The number, size and spatial distribution of neurons in Lamina IV of the mouse SmI neocortex†
Some of this work was presented at the Third Annual Meeting of the Society for Neuroscience, November, 1973.
Abstract
We located the corresponding barrel in Layer IV of the mouse Sml cortex in eleven cerebral hemispheres sectioned in a plane tangential to the pia overlying Sml and in one sectioned in a plane normal to the pia. All of the brains were serially sectioned and prepared by a combined Golgi-Nissl method. In the section in which barrel C-1 could be optimally visualized each neuronal soma was outlined with a camera lucida and the cross-sectional area measured with the aid of a small computer.
In all, nearly 7,000 neurons were measured. We estimate that on average barrel C-1 contains about 2,000 neurons. The mean cross-sectional area of the perikarya is 62.51 μ2 (S.D. ± 14.51 μ2) and the size distribution of the neurons is unimodal and positively skewed. There is no segregation of cells within the barrel on the basis of size. The spatial distribution of cells in the barrel is fairly constant, from specimen to specimen, and the characteristic cytoarchitectonic appearance of the barrel can be related to regional neuronal packing density sicne there are at least 1.6 as many neurons in the sides of the barrel as the hollow.
The constancy of the cellular composition of the barrels indicates that the mechanisms responsible for the development of the mouse SmI cortex are fairly rigidly determined, and that the barrel field should lend itself well to further quantitative, developmental and physiological analysis.
