Understanding Propagated Sensation along Meridians by Volume Transmission in Peripheral Tissue

Propagated sensation along meridians （PSM） is a phenomenon that a sensation moves along meridians during stimulation of an acupoint. PSM has an appearance rate of 1.3% among people and have characteristics of low speed, going toward afflicted sites and being blocked by physical pressure which is difficult to be explained by known neural and blood transmission. Volume transmission （VT） is a widespread mode of intercellular communication in the central nervous system that occurs in the extracellular fluid and in the cerebrospinal fluid. VT signals moves from source to target cells via energy gradients leading to diffusion and convection （flow） which is slow, long distance and much less space filling. VT channel diffuse forming a plexus in the extracellular space with two parameters of volume fraction and tortuosity. Some experiments showed an information transmission between adjacent and distant acupoints along meridians cross spinal segments. This process is a cross-excitation between peripheral nerve terminals which is related to nonsynaptic transmission. Some neurotransmitters or neuropeptides such as glutamate, adenosine triphosphate （ATP） and neuropeptide such as substance P, neurokinin A and calcitonin gene-related peptide relate with the cross-excitation which can be regards as VT signals. Comparing the characteristics of PSM and VT, many similar aspects can be found leading to an assumption that PSM is a process of VT in peripheral tissue along meridians. The reason why VT signals transmit along meridians is that the meridian is rich in interstitial fluid under the condition of low hydraulic resistance which has been proven experimentally. According to Darcy＇s law which descript the flow of interstitial fluid and conservation equation, interstitial fluid will move toward meridians and flow along meridians that restrict the VT signals within the channel and accelerate the flow according to Fick＇s diffusion law. During the process, a degranulation of histamine from mast cells happens on the route which can expand capillary and increase the blood perfusion and interstitial fluid which had already been observed. The mechanism of PSM is featured by alternative axon reflex （wired transmission, WT） and VT in peripheral tissue along meridians, sending simultaneously a continuous sensate signal to control nerve system which can be felt like a PSM.

Electrical Signal Propagated across Acupoints along Foot Taiyang Bladder Meridian in Rats

Objective： To investigate the electrical signals propagated along Foot Taiyang Bladder Meridian （BL） in a rat model. Methods： The experiments were performed on Dark-Agouti （DA）, DA.lU and Sprague Dawley （SD） rats. The antidromic electrical stimulation was applied on the nerve innervating ＂Pishu＂ （BL 20） to mimic the acupoint electro-acupuncture （EA）. The activities recording from adjacent nerve innervating acupoint ＂Danshu＂ （BL 19） or ＂Weishu＂ （BL 21） were recorded as indics for acupoint, including the mechanical threshold and discharge rate. Results： After mimic EA on BL 20, C and A $ units from adjacent BL 19 or BL 21 were sensitized including the decrease in mechanical threshold and increase in discharge rates in DA, DA.1U and SD rats, especially in DA rats. The average discharge rate increased from 2.40± 0.26 to 6.06± 0.55 and from 1.92±0.42 to 6.17± 1.10 impulse/min （P〈0.01）, and the mechanical threshold decreased from 0.52 ± 0.12 to 0.24 ± 0.05 and from 0.27±0.02 to 0.16±0.01 mmol/L （P〈0.01） in C （n=15） and Aδ （n=18） units in DA rats. The net change in discharge rates from C units were 152.5%, 144.7% and 42.4% in DA, DA.1U and SD rats, respectively, among which DA rat＇s was the highest （P〈0.05）. In A δ units, the net change in DA rats were also the highest （221.5%, 139.2% and 49.2% in DA, DA.lU and SD rats）. Conclusions： These results showed that mimic acupoint EA activated adjacent acupoints along BL in three rat strains, which might be related to propagated sensation along meridians （PSM）. In addition, DA rats were more sensitive and might be a good model animal for PSM research.