The use of a sodium tungstate developer markedly improves the electron microscopic localization of zinc by the Timm method

The Timm's sulfide silver method is Frequently used for the demonstration o f the mossy fiber bundle or sprouted mossy fibers in the normal or epilepti c hippocampal dentate gyrus. Under the light microscope the results are exc ellent, but the ultrastructure is considerably impaired;Ind the silver grai ns produced are too large as compared to the sizes of intra-synaptic struct ures. The present study was meant to test a series of physical developers c ontaining, instead of gum arabic, sodium tungstate as protective colloid. O ne of them left the ultrastructure fairly intact and produced small, round silver grains, making it possible to precisely locate zinc in mossy termina ls. With this method, it could be demonstrated that zinc is contained insid e synaptic vesicles in the resting axon terminals of granule cells. As a co nsequence of prolonged sodium sulfide perfusion, zinc is released from syna ptic vesicles and enters the synaptic cleft. (C) 2000 Elsevier Science B.V. All rights reserved.