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Synaptic connection from cortical area V4 to V2 in macaque monkey
Author(s) -
Anderson John C.,
Martin Kevan A.C.
Publication year - 2006
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.20914
Subject(s) - dendritic spine , axon , postsynaptic potential , excitatory postsynaptic potential , biology , neuroscience , synapse , projection (relational algebra) , gabaergic , anatomy , dendrite (mathematics) , layer (electronics) , biophysics , inhibitory postsynaptic potential , geometry , materials science , computer science , receptor , nanotechnology , mathematics , biochemistry , hippocampal formation , algorithm
The major target of the V4 projection in V2 is layer 1, where it forms a tangential spread of asymmetric (excitatory) synapses. This is characteristic of a “feedback” projection. Some axons formed discrete clusters of bouton terminaux between lengths of myelinated axon, while others were unbranched and formed a continuous distribution of en passant boutons with no intercalated myelin. Minor projections were found in layers 2/3 and 6. Dendritic spines were the most frequently encountered targets of the V4 projection (80% in layer 1 and layer 2/3, 94% in layer 6). The remaining targets were dendritic shafts. In layer 1, 69% of target dendrites (12% of all targets) had characteristics identifying them as smooth (GABAergic) cells. In layer 2/3 and layer 6 virtually all the shaft synapses were on smooth dendrites (86% and 100%, respectively). Multisynaptic boutons were rare (mean 1.1 synapses per bouton). Synapses formed in layer 6 were smaller than those of layer 1 (mean area 0.073 μm 2 vs. 0.117 μm 2 ). Synapses formed with spines had a more complex postsynaptic density than those formed with dendritic shafts. With respect to targets and synaptic type and size and morphology of synapses, the feedback projection from V4 to V2 resembles those of feedforward projections. The principal difference between the feedforward and feedback projection is in the lamina location of their terminal boutons. The concentration of the V4 projection on layer 1, where it forms asymmetric synapses mainly with spines, suggests that it excites the distal apical dendrites of pyramidal cells. J. Comp. Neurol. 495:709–721, 2006. © 2006 Wiley‐Liss, Inc.