Triller A, Korn H
J Neurocytol. 1985 Apr;14(2):177-92. doi: 10.1007/BF01258446.
In the CNS, the exocytosis which accompanies transmitter releases occurs at the level of a presynaptic grid. Possible alterations in the grid as a function of this phenomenon were searched for at the synapses established by unmyelinated club endings on the Mauthner cell of teleosts. The number of vesicle openings generated by aldehyde fixation was diminished by cooling the preparation and enhanced after perfusion with a high-KCl Ringer solution. Morphometric analysis of the grid showed that under these conditions the mean distance between its constituent elements, the presynaptic dense projections, increased with the number of exocytotic events. Parallel changes were observed for the mean diameter of the spaces left free between these dense projections, suggesting that vesicle exocytosis produces a transient enlargement of the space where it takes place. These observations indicate that the presynaptic grid is more dynamically involved in the secretory process than previously conceived. It is therefore hypothesized that (i) the movement of the dense projections is a consequence of their interaction with the plasma membrane, and (ii) the distortion of the grid could underlie regulatory mechanisms by which the number of released vesicles is limited after each impulse. It is also proposed that the dense projections contribute to the stabilization of the plasma membrane, thereby preventing its randomization following intense release.
在中枢神经系统中，伴随神经递质释放的胞吐作用发生在突触前网格水平。在硬骨鱼Mauthner细胞上由无髓梢终末建立的突触处，研究了作为这种现象的函数的网格可能发生的变化。通过冷却标本，醛固定产生的囊泡开口数量减少，而用高钾林格溶液灌注后增加。对网格的形态计量分析表明，在这些条件下，其组成成分突触前致密突起之间的平均距离随着胞吐事件的数量增加而增加。在这些致密突起之间留下的自由空间的平均直径也观察到了平行变化，这表明囊泡胞吐作用会使发生胞吐作用的空间产生短暂扩大。这些观察结果表明，突触前网格在分泌过程中的动态参与程度比以前认为的更高。因此，假设（i）致密突起的移动是它们与质膜相互作用的结果，并且（ii）网格的变形可能是调节机制的基础，通过该机制每次冲动后释放的囊泡数量受到限制。还提出致密突起有助于质膜的稳定，从而防止其在强烈释放后随机化。
