[Studies on animal model of depression: review and perspective]

Animal models have played an important role in the history of research on depression. Various models, such as spontaneous depression in natural environment, drug-induced deductive models and several stress models including "learned helplessness" and "forced-running model", were introduced. Conclusions from the models reviewed in this article would be (1) some, not all, individuals of some species possibly fall into depressive state as a result of certain conditions, such as separation, repeated stress and uncontrollable aversive stimuli; (2) such depressive stage can be reversed by antidepressant drugs; (3) disrupted functional activity of norepinephrine, especially in locus coeruleus, may be closely related with neurochemical background of animal models. Significance of other systems, like GABA or serotonin, is still less evident as compared with norepinephrine. In future studies on depression, there is a need for an experimental system in which interrelation between "endogenous" and "exogenous" factors in the etiology of depression can be studied. Animal models would be a useful strategy in this context.