**7.2. AVP and female animal aggression**

Several studies have reported that AVP has inhibitory effects on maternal aggression towards a male intruder, which contrasts with the stimulatory role of AVP in male rodent aggression. V1a antagonist treatment increases maternal aggression in both primiparous and multiparous dams, and AVP injection decreases maternal aggression in highly aggressive multiparous rats [171, 172]. An inhibitory role for AVP in females is also supported by multiple experiments in non-maternal female hamsters [173]. Gene expression analysis of primiparous and multiparous rats indicates that changes in both AVP and OXT may be involved in the parity associated increase in maternal aggression in multiparous rats, as high levels of aggression are associated with low levels of AVP and OXT activity in several nuclei [45]. fMRI study of the neural effects of V1a antagonist treatment during the presentation of a novel male intruder reveal that this treatment may increase aggressive responding by enhancing the somatosensory responses to a male intruder and reducing fear responses in the cortical amygdala and ventromedial hypothalamus [174]. One hypothesis derived from these data is that AVP increases the perceived threat from the male intruder. Although some studies have found increased AVP release associated with maternal aggression, it is hypothesized that this release is triggered by the stressful nature of the encounter [36]. Manipulations of AVP in rat strains selected for anxiety behaviors reveal an excitatory function of AVP on aggression, but this effect on aggression only involves behavioral frequencies, and it is not known if the decreased frequencies are associated with increased durations of aggressive bouts [175].

#### **7.3. AVP and animal maternal behavior**

Recent studies indicate that OXT is not the only nonapeptide involved in the modulation of mammalian maternal care. Both AVP and V1a antagonist treatments decrease maternal care during exposure to a male intruder, with the effects of AVP associated with increased self grooming and the effects of V1a antagonist associated with elevated maternal aggression during resident intruder tests of maternal aggression [171]. Studies focusing specifically on maternal care conclude that central AVP promotes ongoing maternal care [48]. Furthermore, the blockade of V1a receptors around parturition impairs maternal memory, the ability of a maternal dam to return to maternal care following a prolonged separation from her pups [68]. Although it has been postulated that maternal nurturing is linked to innate anxiety and OXT and AVP activity, this is based mostly on studies of rodent lines selected for anxiety [175]. Low anxiety mice display lower levels of maternal care compared to high anxiety mice, and acute icv injection of AVP increases maternal care and has anxiogenic effects [176]. These effects in mice were only moderately attenuated by cross fostering. An association between maternal care and innate anxiety was not supported in another study of maternal mice, although V1a receptors were correlated with pup grooming [177]. Animal studies suggest that AVP may be a worthwhile target for the development of treatments for anxiety associated disorders that affect maternal behavior, such as postpartum depression, which is often comorbid with anxiety.
