Electron microscopic demonstration of horseradish peroxidase-tetramethylbenzidine reaction product as a method for identifying sensory nerve fibers in the rat tooth pulp.

The purpose of the present investigation was to determine if the horseradish peroxidase (HRP) technique could be used as a method for labeling sensory nerve fibers (specifically, tooth pulp afferents) for detailed ultrastructural analyses. HRP injected into the trigeminal ganglion of adult rats was taken up by ganglion cell bodies and transported anterogradely to their peripheral endings in the dental tissues. Following perfusion-fixation, the teeth were decalcified in EDTA, sectioned, reacted for HRP activity according to the tetramethylbenzidine (TMB) technique, and processed for electron microscopy. The HRP-TMB reaction product was clearly visible within most of the axons in the dental pulp, appearing as conspicuous, rectangular shaped aggregates of fine rods or needles.