THE DEVELOPMENT OF PARVALBUMIN AND CALBINDIN-D28K IMMUNOREACTIVE INTERNEURONS IN KITTEN VISUAL CORTICAL AREAS

Calbindin-D and parvalbumin are calcium binding proteins which are fou nd in non-overlapping subpopulations of GABA-ergic interneurons in mam malian neocortex. We studied the development of these calcium-binding proteins in interneurons of cat striate and extrastriate cortical area s which have differing patterns of connectivity and follow different d evelopmental timetables. We examined primary visual areas 17 and 18, s econdary visual area 19, medial lateral suprasylvian and lateral supra sylvian areas (MLS and LLS) and association areas 7 and the splenial v isual area from the day of birth (PO) through P101. Parvalbumin-immuno reactive (ir) interneurons followed the inside-out pattern of maturati on of cortical laminae. They were located only in infragranular layers at the earliest ages and were not observed in the overlying cortical plate. At 3 weeks of age, when cortical lamination is mature, parvalbu min stained cells were found in all cortical layers except layer I. Th e number of stained secondary and tertiary dendrites in the parvalbumi n-ir interneuronal population decreased with age. This change was asso ciated with a shift in the molecular weight of parvalbumin detected on Western blots. During the first postnatal week, the area 17/18 border contained more parvalbumin-ir neurons than other visual areas. The de velopmental pattern of calbindin staining differed considerably from t he parvalbumin staining pattern. Very few calbindin-ir interneurons we re seen in area 17 during the first 2 weeks of life. In lateral cortic al areas, calbindin-ir neurons were located in cortical plate, infragr anular layers of cortex and white matter/subplate. Calbindin-ir neuron s increased in supragranular layers of secondary cortical areas by P7 and in area 17 by P20. In the mature cortex, the calbindin staining pa ttern was bilaminar, with a dense band of calbindin-ir cells in layer II and a second band in layers V-VI. There was no difference in the di stribution of calbindin-ir neurons among visual areas at maturity.