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Targets of horizontal connections in macaque primary visual cortex

Targets of horizontal connections in macaque primary visual cortex Pyramidal neurons within the cerebral cortex are known to make long‐range horizontal connections via an extensive axonal collateral system. The synaptic characteristics and specificities of these connections were studied at the ultrastructural level. Two superficial layer pyramidal cells in the primate striate cortex were labeled by intracellular injections with horseradish peroxidase (HRP) and their axon terminals were subsequently examined with the technique of electron microscopic (EM) serial reconstruction. At the light microscopic level both cells showed the characteristic pattern of widespread, clustered axon collaterals. We examined collateral clusters located near the dendritic field (proximal) and approximately 0.5 mm away (distal). The synapses were of the asymmetric/round vesicle variety (type I), and were therefore presumably excitatory. Three‐quarters of the postsynaptic targets were the dendritic spines of other pyramidal cells. A few of the axodendritic synapses were with the shafts of pyramidal cells, bringing the proportion of pyramidal cell targets to 80%. The remaining labeled endings were made with the dendritic shafts of smooth stellate cells, which are presumed to be (GABA)ergic inhibitory cells. On the basis of serial reconstruction of a few of these cells and their dendrites, a likely candidate for one target inhibitory cell is the small‐medium basket cell. Taken together, this pattern of outputs suggests a mixture of postsynaptic effects mediated by monosynaptic excitation followed by combined disynaptic inhibition and excitation. As a consequence the horizontal connections may well be the substrate for the variety of influences observed between the receptive field center and its surround. http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.png The Journal of Comparative Neurology Wiley

Targets of horizontal connections in macaque primary visual cortex

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References (76)

Publisher
Wiley
Copyright
"Copyright © 1991 Wiley Subscription Services, Inc., A Wiley Company"
ISSN
0021-9967
eISSN
1096-9861
DOI
10.1002/cne.903050303
pmid
1709953
Publisher site
See Article on Publisher Site

Abstract

Pyramidal neurons within the cerebral cortex are known to make long‐range horizontal connections via an extensive axonal collateral system. The synaptic characteristics and specificities of these connections were studied at the ultrastructural level. Two superficial layer pyramidal cells in the primate striate cortex were labeled by intracellular injections with horseradish peroxidase (HRP) and their axon terminals were subsequently examined with the technique of electron microscopic (EM) serial reconstruction. At the light microscopic level both cells showed the characteristic pattern of widespread, clustered axon collaterals. We examined collateral clusters located near the dendritic field (proximal) and approximately 0.5 mm away (distal). The synapses were of the asymmetric/round vesicle variety (type I), and were therefore presumably excitatory. Three‐quarters of the postsynaptic targets were the dendritic spines of other pyramidal cells. A few of the axodendritic synapses were with the shafts of pyramidal cells, bringing the proportion of pyramidal cell targets to 80%. The remaining labeled endings were made with the dendritic shafts of smooth stellate cells, which are presumed to be (GABA)ergic inhibitory cells. On the basis of serial reconstruction of a few of these cells and their dendrites, a likely candidate for one target inhibitory cell is the small‐medium basket cell. Taken together, this pattern of outputs suggests a mixture of postsynaptic effects mediated by monosynaptic excitation followed by combined disynaptic inhibition and excitation. As a consequence the horizontal connections may well be the substrate for the variety of influences observed between the receptive field center and its surround.

Journal

The Journal of Comparative NeurologyWiley

Published: Mar 15, 1992

Keywords: ; ; ; ;

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