3D Quantitative Analysis of Synaptic Ultrastructure in Identified Long-Range Projection Axons

Thalamocortical synapses are key cellular links in sensory, motor, and cognitive information processing. Quantitative data on the subcellular structure of these synapses is important to model interactions between the thalamus and cortex. Specifically, we chose the ventral posteromedial (VPM) and posterior (Po) thalamic nucleus axons that both converge in different layer patterns in the primary and secondary somatosensory cortex. Here, we set out to measure and compare the ultrastructure of these synapses and their postsynaptic targets. Serial image samples of selected areas were obtained with serial sectioning electron microscopy, to further 3D reconstruct structures of interest. Our goal is to provide the reader with guidelines on how to apply techniques to selectively label long-range axonal projections and analyze its ultrastructure parameters as well as to highlight advantages and limitations of such approach.