大鼠脊髓胶状质内含P物质(SP)及脑啡肽(ENK)神经终末的超微结构

水文应用超微免疫组织化学技术探讨正常及切断后根大鼠胶状质(SG)内P物质(SP)及脑啡肽(ENK)轴突终末的分布及其突触联系。电镜观察发现:SP或ENK免疫反应产物主要分布于轴突终末的大颗粒囊泡的内面,小清亮囊泡及线粒体的外表面,在未应用秋水仙素的情况下,ENK样免疫反应性也可出现于树突及核周质,但电子密度较低。大量的含SP或ENK的终末,分别和未标记树突形成突触。但也偶然见到肽能神经终末与未标记轴突或胞体接触或形成突触联系。常遇到三或四联体,亦偶可见到以含SP轴突终来为中心的突触球。切断后根,手术侧既可见到变性轴突(SP阳性)与未标记轴突接触,又可见到ENK阳性轴突终末与溃变轴突接触,但为数不多。因此认为:通过SP阳性一级传入细纤维传递的感觉信息既可汇集于神经元的一个树突又可多向传递于若干个神经元。ENK在胶状质的抑制作用主要为突触后,但ENK对含SP的一级传入纤维的突触前抑制也不能排除。

THE ULTRASTRUCTURE OF SUBSTANCE P (SP)- AND ENKEPHALIN (ENK)-CONTAINING AXON TERMINALS IN THE SUBSTANTIA GELATINOSA (SG) OF RAT SPINAL CORD

The distribution and synaptic association of SP- and ENK- containing axon terminals in Rexed's layer Ⅱ of spinal cord were examined in normal and rhizotomized rats using immunocytochemical technique. Observations under electron microscope revealed that the SP-like immunoreactivity (LI) and ENK-LI was evident in axonic terminals mainly distributing in large dense cored vesicles and on the surface of small clear vesicles as well as the outer membrane of mitochondria. The dendrites and the perikaryon within lamina Ⅱ could be also lightly labelled with ENK in rats without pretreatment of colchicine. A majority of SP or ENK positive nerve endings synapsed with unlabelled dendrites and occasionally made direct contact or synapsis with unstained axon (axo-axonic) or cell body (axo-somatic). The occurence of triad or tetrad arrangement of peptidergic endings and unlabelled processes was usually met but the existence of synaptic glomeruli with SP-Containing central terminal was less frequently observed. In addition, the synapse-like contact either between a degenerating axon (SP-positive) and an unstained ending, or between an ENK-containing terminaland a degenerating unlabelled ending was also occasionally demonstrated at the lesioned side after transection of dorsal roots. From the foregoing results it is indicated that the sensory input transmitted by SP-containing endings may converge to a single postsynaptic dendrite of neuron or disperse to multiple targets of neurons. The inhibitory effect of ENK in SG is predominantly postsynaptic, however, the presynaptic inhibition of ENK to SP-containing afferent sensory nerve in modulating; transmission of nociceptive information could not be excluded.