Effect Of Orexins On Emergence And Cognitive Function Of Rats Receiving Ketamine-midazolam Anesthesia

With the progress of modern medicine, patients with multiple medical problems are now able to undergo complex surgical procedures relatively late in life.The application of new anesthetic techniques and agents remarkably improve the safety of operations, however, the incidence of delayed recovery from anesthesia and Postoperative cognitive dysfunction(POCD)is still high. Delayed recovery from anesthesia and POCD prolongs the length of stay and increases the cost of hospitalization, diminishes the quality of the patient's life, Furthermore, it raises the mortality and morbidity, which are becoming the tough problems to us.More attentions have been paid on how to promote recovery from anesthesia and the recovery of the postoperative cognitive function now days.Orexins(orexinA and orexinB), a new kind of neuropeptides which are synthetized and secreted by the lateral hypothalamus are discovered in 1998. Evidences indicate that these peptides play a critical role in promotion and maintenance of wakefulness. Additionally, their role in regulation of the recovery of anesthesia has been revealed by recent studies,exogenous orexins can decrease the duration or depth of anesthesia, in other words, orexins have the wake-promoting effect. However, whether orexins could facilitate the recovery of cognitive function after anesthesia has not been reported.Another important role of orexins system is regulation of energy homeostasis.Human body must perceive the change of the energy before it's exhausted, and then accommodate awareness function in order to supply energy. Orexins system could play this role. A series of experiments have confirmed that hypoglycemia could activate orexins system and promote awakening from sleep. Will this also affect anesthesia recovery? In the past, it's generally considered that severe hypoglycemia is one of the most important factors which leads to the delay of anesthetic recovery, but few reports have discussed the effect of varying degrees of hypoglycemia on anesthetic recovery.Therefore, Our study was performed on the rat model which is anesthetized by ketamine and midazolam. First of all, we studied the effect of icv injection of orexinA on the emergence and cognitive function of anesthetized rats,with the methods of electroencephalographic recording, behavior observation and the morris water maze test. secondly, we produced the rat model of varying degrees of hypoglycemia by injection of insulin intraperitoneally or fasting.Then,we studied the impact of varying degrees of hypoglycemia on the expression of the orexinA in the hypothalamus of the anesthetized rats and the expression of the c-fos in frontal cortex with the methods of immunohistochemistry and RT-PCR. Finally ,we studied the effect of varying degrees of hypoglycemia on the emergence and cognitive function of the anesthetized rats. The results show as follow:1. Effect of icv injection of orexinA on recovery of rats receiving anesthesia10 min after anesthesia, different doses of orexinA were injected .Compared with the control group,high dose of orexinA(4nmol) induced significant decrease in the percent ofδwave in ECoG, the duration of LRR and post-LRR ataxia(P<0.01).However, there was no significant change in these parameter in the low dose orexinA group(1nmol)(P>0.05). Therefore, these results suggest that orexinA can decrease the duration or depth of anesthesia,and has a potent arousal effect on anesthetized rats.2. Effect of orexinA on morris water maze test performance of anesthetized ratsMorris water maze test were performed 4h after anesthesia,the results showed that , high dose of orexinA decreased the escape latency(P<0.01) and increased the duration that spent in the target quadrant significantly(P<0.05).However, there was no significant change in these parameter in low dose orexinA group with respect to the control group(P>0.05). These results indicate that orexinA can improve the learning and memory function of anesthetized rats3. Effect of hypoglycemia on the Hypothalamic orexins expression of anesthetized ratsIn the immunohistochemistry and RT-PCR test, Compared with the control group,the expression of orexinA and propro-orexins mRNA were increased significantly in both mild hypoglycemia group and severe hypoglycemia group(P<0.01), These findings illuminate that hypoglycemia can promote orexins expression in anesthetized rats.4. Effect of hypoglycemia on the expression of c-fos of frontal cortex in anesthetized rats. Immunohistochemistry results showed that, the expression of c-fos in the frontal cortex of anesthetied rats increased significantly in the mild hypoglycemia group(P<0.01).However, there was no significant change in the severe hypoglycemia group with respect to the control group(P>0.05). These findings illuminate that mild hypoglycemia may have a potent arousal effect on anesthetized rats.5. Effect of hypoglycemia on the recovery and cognitive function of anesthetized ratsCompared with the control group,mild hypoglycemia induced significant decrease in the percent ofδwave in ECoG, the duration of LRR and post-LRR ataxia(P<0.05), and increased the performance of morris water maze test(P < 0.05). Whereas severe hypoglycemia significantly increased the percent ofδwave in ECoG, the duration of LRR and post-LRR ataxia(P<0.01),and decreased the performance of morris water maze test(P<0.05)with respect to the control group . These results indicate that mild hypoglycemia has a potent arousal effect on anesthetized rats,but severe hypoglycemia delays emergence from anesthesia.In summary, we demonstrated that icv injection of orexinA could improve emergence from anesthesia and temporal postoperative cognition.Mild hypoglycemia could facilitate the expression of orexins and then improve emergence from anesthesia and temporal postoperative cognition。However, severe hypoglycemia could result in delayed recovery even though it facilitated the expression of orexins, indicated that suitable blood glucose was necessary for emergence from anesthesia...