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Objective The hyperexcitability of neurons caused by excitatory and inhibitory amino acid imbalance is considered as the essential mechanism underlying epilepsy.Excitatory glutamate receptor overactivation plays important role in pathogenesis processes of epilepsy.Therefore, Inhibiting NMDA receptor (NMDAR) activity could be one of methods for treatment of epilepsy.Scorpion is used as a traditional Chinese Medicine for epilepsy treatment.The therapeutically effective constituent of scorpion is scorpion venom (SV).However, the elements of SV are complex, highly toxic, so that its clinical application is limited.By means of a special method we obtained a kind of SV extract named the scorpion venom neuro-nourishing peptide (svNNP).Experiments show that svNNP has higher anti-epileptic but lower neurotoxic side effects than SV.So, the aim of this study is to further explore antiepileptic mechanism of svNNP.Methods Western-blot analysis and whole cell patch clamp technique were used in epilepsy model in vivo and cultured hippoeampal neurons in vitro.Results (1)Using lithium chloride (LiCl)-pilocarpine (PILO) epilepsy rat model, the effects of svNNP were observed by western-blot analysis.The animals were divided into four groups: NS + NS group, PILO epilepsy model + NS group, PILO epilepsy model + svNNP treatment group, PILO epilepsy model + sodium valproate (VPA) positive treatment control group.The results were that the expressions of NR2 subunit of NMDA receptor were significantly decreased for svNPP treatment group compared with PILO epilepsy model group and VPA treatment control group.(n=3, P<0.05), but there are no significant among NS group, PILO epilepsy model group and VPA treatment control group.(2) Using whole-cell patch clamp, modulatory effects of svNNP on NMDA-activated current (INMDA) from cultured hippocampal neurons were observed.Application of 1 mM NMDA and its co-agonist Gly of 10 μM for 30 ms onto cultured hippocampal neuron, an inward current was recorded.After treatment with svNNP (0.1 μg/ml), the amplitude of INMDA was obviously smaller (n=8) than before treatment.INMDA was suppressed to (70.0 ± 10.3)% by 0.1 μg/ml svNNP.The difference was very significant between the current amplitudes before and after svNNP (0.1 μg/ml) treatment (n=8, P<0.01).We also observed the inhibition of svNNP (0.1 μg/ml) on 0.1 mM NMDA-activated currents.After treatment of svNNP, the current amplitudes were suppressed from (248.3 ± 55.5) to (70.9 ± 21.2) pA and the inhibitory rate was (70.8 ± 8.3)% (n =8, P < 0.01).The effects of different concentrations of svNNP (10-3, 10-4, 10-5, 10-6, 10-7 and 10-8 μg/ml) on INMDA were also investigated.Five different concentrations of svNNP all could reduce INMDA of hippocampal neurons (P < 0.01, n =8), the concentration-response curve of svNNP inhibition of INDA was S shaped.The results show that modulatory effects of svNNP on INMDA appeared concentration-dependent manner.Conclusion These results indicated that svNNP could not only make NMDAR expression down regulation but also inhibit NMDA-activated currents from the hippocampal neurons in a dose-dependent manner.That could explain its neuroprotective effect by preventing excessive activation of NMDAR during seizures.