engleski

Transient role of the subplate neurons in differential ingrowthof pulvinocortical and geniculocortical axons int the prospective striate and extrastriate cortex of the human fetal brain.

The final development of cortical arealization and function establishment requires complex mechanisms, such as the interaction of axon guidance molecules and morphogenes in a strictly defined spatio-temporal frame. In the future visual (striate, extrastriate) cortex, cytoarchitectonic parcellation was extensively studied in the context of histogenetic and neurogenetic processes within the transient fetal zones. We analyzed 7 postmortem human fetal brain samples from 12 to 17 postconceptional weeks (PCW) using classical histological methods, immunohistochemical and immunofluorescent cellular and fibrillary stainings to study cellulo- fibrillar architecture and its developmental dynamics regarding the establishment of the prospective visual neocortex. Our study revealed a conspicuous cellular “corridor” monolayer present during the 13-15 PCW, positioned at the interface of the intermediate zone and deep subplate. It occupies a caudo-ventro-medial position regarding the three-dimensional axis of the developing occipital lobe, approaching but never reaching the incipient calcarine fissure. Immunohistochemistry and double-labeling immunofluorescence revealed that “corridor” cells are NeuN+, Tbr1+, Cplx3+, VLGUT1+, EphA6+, Sema3A+, GFAP- with an underlying Fibronectin+, Synaptophysin+, SNAP25+ fibrillary zone, speaking in favor that they are subplate neurons expressing axon guidance molecules, positioned above the growing axons of the intermediate zone. Considering their position towards the incipient calcarine fissure and guidance molecule expression, they are likely to have a transient role in the navigation of pulvinocortical axons to the prospective extrastriate area and the repulsion of geniculocortical axons to reach their final destination - the prospective striate cortex. This study confirms the importance of the tangential continuum of subplate neurons, this time in the context of precise differential target-oriented growth of massive visual projections.

subplate neurons ; pulvinocortical axons ; geniculocortical axons ; fetal brain

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