Layer-specific cellular composition of mouse primary somatosensory and human temporal cortex: a direct 3D confocal...

Accurate quantification of cellular composition is fundamental to understanding the structural and functional organization of the cerebral cortex. In the present study, we quantified the proportions of neurons, glia, and vascular cells (primarily endothelial cells) across the full cortical thickness (layers I-VI) of the mouse primary somatosensory cortex (S1HL) and the human temporal cortex (BA21) using immunocytochemical techniques and a direct 3D counting method. Over 25,000 cells in the mouse and 13,000 cells in the human cortex were individually identified and classified. For this purpose, we utilized EspINA software, which enables precise cell identification and volumetric analysis while preserving laminar and spatial context. Our results reveal marked species-specific differences in cellular proportions: neurons represent approximately 60% of all cells in the mouse S1HL but only 30% in the human BA21. These differences are reflected in the glia-to-neuron ratio (GNR) and non-neuron-to-neuron ratio (nNNR), which were consistently below 1.0 in the mouse (GNR: 0.4; nNNR: 0.6) but significantly higher in the human samples (GNR: 1.5; nNNR: 2.3). By overcoming the limitations of traditional stereological and tissue-homogenization techniques, this study provides a detailed laminar characterization of the cellular composition in these particular cortical regions (mouse S1HL and human BA21).