Electron Microscopy of Mossy Fibre Endings in Ammon's Horn

Abstract

THE endings of the axons of the granule cells of the dentate fascia in relation to Lorente de Nó's areas CA3 and CA4¹ of Ammon's horn have certain special morphological characteristics as seen in Golgi preparations. These have been described by Cajal², who termed them mossy fibres, analogous to those of the cerebellum. He found that these axons have a tortuous course and that they show characteristic vari-cosities consisting of triangular or star-shaped masses of protoplasm, from the angles of which both short and long processes arise. The main course of this dentate-ammonic tract runs across the bases of the apical dendrites of CA4 and CA3 neurons at right angles to them. The protoplasmic masses come into intimate contact with the apical dendrite or occasionally with the neuronal perikaryon, and were considered by Cajal to be sites of synaptic contact. Lorente de Nó¹ was also of this opinion, but could not decide whether the structures were part of the pyramidal neuron or of the axon terminating on it. According to Cajal² these ‘mossy endings’ could not be stained by reduced silver techniques.