On picking up this first volume of a new series of books the reader may ask the two questions: (a) why research methods? and (b) why in neurochem istry? The answers to these questions are easy - they more than justify the volumes to come and show the strong need for their existence. It is customary to think of methods as a necessary but unexciting means to an end - to relegate advances in methodology to a minor role in the creative, original portion of advances in science. This is not the case; the pace-setting function of methodology is well illustrated in most areas of neurobiology. To formulate our questions to Nature (which is the essence of experimental design), methodology is needed; to get answers to our ques tions we have to devise yet new methods. The chapters of the present volume fully illustrate how the development of a new method can cut a new path how it can open new fields, just as the microscope founded histology. Heter ogeneity of structures presents a formidable challenge for methodology in the nervous system, yet methods for separating the structures are essential if we ever want to decipher the enigma of functional contribution of the ele ments to the whole. The problem is not only physical separation-clearly methods are essential to study complex structures in situ.

Cell Fractionation by Centrifugation Methods.- - Introduction.- - Homogenization.- - Fractionation methods.- - Analysis of the fractions and interpretation of the results.- - Conclusion.- - References.- Binding of Ligands to Receptors: Theory.- - Introduction.- - Experimental approach to the hormone-receptor interaction.- - Molecular models of receptors.- - Graphical representations of saturation experiments.- - Methodologic errors and graphical representations.- - Conclusion.- - References.- On the Modes of Regulation of Intracellular Cyclic AMP: Desensitization of Adenylyl Cyclases to Hormon.

This volume continues the tradition of SUBCELLULAR BIOCHEMISTRY of trying to break down interdisciplinary barriers in the study of cell function and of bringing the reader's attention to less well studied, but nevertheless useful, biological systems. We start with an extensive article by T. P. Karpetsky, M. S. Boguski and C. C. Levy on the structure, properties and possible functions of polyadenylic acid. Apart from revealing a general lack of appreciation of many important aspects of the chemical properties of poly adenylic acid, the literature also shows that there is a great gulf between those who study the biological role of polyadenylic acid. and those who study its physicochemi cal properties. The article by Karpetsky and his colleagues is an attempt to overcome this lack of communication and to present an integrated view of the subject. The authors go into the subject in full detail and the more biologically inclined reader may on occasion have to reread his nucleic acid physical chemistry notes! However, the effort is worthwhile and the article is a timely reminder that we cannot treat nucleic acids as mere abstractions, but that they are complex organic macromolecules capable of equally complex, but nevertheless important, interactions. The next article is by J. Steensgaard and N. P. Hundahl M0ller and deals with computer simulation of density gradient centrifugation systems.