IGF-1对海马神经元抑制性突触传递的影响

Effects of IGF-1 on Inhibitory Synaptic Transmission in Cultured Rat Hippocampal Neurons

目的：观察胰岛素样生长因子1（IGF-1）对原代培养海马神经元抑制性突触传递的影响并探讨其可能机制。方法：采用无血清培养基培养海马神经元,在10～14d时用于实验。电生理实验分为正常对照组和IGF-1处理组（实验前24h加入IGF-1,终浓度为10μmol/L）。细胞免疫化学实验分为正常对照组、IGF-1处理组和MAPKS转导通路抑制剂（PD98059）预处理组（IGF-1处理前1h加入PD98059,终浓度为10μmol/L）。采用全细胞膜片钳记录方法观察IGF-1对抑制性突触后电流（IPSC）的影响,用细胞免疫化学方法观察其对γ-氨基丁酸能细胞数目影响。结果：IGF-1能够显著降低IPSC的频率,但与对照组比较其幅度差异无统计学意义;IGF-1能够明显减少GABA阳性细胞数目,应用PD98059后可阻断这种作用。结论：IGF-1的上述作用可能参与海马对学习记忆功能的调节过程。

Objective To observe the effect of IGF-1 on inhibitory synaptic transmission in cultured rat hippocampal neurons and explore the possible mechanism. Methods Hippocampal neurons of rat were cultured with serum-free medium and used for experiment at 10 ～ 14 days. The cells were divided into 2 groups in the electrophysiology experiment ： the control group and the IGF-treated group （ in this group neurons were treated with 10 μmol/L IGF-1 24 h before experiment）. While, 3 groups were included in the immunocytochemistry section： the control group, the IGF-treated group and PD98059 （10 μmol/ L） pretreated group（ PD98059 was added to the medium 1 h before the addition of IGF-1 ）. We observed the effects of IGF-1 on inhibitory postsynaptic current（IPSC） with the whole-cell patch clamp recording method and on the ratio of GABAergic neurons with immunocytochemical method. The patch-pipette solution contained （ in mmol/ L） ： 140 KCl, 10 HEPES, 10 EGTA, 2 MgCl2,2 Na2ATP, 1 CaCl2, pH 7.3. The typical resistance of glass electrodes was 3 ～7 MΩ when filled with intracellular pipette solution. The range of the whole-cell series resistance is 10 ～ 15 MIL During experiments, culture dishes were rinsed and perfused with extracellular solution containing （in mmol/L） ：140 NaCl, 5 KCl, 1 MgCl2, 10 HEPES, 10 Glucose, 3 CaCl2, pH 7.4. Synaptically spontaneous IPSCs were isolated by the application of 20 M 6, 7-dinitroquinoxaline-2, 3-dione （DNQX） and 50 μmol/L aminophosphonobutyrate（APV）, the antagonist to the excitatory-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid （AMPA） and N-methy-d-aspartate（NMDA） receptors, respectively. Results IGF-1 remarkably reduced the frequency of IPSC, while had little effect on the mean amplitude. IGF-1 decreased the ratio of GABAergic neurons, which could be blocked by the inhibitor of mitogen-actived protein kinase（MAPK）. Conclusion IGF-1 depressed inhibitory synaptic transmission,which may prevent induction long-term potentiation. IGF-1 reduces the ratio of GABAergic neurons. IGF-1 may influence inhibitory synaptic transmission through MAPK signal transduction pathway. As the activation of GABA receptor may depress the LTP, IGF-1 may modulate the function of learning and memory by disinhibition of hippocampal neurons. IGF-1 may be a promising target for learning and memory.