Dendrosomes: a new preparation of isolated neurosecretory dendrites

To investigate secretion from dendrites of magnocellular neurosecretory neurons we have developed a preparation of isolated portions of the dendrites analogous to synaptosomes and neurosecretosomes. The dendrites of magnocellular neurons extend into the ventral glial lamina ventral and lateral to the nucleus. The ventral glial lamina is dissected out and gently homogenized to shear off portions of the dendrites. These re-seal to form granule-filled, membrane-bound structures which we refer to as 'dendrosomes'. Dendrosomes were recovered by differential centrifugation and identified by light and electron microscopy either in unlabelled preparations or by immunocytochemistry. Stimulation of dendrosomes with 56 mM potassium in the presence of tannic acid, which preserves exocytosed granule cores so that they can be visualized electron microscopically, demonstrates that, in response to a depolarizing stimulus, dendrosomes are capable of secreting by exocytosis the neuropeptides oxytocin (OT) and vasopressin (VP) and their co-packaged neurophysins.