Stereotyped behaviour, hyperaggressiveness and "tyrannic" hierarchy induced in bank voles (Clethrionomys glareolus) by a restricted cage milieu.

This investigation was originally conceived as a further development of studies made with the "amphetamine model" of psychosis. Since amphetamine itself seemed to be the most important flaw in this model, it was judged promising to study abnormal behaviour in animals elicited without the use of drugs. Bank voles were placed in two different cage milieux, a restricted milieu approaching usual laboratory conditions for experimental animals, and an enriched milieu offering opportunities for satisfaction of natural behavioural (ethological) needs. During an experimental period of 6 months normal behaviours (known from the ethogram of the bank vole) and abnormal behaviours were recorded in eight 5-min observation periods of each cage. Social structure (hierarchy) was studied by the intruder method and social function (peaceful or tyrannic hierarchy) by inspection of the subordinate voles for wounds. Stereotypies, hyperaggressive behaviour and tyrannic hierarchy, replacing normal behaviour and social structure, were seen frequently in the restricted milieu, but only occasionally in the enriched milieu (differences highly significant). It is concluded that these findings indicate possibilities for further development of the basic studies of abnormal behaviour made by means of the "amphetamine model" of psychosis. Opportunities exist for investigation of the interaction of milieu factors with genetic, pharmacological and other factors relevant to the development, prevention and treatment of abnormal behaviour and mental disease.