Investigation of molecular mechanisms on amphetamine induced conditioned place preference: the role of Brain-Derived Neurotrophic Factor (BDNF)

制約場地偏好行為為研究藥物成癮的常用模式之一，對於其行為表現及再復發的神經機制，多巴胺系統佔有舉足輕重的地位。而大腦神經滋養因子(BDNF)與多巴胺系統密切相關，影響其神經元可塑性。故本研究以BDNF來作為目標分子，進行一系列的實驗探討制約場地偏好的神經機制。實驗一A以不同劑量安非他命建立制約場地偏好行為，並分析其BDNF mRNA的表現量。實驗結果顯示1 mg/kg安非他命能夠引發制約場地偏好行為，但是對於內側前額葉、紋狀體、依核、背側海馬迴、杏仁核等五個區塊的BDNF mRNA無顯著的影響效果。實驗一B再次確認實驗一A的結果，顯示俱有安非他命引發制約場地偏好行為的受試，其大腦五個區塊BDNF mRNA沒有顯著的變化。實驗二探測制約場地偏好行為再復發對於相同的五個區塊BDNF mRNA變化。結果發現0.75 mg/kg安非他命能誘發制約場地偏好再復發行為，並且能引發內側前額葉中BDNF mRNA的增加，但對其餘四個區塊則無明顯的影響效果。實驗三以單次注射安非他命探討對於BDNF mRNA是否有立即性的影響，結果顯示五個區塊皆無明顯的變化。實驗四以安非他命引發的行為致敏化反應為行為模式，偵測BDNF mRNA的表現情形。結果發現藥物制約配對組與單次注射安非他命組在活動量上無顯著的差異，顯示出無行為致敏化反應的發生。檢驗五個區塊BDNF mRNA的表現，亦沒有發現明顯的改變。綜合以上的實驗結果，本研究得到安非他命制約場地偏好再復發行為，會伴隨內側前額葉BDNF mRNA的增加。而單獨的安非他命引發制約場地偏好行為，並不會改變BDNF mRNA。這些結果顯示BDNF參與在較複雜的制約學習行為歷程，而不是在單獨的藥物注射或與環境配對的制約過程。Conditioned place preference (CPP) is widely used as an experimental behavioral model in the study of drug addiction and reward learning. Brain dopamine systems play an important role to drive the CPP performance and its relapse. Brain-derived neurotrophic factor (BDNF) is closely related to dopamine system that can promote neuron plasticity involved in certain types of behavior. Taking BDNF as the target molecule, this project conducted a series of experiments to delve into the neural mechanism of CPP. Different doses of amphetamine on the CPP behavior were assessed in Experiment 1A, and BDNF mRNA was tested after CPP test. The results show that 1 mg/kg amphetamine significantly induced CPP, but no significant effect on BDNF mRNA in any of five brain areas tested, including medial prefrontal cortex, striatum, nucleus accumbens, dorsal hippocampus and amygdala. The results of Experiment 1A was further confirmed by Experiment 1B, indicating no significant change on BDNF mRNA in five brain areas of rats with significant amphetamine-induced CPP. Experiment 2 examined the effects of CPP relapse and tested BDNF mRNA in the aforementioned five brain areas. The results show that 0.75 mg/kg amphetamine significantly induced CPP relapse and also increased BDNF mRNA level in medial prefrontal cortex. Such an increase of BDNF mRNA was not observed in any other four areas. Single acute injection of amphetamine was administered in Experiment 3 to delve into the possible immediate drug effect on BDNF mRNA. Its results show no significant change on five brain areas following this acute drug treatment. Experiment 4 used amphetamine-induced behavioral sensitization as a behavioral mode to determine the expression of BDNF mRNA. The results show no significant difference both for amphetamine-paired group and acute amphetamine group on locomotion, that indicated no behavioral sensitization formed in this test. There was no significant difference in the expression of BDNF mRNA in five brain areas. These results indicate that amphetamine-induced CPP relapse, but not CPP performance itself, is accompanied by the increase of BDNF mRNA level in medial prefrontal cortex. These findings indicate that BDNF is involved in place conditioning formed by psychostimulant drug when it is reinstated after extinction, rather than by a solitary drug injection or a relatively simple conditioning process by pairing drug with the environmental context