NONSYNAPTIC AND DENDRITIC EXOCYTOSIS FROM DENSE-CORED VESICLES IN THESUPRACHIASMATIC NUCLEUS

THE sites of exocytosis by dense-cored vesicles (DCVs) from neurones i n the rat suprachiasmatic nucleus (SCN) were studied at the ultrastruc tural level. The tannic acid procedure, which stabilizes extruded prot einaceous substances, was used to demonstrate exocytosis of DCV cores. Fresh brain slices containing the SCN were incubated in media contain ing high levels of potassium (56 mM) or glutamate (10 mM) in the prese nce of tannic acid. Long-term slice explant cultures of the SCN were s imilarly treated. Exocytosis from DCVs occurred from axonal terminals, from dendrites, and occasionally from somata. The sites of DCV exocyt osis were generally nonsynaptic or para-synaptic, including release im mediately adjacent to axo-spinous synaptic densities. These observatio ns show that, in the suprachiasmatic nucleus, neuroactive substances c ontained in DCVs do not necessarily function at synaptic contact zones , but could also act as neuromodulators at non-synaptic sites.