Physiological amino acids in brain tissue of the lepismatids, Lepisma saccharina and Thermobia domestica (Insecta, Thysanura)

1. The free (physiological) amino acid profile in the brain tissue of Lepisma saccharina and Thermobia domestica (Thysanura, Lepismatidae) was investigated. 2. Nitrogenous waste products (ammonia and urea) together constituted 28% of the total ninhydrinpositive compounds for both species. 3. GABA accounted for 3% of the total ninhydrin-positive compounds in the brain of L. saccharina , and T. domestica. 4. Glutamate comprised 7% of the total ninhydrin-positive compounds in the brain of L. saccharina , and 8% in T. domestica. 5. The most abundant amino acids were alanine, proline, arginine and taurine. 6. The possible role of amino acids as neurotransmitters and/or modulators of neurotransmitter activity is discussed as well as the comparative free amino acid composition of the brain tissues of various arthropod groups.