Papke_2012_Biochem.Pharmacol_84_352

Zebrafish (Danio rerio) have been used to study multiple effects of nicotine, for example on cognition, locomotion, and stress responses, relying on the assumption that pharmacological tools will operate similarly upon molecular substrates in the fish and mammalian systems. We have cloned the zebrafish nicotinic acetylcholine receptor (nAChR) subunits and expressed key nAChR subtypes in Xenopus oocytes including neuronal (alpha4beta2, alpha2beta2, alpha3beta4, and alpha7) and muscle (alpha1beta1(b)varepsilondelta) nAChR. Consistent with studies of mammalian nAChR, nicotine was relatively inactive on muscle-type receptors, having both low potency and efficacy. It had high efficacy but low potency for alpha7 receptors, and the best potency and good efficacy for alpha4beta2 receptors. Cytisine, a key lead compound for the development of smoking cessation agents, is a full agonist for both mammalian alpha7 and alpha3beta4 receptors, but a full agonist only for the fish alpha7, with surprisingly low efficacy for alpha3beta4. The efficacy of cytisine for alpha4beta2 was somewhat greater than typically reported for mammalian alpha4beta2. The ganglionic blocker mecamylamine was most potent for blocking alpha3beta4 receptors, least potent for alpha7, and roughly equipotent for the muscle receptors and the beta2-containing nAChR. However, the block of beta2-containing receptors was slowly reversible, consistent with effective targeting of these CNS-type receptors in vivo. Three prototypical alpha7-selective agonists, choline, tropane, and 4OH-GTS-21, were tested, and these agents were observed to activate both fish alpha7 and alpha4beta2 nAChR. Our data therefore indicate that while some pharmacological tools used in zebrafish may function as expected, others will not.