Frequency Dependent Propagation of Sodium Action Potentials in Dendrites of Hippocampal CA1 Pyramidal Neurons. Callaway, Joseph C. and William N. Ross. Department of Physiology, New York Medical College, Valhalla, NY 10595, TEL: 914-993-4092, FAX: 914-993-4018, EMAIL: callaway@nymc.edu.
APStracts 2:0169N, 1995.
SUMMARY AND CONCLUSIONS
1. The propagation of antidromically activated action potentials in CA1 pyramidal neurons was examined with intrasomatic and intradendritic electrical recording and optical measurements using the fluorescent calcium indicator Calcium Green-1. 2. In somatic recordings trains of 40 action potentials, activated at rates up to 100 Hz, showed modest amplitude reduction. Recordings in the apical dendrites, 150 [mu]m from the soma, showed smaller initial amplitudes and much greater decrement during trains. Higher frequencies caused a greater rate of reduction with a lower final amplitude. 3. Calcium concentration changes ([Ca 2+ ] i ), measured with the fluorescent indicator Calcium Green-1 and a fast, cooled CCD camera, were detected over the entire length of the apical dendrites in response to single antidromic action potentials, although the changes in distal dendrites were smaller. These changes were rapid, decaying to half amplitude in less than 150 ms in distal dendritic locations. 4. Trains of action potentials at all frequencies up to 100 Hz caused transient [Ca 2+ ] i increases for each spike at 150 [mu]m from the soma. In the last 100 [mu]m of the distal branches only the first few spikes caused a [Ca 2+ ] i increase for frequencies above about 40 Hz. These patterns could be matched with a simple model of calcium influx and removal where later spikes in a train brought in less calcium than earlier spikes. 5. These results show that the action potential amplitude and the spatial extent of their propagation in the dendrites is frequency dependent. 

Received 23 February 1995; accepted in final form 18 May 1995.
APS Manuscript Number J127-5.
Article publication pending J. Neurophysiol.
ISSN 1080-4757 Copyright 1995 The American Physiological Society.
Published in APStracts on  8 June 1995.