Fig. 1.

Summary of the experimental paradigm, and an example of loss of dendritic orientation bias after deafferentation. (A) Schematic of rat head and brain indicating the barrel-field cortex. The barrels can be delineated by lighter labeling with myelin stains of upper layer tangential sections (as in B) and in deeper layers by a densely stained center (as in D). Each barrel is designated by the primary vibrissa it represents; those colored in the schematic were deafferented in the experimental animals (either two or three rows). Photomicrographs in C and E show the basal dendritic fields of filled layer III pyramidal cells with an overlay of the barrel boundaries. In the barrel field of normal adults, the dendrites of these cells are seen to respect the barrel boundaries and are largely contained within one barrel (C). After 8.5 weeks of peripheral denervation, it is apparent that this dendritic bias is lost and that dendrites of layer III pyramidal cells cross barrel boundaries. This is seen for cells within the barrels drawn with gray boundaries in E [vibrissae of the barrels drawn in pale blue were intact, and vibrissa ∂ showed regrowth (pink outline)]. Blue arrows point to blood vessels used to align sections; orientation of B and D are shown by arrows indicating the medial and caudal directions. (Scale bars, 250 μm.)