Estimate of the quantum value variability in excitatory synapses of CA1 area in hippocampal slices and its effects on the quantum value estimate

Excitatory postsynaptic potentials (EPSPs) evoked by near-threshold stimulation of the radial layer were recorded from the CA1 area of guinea pig hippocampal slices. An optimization method based on the deconvolution technique was used to reconstruct a noise-free discrete distribution of the amplitudes with regular (quantal) intervals (v) between the discrete components. The standard deviation of v (Sv) was studied for its effect on the estimate of the v value. Twenty-two amplitude distributions with approximately regular, visually distinguishable peaks were analyzed. It was found that, in some cases, too small (<0.1–0.15 v) or too large (>0.3–0.4 v) Sv led to lower v estimates in comparison with those obtained for Sv in the range of 0.1–0.3 v. Computer experiments have shown that too small or too large Sv values may lead to underestimates of the stimulated v values. The average underestimate for physiological data is probably 10–15%, but, in some cases, it may be higher. Judging from a maximal verisimilitude criterion, optimal v estimates are obtained for Sv between 0 and 0.15 v. Comparison of simulated and physiological data suggests that the variation coefficient of v for hippocampal synapses formed by radial fibers on CA1 neurons is equal to 0.1–0.2 Sv values generally accepted for the deconvolution procedure (0 or 0.05 v) seem to be underestimated for central synapses, while Sv>0.3 v are overestimated. Underestimates of Sv known from literature may be due to a dependence of the deconvolution procedure results on the noise level, as well as due to a probable nonlinear interaction between the signal and noise. Overestimates may be a result of multiple spontaneous quantal release.Translated from Neirofiziologiya, Vol. 25, No. 1, pp. 10–17, January–February, 1993.