Characteristics, Quantity, and Spatial Distribution of Human Cervical Vagus Nerve and its Cardiac Superior Branch Nerve Fibers

Introduction

In modern medicine, Vagus Nerve Stimulation (VNS) is widely used to treat various diseases such as epilepsy, obesity, depression, and heart diseases. Although the overall Vagus nerve stimulation method has proven to be effective, non-selective global nerve stimulation often brings a series of side effects, limiting the efficacy of the therapy. Therefore, a deep understanding of the neuroanatomy of the Vagus nerve is crucial for developing more precise selective stimulation methods.

This study aims to perform a detailed analysis of the nerve fibers in the middle segment of the human cervical Vagus nerve and its cardiac superior branch, with the objective of providing fundamental data to optimize Vagus nerve stimulation strategies and reduce potential side effects for patients. This study not only expands basic anatomical knowledge but also challenges the existing anatomical concepts regarding the autonomic nervous system and cardiac innervation.

Source of the Study and Author Introduction

The study was jointly completed by scientists Bettina Kronsteiner, Genova Carrero-Rojas, and Lukas F. Reissig, all affiliated with various departments of the Medical University of Vienna, including the Center for Medical Physics and Biomedical Engineering, the Department of Anatomy, and the Center for Regenerative Medicine. The research findings were published in the April 25, 2024 issue of the journal “Brain Stimulation,” published by Elsevier Inc., and comply with the CC BY license agreement.

Research Methods

1. Sample Selection and Tissue Collection

The study subjects were eight adult human bodies donated for research (5 females, 3 males) aged between 69 and 82, with no history of neurological diseases. The authors obtained the cervical Vagus nerves and their cardiac superior branches from these bodies, and conducted fixation, processing, and sectioning according to experimental standards.

2. Immunofluorescence and Quantitative Analysis

The study used multicolor immunofluorescence techniques to identify different types of nerve fibers through antibody markers and utilized semi-automated fiber segmentation tools for quantitative analysis of the nerve fibers. The specific steps were as follows:

1. Sectioning and Microscopic Analysis: Double and triple immunofluorescence labeling was performed using specific antibodies targeting neurofilament (Neurofilament, NF), myelin basic protein (Myelin Basic Protein, MBP), tyrosine hydroxylase (Tyrosine Hydroxylase, TH), and choline acetyltransferase (Choline Acetyltransferase, ChAT).
2. Image Processing and Nerve Fiber Segmentation: Fluorescent images were obtained using laser confocal microscopy, then processed with Fiji software for preprocessing and detection and quantitative analysis of nerve fibers.

3. Distribution and Quantity of Nerve Fibers

The analysis results showed that the right and left cervical Vagus nerves contained 25,489±2781 and 23,286±3164 fibers, respectively, with two-thirds being unmyelinated fibers and one-third myelinated fibers. Sensory fibers constituted about 74% of the total fibers in both cervical Vagus nerves, with specific visceral motor and parasympathetic nerve fibers accounting for about 13%, and sympathetic nerve fibers also about 13%.

4. Results and Data Analysis

The study discussed in detail the characteristics and distribution of different types of nerve fibers in the cervical Vagus nerve and its cardiac superior branch. The right and left cardiac superior branches contained 593.5±239.3 and 533.3±206 fibers respectively, with significantly more sympathetic nerve fibers in the left cardiac superior branch compared to the right, resulting in a greater influence of the left side’s sympathetic fibers on the heart.

Study Conclusions and Practical Value

The study findings indicate that through detailed anatomical research on the Vagus nerve, it is feasible to selectively stimulate the sensory and motor fibers of the Vagus nerve. However, it should also be noted that while the right cervical Vagus nerve holds a significant position in heart rate regulation, stimulating the left cardiac superior branch’s sympathetic fibers might pose risks of arrhythmias.

The study’s notable contribution is the first to clarify the exact number and distribution of different types of fibers within the human Vagus nerve, providing theoretical support for future development of new Vagus nerve stimulation methods. Moreover, the study expands the foundational anatomical knowledge regarding the Vagus nerve and cardiac innervation, making significant contributions to refining existing concepts of the autonomic nervous system.

Highlights and Value of the Study

1. First Quantitative Analysis

This study carried out the first detailed quantitative analysis of the fiber numbers in the human cervical Vagus nerve and its cardiac superior branch, clarifying the spatial distribution characteristics of various types of fibers.

2. Clinical Application Value

The findings provide critical anatomical foundations for developing new, precise Vagus nerve stimulation methods, helping to reduce side effects during stimulation and improve the effectiveness of the therapy.

3. Expanding Basic Anatomical Knowledge

The study challenges and expands previous anatomical concepts about the Vagus nerve and cardiac innervation, offering new perspectives for further exploration of the complexity of the human autonomic nervous system.

4. Technological Innovation

The study combines multicolor immunofluorescence labeling and semi-automated image analysis techniques, enhancing the precision and efficiency of nerve fiber quantitative analysis, and is worth promoting in more related research.

Conclusion

Through detailed anatomical analysis of the human Vagus nerve and its branches, this study reveals the specific quantity and spatial distribution characteristics of different types of fibers, providing valuable basic data for the optimization of Vagus nerve stimulation therapy. Looking forward, further research and technological innovation will hopefully achieve more precise and safe Vagus nerve stimulation, bringing greater clinical benefits to patients.