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Abstract
The aim of this study was to translate the “orientation” query of the ADAS-Cog inventory to rats and to investigate whether they can determine which time of the day they are. For this purpose, we established a modified Morris water-maze navigation task where the escape platform was placed onto various locations at different times of the day: “morning”, “noon” and “evening”. In each of these sessions rats swam a “query” trial and a “confirmatory” trial, 30 min apart. Lister Hooded rats randomly chose among the three possible target locations, while Long Evans rats partly followed a win-stay strategy by preferring to visit first to the platform position of the previous session. Despite simplifying the task to a morning–evening discrimination, Lister Hooded rats continued searching by chance, while Long Evans rats switched to the mentally less demanding random strategy. We then inserted a board into the pool which required longer swimming path from the animals when they were correcting an initial wrong choice, but this modification did not result in a change in the above strategies. Lastly, in a separate group of Long–Evans rats, the training conditions were modified inasmuch an incorrect choice was definitely punished by impeding the animals to correct it and confining them to a platform-free part of the maze for the whole trial period. However, even these stricter conditions were not sufficient to make the rats distinguish times of the day. The observed lack of time discrimination may source from an evolutionary built in mechanism characteristic for the rat species or this ability may have only been lost in laboratory rats.
Highlights
Patients suffering from Alzheimer’s disease (AD) have difficulties in remembering recent events that took place at a particular time and place. is indicates one of the first cognitive and behavioral symptoms which is the deterioration of episodic memory
Water was available ad libitum. e weight of the rats were in the range of 250–319 g and 371–544 g in case of Lister Hooded rats, 325–440 g and 377–556 g in case of Long Evans rats, while “LEJ2” rats weighed 415–518 g and 413–505 g at the beginning and at the end of the test, respectively. ey were housed in groups of three rats in 1500 cm2 polycarbonate cages, in enriched environment with paper tube and wooden bricks to chew and were habituated to handling intensively throughout the measurements. e animals were studied lifelong in several food-rewarded cognitive tests
Out of the animals that were trained in the standard Morris water maze task, 12 LE and 12 Lister Hooded (LH) rats were used for the 3-platform experiment. e daily mean of escape latency to the actual target zones diminished continuously through the experiment period. e performance of the two groups did not differ significantly according to the repeated measures ANOVA performed on data of the first 8 days (“days” effect 퐹(7,154) = 18.5, 푝 < 0.001; Figure 2)
Summary
Patients suffering from Alzheimer’s disease (AD) have difficulties in remembering recent events that took place at a particular time and place. is indicates one of the first cognitive and behavioral symptoms which is the deterioration of episodic memory. Tulving conceptualized episodic memory as a conscious awareness of a unique prior experience, and as the knowledge about what a particular event was and where and when it occurred [1]. Episodic memory is conceived to be unique to humans; many investigators could reveal an episodic-like memory system in animals akin to that of humans with respect to fulfilling the criteria of the what-where-when triad. Clayton and Dickinson provided conclusive behavioral evidence of a so-called “episodic-like” memory in scrub jays that remembered in a food-caching paradigm when, where and what kind of food items were stored [2]. With varying the entity and location of objects it was shown that mice could reflect memory of “what”, “when,” and “where”, that fulfills behavioral criteria of an episodic-like memory [3]. With varying the entity and location of objects it was shown that mice could reflect memory of “what”, “when,” and “where”, that fulfills behavioral criteria of an episodic-like memory [3]. e same group demonstrated that this novelty-preference paradigm works with rats [4]
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