DISCRETE AXONAL ELECTROGENIC AREA DURING PAROXYSMAL DEPOLARIZATION IN AN APLYSIA NEURON

1. The paroxysmal depolarizations (burst-plateau patterns) produced by barium (10 to 40 mM) were studied in R2Aplysia neurons. The electrical activity was recorded in the soma and in the axon with both extracellular and intracellular electrodes. 2. Extra-axonal recordings during long somatic plateaus showed that the distal axon was firing while the proximal axon (up to 11 mm from the soma) could be invaded by the plateau. Intra-axonal recordings confirmed the existence of proximal axon plateaus which were not due to the electrotonic spread of soma plateaus. 3. The somatic and proximal axonal spikes but not the distal axonal spikes were lengthened by barium. Additional lengthening was produced by repetitive firing. The lengthening was blocked by cadmium, cobalt and calcium. 4. Differential lengthening of either soma spikes or axon spikes resulted in doublets produced respectively in the axon or in the soma. 5. In different experimental conditions (antidromic stimulation, local application of barium, section of the proximal axon), the production of burst-plateau patterns was restricted to part of the proximal axon. 6. It is concluded that both the soma and the second half of the proximal axon (6 to 11 mm from the soma) can generate depolarizing plateaus. Interactions between these two electrogenic areas are operated through a region of reduced space constant. These areas must have a relatively high density of calcium channels compared to the first half of the proximal axon and to the distal axon. © 1979 Springer-Verlag.