5-Iodo-A-85380, a specific ligand for α4β2 nicotinic acetylcholine receptors, prevents glutamate neurotoxicity in rat cortical cultured neurons

5-iodo-3-(2(S)-azetidinylmethoxy)pyridine (5-iodo-A-85380, 5IA) has very high affinity and selectivity to nicotinic acetylcholine receptor (nAChR) α4β2 subtype, and a relative safe profile. To assess whether 5IA has neuroprotective properties, we examined the effect of 5IA on glutamate (Glu)-induced neurotoxicity using primary cultures of rat cortical neurons. A 10-min exposure of cultures to Glu followed by 2-h incubation with drug-free medium caused a marked loss of viability, as determined by trypan blue exclusion method. Glu-induced neurotoxicity was prevented by 5IA both in a time- and concentration-dependent manner. 5IA-induced neuroprotection required pretreatment of 5IA prior to Glu exposure with an optimal concentration of 10 nM and an optimal pretreatment time of 2 h. Treatment after Glu exposure could not rescue the cultured cells. The neuroprotective effect of 5IA was antagonized by mecamylamine, a nAChR antagonist, but not by scopolamine, a muscarinic acetylcholine receptor antagonist. Dihydro-β-erythroidine, an α4β2 nAChR antagonist, completely inhibited 5IA-induced neuroprotection, whereas α-bungarotoxin, an α7 nAChR antagonist, had no effect. Furthermore, 5IA did not show neuroprotective effects in the absence of extracellular Ca²⁺. These results suggest that the neuroprotective effects of 5IA are produced by activation of α4β2 nAChRs followed by the influx of extracellular Ca²⁺. In conclusion, 5IA is possibly not only useful for the treatment and prevention of glutamate neurotoxicity, but also as an available tool for elucidating the mechanism of neuroprotection associated with α4β2 nAChRs.