Prenatal development of calbindin D-28K in human visual cortex

The distribution of the calcium-binding protein calbindin D-28K (CB) wasinvestigated in human fetal primary visual cortex. CB is present inCajal-Retzius cells of layer I, in sparse neurons of the ventricular andintermediate 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 inlayers II-VI mainly from 26W, following an inside-outside sequence. Until34W, CB labelling is in somata and neuropil located primarily in layersIVA, IVC and V. Then reactive perikarya and puncta increase in layersII-IVA and deep IVB and C, but are reduced in infragranular layers from 34Wto term. From 30W positive somata form clusters in the cell-rich bands inlayers IV and V and labelled neuropil in layers III and IV has a periodicpattern from 34W. Also from 34W, numerous lightly reactive pyramidal cellsare present in layers II to IVA in primary, but not secondary, visualcortex. Our results show precocious expression of CB before full laminardifferentiation of the cortex and that some of this expression istransient.