Functional Nicotinic Acetylcholine Receptor Expression in Stem and Progenitor Cells of the Early Embryonic Mouse Cerebral Cortex

Abstract

The adult cerebral cortex contains nicotinic acetylcholine (ACh) receptors vital to cortical function. However, little is known about the assembly of embryonic nicotinic receptor subunits into functional receptors or whether they play an active role in cortical development. We now report evidence of functional nicotinic acetylcholine receptor channels in fetal mouse cerebral cortex as early as embryonic day 10 (E10), when the cortex consists of dividing stem and progenitor cells. Patch–clamp electrophysiological measurements indicate that nicotine and ACh evoke sizable inward currents characteristic of nicotinic receptors, that are strongly rectifying with a reversal potential near 0 mV. Three different nicotinic agonists, ACh, nicotine, and dimethylphenylpiperazinium, evoked cytosolic Ca2+ signals. Agonist-evoked Ca2+ signals and electrophysiological responses were found in greater than 70% of all E10–E11 cells tested and were blocked by nicotinic receptor antagonists. The Ca2+ response to nicotinic agonists was markedly prolonged in cells from early embryonic stages relative to later stages of development. α3, α4, and α7 receptor subunit proteins were detected immunocytochemically in cortical cells from E10 to birth. The incidence of each subunit declined with embryonic age, suggesting a role in early development. We discuss the possible function of nicotinic receptors in early cortical development and their role as a target for nicotine in the developmental pathologies associated with the fetal tobacco syndrome.