Tacrine improves reversal learning in older rats

Age-related decline has been reported in most cognitive domains, including executive function: in particular, attentional set-shifting and reversal learning, as measures of executive control, are impaired in aged populations of both humans and rats. Despite the importance of the cholinergic system in age-related cognitive decline, no data are available on the effects of cholinergic enhancement on age-related performance deficits in tests of attentional set-shifting. We investigated the effects of the cholinesterase inhibitor tetrahydroacridin-9-amine (tacrine) on reversal learning and attentional set-shifting in older rats (aged 16-21 months) using the rodent version of the intradimensional/extradimensional attentional set-shifting task in a repeated-measures design. Discrimination acquisition was not impaired, but age-related impairments in reversal learning were persistent between tests, and ameliorated by the 3 mg/kg dose of tacrine. No age-related impairments in set-shifting were seen, but there was a tendency for tacrine to reduce the cost of shifting set. Given the lack of previous evidence for a role of cortical acetylcholine in attentional set-shifting tasks, it is likely that altered neurotransmitter interactions in striatum underlie this improvement.