电针刺激猫“足三里”的脊髓突触变化的实验形态学研究

EXPERIMENTAL AND ULTRASTRUCTURAL STUDY OF SYNAPSES IN THE CAT SPINAL CORD AFTER ACUPUNCTURE IN ZUSANLI

为了探讨针刺镇痛的神经形态学基础,在猫的“足三里”穴,电针刺激30分钟(电压16.5V频率180次/分)后,电镜观察了支配“足三里”的初级传入纤维在腰髓后角(L7)Rexed Ⅰ—Ⅵ层的M(monosynaptic)型神经终末及其突触变化,并与正常超微结构进行了比较。在用WGA—HRP追踪支配“足三里”初级传入纤维在脊髓内分布的实验中,看到细纤维的神经终末分布在后角背外删Ⅰ—Ⅲ层,粗纤维的大型终末分布在Ⅳ—Ⅵ层。超微结构的改变主要有 1、球形突触小泡向活性带集中。2、突触小泡全量减少。3、出现大量糖原颗粒、溶酶体和空泡。在支配“足三里”初级传入纤维的M型终末中这些改变有的可出现一种,有的同时出现几种。这些改变具有可塑性,容易恢复。变化出现的原因可能是突触活性增强,产生疲劳、乏氧、贫血、低营养等造成的。与此同时还观察到来自后根的M型终末上有与之形成轴—轴突触的p型抑制性终末,终末内有椭圆形小泡向活性带集中,活性带较正常显著增厚,这些事实意味着突触前抑制增强,抑制其兴奋性,这可能是产生针刺镇痛效果的形态学基础之一。

Using light and electron microscopy, we studied the synaptic changes in the cat spinal cord after stimulating electrically via acupuncture needles placed at Zusanli, an acupoint widely used in clinical practice. We attempted to identify the cell origins in spinal ganglion and the terminal distributions of Zusanli afferents in the dorsal horn by means of WGA-HRP techniques. Several significant findings are as follows. Under light microscope: two types (small and medium sized neurons) in the spinal ganglion at the level L7 are the cell origins of Zusanli afferents. Zusanli-innervating fine fibers terminated mainly in Lamina Ⅰ-Ⅲ, while the thick fibers terminated exclusively in Lamina Ⅳ-Ⅵ. Under electron-microscope: the Zusanli afferent terminals could be distinguished as M-boutons on the basis of their large sizes, synaptic vesicle populations (spherical vesicles)-asymmetric synapses and wide synaptic clefts (180(?)). M-boutons were further identified by the presence of P-boutons which contained elliptical or polymorphic vesicles and made symmetric synapses on it. In comparison with normal M-boutons, ultrastructural changes have been observed in many cases that spherical vesicles were obviously clustered toward the presynaptie membrane, dense material was accumulated in the active zone, the number of the spherical vesicles tended to decrease after acupuncty re, aecmulation of glycogen granules was appeared, and that lysosomes and vacuolated structure were also noted. Some mitochondria have changed in their forms, sizes and numbers. This suggests that such fine structural alterations might be caused by the metabolic changes of synapses such as anoxia, malnutrition or anemia due to high activity and that the morphological changes of pattern did not occur in a predictable manner. As for the morphological basis of acupuncture anesthesia, we observed frequently axo-axonic synapses in which P-boutons are presynaptic to the M-boutons suggesting presynaptic inhibition. In all axo-axonic synapses, elliptical or polymorphic vesicles in P-boutons are clustered on presynaptic side of the active zone, M-boutons containing spherical vesicles being postsynaptic. The observed features suggest the synapses were activated by electric acupuncture.