Department of Pharmacology, Faculty of Medicine, Campus de Espinardo, 30100 Murcia, Spain.
Neurochem Int. 2012 Aug;61(3):433-40. doi: 10.1016/j.neuint.2012.06.011. Epub 2012 Jun 17.
Dopamine (DA) neurons not only show a pattern signaling the magnitude, delay and probability of rewards but also code negative motivation and aversive events. Beside DA, other systems such as noradrenaline (NA) and serotonin (5-HT) may also be implicated in naloxone-induced conditioned place aversion (CPA; an index of the aversive consequences of withdrawal). The purpose of the present study was to evaluate: (i) the turnover of DA, NA and 5-HT in the nucleus accumbens (NAc), one of the most important substrates for aversive states, (ii) the changes in tyrosine hydroxylase (TH) gene expression in the ventral tegmental area, and (iii) total TH protein levels and TH phosphorylation in the NAc after naloxone-induced morphine withdrawal. DA, NA and 5-HT turnover was evaluated by high-performance liquid chromatography (HPLC). TH gene expression was determined by real time quantitative PCR (RT-PCR) and total TH and TH phosphorylated at Ser31 and Ser40 were analyzed by Western blot. Present results show that the aversion for environmental cues paired with opioid withdrawal was higher than that observed in the saline group treated with naloxone, which indicates that morphine pretreatment potentiated the ability of naloxone to produce place aversion. In addition, present data show that naloxone-induced CPA positively correlated with an increase of DA and NA turnover in the NAc, which paralleled an increase in TH gene expression in the VTA and TH phosphorylation and enhanced TH protein levels in the NAc. Thus, the present study indicates that naloxone-induced aversion in morphine-dependent mice enhances DA and NA activity in the NAc and suggests that transcriptional and post-transcriptional regulation of TH could be involved in the hyperactivity of mesolimbic dopaminergic system observed in morphine-withdrawn mice.
多巴胺（DA）神经元不仅表现出信号幅度、延迟和奖励概率的模式，还编码负动机和厌恶事件。除了 DA，其他系统，如去甲肾上腺素（NA）和 5-羟色胺（5-HT），也可能与纳洛酮诱导的条件位置厌恶（CPA；戒断的厌恶后果的指标）有关。本研究的目的是评估：（i）伏隔核（NAc）中 DA、NA 和 5-HT 的周转率，NAc 是厌恶状态的最重要底物之一，（ii）腹侧被盖区中酪氨酸羟化酶（TH）基因表达的变化，以及（iii）纳洛酮诱导吗啡戒断后 NAc 中的总 TH 蛋白水平和 TH 磷酸化。DA、NA 和 5-HT 周转率通过高效液相色谱（HPLC）进行评估。TH 基因表达通过实时定量 PCR（RT-PCR）确定，总 TH 和 TH 在 Ser31 和 Ser40 处磷酸化通过 Western blot 进行分析。目前的结果表明，与阿片类药物戒断相关的环境线索的厌恶程度高于纳洛酮处理的盐水组观察到的，这表明吗啡预处理增强了纳洛酮产生位置厌恶的能力。此外，目前的数据表明，纳洛酮诱导的 CPA 与 NAc 中 DA 和 NA 周转率的增加呈正相关，这与 VTA 中 TH 基因表达的增加、TH 磷酸化和 NAc 中 TH 蛋白水平的增强相平行。因此，本研究表明，纳洛酮诱导的吗啡依赖小鼠的厌恶感增强了 NAc 中的 DA 和 NA 活性，并表明 TH 的转录和转录后调节可能与吗啡戒断小鼠中观察到的中脑边缘多巴胺能系统的过度活跃有关。
