Effects of nicotinic acetylcholine receptor-activating alkaloids on anxiety-like behavior in zebrafish

Abstract

Alkaloids are a structurally complex group of natural products that have a diverse range of biological activities and significant therapeutic applications. In this study, we examined the acute, anxiolytic-like effects of nicotinic acetylcholine receptor (nAChR)-activating alkaloids with reported neuropharmacological effects but whose effects on anxiety are less well understood. Because α4β2 nAChRs can regulate anxiety, we first demonstrated the functional activities of alkaloids on these receptors in vitro. Their effects on anxiety-like behavior in zebrafish were then examined using the zebrafish novel tank test (NTT). The NTT is a relatively high-throughput behavioral paradigm that takes advantage of the natural tendency of fish to dive down when stressed or anxious. We report for the first time that cotinine, anatabine, and methylanatabine may suppress this anxiety-driven zebrafish behavior after a single 20-min treatment. Effective concentrations of these alkaloids were well above the concentrations naturally found in plants and the concentrations needed to induce anxiolytic-like effect by nicotine. These alkaloids showed good receptor interactions at the α4β2 nAChR agonist site as demonstrated by in vitro binding and in silico docking model, although somewhat weaker than that for nicotine. Minimal or no significant effect of other compounds may have been due to low bioavailability of these compounds in the brain, which is supported by the in silico prediction of blood–brain barrier permeability. Taken together, our findings indicate that nicotine, although not risk-free, is the most potent anxiolytic-like alkaloid tested in this study, and other natural alkaloids may regulate anxiety as well.

Embryonic Nicotine Exposure Disrupts Adult Social Behavior and Craniofacial Development in Zebrafish

“…Cotinine can cross the blood-brain barrier in zebrafish, but is a weak agonist of nicotinic acetylcholine receptors [ 37 , 38 ]. The effects of the combination of nicotine and cotinine during development are unclear and little studied.…”

Behavioral Study of 3- and 5-Halocytisine Derivatives in Zebrafish Using the Novel Tank Diving Test (NTT)

“…The α4β2 subtypes, which are the major nAChRs present in the central nervous system (CNS) [ 6 , 7 ] have been proposed as the principal subtypes involved in anxiety and nicotine addiction; however, another nAChR subtype could contribute to these disorders. The nAChR subtypes have been studied in different animal models such as non-human primates, cats, frogs, rats, mice, and zebrafish, associated with different behaviors such as memory loss and drug abuse, among others, and play a key role in the anxiolytic activity of nicotine [ 8 , 9 , 10 , 11 , 12 , 13 , 14 ].…”

“…In the NTT paradigm, the swimming behavior of zebrafish has been studied using different drugs, such as nicotine, fluoxetine, caffeine, and cytisine among others [ 11 , 12 , 20 , 30 , 31 , 32 , 33 ]. These drugs have also been shown to interact with nAChRs [ 11 , 14 , 34 , 35 , 36 ].…”

“…A fish feels anxious when it spends a longer time at the bottom of the tank, and this behavior allows us to determine if a new drug has an anxiolytic effect when the bottom dwelling time is decreased (Scheme 1); however, there are any others parameters to observe such us latency, average velocity and freezing that as a whole can generate an anxiolytic profile of the behavior of zebrafish [27][28][29]. In the NTT paradigm, the swimming behavior of zebrafish has been studied using different drugs, such as nicotine, fluoxetine, caffeine, and cytisine among others [11,12,20,[30][31][32][33]. These drugs have also been shown to interact with nAChRs [11,14,[34][35][36].…”

“…These compounds have shown a high affinity (sub nM) for the nAChR subtypes; the 3-bromo derivative displays selectivity for the heteromeric α4β2 (IC50 = 0.30 nM) and α4β4 (IC50 = 0.28 nM) nAChRs over the homomeric α7 subtype (IC50 = 31 nM). In the NTT paradigm, the swimming behavior of zebrafish has been studied using different drugs, such as nicotine, fluoxetine, caffeine, and cytisine among others [11,12,20,[30][31][32][33]. These drugs have also been shown to interact with nAChRs [11,14,[34][35][36].…”