GLIAL REGULATION OF ALPHA-7-TYPE NICOTINIC ACETYLCHOLINE-RECEPTOR EXPRESSION IN CULTURED RAT CORTICAL-NEURONS

Primary embryonic cortical cultures were used as an in vitro model to evaluate the influence of glia on developmental expression of alpha 7- type nicotinic acetylcholine receptors in rat brain. In cells cultured in serum-containing medium without mitotic inhibitors, specific I-125 -alpha-bungarotoxin binding to alpha 7-type nicotinic receptors was ma ximal 4-8 days after plating. Treatment with 5'-fluorodeoxyuridine (80 mu M) from 1 to 3 days in vitro significantly reduced glial prolifera tion and concomitantly increased I-125-alpha-bungarotoxin binding, whe reas plating onto a glial bed layer decreased binding. There was no si gnificant binding to pure glial cultures. Treatment-induced changes in neuronal binding resulted from alterations in receptor density, with no change in affinity, 5'-Fluorodeoxyuridine treatment also increased cellular expression of alpha 7 receptor mRNA but had no effect on N-[H -3] methylscopolamine binding to muscarinic receptors. Glial condition ed medium decreased I-125-alpha-bungarotoxin binding in both control a nd 5'-fluorodeoxyuridine-treated cultures, suggesting the release of a soluble factor that inhibits alpha 7-type nicotinic receptor expressi on. An additional mechanism of glial regulation may involve removal of glutamate from the surrounding medium, as added glutamate (200 mu M) increased I-125 alpha-bungarotoxin binding in astrocyte-poor cultures but not in those that were astrocyte enriched. These results suggest t hat glia may serve a physiological role in regulating alpha 7-type nic otinic receptors in developing brain.