Not all the people that consume drugs of abuse develop addiction. In this sense, just a percentage of rats express locomotor sensitization after repeated psychostimulant exposure. Neurochemical evidence has shown that locomotor sensitization is associated with changes in dorsolateral striatum (DLS) activity. However, it is unknown if individual differences observed in locomotor sensitization are related to differential neuro-adaptations in DLS activity. In this study, we measured basal dopamine (DA) levels and single unit activity in the DLS of anesthetized rats, after repeated amphetamine (AMPH) administration. Rats were treated with AMPH 1.0 mg/kg ip or saline ip for 5 days. Following 5 days of withdrawal, a challenge dose of AMPH 1.0 mg/kg ip was injected. In-vivo microdialysis experiments and single unit recording were carried out twenty-four hours after the last AMPH injection. Sensitized rats showed increased basal DA levels and baseline firing rate of medium spiny neurons (MSNs) compared to non-sensitized rats. The local variation index (Lv) was used to measure the firing pattern of MSNs. In saline rats, a bursty firing pattern was observed in MSNs. A decrease in MSNs baseline Lv accompanies the expression of AMPH locomotor sensitization. Moreover, a decrease in Lv after an acute AMPH 1.0 mg/kg injection was only observed in saline and sensitized rats. Our results show individual differences in DLS basal DA levels and firing pattern after repeated AMPH administration, suggesting that an hyperfunction of nigrostriatal pathway, accompanied by a decrease in DLS MSNs firing irregularity underlies the expression of AMPH locomotor sensitization.

中文翻译：

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苯丙胺运动敏化的个体差异与大鼠背外侧纹状体中多巴胺释放和射击方式的变化有关。

并非所有吸食滥用毒品的人都会上瘾。从这个意义上讲，在反复的精神刺激剂暴露后，只有一定比例的大鼠表达运动性敏化。神经化学证据表明，运动敏化与背外侧纹状体（DLS）活性变化有关。然而，尚不清楚在运动敏化中观察到的个体差异是否与DLS活性的差异性神经适应有关。在这项研究中，我们在重复给予安非他明（AMPH）后，测量了麻醉大鼠DLS中的基础多巴胺（DA）水平和单单位活性。用1.0 mg / kg腹膜内注射AMPH或腹膜内注射生理盐水处理大鼠5天。停药5天后，注射1.0 mg / kg ip的AMPH激发剂量。在最后一次AMPH注射后24小时进行了体内微透析实验和单个单位记录。与未致敏大鼠相比，致敏大鼠显示中度棘状神经元（MSN）的基础DA水平升高和基线放电速率增加。局部变化指数（Lv）用于测量MSN的触发模式。在生理盐水大鼠中，在MSN中观察到爆发性的放电模式。MSNs基线Lv的降低伴随着AMPH运动敏化的表达。此外，仅在盐水和致敏大鼠中观察到急性AMPH 1.0 mg / kg注射后Lv降低。我们的研究结果表明，重复服用AMPH后，DLS基础DA水平和放电模式存在个体差异，这表明黑质纹状体通路功能亢进，