Combinatorial targeting of NMDARs and 5-HT4Rs exerts beneficial effects in a mouse model of Alzheimer's disease.

Background: Alzheimer's disease (AD) is the leading cause of dementia. There are limited approved medications that delay cognitive decline or lessen neuropsychiatric symptoms. Numerous clinical trials for AD using a single drug administration have failed to meet therapeutic endpoints, which is most likely due to the complexity of AD. A multimodal therapeutic intervention is more likely to improve symptoms by targeting multiple targets implicated in AD. Here, we investigated if targeting both N-Methyl-D-aspartic acid receptors (NMDARs) and serotonin type 4 receptors (5-HT₄R) may have beneficial effects in a mouse model of AD, as they have separately been shown to improve cognition and/or mood.

Methods: Male and female control (Ctrl) or APP/PS1 mice were administered single, intermittent, or chronic administration of 1) saline; 2) (R,S)-ketamine, an NMDAR antagonist; 3) prucalopride, a 5-HT₄R agonist; or 4) (R,S)-ketamine + prucalopride to simultaneously target co-morbid neuropsychiatric and cognitive deficits. Behavioral assays were then administered to measure cognition, perseverative behavior, hyponeophagia, and/or sleep. Brains were processed for glial fibrillary acidic protein (GFAP) immunohistochemistry.

Results: Single and chronic administration of (R,S)-ketamine + prucalopride administration improved cognitive decline by increasing memory retrieval in a contextual fear conditioning (CFC) paradigm in APP/PS1 mice. Drug efficacy was less effective in females than in males and was age dependent. Hippocampal GFAP immunoreactivity was decreased by chronic (R,S)-ketamine + prucalopride treatment in females.

Conclusions: Our results indicate that combined administration of (R,S)-ketamine + prucalopride is a novel multimodal therapeutic strategy to treat cognitive decline in AD. Future work will further characterize these interactions with the goal of clinical development.