Memory performance in a novel ten-compartment water maze: normal behaviour and chlordiazepoxide-induced place learning impairment in rats

Abstract

The primary aim of this study was to develop a novel water maze in which the role of extramaze and intramaze cues in the acquisition, storage and retrieval of a place learning task could be evaluated. Animals were not impaired in their ability to locate the submerged escape platform irrespective of whether extramaze cues were present or not in the initial training, even when the starting compartment was rotated to a different location. The results of this study further demonstrated that rats trained in the presence of both sets of cues had considerable exploratory behaviour and a more flexible swim path trajectory, but were more prone to interfering factors on being presented with a new escape response in the absence of extramaze cues. Moreover, it would appear that the animals were able to acquire both mapping and non-mapping strategies during the place learning task and the use of this particular water maze is important in studying the different roles played by intra and extramaze cues during place learning and retrieval. In order to verify whether this particular water maze could be used to study drug induced memory impairment similar to previously developed water mazes, the effect of the benzodiazepine receptor agonist chlordiazepoxide (CDP) on the acquisition and retention of a place learning task in the presence or absence of extramaze cues was investigated. Rats (n=70) were first trained to swim and locate a submerged escape platform placed in one of the compartments of the water maze. They were then divided into two groups of five subgroups each and administered chlordiazepoxide at a dose of 0 (control), 2, 4, 8 and 16 mglkg and tested with a new escape response. All subgroups were then reversed on saline and a new platform location tested. Chlordiazepoxide, in a dose-dependent manner, produced an impairment in the acquisition of new platform location, but only in the presence of extramaze cues. The observed chlordiazepoxide induced memory impairments were completely reversed when the drug was substituted by the vehicle. These results, in agreement with other studies, emphasise the importance of benzodiazepine receptors in the consolidation of place learning tasks, especially in the presence of distal spatial cues. The ease with which the ten-compartment water maze can be configured to measure learning in the presence or absence of extramaze cues together with its ability to dissociate non-mnemonic from mnemonic processes adds an important tool in the study of learning and memory.