Assessing accurate sizes of synaptic vesicles in nerve terminals

Chemical synaptic transmission occurs when vesicles within a presynaptic ne uron fuse to the membrane and release their neurotransmitter content into t he synaptic cleft, eliciting a response in the postsynaptic cell. If concen tration of neurotransmitter is the same in all synaptic vesicles, the volum e of the vesicle determines how much transmitter is released. Thus, variati on in vesicular volume may contribute to observed variance of synaptic quan tal unit size. The present study provides an approach to more fully and acc urately characterize the dimensions of synaptic vesicles within a populatio n containing varied sizes of vesicles. The methodology can be applied in a wide range of stereological problems. The approach characterizes the distri bution of vesicle sizes within a population and provides a means to assess effects of experimental manipulations on vesicle dimensions. The mathematic al treatments to obtain the true distribution of vesicle sizes involve extr action of the observed distribution from an enlarged population containing smaller vesicle diameters produced by sectioning of the specimens. A FORTRA N program is provided. (C) 2000 Elsevier Science B.V. All rights reserved.