Fig. 7. Synopsis of the evolution of the monoaminergic system.

A simplified time-calibrated species tree illustrating the origin of the key monoaminergic genes and the presence of neurons. A Sturtian glaciation, B Marinoan glaciation, C Gaskiers glaciation, D Occurrence of Ediacaran Biota/early animal fossils, E the Cambrian explosion. Species tree dated following Dos reis et al.¹⁰⁵, Geological column is shown in accordance with the ICS International Chronostratigraphic Chart (updated 2017)¹⁰⁶. Bil Bilateria, OG orthogroup, PAH phenylalanine hydroxylase, TPH tryptophan hydroxylase, TH tyrosine hydroxylase, DDC dopa decarboxylase, TDC tyrosine decarboxylase, HDC histidine decarboxylase, DBH dopamine beta hydroxylase, PNMT phenylethanolamine-N-methyltransferase, VMAT vesicular monoamine transporter, GCH GTP cyclo-hydrolase, MAO monoamine oxidase, HNMT histamine-N-methyltransferase, SERT serotonin transporter, MAT monoamine transporter, IDAT invertebrate dopamine transporter, 5HT3R 5-hydroxytryptamine receptor 3.