Analysis of fluctuations of "minimal" excitatory postsynaptic potentials during long-term potentiation in guinea pig hippocampal slices.
In previous studies, quantal analysis assuming a simple binomial model has shown that long-term potentiation (LTP) is accompanied by an increase in both mean quantal content (m) and quantal size (v), whereby the increase in m predominates. In the present study, "compound" binomial distributions with variable probabilities were convolved with Gaussian distributions in computer experiments to simulate amplitude histograms of intracellular excitatory postsynaptic potentials (EPSPs). A deconvolution procedure assuming equal "quantal" separation (v) between discrete components, but without assuming binomial statistics, was applied to the simulated distributions to determine v. It was found that with a small ratio of standard deviation of noise to v (Sn/v less than 0.4), a reliable estimate of v can be obtained even for small samples (N = 100). When Sn/v was larger (0.4-0.6), approximate v estimates (within +/- 10-20% of the simulated v) could be obtained by averaging estimates from about 10 small samples (N = 100). "Minimal" EPSPs were recorded in area CA1 of guinea pig hippocampal slices. 37 EPSP amplitude samples of 9 neurones were measured before and up to 55 min after 10 tetanizations of stratum radiatum. In accordance with the previous data, the increase in v accounted for only about 10% of the average post-tetanic increase in EPSP amplitude and was not correlated with the latter. However, for an EPSP subset with small LTP magnitude, the increase in v accounted for an essential part of the LTP magnitude while the increase in m did not correlate with it. The results are in agreement with previous data obtained in the context of the simple binomial model and are interpreted as indicating primarily a presynaptic mechanism of LTP maintenance. The results suggest two types of synaptic mechanism of LTP maintenance related to the increases in m and v, respectively. The latter mechanism is saturated at about 10 to 30% increase in post-tetanic amplitude above the pre-tetanic EPSP amplitude.
Voronin
L L
LL
Max-Planck-Institute for Biophysical Chemistry, Department of Neurobiology, Göttingen, Federal Republic of Germany.
Kuhnt
U
U
Gusev
A G
AG
D000818:Animals; D004558:Electric Stimulation; D005073:Evoked Potentials, Somatosensory / Q000502:physiology*; D006168:Guinea Pigs; D006624:Hippocampus / Q000166:cytology / Q000502:physiology*; D066298:In Vitro Techniques; D008959:Models, Neurological; D009010:Monte Carlo Method; D013569:Synapses / Q000502:physiology*