The Phylogenetic Background of Neurotransmitters in the Unicellular Organism Tetrahymena Pyriformis

Abstract

The Human Central Nervous System (CNS) is governed by electrochemical networks forming a delicate interplay between the different regions of the brain. The objective of the present experiment is to investigate the phylogenetic background of this electrochemical network by creating a comparable binary and ternary interplay of interactions between different neurotransmitters (noradrenaline, histamine, serotonin, acetylcholine, glutamate, and dopamine) in the unicellular eukaryote Tetrahymena pyriformis. Tetrahymena – as a protozoon – has no nervous system; however, it has been shown that it has not only the ability to store, synthesize and secrete biogenic amines but it also bears binding sites for the corresponding receptors of some of these molecules. The chemotactic responsiveness elicited by the neurotransmitters was examined in Tetrahymena cells, using a modified version of Leick’s two-chamber capillary chemotaxis assay with 20-minute incubation times. The concentration course of each neurotransmitter was determined and the concentration eliciting the strongest effect was further used to examine the chemotactic response of the neurotransmitters when used in pairs and in groups of three. Adequate cellular responses (chemoattractant and chemorepellent) were detected in both cases when the neurotransmitters were used alone and in combinations. A pattern detected in these responses was related to the neurotransmitters’ physicochemical characteristics (XlogP, TPSA). These provide evidence that the chief regulatory molecules of the CNS can be identified even in lower, eukaryotic unicellular levels of phylogeny and possibly alter the basic functions of these organisms. In summary, our results support the theory that any evolved nervous system-like interplay could stem from a common origin. Therefore, identifying the “ancient” function of a molecule or its receptor effect can open new windows in the advancement of therapeutic interventions.