Historically, the development of biological science has proceeded from the anatomy to the physiology of particular systems. Knowledge about neurotransmitters in the brain has evolved from the discovery of the compounds per set through the elucidation of their biosynthetic and degradative pathways, and finally to the current focus, the regulation of these processes. Regulation in a biological system implies the capacity to respond to perturbations. The introduction of standard and speci fiable disturbances in a biological system followed by examination of the mechanisms involved in response,...