Morphometric analysis of the columnar innervation domain of neurons connecting layer 4 and layer 2/3 of juvenile rat barrel cortex.
We have investigated the dendritic and axonal morphology of connected pairs of L4 spiny neurons and L2/3 pyramidal cells in rat barrel cortex. The 'projection' field of the axons of L4 spiny neurons in layers 2/3, 4 and 5 has a width of 400-500 microm thereby defining an anatomical barrel-column. In layer 2/3, the averaged axonal 'projection' field of L4 spiny neurons together with the dendritic 'receptive' field of the connected L2/3 pyramidal cells form a mostly column-restricted anatomical L4-to-L2/3 'innervation domain' that extends 300-400 microm and includes mostly basal dendrites. In the L4-to-L2/3 innervation domain a single L4 spiny neuron contacts approximately 300-400 pyramidal cells while in the L4-to-L4 innervation domain it contacts approximately 200 other L4 spiny neurons. Similarly approximately 300-400 L4 spiny neurons converge onto a single pyramidal cell and approximately 200 L4 spiny neurons innervate another L4 spiny neuron. The L2/3 pyramidal cell axon has a vertical projection field spanning all cortical layers, and a long-range horizontal field in layers 2/3 (width 1,100-1,200 microm) and 5 (700-800 microm) projecting across column borders. The results suggest that the flow of excitation within a barrel-column is determined by the largely columnar confinement of the L4-to-L4 and L4-to-L2/3 innervation domains. A whisker deflection activates approximately 140 L4 spiny neurons that will generate EPSPs in most barrel-related L2/3 pyramidal cells of a principal whisker column. The translaminar synaptic transmission to layer 2/3 and the axonal projection fields of L2/3 pyramidal cells are the major determinants of the dynamic, multi-columnar map in which a single whisker deflection is represented in the cortex.
Lübke
Joachim
J
Anatomisches Institut der Albert-Ludwigs-Universität Freiburg, Albertstrasse 17, D-79104 Freiburg, Germany.
Roth
Arnd
A
Feldmeyer
Dirk
D
Sakmann
Bert
B
D000367:Age Factors; D000818:Animals; D001369:Axons / Q000502:physiology / Q000648:ultrastructure; D002540:Cerebral Cortex / Q000166:cytology* / Q000502:physiology; D003712:Dendrites / Q000502:physiology / Q000648:ultrastructure; D019706:Excitatory Postsynaptic Potentials / Q000502:physiology; D009415:Nerve Net / Q000166:cytology* / Q000502:physiology; D009474:Neurons / Q000166:cytology* / Q000502:physiology; D017966:Pyramidal Cells / Q000166:cytology / Q000502:physiology; D051381:Rats; D017208:Rats, Wistar