关键词: 空间工作记忆, 空间参考记忆, 东莨菪碱, 胆碱能受体, Morris水迷宫

Abstract: Despite of many years of intensive studies, the role of cholinergic system in spatial reference memory and spatial working memory remains controversial. It was found that scopolamine, an antagonist to cholinergic muscarinic receptor, impaired the encoding and retrieval process of spatial memory. It was also found that the spatial working memory was more sensitive to muscarinic receptor antagonists than spatial reference memory. In this study, the effects of scopolamine on the acquisition, retention and retrieval processes of spatial reference memory and spatial working memory were observed and compared using the Morris water maze (MWM) task.
Experiment 1 were performed on 46 adult rats, which were divided randomly into 6 groups and trained in a reference memory version of the MWM with two blocks of four trials per day for three consecutive days. Scopolamine was injected (1 mg/kg, i.p.) 20 min prior to the day’s first trial in group 1, immediately after the day’s last trial in group 2, or 20 min prior to the probe trial in group 3. The remaining 3 groups were injected with saline for control. Experiment 2 were performed on 42 adult rats, which were divided randomly into 6 groups and trained in a working memory version of the MWM task to find a new target position (trial 1). Retrieval (trial 2) was tested 75 min later. Similar to experiment 1, scopolamine was injected (1 mg/kg, i.p.) 20 min prior to trial 1 in group 1, immediately after trial 1 in group 2, or 20 min prior to trial 2 in group 3. The remaining 3 groups were injected with saline for control. The swimming latency, length, strategy and velocity were recorded.
For experiment 1, animals in group 1 and group 3 showed deteriorated learning curves and no spatial bias to the goal quadrant was observed, indicating that scopolamine interfered encoding and retrieval process of the spatial reference memory. Animals in group 2 showed no significant difference from the saline control, indicating that scopolamine has no effects on the retention of spatial reference memory.
For experiment 2, animals in all the three groups showed significant prolongation of swimming latency, indicating that the scopolamine impaired encoding, retention, and retrieval of the spatial working memory.
In conclusion, the present study demonstrated that the muscarinic receptors played differential roles in spatial working memory and spatial reference memory.

Key words: spatial working memory, spatial reference memory, scopolamine, muscarinic receptor, Morris water maze