Untitled

180 EFFECTS OF EARLY MALTREATMENT AND STRESSor the postpartum period (via lactation) could potentially affect AVP in the offspring.The relationship between AVP and nicotine also might have special relevancein adolescent or preadolescent users of tobacco.Developmental Manipulation of OT AffectsLater Behavior and NeurobiologyDevelopmental studies in rats have shown long-term physiological effects of neonatalexposure to OT. Neonatal exposure to OT can lead to lower corticosteronelevels in rats (Sohlstrom, Carlsson, & Uvnas-Moberg, 2000), higher body weight(Sohlstrom et al., 2000), lower blood pressure (Holst, Uvnas-Moberg, & Petersson,2002), and alleviation of effects caused by maternal malnutrition (Olausson,Uvnas-Moberg, & Sohlstrom, 2003). Rats are not, however, an ideal model forstudying the role of early exposure to OT and AVP on social behavior. In particular,behaviors such as social bonding and behavioral responses to an infant thatare a normal component of the behavioral repertoire of prairie voles have provena useful model for examining the long-term consequences of developmental exposureto peptides. Behaviors toward an infant may be considered a measure ofalloparental behavior, but also may be indicative of general sociality (Baleset al., 2004a; Kim & Kirkpatrick, 1996) or of reactivity to novelty (Carter, 1998).A series of studies in prairie voles, modeled on manipulation of OT that mayoccur in humans, has analyzed the possible behavioral consequences of neonatalexposure to exogenous OT and substances that block the OT receptor (known asoxytocin antagonists or OTAs; Carter, 2003). Prenatal changes in OT also couldhave long-term consequences but are more difficult to study because prenatalhormonal manipulations can lead to premature labor. These studies focused ondependent variables, such as social behaviors and stress management, in whichOT also has been implicated. Using the prairie vole model, OT was manipulatedwithin the first 24 hours postpartum by injecting pups with one of the followingtreatments: 1 mg/kg OT, 0.1 mg/kg OTA, or a saline vehicle; or animals werehandled without injection. A smaller dosage of OTA (compared to OT) was usedbecause it is 10 to 100 times more effective in receptor binding than the naturalligand (Barberis and Tribollet, 1996). In early life, the rodent neonatal blood-brainbarrier is permeable to peripherally injected peptides (Vorbrodt, 1993), and in volepups, systemically injected OT or OTA does reach and affect the nervous system,as indicated by increased expression of the immediate early gene c-Fos, a sign ofcellular activation (Cushing, Yamamoto, Hoffman, & Carter, 2003). In these experiments,animals with different hormonal experiences were later exposed to pups(which were not their own, hence termed “alloparental” behavior) during theimmediate postweaning period (Roberts, Williams, Wang, & Carter, 1998). Ani-