Importance of Apparatus Scaling in Novel Object Recognition for Juvenile and Adult Rats.

The growing interest in ontogenetic studies of learning and memory, along with early-life perturbations, has led to the use of younger rodents as a key biological variable in many investigations. This development prompts an important question about whether procedures and apparatuses designed for studying learning and memory in adults should be simply adapted for use with younger and smaller rodents. The current study examined how arena size affects novel object recognition (NOR) performance in juvenile and adult rats. A commonly used larger arena reliably detected novel object preference in adults but not in juveniles. Adjusting the arena size based on average weight differences between age groups improved the consistency of NOR performance in juvenile rats. Sex differences were observed: adult males performed reliably across all arena sizes, whereas adult females required larger arenas to demonstrate effective NOR performance. These findings highlight the importance of tailoring arena dimensions to developmental stage and sex for accurate cognitive assessment. Specifically, they support the use of weight-based arena scaling as a methodological approach in developmental neurobehavioral research and emphasize the importance of careful design when studying female rodents. Future studies should explore similar environmental adjustments for other behavioral tests in juvenile and female populations.