Nicotine Stimulates Peristalsis in N. Vectensis: From Behavior to Nicotinic Receptor Genes

Abstract Nicotinic acetylcholine receptors (nAChRs) play a pivotal role in the nervous system, and there is great interest in understanding their evolution. Cnidarians, an ancestral group of metazoans, display an early nervous system utilizing complex neural architecture that provides insight into the early evolution and function of nAChRs. Using the anthozoan Nematostella vectensis, we found that the rate of peristalsis, a radial constriction of the body column, is modulated by nicotinic agonists. Nicotine caused a robust, dose dependent increase in the rate of peristalsis. The peristalsis rate also increased in response to ACh in the presence of edrophonium, an acetylcholine esterase inhibitor. Thus, N. vectensis possesses functional nAChRs. We developed a phylogeny of nAChRs from 15 cnidarian and 16 bilaterian species. Our results indicate that the large number of cnidarian and bilaterian nAChR gene copies is convergent, resulting from gene expansions after the two lineages diverged. These independent expansions led to an average of 31 and 34 paralogous nAChR gene copies in sampled bilaterians and cnidarians, respectively. The N. vectensis proteome contains 49 paralogous nAChR copies. The independent expansions indicate that nAChRs receptors in cnidarians may have distinct pharmacological and biochemical characteristics in comparison to their bilaterian counterparts.