Keegan Bradley M, Dreitzler Annie L, Sexton Tammy, Beveridge Thomas J R, Smith Hilary R, Miller Mack D, Blough Bruce E, Porrino Linda J, Childers Steven R, Howlett Allyn C
Center for the Neurobiology of Addiction Treatment, Department of Physiology and Pharmacology, Wake Forest School of Medicine, Medical Center Blvd., Winston-Salem, NC 27157, USA.
Center for Drug Discovery, RTI International, Research Triangle Park, NC 27709, USA.
Brain Res. 2021 Feb 23;1761:147387. doi: 10.1016/j.brainres.2021.147387.
Phenmetrazine (PHEN) is a putative treatment for cocaine and psychostimulant recidivism; however, neurochemical changes underlying its activity have not been fully elucidated. We sought to characterize brain homeostatic adaptations to chronic PHEN, specifically on functional brain activity (local cerebral glucose utilization), G-Protein Coupled Receptor-stimulated G-protein activation, and phosphorylation of ERK1/2, GSK3β, and DARPP-32. Male Sprague-Dawley rats were implanted with sub-cutaneous minipumps delivering either saline (vehicle), acute (2-day) or chronic (14-day) low dose (25 mg/kg/day) or high dose (50 mg/kg/day) PHEN. Acute administration of high dose PHEN increased local cerebral glucose utilization measured by 2-[C]-deoxyglucose uptake in basal ganglia and motor-related regions of the rat brain. However, chronically treated animals developed tolerance to these effects. To identify the neurochemical changes associated with PHEN's activity, we performed [S]GTPγS binding assays on unfixed and immunohistochemistry on fixed coronal brain sections. Chronic PHEN treatment dose-dependently attenuated D dopamine and α-adrenergic, but not 5-HT, receptor-mediated G-protein activation. Two distinct patterns of effects on pERK1/2 and pDARPP-32 were observed: 1) chronic low dose PHEN decreased pERK1/2, and also significantly increased pDARPP-32 levels in some regions; 2) acute and chronic PHEN increased pERK1/2, but chronic high dose PHEN treatment tended to decrease pDARPP-32. Chronic low dose, but not high dose, PHEN significantly reduced pGSK3β levels in several regions. Our study provides definitive evidence that extended length PHEN dosage schedules elicit distinct modes of neuronal acclimatization in cellular signaling. These pharmacodynamic modifications should be considered in drug development for chronic use.
苯甲曲秦（PHEN）被认为是一种治疗可卡因和精神兴奋剂复吸的药物；然而，其作用背后的神经化学变化尚未完全阐明。我们试图描述大脑对慢性PHEN的稳态适应性，特别是对功能性脑活动（局部脑葡萄糖利用）、G蛋白偶联受体刺激的G蛋白激活以及细胞外信号调节激酶1/2（ERK1/2）、糖原合成酶激酶3β（GSK3β）和多巴胺和腺苷酸环化酶调节蛋白32（DARPP-32）的磷酸化的影响。将雄性Sprague-Dawley大鼠皮下植入微型泵，分别给予生理盐水（载体）、急性（2天）或慢性（14天）低剂量（25毫克/千克/天）或高剂量（50毫克/千克/天）的PHEN。高剂量PHEN的急性给药通过2-[C]-脱氧葡萄糖摄取增加了大鼠脑基底神经节和运动相关区域的局部脑葡萄糖利用。然而，长期治疗的动物对这些作用产生了耐受性。为了确定与PHEN活性相关的神经化学变化，我们对未固定的脑切片进行了[S]GTPγS结合测定，并对固定的冠状脑切片进行了免疫组织化学分析。慢性PHEN治疗剂量依赖性地减弱了多巴胺D和α-肾上腺素能受体介导的G蛋白激活，但对5-羟色胺受体介导的G蛋白激活没有影响。观察到对磷酸化ERK1/2（pERK1/2）和磷酸化DARPP-32（pDARPP-32）有两种不同的作用模式：1）慢性低剂量PHEN降低了pERK1/2，并且在某些区域也显著增加了pDARPP-32水平；2）急性和慢性PHEN增加了pERK1/2，但慢性高剂量PHEN治疗倾向于降低pDARPP-32。慢性低剂量而非高剂量的PHEN显著降低了几个区域的磷酸化GSK3β（pGSK3β）水平。我们的研究提供了确凿的证据，表明延长PHEN给药方案会在细胞信号传导中引发不同模式的神经元适应性变化。在开发慢性使用的药物时应考虑这些药效学改变。
