Centro Ingegneria Genetica Biotecnologie Avanzate, 80131 Naples, Italy.
J Neurosci. 2010 Aug 18;30(33):11043-56. doi: 10.1523/JNEUROSCI.1682-10.2010.
Attention deficit/hyperactivity disorder (ADHD) is characterized by inattention, impulsivity, and motor hyperactivity. Several lines of research support a crucial role for the dopamine transporter (DAT) gene in this psychiatric disease. Consistently, the most commonly prescribed medications in ADHD treatment are stimulant drugs, known to preferentially act on DAT. Recently, a knock-in mouse [DAT-cocaine insensitive (DAT-CI)] has been generated carrying a cocaine-insensitive DAT that is functional but with reduced dopamine uptake function. DAT-CI mutants display enhanced striatal extracellular dopamine levels and basal motor hyperactivity. Herein, we showed that DAT-CI animals present higher striatal dopamine turnover, altered basal phosphorylation state of dopamine and cAMP-regulated phosphoprotein 32 kDa (DARPP32) at Thr75 residue, but preserved D(2) receptor (D(2)R) function. However, although we demonstrated that striatal D(1) receptor (D(1)R) is physiologically responsive under basal conditions, its stimulus-induced activation strikingly resulted in paradoxical electrophysiological, behavioral, and biochemical responses. Indeed, in DAT-CI animals, (1) striatal LTP was completely disrupted, (2) R-(+)-6-chloro-7,8-dihydroxy-1-phenyl-2,3,4,5-tetrahydro-1H-3-benzazepine hydrobromide (SKF 81297) treatment induced paradoxical motor calming effects, and (3) SKF 81297 administration failed to increase cAMP/protein kinase A (PKA)/DARPP32 signaling. Such biochemical alteration selectively affected dopamine D(1)Rs since haloperidol, by blocking the tonic inhibition of D(2)R, unmasked a normal activation of striatal adenosine A(2A) receptor-mediated cAMP/PKA/DARPP32 cascade in mutants. Most importantly, our studies highlighted that amphetamine, nomifensine, and bupropion, through increased striatal dopaminergic transmission, are able to revert motor hyperactivity of DAT-CI animals. Overall, our results suggest that the paradoxical motor calming effect induced by these drugs in DAT-CI mutants depends on selective aberrant phasic activation of D(1)R/cAMP/PKA/DARPP32 signaling in response to increased striatal extracellular dopamine levels.
注意缺陷多动障碍（ADHD）的特征是注意力不集中、冲动和运动过度活跃。有几条研究线索支持多巴胺转运体（DAT）基因在这种精神疾病中的关键作用。一致地，ADHD 治疗中最常开的药物是兴奋剂，已知它们优先作用于 DAT。最近，一种携带可卡因不敏感 DAT 的基因敲入小鼠（DAT-可卡因不敏感（DAT-CI））被产生，这种 DAT 是功能性的，但多巴胺摄取功能降低。DAT-CI 突变体显示出增强的纹状体细胞外多巴胺水平和基础运动过度活跃。在此，我们表明 DAT-CI 动物表现出更高的纹状体多巴胺周转率，多巴胺和 cAMP 调节磷酸蛋白 32kDa（DARPP32）在 Thr75 残基处的基础磷酸化状态改变，但保留了 D2 受体（D2R）功能。然而，尽管我们证明了纹状体 D1 受体（D1R）在基础条件下具有生理反应性，但它的刺激诱导激活导致了矛盾的电生理、行为和生化反应。事实上，在 DAT-CI 动物中，（1）纹状体 LTP 完全被破坏，（2）R-（+）-6-氯-7,8-二羟基-1-苯基-2,3,4,5-四氢-1H-3-苯并氮杂卓氢溴化物（SKF 81297）治疗诱导了矛盾的运动镇静作用，（3）SKF 81297 给药未能增加 cAMP/蛋白激酶 A（PKA）/DARPP32 信号。这种生化改变选择性地影响多巴胺 D1R，因为氟哌啶醇通过阻断 D2R 的紧张性抑制，使突变体中纹状体腺苷 A2A 受体介导的 cAMP/PKA/DARPP32 级联反应正常激活。最重要的是，我们的研究强调，安非他命、诺米芬辛和安非他酮通过增加纹状体多巴胺能传递，能够逆转 DAT-CI 动物的运动过度活跃。总的来说，我们的结果表明，这些药物在 DAT-CI 突变体中诱导的矛盾性运动镇静作用取决于对增加的纹状体细胞外多巴胺水平的选择性异常相激活 D1R/cAMP/PKA/DARPP32 信号。
