铝对大鼠海马CA3区诱发电位的抑制及其与胆碱能、γ-氨基丁酸系统的关系

背景以往的研究表明,铝可通过影响细胞内钙稳态、降低蛋白激酶C(PKC)的活性、影响谷氨酸的释放等多种途径影响动物的学习和记忆.含铝饲料喂养的大鼠,其海马CA3区长时程增强(LTP)形成减弱.经进一步采用急性给铝的方法,将三氯化铝(AlCl3)直接微量注射到海马CA3区,观察到铝能减弱海马CA3区的诱发电位、阻抑LTP的产生,这种作用可能与铝损害了L-Arg-NO途径有关.目的探讨铝对学习记忆的损害及与胆碱能系统和γ-氨基丁酸(GABA)系统的相关性.设计以实验动物为研究对象,完全随机对照的研究.单位一所大学生理系、一所职业技术学院医学院.材料实验于2000-09/2001-04在华中科技大学同济医学院生理系神经电生理实验室完成.实验用SD大鼠68只,由华中科技大学同济医学院实验动物学部提供,普通级,体质量150～250 g,雌雄不拘.干预SD大鼠随机分为9组,分别为生理盐水组对照组6只,在其海马CA3区内先后(间隔1 min)2次微量注射生理盐水各1 μL;生理盐水+AlCl3组6只,在海马CA3区内先(间隔1 min)微量注射生理盐水与0.5 mol/L AlCl3各1 μL.生理盐水+Tac组6只,在CA3区先后微量注射生理盐水与1×10-9mol/L各Tacrine 1 μL.生理盐水+Bic组6只,在CA3区先后微量注射生理盐水和1×10-3mol/L Bicuculline各1 μL.Tac+AlCl3组预先分别向大鼠海马CA3区注入1×10-9mol/L(n=8),1×10-10mol/L(n=6)和1×10-8mol/L(n=6)Tacrine 1 μL, min后再注入0.5 mol/L AlCl3 1 μL.Bic+AlCl3组向海马CA3区先分别注入1×10-3mol/L(n=9),×10-4mol/L(n=7)Bicuculline 1μL, min后再注入0.5 mol/L AlCl3 1μL.单个脉冲刺激穿通纤维(PP)后,记录海马CA3区诱发的群体峰电位(PS).待PS稳定后,向海马CA3区微量注射药物,观察铝对海马CA3区诱发电位的影响及某些中枢递质对铝抑制PS效应的影响.主要观察指标海马CA3区诱发的群体峰电位.CA3区诱发电位的影响及某些中枢递质对铝抑制PS效应的影响.结果①海马CA3区局部微量给予0.5 mol/L AlCl3,记录的PS幅度1 min时下降达峰值,为给药前的(33.8±11.0)%(n=6).AlCl3的这种抑制作用持续120 min.②预先CA3区微量注入1×10-9mol/L Tacrine(胆碱酯酶抑制剂), min后再注入AlCl3,结果1～30 min内拮抗了AlCl3抑制PS的效应(n=8);给予1×10-8mol/LTacrine(n=6),则拮抗作用延长至60min;而给予1×10-10mol/LTacrine(n=6),拮抗作用在3～5 min弱于1×10-9mol/L组.③海马CA3区先给予1×10-3mol/LBicuculline, min后再注入AlCl3,在1～20 min内Bicuculline部分减弱了AlCl3的作用(n=9).结论一定浓度的铝可抑制海马CA3区的诱发PS幅度;Tacrine能拮抗这种作用,且可能与剂量有关.因此提示铝的抑制作用可能与损害了ACh递质系统有关;应用GABAA受体阻断剂Bicuculline也使铝对PS抑制效应减弱,表明铝的抑制作用也可能部分通过GABA途径起作用.

Inhibitive effect of aluminium on evoked potentials in hippocampal CA3 region in rats and the relationship with cholinergic and gamma-aminobutyric acid system

BACKGROUND: As indicated by previous researches, aluminium (Al) could affect learning and memory of animals through many approaches in cluding affecting the stable status of intracellular calcium, decreasing protein kinase C(PKC) activity, and affecting the release of glutamic acid (Glu) . The formation of long-term potentiation(LTP) weakens in hip pocampal CA3 region of rats fed by forage containing Al. It could be found that Al would weaken evoked potential(EP) in hippocampal CA3 region and inhibit LTP formation, which might be related with the damaging effect of Al on L-Arg-NO approach through further application of acute Al administration, i.e., AlCl3 is directly injected into hippocampal CA3 region by microinjection.OBJECTIVE: To investigate the damaging effect of Al on learning and memory, and its correlation with cholinergic system and gamma-aminobutyric acid (GABA) system.DESIGN: A completelyrandomized controlled verifying study based on the experimental animals.SETTING: Department of psychology in a university and the medical college of an occupational technology college.MATERIALS: The study was conducted in the Laboratory of Neuro-Electrophysiology, the Faculty of Physiology, Tongji Medical College,Huazhong University of Science and Technology between September 2000 and April 2001. Totally 68 SD rats of ordinary grade in either gender with a body mass between 150 g and 250 g were obtained from the Department of Experimental Animals of Tongji Medical College, Huazhong University of Science and echnology.INTERVENTIONS: SD rats were randomly divided into 9 groups including normal NS ( NS ) control group ( n = 6): 1 μL of NS was injected twice ( 1 minute interval) into hippocampal CA3 region by microinjection; NS + AlCl3 group( n = 6): 1 μL of NS and 0.5 mol/L of AlCl3 were injected(1 minute interval) into hippocampal CA3 region by microinjection;NS + Tac group( n = 6): 1 μLof NS and 1 × 10-9 mol/L of Tacrine were injected in turn into hippocampal CA3 region by microinjection; NS + Bic group(n=6): 1 μL of NS and 1 × 10-3 mol/L of Bicuculline were injected in turn into hippocampal CA3 region by microinjection; Tac +AlCl3 group: 1 μL of 1 × 10-9 mol/L( n =8),1 × 10-10 mol/L ( n = 6) and 1 × 10-8 mol/L of Tacrine were firsdy injected into hippocampal CA3 region by microinjection, and 1 μL of 0. 5 mol/L AlCl3was injected 1 minute later; Bic + AlCl3 group: 1 μL of 1 × 10-3 mol/L( n = 9) and 1 × 10 -4 mol/L( n = 7) of Bicuculline were firstly injected into hippocampal CA3 region by microinjection, and 1 μL of 0.5 mol/L AlCl3 was injected 1 minute later. Population spike(PS) in hippocampal CA3 region was recorded after using single pulse to stimulate perforating fiber(PF). When PS became stable, medication was injected into hippocampal CA3 region to observe the impacts of Al on EP in hippocampal CA3 region and the impacts of some central transmitters on the effect of Al in in hibiting PS.MAIN OUTCOME MEASURES: PS evoked in hippocampal CA3 region;the impacts of Al on EP in CA3 region and the impacts of some central transmitters on the effect of Al in inhibiting PS. RESULTS: ① After the application of 0.5 mol/L of AlCl3 in hippocampal CA3 region by microinjection, the recorded amplitude of PS reduced to peak at 1 minute, which accounted for(33.8 ± 11. 0) % of the level before medication( n = 6). The inhibitive effect of AlCl3 lasted for 120 minutes. ② After the pre-application of 1 × 10-9 mol/L of Tacrine(cholinesterase in hibitor) into CA3 region by microinjection and the application of AlCl3 at one minute later, it was found that Tacrine antagonized the inhibitive effects of AlCl3 on PS within 1 to 30 minutes( n = 8) . Its antagonism would extend to 60 minutes if 1 × 10-8 mol/L of Tacrine was administrated( n = 6) . How ever, the antagonism of 1 × 10-10 mol/L of Tacrine was weaker than that of 1×10-9 mol/L group within 3-5 minutes(n=6) ③ After the pre-application of 1 × 10-3 mol/L of Bicuculline into CA3 region by mi croinjection and the application of AlCl3 at one minute later, Bicuculline could partially weaken the effects of AlCl3 within 1 to 20 minutes( n = 9). CONCLUSION: Al of certain concentration can inhibit the evoked PS am plitude in hippocampal CA3 region; Tacrine can antagonize Al' s effects and its antagonism might be related with dose. Hence, the inhibitive effects of Al might be related with the damage in Ach transmitter system. The application of Bicuculline, a GABAA inhibitor, also can weaken the PS inhibitive effects of Al, which indicates that the inhibitive effect of Al also might be effective through GABA approach.