Characterization of Oscillatory Olfactory Interneurones in the Protocerebrum of the Crayfish

Abstract

ABSTRACT 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. 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. 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. 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. These findings support the conclusion that hemi-ellipsoid interneurones are an integral link in the central olfactory pathway of the crayfish.