Landa Leos, Jurajda Michal, Sulcova Alexandra
Department of Pharmacology and Pharmacy, University of Veterinary and Pharmaceutical Sciences Brno, Czech Republic.
Neuro Endocrinol Lett. 2012;33(4):446-52.
In our previous studies we found that both acute administration of CB1 receptor agonist methanandamide and repeated methanandamide pre-treatment prior to methamphetamine challenge dose elicited increase in the CB1 receptor mRNA expression in the mouse mesencephalon. As a reciprocal cross-talk is reported between the cannabinoid CB1 and dopamine receptors, that are highly co-localized on brain neurones, we targeted possible changes in relative expression of dopamine D1 and D2 receptor mRNA in mesencephalon in mice sensitized by repeated treatments to methamphetamine stimulatory effects and cross-sensitized to methamphetamine by cannabinoid CB1 receptor agonist methanandamide pre-treatment.
To confirm development of behavioural sensitization or cross-sensitization, respectively, we observed changes in locomotion using the open field test. Mice were treated repeatedly with either methamphetamine or methamphetamine after repeated pre-treatment with methanandamide. After each measurement of locomotion one third of animals were sacrificed and the brain was stored. RNA was isolated from the midbrain and used for reverse transcription and subsequent real-time PCR.
As in many of our earlier studies with the same dosage regimen we found in the behavioural part both development of sensitization to methamphetamine stimulatory effects after repeated treatment and cross-sensitization to them by pre-treatment with cannabinoid receptor CB1 agonist methanandamide. Real-time PCR analyses showed an increase in D1 receptor mRNA expression after the first dose of methamphetamine (that persisted also after the last dose of methamphetamine) and after the first dose of methanandamide (which also persisted after the methamphetamine challenge dose). In opposite a significant decrease in D2 receptor mRNA expression both after the first dose of methamphetamine and methanandamide (that persisted also after the methamphetamine challenge doses) was registered. Thus, our results suggest that both methamphetmine and methanandamide treatment can provoke changes in dopamine receptor density in mouse mesenpcephalon, the increase in D1 and decrease in D2 receptor subtypes.
在我们之前的研究中，我们发现急性给予CB1受体激动剂甲磺酰胺以及在给予甲基苯丙胺激发剂量之前重复给予甲磺酰胺预处理，均可使小鼠中脑CB1受体mRNA表达增加。由于据报道大麻素CB1受体和多巴胺受体之间存在相互的串扰，且它们在脑神经元上高度共定位，因此我们针对经重复治疗对甲基苯丙胺刺激作用产生敏化并经大麻素CB1受体激动剂甲磺酰胺预处理对甲基苯丙胺产生交叉敏化的小鼠中脑多巴胺D1和D2受体mRNA相对表达的可能变化进行了研究。
为分别确认行为敏化或交叉敏化的发展情况，我们使用旷场试验观察运动变化。小鼠分别经甲基苯丙胺重复处理或在经甲磺酰胺重复预处理后再给予甲基苯丙胺。每次运动测量后，处死三分之一的动物并保存大脑。从中脑分离RNA，用于逆转录及随后的实时PCR。
正如我们之前许多采用相同给药方案的研究一样，在行为学部分我们发现，重复治疗后对甲基苯丙胺刺激作用产生了敏化，且经大麻素受体CB1激动剂甲磺酰胺预处理后对其产生了交叉敏化。实时PCR分析显示，在给予第一剂甲基苯丙胺后（在最后一剂甲基苯丙胺后也持续存在）以及给予第一剂甲磺酰胺后（在甲基苯丙胺激发剂量后也持续存在），D1受体mRNA表达增加。相反，在给予第一剂甲基苯丙胺和甲磺酰胺后（在甲基苯丙胺激发剂量后也持续存在），D2受体mRNA表达均显著下降。因此，我们的结果表明，甲基苯丙胺和甲磺酰胺处理均可引发小鼠中脑多巴胺受体密度的变化，即D1受体亚型增加而D2受体亚型减少。
