大颗粒小泡非突触部位的胞吐——论神经肽释放的另一种形式

本文在以前的工作基础上,进一步用电镜及免疫细胞化学方法,研究了大颗粒小泡非突触部位胞吐作用。实验结果表明,切除大鼠刚髭部皮肤1—24小时之后,术侧延髓后角浅层大颗粒小泡胞吐比对照侧明显增多(P<0.01),术后3—9天复又下降(近似对照动物),术后14—15天又急剧上升(P<0.01)。这些胞吐大部分出现于延髓后角浅层四种轴突终末的非突触部位,少最也发生于树突及轴突中。从术后第6天开始,术侧P物质明显减弱,而甲硫-脑腓肽略有增强。研究结果提示;1)后角浅层胞吐增多,P物质下降及脑腓肽增高,反映了中枢内不同神经元对去传入神经的功能调整作用;2)大颗粒小泡在非突触部位释放神经肽,弥散地作用于远距离的受体,可能起着神经调制物的作用。

NONSYNAPTIC EXOCYTOSIS FROM LARGE DENSE CORED VESICLES: ANOTHER FORM OF NEUROPEPTIDE RELEASE

Previous studies have shown that exocytosis from large dense cored vesicles can occur at structurally non-specialized area of terminals within trigeminal subnucleus caudalis. The present study was to examine by electron microscopy and immunochemical method and to find further evidence for a role of large dense cored vesicles in nonsynaptic exocytosis. The number of exocytotic figures was significantly (P<0.01) increased on the ipsilateral side in rat medullary dorsal horn 1-24 h. after a unilateral skin lesion in the vibrissae area. A second increase (P<0.001) occurred 14-15 days after the lesion. There was no significant increase in exocytosis 3-9 days and 21-30 days after lesion. Vertually all examples of large vesicle exoeytosis took place at nonsynaptic sites from four types of axon terminals and occasionally from dendrites and axons within the neuropil of the medullary dotal horn. At the same time, substance P immunoreactivity declined in the ipsilateral laminal Ⅰ and Ⅱ 6 days after lesion. In contrast, immunostaining of enkephalin was increased.It is suggested that 1) the increase in large dense cored vesicle exocytosis and in enkephalin, the decrease in substance P reflected functional adjustments of different neurons in the dorsal horn in response to the lesion; 2) small vesicles selectively released transmitters at the synaptic active zone into the narrow synaptic cleft for interaction with receptors, while the large dense cored vesicles discharged neuropeptides at nonsynaptic sites. This allows diffusion of neuropeptides modulators to interact with appropriate receptors over a far greater distance.