EFFECTS OF ENVIRONMENTAL ENRICHMENT ON AGGRESSIVE-BEHAVIOR, DOMINANCEHIERARCHIES, AND ENDOCRINE STATES IN MALE DBA 2J MICE/

Adult male mice (DBA/2J) siblings were housed three per cage for 6 wk, either in standard cages (SC) or in enriched cages (EC). Both attacks among group members and attacks against strange intruders were monito red once a week within each of 22 experimental groups. According to it s attacking behavior, each mouse was categorized into one of three dom inance categories: dominant, subdominant active, subdominant passive. Aggressive behavior and social organization were compared between the two types of housing conditions, and the effects of housing condition and dominance category on endocrinological and some organometrical par ameters were analysed. The main findings were: (a) Mice in EC attacked intruders significantly more frequently compared to mice in SC; (b) I n EC groups the position of the dominant male was less stable than in SC groups; (c) Plasma corticosterone titers (PCT) were significantly e levated in EC. Activities of tyrosinehydroxylase (TH) and phenylethano lamine-N-methyltranferase (PNMT) did not differ significantly between the housing conditions; (d) TH and PNMT activity were significantly en hanced in the dominant males of SC groups compared to subdominant pass ive males. Intermediate activities for both enzymes were determined fo r subdominant active males; acid (e) PCT were significantly elevated i n dominant males of the EC groups compared tb subdominant active and s ubdominant passive males and also compared to the dominant males in th e SC groups. Findings suggest that keeping adult male mice in structur ed cages can result in increased aggression towards intruders, a chang e in the social organization, and altered endocrine states, depending on the individual dominance position.