大鼠延髓后角神经降压肽(NT)的亚细胞定位和胞吐释放

神经降压肽(NT)广泛分布于哺乳动物的中枢神经系统,具有明显的镇痛作用,为了探索其镇痛机理的形态学基础,本文应用电镜免疫组化技术,对大鼠延髓后角NT的超微结构和胞吐释放进行了研究。超微结构显示延髓后角浅层NT轴突终末形态多样,大小不一,含有圆形或多形性清亮小泡及数量不等的大颗粒小泡,它们主要与未标记的树突形成轴-树突触,其突触后成分有的还含有少量清亮小泡。NT免疫反应阳性树突可分为两类:一类主要含微管;另一类主要含大颗粒小泡,有的尚可见少量清亮小泡。这两类NT树突可成为未标记的含圆形小泡终末、多形性小泡终末以及突触小球中央轴突终末的突触后成分,提示后角浅层NT神经元可接受不同种类轴突终末(包括一级伤害性传入纤维)的传入(?)动,然后可能再通过一个抑制性中间神经元,抑制痛觉的传递。本文还观察到有少量NT终末内的大颗粒小泡靠近突触活性区处,而更多见它们沿非突触部位轴膜分布,并与其融合,形成胞吐。本文认为NT既可在突触活性区处又可能在非突触部位释放。

SUBCELLULAR LOCALIZATION AND EXOCYTOTIC RELEASE OF NEUROTENSIN WITHIN THE DORSAL HORN OF MEDULLA OBLONGATA IN THE RAT

Neurotensin(NT)is widely distributed in the central nervous system of mammals and can cause analgesia. In order to reveal the mechanism by which NT causes analgesia at the level of the medullary dorsal horn, immunoelectron microscopic technique was used to examine the ultrastructural localization of NT and to observe its exocytotic release in medullary dorsal horn of the rat.It was found that NT-containing axon terminals varied considerably in shape and size and contained clear small round or pleomorphic vesicles and some large granular vesicles(LGV). The majority of NT-containing axon terminals were presynaptic to unlabelled dendrites, some of which contained a few clear small vesicles. Two types of NT-containing dendrites was found in dorsal horn, Class I contained some microtubules, while class Ⅱ contained clusters of LGV, some of which also contained a few small clear vesicles, these dendrites of NT neurons were postsynaptic to profiles containing the clear round or pleomorphic vesicles, and also were postsynaptic to the unlabelled central axon terminals of synaptie glomeruli. These results indicate that NT-containing neurons might receive a variety, of synaptic inputs which include those coming from primary afferents. In turn, NT-containing neurons might have influence on nociceptive transmission through a second inhibitory interneuron.It was found that NT immunoreactive LGV might be located in direct vicinity of the synaptic contact zone occasionally, and the LGVs, however, were mostly adjacent to the axon membrane devoid of synaptic specialization, and exocytosis of NT-containing LGV was found at structurally nonsynaptic sites.These findings suggest that in the medullary dorsal horn neurotensin might be relea sed at both synaptic and nonsynaptic sites.