Roles of Serotonin in Depression

INTRODUCTION

Serotonin is a monoamine neurotransmitter derived biochemically from L-tryptophan. It is mainly found in the gastrointestinal tract (about 90% in enterochromaffin cells), platelets and in the central nervous system of humans and animals. It is an important biogenic amine that play combined role of neurotransmitter as well as neuromodulator (Gyermek, 1996). Serotonin, a neurotransmitter synthesized in the brain, acts importantly in the functioning of the cardiovascular, renal, immune, and gastrointestinal systems. Any disruption in the synthesis, metabolism or uptake of this neurotransmitter has been found to be partly responsible for certain manifestations of schizophrenia, depression, compulsive disorders (type of anxiety disorder delineated by continued, persistent, unwanted and unpleasant thoughts) and learning problems. Serotonin can be released in response to several stimuli such as mechanical distortion, mucosal stroking, or electrical stimulation of enteric neurons on release. Serotonin activates enteric neurons (directly controls the gastrointestinal system) to affect motor responses in the gut (Michel et al., 2005). It is a thoroughly known contributor to feelings of well-being. The serotoninergic system is known to alter mood, emotion, sleep and appetite and, thus, is involved in the control of various behaviors related to physiological functions (Schloss et al., 1998; Johansson et al., 2001). It has been known that a serotonergic system is associated with many psychiatric disorders and it predominates the cause of one important endophenotype, depression.

Depression is related to the normal emotions of sadness and bereavement, but it does not remit even when the external cause of these emotions is gone, and it is not usually proportional to their cause. Some severe states of depression often have no external stimulating cause. It is difficult, however, to draw clear difference between depressions with and those without psychosocial stimulating events. The diagnosis of depression requires a distinct change of mood, characterized by sadness or irritability and accompanied by at least several psychophysiological changes, such as disturbances in sleep, appetite, or sexual desire; constipation; loss of the ability to experience pleasure in work or with friends; crying; suicidal thoughts; and slowing of speech and action. These changes must last a minimum of 2 weeks and interfere considerably with work and family relations before it can be considered as depression.

Contents

• Introduction
• Serotonin
• Serotonin synthesis and metabolism
• Serotonin receptors and transporters
• Depression
• Type,causes and symptoms of depression
• Role of serotonin in depression