Anterograde tracing of horseradish peroxidase (HRP) with the electron microscope using the tetramethylbenzidine reaction.

A technique is described for anterograde horseradish peroxidase (HRP) tracing with the electron microscope using tetramethylbenzidine (TMB) histochemistry. Following HRP injection into the primary visual cortex or one eye of rabbits the superior colliculus was studied with the light and electron microscope in adjacent sections. In target preparations from the colliculus examined with the electron microscope labelled axons and axon terminals were found. The TMB reaction product was identified as crystal like electron-dense structures. In control sections from the opposite colliculus the neuropil was free from label.