Abstract: The present invention has provided a human-derived novel G protein-coupled receptor protein expressed in the brain, rat-derived protein corresponding to it, and their genes. Use of the receptors makes it possible to screen their ligands and compounds that are candidates for medicines. These ligands and candidate compounds would be useful in the diagnosis and treatment of diseases arising from disorders of signal transduction pathway mediated by the G protein-coupled receptor of the invention.

Abstract: A full-length cDNA encoding a human-derived G protein-coupled receptor protein is isolated by screening a human hippocampus library. Also, a rat-derived cDNA corresponding to the human-derived cDNA is isolated. Proteins encoded by these cDNAs have an activity of lowering intracellular cAMP concentration under stimulation with histamine. These proteins are usable as tools in screening ligands thereof or in screening candidate compounds for drugs capable of regulating signal transduction from the above proteins.

Abstract: A substituted pyridine derivative represented by the general formula ##STR1## wherein R.sup.1 represents a phenyl or naphthyl group which may optionally be substituted by a substituent selected from the class consisting of a hydroxyl group, lower alkyl groups, lower alkoxy groups, cycloalkyl groups, lower alkoxycarbonyl groups, a phenyl group and halogen atoms; X represents an oxygen atom, a sulfur atom, a carbonyl group, or a group of the formula --CH(OH)-- or --N(R.sup.a)-- in which R.sup.a is a hydrogen atom or a lower alkyl group; Y represents a linear or branched lower alkylene group or a vinylene group which may optionally be substituted by a lower alkyl group, with the proviso that when X is an oxygen or sulfur atom, Y represents the lower alkylene group; R.sup.2 and R.sup.3 are identical or different and each represents a hydrogen atom or a lower alkyl group; R.sup.