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Neuronal and synaptic organization of the normal dorsal lateral geniculate nucleus of the squirrel monkey, Saimiri sciureus
Author(s) -
WongRiley Margaret T. T.
Publication year - 1972
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.901440103
Subject(s) - biology , synaptic vesicle , golgi apparatus , axon , electron microscope , vesicle , squirrel monkey , saimiri sciureus , geniculate , neuroscience , synapse , lateral geniculate nucleus , anatomy , nucleus , retina , microbiology and biotechnology , membrane , genetics , physics , endoplasmic reticulum , optics
The normal cellular architecture and synaptic organization of the dorsal lateral geniculate nucleus (LGN) of Saimiri sciureus has been studied with light and electron microscopic techniques. Golgi preparations reveal at least four types of neurons: type I and II are large and medium‐sized cells; type II cells have grape‐like dendritic protrusions, while type I cells do not. Type III small neurons have very long dendrites that cross laminar borders freely; and type IV very small neurons resemble glial cells. The last type may correspond to small, spindle‐shaped or round, neurons which show somato‐dendritic synapses under the electron microscope. Types I and II neurons are regarded as geniculocortical relay cells. Types III and IV are good candidates for interneurons. A serial dorsal to ventral interlaminar dendritic overlap is noted throughout the LGN. With the electron microscope, several types of axonal profiles can be seen: large axons with round vesicles (RL's), small axons with round vesicles (RS's), and intermediate axons with flattened or pleomorphic vesicles (F's). The RL's are retinal terminals; some of the RS's are corticogeniculate fibers; while the F's are believed to be intrageniculate in origin. The F type is then subdivided into F 1 and F 2 ; F 1 being darker and containing more evenly dispersed synaptic vesicles than F 2 . There is also a distinct class of presynaptic dendrites, F d , which contains pleomorphic vesicles and has a light cytoplasmic density similar to that of the F 2 profiles. It is possible that some or all of the F 2 processes may prove to be dendritic. Somato‐dendritic synapses arise from very small neurons and form a part of the normal synaptic organization in the LGN. The RL and RS axons form asymmetrical synaptic contacts, whereas the F (F 1 , F 2 and F d ) processes mainly form symmetrical ones. Non‐synaptic filamentous contacts are also found. The rules of synaptic connectivity are such that the RL and RS terminals are never synaptic to either the RL or the RS terminals, and presynaptic to other dendrites. If the F profiles contact each other, the F 1 axon is never the post‐synaptic element. The RL and F processes synapse upon any part of the perikaryal and dendritic surfaces, whereas the RS terminals do not contact the soma.