GABA及受体拮抗剂对大鼠海马CA3区长时程增强效应的影响

Effects of GABA on long-term potentiation(LTP)in hippocampus CA3 region in rats

目的探讨GABA在海马CA3区长时程增强(long-term potentiation,LTP)诱导和形成中的作用。方法应用在体电生理研究方法,观察局部给予GABA及GABAA受体拮抗剂bicuculline对海马CA3区LTP诱导和维持的影响;应用高效液相色谱荧光检测技术测定LTP诱导90min后实验侧海马组织GABA含量变化。结果①强直刺激PP纤维诱导LTP90min后,海马组织GABA水平(119.3±10.8)μmol.g-1protein较对照组(206.4±24.7)μmol.g-1protein降低(P<0.01);谷氨酸含量与对照组比差异无显著性(P>0.05)。②强直刺激前5min局部给予GABA200nmol,LTP诱导明显被抑制,相对PS幅值在各个时间点均低于LTP诱导组(P<0.01)而与对照组接近(P>0.05);给予GABAA受体拮抗剂甲基溴化荷包牡丹碱(bicuculline methbromide,BMB)1nmol1min再给予GABA200nmol,发现GABA对LTP的抑制作用减弱,PS幅值高于只给予GABA组(P<0.01)。③强直刺激PP纤维诱导LTP形成30min后,海马CA3区局部给予GABA200nmol,LTP效应被翻转,相对PS幅值在各时间点均低于LTP诱导组(P<0.01)而与对照组接近(P>0.05);给予BMB1nmol1min后再给予GABA200nmol,GABA对LTP效应的抑制作用减弱,PS幅值高于只给予GABA组(P<0.01)而低于LTP组(P<0.01)。④BMB1nmol可使低频测试刺激诱发的场电位PS幅值明显升高,90min内稳定在基础幅值的194.8%±3.6%水平,与强直刺激诱导的LTP组PS幅值接近(P>0.05)。结论GABA可抑制大鼠海马CA3区LTP的诱导和形成。

Aim To investigate the role of GABA in the induction and maintence of long-term potentiation （LTP）in the hippocampus CA3 region in rats. Methods The concentration of GABA in experimental-side hippocampus at 90 rain after the establishment of LTP induced by tetanic electrical stimulation （TS） was measured by high-performance liquid chromatography （HPLC） with fluorescence detection. Effects of microinjection of GABA and GABAA antagonist bicuculline methbromide（ BMB）on LTP were observed. Results① Compared with control group, the content of GABA in hippocampal tissues of LTP-induction rats obviously decreased（ P 〈 0. 01 ）, and the concentration of glutamate showed no statistical difference. ②After microinjeetion of GABA 200 nmol in CA3 region at 5 min before TS, the PS3 amplitudes at each time point were significantly decreased compared with LTP-induction group（ P 〈 0. 01 ） and were almost completely suppressed. But after simultaneous microinjection of GABAA antagonist bicuculline methbromide （BMB） 1 nmol and GABA 200 nmol in CA3 region before TS, the PS amplitudes were higher than those in GABA-TS group（P 〈 0. 01 ） but lower than those in LTP-induction group （ P 〈 0. 01 ）, indicating that the inhibitory effects of GABA on LTP induction could be attenuated by BMB. ③Microinjection of GABA 200 nmol in CA3 region at 30 min after TS could significantly decrease the PS amplitudes （ P 〈 0. 01 ） and TS-induced LTP effects were completely reversed by GABA. But after simultaneous microinjection of BMB 1 nmol and GABA 200 nmol in CA3 region at 30 min after TS, the PS amplitudes were higher than those in TS-GABA group or control group （ P 〈 0. 01 ） but lower than those in LTP-induction group （ P 〈 0. 01 ）, indicating that the inhibitory effects of GABA on LTP maintenance could be attenuated by BMB.④After microinjection of BMB 1 nmol at 5 min befre recording （only given single pulse test stimulation ） , the PS amplitudes obviously increased and kept at 194. 8% ± 3.6% of baseline, and were near to LTP-induction group during the recording period of 90 min. Conclusion The results suggested that GABA can obviously suppress the induction and maintenance of long-term potentiation （LTP） in hippocampus CA3 region in rats.