CHARACTERIZATION OF OSCILLATORY OLFACTORY INTERNEURONS IN THE PROTOCEREBRUM OF THE CRAYFISH

1. We obtained intracellular electrophysiological recordings from local interneurones within the hemi-ellipsoid neuropile of the brain in the freshwater crayfish Cherax destructor and Procambarus clarkii. The recordings were made from perfused, isolated head preparations that provided several indications of a healthy physiological condition. 2. The hemi-ellipsoid interneurones are spontaneously active, generating bursts of action potentials at regular intervals. The inter-burst period differs among neurones, varying from about 1.0 s at the shortest periods to around 30 s for the longest periods. 3. Evidence from both electrophysiological recordings and from injection of Lucifer Yellow and Neurobiotin dyes into hemi-ellipsoid interneurones suggests that some of the cells in the populations are electrically coupled to one another. 4. Hemi-ellipsoid interneurones are driven postsynaptically by axons within the lateral protocerebral tract. Experiments with focal electrical stimulation strongly suggest that the pathways responsible include axons of the olfactory-globular tract. These findings support our previous electron microscopical data showing that olfactory-globular tract axons are presynaptic to the hemi-ellipsoid interneurones. 5. These findings support the conclusion that hemi-ellipsoid interneurones are an integral link in the central olfactory pathway of the crayfish.