Abstract
This investigation was undertaken to determine whether the laminar distribution of corticostriatal neurons differs between different anatomical and functional areas of the frontal lobe. Injections of lectin-conjugated horseradish peroxidase were made into the lateral, intermediate, and medial parts of the head of the caudate nucleus. After injections into the medial part of the caudate, most of the labeled neurons were found in the proreal and subproreal gyri of the prefrontal region. In both gyri, the majority of labeled cells were localized within layer V, and fewer neurons were located in the deeper part of layer III and in layers IV (proreal gyrus) and VI. No labeled neurons were noted in layer II. This distribution contrasted with that seen following injections into the intermediate and lateral parts of the caudate nucleus. In those cases, the majority of labeled cells were located in the pericruciate region (areas 4 and 6) and on the medial and lateral banks of the presylvian sulcus (paraorbital and internal composite areas, respectively). In the paraorbital and internal composite areas, the majority of labeled cells were still localized within layer V, but a larger percentage of labeled neurons were also noted in layer III. In areas 4 and 6, the laminar distribution shifted so that the majority of labeled cells were now located in layer III, with a widespread distribution of neurons throughout layers II-VI. These results indicate that corticostriatal neurons in the frontal lobe have different laminar distributions, depending on the particular anatomical or functional area in which they are located. The majority of neurons in the prefrontal region are located in infragranular layers, while those in the pericruciate region are located in supragranular layers.