Behavioural and pharmacological profiles of zebrafish administrated pyrrolidinyl benzodioxanes and prolinol aryl ethers with high affinity for heteromeric nicotinic acetylcholine receptors

Rationale Prolinol aryl ethers and their rigidified analogues pyrrolidinyl benzodioxanes have a high affinity for mammalian a4β2 nicotinic acetylcholine receptors (nAChRs). Electrophysiological studies have shown that the former are full agonists and the latter partial agonists or antagonists of human a4β2 receptors, but their in vivo effects are unkown. Objectives and Methods As a4b2 nAChRs play an important role in cognition and the rewarding effects of nicotine we tested the effects of two full agonists and one antagonist on spatial learning, memory and attention in zebrafish using a T-maze task and virtual object recognition test (VORT).The effect of a partial agonist in reducing nicotine-induced conditioned place preference (CPP), was also investigated. Results In comparison with the vehicle alone, the full agonists MCL-11 and MCL-28 induced a significant cognitive enhancement as measured by the reduced running time in the T-maze and increased attention as measured by the increased discrimination index in the VORT. MCL-11 was 882 times more potent than nicotine. The two compounds were characterised by an inverted U-shaped dose– response curve, and their effects were blocked by the co-administration of the antagonist MCL117, which alone had no effect. The partial agonist MCL-54 induced CPP and had an inverted U-shaped dose–response curve similar to that of nicotine, but blocked the reinforcing effect of co-administered nicotine. Binding studies showed that all of the compounds have a higher affinity for heteromeric [3H]- epibatidine receptors than [125I]-aBungarotoxin receptors. MCL-11 was the most selective of heteromeric receptors. Conclusions. These behavioural studies indicate that full-agonist prolinol aryl ethers, are very active in increasing spatial learning, memory and attention in zebrafish. The benzodioxane partial agonist MCL-54 reduced nicotine-induced CPP, and the benzodioxane antagonist MCL-117 blocked all agonistinduced activities.