Pharmacological characterization of acetylcholine receptors on the dendritic membrane of an identified sensory nonspiking interneuron in crayfish

LDS中间神经元是小龙虾克氏原螯虾腹末神经节中发现的一种感觉非尖峰中间神经元，它是由其体同侧侧的机械感觉传入单突触输出的。通过使用细胞内记录技术检测乙酰胆碱（ACh）激动剂对电刺激感觉传入引起的突触反应的影响，研究了这种突触传递的药理学特征。灌注乙酰胆碱或其通用激动剂恰巴醇时，中间神经元呈去极化，突触反应峰幅降低。目前的注射实验证实，突触反应的减少不是由于药物引起的去极化。在低ca ^<2+>，高Mg^<2+>的条件下用药，也得到了类似的结果。经生理盐水冲洗后，膜电位和突触反应均恢复到原来的状态。由此可见，LDS中间神经元的树突膜具有乙酰胆碱受体。应用乙酰胆碱的选择性烟碱激动剂TMA也会引起膜去极化和突触反应的降低，而应用氧tremorine和其他毒蕈碱激动剂也会引起类似的突触抑制，但不会引起膜去极化。结果表明，LDS中间神经元的乙酰胆碱受体与烟碱乙酰胆碱受体对激动剂的敏感性相似，而肌碱激动剂可能通过其突触前作用抑制突触传递。电压钳实验显示，感觉刺激引起的突触电流的半衰减时间约为10msec。这种短时间的突触反应似乎是基于LDS神经元间膜上乙酰胆碱受体的快速作用，这将通过打开离子通道直接响应递质分子来发挥脊椎动物尼古丁乙酰胆碱受体的作用。少

The LDS interneuron, a sensory nonspiking interneuron identified in the terminal abdominal ganglion of the crayfish Procambarus clarkii Girard, is monosynaptically exited by mechanosensory afferents on the side ipsilateral to its soma.Pharmacological characteristics of this synaptic transmission were studied by examining the sffects of acetylcholine (ACh) agonists on the synaptic response evoked by electrical stimulation of sensory afferents using intracellular recording techniques.When ACh or its general agonist carbachol was applied by perfusion, the interneuron showed depolarization and the peak amplitude of the synaptic response was decreased.Current injection experiments confirmed that the decrease in the synaptic response was not due to the depolarization caused by the drug.Similar results were obtained by applying the drug under the low-Ca^<2+>, high Mg^<2+> condition.Both the membrane potential and the synaptic response returned to their original state after washing the prepara … More tion with normal saline.It is thus concluded that the dendritic membrane of the LDS interneuron possesses receptors for ACh.Application of TMA,a selective nicotinic agonist of ACh, also caused the membrane depolarization and a decrease of the synaptic response, whereas application of oxotremorine and other muscarinic agonists caused similar synaptic suppression but never elicited the membrane depolarization.The results suggest that ACh receptors the LDS interneuron resemble the nicotinic ACh receptors in their sensitivity to agonists and that the muscarrinic agonists suppress the synaptic transmission presumably through their presynaptic action.Voltage clamp experiments revealed that the half decay time of the synaptic current evoked by sensory stimulation was about 10msec.This short time course of the synaptic response seems to be based on the rapid action of ACh receptors on the LDS interneuron membrane which would work as the vertebrate nicotinic ACh receptors by opening the ionic channels in direct response to the transmitter molecules. Less