| Background and ObjectiveThe meridian theory is one of the key foundations of Traditional Chinese Medicine. For over two thousand years, the meridian theory has been widely applied in the academic and clinical practice in the history of Chinese traditional medicine. Meridian is particularly important in the application of acupuncture and related therapeutic methods. However, so far there is poor understanding of the basic mechanism of meridian due to the lack of experimental evidence. It would be of great scientific importance and clinical application value to elucidate the basic mechanisms of meridian and meridian propagation that is a unique relevant phenomenon.Previous studies have discovered that for the three Yang-meridians in the rats labeled by Cholera toxin subunit B conjugated with horseradish peroxidase (CB-HRP), the motor neurons related to the same meridian formed a column in the spinal ventral (anterior) horn via dendritic projections connecting each other. Inputs from stimuli to the meridian points on the Stomach Channel of Foot-Yangming may activate other motor neurons innervating muscles on the same meridian channel via a reflex mechanism. These mechanisms may form the neurobiological basis of ’Deqi’ and meridian propagation. The purposes of this study are to explore the characteristics of spacial distribution and dendritic projects of motor neurons innervating the muscles on the Kidney Channel of Foot-Shaoyin and the Stomach Channel of Foot-Yangming, and the relationshop between these two channels. The motor neurons innervating the Large Intestine Channel of Hand-Yangming and the Pericardium Channel of Hand-Jueyin will also be studied to confirm the universality of our findings on the foot channels.Materials and MethodCB-HRP was injected as a neurotracer into the muscles on the acupoints in the rats to label the motor as well as primary sensory neurons related to the following channels:the Kidney Channel of Foot-Shaoyin and the Stomach Channel of Foot-Yangming on the abdominal wall, the Large Intestine Channel of Hand-Yangming and the Pericardium Channel of Hand-Jueyin on the forelimbs. Each acupoint received an intramuscular injection of CB-HRP (5 μL, containing 1% of HRP). Three to 4 days after injection, rats were perfused with fixatives and the cervical spinal cord was harvested, followed by TMB chemo-histological reactions to label the motor neurons. The somata and dendrites of CB-HRP positive motor neurons were observed with light microscope in the transverse and the horizontal sections.Result1. The Kidney Channel of Foot-Shaoyin and the Stomach Channel of Foot-Yangming on the abdominal wall in the rat.(1) Motor neurons labeled from acupoints on each meridian channel formed a clearly defined longitudinal column in the thoracic-lumbar spinal ventral horn.(2) For each meridian channel, the motor neuron column is constructed by numerous dendritic-dendritic and dendritic-somal projections connecting each other.(3) There are inter-column projections between the motor neuron columns related to acupoints on the Kidney Channel of Foot-Shaoyin and the Stomach Channel of Foot-Yangming corresponding to acupoints located in the same group of rectus abdominis muscles.2. The Large Intestine Channel of Hand-Yangming and the Pericardium Channel of Hand-Jueyin on the forelimbs of rat(1) Motor neurons labeled from acupoints on each meridian channel formed a clearly defined longitudinal column in the cervical 3-7 spinal ventral horn.(2) For each meridian channel, the motor neuron column is constructed by numerous dendritic-dendritic and dendritic-somal projections connecting each other.ConclusionOur results indicate that:1. Motor neurons related to a given meridian channel formed a longitudinal motor neuron column in the spinal cord ventral horn. The dendritic-dendritic and dendritic-somal projections exclusively within the same motor neuron column corresponding to a given meridian channel might be the morphological basis of the reflex activities of meridian propagation.2. The characteristics of the motor neuron column is universal for all the meridian channels studied. Each meridian channel is corresponding to a clearly-defined motor neuron column, which locates in a certain position in the spinal ventral horn and is constructed by dendritic projections from each of the labeled motor neurons connecting other neurons related to the same meridian channel3. The inter-column projections between the motor neuron columns related to the Kidney Channel of Foot-Shaoyin and the Stomach Channel of Foot-Yangming in the abdominal wall may suggest a specific correlation for these two meridian channels corresponding to the same group of rectus abdominis muscles. |
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