Cell and Molecular Biology, The College of Pharmacy, The University of Texas at Austin, Austin, TX 78712-1074, USA.
Neuroscience. 2011 Jan 13;172:94-103. doi: 10.1016/j.neuroscience.2010.10.046. Epub 2010 Oct 23.
Activation of the dopaminergic (DA) neurons of the ventral tegmental area (VTA) by ethanol has been implicated in its rewarding and reinforcing effects. We previously demonstrated that ethanol enhances GABA release onto VTA-DA neurons via activation of 5-HT2C receptors and subsequent release of calcium from intracellular stores. Here we demonstrate that excitation of VTA-DA neurons by ethanol is limited by an ethanol-enhancement in GABA release. In this study, we performed whole-cell voltage clamp recordings of miniature inhibitory postsynaptic currents (mIPSCs) and cell-attached recordings of action potential firing from VTA-DA neurons in midbrain slices from young Long Evans rats. Acute exposure to ethanol (75 mM) transiently enhanced the firing rate of VTA-DA neurons as well as the frequency of mIPSCs. Simultaneous blockade of both GABA(A) and GABA(B) receptors (Picrotoxin (75 μM) and SCH50911 (20 μM)) disinhibited VTA-DA firing rate whereas a GABA(A) agonist (muscimol, 1 μM) strongly inhibited firing rate. In the presence of picrotoxin, ethanol enhanced VTA-DA firing rate more than in the absence of picrotoxin. Additionally, a sub-maximal concentration of muscimol together with ethanol inhibited VTA-DA firing rate more than muscimol alone. DAMGO (3 μM) inhibited mIPSC frequency but did not block the ethanol-enhancement in mIPSC frequency. DAMGO (1 and 3 μM) had no effect on VTA-DA firing rate. Naltrexone (60 μM) had no effect on basal or ethanol-enhancement of mIPSC frequency. Additionally, naltrexone (20 and 60 μM) did not block the ethanol-enhancement in VTA-DA firing rate. Overall, the present results indicate that the ethanol enhancement in GABA release onto VTA-DA neurons limits the stimulatory effect of ethanol on VTA-DA neuron activity and may have implications for the rewarding properties of ethanol.
腹侧被盖区（VTA）中的多巴胺能神经元的激活被认为与乙醇的奖赏和强化作用有关。我们之前的研究表明，乙醇通过激活 5-HT2C 受体并随后从细胞内储存中释放钙来增强 VTA-DA 神经元上的 GABA 释放。在这里，我们证明乙醇对 VTA-DA 神经元的兴奋作用受到乙醇增强 GABA 释放的限制。在这项研究中，我们对来自幼年长耳大野鼠中脑切片中的 VTA-DA 神经元进行了全细胞膜片钳记录的微小抑制性突触后电流（mIPSCs）和细胞贴附记录的动作电位发放。急性暴露于乙醇（75mM）会短暂增强 VTA-DA 神经元的发放率以及 mIPSCs 的频率。同时阻断 GABA(A)和 GABA(B)受体（Picrotoxin（75μM）和 SCH50911（20μM））会使 VTA-DA 神经元的发放率去抑制，而 GABA(A)激动剂（muscimol，1μM）则强烈抑制发放率。在 Picrotoxin 存在的情况下，乙醇增强 VTA-DA 神经元的发放率比没有 Picrotoxin 存在的情况下更强。此外，与乙醇一起使用亚最大浓度的 muscimol 抑制 VTA-DA 神经元的发放率比 muscimol 单独使用更强。DAMGO（3μM）抑制 mIPSC 频率，但不阻断 mIPSC 频率的乙醇增强。DAMGO（1 和 3μM）对 VTA-DA 神经元的发放率没有影响。纳曲酮（60μM）对基础或乙醇增强的 mIPSC 频率没有影响。此外，纳曲酮（20 和 60μM）没有阻断乙醇对 VTA-DA 神经元发放率的增强作用。总体而言，目前的结果表明，乙醇增强 VTA-DA 神经元上的 GABA 释放限制了乙醇对 VTA-DA 神经元活性的刺激作用，这可能对乙醇的奖赏特性具有重要意义。
