Somatic Ultrastructure May Shape Calcium Dynamics in Purkinje Neurons

The spatiotemporal organization of intracellular features is fundamental to understanding the intercommunication of neurons in the brain. Neuronal communication is regulated by receptor activation, which is influenced by signaling messenger availability and internal calcium (Ca2+) concentrations. An excess or deficiency of cytoplasmic Ca2+ can lead to changes in secondary messenger diffusion, synaptic plasticity, gene expression, and even cause cell apoptosis. Existing models of intracellular calcium movement have used image-based recording methods to approximate a uniform distribution within the cytosolic space, but it is still unclear whether or how somatic features shape calcium mobility. A methodic analysis of the relationship between somatic arrangement and the Ca2+ signaling pathway does not currently exist. In this study, we used fine-scale electron tomogram reconstructions of cerebellar Purkinje neurons to create a precise model of the interior of the cell. We established structural motifs of endoplasmic reticulum (ER) and noticed a heterogeneous arrangement of organelles within the soma. In addition, we used fluorescent immunohistochemistry to analyze localization patterns of signaling proteins and observed how two receptors that mediate Ca2+ efflux from internal ER stores: inositol 1,4,5-trisphosphate receptor 1 (IP3R1) and ryanodine receptor 1 (RyR1) have distinct angular and radial domains. Overall, we found that ER serves as a diffusion barrier and can cause nonuniform diffusion of Ca2+. This thesis demonstrates how the localization organelles and calcium modulating proteins significantly contribute to intracellular communication and provides an architectural reference for emerging research on somatic neuronal signaling