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[Ghrelin protects against hippocampal injury after global cerebral ischemia/reperfusion and regulate glutamic acid/γ-aminobutyric acid sensitive neuron discharge]

Objective
To observe the protective effect of ghrelin on hippocampal injury induced by global cerebral ischemia/reperfusion (I/R) and explore its effect mechanisms.


Methods
The male Sprague-Dawley (SD) rats were randomly divided into four groups,namely sham group, I/R group,normal saline (NS)+I/R group and Ghrelin+I/R group, with 42 rats in each group. The model of I/R was reproduced by clipping bilateral carotid artery of rats 15 minutes and then releasing them for 60 minutes. There were no challenges for rats in sham group,just exposed their carotid artery.Ghrelin+I/R group and NS+I/R group were challenged by injecting 1 μ.L ghrelin or NS into lateral ventricle before I/R. Some of brain tissue in the rats was harvested after experiment to determine the levels of malonaldehyele (MDA),myeloperoxidase (MPO) and glutathione (GSH) in hippocampus by using chemical colorimetry and observe infarct sizes and histopathology. Single extracellular neuron discharge in other rats was recorded to observe the activity of glutamic sensitive neurons (Glu-N) and γ-aminobutyric acid (GABA) sensitive neurons (GABA-N) in hippocampus CA1 region of rats suffered I/R.


Results
Compared with sham group, the levels of MDA and MPO in hippocampus of rats in the I/R group were raised markedly, the level of GSH was decreased significantly, the infarct sizes was increased significantly and pycnosis neurons were increased markedly. All sorts of indexes between NS+I/R group and I/R group showed no significantly statistical significance.Compared with NS+I/R group,the levels of MDA and MPO in hippocampus of rats in the Ghrelin+I/R group were decreased significantly [MDA (nmol/g): 16.4 ± 4.2 vs.24.5 ± 6.7,MPO (nmol/g):6.4 ± 1.8 vs.10.2 ± 2.9,both P ＜ 0.05],the activity of GSH was risen remarkably (μmol/g:2.65 ± 0.72 vs.1.66 ± 0.50,P ＜ 0.05),the infarct sizes of hippocampus were reduced markedly [(43.9 ± 9.5)％ vs.(77.0 ± 12.7)％,P ＜ 0.01],the number of pycnosis neuron was reduced markedly (cells:36.2±4.5 vs.47.1 ±6.1,P ＜ 0.01).The results of electrophysiology showed that the discharge frequency of Glu-N and GABA-N in hippocampus CA1 region of rats in I/R group increased markedly as compared with sham group, and no significant difference in the discharge frequency of Glu-N and GABA-N between NS+I/R group and I/R group. Compared with NS+I/R group, injected ghrelin could make the discharge frequency of Glu-N in hippocampus CA1 region of rats decreased markedly (Hz:3.81 ±0.67 vs.4.98±0.33 at ischemia,3.01 ±0.37 vs.3.77 ± 0.41 at reperfusion, both P ＜ 0.05),and the discharge frequency of GABA-N increased markedly (Hz:5.62 ± 0.54 vs.3.62±0.39 at ischemia,4.81±0.48 vs.3.71±0.21 at reperfusion, both P ＜ 0.05)..


Conclusion
Ghrelin might protect hippocampal neuron after I/R iniury, and neuron excitability decrease might be related