Problems of recordings of nervous activity with glass microelectrodes in the CNS of insects

1. Extracellular single unit recordings with glass microelectrodes in the central nervous system of insects display action potentials of variable amplitude, polarity and time course. This phenomenon is due to capacitive influences at the electrode in contact with the tissue. This is demonstrated by an electrical model circuit simulating extracellular recording conditions. 2. Extracellularly recorded potentials often are very similar to intracellularly recorded ones. Criteria for the decision whether the electrode is intracellularly or not are discussed. 3. Action potentials and slow potentials were recorded simultaneously in the acoustic neuropiles of Locusta. Since slow potentials may not only be distorted by capacitive properties of both the tissue and the electrode, but also are influenced by the anatomical organization of the nervous tissue, their interpretation is ambiguous.