Localization of Synaptotagmin in the Regenerating Sprouts Emanating from the Nodes of Ranvier.

Abstract

Localization of synaptotagmin, a Ca2+-binding protein associated with synaptic vesicles, in regenerating axons was investigated by immunocytochemistry in the injured rat sciatic nerves. The early regenerating axonal sprouts emanating from nodes of Ranvier exhibited synaptotagmin immunoreactivity on vesicles, vacuoles and surface plasma membranes. In 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 immunoreaction on vesicles, vacuoles and surface plasma membranes, while the stem regions where the sprouts were continuous with the parent axon exhibited almost no immunoreaction on any organelles including plasma membranes. These findings suggest that synaptotagmin-immunoreactive vesicles and vacuoles might be utilized for the supply of membrane components to the surface plasma membrane in the growth cone. Synaptotagmin which is known to regulate membrane fusion of synaptic vesicles with presynaptic plasma membranes in a Ca2+-dependent manner in synapses may participate in the regulation of the membrane fusion between the vesicles and plasma membranes in growth cones.