UC San Diego

The organization of intracellular organelles is crucial to understanding how intracellular communication, which is shaped by signaling messengers, occurs within neurons in the brain. Neuronal communication through electrical and chemical signals causes dramatic fluctuations in calcium concentration, which regulates many neuronal processes such as synaptic plasticity, memory formation, and learning. Due to calcium’s high-stakes involvement, much work has been done to understand its role, function, and regulatory mechanisms. However, it is still unclear how the spatiotemporal dynamics of calcium are influenced by the precise orientation and positioning of the intracellular ultrastructure. While previous research has focused on the ultrastructure’s influence in small spatial compartments, such as dendritic spines, its role in regulating calcium dynamics within large spatial compartments, such as the somatic space, remains unclear. In this study, we used a combination of high-resolution electron tomography (ET) and serial block-face scanning electron microscopy (SBEM) to create a precise three-dimensional (3D) reconstruction of the intracellular space of the cerebellar Purkinje soma. From these 3D reconstructions, we were able to quantify and characterize the heterogeneous nature of the endoplasmic reticulum (ER). Furthermore, we were able to quantify the cell-wide distribution patterns of integral calcium-signaling proteins using fluorescent immunohistochemistry to determine if protein populations were also heterogeneously distributed across the soma. Overall, we found that ER acts as a diffusion barrier and signal amplifier in regards to calcium/IP3 signaling. These findings demonstrate how the precise localization of membrane structures and calcium-signaling proteins influence neuronal signaling within the soma.