NICOTINIC AND MUSCARINIC ACTIVATION OF MOTONEURONS IN THE CRAYFISH LOCOMOTOR NETWORK
NICOTINIC AND MUSCARINIC ACTIVATION OF MOTONEURONS IN THE CRAYFISH LOCOMOTOR NETWORK
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DOI：
10.1152/jn.1994.72.4.1622
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发表时间：
1994-10-01
影响因子：
2.5
通讯作者：
CLARAC, F
中科院分区：
文献类型：
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作者：
CATTAERT, D;ARAQUE, A;CLARAC, F
1.我们研究了乙酰胆碱（Ach）的影响，确定运动神经元（MN）使用在体外制备的小龙虾胸神经系统。沿着微量管压力喷射Ach（或激动剂）至记录电极附近，对50个MN进行不连续电流钳和单电极电压钳记录.将相对较大体积（500- 2500 μ l）的Ach（10（-2）M）或毒蕈碱激动剂oxotremorine（Ore，10（-2）M）局部喷射到MN神经桩区，通常（90%的病例）在拮抗性MN中诱导缓慢的交替节律性活动。在其他情况下（4个实验），与类似的交付乙酰胆碱或矿石，MN开发的能力，有节奏地发射，但只有当去极化持续电流注入。在接近记录的MN的情况下，压力喷射较小体积（50-200 pl）的Ach（10（-2）M）可引起快速（1-2 s）的大幅度（小于或等于20 mV）的膜去极化（12%），持续时间长（10 s至几分钟）和小幅度（2-5 mV）的去极化（14%），以及两者的组合（74%）。这些反应似乎涉及神经突的不同区域，因为当药物喷射吸管在神经堆中移位时，它们会发生变化。此外，快速和持久的去极化成分是Ach对MN的直接作用，因为它们在河豚毒素（TTX，10（-6）M）和钴（Co 2+，5 × 10（-3）M）灌流下持续存在.而膜电阻下降，在快速乙酰胆碱诱导的去极化，它增加了在长期持续的去极化。膜电阻的增加在去极化电位大于-55 mV时更为明显，并涉及K+电导的降低.用烟碱和毒蕈碱拮抗剂灌流显示，乙酰胆碱诱导的快速去极化涉及烟碱受体、毒蕈碱受体或两者，而缓慢去极化仅涉及毒蕈碱。用电压钳法研究乙酰胆碱诱发的内向电流。快速烟碱成分（I-nic）随超极化保持电位增加而增加，随去极化电位减少，在10和30 mV之间逆转。快毒蕈碱电流（I-fmus）显示出类似的特性，并在约-10 mV时逆转。而这两个快速组件是电压无关的，持久的毒蕈碱成分（I-smus）是电压依赖性的。该反应随膜去极化而增强，但当保持电位超极化至静息水平以下时，该反应在-60 mV及以上时逐渐减弱直至消失.持久的胆碱能反应涉及抑制电压依赖性K+电导，其在-60 mV的正电位下具有张力活性，并导致静息和去极化水平周围的向外整流。提供的证据表明，持久的毒蕈碱传导在步行系统的节律活动的产生中起着关键作用。
1. We investigated the effects of acetylcholine (Ach) on identified motoneurons (MNs) using an in vitro preparation of the crayfish thoracic nervous system. Discontinuous current-clamp and single electrode voltage-clamp recordings from 50 MNs were performed along with micropipette pressure ejection of Ach (or agonists) close to the recording electrode.2. Localized ejections of relatively large volumes (500-2,500 pl) of Ach (10(-2) M) or of the muscarinic agonist oxotremorine (Ore, 10(-2) M) onto the MN neuropile region, usually (90% of the cases) induced a slow, alternating rhythmic activity in antagonistic MNs. In other cases (4 experiments), with similar deliveries of Ach or Ore, MNs developed the ability to fire rhythmically but only when depolarized by sustained current injection. Pressure ejections of smaller volumes (50-200 pl) of Ach (10(-2) M) close to the recorded MN could give rise to a fast (1-2 s) large amplitude (less than or equal to 20 mV) membrane depolarization (12%), a long-lasting (10 s to several minutes) and small (2-5 mV) depolarization (14%), and a combination of the two (74%). These responses appeared to involve different regions of the neurite because they changed when the drug-ejection pipette was displaced in the neuropile. Moreover, fast and long-lasting depolarizing components resulted from a direct effect of Ach onto the MNs because they persisted under tetrodotoxin (TTX, 10(-6) M) and cobalt (Co2+, 5 X 10(-3) M) superfusion.3. Whereas the membrane resistance decreased during the fast Ach-induced depolarization, it increased during the long-lasting depolarization. The increase in membrane resistance was more pronounced at depolarized potentials more than -55 mV and involve a reduction in K+ conductance.4. Superfusion with nicotinic and muscarinic antagonists revealed that the fast Ach-induced depolarization involved nicotinic receptors, muscarinic receptors, or both, whereas the slow depolarization was exclusively muscarinic.5. The Ach-evoked inward currents were studied under voltage clamp. The fast nicotinic component (I-nic) increased with hyperpolarizing holding potentials and decreased with depolarizing potentials, reversing at between 10 and 30 mV. The fast muscarinic current (I-fmus) displayed similar characteristics and reversed at about -10 mV. Whereas both fast components were voltage independent, the long-lasting muscarinic component (I-smus) was voltage dependent. The response grew with membrane depolarization, but when the holding potential was hyperpolarized below resting level, the response declined to disappear at about -60 mV and beyond.6. The long-lasting cholinergic response involved the inhibition of a voltage-dependent K+ conductance, which was tonically active at potentials positive to -60 mV and that resulted in outward rectification around resting and depolarized levels. Evidence is provided indicating that the long-lasting muscarinic conductance plays a key role in the generation of rhythmic activity in the walking system.