海兔5-羟色胺能神经纤维与侧节感觉神经元的关系 Ⅰ免疫光镜研究

The Relationship between 5-HT Immunoreactive Fibers and Pleural Sensory Neurons in Aplysia Ⅰ.Immunolight Microscopic Study

应用 ABC 免疫组化技术,研究了海兔5-羟色胺免疫反应阳性(5-HT-IR)纤维在侧节感觉神经元簇(PSC)中的分布及其与侧节感觉神经元(PSN)的关系。可见 PSN 胞体和轴突的近侧段被含有大量膨体的5-HT-IR 纤维所包绕。光镜下测量4个视野区的5-HT-IR,膨体平均短径为1.1±0.6μm,分布范围为0.2～3.8μm。膨体大小的频数分布呈正偏态,79%的膨体短径分布于0.2～1.4μm 之间。5-HT-IR 纤维至少存在4种类型。少数5-HT-IR 纤维可有分支发出,发出点通常是在膨体上,从膨体发出2～4条细分支,每条分支上又可见数个子膨体存在。发出分支的膨体平均短径为1.70±0.5μm,分布范围在1.0～2.4μm,某些小的膨体似与 PSN 胞体表面形成接触,但现有结果尚不足以说明5-HT-IR 纤维与 PSN 之间存在着突触样联系,因为 PSN 细胞胞体表面有胶质细胞形成的胶质鞘包绕,这一结构或许阻碍5-HT-IR 纤维与 PSN 形成真正的突触联系。

The 5-HT immunoreactive fibers(5-HT-IR fibers)in pleural sensory cluster of aplysia were examined at the light microscopic level using ABC immunohistochemical method.Both the cell bodies and the proximal axon segments of pleural sensory neurons were surrounded by 5-HT-IR fibers with numerous 5-HT-IR varicosities.To analyze the size distribution of the 5-HT-IR varieosities quantitatively,4 microscopic fields of approximately 32 000 μm were drawn with a camera lueida.The size of individural 5-HT-IR varicosities was then esti- mated from the camera lucida drawings by measuring their diameters along the short axis.The average short axis diameter of the varicosities was 1.1±0.6 μm(mean±S.D.;n =574),ranging from 0.2～3.8 μm.The shape of the size distribution of the 5-HT-IR vari- cosities was skewed towards the smaller diameter.Based on the size distribution of the vari- cosities along a strand of fibers,at least four different types of 5-HT-IR fibers were ob- served.Some fibers sent out branches,which usually emerged from a varicosity.A branched varicosity might generate 2～4 daugher branches with sub-varicosity.A average short axis diameter of branched varieosities was 1.7±0.5 μm(n=35),ranging from 1.0 μm to 2.4 μm.Some small varicosities seemed to contact with the somata surface of pleural sensory neurons.But this level of resolution was not sufficient to determine if these immunoreactive varicosities actually contact with pleural sensory neurons in synaptic.The cell body of the sensory neuron was covered by a thin sheath of glial cells that might hinder access of the transmitter secreted from the 5-HT-IR varicosities.