Frazier C J, Rollins Y D, Breese C R, Leonard S, Freedman R, Dunwiddie T V
Neuroscience Program, University of Colorado Health Sciences Center, Denver, Colorado 80262, USA.
J Neurosci. 1998 Feb 15;18(4):1187-95. doi: 10.1523/JNEUROSCI.18-04-01187.1998.
The effects of acetylcholine on both pyramidal neurons and interneurons in the area CA1 of the rat hippocampus were examined, using intracellular recording techniques in an in vitro slice preparation. In current-clamp mode, fast local application of acetylcholine (ACh) to the soma of inhibitory interneurons in stratum radiatum resulted in depolarization and rapid firing of action potentials. Under voltage-clamp, ACh produced fast, rapidly desensitizing inward currents that were insensitive to atropine but that were blocked by nanomolar concentrations of the nicotinic alpha7 receptor-selective antagonists alpha-bungarotoxin (alphaBgTx) and methyllycaconitine. Nicotinic receptor antagonists that are not selective for alpha7-containing receptors had little (mecamylamine) or no effect (dihydro-beta-erythroidine) on the ACh-induced currents. Glutamate receptor antagonists had no effect on the ACh-evoked response, indicating that the current was not mediated by presynaptic facilitation of glutamate release. However, the current could be desensitized almost completely by bath superfusion with 100 nM nicotine. In contrast to those actions on interneurons, application of ACh to the soma of CA1 pyramidal cells did not produce a detectable current. Radioligand-binding experiments with [125I]-alphaBgTx demonstrated that stratum radiatum interneurons express alpha7-containing nAChRs, and in situ hybridization revealed significant amounts of alpha7 mRNA. CA1 pyramidal cells did not show specific binding of [125I]-alphaBgTx and only low levels of alpha7 mRNA. These results suggest that, in addition to their proposed presynaptic role in modulating transmitter release, alpha7-containing nAChRs also may play a postsynaptic role in the excitation of hippocampal interneurons. By desensitizing these receptors, nicotine may disrupt this action and indirectly excite pyramidal neurons by reducing GABAergic inhibition.
利用体外脑片制备中的细胞内记录技术，研究了乙酰胆碱对大鼠海马CA1区锥体细胞和中间神经元的影响。在电流钳模式下，将乙酰胆碱（ACh）快速局部施加到辐射层抑制性中间神经元的胞体上，可导致去极化和动作电位的快速发放。在电压钳模式下，ACh产生快速、迅速脱敏的内向电流，该电流对阿托品不敏感，但可被纳摩尔浓度的烟碱型α7受体选择性拮抗剂α-银环蛇毒素（αBgTx）和甲基lycaconitine阻断。对含α7受体无选择性的烟碱型受体拮抗剂对ACh诱导的电流几乎没有影响（美加明）或没有影响（二氢β-刺桐碱）。谷氨酸受体拮抗剂对ACh诱发的反应没有影响，表明该电流不是由谷氨酸释放的突触前促进介导的。然而，通过用100 nM尼古丁进行浴式灌流，该电流几乎可以完全脱敏。与对中间神经元的作用相反，将ACh施加到CA1锥体细胞的胞体上不会产生可检测到的电流。用[125I]-αBgTx进行的放射性配体结合实验表明，辐射层中间神经元表达含α7的烟碱型乙酰胆碱受体，原位杂交显示有大量的α7 mRNA。CA1锥体细胞未显示[125I]-αBgTx的特异性结合，仅显示低水平的α7 mRNA。这些结果表明，除了在调节递质释放中所提出的突触前作用外，含α7的烟碱型乙酰胆碱受体在海马中间神经元的兴奋中也可能起突触后作用。通过使这些受体脱敏，尼古丁可能会破坏这种作用，并通过减少GABA能抑制间接兴奋锥体细胞。
