Reactivity to novelty in cognitively-impaired and cognitively-unimpaired aged rats and young rats
Section snippets
Subjects
Aged, Long–Evans rats were retired breeders originally obtained from Charles River (Raleigh, NC) at nine months of age. They were housed two to three per cage (45×30×18 cm) until the time of testing (22–24 months of age). The animals were maintained on a 12:12 h light:dark schedule (lights off: 20.00) with free access to food (Purina Rat Chow) and water. Health of the animals was monitored regularly by a veterinarian, those displaying overt signs of chronic respiratory difficulties or tumours
Morris water maze
The upper panel of Fig. 1 displays the mean latencies to find the submerged platform for AI, AU and Y animals across the five days of testing in the Morris water maze. The ANOVA conducted on the latency scores yielded a significant group×days interaction, F8,428=8.79, P<0.0001. As would be expected given the criteria used to define AI and AU animals, subsequent analyses indicated that AI animals displayed significantly longer latencies to find the platform on days two to five in comparison to
Discussion
The present results demonstrate that aged rats characterized as impaired in the Morris water maze can also be discriminated on the basis of other behavioural measures. In comparison to Y animals, AI animals consumed less of a novel milk solution, displayed a more prolonged degree of novelty-induced pain inhibition, made fewer rears, open and total arm entries in the elevated plus maze. In the open field, AI animals made fewer total square entries, reared less and engaged in non-exploratory
Are the water maze impairments related to reactivity to novelty?
The facts that AI animals were more reactive to novel stimuli and displayed deficits in habituation raise the intriguing issue of whether these deficits are related to the spatial learning and memory deficits observed in the Morris water maze. It could be argued that animals with memorial deficits would show deficits in habituation because they would be less able to recall previous stimulus exposures. Such “forgetting” would tend to maintain stimulus novelty. Whereas this hypothesis is able to
Unlinked References
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Acknowledgements
This work was supported by research grants from the Medical Research Council of Canada (MRCC)to RQ, National Institute of Aging (Grant No. AG90488) to MJM, and the Natural Sciences and Engineering Research Council of Canada to JR. RQ and JR hold Chercheur Boursier awards from le Fonds de Recherche en Santé du Québec. MJM is an MRCC Scientist. WBR is supported by a graduate fellowship from Les Fonds FCAR and a fellowship from McGill University, Faculty of Medicine (Claude J. P. Giroud Bursary in
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2019, Behavioural Brain ResearchCitation Excerpt :However, aged mice (9 months old) or rats (24 months old) habituated for short period (1 or 2 days) can perform the short-term object recognition memory [33,34]. Aged (24 months old) rats with cognitive impairments (measured in Morris water maze) show a reduction of motor activities without any alteration of anxiety in open field (OF) test and elevated plus maze (EPM) test compared to aged cognitively unimpaired or young rats where habituation to stimuli imparts an important role for behavioural output [35]. The effect of LAN has been extensively studied in young adult rodents too.