The Involvement of Serotonin in Psychiatric Disorders and Behaviour

There is evidence that serotonin (5-HT) is involved both in a wide range of psychiatric conditions and in specific behaviours which, in themselves, cannot be considered pathological. Besides the affective disorders (both depressive and manic, and both in full-blown episodes and during the intervals between these, which are seen as vulnerability to relapse) several other conditions need to be considered (Table I). There are also claims that serotonin metabolites or structurally related substances are involved, in their role as false neurotransmitters, in delusions and psychedelic phenomena, as in the case of LSD (Mantegazzini, 1960) or 5-hydroxytryptolines in delusions related to alcoholism (Daviset al, 1967).This wide range of conditions raises the questions of how specific is the involvement of serotonin, and of what artifacts are present in attempts to investigate its actions. Page, who isolated 5-HT in 1948, stated (1968) that “serotonin has many functions but few have been sharply defined. The great variety of suggested roles can be said to be a tribute to man's ingenuity and his unquestionable willingness to write papers”. Since then, many more roles have been proposed for the involvement of 5-HT in functions of the central nervous system. Nevertheless, good evidence does exist that serotonin has some specific relationships to psychiatric disorders which are worth pursuing, in spite of great methodological difficulties.