Lin Min, Sambo Danielle, Khoshbouei Habibeh
Department of Neuroscience, Evelyn F. and William L. McKnight Brain Institute, University of Florida, Gainesville, Florida 32610.
Department of Neuroscience, Evelyn F. and William L. McKnight Brain Institute, University of Florida, Gainesville, Florida 32610
J Neurosci. 2016 Oct 5;36(40):10376-10391. doi: 10.1523/JNEUROSCI.1392-16.2016.
Methamphetamine (METH) is a substrate for the dopamine transporter that increases extracellular dopamine levels by competing with dopamine uptake and increasing reverse transport of dopamine via the transporter. METH has also been shown to alter the excitability of dopamine neurons. The mechanism of METH regulation of the intrinsic firing behaviors of dopamine neurons is less understood. Here we identified an unexpected and unique property of METH on the regulation of firing activity of mouse dopamine neurons. METH produced a transient augmentation of spontaneous spike activity of midbrain dopamine neurons that was followed by a progressive reduction of spontaneous spike activity. Inspection of action potential morphology revealed that METH increased the half-width and produced larger coefficients of variation of the interspike interval, suggesting that METH exposure affected the activity of voltage-dependent potassium channels in these neurons. Since METH has been shown to affect Ca homeostasis, the unexpected findings that METH broadened the action potential and decreased the amplitude of afterhyperpolarization led us to ask whether METH alters the activity of Ca-activated potassium (BK) channels. First, we identified BK channels in dopamine neurons by their voltage dependence and their response to a BK channel blocker or opener. While METH suppressed the amplitude of BK channel-mediated unitary currents, the BK channel opener NS1619 attenuated the effects of METH on action potential broadening, afterhyperpolarization repression, and spontaneous spike activity reduction. Live-cell total internal reflection fluorescence microscopy, electrophysiology, and biochemical analysis suggest METH exposure decreased the activity of BK channels by decreasing BK-α subunit levels at the plasma membrane.
Methamphetamine (METH) competes with dopamine uptake, increases dopamine efflux via the dopamine transporter, and affects the excitability of dopamine neurons. Here, we identified an unexpected property of METH on dopamine neuron firing activity. METH transiently increased the spontaneous spike activity of dopamine neurons followed by a progressive reduction of the spontaneous spike activity. METH broadened the action potentials, increased coefficients of variation of the interspike interval, and decreased the amplitude of afterhyperpolarization, which are consistent with changes in the activity of Ca-activated potassium (BK) channels. We found that METH decreased the activity of BK channels by stimulating BK-α subunit trafficking. Thus, METH modulation of dopamine neurotransmission and resulting behavioral responses is, in part, due to METH regulation of BK channel activity.
甲基苯丙胺（METH）是多巴胺转运体的底物，它通过与多巴胺摄取竞争并增加多巴胺经转运体的逆向转运来提高细胞外多巴胺水平。METH还被证明会改变多巴胺能神经元的兴奋性。METH调节多巴胺能神经元固有放电行为的机制尚不清楚。在这里，我们发现了METH在调节小鼠多巴胺能神经元放电活动方面一个意想不到的独特特性。METH使中脑多巴胺能神经元的自发放电活动短暂增强，随后自发放电活动逐渐减少。对动作电位形态的检查显示，METH增加了动作电位的半高宽，并使峰间期的变异系数增大，这表明暴露于METH会影响这些神经元中电压依赖性钾通道的活性。由于已证明METH会影响钙稳态，METH使动作电位变宽并降低超极化后电位幅度这一意外发现促使我们探究METH是否会改变钙激活钾（BK）通道的活性。首先，我们通过其电压依赖性以及对BK通道阻滞剂或开放剂的反应来鉴定多巴胺能神经元中的BK通道。虽然METH抑制了BK通道介导的单位电流幅度，但BK通道开放剂NS1619减弱了METH对动作电位变宽、超极化后电位抑制和自发放电活动减少的影响。活细胞全内反射荧光显微镜、电生理学和生化分析表明，暴露于METH会通过降低质膜上BK-α亚基的水平来降低BK通道的活性。
甲基苯丙胺（METH）与多巴胺摄取竞争，通过多巴胺转运体增加多巴胺外流，并影响多巴胺能神经元的兴奋性。在这里，我们发现了METH在多巴胺能神经元放电活动方面一个意想不到的特性。METH使多巴胺能神经元的自发放电活动短暂增加，随后自发放电活动逐渐减少。METH使动作电位变宽，增加峰间期的变异系数，并降低超极化后电位的幅度，这些与钙激活钾（BK）通道活性的变化一致。我们发现METH通过刺激BK-α亚基的转运来降低BK通道的活性。因此，METH对多巴胺神经传递的调节以及由此产生的行为反应，部分是由于METH对BK通道活性的调节。
