Several studies have demonstrated the importance of nicotinic mechanisms in the pathophysiology of neurodegenerative and
cognitive disorders, warranting the search and development of novel nicotinic
ligands as potential therapeutic agents. The present study was designed to assess whether the subtype-selective
nicotinic acetylcholine receptor (nAChR)
ligand SIB-1553A [(+/-)-4-([2-(1-methyl-2-pyrrolidinyl)ethyl]thio)
phenol hydrochloride], with predominant agonist activity at beta4 subunit-containing human nAChRs, and no activity at muscle nAChR subtypes, could enhance cognitive performance in rodents with a more desirable safety/tolerability profile as compared to the nonselective prototypic nAChR
ligand nicotine.
SIB-1553A was equi-efficacious to
nicotine in improving working memory performance in
scopolamine-treated mice as measured by increased alternation in a T-maze, and was more efficacious than
nicotine in improving the baseline cognitive performance of aged mice. This effect on working memory was confirmed in a delayed nonmatching to place task using the eight-arm radial maze.
SIB-1553A produced dose-dependent side effects (ie motor deficits and
seizures), although these effects were observed at doses 12 to 640-fold above those required to increase cognitive performance. Overall,
SIB-1553A was significantly less potent than
nicotine in eliciting these undesirable effects. Thus, the subtype-selective profile of
SIB-1553A appears to translate into a more efficacious and better tolerated nAChR
ligand as compared to
nicotine. In the present studies, cognitive enhancement induced by
SIB-1553A was similar in magnitude to that produced by the clinically efficacious
acetylcholinesterase inhibitor donepezil. Taken together, the present data confirm the importance of nAChR subtypes in modulating cognitive processes, and suggest that activation of nAChR subtypes by selective nAChR
ligands may be a viable approach to enhance cognitive performance.