Strategies for Autonomic Nervous System Mapping of Fiber Composition and Neural Circuitry Using Transmission Electron Microscopy in Support of SPARC Projects

The optimization of neuromodulation strategies is important for a development and refinement of therapies. The design of customized tools, such as electrical stimulating devices, depends on the detailed knowledge of nerve fiber composition and inter‐relationships between target organs, nerve populations, and synaptic circuitry. The autonomic nervous system gives support to organs and are composed by myelinated and unmyelinated fibers as well as pre‐ and post‐ganglionic neurons. Mapping an autonomic nerve such as the pelvic or vagus nerve that innervates peripheral tissues and understanding the synaptology of neurons in the cardiac and stellate ganglia may provide advanced knowledge for improved neuromodulation strategies. Transmission electron microscopy (TEM) is a high‐level technology that helps to identify and characterize axonal myelination and ultrastructure of unmyelinated fibers. TEM also allows for fine structural analysis of neural circuitry and innervation of autonomic targets. Immunogold detection techniques using TEM permits the identification and characterization of neuronal tracers in the nervous system. With the support from the Stimulating Peripheral Activity to Relieve Conditions (SPARC) program at NIH, we developed customized ultrastructural studies of the autonomic nervous system to facilitate refinement of neuromodulation strategies related to the autonomic control of cardiac, gastrointestinal, and lower urinary tract systems. Morphometric analysis is performed by automatic segmentation, and the development of a new strategy to calculate measurements of axon diameter, fiber diameter, myelin thickness, and G‐ratio provides a better understanding of fiber size for modelling studies. Both males and females from different species, including humans, are analyzed and compared. Implementation of common sampling techniques for nerves and ganglia across species provides increased rigor and reproducibility. TEM studies promote an improved understanding of functional studies and provide critical ultrastructural information for the development of new neuromodulation strategies. Support or Funding Information SPARC/NIH 1OT2OD026585‐01 and Dr Miriam and Sheldon G. Adelson Medical Research Foundation (AMRF)