Long-lasting cognitive improvement with nicotinic receptor agonists: mechanisms of pharmacokinetic-pharmacodynamic discordance.

Agonists of nicotinic acetylcholine receptors (nAChRs) produce long-lasting cognitive effects in animal models and humans. The duration of these cognitive effects can outlast the presence of the agonists in the system, and the persistence of cognitive enhancement is increased further by repeated exposure. The basis for this discrepancy appears be the cellular and systemic mechanisms of learning and memory. Agonists of nAChRs induce long-term potentiation (LTP), which is a strengthening of synaptic connections that is associated with learning and memory formation. Some of the cellular effects of nAChR agonists overlap with the known cellular mechanisms of LTP, including long-lasting increases in intracellular concentrations of Ca2+, activation of second-messenger systems and transcription factors, elevated levels of gene products and enhanced neurotransmitter release. A better understanding of this phenomenon might shed new light on the role of nAChR systems in memory formation and retrieval.