ABSTRACT
Objective:To investigate the relationship between the mechanism of mental dependence of propofol and adenosine A2A receptor-neurotransmitter-extracellular signal-regulated kinase (ERK) pathway in rats.Methods:Forty-eight healthy male Sprague-Dawley rats, aged about 7 weeks, weighing 200-300 g, were used in this study.The model of propofol dependence was established by intraperitoneal injection of propofol 40 mg/kg for 14 consecutive days.The rats were divided into 6 groups ( n=8 each) using a random number table method: central control group (group c-C), central agonist group (group c-CGS), central antagonist group (group c-DMPX), peripheral control group (group p-C), peripheral agonist group (group p-CGS) and peripheral antagonist group (group p-DMPX). Adenosine A2A agonist CGS-21680 2.5 ng/0.5 μl was intracranially injected immediately after establishing the model in group c-CGS, while the equal volume of normal saline was given instead in c-C group.CGS-21680 0.1 mg/kg was intraperitoneally injected in group p-CGS, while the equal volume of normal saline was given instead in group p-C.Adenosine A2A receptor antagonist DMPX 50 ng/0.5 μl was intracranially injected at 20 min before each propofol injection in group c-DMPX, and DMPX 0.25 mg/kg was intraperitoneally injected in group p-DMPX.The position preference value (CPP value) was determined before establishing the model, immediately after establishing the model, and after administration of agonist or normal saline (after intervention). The animals were sacrificed at 1 day after establishing the model, and blood samples and brain tissues were obtained for determination of the levels of dopamine (DA) and glutamate (Glu) in plasma and hippocampus and content of serotonin (5-HT) in cerebral cortex (by enzyme-linked immunosorbent assay) and expression of phosphorylated ERK1/2 (p-ERK1/2) in cerebral cortex (by Western blot). Results:Compared with the baseline before establishing the model, CPP value was increased immediately after establishing the model in c-C, c-CGS, p-C and p-CGS groups ( P<0.05), and no significant change was found in CPP value immediately after establishing the model in c-DMPX and p-DMPX groups ( P>0.05). Compared with the value immediately after establishing the model, no significant change was found in CPP value after intervention in c-C and p-C groups ( P>0.05), and CPP value was increased after intervention in c-CGS and p-CGS groups ( P<0.05). Compared with group c-C, the contents of hippocampal DA and Glu were significantly increased in group c-CGS, and the contents of hippocampal Glu were decreased, the content of 5-HT in cerebral cortex was increased, and the expression of p-ERK1/2 was down-regulated in group c-DMPX ( P<0.05). Compared with group p-C, no significant change was found in levels of DA and glutamate (Glu) in plasma and hippocampus and 5-HT and p-ERK1/2 in cerebral cortex in group p-CGS ( P>0.05), and the contents of hippocampal DA and Glu were significantly decreased, the content of 5-HT in cerebral cortex was increased, and the expression of p-ERK1/2 was down-regulated in group p-DMPX ( P<0.05). Conclusion:The mechanism underlying the development of propofol mental dependence may be related to activating adenosine A2A receptors, increasing excitatory neurotransmitters in brain, and thus up-regulating ERK activity in rats.