LOCALIZATION OF SYNAPTOTAGMIN IN THE REGENERATING SPROUTS EMANATING FROM THE NODES OF RANVIER

Localization of synaptotagmin, a Ca2+-binding protein associated with synaptic vesicles, in regenerating axons was investigated by immunocyt ochemistry in the injured rat sciatic nerves, The early regenerating a xonal sprouts emanating from nodes of Ranvier exhibited synaptotagmin immunoreactivity on vesicles, vacuoles and surface plasma membranes. I n the well-developed regenerating sprouts extending through the space between Schwann cell basal lamina and myelin sheath of the parent axon , the growing tips, i.e., typical growth cones, exhibited an intense i mmunoreaction on vesicles, vacuoles and surface plasma membranes, whil e the stem regions where the sprouts were continuous with the parent a xon exhibited almost no immunoreaction on any organelles including pla sma membranes, These findings suggest that synaptotagmin-immunoreactiv e vesicles and vacuoles might be utilized for the supply of membrane c omponents to the surface plasma membrane in the growth cone, Synaptota gmin which is known to regulate membrane fusion of synaptic vesicles w ith presynaptic plasma membranes in a Ca2+-dependent manner in synapse s may participate in the regulation of the membrane fusion between the vesicles and plasma membranes in growth cones.