DARK PROFILES IN APPARENTLY-NORMAL CENTRAL NERVOUS SYSTEM - A PROBLEM IN ELECTRON MICROSCOPIC IDENTIFICATION OF EARLY ANTEROGRADE AXONAL DEGENERATION

Tissue taken from the ventrobasal thalamic nucleus of normal adult cats and examined in the electron microscope contained electron‐dense profiles which were morphologically indistinguishable from those seen in tissue from the same area of cats with dorsal column nucleus lesions of two and four days'duration. The number of dense profiles seen in some sections from normal material was greater than the number seen in any of the sections from lesioned material. It is proposed that such dense profiles may represent portions of the “dark” cells of light microscopy. Increased electron density is currently used as the major criterion in electron microscopy for recognizing certain types of experimentally‐induced anterograde axonal degeneration in the central nervous system. It is suggested, on the basis of the data presented here, that a careful review may be necessary of the validity of this criterion. Copyright © 1969 The Wistar Institute of Anatomy and Biology