Classification of plastic-embedded rat seminiferous epithelium prior to electron microscopy

Systematic electron microscopic studies of the changes which take place during the cycle of the rat seminiferous epithelium require that each of the 14 stages of the cycle are identified in the light microscope in plastic-embedded material allowing each stage to be trimmed out separately before the electron microscopic study. The classification of the 14 stages has originally been based on the morphological characteristics seen in paraffin-embedded tissue after PAS-staining. PAS-staining is less effective in plastic-embedded material, and this may be a main reason why electron microscopic findings of the seminiferous epithelium relatively seldom are related to the stages of the cycle. In the present paper a method is described by which the 14 stages of the cycle can be easily identified in the light microscope in plastic-embedded tissue. Some of the stages could be subdivided and a total of 23 stages were distinguished. This constitutes a safe method allowing accurate classification prior to electron microscopic examination of the seminiferous epithelium.