Involvement of various senses in responses to individual housing in laboratory albino mice: 1.The olfactory sense

‘Isolation’ of male mice is much used to induce aggressiveness but, as practised in most laboratories, does not preclude communication between neighbouring conspecifics. This study examines the influence of olfaction on individual housing-induced social conflict between male laboratory mice. Attempts were made both to eliminate and to intensify the exposure to presumably socially meaningful odours. First, the effects of acute and chronic anosmia induced by application of four per cent zinc sulphate solution to the nostrils were determined in mice from a range of ages and social experiences. Secondly, the influences on the subsequent aggressiveness of the individually-housed male mice were estimated after introducing into their cages odoriferous bedding from groups of male and of female conspecifics. Both acute and chronic anosmia depressed the attacks directed towards ‘standard opponents’; indeed the chronic treatment virtually abolished this behaviour. Adding odoriferous bedding from the cages of grouped males to the cages of individually-housed males increased the latter's speed of attack on intruders, whereas bedding from groups of females suppressed aggression. The data clearly confirm that olfaction is important in this species and that communication between cages via this sense may change the level of ‘isolation-induced aggression’. This is a variable which is not normally controlled in most laboratory studies.