Immunocytochemical localization of calcium-binding proteins, calbindin D28K-, calretinin-, and parvalbumin-containing neurons in the dog visual cortex.

Although the dog is widely used to analyze the function of the brain, it is not known whether the distribution of calcium-binding proteins reflects a specific pattern in the visual cortex. The distribution of neurons containing calcium-binding proteins, calbindin D28K, calretinin, and parvalbumin in adult dog visual cortex were studied using immunocytochemistry. We also compared this labeling to that of gamma-aminobutyric acid (GABA). Calbindin D28K-immunoreactive (IR) neurons were predominantly located in layer II/III. Calretinin- and parvalbumin-IR neurons were located throughout the layers with the highest density in layers II/III and IV. The large majority of calbindin D28K-IR neurons were multipolar stellate cells. The majority of the calretinin-IR neurons were vertical fusiform cells with long processes traveling perpendicular to the pial surface. And the large majority of parvalbumin-IR neurons were multipolar stellate and round/oval cells. More than 90% of the calretinin- and parvalbumin-IR neurons were double-labeled with GABA, while approximately 66% of the calbindin D28K-IR neurons contained GABA. This study elucidates the neurochemical structure of calcium-binding proteins. These data will be informative in appreciating the functional significance of different laminar distributions of calcium-binding proteins between species and the differential vulnerability of calcium-binding proteins-containing neurons, with regard to calcium-dependent excitotoxic procedures.