The rat orbital and agranular insular prefrontal cortical areas: a cytoarchitectonic and chemoarchitectonic study.

Cytoarchitectonic characterization of borders is necessary for stereological studies (e.g., total cell number estimation), in which particular cortical areas have to be defined. In this study, cytoarchitectonic characteristics are described and illustrated for the rat ventral or orbital frontal cortical areas, i.e., the lateral-, ventrolateral-, ventral- and medial-orbital areas; and for the lateral frontal cortical areas, i.e., the agranular insular and the dorsolateral orbital cortical area. Each cytoarchitectonic-defined boundary is corroborated by one or more of the immunocytochemical stainings for dopaminergic fibers, SMI-32 positive neurons, calbindin and parvalbumin positive neurons. Each immunocytochemical staining, however, shows a characteristic subset of the cytoarchitectonical borders. The dorsal agranular insular area (AId) and the dorsolateral orbital area (DLO) have been subdivided into a dorsal and a ventral part based upon differences between these parts in the Nissl and immunocytochemical stainings. The posterior part of VLO has a different structure and is, therefore, indicated as VLOp (VLO, posterior part).