Biological concepts of anxiety disorders

Since the seminal work of Geller and Blum there is a vast expanding literature relating anxiety symptoms to serotonin (5-hydroxytryptamine; 5-HT). The general picture emerging from animal research is that increasing 5-HT function is anxiogenic. However, animal research is confined by the fact that extrapolations from animal behavior to human emotions have limited validity. Human anxiety can range from normal emotions to clinical syndromes. It can be a component of different physical and mental disorders, but also the central feature of a syndromes. During the last decade, a wealth of knowledge about the origin and anatomical distribution of 5-HT neuronal systems has been obtained. Our understanding of the neuroanatomy and neurochemistry of anxiety has also considerably advanced, but the picture is still puzzling. We are faced with a large number of 5-HT-receptor subtypes, each with its own specific distribution and presumably specific function. The complexity of the 5-HT system in terms of receptor heterogeneity offers a dazzling opportunity to the development of new drugs affecting selective 5-HT functions, but it also precludes that firm conclusions can be drawn when less selective agents are being used.