The Journal of Neurophysiology Vol. 81 No. 5 May 1999, pp. 2234-2242
Copyright ©1999 by the American Physiological Society

Asynchrony of Quantal Events in Evoked Multiquantal Responses Indicates Presynaptic Quantal Interaction

 ¹Department of Molecular Physiology and Biological Physics, University of Virginia Health Sciences Center, Charlottesville, Virginia 22906-0011; and  ²Sechenov Institute of Evolutionary Physiology and Biochemistry, St. Petersburg, Russia 194223

Bykhovskaia, Maria, John T. Hackett, and Mary Kate Worden. Asynchrony of Quantal Events in Evoked Multiquantal Responses Indicates Presynaptic Quantal Interaction. J. Neurophysiol. 81: 2234-2242, 1999.Asynchrony of quantal events in evoked multiquantal responses indicates presynaptic quantal interaction. We have analyzed the possibility of quantal interactions by inspecting action potential-evoked postsynaptic multiquantal responses recorded extracellularly from the lobster neuromuscular junction. These recorded responses were compared with simulated multiquantal responses constructed from statistically independent quantal events. The simulated multiquantal responses were generated by random superposition of single quantal responses aligned according to the timing of the action potential. The methods of analysis consisted of 1) the comparison of quantal contents obtained from direct counting or by measuring of the size of the responses and 2) the analysis of distributions of quantal latencies. This analysis revealed a large error in the detection of quantal events for responses simulated with no quantal interaction. In contrast, very few errors in quantal detection were made in the analysis of experimental recordings. Latency histograms of recorded responses demonstrate that the proportion of late quantal events (those with latencies of 5 ms) increased as a function of quantal content. This shift in latency histograms was not observed for simulated responses. Our interpretation is that quanta interact presynaptically to cause asynchrony of quantal events in evoked responses.