Retrograde tracing of neural pathways with a protein-gold complex. I. Light microscopic detection after silver intensification.

In this study I have used a tracer complex made of wheat germ agglutinin horseradish peroxidase conjugate (WGA*HRP) coupled to colloidal gold for retrograde tracing of neuronal pathways at the light microscopic level. Visualization of the gold was achieved by silver precipitation (the gold silver intensification method) with gold particles acting as specific cores of nucleation. The presence of horseradish peroxidase in the protein conjugate allowed this method to be compared with classical histochemistry using tetramethylbenzidine as a chromogen. The gold silver intensification method proved to be reliable, specific and sensitive. It has been demonstrated to be useful with fixatives containing a high percentage of paraformaldehyde and compatible with histochemical procedures to show projections of transmitter specific pathways.