Electrical stimulation of the vagus nerve (VN) is a therapy for epilepsy, obesity, depression, and heart diseases. However, whole nerve stimulation leads to side effects. We examined the neuroanatomy of the mid-cervical segment of the human VN and its superior cardiac branch to gain insight into the side effects of VN stimulation and aid in developing targeted stimulation strategies. Nerve specimens were harvested from eight human body donors, then subjected to immunofluorescence and semiautomated quantification to determine the signature, quantity, and spatial distribution of different axonal categories. The right and left cervical VN (cVN) contained a total of 25,489 ± 2,781 and 23,286 ± 3,164 fibers, respectively. Two-thirds of the fibers were unmyelinated and one-third were myelinated. About three-quarters of the fibers in the right and left cVN were sensory (73.9 ± 7.5% versus 72.4 ± 5.6%), while 13.2 ± 1.8% versus 13.3 ± 3.0% were special visceromotor and parasympathetic, and 13 ± 5.9% versus 14.3 ± 4.0% were sympathetic. Special visceromotor and parasympathetic fibers formed clusters. The superior cardiac branches comprised parasympathetic, vagal sensory, and sympathetic fibers with the left cardiac branch containing more sympathetic fibers than the right (62.7 ± 5.4% versus 19.8 ± 13.3%), and 50% of the left branch contained sensory and sympathetic fibers only. The study indicates that selective stimulation of vagal sensory and motor fibers is possible. However, it also highlights the potential risk of activating sympathetic fibers in the superior cardiac branch, especially on the left side.

While the recently developed tissue clearing protocols pathoDISCO and activeDISCO significantly accelerate the clearing of large tissue specimens through active chemical dehydration using 2,2-dimethoxypropane, the final step of refractive index (RI) matching with viscous organic solvents as dibenzyl ether (DBE) remains restricted by slow passive diffusion. To overcome this bottleneck, we applied 40 kHz ultrasound using a standard, cost-effective laboratory bath to significantly enhance the diffusion kinetics of the clearing medium into large specimens. Our investigation on multi-centimeter-sized porcine muscle and human earlobe samples demonstrates that 40 kHz acoustic oscillations generated by a standard ultrasound cleaning device not only accelerate the clearing process but also yield superior and stable long-term optical transparency. We also tested 1 MHz high-frequency ultrasound but it offered no kinetic advantages and tended to induce tissue micro-fractures, an artifact we have not observed at 40 kHz at comparable energy levels. We therefore propose that standard 40 kHz ultrasound baths, ubiquitous in laboratories for cleaning purposes, represent an ideal and accessible tool for optimizing solvent-based tissue clearing.