Statistical methods for assessing the dimensions of synaptic vesicles in nerve terminals

Chemical transmission between neurons occurs by the release of neurotransmi tter packaged within Vesicles of the presynaptic neuron onto a postsynaptic target. The amount of transmitter contained within a vesicle is in part re gulated by the size of the vesicle. Thus, it is of general interest to quan tify the dimension of vesicles in understanding the basic principles of che mical synaptic transmission. These vesicles can only be measured by electro n microscopic techniques. Obtaining the true dimensions of synaptic structu res is therefore complicated by stereological considerations. In this study , we suggest improved methods for determining the distributions (and mean s izes) for populations of vesicle diameters by mathematical processes involv ing (1) an implicit inversion of the empirical data distribution, (2) an ex plicit inversion approach, and (3) an approach based on substituting the em pirical distribution into the inversion formula and then isotonizing using an iterated convex minorant algorithm. These procedures provide distributio ns that better represent the true population distributions (and means) for comparisons with other data sets of vesicle diameter measures. (C) 2000 Els evier Science B.V. All rights reserved.