Improvement of the electron microscopic detection of peroxidase activity by means of the silver intensification of the diaminobenzidine reaction in the rat nervous system.

For the detection of the peroxidase activity at the electron microscopic level, a recently developed post-intensification method is applied, which plates metallic gold onto the end-product of the diaminobenzidine (DAB) reaction. Ultrastructural analysis of rat hypoglossal neurons labeled with horseradish peroxidase (HRP) through axonal transport reveals that the method is highly specific and more sensitive than the classical HRP--DAB--OsO4 sequence. Gold grains of 2--15 nm in diameter are present in the HRP-containing organelles of the neuron, whereas other elements of the brain tissue do not contain metallic gold.