Effects Of δ-opioid Receptor On The Hippocampal Synaptic Plasticity In The Global Ischemic Rats

When the blood flow to brain reduced, it will cause ischemia. Cerebral ischemia can be divided into stroke (caused by local infarction) and global ischemia (due to cardiac arrest, massive blood loss). Cerebral ischemia can lead to serious consequences including action and speak disorders and cognitive impairment, brings a lot of trouble to people physically and mentally and lives. Brain function is associated with synaptic plasticity, suggesting that the synaptic plasticity will change after ischemia.Opioid receptor is a class of G-protein-coupled receptors, there are various subtypes, primarily associated with modulations of pain, myocardial protection and gastrointestinal motility. It has been well documented that, in addition to participating in the analgesic, the DOR also participates in myocardial ischemia protection.This study was therefore conducted to investigate the effects of DOR, by using the selective agonist [D-Ala2, D-Leu5]-Enkephalin (DADLE) and antagonist naltrindole of DOR, on synaptic plasticity and the possible underlying mechanisms in hippocampus of the cerebral ischemic rats. The main results of the study are as following.1. The global cerebral ischemia-reperfusion modelThe standard four-vessel occlusion (4-VO) approach (permanent electric condensate blocking bilateral vertebral artery and temporary blocking bilateral carotid artery) was taken to establish the rat model of cerebral ischemia and reperfusion following the implantation of cannula into the lateral ventricle for administration of DADLE or naltrindole. To avoid scratching between animals and the cannula falling off, each animal was accommodated in a single cage. As the size and location of the alar foramina of rats may have differences, the alar foramina was accurately positioned for the electric condensate blocking, which improved the success rate of the model construction.2. Effect of DOR on neuronal morphology after global cerebral ischemia and reperfusionHippocampal CA1 area is highly sensitive to ischemia, and neuronal death commonly occurs in the area due to the ischemia-reperfusion injury. We firstly examined the effects of DOR modulation on the morphological changes of neurons and dendritic spines in CA1 of the ischemic rats. The results showed that, at 3 and 7 days after ischemia reperfusion the hippocampal neurons appeared to be shrinkage markedly and reduced in the density of dendritic spines, while activation of DOR significantly improved the neurons shrinkage and the density of spines.3. Effect of DOR on synaptic transmission after global cerebral ischemia and reperfusionBy using the method of electrophysiological, we observed the effects of DOR modulations on the basic synaptic transmission and short-term plasticity in hippocampal CA3-CA1 at the 7 days after global cerebral ischemia and reperfusion. The results showed that, the basic synaptic transmission and short-term synaptic plasticity were affected by the injury, while the activation of DOR improved the basic synaptic transmission and paired pulse facilitation, suggesting that DOR can improve the synaptic transmission and reduce the injury from4. Effect of DOR on neuro transmitters after global cerebral ischemia and reperfusionUsing HPLC-MS technique, we further examined the effects of DOR modulations on the changes of several neurotransmitters levels, including glutamate, dopamine, γ-aminobutyric acid and acetylcholine, in hippocampus of the rats. No obvious differences of concentrations of these molecules were found amongst the experimental groups of the rats.5. Effect of DOR on the synaptic-related signal pathway after cerebral ischemia reperfusionOur previous findings showed that, the expression of MARCKS, a specific substrate was changed in response to DOR modulation at different time points after ischemia reperfusion. We then further examined expression changes of PKC and its subtypes including PKCε and PKCγ. The results showed that, PKCε and PKCγ at 3 and 7 days after ischemia reperfusion had no obvious changes. We also studied the roles of NR2B-ERKs-CREB pathway in the plasticity modulation after DEDLE/Naltrindole treatment. The results showed that NR2B had no significant change at 3 days and was down-regulated at 7 days after reperfusion. After DEDLE treatment, the expression of this protein appeared to be up-regulated. p-ERK1/2 were reduced at 3 and 7 days after ischemia, and were up-regulated at these time points after DOR activation. p-CREB had no significant changes at 3 and 7 days, suggesting that ERK may activate the downstream of other protein instead of CREB.