Buma P
Department of Anatomy and Embryology, Faculty of Medicine and Dentistry, University of Nijmegen, The Netherlands.
Acta Morphol Neerl Scand. 1988;26(2-3):81-113.
Different types of release site were studied ultrastructurally with tannic acid and immunohistochemical techniques in the central nervous system (CNS) of the invertebrate pond snail Lymnaea stagnalis and in two neuromediator rich core regions in the CNS of the rat, viz., the median eminence (ME) and the mesencephalic central grey substance (MCG). In the CNS of the snail, release of the contents of the secretory granules could be clearly demonstrated in (1) neurohaemal axonterminals, (2) synapses and (3) in nonsynaptic release sites: neuronal processes without morphological synaptic specializations. In the ME, release of secretory products by exocytosis was found in neurohaemal axonterminals in the external part of the palisade layer and in nonsynaptic release sites in all other layers of the median eminence. It was found that oxytocine and vasopressin were released by exocytosis into the extracellular space from such (preterminal) nonsynaptic release sites. Serial section analysis revealed three types of fibre in the MCG, viz. (1) varicose fibres that made synaptic contacts with MCG dendrites on every varicosity, (2) fibres with two types of varicosity, viz. synapse-bearing varicosities and varicosities without synaptic specializations, and (3) varicose fibres without any synaptic specializations. It has been discussed that the nonsynaptic release sites in the CNS of the snail Lymnaea stagnalis, and the nonsynaptic varicosities in the rat brain are the morphological correlates of nonsynaptic communication in the CNS. The results further indicate that particular peptidergic neuromediators are released from such nonsynaptic varicosities, and may reach via the extracellular space receptors located at some distance.
运用单宁酸和免疫组织化学技术，在无脊椎动物椎实螺的中枢神经系统（CNS）以及大鼠中枢神经系统中富含神经介质的两个核心区域，即正中隆起（ME）和中脑中央灰质（MCG），对不同类型的释放位点进行了超微结构研究。在椎实螺的中枢神经系统中，分泌颗粒内容物的释放可在以下部位清晰显示：（1）神经血窦轴突终末；（2）突触；（3）非突触释放位点：即无形态学突触特化的神经突起。在正中隆起中，在栅栏层外部的神经血窦轴突终末以及正中隆起所有其他层的非突触释放位点发现了通过胞吐作用释放分泌产物的现象。研究发现，催产素和血管加压素通过胞吐作用从这些（终末前）非突触释放位点释放到细胞外空间。连续切片分析揭示了中脑中央灰质中有三种类型的纤维，即：（1）在每个膨体上都与中脑中央灰质树突形成突触联系的曲张纤维；（2）具有两种类型膨体的纤维，即带有突触的膨体和无突触特化的膨体；（3）无任何突触特化的曲张纤维。已经讨论过，椎实螺中枢神经系统中的非突触释放位点以及大鼠脑中的非突触膨体是中枢神经系统中非突触通讯的形态学相关物。结果进一步表明，特定的肽能神经介质从这些非突触膨体释放，并可能通过细胞外空间到达距离较远的受体。
