SPONTANEOUS SWITCHING BETWEEN ORTHO - AND ANTIDROMIC SPIKING AS THE NORMAL MODE OF FIRING IN THE CEREBRAL GIANT NEURONS OF FREELY BEHAVING LYMNAEA STAGNALIS. Jansen, Rene F., Anton W. Pieneman and Andries ter Maat. Graduate School Neurosciences Amsterdam, Research Institute Neurosciences Vrije Universiteit, Faculty of Biology, De Boelelaan 1087, 1081 HV Amsterdam,The Netherlands, Tel: +31-20-4447094, Fax:+31-20-4447123, email: renej@bio.vu.nl.
APStracts 3:0184N, 1996.
SUMMARY AND CONCLUSIONS
1. Action potential generation at sites remote from the cell body leads to antidromic firing, and occurs in a wide variety of animals and experimental circumstances. Remote sites of spike generation may play a role in the functional subdivision of the axonal branches of a neuron, and are also thought to play a role in synaptic integration. 2. Spontaneous ortho- and antidromic firing was investigated by recording the electrical activity of somata and axons of a pair of identified giant neurons (Cerebral Giant Cells; CGCs) in freely behaving animals. 3. At the soma of each CGC the shape of the extracellular action potential was not constant, but jumped between two well defined levels. Subsequent recordings of synchronous firing in both cell bodies showed that the shape of the extracellular action potential depended on the firing sequence of the two CGCs. 4. Simultaneous recordings of the cell body and the main axon of a single CGC showed that spontaneous changes in the direction of spike conduction (orthodromic or antidromic) occurred. These changes in the direction of spike conduction coincided with the changes in the shapes of the extracellular action potentials recorded from the somata. 5. These results show that under physiological conditions spontaneous switching occurs between ortho-and antidromic spiking in the CGCs, and that action potential generation at sites remote from the cell body is a physiologically relevant mechanism . 

Received 3 June 1996; accepted in final form 28 August 1996.
APS Manuscript Number J443-6.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1996 The American Physiological Society.
Published in APStracts on 7 October 1996