation induced peep-calls, and plasma levels of cortisol were assessed from 29 to 37 weeks of age. Significant postnatal rearing effects and the lowest heritabilities were detected in peak elevations of cortisol measured 1 day after the removal of mothers from otherwise undisturbed groups. Individual differences in cortisol 3-7 days later revealed negligible postnatal rearing effects and the highest heritabilities (h(2) approximately. 70), as offspring sired by certain fathers failed to return to the preseparation level found in undisturbed natal groups. Paternal half-siblings that responded with long lasting increases in cortisol spent more time near their mother in undisturbed groups and exhibited long-lasting increases in separation induced peep-calls. These findings concur with human twin studies that suggest genetic and experiential factors contribute to individual differences in vulnerability to emotional distress.

Differential rearing affects corpus callosum size and cognitive function of rhesus monkeys

This study investigated the effects of different rearing conditions on neural and cognitive development of male rhesus monkeys (Macaca mulatta). Infants raised individually in a nursery from 2 to 12 months of age (NURSERY, n=9) were compared to age-matched infants raised in a semi-naturalistic, social environment (CONTROL, n=11). Various brain regions were measured by MRI. Although overall brain volumes did not differ between NURSERY and CONTROL animals, corpus callosum (CC) size, measured in mid-sagittal sections, was significantly decreased in the NURSERY group. Group differences were most evident in the posterior aspects of the corpus callosum and appeared to result from changes in the number of cross-hemispheric projections rather than from a decrease in cortical gray matter volume. The decrease in corpus callosum size in the NURSERY animals persisted after 6 months of social housing in a peer-group. Rearing group differences were not found in other structures analyzed, including the hippocampus, cerebellum and anterior commissure. In cognitive testing, NURSERY animals had more difficulty acquiring the delayed non-matching to sample (DNMS) task, but showed no deficits in subsequent memory performance when a 2 or 10 min delay was imposed. The NURSERY infant monkeys were also impaired in object, but not in spatial, reversal learning, although there were no differences in a simple object discrimination task. The cognitive deficits exhibited by the NURSERY animals were significantly correlated with the alterations found in the CC. In summary, rearing environment was associated with sustained differences in cross-hemispheric projections, white matter volume and cognitive performance.

Brain plasticity and behavior

Brain plasticity refers to the brain's ability to change structure and function. Experience is a major stimulant of brain plasticity in animal species as diverse as insects and humans. It is now clear that experience produces multiple, dissociable changes in the brain including increases in dendritic length, increases (or decreases) in spine density, synapse formation, increased glial activity, and altered metabolic activity. These anatomical changes are correlated with behavioral differences between subjects with and without the changes. Experience-dependent changes in neurons are affected by various factors including aging, gonadal hormones, trophic factors, stress, and brain pathology. We discuss the important role that changes in dendritic arborization play in brain plasticity and behavior, and we consider these changes in the context of changing intrinsic circuitry of the cortex in processes such as learning.

The behavioral neurobiology of self-injurious behavior in rhesus monkeys. Current concepts and relations to impulsive behavior in humans

The objective of this report is to critically review past reports and present new data on the psychobiology of self-injurious behavior (SIB) and/or "risky" or "impulsive" behavior in primates (human and nonhuman). One aim was to reexamine how early social deprivation and neurobiological changes caused by deprivation might contribute to SIB in monkeys, and how the causes of SIB in monkeys might inform us about the psychobiology of suicide in humans. A second aim was to examine the evidence that social deprivation in monkeys produces reductions in brain 5-HT system function that are causal or coincident factors associated with self-injurious or impulsive behavior. Prior studies and new data indicate that the environmental causes of SIB and unusual aggression in rhesus monkeys do not produce reductions in brain 5-HT system activity and that experimental production of low levels of brain 5-HT system activity does not reliably promote either SIB or unusual other-directed aggression in monkeys. A third and final aim was to suggest that in severe cases of environmentally induced SIB and/or aggression in monkeys, having relatively high or low levels of 5-HT system activity may not be related to ongoing behavior because the 5-HT system may not interact with other neurotransmitter systems in the usual way. Overall, the contention is that primates exhibiting SIB and unusual aggression may have altered 5-HT system function, but this may be but one aspect of a more profound disorganization of brain function involving many neurohormonal and transmitter systems. Contemporary theorizing and experimentation tends to be restricted to the idea that altered function in one key system might be the cause of a specific form of psychopathology. In the future, research examining the probable change interactions of neurotransmitter and neuroendocrine systems as underlying causes of behavioral disorders should have a high priority.

The noradrenergic innervation density of the monkey paraventricular nucleus is not altered by early social deprivation

A series of neuroanatomic analyses have been undertaken to identify potential neuropathological changes seen in monkeys exposed to early social deprivation, which leads to psychopathology, inappropriate responses to stress and appetitive disorders. The animals used in this study were either socially reared or maternal- and peer-deprived. Within this framework, the distribution and density of noradrenergic (and adrenergic) varicosities was assessed in the hypothalamic paraventricular nucleus of rhesus monkeys using dopamine-beta-hydroxylase immunohistochemistry combined with laser scanning microscopy. Quantitative analysis of dopamine-beta-hydroxylase-immunoreactive varicosity density within magnocellular and parvicellular regions revealed no significant differences between rearing conditions, suggesting that this chemically identified afferent input to the paraventricular nucleus was not affected by the early environmental insult of social deprivation. The apparent lack of vulnerability of the paraventricular nucleus to differential rearing conditions contrasts with the neuropathological changes observed in several discrete brain regions.

Effects of social deprivation in prepubescent rhesus monkeys: immunohistochemical analysis of the neurofilament protein triplet in the hippocampal formation

Social deprivation during early postnatal life has profound and long-lasting effects on the behavior of primates, including prolonged and exaggerated responses to stress as well as impaired performance on a variety of learning tasks. Although the cellular changes that underlie such alterations in behavior are unknown, environmentally induced psychopathology may involve morphologic or biochemical changes in select neuronal populations. The hippocampal formation of both socially deprived and socially reared prepubescent rhesus monkeys was selected for immunocytochemical investigation because of its association with the behavioral stress response and learning. Immunocytochemical analysis using antibodies specific for the neurofilament protein triplet was performed since these proteins are modified within degenerating neurons in a variety of neurodegenerative disorders. Results from optical density measurements indicate an increase in the intensity of non-phosphorylated neurofilament protein immunoreactivity in the dentate gyrus granule cell layer of socially deprived monkeys in comparison with that of socially reared animals, suggesting that early social deprivation may result in an increase in the amount of non-phosphorylated neurofilament protein in these cells. This phenotypic difference in dentate granule cells between differentially reared monkeys supports the notion that specific subpopulations of neurons in brain regions that subserve complex behaviors may undergo long-term modifications induced by environmental conditions. Furthermore, the data suggest that constitutive chemical components related to structural integrity may be as susceptible to early environmental manipulations as the more traditionally viewed measures of cellular perturbations, such as neurotransmitter dynamics, cell density and the establishment of connectivity. The observed modifications may serve as an anatomical substrate for behavioral abnormalities that persist in later life.

Dopaminergic and serotonergic function following isolation rearing in rats: study of behavioural responses and postmortem and in vivo neurochemistry

This series of experiments compared isolation-reared and socially reared rats for their locomotor activity, behavioural stereotypy, and monoamine function both postmortem and in vivo using intracerebral dialysis. In Experiment 1, isolates showed an altered time course of locomotor activity following d-amphetamine sulphate (AMPH) administration (0.5, 2.0, 3.0, or 5.0 mg/kg, SC). Isolation-reared rats also showed increased sensitivity to the sedative effects of a low dose of apomorphine hydrochloride (0.1 mg/kg) but did not differ from social controls following higher doses of the drug (0.5, 1.5, or 3.0 mg/kg, SC). Isolates showed a decrease in the intensity of apomorphine-induced stereotyped behaviours but no change in stereotypy induced by AMPH. In Experiment 2, isolates had higher postmortem dopamine (DA) concentrations and an altered asymmetry in DA function in the medial prefrontal cortex (PFC) but not in the nucleus accumbens (NAC) or caudate putamen (CPu). Isolated rats also had a lower 5-hydroxyindoleacetic acid (5-HIAA)/5-hydroxytryptamine (5-HT) ratio in the NAC (but not in the PFC or CPu) compared to controls. Experiment 3 used intracerebral dialysis to examine monoamine function in vivo following isolation rearing. Isolates showed greater increases in extracellular DA and greater decreases in DOPAC in response to 2 mg/kg AMPH SC in both the NAC and CPu. There were no apparent differences in the perfusate concentrations of either dopamine (DA), dihydroxyphenylacetic acid (DOPAC), or homovanillic acid (HVA) prior to drug administration. However, consistent with the results of Experiment 2, isolates had a reduced basal perfusate concentration of 5-HIAA from the NAC but not from the CPu. Experiment 4 measured postsynaptic DA function in CPu tissue slices following isolation. Isolation rearing did not affect cAMP accumulation in response to stimulation of D1 DA receptors by DA (0, 2.7, 9, or 30 microM). In addition, isolation rearing did not affect the coupling between D1 and D2 receptors, as measured by the increase in cAMP accumulation with 1 microM 2,3,4,5-tetrahydro-7,8-dihydroxy-1-phenyl-1 H-3-benzazepin (SK&F 38393) and its reduction by 10 microM quinperole hydrochloride (LY 171555). These results are discussed in terms of the possible relationship between these neurochemical findings and the behavioural disturbances following isolation rearing of rats.