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 125I-alpha-bungarotoxin binding to alpha 7-type nicotinic receptors was maximal 4-8 days after plating. Treatment with 5'-fluorodeoxyuridine (80 microM) from 1 to 3 days in vitro significantly reduced glial proliferation and concomitantly increased 125I-alpha-bungarotoxin binding, whereas plating onto a glial bed layer decreased binding. There was no significant 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-[3H]methylscopolamine binding to muscarinic receptors. Glial conditioned medium decreased 125I-alpha-bungarotoxin binding in both control and 5'-fluorodeoxyuridine-treated cultures, suggesting the release of a soluble factor that inhibits alpha 7-type nicotinic receptor expression. An additional mechanism of glial regulation may involve removal of glutamate from the surrounding medium, as added glutamate (200 microM) increased 125I-alpha-bungarotoxin binding in astrocyte-poor cultures but not in those that were astrocyte enriched. These results suggest that glia may serve a physiological role in regulating alpha 7-type nicotinic receptors in developing brain.