An experimental electron microscopic study on the striatonigral projection in the cat

Summary The ultrastructure of the cat's substantia nigra was investigated from 2–21 days following large lesions of the caudate nucleus and the putamen. From 4 days on a large number of degenerating boutons and degenerating unmyelinated fibers are seen in the substantia nigra, in the pars compacta as well as the pars reticulata. Both parts, mainly the latter, receive striatal afferents. The degeneration in the substantia nigra following striatal lesions is of the dark type. Most of the degenerating boutons apparently are of the type I (see Rinvik and Grofová, 1970) and end on all parts of the nigral cell surface, including the dendritic spines. One instance of a degenerating presynaptic bouton in an axo-axonic synapse has been found. Some degenerating boutons also probably belong to the type II bouton, while degenerating boutons of type III were never seen following the striatal lesions. The electron microscopic identification of early axonal degeneration in the central nervous system, is discussed with reference to the paper of Cohen and Pappas (1969). Problems concerning the pars compacta versus the pars reticulata of the substantia nigra are taken up. The possible sources of origin of the different types of boutons in the cat's substantia nigra, is discussed.On leave of absence from the Anatomical Institute of the Medical Faculty, Charles' University in Prague, with an IBRO grant nr. E. 29.99-1.A preliminary report of some of the observations was presented at the XIIth Congress for Morphologists in Prague, October '69.We gratefully acknowledge the valuable technical assistance of Mrs. J. L. Vaaland and the skilful help by Mrs. B.E. Branil in the preparation of the microphotographs.