Neuronal Protective Effect Of Propofol Against Global Brain Ischemia And Its Mechanism In Rats

Ischemic neuropathy is becoming the most important cause to harm the health of human with its high morbidity. In neurosurgery, cardiac surgery, vascular surgery and the elderly surgery, cerebral blood vessel complication is also becoming a problem needed to deal with in clinical practice. Propofol (2,6-diisopropylphenol) is an intravenous agent widely used in clinical practice. Many experimental studies suggested that propofol has potential neuronal protective effect, but some controversial results have also been reported. By analyzing the reports, it could be found that many factors such as animal models, administrating doses and protocols of propofol, etc. are quite different in these reports. These differences might be responsible for the controversy. So it is important to verify more effective doses, time points and protocols for propofol administration including pre- and post-treatment for advocating the potential neuronal protective effect of propofol in clinical practice.More and more attention has been paid to the effect of propofol on excitatory neurotoxicity of glutamate induced by ischemia when the mechanisms of the neuroprotective effects of propofol are discussed. Glutamate, which is the most important excitatory neurotransmitter in brain, is accumulated out of cells by either increasing glutamate release, or depressing the function of glial cells for glutamate uptake induced by ischemia or cerebral injury. Stimulation of glutamate on its receptors leads to Ca2+ influx into the cells and the subsequent excessive accumulation of intracellular calcium which is the common causes and pathway of many neuronal diseases such as brain ischemia, epilepsy, and cerebral injury. The effect of propofol, as an effective neuroprotective agent, on many segments of excitatory neurotoxicity of glutamate was observed in many studies. For example, propofol could inhibited glutamate release, recovered the function of glial cells for glutamate uptake and decreased the concentration of glutamate out of neurons in cerebral ischemia in rat. But the effect of propofol on the amount and affinity of glutamate receptor has not been reported in cerebral ischemia rat. In addition, it is difficult to simulate real response of glutamate uptake to propofol in cerebral ischemia in vivo, although Glutamate uptake of cultured neurons and glials was observed under various conditions such as oxygen glucose deprivation, etc.Therefore, the present study was undertaken to investigate the neuronal protective effect of propofol administrated with different doses, time points and protocols against delayed neuronal death of pyramidal neurons in the CA1 hippocampus normally induced by brain ischemic insult. Furthermore, the effect of propofol on the amount and affinity of glutamate receptor and glutamate uptake in the CA1 hippocampus was observed by radio-ligand binding method in rat global brain ischemic model. The findings provided valuable references for clinical practice and elucidating the mechanisms underlying the neuronal protective effect of propofol.1 Neuronal protective effect of propofol on pyramidal neurons in the CA1 hippocampus against global brain ischemia in ratsUsing global brain ischemia produced by the four vessels occluding method, the neuronal protective effect of propofol against delayed neuronal death (DND) of pyramidal neurons in the CA1 hippocampus normally induced by global brain ischemic insult was observed with different doses, time points and protocols.Methods:Eighty male Wistar rats were randomly divided into the following four groups(n=5 per group):â‘ Sham group: Rats were just subjected to a sham operation of global brain ischemia.â‘¡Global brain ischemia group: Rats were subjected to permanently occluding the bilateral vertebral arteries, and 2d later attacked by a global brain ischemia for 8 minutes. â‘¢Propofol pre-treated groups: Rats were treated with propofol before the global brain ischemia and divided into 8 subgroups from propofol-pre-1 to propofol-pre-8 according to doses, time points and protocols of propofol administration(The details in table 1).â‘£Propofol post-treated groups: Rats were treated with propofol after the global brain ischemia and divided into 6 subgroups from propofol-post-1 to propofol-post-6 according to doses, time points and protocols of propofol administration(The details in table 1). The rats were sacrificed by decapitation on the seventh day after the global brain ischemia. Brain sections in a thickness of 6μm were cut, mounted and stained with thionin. The profile of DND in the CA1 hippocampus was evaluated under a light microscope and quantitatively represented with histological grade(HG) and neuronal density(ND). The HG was divided into 4 grades according to the following standard: grade 0, no neuron death; gradeâ… , scattered single neuron death; gradeâ…¡, death of many neurons; gradeâ…¢, death of almost complete neurons. The ND was determined by counting the number of surviving pyramidal neurons with intact cell membrane, full nucleus and clear nucleolus within 1mm linear length of the CA1 hippocampus.Results: In sham group, pyramidal neurons in the CA1 hippocampus were arranged in order with 2³ cell layers. The outline of the neurons was intact, nucleus was full and nucleolus was clear. The HG of all rats was 0, and the ND was 184.5±11.1. Almost complete pyramidal neurons in the CA1 hippocampus died in rats subjected to the global brain ischemia for 8 minutes. The HG significantly increased and the ND significantly decreased compared with the sham group. In the groups of propofol-pre-2 to propofol-pre-4 (administrating dose from 40mg.kg^-1 to 90mg.kg^-1), most of the pyramidal neurons in the CA1 hippocampus were survival. The HG was decreased and the ND was increased compared with those in ischemia group and the changes in the HG and ND in the groups showed an obvious dose-dependency to the dose of propofol administrated. In the group of propofol-pre-1(just 40mg.kg^-1), most of the pyramidal neurons were died and no significant changes in the HG and ND were detected compared with ischemia group. In the group of propofol-pre-5(propofol was administrated with the same protocol to above groups, but the beginning time of administration was much earlier to 24 hours before ischemia), most pyramidal neurons were survival and the HG was decreased and the ND was increased compared with ischemia group. However, the magnitudes of the changes in the HG and ND were smaller than those in the group of propofol-pre-4. Alternatively, administrations of propofol in the same dose and time point to those in the group of propofol-pre-4, but intermittent intravenous injections(propofol-pre-6) or a bolus intraperioneal injection(propofol-pre-7) also showed preventive effect on the DND in certain degree, but it was weaker than that in the group of propofol-pre-4 too. In the group of propofol-pre-8(intermittently intravenous injection), almost complete pyramidal neurons were died and no significant changes in the HG and ND were detected compared with ischemia group.In each post-treatment group except for the propofol-post-1 group, most of the pyramidal neurons were survival and the HG was decreased and the ND was increased compared with ischemia group. Also, the changes in the HG and ND in groups from propofol-post-2 to propofol-post-4 showed an obvious dose-dependency. In the group of propofol-post-1(just 40mg.kg^-1) most pyramidal neurons died and no significant changes in the HG and ND were detected compared with ischemia group. In the large dose groups of 90 mg.kg^-1 of propofol including groups of propofol-post-4, propofol-post-5 and propofol-post-6, similar neuronal protection was showed, although the time points of the propofol administration were different among them.It could be concluded that treatment with propofol in anesthetic doses within a short period before or after global brain ischemia could play neuronal protective effect and that propofol administrated in a protocol consisted of an initial bolus injection and following persistent infusion might play better neuronal protective effect.2 Propofol down-regulates the amount and affinity of glutamate receptor in the CA1 hippocampus in global cerebral ischemia ratIn order to explore mechanisms involved in the neuronal protection of propofol, the effect of propofol on the amount and affinity of glutamate receptors in the CA1 hippocampus was observed in rat global brain ischemia model using radioligand binding method.Methods: Sixty male Wistar rats were randomly divided into 4 groups:â‘ Sham group(n=6): Rats were just subjected to a sham operation of global brain ischemia. â‘¡Global brain ischemia group(n=18): Rats were subjected to permanently occluding the bilateral vertebral arteries, and 2d later attacked by a global brain ischemia for 8 minutes.â‘¢Propofol control group(n=18): Rats were just subjected to a sham operation without global brain ischemia and infused persistently with propofol (90mg.kg^-1) by vein.â‘£Propofol+global brain ischemia group(n=18): Rats were infused persistently with propofol(90mg.kg^-1) via vein for 1h from 3 hours before the global brain ischemia.The animals in global brain ischemia groups and propofol+global brain ischemia groups were sacrificed with decapitation at 0h,1h and 3h after the global brain ischemia(n=5 per time point). In order to correspond to above-mentioned time point, the rats in sham group were sacrificed at 48h after sham operation, and the rats in propofol control group were sacrificed at 48h, 49h and 51h after sham operation. The amount and affinity of glutamate receptors were determined by calculating the values of Bmax and Kd, respectively, by using radio-ligand binding assay. The more the value of Bmax, the more the amount of glutamate receptors, and the more the value of Kd, the less the affinity of glutamate receptors.Results: The value of Bmax of glutamate receptors increased gradually with time in global brain ischemia group. The Bmax had no significant difference at 0h(1933.94±336.30fmol/mg protein) after the global brain ischemia compared with sham group, but was significant increased at 1h (2543.64±374.12fmol/mg protein) and 3h(3260.61±590.85fmol/mg protein) after the global brain ischemia compared with sham group.The value of Bmax of glutamate receptors decreased significantly in propofol+global brain ischemia and propofol control groups at 0h and 1h after the global brain ischemia the corresponding time points(propofol control group) compared with sham or global brain ischemia group at the corresponding time points. The value of Bmax increased gradually and reached the level near to sham group at 3h after the global brain ischemia, but was still larger than that in global brain ischemia group.The value of Kd of glutamate receptors in global ischemia group had no significant difference compared with sham group at every time points after global brain ischemia. Propofol treatment in propofol+global brain ischemia and propofol control groups significantly increased the value of Kd at time point of 1h after the global brain ischemia, or the corresponding time point in propofol control group, while had no significant effect on the value at other time points compared with sham or global brain ischemia group.It could be concluded that propofol can depress the increase of amount of glutamate receptors induced by global brain ischemia and decrease the affinity of glutamate receptors in the CA1 hippocampus in global brain ischemic rats.3 Propofol up-regulates the glutamate uptake of CA1 hippocampus in global cerebral ischemia ratIn order to explore mechanisms involved in the neuronal protection of propofol, the effect of propofol on the glutamate uptake of CA1 hippocampus in global cerebral ischemia rat was observed using L-3H-glutamate method.Methods: Fifty male Wistar rats were randomly divided into 4 groups:â‘ Sham group(n=5): Rats were just subjected to a sham operation of global brain ischemia.â‘¡Global brain ischemia group(n=15): Rats were subjected to permanently occluding the bilateral vertebral arteries, and 2d later attacked by a global brain ischemia for 8 minutes.â‘¢Propofol control group(n=15): Rats were just subjected to a sham operation of global brain ischemia and infused persistently with propofol (90mg.kg^-1) by vein.â‘£Propofol+global brain ischemia group(n=15): Rats were infused persistently with propofol(90mg.kg^-1) via vein for 1h from 3 hours before the global brain ischemia. The animals in global brain ischemia groups and propofol+global brain ischemia groups were sacrificed with decapitation at 0h,1h and 3h after the global brain ischemia(n=5 per time point). In order to correspond to above-mentioned time point, the rats in sham group were sacrificed at 48h after sham operation(n=5), and the rats in propofol control group were sacrificed at 48h, 49h and 51h after sham operation(n=5 per time point). L-3H-glutamate was used for the glutamate uptake assay.Results: The glutamate uptake in the CA1 hippocampus was 345.00±70.16cpm/50μg in sham group. The glutamate uptake had no significant difference at every time points in global brain ischemia groups compared with sham group, which indicated that global brain ischemia had no effect on the ability of glutamate uptake of the CA1 hippocampus. The treatment of propofol in propofol+global brain ischemia and propofol control groups significantly increased the glutamate uptake at time point of 0h and 1h after the global brain ischemia, or at the corresponding time point in propofol control group. The increased glutamate uptake induced by propofol gradually recovered and reached to sham level at 3h after the global brain ischemia.It could be concluded that propofol can enhance the ability of glutamate uptake of CA1 hippocampus in global brain ischemic rats.4 Conclusionsâ‘ Treatment with propofol in anesthetic doses within a short period before or after global brain ischemia could play neuronal protective effect and that propofol administrated in a protocol consisted of an initial bolus injection and following persistent infusion might play better neuronal protective effect.â‘¡Propofol can depress the increase of amount of glutamate receptors induced by global brain ischemia, and decrease the affinity of glutamate receptors, and increase the glutamate uptake of the CA1 hippocampus in global brain ischemic rats. These mechanisms might be contributory to the neuronal protection of propofol.