Enhanced delayed matching performance in younger and older macaques administered the 5-HT₄ receptor agonist, RS 17017

Recent evidence indicates that the 5-HT₄ subtype of serotonin receptor may modulate central cholinergic activity in regions of the mammalian CNS important to memory such as the frontal cortex, hippocampus and amygdala. These receptors could represent targets for drugs designed for the symptomatic therapy of Alzheimer's disease (AD) and other disorders of memory. In the present study, the binding activity of RS 17017 (previously described as a selective 5-HT₄ agonist) was assessed across a number of neurotransmitter receptors and binding sites, pharmacokinetic data were obtained, and the compound was evaluated in macaques for mnemonic effects via a computer-assisted delayed matching-to-sample task (DMTS). Binding data confirmed the 5-HT₄ selectivity of the compound, while pharmacokinetic results revealed low oral bioavailability, but a large volume of distribution of the compound. Significant and reproducible improvements in DMTS accuracy were observed after oral administration of the compound across a dose-effect series in both younger and older monkeys. The results suggest that RS 17017 offers a potential for memory enhancement in disorders involving cognitive decline, and are consistent with a role for central 5-HT₄ receptors in memory. Improvements in DMTS performance in aged monkeys may have particular implications for neurodegenerative conditions such as AD, whereas positive results in the younger monkeys indicate that RS 17017 (or similar compounds) may have additional potential in the therapeutics of memory disorders not necessarily associated with advanced age.