The tip of the iceberg: clock neurons and structural remodeling of the postnatal brain

Plasticity – the ability to make adaptive changes- is a fascinating property of the nervous system. Plasticity occurs at different timescales and in different structures, ranging from spines and boutons to axonal and dendritic arbors. While experience-dependent synaptic plasticity has been extensively studied, the mechanisms underlying structural plasticity, particularly the large-scale growth and remodeling of axons and dendritic arbors in the postnatal brain, have received less attention. Our laboratory has focused on a group of circadian neurons, the small ventral lateral neurons (s-LNvs), which daily undergo extensive remodeling.

Circadian remodeling correlates with rhythmic changes in synapse number and thus the ability to synapse onto specific targets at specific times across the day. To explore the extent to which dynamic changes in the membrane describe the underlying subcellular organization, we used serial block-face scanning electron microscopy (SBEM). Through volumetric electron micrographs of dorsal termini acquired at times with a distinct degree of complexity our work revealed the basis by which s-LNvs differentially contribute to the circadian network. We also examined some of the cellular mechanisms underlying this unusual form of plasticity, demonstrating that it relies on both activity dependent and independent mechanisms and it is not just limited to a subset of circadian neurons.