Amino Acid Concentrations in the Aplysia Nervous System: Neurons With High Glycine Concentrations

The levels of the amino acids glycine, aspartic acid and glutamic acid were determined in the ganglia and in identified neurons of A. californica. All of the determinations were done by gas chromatography–mass spectrometry–selected ion monitoring using deuterium‐labelled amino acids as internal standards. Aspartate and glutamate concentrations vary 2‐ to 3‐fold among the ganglia and individual neurons. Glycine levels are 3–10 times higher in the abdominal ganglion than in the other ganglia. This is in large part due to the glycine concentrations in the abdominal ganglion neurons R3–R14 being about 20 times higher than in the somata of most other Aplysia neurons. The concentrations of all three amino acids are several times lower in the muscle than in ganglia, and orders of magnitude lower in the hemolymph than in tissue.