Distribution of neuronal populations containing neurofilament protein and calcium-binding proteins in the canine neocortex: regional analysis and cell typology.

Neurophysiological experiments in carnivores have revealed the existence of a large number of cortical regions and an organization of sensory systems quite similar to that found in primates. However, the cyto- and chemoarchitecture of the cerebral cortex is relatively poorly known in carnivores. We analyzed the distribution and typology of classes of neurons containing neurofilament protein or the calcium-binding proteins parvalbumin, calbindin, and calretinin in six neocortical regions of the dog. In all these areas, neurofilament protein was present in a subpopulation of medium-to-large size pyramidal neurons predominantly distributed in layers III and V. Parvalbumin was present in a large population of morphologically diverse interneurons. Small ovoid and multipolar neurons were observed throughout the cortical layers, but predominated in layers II and IV. Layers III and V-VI were characterized by the presence of larger and intensely immunoreactive neurons with bitufted or multipolar morphology, and layers V-VI also contained large multipolar neurons. Calbindin was observed in small round and multipolar interneurons in layer II, and typical double bouquet cells in layer III. Layers IV-VI contained isolated double bouquet cells and large multipolar neurons. A few calbindin-immunoreactive pyramidal neurons were also observed in layer V. Calretinin was localized in bipolar and double bouquet cells in layers II and upper III. The lower part of layer III and layers IV-VI contained rare calretinin-immunoreactive neurons. In some areas, layer III displayed a few large isolated multipolar neurons and pyramidal neurons containing calretinin. In addition, the results show that there is a substantial degree of variability in the distribution of these proteins among cortical regions, and that although they are found in morphologically comparable neuronal types in dog, monkeys, and humans, many differences exist in their regional distribution patterns between carnivores and primates.