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.