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186 EFFECTS OF EARLY MALTREATMENT AND STRESSchanges in centrally active neuropeptides, including OT and AVP and their receptors,remain to be identified but presumably rely on related processes.Primate ModelsThe large number of differences between human and rodent neurobiology limitsthe utility of a rodent model; yet many studies are impossible or unethical to conductin human subjects. Nonhuman primate models offer another opportunity toexamine the relationship between early experience and neuroendocrine factors,including OT and AVP, in behavioral development. The titi monkey (Callicebuscupreus) exhibits the traits of social monogamy, including the formation of longtermpair bonds and high levels of male parental care (Mason & Mendoza, 1998;Mendoza & Mason, 1997; Mendoza, Reeder, & Mason, 2002). Pilot studies ofplasma OT and AVP levels in titi monkeys indicate individual stability in OT levels,with repeated samples from the same monkeys achieving nearly perfect correlations(Bales et al., 2005a); it is possible that OT production might be associatedwith individual behavioral traits. Plasma AVP, on the other hand, is more variableand may be more responsive to environmental factors, including stressors.Additional support for a role for OT in the mediation of, or response to, differentialearly experience comes from a comparison of rhesus monkeys reared either bya mother or under nursery conditions (Winslow, Noble, Lyons, Sterk, & Insel, 2003).As predicted by other research on OT, the levels of this peptide measured later inlife, especially in CSF, were highest in maternally reared animals.Oxytocin and Vasopressin Have Been Linkedto Human PsychopathologyThe importance of parenting behavior and early stimulation has long been recognizedin human psychology and psychiatry (Bowlby, 1969; Harlow, 1959). However,whether mechanisms for the lasting effects of early experience in humansparallel those in animal models is difficult to prove. Controlled “rearing” experimentson children or adolescents are of course not ethical. However, children whohave experienced different degrees of deprivation in early life have been studied(O’Conner, Rutter, & English and Romanian Adoptee Study Team, 2000). At thebehavioral level, it has been suggested that in humans the effect of early experienceon subsequent social behavior may be mediated by the child or adolescent’s abilityto exert effortful control (Eisenberg et al., 2005), a relationship that holds up acrossmore than one culture (Zhou, Eisenberg, Wang, & Reiser, 2004). This lack of effortfulcontrol over behavior, presumably due at least in part to lack of neural maturation,can lead to many externalizing problems of childhood and adolescence.Depression and anxiety have also been linked to early social deprivation (Teicheret al., 2003). In addition, it is possible that OT and AVP may influence reactivityto stressors and anxiety (Carter & Altemus, 2004). It has been noted that an increasein depression in females may occur around adolescence when gonadal