TRANSIENT EXPRESSION OF CALBINDIN-D28K IMMUNOREACTIVITY IN LAYER-V PYRAMIDAL NEURONS DURING POSTNATAL-DEVELOPMENT OF KITTEN CORTICAL AREAS

Calbindin-D28k is a 28 kDa calcium binding protein that has been shown to colocalize with a specific subpopulation of gamma-aminobutyric aci d inhibitory interneurons in mammalian neocortex. We have examined the ontogeny of calbindin in neonatal kitten cortex in areas 17,18,19,7, medial and lateral suprasylvian visual areas, splenial visual area and cingulate cortex from the day of birth (PO) through maturation of the brain (P101). Transient staining of immature layer V pyramidal cells was seen in kittens six weeks old and younger. This transient staining of pyramidal cells was most intense and the stained neurons were most numerous in cingulate cortex. Apical dendrites of pyramidal cells in cingulate cortex were prominently stained and could be followed to lay er 1, where they were seen to branch extensively. There were very few calbindin immunoreactive pyramidal cells in primary cortical areas pos tnatally. Transient staining in extrastriate visual cortical areas dis appeared first from the lateral suprasylvian areas, and persisted long est in area 7. Pyramidal neurons in the cingulate gyrus expressed calb indin longest, but calbindin expression by pyramidal neurons ceased by the sixth postnatal week in all areas of the brain.