Horseradish peroxidase uptake of the synaptic vesicles in the superior cervical ganglion of the cat.

The function-dependent changes in synaptic vesicle number and horseradish peroxidase (HRP) labeling were studied in the synapses of cat superior cervical ganglia. It was found that only a low percentage of vesicles contained the extracellular marker. Supra-maximal stimulation (15 min) and subsequent rest (5 min) did not result in significant changes in vesicle number and the percentage of labeled vesicles also remained at about the same level. The low and activity-independent HRP labeling rate does not exclude the possibility of vesicle recycling but indicates that it might be only indirectly connected to the transmitter release itself.