In vivo stimulation of a cholinergic synapse of the chick ciliary ganglion induces a reduction in the number of dense core vesicles.

The Edinger-Westphal nucleus of young chicks (1 day old) was stimulated in vivo with a monopolar electrode at 100 Hz during 15, 60 or 225 min. This stimulation produced quantitative morphological changes in the cholinergic synaptic terminal located in the ciliary ganglion. As previously observed at the neuromuscular junction, there is a significant reduction of the numerical density on area (NA) of the coated vesicles. We have also observed, however, a significant reduction of the NA of the clear vesicles and an increase in the NA of the coated vesicles. We have also observed, however, a significant reduction of the NA of the dense core vesicles (DCVs). It is suggested that these DCVs contain a peptide neurotransmitter and that their reduced NA is due to exocytosis which would liberate the peptide during synaptic activity.