Serotonin receptors and their function in sleep, anxiety disorders and depression

Thirty-three years ago, Gaddum and Picarelli classified the serotonin receptors in the guinea pig ileum into D and M types based on the activity of dibenzyline (D) and morphine (M) to block contractions of intestinal smooth muscle caused by serotonin. The subsequent location of specific ligand binding sites for serotonin in the brain has led to the identification of 14 serotonin receptor sub-types in rat brain. The cloning of these receptor sub-types has been of importance in enabling them to be classified as specific-protein molecules encoded by specific genes. The problem now arises with regard to the linking of the changes in the cellular activity of the various receptor sub-types with the plethora of behavioural changes that arise as a consequence of the actions of serotonin in the brain. The present review summarizes the evidence implicating the role of specific serotonin receptor sub-types in sleep, anxiety states, schizophrenia and depression. A summary of the relationship between these receptor sub-types and their possible involvement in the aetiology of schizophrenia, depression, anxiety and sleep disorders.