Distribution of granular vesicles in normal and constricted sympathetic neurones.

1. A quantitative analysis has been made of the characteristics of granular vesicles in different parts of normal and ligated post-ganglionic sympathetic neurones supplying the cat spleen. The least diameter of the vesicle membrane and its electron-dense core was measured from electron micrographs with an automated particle size analyser.2. Vesicles of average diameter 443 A, with and without electron-dense cores (192 A), were concentrated in the axon terminals of the spleen, whereas in the cell bodies in the coeliac ganglion and their axons there were only a few large vesicles (787 A) with large granules (562 A).3. Ligation of the splenic nerves for 24 hr resulted in an accumulation proximal to the constriction of granular vesicles significantly larger (688 A) and more completely granulated (478 A) than those in the terminals.4. Reserpine reduced the number of vesicles with granular cores without discrimination between the two populations.5. Since the distribution of noradrenaline in sympathetic neurones can be correlated with the presence of large as well as small granular vesicles, it is suggested that the larger, more granular type found mainly proximally in the neurone is in transit from its perikaryal site of synthesis to the axon terminals, where it is transformed into the smaller synaptic vesicles.