Since the first Hiroshima Symposium of Neurotransmitter Receptors in 1983, there have been conspicuous advances in this field. For instance, our knowledge on transmembrane signalling mechanism has increased almost exponentially and this great stride has been linking areas of biology that had been previously considered of as being separate. The Second Hiroshima International Neurotransmitter Receptor Symposium was held on October 6 to 9 bringing together an outstanding group of neuroscientists from various disciplines to integrate these advances in the hope that their valuable contributions will make this meeting a tradition in this city. The original title of the Symposium was "Receptor Mechanism of Neurotransmitter and Neuropeptides". This volume is based on papers presented at this Second Hiroshima Symposium. Our aim editing this book is to discuss various neurotransmitter receptors in terms of their structural and biochemical properties, functions, ligands and related intracellular control mechanism, and to know the general denominators of all receptors. The editors believe that this book will provide a useful state-of-the-art summary of neuroreceptor fields at present and profit for those who could not participate in the Hiroshima Conference vicariously by reading the texts included in this volume. The editors acknowledge the help of many friends and colleagues in making this book possible. We are especially grateful to Dr. Shinobu Inagaki, former assistant professor of Third De-partment of Internal Medicine, Hiroshima University School of Medicine who made the Symposium successful as secretary-general through her devoted efforts. In 1988, Dr.