Topographic Anatomic Mapping of the Superior Cervical Ganglion with Novel Optical Clearing Method (LIMPID)

BACKGROUND/AIM The Superior Cervical Ganglion (SCG) contains cell bodies that project to various structures within the head and neck, including the nasopharynx, larynx, and submandibular glands. With the emergence of electrical stimulation of peripheral nerves as a treatment for disease pathologies, an emphasis must be placed on the anatomic mapping of end‐point structures. Topographic location within the ganglion as well as post ganglionic projections from the SCG are not well defined as of yet. The 2 main postganglionic sympathetic branches that exit the SCG are the Internal Carotid Nerve (ICN) and the External Carotid Nerve (ECN). The main focus of this work is to utilize a novel optical clearing method to create a topographic map of the SCG, as well as identify the anatomic pathways that these cell bodies travel to their end‐point structures. METHODS Male adult Sprague Dawley rodents (n=18) were anesthetized with Sevofluorane. These rats were separated into 3 equal groups; (1) Tract tracer injections with Hamilton micro syringe (1 μl DiI (8.3mg/ml)) in submandibular gland, (1 μl DiO (8.3mg/ml)) in nasopharynx, and (0.25–0.5 μl DiD (8.3mg/ml)) in larynx; (2) Unilateral surgical transection of the left ECN with bilateral SMG injections of 1μl DiI (8.3mg/ml) (3) Unilateral surgical transection of the left ICN with bilateral nasopharynx injections of 1μl DiO (8.3mg/ml). The SCG was harvested 7 days later through whole body perfusion/fixation with 1X Phosphate buffered saline (PBS)/4% Paraformaldehyde. SCG was placed in a clearing solution for 3‐D topographic mapping for visualization method called lipid‐preserving index matching for prolonged imaging depth (LIMPID). Imaging was performed using a Leica TCS SP8 gated STED. RESULTS Our results show distinct locations of cell populations for SMG, larynx, and nasopharynx respectively. In addition, the anatomical connection from SCG to SMG was ablated almost entirely or entirely following surgical ECN transection (>95% of ganglion cell population absent between transected and control lateralities in all experiments). Transection of the ICN nerve was also shown to entirely prevent the appearance of positive cells projecting to the nasopharynx unilaterally. CONCLUSION Our findings represent a novel topographic mapping of the SCG, and identify the postganglionic branches where cell bodies project to the nasopharynx and submandibular glands specifically. As bioelectronics moves forward, these anatomic mappings will be essential in the identification of intervention points for optimal therapy. Support or Funding Information Supported by NIH1OT2OD023860‐01 This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .