Three Dimensional Reconstructions of Brain Circuitry in the Visual Thalamus: An Application of Serial Blockface Electron Microscopy

How we detect and perceive our environment, and how we reach to it, is a direct function of the electrical activity of our brain cells, neurons, and how they those cells are connected to each other via synapses to form neuronal pathways and brain circuitries. The studies of the past decades using an electron microscope, which allows visualization of very small biological structures, including synapses, have revealed many properties of synaptic circuitries, bringing many advances in our understanding of how the brain works. While these approaches relied on interpolating the structures of 3D objects from their 2D cross-sections, more recent technical developments in electron microscopy instrumentation are now allowing us to obtain 3D volumetric data for dendrites, axon terminals, and synapses. In this study, we take advantage of these advances to study the patterns of synapse formation of various inputs on visual thalamus neurons. In particular, I use a program Reconstruct to construct 3D images of dendrites and terminals that are captured in Serial Block-facing Electron Microscopy (SBEM) image stacks. This has allowed for more accurate measurements of volume and length for the structures, which is useful for identifying various aspects of the dendrites and terminals, such as dendritic order and type of terminal. We found various patterns in terminal size and type of neurotransmitter, as well as a correlation between terminal volume and dendritic order. These patterns and methods will help future research into the brain and understanding how it works.