BACKGROUND: Patients suffer from changes of cognitive function postoperatively, which has attracted extensive attentions in clinic. It is still to be investigated whether operation damages both antegrade memory and retrograde memory, or either of them.OBJECTIVE: To observe the effects of operation on the anterograde and retrograde memory with Y maze test.DESIGN: A randomly controlled animal trial.SETTING: Department of Anesthesiology, Pudong New Area Gongli Hospital of Shanghai City. MATERIALS: Sixty-three male healthy Sprague-Dawley (SD) rats of clean degree, weighing 200 - 250 g, 10 weeks old, were provided by the animal center of Chinese Academy of Sciences. The rats were tested by antegrade and retrograde respectively. The rats were randomly divided into normal control group (n =7), anesthesia group (n =14), sham-operated group (n =14); partial hepatectomy group (n =14), short-term retrograde memory group (n =7) and long-term retrograde memory group (n =7). According to the time of Y maze training started, rats in the anesthesia group, sham-operated group and partial hepatectomy group were observed at 1 and 7 days after anesthesia.METHODS: The experiments were carried out in the central laboratory of Pudong New Area Gongli Hospital of Shanghai City from February to June in 2006.①Test for antegrade memory: Rats in the normal control group were only treated with intraperitoneal injection of saline without aesthesia and operation; Those in the anesthesia group were anesthetized with intraperitoneal injection of 10 g/L pentobarbital sodium (40 mg/kg); Those in the sham-operated group were anesthetized, then intraperitoneal exploration was performed without hepatectomy; Those in the partial hepatectomy group were anesthetized, then fixed in a supine position after righting reflex disappeared, and an incision of 1.5 - 2.0 cm was made along the midline of xiphoid lower abdomen, then left lateral lobe of liver (about 1/3 of total liver) was freed, and ligated at distal pedicel with 1* filament. The abdomen was closed layer by layer after complete hemostasis. The learning and memory abilities were tested after operation. The rats were exposed to Y maze exercise from the 1st or 7th day after surgery, the error numbers, the time to complete whole trials per day and active avoidance numbers were recorded to evaluate the antegrade memory ability.②Test for short-term retrograde memory: Rats in the short-term retrograde memory group were trained in Y maze as the above methods for 1 day, then partial hepatectomy was performed immediately, and the effects on short-term memory were evaluated at 24 hours postoperatively.③Test for long-term retrograde memory: Rats in the long-term retrograde memory group were trained in Y maze till reached the standard for grasping, then partial hepatectomy was performed in those reached the standard for grasping within 3 days, and the effects on long-term memory were evaluated at 48 hours postoperatively.MAIN OUTCOME MEASURES: The error times, the time to complete whole trials per day and active avoidance times were observed every day.RESULTS: Totally 63 SD rats were used, including 6 failed in the partial hepatectomy in the partial hepatectomy group, 3 died due to over-anesthesia, and 5 in the long-term retrograde memory group grasped the tasks in Y maze till the 4th day, which were supplemented by other rats.①Impairment of anterograde memory after partial hepatectomy: The results of Y maze test in the partial hepatectomy group were not obviously different from those in the other groups on the 1st day. The error times on the 2nd and 3rd days of training in the partial hepatectomy group at 1 and 7 days after anesthesia were obviously more than those in the normal control group (F =6.08, P＜0.01), and the active avoidance numbers were obviously fewer than those in the normal control group (F =10.85, P＜0.05); For the rats at 1 day after anesthesia, the error times on the 3rd day of training in the partial hepatectomy group were obviously more than those in the normal control group (F=12.34, P＜0.01), and the active avoidance numbers were obviously fewer than those in the normal control group (F =3.91, P＜0.05). There were no obvious differences in the anesthesia group and sham-operated group as compared with those in the normal control group.②Impairment of retrograde memory after partial hepatectomy: The results of Y maze test in the normal control group and retrograde short-term memory group at 24 hours after operation were better than those in each group on the 1st day of training (F =35.22, 22.56, P＜0.01), and the results on the 2nd day had no obvious differences between the two groups. For the rats reached the standards for grasping in the retrograde long-term memory group, the results of Y maze test on the 3rd day of training were obviously better than those on the 1st day (F=52.38, 43.86, P＜0.01). At 48 hours after operation (the 5th day of training), the results of Y maze test in the normal control group and retrograde short-term memory group were still obviously better than those in each group on the 1st day of training (F =52.38, 43.86, P＜0.01), but there were no obvious differences between the two groups on the 5th day.CONCLUSION: Partial hepatectomy mainly impaires the anterograde memory abilities of rats, and it has no effect on the retrograde short-term memory and long-term memory.