This work is dedicated to Steven A. Joseph.
Layer V in cat primary auditory cortex (AI): Cellular architecture and identification of projection neurons †
Article first published online: 1 MAY 2001
Copyright © 2001 Wiley-Liss, Inc.
Journal of Comparative Neurology
Volume 434, Issue 4, pages 379–412, 11 June 2001
How to Cite
Winer, J. A. and Prieto, J. J. (2001), Layer V in cat primary auditory cortex (AI): Cellular architecture and identification of projection neurons . J. Comp. Neurol., 434: 379–412. doi: 10.1002/cne.1183
- Issue published online: 1 MAY 2001
- Article first published online: 1 MAY 2001
- Manuscript Accepted: 8 FEB 2001
- Manuscript Revised: 12 SEP 2000
- Manuscript Received: 10 MAY 2000
- National Institutes of Health. Grant Number: R01 DC 02319-21
- layer 5;
- cerebral cortex;
- corticothalamic projection cells
The cytoarchitectonic organization and the structure of layer V neuronal populations in cat primary auditory cortex (AI) were analyzed in Golgi, Nissl, immunocytochemical, and plastic-embedded preparations from mature specimens. The major cell types were characterized as a prelude to identifying their connections with the thalamus, midbrain, and cerebral cortex using axoplasmic transport methods. The goal was to describe the structure and connections of layer V neurons more fully. Layer V has three sublayers based on the types of neuron and their sublaminar projections. Four types of pyramidal and three kinds of nonpyramidal cells were present. Classic pyramidal cells had a long apical dendrite, robust basal arbors, and an axon with both local and corticofugal projections. Only the largest pyramidal cell apical dendrites reached the supragranular layers, and their somata were found mainly in layer Vb. Three types departed from the classic pattern; these were the star, fusiform, and inverted pyramidal neurons. Nonpyramidal cells ranged from large multipolar neurons with radiating dendrites, to Martinotti cells, with smooth dendrites and a primary trunk oriented toward the white matter. Many nonpyramidal cells were multipolar, of which three subtypes (large, medium, and small) were identified; bipolar and other types also were seen. Their axons formed local projections within layer V, often near pyramidal neurons. Several features distinguish layer V from other layers in AI. The largest pyramidal neurons were in layer V. Layer V neuronal diversity aligns it with layer VI (Prieto and Winer  J. Comp. Neurol. 404:332–358), and it is consistent with the many connectional systems in layer V, each of which has specific sublaminar and neuronal origins. The infragranular layers are the source for several parallel descending systems. There were significant differences in somatic size among these projection neurons. This finding implies that diverse corticofugal roles in sensorimotor processing may require a correspondingly wide range of neuronal architecture. J. Comp. Neurol. 434:379–412, 2001. © 2001 Wiley-Liss, Inc.