The study for new regulating mechanism of neuronal nicotinic acetylcholine receptor and the development of new therapeutics for psycho-neurological disorders

α - 7型烟碱受体（nAChRs）是具有高Ca^<2+>通透性的同戊二胺离子通道。虽然nachr被认为主要在神经元细胞中表达，但最近的证据表明，这些受体在一些非神经元细胞类型中也起作用。我发现，在大鼠原代培养的小胶质细胞中，尼古丁引起细胞内Ca^<2+>水平的短暂增加，这被特定的nachr阻滞剂、甲基莱卡乌碱和α -班加罗毒素所消除。然而，这种反应不受细胞外Ca^<2+>缺失的影响，并被磷脂酶C （PLC）抑制剂U73122和IP_3受体阻滞剂xestospongin C阻断。广泛的电生理测量未能揭示任何尼古丁诱导的小胶质细胞电流。这些结果表明，小胶质nachr驱动一个信号传导过程，涉及PLC和Ca^<2+>从1p_3敏感存储的激活，而不是作为离子通道运作。此外，nAChRs的激活增强了bzatp刺激的TNF释放（P2X_7受体激活），但抑制了脂多糖（LPS）诱导的TNF释放（toll样受体4激活），而不影响TNF mRNA的表达。在lps刺激的小胶质细胞中，尼古丁诱导的TNF释放减少与JNK和p38 MAP激酶的激活抑制有关，JNK和p38 MAP激酶调节TNF合成的转录后步骤。另一方面，尼古丁对BzATP诱导的两种MAP激酶的激活均无影响，但会增强BzATP诱导的Ca^<2+>内流。尽管小胶质细胞nachr的cDNA序列与神经元相同，但它们为何没有离子通道活性仍有待研究。

The alpha7 type of nicotinic acetylcholine receptors (nAChRs) are homopentameric ion channels with high Ca^<2+> permeability. Although the nAChRs were thought to be expressed mainly in neuronal cells, recent evidence indicates that these receptors also function in some non-neuronal cell types. I have found that in rat primary culture microglia, nicotine elicits a transient increase in intracellular Ca^<2+> levels, which is abolished by specific blockers of nAChRs, methyllycaconitine and alpha-bungarotoxin. However, this response is not affected by the absence of extracellular Ca^<2+> and is blocked by U73122, an inhibitor of phospholipase C (PLC), and xestospongin C, a blocker of the IP_3 receptor. Extensive electrophysiological measurements failed to reveal any nicotine-induced currents in microglia. These results suggest that microglial nAChRs drive a signaling process involving the activation of PLC and Ca^<2+> release from 1P_3-sensitive stores, rather than operating as ion channels. Furthermore, the activation of nAChRs enhanced BzATP-stimulated TNF release (P2X_7 receptor activation), but suppressed lipopolysaccahride (LPS)-induced TNF release (Toll-like receptor 4 activation), without affecting the expression of TNF mRNA. In LPS-stimulated microglia, the decreased TNF release induced by nicotine was associated with the suppression of the activation of JNK and p38 MAP kinases, which regulate the post-transcriptional steps of TNF synthesis. On the other hand, nicotine had no effect on the activation of either MAP kinase induced by BzATP, but enhanced BzATP-elicited Ca^<2+> influx. It still remains to study why the microglial nAChRs have no ion channel activities, although their cDNA sequences are as same as those of neurons.