Areas of cat auditory cortex as defined by neurofilament proteins expressing SMI-32

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The monoclonal antibody SMI-32 was used to characterize and distinguish individual areas of cat auditory cortex. SMI-32 labels non-phosphorylated epitopes on the high- and medium-molecular weight subunits of neurofilament proteins in cortical pyramidal cells and dendritic trees with the most robust immunoreactivity in layers III and V. Auditory areas with unique patterns of immunoreactivity included: primary auditory cortex (AI), second auditory cortex (AII), dorsal zone (DZ), posterior auditory field (PAF), ventral posterior auditory field (VPAF), ventral auditory field (VAF), temporal cortex (T), insular cortex (IN), anterior auditory field (AAF), and the auditory field of the anterior ectosylvian sulcus (fAES). Unique patterns of labeling intensity, soma shape, soma size, layers of immunoreactivity, laminar distribution of dendritic arbors, and labeled cell density were identified. Features that were consistent in all areas included: layers I and IV neurons are immunonegative; nearly all immunoreactive cells are pyramidal; and immunoreactive neurons are always present in layer V. To quantify the results, the numbers of labeled cells and dendrites, as well as cell diameter, were collected and used as tools for identifying and differentiating areas. Quantification of the labeling patterns also established profiles for ten auditory areas/layers and their degree of immunoreactivity. Areal borders delineated by SMI-32 were highly correlated with tonotopically-defined areal boundaries. Overall, SMI-32 immunoreactivity can delineate ten areas of cat auditory cortex and demarcate topographic borders. The ability to distinguish auditory areas with SMI-32 is valuable for the identification of auditory cerebral areas in electrophysiological, anatomical, and/or behavioral investigations.

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