**6.2. AVP and male animal aggression**

Initial studies in male hamsters reported that V1a antagonist administration into the anterior hypothalamus inhibits aggression [130, 131], results which have since been confirmed in several other labs [132-134]. Exogenous AVP in the anterior hypothalamus can stimulate offensive aggression [133, 135], but this effect may be modulated by social environment [136]. Further work in hamsters has revealed that an orally active V1a antagonist decreases aggression in male hamsters, but does not affect social investigation or sexual motivation [137]. Anabolic steroid treatment of adolescent males increases aggression which can be inhibited by V1a antagonist treatment in the AH [138], indicating that the elevated aggression is mediated by central AVP activity. A similar effect of amphetamine has been documented in male prairie voles, where increased aggression is associated with increased V1a receptor binding in the AH [134]. Developmental effects of AVP have been reported in male prairie voles, where early postnatal peripheral injections of AVP increase adult aggression [139]. However, maternal separation in mice increases AVP in the paraventricular nucleus and decreases intermale aggression [38]. This effect is similar to much of the behavioral data from female animals, which indicate that AVP has suppressive effects on maternal aggression and intraspecies aggression.

#### **6.3. AVP and animal paternal behavior**

Research on AVP and offspring care by males includes studies in several rodent species. The increase in paternal behavior in cohabitating meadow voles is mediated by AVP, as treatment with AVP antagonist decreases paternal behavior [14, 140]. Elevated AVP in meadow voles stimulates paternal behavior through both a decrease in pup directed 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 role in social bonding.
