Muller K J, Nicholls J G
J Physiol. 1974 Apr;238(2):357-69. doi: 10.1113/jphysiol.1974.sp010529.
In leech ganglia, an individual sensory cell that responds specifically to noxious mechanical stimulation of the skin (N cell) excites two different motoneurones. One raises the annuli of the skin into ridges (the AE cell), while the other innervates logitudinal muscles and thereby shortens the body segment (L cell). A comparison has been made of the way in which these two synapses behave when their common presynaptic cell is stimulated in various conditions.1. Using previously described criteria, N sensory cells have been shown to make monosynaptic chemical connexions with both the AE and L motoneurones (Nicholls & Purves, 1972). Following a single stimulus, the excitatory synaptic potential recorded in the AE motoneurone was only about one tenth the size of that in the L cell (approximately 0.5 mV compared to 5 mV). Trains of impulses in the same N sensory cell gave rise to synaptic potentials in the AE and the L motoneurones that underwent phases of facilitation and depression; the facilitation, however, was characteristically greater and longer lasting at synapses upon the AE motoneurone.2. The differences between the two synapses were accentuated in Ringer fluid containing increased concentrations of Ca and also in the cold. Under both of these conditions repetitive firing by the N sensory cell could give rise to synaptic potentials in the AE motoneurone which progressively increased in amplitude, while those in the L motoneurone became smaller.3. The results suggest that the differences in synaptic transmission can be accounted for by variations in the amount of transmitter released at the presynaptic N cell terminals, rather than by differences in the post-synaptic cells. The animal's behaviour corresponds to expectations from the physiology of the synapses.
在水蛭神经节中，一个对皮肤有害机械刺激产生特异性反应的单个感觉细胞（N细胞）会兴奋两种不同的运动神经元。一种使皮肤环带隆起形成嵴（AE细胞），而另一种支配纵肌从而使身体节段缩短（L细胞）。已经比较了在各种条件下刺激它们共同的突触前细胞时这两种突触的行为方式。1. 根据先前描述的标准，已证明N感觉细胞与AE和L运动神经元都形成单突触化学连接（Nicholls和Purves，1972年）。单次刺激后，在AE运动神经元中记录到的兴奋性突触电位仅约为L细胞中的十分之一（分别约为0.5 mV和5 mV）。同一N感觉细胞中的一连串冲动在AE和L运动神经元中产生了经历易化和抑制阶段的突触电位；然而，在AE运动神经元上的突触处，易化作用通常更大且持续时间更长。2. 在含有增加浓度钙的林格液中以及在低温下，这两种突触之间的差异更加明显。在这两种条件下，N感觉细胞的重复放电可在AE运动神经元中产生幅度逐渐增加的突触电位，而在L运动神经元中的突触电位则变小。3. 结果表明，突触传递的差异可以由突触前N细胞终末释放的递质数量变化来解释，而不是由突触后细胞的差异来解释。动物的行为与突触生理学的预期相符。
