(A) Affiliative behavior measured on the fifth agonistic encounter when the social hierarchy is established. Old, Middle (Mid) and Young (Yng) groups (respectively, n =20, 19 and 20) showed a higher propensity to interact with a conspecific compared to standard nesting (SN) mice (n =18). (B) OTR binding. Old, Middle and Young mice (respectively, n =10, 9 and 10) showed higher levels of oxytocin receptor binding in the ACo and the CeA, compared to SN mice (n= 9). ACo, anterior cortical nucleus of the amygdala; CeA, central amygdala; LA, lateral amygdala; BLA, basolateral amygdala. The cage was considered as the statistical unit.* and ** = respectively p < 0.05 and < 0.01 vs. SN mice. Data shown are means ± SEMs.