PRENATAL DEVELOPMENT OF CALBINDIN D-28K IN HUMAN VISUAL-CORTEX

The distribution of the calcium-binding protein calbindin D-28K (CB) w as investigated in human fetal primary visual cortex. CB is present in Cajal-Retzius cells of layer I, in sparse neurons of the ventricular and intermediate zones (VZ, IZ), and in tangential fibres in IZ by 15 weeks (W) of gestation. Cajal-Retzius cells lose their staining by 30W . CB appears in layers Il-VI mainly from 26W, following an inside-outs ide sequence. Until 34W, CB labelling is in somata and neuropil locate d primarily in layers VA, IVC and V. Then reactive perikarya and punct a increase in layers II-IVA and deep IVB and C, but are reduced in inf ragranular layers from 34W to term. From 30W positive somata form clus ters in the cell-rich bands in layers IV and V and labelled neuropil i n layers III and IV has a periodic pattern from 34W. Also from 34W, nu merous lightly reactive pyramidal cells are present in layers II to IV A in primary, but not secondary, visual cortex. Our results shaw preco cious expression of CB before full laminar differentiation of the cort ex and that some of this expression is transient.