**6.1. AVP and male animal affiliation**

There is a wealth of studies of AVP and affiliation in voles [11]. Central administration of AVP to monogamous prairie voles that live in burrows with extended families induces several forms of bonding behaviors [124, 125], and AVP V1a receptor antagonist treatment blocks pair bonding behaviors in males [124, 125]. In polygamous montane voles (*Microtus montanus*) that live in solitary burrows, AVP or V1a antagonist treatments have no effects on social behavior. These behavioral differences are reflected in the neural OXT and AVP maps of these species [5]. Over-expression of V1a receptors in the forebrain of male prairie voles enhances pair bonding [126], and V1a antagonist injection into specific brain regions inhibit pair bond formation [127, 128]. The pattern of AVP mediated pair bonding in males and OXT mediated pair bonding in females has been identified in several other species [129]. Although there is no clear picture of how AVP expression patterns relate to social structure, AVP is an important mediator of affiliation in many vertebrate species, including fish [2] and birds [1]. The variety of social structures and central AVP circuitry among vertebrate species presents a valuable opportunity for both descriptive and manipulative comparative studies.

Behavioral Roles of Oxytocin and Vasopressin 59

aggression and an increase in paternal behaviors [14]. Alloparental behavior in naïve male prairie voles also involves central AVP actions [15]. Monogamous male California mice are more paternal and aggressive towards nest intruders than polygamous male while footed mice, and these differences are associated with elevated AVP in the BNST and LS [141]. These paternal styles may be transmitted through behavioral effects, as cross-fostering paternal behavior is similar to the foster parent behavior [142]. Pup directed aggression may be decreased and paternal care increased through social bonding mediated changes in central AVP. It is likely that the effects of AVP on paternal behavior are related to its general

Anxiety related behavior on the elevated plus maze is decreased following septal AVP antagonist treatment or antisense treatment in male rats [143, 144]. In contrast, other studies report that intraseptal and intraperitoneal AVP is anxiolytic [145]. An anxiogenic role of AVP is supported by male AVP V1a receptor knockout mice which exhibit lower levels of anxiety compared to wild type [24, 146]. Once again, other investigations of this line have failed to find differences in anxiety [147]. The oral and intraperitoneal administration of an AVP V1b antagonist is anxiolytic in several tests of anxiety [148-150], but AVP V1b receptor knockout males may not exhibit decreased anxiety [147, 151]. The lack of differences in anxiety related behaviors in these knockout mice may be due to compensatory mechanisms during development. In male rats bred for high levels of anxiety, AVP level and release from the PVN are elevated when compared to low anxiety males [152-154] and the differential expression of AVP in rats selected for high anxiety has been linked to specific single nucleotide polymorphisms [155, 156]. Central AVP V1a receptor antagonist treatment decreases anxiety and depression associated behaviors in high anxiety males [154]. The forced swim test induces both depression associated behavior and elevated AVP in the SON and PVN [157, 158]. V1a antagonist treatment to both the mediolateral septum and amygdala has antidepressant like effects in male animals [159, 160], and similar effects are documented following V1b receptor antagonist treatment [148, 161]. For male animals, there is evidence to support the hypothesis that depression and anxiety related behaviors are

Infusion of AVP into the lateral septum of wild type and AVP deficient Brattleboro rats enhances social memory, and these effects are impaired by antagonist or antisense treatments [162, 163]. The over expression of vole V1a receptors in rats enhances social discrimination abilities [164]. However, studies of V1a and V1b KO mice have had mixed results, with some reporting impaired social recognition [24, 151] and others failing to find impairments [165]. AVP has also been implicated in both memory consolidation [166] and memory retrieval [167, 168]. The social aspects of AVP's effect on memory suggest the roles

**6.4. AVP and male animal models of depression and anxiety** 

associated with elevated AVP activity in both brain and plasma.

**6.5. AVP and male animal learning and memory** 

of this nonapeptide in memory and affiliation are related.

role in social bonding.
