Ontogeny of Rat Recognition Memory, Exploratory Activity and Anxiety Measured by Novel Object Recognition Test and Open Field Test.

BACKGROUND

Ontogeny refers to the gradual changes in behaviour and physiological processes that occur across the lifespan of an organism, which are associated with significant changes in sensory, emotional and social systems.

PURPOSE: In this study, the changes that occur in object recognition memory, exploratory activity and anxiety-like behaviour were studied in 6-, 12- and 24-month-old rats as a result of their normal developmental and/or ageing process, with the help of two behavioural testing paradigms, such as the novel object recognition test (NORT) and open field test (OFT).

METHODS

Animals were randomly assigned to three experimental groups: Group 1: 6-month-old-representing early adulthood, a stage characterised by peak physiological and cognitive function. Group 2: 12-month-old-representing middle-aged, a transitional phase with potential early signs of age-related changes. Group 3: 24-month-old-representing late adulthood and early ageing, a period associated with progressive neurobiological and behavioural alterations. The NORT and OFT were carried out using the Panlab-SMART automated behavioural video tracking system.

RESULTS

Results demonstrate that recognition memory was only mildly decreased in middle-aged animals, and remained mostly intact throughout adulthood and in aged animals. Anxiety-like behaviour did not show significant differences across age groups. In contrast, rearing and exploratory activity declined with age, suggesting the behavioural changes are more reflective of exploratory and locomotor behaviours. Stretching and other risk-assessment behaviours did not change as the age progressed.

CONCLUSION

When combined, these results imply that exploratory and locomotor behaviours are more susceptible to ageing, compared to recognition memory and anxiety-like behaviours. The results also highlight the importance of using multiple behavioural assays to holistically unravel emotionality changes across various age groups in rats. Further research is needed to understand better the molecular, cellular and neurobiological mechanisms driving these behavioural trajectories in rats.