Rl. Cooper et al., QUANTAL MEASUREMENT AND ANALYSIS-METHODS COMPARED FOR CRAYFISH AND DROSOPHILA NEUROMUSCULAR-JUNCTIONS, AND RAT HIPPOCAMPUS, Journal of neuroscience methods, 61(1-2), 1995, pp. 67-78
Quantal content of transmission was estimated for three synaptic syste
ms (crayfish and Drosophila neuromuscular junctions, and rat dentate g
yrus neurons) with three different methods of measurement: direct coun
ts of released quanta, amplitude measurements of evoked and spontaneou
s events, and charge measurements of evoked and spontaneous events. At
the crayfish neuromuscular junction, comparison of the three methods
showed that estimates from charge measurements were closer to estimate
s from direct counts, since amplitude measurements were more seriously
affected by variable latency in evoked release of quantal units. Thus
, charge measurements are better for estimating quantal content when d
irect counts cannot be made, as in crayfish at high frequency of stimu
lation or in the dentate gyrus neurons. At the Drosophila neuromuscula
r junction, there is almost no latency variation of quantal release in
realistic physiological solutions, and the methods based upon amplitu
des and charge give similar results. Distributions of evoked synaptic
quantal events obtained by direct counts at the crayfish neuromuscular
junction were compared to statistical distributions obtained by best
fits. Binomial distributions with uniform or non-uniform probabilities
of release generally provided good fits to the observations. From bes
t fit distributions, the quantal parameters n (number of release sites
) and p (their probability of release) can be calculated. We used two
algorithms to estimate n and p: one allows for non-uniform probability
of release and uses a modified chi-square (chi(2)) criterion, and the
second assumes uniform probability of release and derives parameters
from maximum likelihood estimation (MLE). The bootstrap estimate of st
andard errors is used to determine the accuracy of n and p estimates.