Comparative strength and dendritic organization of thalamocortical and corticocortical synapses onto excitatory layer 4 neurons.
Thalamus is a potent driver of cortical activity even though cortical synapses onto excitatory layer 4 neurons outnumber thalamic synapses 10 to 1. Previous in vitro studies have proposed that thalamocortical (TC) synapses are stronger than corticocortical (CC) synapses. Here, we investigated possible anatomical and physiological differences between these inputs in the rat in vivo. We developed a high-throughput light microscopy method, validated by electron microscopy, to completely map the locations of synapses across an entire dendritic tree. This demonstrated that TC synapses are slightly more proximal to the soma than CC synapses, but detailed compartmental modeling predicted that dendritic filtering does not appreciably favor one synaptic class over another. Measurements of synaptic strength in intact animals confirmed that both TC and CC synapses are weak and approximately equivalent. We conclude that thalamic effectiveness does not rely on enhanced TC strength, but rather on coincident activation of converging inputs.
Department of Neuroscience and Kavli Institute for Brain Science, Columbia University, New York, New York 10032.
Carl E
CE
Schoonover
Department of Neuroscience and Kavli Institute for Brain Science, Columbia University, New York, New York 10032.
Juan-Carlos
JC
Tapia
Max Planck Institute for Medical Research, D-69120 Heidelberg, Germany.
Verena C
VC
Schilling
The Florey Institute of Neuroscience and Mental Health, Parkville VIC 3010, Australia, and.
Verena
V
Wimmer
Department of Pathology, Columbia University, New York, New York 10032.
Richard
R
Blazeski
Department of Neuroscience and Kavli Institute for Brain Science, Columbia University, New York, New York 10032.
Wanying
W
Zhang
Department of Neuroscience and Kavli Institute for Brain Science, Columbia University, New York, New York 10032, Department of Pathology, Columbia University, New York, New York 10032.
Carol A
CA
Mason
Department of Neuroscience and Kavli Institute for Brain Science, Columbia University, New York, New York 10032, randybruno@columbia.edu.
Randy M
RM
Bruno
D000200:Action Potentials / Q000502:physiology; D000818:Animals; D002540:Cerebral Cortex / Q000502:physiology*; D003712:Dendrites / Q000502:physiology*; D049229:Dendritic Spines / Q000502:physiology; D008959:Models, Neurological; D009434:Neural Pathways / Q000502:physiology; D009474:Neurons / Q000502:physiology*; D051381:Rats; D017208:Rats, Wistar; D013569:Synapses / Q000502:physiology*; D009435:Synaptic Transmission / Q000502:physiology; D013788:Thalamus / Q000502:physiology*
compartmental; confocal; dendrite; in vivo; optogenetics; synapse