Neuroanatomical, Biochemical, and Functional Modifications in Brain Induced by Treatment with Antidepressants

Depression is a psychosomatic disorder. The pharmacological treatment of depression has been based on the pathophysiology of deficiency in monoamines, mainly serotonin and noradrenaline. All approved antidepressants designed to enhance central monoaminergic tone possess many limitations such as 2 to 5 weeks delay in response, a limited clinical efficacy, and severe side effects. Since the pathophysiological aberrations associated to depression go beyond monoamines, the development of better antidepressants would depend on the identification and understanding of new cellular targets. The pharmacological studies of antidepressants, however, indicate the involvement of the blockade of neuronal uptake systems for norepinephrine and serotonin (5-hydroxytryptamine) including receptors for neurotransmitters. Many preclinical studies have suggested that hippocampus containing abundant agonists such as5-HT_1A and 5-HT4 receptor subtypes in the dentate gyrus (DG) is critically involved in the mechanism of action of antidepressants. DG being a part of hippocampus possibly contributes to the brain functions such as formation of new sporadic memories. It is reported that antidepressants cause significant alterations in the structure and function of different brain regions in order to finally lead to their therapeutic effects. This review presents an overview of structural changes in the brain during depression; different neurobiological theories and novel drug development; strategy of augmentation with combinatorial therapy; receptors and targets of actions of antidepressants; and involvement of key signaling factors in the regulation of depression, pharmacology, metabolism, and the underlying principles involved in displaying how the application of antidepressants modulates the structure and function of the brain.