Task-dependent learning and memory deficits in the TgF344-AD rat model of Alzheimer's disease: three key timepoints through middle-age in females

The Tg F344 rat model of Alzheimer's disease (AD) provides a comprehensive neuropathology presentation, with age-dependent development of tau tangles, amyloid-beta (Afl) plaques, neuronal loss, and increased gliosis. The behavioral trajectory of this model, particularly relating to spatial learning and memory, has yet to be fully characterized. The current experiment evaluated spatial working and reference memory performance, as well as several physiological markers of health, at 3 key age points in female TgF344-AD rats: 6-months, 9-months, and 12-months. At 6 months of age, indications of working and reference memory impairments were observed in transgenic (Tg) rats on the water radial-arm maze, a complex task that requires working and reference memory simultaneously; at 12 months old, Tg impairments were observed for two working memory measures on this task. Notably, no impairments were observed at the 9-month timepoint on this maze. For the Morris maze, a measure of spatial reference memory, Tg rats demonstrated significant impairment relative to wildtype (WT) controls at all 3 age-points. Frontal cortex, entorhina I cortex, and dorsal hippocampus were evaluated for A beta(1-42) expression via western blot in Tg rats only. Analyses of A beta(1-42) expression revealed age-dependent increases in all 3 regions critical to spatial learning and memory. Measures of physiological health, including heart, uterine, and body weights, revealed unique agespecific outcomes for female Tg rats, with the 9-month timepoint identified as critical for further research within the trajectory of AD-like behavior, physiology, and pathology.