Graduate Program in Neuroscience, University of Minnesota, Minneapolis, MN 55455.
Department of Pharmacology, University of Minnesota, Minneapolis, MN 55455.
eNeuro. 2021 Mar 26;8(2). doi: 10.1523/ENEURO.0081-21.2021. Print 2021 Mar-Apr.
Drugs of abuse engage overlapping but distinct molecular and cellular mechanisms to enhance dopamine (DA) signaling in the mesocorticolimbic circuitry. DA neurons of the ventral tegmental area (VTA) are key substrates of drugs of abuse and have been implicated in addiction-related behaviors. Enhanced VTA DA neurotransmission evoked by drugs of abuse can engage inhibitory G-protein-dependent feedback pathways, mediated by GABA receptors (GABARs) and D DA receptors (DRs). Chemogenetic inhibition of VTA DA neurons potently suppressed baseline motor activity, as well as the motor-stimulatory effect of cocaine and morphine, confirming the critical influence of VTA DA neurons and inhibitory G-protein signaling in these neurons on this addiction-related behavior. To resolve the relative influence of GABAR-dependent and DR-dependent signaling pathways in VTA DA neurons on behavioral sensitivity to drugs of abuse, we developed a neuron-specific viral CRISPR/Cas9 approach to ablate DR and GABAR in VTA DA neurons. Ablation of GABAR or DR did not impact baseline physiological properties or excitability of VTA DA neurons, but it did preclude the direct somatodendritic inhibitory influence of GABAR or DR activation. DR ablation potentiated the motor-stimulatory effect of cocaine in male and female mice, whereas GABAR ablation selectively potentiated cocaine-induced activity in male subjects only. Neither DR nor GABAR ablation impacted morphine-induced motor activity. Collectively, our data show that cocaine and morphine differ in the extent to which they engage inhibitory G-protein-dependent feedback pathways in VTA DA neurons and highlight key sex differences that may impact susceptibility to various facets of addiction.
滥用药物通过重叠但不同的分子和细胞机制来增强中脑边缘多巴胺（DA）信号通路。腹侧被盖区（VTA）的 DA 神经元是滥用药物的关键底物，并与成瘾相关行为有关。滥用药物引起的 VTA DA 神经传递增强可以激活抑制性 G 蛋白依赖性反馈途径，由 GABA 受体（GABARs）和 D 型 DA 受体（DRs）介导。VTA DA 神经元的化学遗传抑制强烈抑制了基础运动活动以及可卡因和吗啡的运动刺激作用，证实了 VTA DA 神经元和抑制性 G 蛋白信号在这些神经元中对这种成瘾相关行为的关键影响。为了解决 VTA DA 神经元中 GABAR 依赖性和 DR 依赖性信号通路对药物滥用行为敏感性的相对影响，我们开发了一种神经元特异性病毒 CRISPR/Cas9 方法来敲除 VTA DA 神经元中的 DR 和 GABAR。GABAR 或 DR 的缺失不影响 VTA DA 神经元的基础生理特性或兴奋性，但确实阻止了 GABAR 或 DR 激活的直接体树突抑制作用。DR 的缺失增强了可卡因对雄性和雌性小鼠的运动刺激作用，而 GABAR 的缺失仅选择性地增强了雄性小鼠中可卡因引起的活动。DR 或 GABAR 的缺失均不影响吗啡引起的运动活动。总的来说，我们的数据表明，可卡因和吗啡在 VTA DA 神经元中激活抑制性 G 蛋白依赖性反馈途径的程度不同，并强调了可能影响对各种成瘾方面易感性的关键性别差异。
