FINE STRUCTURE OF NEURONS AND SYNAPSES IN ENTOPEDUNCULAR NUCLEUS OF CAT

Cat brains were fixed by vascular perfusion with glutaraldehyde and paraformaldehyde and the entopeduncular nucleus was examined by electron microscopy. The fine structure of most neurons in this region does not significantly differ from earlier descriptions of large neurons. Distinctive features of perikarya and dendrites include juxtanuclear Nissl bodies, unique lamellar configurations composed of agranular cisternae separated by thin layers of dense granular matrix and continuous with the granular endoplasmic reticulum, localized swellings of dendrites, and dendritic branchlets or gemmules which invaginate a single nerve terminal. Cell surfaces are ensheathed by interdigitating nerve terminals and glial lamellae. Two types of endings are distinguished on the basis of their diameter and the size of their synaptic vesicles. Further division depends on distribution of the vesicles within a terminal, where the synapses occur, and the presence of postsynaptic bodies. Most terminals are about one micron and contain closely packed synaptic vesicles measuring 515 Å (S. D. 72.7 Å). Larger terminals containing fewer smaller (312 Å) synaptic vesicles and neurofilaments or neurotubules near the periphery have been interpreted as boutons‐en‐passage. It is suggested that different afferent projections end in a similar manner on restricted portions of the neuronal surfaces in the entopeduncular nucleus. Copyright © 1969 The Wistar Institute of Anatomy and Biology