Serotonin in affective disorders.

Serotonin (5-hydroxytryptamine; 5-HT) is a signalling molecule within the central nervous system. Overall, the impression gained from biochemical, pharmacological, and neuroendocrine studies is that 5-HT synthesis or function is reduced in the brains of depressed patients. There is more direct evidence from animal studies and indirect evidence in man that drugs (and electroconvulsive therapy--ECT) which are efficacious in various facets of affective disorders have clear effects on 5-HT function. 5-HT function is complex. There are at least seven different 5-HT receptor subtypes, several anatomically different 5-HT neuronal tracts emanating from the raphe nuclei in the pons/medulla and projecting widely throughout the brain and downwards into the spinal cord. There are fine mechanisms controlling almost every aspect of function in the 5-HT neurone and the action of 5-HT released from it. There is ample scope for 5-HT to influence many areas of the brain involved in psychological, cognitive, sensory, autonomic, neuroendocrine, and emotional function. Inhibition of reuptake by drugs selective for 5-HT, such as paroxetine, has important acute and chronic effects on 5-HT systems and function, and upon other neurotransmitter systems with which 5-HT interacts. It is of great interest that selective and non-selective monoamine uptake blocking agents, monoamine oxidase inhibitors, lithium and ECT, all affect 5-HT function, albeit slightly differently, and that they should be efficacious in various aspects of affective illness.