Animal models of affective disorders

The classification of affective (mood) disorders according to the Diagnostic and Statistical Manual of Mental disorders, fourth edition, is reviewed. Much is now known on the pathophysiology of affective disorders and recent brain imaging studies have yielded additional information of potential use to research and treatment. A clear genetic influence has been established for many affective disorders and in particular for bipolar disorders. Major depression is amongst the most common of the affective disorders: a recent European study demonstrated a 6-month prevalence rate of 6.9%. Major depression is also the disorder most commonly studied using animal models and consequently many useful animal models of depression have been developed. However there is no direct animal model of clinical depression, instead there are models covering different facets of drug action and disease state. These models can be divided into pharmacological models, based around known drug effects or specific receptor mediated effects on behaviour, symptomatic models, providing information on different features of the symptomatology and time course of depressive episodes, and genetic models. A combination of models will probably yield the most informative data on prospects for new treatments and further understanding of the disease process.