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The conformation, cytology and synaptology of the opossum inferior olivary nucleus
Author(s) -
Bowman Michael H.,
King James S.
Publication year - 1973
Publication title -
journal of comparative neurology
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.855
H-Index - 209
eISSN - 1096-9861
pISSN - 0021-9967
DOI - 10.1002/cne.901480407
Subject(s) - inferior olivary nucleus , anatomy , biology , cytoarchitecture , nissl body , neuropil , superior olivary complex , opossum , medulla oblongata , hypoglossal nucleus , nucleus , inferior colliculus , neuroscience , central nervous system , staining , genetics
This investigation was undertaken to determine the detailed structure and ultrastructure of the inferior olivary nucleus of the opossum ( Didelphis marsupialis virginiana ). Serial sections of the medulla oblongata were cut in either the frontal, parasagittal or horizontal plane and stained by routine Nissl procedures to determine the cytoarchitecture of the inferior olivary nuclear mass. Because of the apparent lack of distinct principal and accessory olivary subnuclei, a polyethylene plastic scaled reconstruction was made to determine the morphological features of the opossum olivary complex. A descriptive nomenclature was adopted rather than a terminology that would imply analogy with other species. Both light microscopic (Nissl and Golgi) and electron microscopic analyses disclosed a single type of neuron throughout the inferior olivary nucleus. These small to medium (10–30 μ), pleomorphic nerve cells contain a round, eccentric nucleus and a modest amount of cytoplasm. Additional features of olivary somata include diffuse Nissl substance, abundant subsurface cisternae and spines. The moderately branched and entangled dendritic arbor of the olivary neuron bears simple thorns on its proximal, intermediate and distal portions. Multiple spine clusters and unique excrescences termed spine crowned appendages are located on intermediate and distal dendrites. Complex synaptic islands (glomeruli) are found throughout the nucleus and contain a central core of profiles identifiable as spine crowned appendages and small dendrites and/or spines. These core elements are surrounded by numerous boutons which synaptically contact them, and by a small intermediate dendrite. A mantle of astroglial lamellae appears to isolate the glomerulus from the surrounding neuropil. The majority of the synaptic profiles that contact the soma and proximal, intermediate and distal dendrites contain either round vesicles (type 1) or pleomorphic vesicles (type 2). An estimation of the distribution of these terminals indicates that a predominance of type 2 terminals end upon the somata and proximal dendrites, whereas more distal dendritic ramifications receive an approximately equal proportion of the two types of endings. In addition to these endings ( types 1 and 2 ), large efflorescent terminals contact distal dendrites located throughout the nucleus. Furthermore, in different areas of the nuclear realm, small boutons containing only flattened vesicles and fibrous profiles containing pleomorphic vesicles contact intermediate and distal dendrites, respectively. A few large marginal reticular neurons are present around the permiter of the inferior olivary nucleus. These cells send one or more dendrites into the nuclear domain. Such intraolivary dendrites may be synaptically contacted by the same types of terminals that end upon olivary neurons.