engleski

Changing patterns of synaptotagmin and synaptoporin expression in the subplate and adjacent structures of the human fetal brain

The subplate (SP), representing and outstandingly wide zone in the developing human brain, has no direct counterpart in the adult. It plays a major role in various developmental key events involved in the formation of mature connections of the cerebral cortex. Despite its functional and morphological prominence it has so far only seldom been considered adequately in studies on normal or disturbed development. The objective of this study was to investigate the expression paterns of two synapse-related proteins ; synaptotagmin (st) and synaptoporin (sp) ; within the SP and adjacent structures at different stages of fetal development. At 19 weeks of gestation (wg) the intermediate zone, subjacent to the subplate, contains stimmunoreactive (ir) parallel oriented fibers. Later on (at 24 wg) obliquely oriented fibers are observed in the SP. Moreover, the SP contains a high number of st-ir nerve cells ; variuos large to medium- sized SP neurons are immunolabelled. The number of irfibers and neurons is distincly reduced by 33 wg. From that age onwards ir puncta in the cortical plate predominate. At 25 wg sp-ir fibers, mainly lying singly, are seen in the upper part of the SP and in the cortical plate. The latter, moreover, displays pericellularly arranged fibers. Such fibers are no longer visible in brains at later stages of development (i.e. after 30 wg). The SP is known to be an intermediate target (waiting compartment) for various afferents of the cerebral cortex which sequentially appear in the SP. Accordingly the results of this study show that the SP continuously undergoes profound changes during the second half of gestation. The time frame of fibrous st expression suggests that thalamocortical fibers contain this protein. The high number of st-ir SP nerve cells (from 24 wg) suggets an involvement of st in a transient neuronal circuit. The pattern of sp-ir structures may point to an involvement of this protein in a SP projection to the cortical plate. On the whole, the dynamic changes in the SP and adjacent structures should be considered in developmental neuropathology and might explain the changing developmental outcome after SP-lesion in prematurely born infants.

subplate; human fetal brain; synaptoporin; synaptotagmin

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