engleski

Morphology, molecular phenotypes and distribution of neurons in developing human corpus callosum

We analyzed distribution, morphology, molecular phenotypes and developmental history of neurons in the human corpus callosum of 26 fetuses, 3 newborns, 5 infants and children and 8 adults (age range: 15 postconceptional weeks - PCW, to 59 years) by means of acetylcholinesterase (AChE) histochemistry and immunocytochemistry for neuronal markers (MAP2, NeuN, NPY, calretinin, and calbindin). In addition to neurons present in developing, callosum-related midline structures (midline sling, callosal septa, subcallosal zone), we found a heterogeneous neuronal population which was present within the callosal trunk itself and most numerous during the fetal period and early postnatal years. This population of intracallosal neurons was already present at 15 PCW and consisted of two subsets of cells: (1) migratory-like or fusiform (MAP2 or calretinin-positive) neurons observed predominantly during mid-gestation and (2) morphologically diverse, differentiated neurons (MAP2- NPY-, calbindin-, and AChE-positive) which were continuously present from 22 PCW onwards, but their numerical density significantly decreased after the early postnatal period due to the growth of the corpus callosum. The morphological differentiation of these neurons reached its peak in the newborn and they remained well developed in early postnatal years, but were only sporadically found in adult brains where they mostly had shrunken somata and poorly stained dendrites. In conclusion, a prominent population of well differentiated intracallosal neurons was present in rapidly growing corpus callosum during the second half of gestation and early postnatal period of human brain development. Therefore, we propose morphogenetic role for intracallosal neurons in guidance, growth and withdrawal of callosal axons.

fetal brain; telencephalic midline; subplate neurons; callosal septa; interhemipheric connectivity

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