Ultrastructure of HRP-labelled neurons: a comparison of two sensitive techniques.

Rat sciatic nerves were transected and placed in a solution of HRP. Following perfusion, L4-6 spinal segments and sensory ganglia were cut into 60 micron sections. Alternate sections were processed with the glucose oxidase (GOD) or the benzidine dihydrochloride (BDHC) procedure. Sections were then either mounted on glass slides for light microscopic (LM) examination or embedded in epoxy resin for sequential light and electron microscopic (EM) analysis. At the LM level, GOD reaction product was granular and confined to the soma and proximal dendrites of motoneurons, while BDHC reacted tissue was characterized by a diffuse labelling of the cytoplasm, extending as far as tertiary dendrites. At the EM level, neurons in tissue processed with the GOD technique contained lysosomal and vesiculotubular elements that were extremely electron dense. Label in BDHC reacted tissue appeared as dense patches of reaction product dispersed throughout the cytoplasm. Possible reasons for the qualitative differences in the reaction product provided by the two techniques as well as suggested applications of the techniques are discussed.