**2.2. OXT and male animal aggression**

The recent data from stickleback fish suggest that the affiliative actions of OXT in vertebrates are associated with aggression [10]. OXT levels are highest in male sticklebacks that aggressively defend eggs and in subordinate males that fight to change their social status. Disruption of the OXT gene in male mice decreases aggression [12], yet OXT knockout mice display elevated aggression which is postulated to be the result of decreased fearfulness [13]. One potential explanation for this inconsistency is indirect effects through AVP due to the neuroanatomical and biochemical similarities between the two neuropeptide systems. The increased aggression in OXT knockout mice may be mediated by a compensatory increase in AVP in these males.
