POSTNATAL-DEVELOPMENT OF CALCIUM-BINDING PROTEINS CALBINDIN AND PARVALBUMIN IN HUMAN VISUAL-CORTEX

In adult primate visual cortex, the calcium-binding proteins calbindin (CB) and parvalbumin (PV) are localized in different subsets of GABAe rgic neurons with a characteristic laminar distribution. However, the emergence and development of CB and PV in relation to the periods of f unctional maturation of the human visual cortex are not known. Therefo re. we examined (i) postnatal changes in the distribution of immunorea ctivity (ir) for CB and PV in the visual cortex; (ii) the pattern of c hanges in immunoreactivity in relation to the synaptic maturation; and (iii) differences in the maturation of GB and PV immunoreactivity bet ween areas 17 and 18. We found a consistently high expression of CB in neonatal visual cortex, particularly in layer IV and infragranular la yers. However, despite an early appearance of PV, its peak in developm ent occurred only after 2 months of age, characterized by a transient overexpression in the thalamo-recipient layer IV and a continuous insi de-out maturation in supragranular layers. The neonatal pattern of hig h CB-ir in layers IV-VI was transformed during infancy and childhood i nto an adult pattern of high CB-ir in layer II, hut low CB-ir in layer IV and infragranular layers. There was no difference in pattern and t empo of maturation of calcium-binding proteins between area 17 and 18. indicating simultaneous development of cortical inhibitory circuits a mong cytoarchitectonically and functionally distinct cortical areas. I n addition, the reorganization of CB/PV expression temporally and spat ially coincides with the course of cortical synaptogenesis, and deline ates the major stages of maturation of the human visual cortex.