Granzow B, Friesen W O, Kristan W B
J Neurosci. 1985 Aug;5(8):2035-50. doi: 10.1523/JNEUROSCI.05-08-02035.1985.
In the leech Hirudo medicinalis inhibitory motor neurons to longitudinal muscles make central inhibitory connections with excitatory motor neurons to the same muscles. We have used a variety of physiological and morphological methods to characterize these inhibitory connections. The efficacy of the transmission between the inhibitors and the excitors was measured by using three intracellular electrodes, two in the inhibitor (one for injecting current and one for measuring voltage) and a third electrode in the excitor for measuring the resultant voltage changes. We have determined that delta Vpre/delta Vpost, or what we have called the transmission coefficient, is X = 0.51, as measured in the somata of the two cells. Evidence which we have obtained leads us to propose that these inhibitory connections between motor neurons are probably monosynaptic. The synaptic latency is consistent with a monosynaptic connection. In addition, a double-labeling technique, whereby one neuron was filled with Lucifer Yellow and the other with horseradish peroxidase (HRP), was used to determine the anatomical relationship between inhibitors and excitors in whole mounts. This revealed varicosities on the processes of inhibitor motor neurons which appear to make contact with processes of excitor motor neurons. A second double-labeling technique, whereby one neuron was filled with HRP and the other with an electron-dense particulate marker, revealed adjacent processes between an inhibitor and an excitor in electron microscopic thin sections which could be the sites of synaptic contact between the neurons. The connections appear to be mediated largely by graded transmitter release from the inhibitory motor neurons. Three different methods were used to demonstrate that synaptic transmission remained in the absence of impulses in the inhibitory motor neurons. These included eliminating the impulse-supporting portion of the motor neuron by pinching off its axon, abolishing impulses by replacing Na+ with Tris in the medium bathing the nerve cord, and increasing the threshold for impulse production by raising the Mg2+ and Ca2+ concentrations in the medium bathing the nerve cord.
在医用水蛭中，支配纵肌的抑制性运动神经元与支配同一肌肉的兴奋性运动神经元建立中枢抑制性连接。我们运用了多种生理和形态学方法来表征这些抑制性连接。通过使用三个细胞内电极来测量抑制性神经元与兴奋性神经元之间传递的效能，其中两个电极置于抑制性神经元内（一个用于注入电流，一个用于测量电压），第三个电极置于兴奋性神经元内以测量由此产生的电压变化。我们已确定，在两个细胞的胞体中测量得到的δVpre/δVpost（即我们所称的传递系数）为X = 0.51。我们所获得的证据使我们提出，运动神经元之间的这些抑制性连接可能是单突触的。突触潜伏期与单突触连接相符。此外，采用了一种双标记技术，即一个神经元用鲁米诺黄填充，另一个用辣根过氧化物酶（HRP）填充，以确定整装标本中抑制性神经元与兴奋性神经元之间的解剖学关系。这揭示了抑制性运动神经元的突起上存在膨体，这些膨体似乎与兴奋性运动神经元的突起相接触。第二种双标记技术是，一个神经元用HRP填充，另一个用电子致密颗粒标记物填充，在电子显微镜薄切片中显示出抑制性神经元与兴奋性神经元之间相邻的突起，这些突起可能是神经元之间突触接触的部位。这些连接似乎主要由抑制性运动神经元释放的分级递质介导。我们使用了三种不同的方法来证明，在抑制性运动神经元无冲动的情况下，突触传递仍然存在。这些方法包括通过掐断运动神经元的轴突来去除其产生冲动的部分，通过在浸泡神经索的培养基中用Tris替代Na+来消除冲动，以及通过提高浸泡神经索的培养基中Mg2+和Ca2+的浓度来提高产生冲动的阈值。
