Aberrant medial prefrontal cortex activity and flexible behavior in the TgF344-AD rat model of Alzheimer's disease

Abstract

Cognitive deficits, including deficits in the ability to shift behavior following negative consequences, often precede the accumulation of canonical neuropathological markers (A{beta} plaques and tauopathy) and severe dementia in Alzheimers disease (AD) patients. The Tg-F344-AD rat model exhibits age-dependent AD pathology and memory deficits that recapitulate AD, However, it is unknown how medial prefrontal cortex activity is altered in awake and behaving AD rats during learning and/or flexible behavior. Here we determine the ability of in 6-7month-old TgF344-AD rats to learn reward predictive cues and to shift behavior away from reward-predictive cues following outcome devaluation while recording mPFC neurons. Specifically, AD rats (n=17) and wild-type littermates (n=17) were presented with two distinct cues as conditioned stimuli (CS+) predicting distinct outcomes. A conditioned taste aversion to one outcome was induced, after which the rats were tested post-devaluation to evaluate their ability to avoid the CS+ associated with the devalued outcome. We found a loss of motivated behavior during learning and a loss of flexible behavior during testing in 6-7-month-old AD rats relative to WT littermate controls. In addition, there was differential aberrant mPFC encoding of cue-outcome associations in AD rats during conditioning and following outcome devaluation. Specifically, AD animals show fewer neurons during conditioning that encode both the cue and the outcome than WT animals. Also, AD animals also showed a greater proportion of neurons that exhibited an excited response to reward predictive cues post-outcome devaluation. Together, these data contribute to our understanding of alterations in mPFC that may underline prodromal AD behavioral deficits to inform future treatments.