Physiological Consequences of Defeat

The laboratory mouse (Mus musculus) has long been a favoured species in the experimental analysis of fighting behaviour because of the relative ease with which overt attack may be observed 1 . Such research typically involves the use of a “resident-intruder” paradigm in which a non-aggressive male (the intruder) is placed into the home cage of a resident male conspecific that has been rendered aggressive by a short period of individual housing 2 . Physiological manipulation of either animal in advance of such encounters has provided much information on the neurochemical and neuroendocrine regulation of behaviour (i.e. offense, defense, escape, submission) displayed during 3-4 social conflict. Nevertheless it has to be admitted that, until recently, most research in this area has concentrated upon offense with comparatively little attention devoted to the study of defense. As such, it is pertinent to recall that, relative to the victorious animal, the defeated animal is characterized by: low levels of intraspecific fighting, low levels of reproductive behaviour, reduced pituitary-gonadal function, elevated brain catecholamine levels, elevated adrenal medullary catecholamine content, elevated pituitary-adrenal activity 5 .