Naslov
Development of connectivity in the human fetal brain: axonal and synaptic strata and „waiting“ compartments

Autori
Kostović, Ivica

Vrsta, podvrsta i kategorija rada
Sažeci sa skupova, pp prezentacija, znanstveni

Skup
Connect Meeting Tel Aviv 2011

Mjesto i datum
Tel Aviv, Izrael, 01.02.2011. - 03.02.2011

Vrsta sudjelovanja
Predavanje

Vrsta recenzije
Međunarodna recenzija

Ključne riječi
subplate zone

Sažetak
Developmental studies in human fetuses and preterm infants using ultrastructural, microstructural, imaging and electrophysiological techniques have shown that development of connectivity begins early in fetal life. This indirect, non-experimental approach requires delineation of various structural (spatial) and temporal parameters. The following spatial parameters were used: embryonic cellular zones, cytoarchitectonic layers, moduli and columns, synaptic strata, axonal strata, crossroads of pathways, axonal trajectories and segments of white matter. The following key developmental periods were observed: 1) early prenatal areal and laminar differentiation and development of long-range pathways, 2) perinatal reorganization and development of short cortico-cortical circuitry, 3) prolonged fine-tuning of intracortical circuitry during childhood and adolescence. The validity of these parameters was examined on thalamo-cortical, basal forebrain-cortical, cortico-striatal and cortico-cortical connections. Results show that the first (endogeneous) synaptic circuitry develops at 8 weeks post-conception (PCW) in two strata, above and below the cortical plate. This bilaminar pattern continues to exist during mid-end late fetal period (15-23 PCW): 1. deep prominent subplate (SP) zone containing GABAergic-peptidergic, glutamatergic neurons, synapses, large amount of extracellular matrix (ECM) and thalamocortical afferents and 2. Superficial marginal zone containing Cajal-Retzius cells, apical dentritic arborization and „modulatory“ afferents. Major site of circuitry formation in the neocortex is SP, while in limbic cortex main circuitry is formed in the marginal zone. Between 21-23 PCW „waiting“ thalamo-cortical fibers accumulate in the superficial subplate (“access-road” compartment) zone displaying marked regional boundaries. In preterm infants, some thalamocortical fibers relocate to the cortical plate in visual, somatosensory, auditory and associative cortices, causing MR visible lamination and building a framework for sensory-driven connectivity. Cortico-striatal projections were analyzed during formation of cytoarchitectonic modular units (size 1-2, 3 mm in diameter) and histochemical modular compartments in the striatum, which are the most prominent in preterm period. Long cortico-cortical pathways of the neocortex appear in late fetus and preterm infants at the interface between “white” matter and SP. Thalamo-cortical and cortico-cortical fibers are arranged in axonal strata (internal, central and external) and intersect in ECM-rich periventricular crossroads. Development of long and short cortico-cortical “limbic” pathways is faster than in frontal neocortex. However, it is interesting that prefrontal neocortical areas show remarkable circuitry organization in the fetus and that cortico-cortical pathways continue to grow in preterm infants. In the neonatal period, there is a major reorganization of subplate zone, overall lamination of cortex, gyral white matter and different segments of white matter. Development of short cortico-cortical connections, dendritic spines and synapses continue throughout first year of life. In conclusion, analysis of combined histological and MR structural parameters reveals early fetal development of connectivity, strong perinatal reorganization and prolonged fine tuning during childhood and adolescence. (Supported by Unity through Knowledge Fund project 06/07)

Izvorni jezik
Engleski

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