5-HT1A receptor subtype agonist

A method of treating a patient suffering from a disorder-of the central nervous system associated with 5-HT1A receptor subtype, selected from

• (i) bipolar I disorder with most recent hypomanic, manic, mixed, depressed or unspecified episode, and
• (ii) bipolar II disorder with recurrent major depressive episodes with hypomanic episodes, and cyclothymic disorder,
• which comprises administering to said patient a therapeutically effective amount of a carbostyril compound of formula (1), or a pharmaceutically acceptable salt or solvate thereof, wherein said patient is a mammal:
• wherein the carbon-carbon bond between 3- and 4-positions in the carbostyril skeleton is a single or a double bond.