Hindlimb Representation in the Spiny Mouse Sensorimotor Cortex

The Cairo spiny mouse (Acomys cahirinus), a promising animal model in neuroscience, lacks a detailed neuroanatomical map of its cerebral cortex. This study aims to delineate the location and internal subdivision of the sensorimotor cortex, specifically the region controlling the hindlimb. For this purpose, retrograde tracing from the lumbar spinal cord using Fast Blue was combined with immunohistochemical characterization using neuronal markers (NeuN, SMI-32, and calbindin 28 kDa) in adult animals. Fast Blue-labeled neurons were identified in layer V within the cortical region defined as the sensorimotor cortex responsible for hindlimb control. Within this region, the general cytoarchitecture was defined using NeuN, which allowed visualization of all cortical layers. The border between the lateral and medial sub-areas was clearly identified by SMI-32 immunostaining, which showed denser labeling in the lateral zone (presumably the primary somatosensory cortex) compared to the medial zone (presumably the secondary motor cortex). Within the defined layers and sub-areas, a comprehensive analysis of the calbindin-expressing interneuron population was performed, revealing significant interareal differences in soma size and cellular density of calbindin-positive neurons exclusively within layers III-IV. These findings provide the first detailed map of the hindlimb sensorimotor cortex in spiny mice, establishing a crucial neuroanatomical foundation for future studies using this novel model in sensorimotor research.