TRANSIENT COLOCALIZATION OF CALRETININ, PARVALBUMIN, AND CALBINDIN-D28K IN DEVELOPING VISUAL-CORTEX OF MONKEY

This paper reports a double-labelling immunocytochemical study of the three calcium-binding proteins calretinin, parvalbumin, and calbindin- D28k in developing and adult Macaca primary visual cortex. In adult vi sual cortex, each protein marks a subset of GABAergic neurons with a c haracteristic laminar distribution and virtually no co-localization wa s found between these three proteins, suggesting that each calcium-bin ding protein may serve as a marker for one or more cortical subcircuit s. The immature visual cortex, immunostained using identical technique s was then analysed to determine if each calcium-binding protein could serve as a developmental marker for these circuits. The Cajal-Retzius cells of layer 1 contained all three proteins during development. Cal bindin-D28k and calretinin were co-localized starting at Fd (foetal da y) 45 and after Fd125, parvalbumin also was present in the same Cajal- Retzius cells. All three proteins continued to be expressed until the Cajal-Retzius disappeared postnatally. In layers 2-6 calbindin-D28k an d calretinin were never co-localized. In contrast, parvalbumin and cal retinin were found in neurons of deep layer 3 from Fd 155 to postnatal (P6) weeks with a few persisting even later. Before birth almost all PV+ neurons in layers P6 were CaB+, but by P3 weeks only a few PV+/CaB + neurons remained in layer 4C and these completely disappeared by P6 weeks. Co-localization in layer 4 neurons overlaps the period of ocula r dominance segregation, suggesting that the onset of cortical maturit y coincides with segregation of calcium-binding proteins within the GA BA interneurons.