Vol. 4, Issue 1 (2019)
Cellular migration and histogenesis of cerebral cortex with functional correlations in human fetuses at different weeks of gestation
Author(s): Arpan Haldar, Sanjukta Sahoo, Soumya Chakraborty, Provas Banerjee, Dipti Basu
Abstract: Cerebral cortex in humans is thinnest at 8 weeks of intra-uterine life and becomes thicker progressively along the superolateral and inferolateral walls from frontal to occipital poles. Histogenesis of the cerebral cortex (neocortex) - The layered structure of the adult cerebral cortex forms from the telencephalon as the surface area increases. At first there are 3 zones to the cortex: 1) germinal zone, immediately surrounding the lateral ventricle, 2) intermediate zone, becomes the white matter, and 3) marginal zone, becomes the gray matter. Neuroblasts of the germinal zone divide and migrate into the marginal zone to become neurons and glial cells. The marginal zone is formed by cells migrating a) early, which become the deeper layers of the cortex while those that migrate b) later, form the more superficial layers. Between 6 and 8 months 6 layers are observed in the marginal zone of the neocortex, recognized by cellular and fiber laminate. The 6-layered cortex is further distinguished as having two main divisions: 1) the deeper highly cellular pyramidal layer are layers II - VI and 2) the more superficial molecular layer (layer I) is comprised mostly of fibers. The intermediate zone becomes the white matter of the cerebral hemispheres which is traversed by the processes of the cells migrating toward the surface. At birth the neocortex has a 6-layered structure while cortical areas dealing with olfaction (paleocortex) and the hippocampal formation (archicortex) do not have a six-layered structure. Cerebrum of 32 still born human foetuses of both sexes were procured from the Department of Gynaecology after spontaneous miscarriages and therapeutic abortions. 5 mm tissues from frontal, temporal, parietal and occipital cortices were dissected and kept in 10% Formalin overnight for better fixation. Then they were processed for histological examination using H/E stain. The neurons were granular until 18 weeks of gestation and showed few pyramidal cells at 24 weeks and then they showed sesqui laminar pattern with predominance of Betz cells in frontal and temporal cortex and predominance of granule cells were seen in parietal and occipital cortex. Cell migration and histogenesis of cerebral cortices are important in disorders like epilepsy or epilepsy.