Frontiers in Molecular Neuroscience is a first-tier electronic journal devoted to identifying key molecules, as well as their functions and interactions, that underlie the structure, design and function of the brain across all levels. The scope of our journal encompasses synaptic and cellular proteins, coding and non-coding RNA, and molecular mechanisms regulating cellular and dendritic RNA translation. In recent years, a plethora of new cellular and synaptic players have been identified from reduced systems, such as neuronal cultures, but the relevance of these molecules in terms of cellular and synaptic function and plasticity in the living brain and its circuits has not been validated. The effects of spine growth and density observed using gene products identified from in vitro work are frequently not reproduced in vivo. Our journal is particularly interested in studies on genetically engineered model organisms (C. elegans, Drosophila, mouse), in which alterations in key molecules underlying cellular and synaptic function and plasticity produce defined anatomical, physiological and behavioral changes. In the mouse, genetic alterations limited to particular neural circuits (olfactory bulb, motor cortex, cortical layers, hippocampal subfields, cerebellum), preferably regulated in time and on demand, are of special interest, as they sidestep potential compensatory developmental effects.