Epithelial Conduction in Salps: II. The Role of Nervous and Non-Nervous Conduction System Interactions in the Control of Locomotion

Abstract

1. The control of locomotion in Salpa fusiformis was studied by intracellular recordings from motor neurones and swimming muscles. 2. Regular, synaptically driven, volleys of action potentials were recorded from motor neurones. This pattern of activity was consistent with that expected from the waveform of the compound junctional potentials associated with contraction of the swimming muscles. 3. A second class of brain neurone was identified. These cells were synaptically driven. In some, their firing rate was increased while in others it was decreased by activity in an epithelial conduction system, the Outer Skin Pulse (OSP) system. 4. Cells of the outer epithelium were impaled and OSP's were recorded intracellularly as conventional action potentials. The records from many of these cells showed many depolarising synaptic potentials. 5. Numerous gap junctions were observed throughout the outer epithelial layer and several neuroepithelial synapses were found. The distribution of these synapses coincided with that of the epithelial cells from which synaptic events were recorded.