乙醯膽鹼及多巴胺對視丘下核到內側蒼白球興奮性突觸傳導之作用

基底核(basal ganglia)主要是由紋狀體(striatum)、視丘下核(subthalamic neucleus)、蒼白球(globus pallidus)及黑質(substantia nigra)等多個核區所組成，並且已被研究出與動作的產生、動作程序的學習與習慣產生相關。基底核與大腦、視丘(thalamus)相連形成重要的運動迴路，其中由大腦皮質(cortex)傳入訊號至基底核中，經過基底核內數條不同迴路處理再傳出至視丘，最後再傳回大腦皮質。而基底核內部的路徑可以分成直接迴路、間接迴路與超直接迴路，本文要研究的視丘下核與內側蒼白球(globus pallidus internus)正是間接迴路中的重要核區。視丘下核會釋放glutamate作為神經傳導物質來興奮內側蒼白球核區，這當中的突觸變化將會對運動產生相當的影響，本研究將探討各種神經調控物質(neuromodulator)對此迴路的作用。我們使用C57BL/6 mice製作大腦切片進行實驗，在視丘下核處給予電刺激，並在Entopeduncular nucleus(EP，內側蒼白球在齧齒類的同源構造)進行whole-cell voltage clamp分別紀錄AMPAR及NMDAR兩種glutamate ligand-gated channel的電流，並另外加入acetylcholine、dopamine系列的神經調控物質之活化劑或抑制劑來探討這些藥物對此迴路的影響效果。研究結果顯示當我們使用10Hz、20Hz、50Hz三種頻率進行5下刺激，給予Quinpirole(D2 agonist)時AMPA電流在第一下刺激(P1)的電流大小在3種頻率刺激條件都有顯著下降，而且對電流和時間做積分的到的面積也有相同趨勢。但只有在10Hz的條件刺激下第二下刺激(P2)的電流有顯著下降，另外P2/P1的比值(pair pulse ratio,PPR)只有在50Hz刺激時有顯著上升，但是對NMDA電流的大小及PPR都沒有顯著影響。給予Eticlpride(D2 antagonist)時NMDA電流在三種刺激頻率下P1都有顯著下降但PPR卻沒有顯著變化，而AMPA電流不論電流大小或是PPR則都沒有顯著影響。給予A68930(D1 agonist)及SKF83566(D1 antagonist)時，突觸電流不論AMPA或NMDA的電流大小以及pair pulse ratio(PPR)都沒有顯著變化。而給予carbachol(cholinergic agonist)時，AMPA和NMDA電流在P1都有顯著被抑制，電流和時間積分的面積也有明顯變小，在PPR的部分，P2/P1 ratio在AMPA電流在加藥後沒有顯著差異，而NMDA電流在加藥後只有50Hz的組別有顯著上升。而AMPA的P5/P1 ratio在10Hz組別有顯著上升，NMDA的P5/P1 ratio在20Hz組別有顯著上升。這些結果顯示dopamine 主要是透過D2來對視丘下核傳到EP的突觸電流進行一定程度的調控，而D1則對此迴路沒有明顯作用。另外我們也發現acetylcholine 對於視丘下核到EP的迴路有很重要的調控功能。

關鍵字

腦切片；視丘下核；內側蒼白球；電生理；突觸傳遞

並列摘要

The basal ganglia, including the striatum, the subthalamic nucleus (STN), the globus pallidum and the substantia nigra, make an important prat of the motor circuits together with cortex and thalamus. The signals projected from cortex are integrated and mediated in the basal ganglia and then project to thalamus. These signals will finally get back to cortex. The STN and globus pallidus internus (GPi) are commonly thaught as portions of the indirect pathway in basal ganglia. The glutamate realeased from STN can open the AMPA receptor and NMDA receptor channel on the GPi neuron and cause the excitatory postsynaptic currents (EPSCs). The EPSC can regulate the motor behavior but the EPSC itself is also regulated by different neuromodulators. To investigate the effect of different neuromodulators on the STN to GPi fibers, we separately recorded evoked AMPAR and NMDAR currents in the Entopeduncular nucleus (homologous structure of GPi in rodents) in the C57BL/6 mice brain slice via whole-cell patch clamp. We gave 5 pulse stimulation of the STN to GPi fibers with 3 different frequency (10Hz, 20Hz and 50Hz) to evoke EPSCs in the presence or absence of different neuromodulators. We found D2 agonist (quinpirole) markly reduced the P1 amplitude of AMPAergic EPSCs in all frequency and also markly decreased P2 amplitude in 10Hz stimulation. On the other hand, P2/P1 ratio increased in 50Hz stimulation. Quinpirole didn’t affect P1, P2 and pair pulse ratios (PPRs) in NMDAergic EPSC. On the contrary, D2 antagonist (eticlopride) had no effect on AMPAergic EPSC, but markly decreased the amplitude of both P1 and P2 in NMDAergic EPSC, without evident effect on P2/P1 and P5/P1 ratios. In this regard, it is interesting that both D1 agonist (A68930) and antagonist (SKF83566) had no effect on P1, P2 amplitude and P2/P1 as well as P5/P1 ratios in AMPAergic and NMDAergic EPSCs. We also found cholinergic agonist (carbachol) observably reduced the amplitude of both AMPAergic and NMDAergic EPSCs. However, P2/P1 ratio only increased in 50Hz stimulation of NMDAergic EPSCs but had no change in AMPAergic EPSCs. On the side, carbachol increased P5/P1 ratio of AMPAergic EPSCs in 10Hz stimulation and increased P5/P1 ratio of NMDAergic EPSCs in 20Hz stimulation . We conclude that STN-GPi AMPAergic and NMDAergic EPSCs are modulated by dopamine and acetylcholine in different mechanisms. Besides, dopamine modulated the circuit chiefly via D2 rather D1 receptors.

並列關鍵字

brain slice ； subthalamic nucleus ； globus pallidus internus ； electrophysiology ； synaptic transmission

參考文獻

Alexander, Garrett E., and Michael D. Crutcher. 1990. 'Functional architecture of basal ganglia circuits: neural substrates of parallel processing', Trends in Neurosciences, 13: 266-71.

Baldessarini, R. J., N. S. Kula, C. R. McGrath, V. Bakthavachalam, J. W. Kebabian, and J. L. Neumeyer. 1993. 'Isomeric selectivity at dopamine D3 receptors', Eur J Pharmacol, 239: 269-70.

Balleine, B. W., M. R. Delgado, and O. Hikosaka. 2007. 'The role of the dorsal striatum in reward and decision-making', J Neurosci, 27: 8161-5.

Baufreton, J., and M. D. Bevan. 2008. 'D2-like dopamine receptor-mediated modulation of activity-dependent plasticity at GABAergic synapses in the subthalamic nucleus', J Physiol, 586: 2121-42.

Baufreton, J., M. Garret, A. Rivera, A. de la Calle, F. Gonon, B. Dufy, B. Bioulac, and A. Taupignon. 2003. 'D5 (not D1) dopamine receptors potentiate burst-firing in neurons of the subthalamic nucleus by modulating an L-type calcium conductance', J Neurosci, 23: 816-25.

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乙醯膽鹼及多巴胺對視丘下核到內側蒼白球興奮性突觸傳導之作用

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