THE CAGE DESIGN AFFECTS INTERMALE AGGRESSION IN SMALL-GROUPS OF MALE LABORATORY MICE - STRAIN-SPECIFIC CONSEQUENCES ON SOCIAL-ORGANIZATION,AND ENDOCRINE ACTIVATIONS IN 2 INBRED STRAINS (DBA 2J AND CBA/J)/

Effects of the enrichment of conventional laboratory housing cages wit h an additional labyrinth on intermale aggression, social organization , and activations of the pituitary-adrenocortical and sympathetic-adre nomedullary neuroendocrine subsystems are compared between adult male DBA/2J and CBA/J mice, differing genetically in their intermale aggres sion. Mice of both strains were kept three per cage for six weeks eith er in standard laboratory cages (SC) or in enriched cages (EC). Interm ale aggression against a strange intruder and between cagemates was mo nitored once a week within each group. Dominance relations were derive d from the distribution of attacks within a group. Plasma corticostero ne titers (PCT) and activities of the tyrosinehydroxylase (TH) and phe nylethanolamine N-methyltransferase (PNMT) were determined for each mo use at the end of the study. The main findings were: 1. Intermale aggr ession increased in both strains in groups kept in EC. 2. In the more aggressive DBA/2J the pattern of social organization shifted from grou ps with a single permanent dominant mouse in SC to groups with a frequ ently changing dominant mouse in EC. 3. In CBA interchanges of the dom inant mouse was prevailing and did not differ between the two housing conditions. 4. In DBA/2J mice PCT were significantly elevated in EC. 5 . In CBA/J mice activities of TH and PNMT were significantly elevated in EC. 6. Body weight gain was significantly delayed in mice kept in E C in both strains. Findings revealed strainspecific environmental effe cts on both social organization and endocrine states. The PCT increase obtained only in DBA/2J indicate that alterations of the social relat ions between cagemates are more likely to induce states of stress than an increase in intermale aggression alone.