[Effect of orexin-A on recovery from ketamine anesthesia in aged rats].

Objective: To observe the effect of orexin-A on the recovery and cognitive function of aged rats after ketamine anesthesia.

Methods: Fifty-five aged rats were divided randomly into control group, model control group, 1 nmol/L Orexin-A group, and 4 nmol/L Orexin-A group. In the latter 3 groups, the rats received an intraperitoneal injection of ketamine at 100 mg/kg, and normal saline was injected in the control group. Ten minutes after the injections, the rats received intraventricular injections of artificial cerebrospinal fluid (control and model control group) or of 10 microl 1 or 4 nmol/L Orexin-A as indicated. The behavioral changes of the rats were assessed by the duration of loss of righting reflex (LORR). Electroencephalogram (EEG) recordings were used to evaluate the changes in rat brain activity by comparison of the percent of sigma wave in EEG before and after the intraventricular injections. Morris water maze was used to test the learning and spatial localization abilities of the rats.

Results: Ketamine resulted in obvious impairment of learning and memory abilities of the aged rats. Orexin-A at 4 nmol/L induced significant decrease in the duration of LORR and marked reduction of sigma activities in anesthetic rats (P<0.05), and obviously improved the learning and spatial localization abilities of the rats after anesthesia (P<0.05).

Conclusion: Orexin-A can promote the recovery and improve the cognitive function of aged rats after ketamine anesthesia.