Structure and cytoarchitecture of the retrosplenial cortex in the Cairo spiny mouse (Acomys cahirinus)

The retrosplenial cortex is a component of the limbic cortex involved in visually guided memory tasks, including navigation. Using neurochemical markers for the general neuronal population (NeuN), pyramidal neurons (SMI-32), and interneurons (calbindin 28 kDa), we examined the location and cytoarchitectonic divisions of the retrosplenial cortex in the Cairo spiny mouse (Acomys cahirinus). Two distinct regions corresponding to the granular and dysgranular areas (areas 29 and 30) were identified. The criterion for defining the granular cortex was the presence of dendritic bundles located within layers I and II, exhibiting intense SMI-32 staining. SMI-32-positive neuronal somas were predominantly found in layers II and V of area 29 and in layers II-V of area 30. In both areas, calbindin-positive neuronal somas were mainly located in layer II. The total neuronal population was greater in area 29, whereas both SMI-32- and calbindin-positive populations were more numerous in area 30. Based on these findings, we propose that some fundamental features of the retrosplenial cortex in the Acomys are quite similar to those observed in laboratory rodents. At the same time, the retrosplenial cortex in the acomys is larger than in the mouse brain.