Enhancing synaptic plasticity and cellular resilience to develop novel, improved treatments for mood disorders

Abstract

There is mounting evidence that recurrent mood disorders - once considered "good prognosis diseases"- are, in fact, often very severe and life-threatening illnesses. Furthermore, although mood disorders have traditionally been conceptualized as neurochemical disorders, there is now evidence from a variety of sources demonstrating regional reductions in central nervous system (CNS) volume, as well as reductions in the numbers and/or sizes ofglia and neurons in discrete brain areas. Although the precise cellular mechanisms underlying these morphometric changes remain to be fully elucidated, the data suggest that mood disorders are associated with impairments of synaptic plasticity and cellular resilience. In this context, it is noteworthy that there is increasing preclinical evidence that antidepressants regulate the function of the glutamatergic system. Moreover, although clearly preliminary, the available clinical data suggest that attenuation of N-methyl-D-aspartate (NMDA) function has antidepressant effects. Recent preclinical and clinical studies have shown that signaling pathways involved in regulating cell survival and cell death are long-term targets for the actions of antidepressant agents. Antidepressants and mood stabilizers indirectly regulate a number of factors involved in cell survival pathways, including cyclic adenosine monophosphate (cAMP) response element binding protein (CREB), brain-derived neurotrophic factor (BDNF), the antiapoptotic protein bcl-2, and mitogen-activated protein (MAP) kinases, and may thus bring about some of their delayed long-term beneficial effects via underappreciated neurotrophic effects. There is much promise for the future development of treatments that more directly target molecules in critical CNS signaling pathways regulating synaptic plasticity and cellular resilience. These will represent improved long-term treatments for mood disorders.