Longitudinal evaluation of female and male Wistar rats performance in some memory tasks

NATALIA CLAUDIA COLETTIS; MARTIN HABIF; M. V. OBERHOLZER; DIANA ALICIA JERUSALINSKY

Belem

Congreso; 3rd FALAN Congress; 2022

Internation Brain Research Organization

Learning and memory studies in animal models often rely on an overrepresentation of males or do not discriminate by sex. We previously found some differences in memory tasks performances in female and male Wistar rats. We present a comparative longitudinal study that reveals sexual dimorphism in some cognitive functions.Open field task (OF) was used to assess spontaneous (horizontal and vertical) exploration, habituation to the environment and anxiety-like behavior. 4 and 12 month-old female and male Wistar rats showed similar performances, except for a higher vertical activity/exploration (rearings) by females.Novel Object Recognition task (NOR) -mainly depending on cerebral cortex- assesses rat?s capacity to discriminate new from familiar objects. Training session: two similar objects A and A? were presented. Exploration time for each object was neither significantly different between objects nor between males and females. Test-sessions: 1h later, the familiar (A) and a novel object (B) were presented to assess short-term memory (STM); 24h later, (A) and a different object (C) were presented to assess long-term memory (LTM). Animals in all groups spent significantly longer exploring (B) and (C) than (A), indicating that they remembered, recognized, and discriminated the novel item.Novel Object Location task (NOL) was used to investigate spatial reference memory ?mainly depending on hippocampus-. Training session was carried out in similar conditions as for NOR training (similar two objects (a) and (b)). Test session: 24 hours later, same two objects were presented, though one at a different location (b). Young rats of both sexes and middle-aged females though not males, spent significantly more time exploring (b) than (a).Inhibitory avoidance step-through task (IA) involves aversive and spatial components -entailing the hippocampus and the amygdala-, and allows to evaluate associative learning and memory after one training step. Training (Tr): the rat was left in an illuminated compartment connected to a dark one; a mild foot-shock was applied when it entered the dark chamber; latency to get into the latter was recorded. Test-sessions: the same procedure was performed with no foot-shock 24 h later (Te1) to assess LTM, and 14 days later (Te2), to test memory persistence. Te1-latencies were significantly higher than Tr-latencies and similar for both sexes, suggesting similar LTM consolidation and expression. Te2-latencies resulted significantly higher than Tr-latencies for middle-aged females and for both sexes at 4 months of age, but there was a tendency towards an amnesic effect on memory persistence in middle-aged males.Thus, a sexual dimorphism appears to emerge, since middle-aged males evidenced cognitive impairments: for NOL, lacking spatial reference LTM, compared to both females and 4-month-old males, since acquisition and STM of objects were preserved, and for IA, tending to be amnesic for memory persistence compared to females. This dimorphism emphasizes the necessity of considering sex when assessing spatial reference LTM and persistence of associative memories from middle-age on.