Developmental expression of calbindin and parvalbumin in the cat superior colliculus

I have studied the developmental expression of the calcium binding proteins calbindin (CB) and parvalbumin (PV) in the cat superior colliculus (SC). In the adult, CB and PV containing neurons are organized in unique complimentary sublaminar patterns that cross traditional laminar borders and are related to specific afferents. In this study, I have examined when CB and PV are first expressed and when and how the sublaminar patterns are formed. Since radial glia and other glial cells have been implicated in nervous system pattern formation, I also asked whether glial cells are involved in the formation of these laminar patterns. To answer these questions, antibody immunocytochemistry was used to study the developmental expression of CB, PV, and two glial intermediate filament proteins, glial fibrillary acidic protein (GFAP) and vimentin (Vm). Cresyl violet staining was used to study the development of traditional laminae. Cats ranging in age from gestational day (E) 24 to postnatal day (P) 60 and adults were used. The density and size of labeled cells were measured and cell distributions were mapped at each age. Results showed that primordial SC layers were present at E24, and all seven traditional layers were visible by E46. Few CB-ir neurons were present at E24. Incipient CB tiers were present by E34, and the three tier CB pattern was completed between E40-E46. After E40, the number of CB labeled neurons decreased due both to cell death and loss of CB expression. By contrast, PV first appeared at birth and PV labeled neurons increased continuously in number until P35. Adult-like PV labeled cell morphology and lamination was present by P35, and neuronal number decreased slightly after this age. The difference in CB and PV expression suggests they have different roles during development. Radial glia were well labeled by Vm and later by GFAP between E24 to P35. Astrocytes first appeared by E46 and adult astrocytic distribution was present by P60. No glial boundaries were seen during prenatal periods when CB-ir cells formed laminae. Thus astroglia appear not to be involved in the development of the CB, PV nor traditional laminar patterns.