Is GABA present in the nervous system of acoel plathelminthes? An electron immunocytochemical study

Our immunocytochemical investigation positively identified for the first time at the ultrastructural level the presence of GABA‐ir neurones and terminals in the nervous system of a plathelminth, the acoel Symsagittifera psammophila. The gold particles are localized on clear vesicles (about 30–60 nm wide) of somata and terminals prevalently distributed in the neuropile area near the statocyst. GABA‐ir vesicles are also present at neuromuscular junctions. The significance of this finding in a lower invertebrate is discussed.