The interaction of neurotransmitters, neuromodulators and neuroactive drugs with receptors localized at the cell surface initiates a chain of molecular events leading to integrated neuronal responses to the triggering stimuli. Major advancements in the characterization and isolation of recep tor molecules have answered many quest ions regarding the nature of the ele ments that determine the specificity in these interactions. At the same time, recent studies have provided evidence that delicate regulation by intracellular enzymatic systems determines the efficiency of the stimulus response coupling process, mediates the interaction between receptors, operates in feedback control mechanisms and transduces signals from the receptors to various effector sites in a highly coordinated fashion. These studies are at the focus of the present volume, which is an outcome of a symposium held at the University of Vermont College of Medicine on March 21-23, 1986, in conjunction with the seventeenth annual meeting of the Amer ican Society for Neurochemistry. The symposium has demonstrated clearly that the concerted efforts of investigators in neurophysiology, biochemis try, pharmacology, cell-biology, molecular genetics, neurology, and psy chiatry are required to achieve better understanding of the processes under lying neuronal responsiveness. This volume includes contributions provided by prominent investigators in all these research areas. We hope that the readers will find here a useful source of information and ideas for stimu lating further studies which may serve to narrow the gap between basic neuroscience research and its clinical implications.