Quantitative mapping of NF200/ChAT-defined axonal profiles across the anatomical hierarchy of the human brachial...

The brachial plexus is a critical neural network governing upper limb function. However, systematic quantitative data on axon-profile counts and marker-defined axonal composition at intermediate anatomical levels, particularly trunks and divisions, remain limited. Moreover, quantitative data on fascicle numbers across different anatomical levels of the brachial plexus remain scarce. Here, we analyzed brachial plexus specimens from 10 human donors using NF200/ChAT dual immunofluorescence staining to assess axon-profile counts and fascicular organization across five sampled anatomical levels: roots, trunks, divisions, cords, and terminal branches. Within the sampled structures, NF200-positive axon-profile counts were numerically higher at proximal levels and lower at more distal sampled levels, whereas ChAT/NF200 double-positive profile counts showed less variation, with their proportional contribution increasing from 12.61% to 20.84%. Fascicle numbers were numerically highest at the trunk and cord levels. On representative qualitative inspection, no stable intrafascicular spatial pattern of ChAT/NF200 double-positive profiles was apparent. This study provides marker-defined quantitative anatomical reference data on NF200-positive axon-profile counts, ChAT/NF200-defined axonal composition, and fascicle numbers across five sampled anatomical levels of the human brachial plexus, including the under-quantified trunks and divisions. These data may serve as a foundation for future studies of brachial plexus anatomy, nerve repair planning, and neural interface design.