Location of single neurons containing HRP for electron microscopy

A technique is described for finding single neurons containing transported horseradish peroxidase (HRP) for study in the electron microscope. Tissue chopper sections which have been reacted to demonstrate HRP are cleared in glycerol and examined with darkfield light microscopy. The granular reaction product is clearly seen, enabling accurate drawings to be made for later dissection for ultramicrotomy. The neuron sought can then be found within a few microns of the cutting face of the block. While some distortion does occur, most of the cellular morphology remains intact, enabling recognition of specific organelles such as neurosecretory granules in cells which have transported HRP from the neurohypophysis.