Detection of molecules related to the GABAergic system in a single-cell eukaryote, Paramecium primaurelia

γ-Aminobutyric acid (GABA)-related molecules were identified in Paramecium primaurelia by immunocytochemical methods, and GABA A receptors by their histochemical BODIPY-binding sites. Confocal microscope analysis showed different localizations according to the stages of the developmental cycle. A comparison was made with the cholinergic molecules, such as the acetylcholine biosynthetic enzyme (choline acetyltransferase), in double-labelled cells by confocal microscopy. In vivo experiments suggested the involvement of GABA-related molecules in cell–cell interaction.