Neuroplasticity mediated by altered gene expression.

Plasticity in the brain is important for learning and memory, and allows us to respond to changes in the environment. Furthermore, long periods of stress can lead to structural and excitatory changes associated with anxiety and depression that can be reversed by pharmacological treatment. Drugs of abuse can also cause long-lasting changes in reward-related circuits, resulting in addiction. Each of these forms of long-term plasticity in the brain requires changes in gene expression. Upon stimulation, second messenger pathways are activated that lead to an enhancement in transcription factor activity at gene promoters. This stimulation results in the expression of new growth factors, ion channels, structural molecules, and other proteins necessary to alter the neuronal circuit. With repeated stimulation, more permanent modifications to transcription factors and chromatin structure are made that result in either sensitization or desensitization of a circuit. Studies are beginning to uncover the molecular mechanisms that lead to these types of long-term changes in the brain. This review summarizes some of the major transcriptional mechanisms that are thought to underlie neuronal and behavioral plasticity.