Eggers E D, O'Brien J A, Berger A J
Department of Physiology and Biophysics, University of Washington School of Medicine, Seattle, Washington 98195-7290, USA.
J Neurophysiol. 2000 Nov;84(5):2409-16. doi: 10.1152/jn.2000.84.5.2409.
During postnatal motoneuron development, the glycine receptor (GlyR) alpha subunit changes from alpha2 (fetal) to alpha1 (adult). To study the effect this change has on ethanol potentiation of GlyR currents in hypoglossal motoneurons (HMs), we placed neurons into two groups: neonate [postnatal day 1 to 3 (P1-3)], primarily expressing alpha2, and juvenile (P9-13), primarily expressing alpha1. We found that glycinergic spontaneous miniature inhibitory postsynaptic currents (mIPSCs) in neonate HMs are less sensitive to ethanol than in juveniles. Thirty millimolar ethanol increased the amplitude of juvenile mIPSCs but did not significantly change neonatal mIPSCs. However, 100 mM ethanol increased the amplitudes of both neonate and juvenile mIPSCs. There was a significant difference between age groups in the average ethanol-induced increase in mIPSC amplitude for 10, 30, 50, and 100 mM ethanol. In both age groups ethanol increased the frequency of glycinergic mIPSCs, but there was no difference in the amount of frequency increase between age groups. Ethanol (100 mM) also potentiated evoked IPSCs (eIPSCs) in both neonate and juvenile HMs. As we observed for mIPSCs, 30 mM ethanol increased the amplitude of juvenile eIPSCs, but had no significant effect on eIPSCs in neonate HMs. Ethanol also potentiated currents induced by exogenously applied glycine in both neonate and juvenile HMs. These results suggest that ethanol directly modulates the GlyR. To investigate possible mechanisms for this, we analyzed the time course of mIPSCs and single-channel conductance of the GlyR in the presence and absence of ethanol. We found that ethanol did not significantly change the time course of mIPSCs. We also determined that ethanol did not significantly change the single-channel conductance of synaptic GlyRs, as estimated by nonstationary noise analysis of mIPSCs. We conclude that the adult form of the native GlyR is more sensitive to ethanol than the fetal form. Further, enhancement of GlyR currents involves mechanisms other than an increase in the single-channel conductance or factors that alter the decay kinetics.
在产后运动神经元发育过程中，甘氨酸受体（GlyR）α亚基从α2（胎儿型）转变为α1（成年型）。为了研究这种变化对舌下运动神经元（HMs）中GlyR电流乙醇增强作用的影响，我们将神经元分为两组：新生鼠[出生后第1至3天（P1 - 3）]，主要表达α2；幼年鼠（P9 - 13），主要表达α1。我们发现，新生鼠HMs中的甘氨酸能自发性微小抑制性突触后电流（mIPSCs）对乙醇的敏感性低于幼年鼠。30毫摩尔乙醇增加了幼年鼠mIPSCs的幅度，但对新生鼠mIPSCs没有显著影响。然而，100毫摩尔乙醇增加了新生鼠和幼年鼠mIPSCs的幅度。对于10、30、50和100毫摩尔乙醇，不同年龄组在乙醇诱导的mIPSC幅度平均增加量上存在显著差异。在两个年龄组中，乙醇均增加了甘氨酸能mIPSCs的频率，但年龄组之间频率增加量没有差异。乙醇（100毫摩尔）也增强了新生鼠和幼年鼠HMs中的诱发抑制性突触后电流（eIPSCs）。正如我们在mIPSCs中观察到的，30毫摩尔乙醇增加了幼年鼠eIPSCs的幅度，但对新生鼠HMs中的eIPSCs没有显著影响。乙醇还增强了新生鼠和幼年鼠HMs中外源性应用甘氨酸诱导的电流。这些结果表明乙醇直接调节GlyR。为了研究其可能的机制，我们分析了有无乙醇存在时mIPSCs的时间进程以及GlyR的单通道电导。我们发现乙醇没有显著改变mIPSCs的时间进程。我们还确定，通过对mIPSCs的非平稳噪声分析估计，乙醇没有显著改变突触GlyRs的单通道电导。我们得出结论，天然GlyR的成年形式比胎儿形式对乙醇更敏感。此外，GlyR电流的增强涉及单通道电导增加或改变衰减动力学的因素以外的机制。
