Recent progress in brain science has been remarkable, especially with regard to advances in the area of neuroscience. Particularly in the past decade, there have been many important discoveries about signal transduction in the brain. With this background, biological research in affective disorders has become well developed in relation to neural signaling. However, this field is fairly hard to understand comprehensively, and there is relatively little integrative work with clinical psychiatry in spite of the involvement of a wide variety of scien tific disciplines. This monograph brings together up-to-date reviews from several young Japanese scientists who work in basic and clinical neuroscience. The intention is to explain in plain language the information that has evolved on signal transduction in terms of the biological abnormalities and mechanisms of anti depressants. The model shown on the cover (and on page 24) is intended to help the reader understand signal transduction in the brain and the patho physiology of affective disorders as well as the mechanisms of antidepressants.