Human organ donor-derived vagus nerve biopsies allow for well-preserved ultrastructure and high-resolution mapping of myelinated and unmyelinated fibers

The vagus nerve provides motor, sensory, and autonomic innervation of multiple organs, and electrical vagus nerve stimulation (VNS) provides an adjunctive treatment option for e.g. medication-refractory epilepsy and treatment-resistant depression. The mechanisms of action for VNS are not known, and high-resolution anatomical mapping of the human vagus nerve is needed to better understand its functional organization. Electron microscopy (EM) is required for the detection of both myelinated and unmyelinated axons, but access to well-preserved human vagus nerves for ultrastructural studies is sparse. Intact human vagus nerve samples were procured intra-operatively from deceased organ donors, and tissues were immediately immersion fixed and processed for EM. Ultrastructural studies of cervical and sub-diaphragmatic vagus nerve segments showed excellent preservation of the lamellated wall of myelin sheaths, and the axolemma of myelinated and unmyelinated fibers were intact. Microtubules, neurofilaments, and mitochondria were readily identified in the axoplasm, and the ultrastructural integrity of Schwann cell nuclei, Remak bundles, and basal lamina was also well preserved. Digital segmentation of myelinated and unmyelinated axons allowed for determination of fiber size and myelination. We propose a novel source of human vagus nerve tissues for detailed ultrastructural studies and mapping to support efforts to refine neuromodulation strategies, including VNS.

Stain-Free Resolution of Unmyelinated Axons in Transgenic Mice Using Fluorescence Microscopy

Though unmyelinated fibers predominate axon counts within peripheral nerves, they are frequently excluded in histomorphometric assessment as they cannot be readily resolved by light microscopy. Herein, we demonstrate stain-free resolution of unmyelinated axons in Sox10-Venus mice by widefield fluorescence imaging of sciatic nerve cryosections. Optional staining of cryosections using a rapid and nontoxic myelin-specific dye (FluoroMyelin Red) enables robust synchronous resolution of myelinated and unmyelinated fibers, comprising a high-throughput platform for neural histomorphometry.

Peripheral neuropathy in hypereosinophilic syndrome with vasculitis

A 53-year-old woman with non-productive cough of unexplained aetiology for two years, developed a sub-acute symmetrical polyneuropathy involving all four limbs, accompanied by fever, cutaneous rash and myalgia in lower limbs. Laboratory studies revealed a leukocytosis with 70% eosinophils and excluded any cause for the hypereosinophilia. An echocardiogram showed increase in thickness of the atrial septum. Motor and sensory conduction velocity were reduced in ulnar and median nerve, and unrecordable in peroneal and tibial nerves. A sural nerve biopsy showed an axonal degeneration involving myelinated and unmyelinated fibers as well as a vasculitis with fibrinoid necrosis and perivascular infiltration of eosinophils. There was considerable clinical and laboratorial improvement with the use of steroids. The differential diagnosis between idiopathic hypereosinophilic syndrome and other disorders known to course with vasculitis and hypereosinophilia is discussed.