AIM: To analyze the effect of morphine and its interaction with cholinergic system on the spatial recall process of rats by Morris water maze performance. METHODS: The experiment was carried out in the Beijing Key Laboratory (Learning and Cognition Laboratory) of Capital Normal University in September 2004. The experimental animals were thirty-six Wistar rats of 5 months weighing 180-210 g. Morris water maze was used to train all the rats to find the covert platform in it within 20 seconds. On the 1st day after the end of training, the rats were randomly divided into six groups in each group with 6 rats in each group: one control group and 5 experimental groups, the recall ability was tested. On the 2nd and 9th days, the animals received intraperitoneal injection for twice while grouping: rats in Group 1 (control group) were injected with saline and saline, Group 2 received 10 mg/kg morphine and saline, Group 3 received 0.1 mg/kg physostigmine and saline, Group 4 received 10 mg/kg morphine and 0.1 mg/kg physostigmine, group 5 received 10 mg/kg morphine and 0.2 mg/kg physostigmine, Group 6 received 10 mg/kg morphine and 0.5 mg/kg naloxone. The latencies of rats with drugs treatment to find the covert platform were measured at 30 minutes after injections.RESULTS: No animal died during the experiment, and all were involved in the analysis of results. ①On the 1st day before drug treatment during the experiment, the latencies for the rats to find the covert platform had no significant differences among the groups. ② On the 2nd and 9th days during the experiment, the latencies for the rats to find the covert platform in Group 2 (injected with morphine) were significantly prolonged as compared with those in the control group (87±22.527), (16.167±3.736) s, P < 0.001; (96.667±20.851), (16.333±2.361) s, P < 0.001 . ③ On the 2nd and 9th days during the experiment, the latencies for the rats to find the covert platform in Group 3 (injected with 0.
1 mg/kg physostigmine) were not significantly different from those in the control group (P > 0.05); The latencies in Group 4 (injected with morphine and 0.1 mg/kg physostigmine) were prolonged as compared with those in the control group (P < 0.01), but slightly shortened but insignificantly as compared with those in Group 2 (P > 0.05). The latencies in Group 5 (injected with morphine and 0.2 mg/kg physostigmine) had no obvious change as comoapred with those in the control group (P > 0.05), but significantly shortened as comarped with those in Group 2 (injected with morphine) on the 2nd day (26±5.790), (16.333±2.361) s, P < 0.01; on the 9th day: (31.667±7.337), (16.333±2.361) s, P < 0.001 . ④ On the 2nd and 9th days during the experiment, the latencies for the rats to find the covert platform in Group 6 (injected with 10 mg/kg morphine and 0.5 mg/kg naloxone) had no obvious changes as compared with those in those in the control group and Group 5 (P > 0.05), but significantly shortened as compared with those in Group 2 on the 2nd day: (34.667±6.746), (87±22.527) s, P < 0.01; on the 9th day: (22.167±6.457), (96.667±20.851) s, P < 0.001 . CONCLUSION: Morphine (10 mg/kg) can evidently inhibit the recall to water maze performance of rats, which may have a close relationship with inhibitory effect of morphine on central cholinergic system. Physostigmine can enhance the activity of cholinergic system, and then antagonizes the morphine-induced spatial recall impairment