Ultrastructural organization of posterior and anterior barrels in the somatosensory cortex of rat.

The somatosensory barrels in layer IV of rat cerebral cortex were studied on uniformly oriented, serial, tangential sections by a combination of light microscope and ultrastructural techniques. Section orientation between sections was maintained by blood vessel patterns. The principal elements of both anterior and posterior barrels were quantified and analyzed in relation to proportional content and nonrandom spatial arrangement over depth in layer IV. Elements studied in this manner included neurons, myelinated axons, apical dendrites, synapses, glial cells, and blood vessels. In general, constituents were found to be arranged in a highly ordered fashion similar to other discretely organized sensory cortical areas. Myelinated axons outlined the basic structure of the barrels with the osmium staining employed. Neurons appeared organized in small clusters. In addition apical dendrites, synapses, and blood vessels also exhibited nonrandom distribution complementary to the organization of axons and neurons. Anterior and posterior barrels differed slightly in their organization of elements.