Department of Physiology and Pharmacology, Wake Forest School of Medicine, Winston-Salem, North Carolina 27157.
J Neurosci. 2014 Apr 16;34(16):5575-82. doi: 10.1523/JNEUROSCI.4050-13.2014.
In light of recent studies suggesting that amphetamine (AMPH) increases electrically evoked dopamine release ([DA]o), we examined discrepancies between these findings and literature that has demonstrated AMPH-induced decreases in [DA]o. The current study has expanded the inventory of AMPH actions by defining two separate mechanisms of AMPH effects on [DA]o at high and low doses, one dopamine transporter (DAT) independent and one DAT dependent, respectively. AMPH concentrations were measured via microdialysis in rat nucleus accumbens after intraperitoneal injections of 1 and 10 mg/kg and yielded values of ∼10 and 200 nM, respectively. Subsequently, voltammetry in brain slices was used to examine the effects of low (10 nM), moderate (100 nM), and high (10 μM) concentrations of AMPH across a range of frequency stimulations (one pulse; five pulses, 20 Hz; 24 pulses, 60 Hz). We discovered biphasic, concentration-dependent effects in WT mice, in which AMPH increased [DA]o at low concentrations and decreased [DA]o at high concentrations across all stimulation types. However, in slices from DAT-KO mice, [DA]o was decreased by all concentrations of AMPH, demonstrating that AMPH-induced increases in [DA]o are DAT dependent, whereas the decreases at high concentrations are DAT independent. We propose that low AMPH concentrations are insufficient to disrupt vesicular sequestration, and therefore AMPH acts solely as a DAT inhibitor to increase [DA]o. When AMPH concentrations are high, the added mechanism of vesicular depletion leads to reduced [DA]o. The biphasic mechanisms observed here confirm and extend the traditional actions of AMPH, but do not support mechanisms involving increased exocytotic release.
鉴于最近的研究表明安非他命 (AMPH) 会增加电刺激引起的多巴胺释放 ([DA]o)，我们检查了这些发现与文献之间的差异，文献表明 AMPH 会降低 [DA]o。本研究通过定义高剂量和低剂量 AMPH 对 [DA]o 的两种独立作用机制，扩展了 AMPH 作用的目录，一种是多巴胺转运体 (DAT) 独立的，另一种是 DAT 依赖的。通过腹腔注射 1 和 10 mg/kg 后在大鼠伏隔核中进行微透析测量 AMPH 浓度，分别产生约 10 和 200 nM 的浓度。随后，在脑切片中使用伏安法研究了低浓度（10 nM）、中浓度（100 nM）和高浓度（10 μM）的 AMPH 在一系列频率刺激（一个脉冲；五个脉冲，20 Hz；24 个脉冲，60 Hz）下的作用。我们发现 WT 小鼠中存在双相、浓度依赖性的作用，其中低浓度的 AMPH 会增加 [DA]o，而高浓度的 AMPH 会降低 [DA]o，适用于所有刺激类型。然而，在 DAT-KO 小鼠的切片中，所有浓度的 AMPH 都降低了 [DA]o，表明 AMPH 诱导的 [DA]o 增加依赖于 DAT，而高浓度时的降低则不依赖于 DAT。我们提出，低浓度的 AMPH 不足以破坏囊泡的隔离，因此 AMPH 仅作为 DAT 抑制剂作用来增加 [DA]o。当 AMPH 浓度较高时，囊泡耗竭的附加机制会导致 [DA]o 减少。这里观察到的双相作用机制证实并扩展了 AMPH 的传统作用机制，但不支持涉及胞吐释放增加的机制。
