Drapeau P, Sanchez-Armass S
Neurosciences Unit, Montreal General Hospital Research Institute, Quebec, Canada.
J Neurosci. 1988 Dec;8(12):4718-27. doi: 10.1523/JNEUROSCI.08-12-04718.1988.
Serotoninergic Retzius neurons reform an inhibitory synapse onto pressure-sensitive mechanosensory (P) neurons when the cells are removed from the nervous system of the leech and are juxtaposed in tissue culture. The somas of P cells in situ and single (uninnervated) P cells in culture have both a depolarizing and Cl-dependent hyperpolarizing response to application of the transmitter serotonin (5-HT). Synaptic release of 5-HT by a Retzius cell in situ and in culture evokes a Cl-dependent postsynaptic response but does not appear to activate the depolarizing receptors. We have characterized the ionic currents induced by synaptically released and applied 5-HT in voltage-clamped P cells in culture in order to determine the responses to transmitter and their modifications following innervation. When 5-HT was applied to single P cells, 2 types of channels were activated by 5-HT and could be distinguished by changing the ionic composition of the superfusion solution. In an impermeant cation (TrisCl) solution, a 5-HT-dependent Cl current was activated. When single P cells were superfused with a Cl-free solution (Cl replaced by impermeant SO4), 5-HT activated a monovalent cation current. Following innervation of a P cell by a cocultured Retzius cell, the reversal potential of the peak postsynaptic current depended on the Cl gradient and the synaptic response was blocked by the Cl channel blocker 9-anthracenecarboxylic acid. Thus, synaptic release of 5-HT activated solely the Cl channels and not the cationic channels. Pipette application of 5-HT onto innervated P cells activated a Cl conductance comparable in magnitude to the synaptic response. In contrast, the cationic conductance was reduced roughly 5-fold. It is concluded that innervation of a P cell by a Retzius cell resulted in clustering of the synaptic 5-HT receptors, which activate Cl channels and reduction of the nonsynaptic, cationic response. The result is a selection of receptors in the cultured P cell that mimics the pattern observed in vivo.
当从水蛭的神经系统中取出5-羟色胺能的雷丘斯神经元并将其并列于组织培养中时，它们会在压力敏感的机械感觉（P）神经元上重新形成抑制性突触。原位P细胞的胞体以及培养中的单个（无神经支配的）P细胞对递质5-羟色胺（5-HT）的应用都有去极化和Cl⁻依赖性超极化反应。原位和培养中的雷丘斯细胞突触释放5-HT会引发Cl⁻依赖性突触后反应，但似乎不会激活去极化受体。我们已经对培养的电压钳制P细胞中突触释放和应用的5-HT所诱导的离子电流进行了表征，以确定对递质的反应及其在神经支配后的变化。当将5-HT应用于单个P细胞时，5-HT激活了2种类型的通道，并且可以通过改变灌流溶液的离子组成来区分。在非渗透性阳离子（TrisCl）溶液中，激活了5-HT依赖性Cl⁻电流。当单个P细胞用无Cl⁻溶液（Cl⁻被非渗透性的SO₄²⁻取代）灌流时，5-HT激活了单价阳离子电流。在共培养的雷丘斯细胞对P细胞进行神经支配后，突触后电流峰值的反转电位取决于Cl⁻梯度，并且突触反应被Cl⁻通道阻滞剂9-蒽甲酸阻断。因此，5-HT的突触释放仅激活了Cl⁻通道而未激活阳离子通道。用移液管将5-HT施加到有神经支配的P细胞上，激活的Cl⁻电导在大小上与突触反应相当。相比之下，阳离子电导大约降低了5倍。得出的结论是，雷丘斯细胞对P细胞的神经支配导致突触5-HT受体聚集，这些受体激活Cl⁻通道并减少非突触性阳离子反应。结果是培养的P细胞中受体的选择模仿了体内观察到的模式。
