Schmidt E D, Roubos E W
Department of Biology, Vrije Universiteit, Amsterdam, The Netherlands.
Neuroscience. 1988 Jul;26(1):327-35. doi: 10.1016/0306-4522(88)90149-2.
The cerebral peptidergic caudodorsal cells of the freshwater snail Lymnaea stagnalis control egg laying and egg-laying behaviour by releasing peptides into (1) the haemolymph, from neurohaemal axon terminals in the periphery of the cerebral commissure and (2) the intercellular space of the central nervous system, from collaterals in the inner compartment of this commissure. Recently, it was shown that collateral release occurs from nonsynaptic release sites, which lack the morphological specializations that are characteristic of classical synapses. Probably, these sites enable the caudodorsal cells to communicate with central neurons in a nonsynaptic ("paracrine", "diffuse", "hormone-like") fashion. The structural and ionic bases of nonsynaptic release were studied using the tannic acid-Ringer incubation-method for the detection of exocytotic release of secretory granule contents in vitro. Elevation of the extracellular potassium concentration strongly stimulates exocytotic activity in the collaterals. No stimulation was found in the absence of extracellular calcium ions. Similar results have been obtained for the neurohaemal axon terminals. Electron-dense material occurs apposed at the cytoplasmic side of the axolemma of collaterals (ethanolic phosphotungstic acid method). This material appears homologous with the presynaptic dense projections forming the "vesicular grid" in classical synapses. Such projections are also present in the neurohaemal axon terminals. It is concluded that secretion from nonsynaptic release sites in caudodorsal cell collaterals shares fundamental characteristics with secretion from conventional neuronal release sites (neurohaemal axon terminals and classical synapses); release occurs by exocytosis of secretory granules, is associated with a vesicular grid, is stimulated by membrane depolarization, and depends on the presence of extracellular calcium ions.(ABSTRACT TRUNCATED AT 250 WORDS)
（1）血淋巴，从脑连合外周的神经血窦轴突终末释放；（2）中枢神经系统的细胞间隙，从该连合内部隔室的侧支释放。最近研究表明，侧支释放发生在非突触释放位点，这些位点缺乏经典突触特有的形态学特化结构。可能这些位点使尾背细胞能够以非突触（“旁分泌”“弥散”“类激素”）方式与中枢神经元进行通讯。利用单宁酸 - 林格氏液孵育法在体外检测分泌颗粒内容物的胞吐释放，研究了非突触释放的结构和离子基础。细胞外钾离子浓度升高强烈刺激侧支的胞吐活性。在没有细胞外钙离子的情况下未发现刺激作用。神经血窦轴突终末也得到了类似结果。侧支轴膜的胞质侧出现电子致密物质（乙醇磷钨酸法）。这种物质似乎与在经典突触中形成“囊泡网格”的突触前致密突起同源。这种突起在神经血窦轴突终末也存在。得出的结论是，尾背细胞侧支非突触释放位点的分泌与传统神经元释放位点（神经血窦轴突终末和经典突触）的分泌具有基本特征；释放通过分泌颗粒的胞吐作用发生，与囊泡网格相关，受膜去极化刺激，并依赖于细胞外钙离子的存在。（摘要截短于250字）
