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. Author manuscript; available in PMC: 2009 Mar 15.
Published in final edited form as: J Neurosci Methods. 2007 Oct 23;168(2):500–513. doi: 10.1016/j.jneumeth.2007.10.006

5. Evaluation of quantal content m.

5

In this experiment, EPSCs (300 sweeps per file) were recorded from the lobster nmj at stimulation frequencies of 5, 10, 20, 30, 40, and 50 Hz (points 0−5). Quantal content was evaluated by four methods (checked): direct counts (circles); the average EPSC amplitude divided by the average amplitude of the unitary EPSC from the highlighted file (light triangles); the average EPSC area divided by the average area of the unitary EPSC from the highlighted file (dark triangles); the area of the average superimosed EPSC divided by the area of the average superimposed unitary EPSC from the highlighted file (squares). At the points 0−2 (5−20 Hz stimulation frequency) the results of all the methods agree, thus direct counts can be considered accurate. At the points 3−5 (30−50 Hz) the area measurements (squares and dark triangles) give the highest quantal content. Since these two m estimates obtained by area measurements are in a good agreement, area measurements can be considered accurate. In contrast, amplitude measurements (light triangles) and direct counts (circles) underestimate quantal content at high stimulation frequencies (30−50 Hz, points 3−5). Other methods available for m evaluation (listed) are: 1) the amplitude of the average superimposed EPSC divided by the amplitude of the average superimposed unitary EPSC in the highlighted file; 2) the average EPSC amplitude or area divided by the average amplitude or area of mEPSCs collected from either the highlighted file or throughout the experiment.