Role of neuronal nicotinic acetylcholine receptors (nAChRs) on learning and memory in zebrafish

Neuronal nicotinic acetylcholine receptors (nAChRs) play a modulatory role in cognition, and zebrafish provide a preclinical model to study learning and memory. We investigated the effect of nicotine (NIC) and some new cytisine-derived partial agonists (CC4 and CC26) on spatial memory in zebrafish using a rapid assay on T-maze task. The role of alpha 4/alpha 6 beta 2 and the alpha 7 nAChRs in NIC-induced memory enhancement was evaluated using selective nAChR antagonists. Low and high doses of NIC, cytisine (CYT), CC4 and CC26 respectively improved and worsened the mean running time, showing an inverted U dose-response function. The effective dose (ED50) (x10(-5) mg/kg) was 0.4 for CC4, 4.5 for CYT, 140 for NIC and 200 for CC26. NIC-induced cognitive enhancement was reduced by the selective nAChR subtype antagonists: methyllycaconitine (MLA) for alpha 7, alpha-conotoxin (MII) for alpha 6 beta 2, dihydro-beta-erythroidine (Dh beta E) for alpha 4 beta 2, the nonselective antagonist mecamylamine (MEC) and the muscarinic antagonist scopolamine (SCOP), with Dh beta E being more active than MLA or MII. All the partial agonists blocked the cognitive enhancement. The improvement with the maximal active dose of each partial agonist was blocked by low doses of Dh beta E (0.001 mg/kg) and MII (0.01 mg/kg). MLA reduced the effects of CC26 and CC4 at doses of 0.01 and 1 mg/kg, respectively, but did not antagonize CYT-induced memory improvement at any of the tested dose. No change in swimming activity was observed. Our findings demonstrate that zebrafish make a useful model for the rapid screening of the effect of new alpha 4 beta 2 nAChR compounds on spatial memory.