Mother-reared and surrogate-peer-reared rhesus monkeys were separated from their respective attachment objects at 6 months of age and tested for the following 9 weeks to determine their home-cage behavior and their pituitary-adrenocortical responses to stress. Both groups displayed a strong immediate behavioral response to separation which was characterized by increased vocalization, increased locomotion, and decreased self-play. However, the surrogate-peer-reared infants showed a subsequent recovery in their levels of self-play whereas the mother-reared infants instead developed stereotypic behavior patterns such as repetitive pacing. The 2 groups displayed similar plasma cortisol responses to weekly sessions in an apparatus equipped with animated toy "monsters". Mother-reared but not surrogate-peer-reared subjects, however, also manifested elevated cortisol levels when an animal in an adjacent cage was captured and removed for stress testing. Mother-reared infant monkeys thus responded in a stronger and more prolonged manner to the loss of their attachment object than surrogate-peer-reared infants. These results suggest that infant rhesus monkeys form stronger attachments to monkey mothers than to inanimate surrogate mothers, a phenomenon which has not been as clearly demonstrated using other indices of attachment strength.
"One major limitation to these early studies is the severity of separation from conspecifics; most humans are not exposed to such extreme deprivation of social contact so early in life. Thus, in the past few decades, experimental rearing conditions have evolved to include more social contact in the form of peer-only rearing (PR), in which monkeys are reared for the first 6 to 12 months of life for up to 24 hours/day with same-aged peers but no adults (Capitanio et al. 2005; Dettmer et al. 2012; Shannon et al. 1998); surrogate-peer-rearing (SPR), in which monkeys are reared alone in single cages for the majority of the day but are provided with up to 2 hours of daily play sessions with agemates (Dettmer et al. 2012; Sackett et al. 2002; Shannon et al. 1998); and repeated brief separations from mothers or social partners versus total separation (Barr, Newman, Shannon et al. 2004; Hennessey 1997; Hoffman et al. 1995; Levine and Mody 2003; Mendoza and Mason 1997; Meyer et al. 1975; Rilling et al. 2001). Even with these less-severe separation paradigms, studies have consistently shown that young monkeys exposed to disruptions in the mother-infant bond or to adverse early rearing exhibit greater behavioral and physiological responsivity to separation; distress vocalizations, freezing behavior, and aggressive behaviors (e.g., cage-biting and cage-shaking) are increased in noncontrol monkeys, whereas object exploration and social contact upon reunion are decreased. "
[Show abstract][Hide abstract] ABSTRACT: This report reviews the scientific literature from the past several decades that focuses on nonhuman primates (NHPs) as models
of neuropsychiatric disorders, including anxiety, and alcoholism. In particular, we highlight the approaches, advantages,
and disadvantages of the rearing, genetic, and epigenetic methodologies behind these studies as a means of evaluating the
application of these methods in assessing disorders in NHPs as models of human disease. Finally, we describe the contributions
the NHP studies have made to neuropsychiatric research and areas for future research.
ILAR journal / National Research Council, Institute of Laboratory Animal Resources 09/2014; 55(2):361-70. DOI:10.1093/ilar/ilu025 · 2.39 Impact Factor
"In non-human primates, while results are not entirely consistent (Dettmer et al., 2012), early social deprivation appears to down-rather than up-regulate the HPA axis (Meyer et al., 1975; Clarke, 1993; Cirulli et al., 2009). This was confirmed recently in a large study of Rhesus macaques (Hawkley et al., 2012). "
[Show abstract][Hide abstract] ABSTRACT: Growing evidence suggests that early social deprivation impacts the activity of the hypothalamic-pituitary-adrenocortical axis. Early adverse care in the form of institutional or orphanage care provides a human model for early social deprivation. The present study examined changes in diurnal cortisol during the transition to family care in the first 2 years post-adoption. Children adopted between 15 and 36 months from institutional care were examined four times during their first 2 years post-adoption (N=58). Comparison groups included same-aged peers reared in their birth families (N=50) and children adopted during their first year from overseas foster care (N=47). Children provided daily cortisol samples at roughly 2, 9, 17, and 25 months post-adoption. Post-institutionalized and post-foster care children exhibited less steep diurnal cortisol compared to non-adopted same-aged peers; these differences did not diminish across the 2 year period. For post-institutionalized children, lower social care quality in institutions was associated with less steep cortisol slopes. Lastly, shallower diurnal cortisol was a mediator between adoption status and increased behavioral problems 2 years post-adoption. Consistent with the non-human primate literature, early social deprivation may contribute to early programming of the HPA axis.
") under various circumstances . In one study in which MR , PR , and SPR infants were compared , both nursery reared groups ( PR and SPR ) exhibited lower basal levels of plasma corti - sol when compared to MR infants ( Shannon et al . , 1998 ) . SPR infants also showed a reduced response to the stress of a brief separation compared to MR infants ( Meyer et al . , 1975 ; Shannon et al . , 1998 ) . Similarly , juvenile ( 1 – 3 years old ) SPR infants exhibited lower salivary cortisol levels than MR juveniles after capture and sedation for a health exam ( Davenport et al . , 2003 ) . One of the limitations of the above work and a possible contributor to the variability of findings is the reliance on pla"
[Show abstract][Hide abstract] ABSTRACT: Numerous stressors are routinely encountered by wild-living primates (e.g., food scarcity, predation, aggressive interactions, and parasitism). Although many of these stressors are eliminated in laboratory environments, other stressors may be present in that access to space and social partners is often restricted. Stress affects many physiological systems including the hypothalamic-pituitary-adrenocortical (HPA) axis, which is the focus of this review. The glucocorticoid, cortisol, is the ultimate output of this system in nonhuman primates, and levels of this hormone are used as an index of stress. Researchers can measure cortisol from several sampling matrices that include blood, saliva, urine, faeces, and hair. A comparison of the advantages and disadvantages of each sampling matrix is provided to aid researchers in selecting an optimal strategy for their research. Stress and its relationship to welfare have been examined in nonhuman primates using two complimentary approaches: comparing baseline cortisol levels under different conditions, or determining the reactivity of the system through exposure to a stressor. Much of this work is focused on colony management practices and developmental models of abnormal behaviour. Certain colony practices are known to increase stress at least temporarily. Both blood sampling and relocation are examples of this effect, and efforts have been made to reduce some of the more stressful aspects of these procedures. In contrast, other colony management practices such as social housing and environmental enrichment are hypothesized to reduce stress. Testing this hypothesis by comparing baseline cortisol levels has not proved useful, probably due to "floor" effects; however, social buffering studies have shown the powerful role of social housing in mitigating reactions of nonhuman primates to stressful events. Models of abnormal behaviour come from two sources: experimentally induced alterations in early experience (e.g., nursery rearing), and the spontaneous development of behavioural pathology (e.g., self-injurious behaviour). Investigators have often assumed that abnormal behaviour is a marker for stress and thus such monkeys are predicted to have higher cortisol levels than controls. However, an emerging finding is that monkeys with abnormal behaviour are more likely to show a pattern of lowered cortisol concentrations which may reflect either an altered set point or a blunting of the stress response system. These findings parallel human clinical studies demonstrating that neuropsychiatric disorders may be associated with either increased or decreased activity of the HPA system, depending on the aetiology and manifestation of the disorder and their potential influence in provoking allostatic shifts in system functioning.
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