Electron microscopy of experimental axonal degeneration in photochemically modified Golgi preparations: a procedure for precise mapping of nervous connections.

A new version is presented of a procedure for bleaching (deimpregnating) silver chromate Golgi preparations through ultraviolet (UV) light irradiation followed by thiosulphate treatment, leaving only scattered particles of metallic silver. This version gives a better ultrastructure of the tissue than obtained before. Moreover, the results of studying a specific connection in such material are reported. The perforant path, connecting the entorhinal area with the hippocampus and fascia dentata, was transected in the rat and after a 2-day survival the brain was subjected to Golgi impregnation followed by the deimpregnation procedure. Blocks of tissue containing impregnated fascia dentata granule cell dendrites were selected for electron microscopy. Postsynaptic thickenings associated with degenerated boutons could be discerned within the deimpregnated dendrites, proving that the entorhino-dentate fibres end on the dendrites of the granule cells (smooth surfaces as well as spines) and that they end at asymmetric junctions (of Gray's type 1). While this conclusion was as expected from previous experimental studies carried out with different methods it is thought that the same strategy for cell-to-cell mapping of nervous connections may be used also in other parts of the central nervous system.