Differential cortical laminar structure revealed by NeuN immunostaining and myeloarchitecture between sulcal and gyral regions independent of sexual dimorphisms in the ferret cerebrum.

The purpose of this study was to quantitatively clarify differences in laminar structure and myeloarchitecture of sulcal and gyral regions of the cerebral cortex of ferrets. Histological sections of cerebrum from male and female ferrets at postnatal day 90 were made at the coronal plane, and were immunostained with anti-NeuN or anti-myelin basic protein (MBP). Thickness was estimated in the entire depth or three strata, that is, layer I, outer (layers II-III) and inner (layers IV-VI) strata of the neocortex in representative five sulcal and seven gyral regions. As with the entire cortical depth, outer and inner strata were significantly thinner in the sulcal bottoms than in the gyral crowns, whereas layer I had about twofold greater thickness in the sulcal bottoms. However, thicknesses of the entire cortical depth and each cortical stratum were not statistically different among five sulcal regions or seven gyral regions examined. By MBP immunostaining, myelin fibers ran tangentially through the superficial regions of layer I in gyral crowns. Those fibers were relatively denser in gyri of frontal and temporal regions, and relatively sparse in gyri of parietal and occipital regions, although their density in any gyri was not different between sexes. These results show a differential laminar structure and myeloarchitecture between the sulcal and gyral regions of the ferret cerebral cortex present in both sexes. Myelination of layer I tangential fibers varied among primary gyri and was weaker in phylogenetically higher-order cortical gyri. Anat Rec, 299:1003-1011, 2016. © 2016 Wiley Periodicals, Inc.