POSTNATAL EXPRESSION PATTERN OF CALCIUM-BINDING PROTEINS IN ORGANOTYPIC THALAMIC CULTURES AND IN THE DORSAL THALAMUS IN-VIVO

The present study describes the postnatal expression of calbindin, cal retinin and parvalbumin and glutamic acid decarboxylase (GAD) and micr otubule-associated protein 2 (MAP2) in organotypic monocultures of rat dorsal thalamus compared to the thalamus in vivo. Cultures were maint ained for up to 7 weeks. Cortex-conditioned medium improved the surviv al of thalamic cultures. MAP2-immunoreactive material was present in s omata and dendrites of small and large-sized neurons throughout the cu ltures. Parvalbumin immunoreactivity was present in larger multipolar or bitufted neurons along the edge of a culture. These neurons also di splayed strong parvalbumin mRNA and GAD mRNA expression, and GABA immu noreactivity. They Likely corresponded to cells of the nucleus reticul aris thalami. Parvalbumin mRNA, but neither parvalbumin protein nor GA D mRNA, was expressed in neurons with large somata within the explant. They Likely represented relay cells. GAD mRNA, but not parvalbumin mR NA, was expressed in small neurons within the explants. Small neurons also displayed calbindin- and calretinin-immunoreactivity. The small n eurons likely represented local circuit neurons. The time course of ex pression of the calcium-binding proteins revealed that all were presen t at birth with the predicted molecular weights. A low, but constant p arvalbumin expression was observed in vitro without the developmental increase seen in vivo, which mast likely represented parvalbumin from afferent sources. In contrast, the explantation transiently downregula ted the calretinin and calbindin expression, but the neurons recovered the expression after 14 and 21 days, respectively. In conclusion, tha lamic monocultures older than three weeks represent a stable neuronal network containing well differentiated neurons of the nucleus reticula ris thalami, relay cells and local circuit neurons. (C) 1998 Elsevier Science B.V. All rights reserved.