AbstractIsolated somata of identified motorneurons in the metathoracic ganglion of the locust were analyzed for glutamate decarboxylase (GAD), choline acetyltransferase (ChAc), acetylcholinesterase (AChE), and aromatic amino acid decarboxylase (AAD). Isolated inhibitory motorneuron somata have GAD activity but those of excitatory motorneurons do not. Since this enzyme is responsible for the synthesis of gamma amino butyric acid there is a metabolic basis for these motorneurons to accumulate GABA. In contrast to the specific localization of GAD in inhibitory motorneurons, AChE was found in large amounts in all motorneurons tested. The specific activity of ChAc and AAD in both inhibitory and excitatory motorneurons were similar or lower than the specific activity of the whole ganglion. Degeneration experiments suggest that ChAc is mainly localized in the sensory neurons.