| Objective:To investigate the change of the content of dopamine (DA) and the DA D1 receptor and D2 receptor immunoactivities in hippocampus during convulsion induced by lidocaine in rats. And using the DA D1 receptor agonist SKF38393 and D2 receptor agonist pergolide to explore the potential mechanism of DA receptors in the process of convulsion.Methods:Twenty-four male Wister rats weighing 250±20mg were randomly divided into 4 groups (n=6): sham group (group S), lidocaine group (group L), lidocaine+SKF group (group LS) and lidocaine+pergolide group (group LP).Anesthesia was induced by 10% Chloral Hydrate at a dose of 350mg/kg (intraperitoneal injection). The vena caudalis of rats was invasived with 24G trochar connecting with heparin cap. Twenty-four hour later, the model of convulsion was induced by the above-mentioned three kinds of local anesthetics via an infusion pump and confirmed by the standard of ethology (Racine standard, above class four). Group S: the rate of normal saline infused was 3ml/h; group L: 2% lidocaine was infused i.v. at 4 mg·kg-1·min-1 until convulsion occurred, and normal saline was infused i.v. at 3ml?h; group LS: SKF38393 was infused i.v. at 10mg/kg, and after one hour, 2% lidocaine was infused i.v. at 4 mg·kg-1·min-1 until convulsion occurred, and normal saline was infused i.v. at 3ml?h; group LP: pergolide was infused i.v. at 1mg/kg ,and after one hour, 2% lidocaine was infused i.v. at 4 mg·kg-1·min-1 until convulsion occurred, and normal saline was infused i.v. at 3ml?h. The lidocaine levels were obtained at the onset of seizure activity. The starting time of seizure were recorded or calculated.Animals were decapitated and their brains were removed 10 minutes after convulsion. The hemi-brains of rat were put into the 4% paraformaldehyde, conventionally dehydrated, dipped into wax, and embedded. Fourμm thick consecutive coronal sections were cut. Immunohistochemical determination of DA receptors were in accordance with EliVision puls immunohistochemical staining kit.Hippocampus sections on the other side of brain were rapidly frozen in liquid nitrogen. The double-antibody sandwich enzyme-linked immunosorbent assay (ELISA) method was used to measure the DA's concentration. The standard liquids and samples were added to the rat's DA monoclonal antibody coated microtiter plate transparent. Sufficient incubation time was needed and the unbound components was washed out, and then the enzyme working solution was added, and lastly the substrate A, B were added. The colour of compounds catalyzed by the horseradish peroxidase (HRP) turned into blue, and into yellow by acids. There was a positive correlation between the colour depth and the concentration of DA. The OD values were measured under 450nm wavelengths, and the DA's content of the samples were calculated according to the OD values of standards and samples.Results:1 There were no significant differences of the rats'weight in four groups.2 The onset time of convulsionThe convulsions were occurred in three groups except group S. The onset time (min) of convulsion was 16.011±0.803, 10.833±1.605 and 19.581±1.361 respective in group L, group LS and group LP. Compared with group L, the onset time of convulsion became shorter in group LS (P< 0.05), and whereas longer in group LP (P< 0.05).3 The expression of DA D1 receptor and D2 receptor in hippocampus CA1 sectionThe immunopositive cells (cells/HP) of DA D1 receptor in hippocampus CA1 section were 45±5, 25±2, 38±2 and 29±2 respective in group S, group L, group LS and group LP. The immunopositive cells (cells/HP) of DA D2 receptor were 41±3, 50±2, 48±3 and 59±3 respective in group S, group L, group LS and group LP.Compared with the group S, the expression of D1 receptor was decreased, but D2 receptor was increased in group L, group LS and group LP (P<0.05). The expression of D1 receptor in group LS was more than group L (P<0.05). There was no difference for the D1 receptor between group LP and group L (P>0.05). The expression of D2 receptor in group LP was more than group L (P<0.05). There was no significant difference for the D2 receptor between group LS and group L (P >0.05).4 The content of DA in the hippocampusThe content of DA (ng/L) in the hippocampus was 53.325±3.690, 66.338±2.205, 78.828±2.042 and 81.931±2.701 respective in group S, group L, group LS and group LP. The content of DA in group L, group LS and group LP was increased significantly compared with group S(P<0.05). Compared with group L, The content of DA was increased in group LS and group LP(P<0.05). There was no difference between group LP and group LS (P >0.05).Conclusion:The expression of dopamine D1 receptor in hippocampus CA1 section reduces, but the expression of D2 receptor increases during convulsion induced by lidocaine in rats. The dopamine D1 receptors play synergic effect, conversely, the D2 receptors play antagonistic effect in the convulsion model.
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