Fast turnover of clear vesicle membrane in frog sympathetic ganglion

Abstract

The results of three independent experiments are presented. In the first experiment, the afferent fibers of the right side IX and X sympathetic ganglia of five frogs were stimulated at 100 Hz and control unstimulated ganglia were taken from five other frogs. In the second experiment, the right IX and X ganglia from eight other frogs were stimulated at 10 Hz; the left side ganglia of the same eight frogs served as controls. A third experiment was performed in the presence of extracellular horseradish peroxidase, the sympathetic ganglia of three frogs were stimulated at 10 Hz, those of three other frogs were stimulated at 100 Hz and control ganglia exposed to horseradish peroxidase, but not stimulated were taken from another three frogs. Postganglionic compound action potentials were recorded in each experiment to verify the effectiveness of the stimulation. Following stimulation, the ganglia were fixed and prepared for electron microscopy. Between 10 and 20 synaptic profiles were photographed for each ganglia. The numerical density on area (i.e. number of vesicles per μm 2) was calculated separately for the clear vesicles and for the large dense-core vesicles of each profile. Statistical tests indicated no significant difference in the numerical density on area of the clear vesicles, or of the dense-core vesicles between the control and the ganglia stimulated at either 10 or 100 Hz. However, in the experiment done in presence of horseradish peroxidase, a significant increase of the percentage of vesicles labeled with horseradish peroxidase was obtained following stimulation at either 10 or 100 Hz. This indicates that a rapid recycling of the vesicular membrane is occurring in this system without any significant change in the numerical density of the clear vesicles. Horseradish peroxidase uptake is therefore a better indicator of synaptic activity than the reduction of the numerical density of vesicles. These results also indicate that the numerical density on area of large dense-core vesicles, presumably containing peptides, is not modified by repeated stimulation as indicated by a few earlier investigations at other synapses.