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

LDS中间神经元是在克氏原螯虾（Procambarus clarkii吉拉德）的终末腹神经节中鉴定的感觉非尖峰中间神经元，通过观察乙酰胆碱（ACh）对大鼠海马索马体同侧机械感觉传入的影响，研究了这种突触传递的药理学特征。用细胞内记录技术观察ACh或其一般激动剂卡巴胆碱对电刺激感觉传入神经诱发的突触反应的影响。灌流后，中间神经元出现去极化，突触反应的峰值幅度降低，电流注入实验证实突触反应的降低不是由于药物引起的去极化，在低Ca ^<2+>条件下应用药物也得到类似的结果，在高Mg^<2+>条件下，膜电位和突触反应在冲洗后均恢复到原来的状态。 关于我们 结果表明，LDS中间神经元树突膜上有ACh受体，应用选择性乙酰胆碱烟碱受体激动剂TMA也可引起树突膜去极化和突触反应减弱，而应用oxotremorine和其他M受体激动剂引起类似的突触抑制，但不引起膜去极化，结果表明，乙酰胆碱受体LDS中间神经元毒蕈碱类激动剂可能通过其突触前作用抑制突触传递。电压钳实验表明，感觉刺激诱发的突触电流的半衰减时间约为10毫秒。这种短暂的突触反应过程可能是基于LDS中间神经元膜上的ACh受体的快速作用，将作为脊椎动物烟碱乙酰胆碱受体，通过打开离子通道直接响应递质分子。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