Dynamics of large dense-cored vesicles in synaptic boutons of the cat superior cervical ganglion.

We have shown previously that stimulation of the cat cervical sympathetic trunk for 2 h at 40 Hz depletes the large dense-cored vesicle store in synaptic boutons of the superior cervical ganglion and that post-depletion recovery of the store takes several days. In the present study, we examine the properties of the depletion and recovery mechanisms. Invaginations of the plasmalemma suggestive of the exocytosis of dense cores were seen frequently in boutons from stimulated ganglia. The depletion process is calcium dependent: in ganglia perfused with calcium-free Krebs solution no depletion was produced by 40 Hz preganglionic stimulation. The depletion process is rapid: during continuous stimulation of the cervical sympathetic trunk with 40 Hz, depletion observed by the end of 2 h was similar to depletion by the end of the initial 5 min of stimulation. The depletion process is frequently dependent: when the cervical sympathetic trunk was stimulated with a constant number of stimuli, no depletion occurred at the frequency of 2 or 10 Hz, while the frequencies of 20 and 40 Hz produced depletion, which was greater at 40 Hz. Recovery of the large dense-cored vesicle store during the initial 24 h after 10 min of 40 Hz stimulation was faster, and of approximately the same magnitude, than during the succeeding five days. Recovery of the store after stimulus-evoked depletion was prevented by application of colchicine to the cervical sympathetic trunk, which suggests dependence of recovery on fast axonal transport. Large dense-cored vesicles accumulated in the colchicine-treated segment of cervical sympathetic trunk axons. In conclusion, these observations suggest that the stimulus-evoked depletion of large dense-cored vesicle stores in synaptic boutons of the cat superior cervical ganglion is the result of calcium-dependent exocytosis of the large dense-cored vesicle core and that the post-stimulus recovery is critically dependent on microtubule-mediated axonal transport.