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176 EFFECTS OF EARLY MALTREATMENT AND STRESSOxytocin and Vasopressin Play a Central Rolein Social Behavior and Social BondingRecent research on the mechanisms underlying selective social behaviors hastended to focus on two major mammalian neuropeptides, oxytocin (OT) and argininevasopressin (AVP). OT and AVP consist of nine amino acids each, and areproduced primarily in the hypothalamus (De Vries & Miller, 1998; Zingg, 2002).OT and AVP receptors are widespread throughout the central and peripheral nervoussystems (Barberis & Tribollet, 1996; Jard, Barberis, Audigier, & Tribollet,1987).OT and AVP are central to sociality (Carter and Keverne, 2002) but have manyother functions as well. Both of these neuropeptides have important physiologicalroles, including the milk ejection reflex during lactation and labor inductionfor OT (Russell, Douglas, & Ingram, 2001) and regulation of water balance andcardiovascular functions for AVP (Ring, 2005).A series of studies (primarily conducted in socially monogamous species) havelinked OT and AVP to sociality in general, and in particular to the formation ofsocial bonds (Carter & Keverne, 2002; Lim, Hammock, & Young, 2004). Thesesame peptides also have been linked to parental behavior (Pedersen, Ascher,Monroe, & Prange, 1982; Pedersen & Boccia, 2002). Research in prairie volesand other socially monogamous rodents has implicated OT in female pair bondingand parental care (Insel & Hulihan, 1995; Pedersen et al., 1982; Pedersen &Prange, 1979; Williams, Insel, Harbaugh, & Carter, 1994), whereas AVP has beenmore extensively studied in the context of male pair bonding and parental care(Aragona & Wang, 2004; Bester-Meredith & Marler, 2003; Lim et al., 2004; Wang,Ferris, & Devries, 1994; Winslow, Hastings, Carter, Harbaugh, & Insel, 1993).However, there is considerable potential for cross-communication between OTand AVP, which differ structurally by only two amino acids and can bind to eachother’s receptors (Barberis and Tribollet 1996). Pharmacological studies of pairbonding behavior have shown that in both males and females access to both OTand AVP receptors is necessary for pair bond formation (Cho, DeVries, Williams,& Carter, 1999). Blocking either set of receptors in either sex resulted in failureto form a pair bond, although these animals given additional OT or AVP still displayedindiscriminate social behavior. Interestingly, when both OT and AVP receptorswere blocked, animals showed a dramatic reduction in sociality and theabsence of selective social behaviors.Both OT and AVP also may be important to male parental behavior, anotherform of sociality (Bales, Kim, Lewis-Reese, & Carter, 2004a). When parental carein male prairie voles was manipulated with intracerebroventricular injections ofdifferent dosages and combinations of OT, AVP, and their antagonists, the ONLYtreatment which significantly reduced overall levels of male parental care was ahigh (10 ng) dosage of both OT antagonist and AVP antagonist. However, in