GAMMA-AMINOBUTYRIC-ACID IN THE NERVOUS-SYSTEM OF A PLANARIAN

The amino acid gamma-aminobutyric acid (GABA) is an important inhibito ry neurotransmitter in both vertebrates and invertebrates. Despite thi s, no reports of GABA in flatworms have to date been published. We hav e studied the presence of GABA in the planarian Dugesia tigrina with i mmunocytochemical methods and high-pressure liquid chromatography. Fib ers showing GABA-like immunoreactivity (GABA-IR) were present in abund ance in the longitudinal nerve cords and lateral nerves. GABA-IR was r evealed in fibers forming commissures in the brain. The ventral part o f the subepidermal plexus showed GABA-IR. No cell somata containing GA BA-IR could be identified with certainty. The chromatographic analysis showed that the average GABA concentration in D. tigrina is 533.6 pmo l/mg protein. This is substantially higher than the concentrations of dopamine (62.87 pmol/mg) and serotonin (233.20 pmol/mg). An enzyme ass ay confirmed the capacity for GABA-synthesis in D. tigrina. The result s indicate that GABA-containing neurons appeared earlier in evolution than was previously thought and that GABA may serve an important role already in the flatworms. (C) 1994 Wiley-Liss, Inc.