New research in animals is beginning to change radically our understanding of the biology of stress and the effects of antidepressant agents. Recent findings from the basic neurosciences to the pathophysiology of depressive disorder suggest that stress and antidepressants have reciprocal actions on neuronal growth and vulnerability (mediated by the expression of neurotrophin) and synaptic plasticity (mediated by excitatory amino acid neurotransmission) in the hippocampus and other brain structures. Stressors have the capacity to progressively disrupt both the activities of individual cells and the operating characteristics of networks of neurons, while antidepressant treatments act to reverse such injurious effects
. Antidepressant drugs increase the expression of several molecules, which are associated with neuroplasticity; in particular the neurotrophin BDNF and its receptor TrkB. Antidepressants also increase neurogenesis and synaptic numbers in several brain areas.
SSRI antidepressant fluoxetine can reactivate developmental-like neuroplasticity in the adult visual cortex, which, under appropriate environmental guidance, leads to the rewiring of a developmentally dysfunctional neural network[11, 12].