[A quantal analysis of the long-term potentiation of the total postsynaptic neuronal potentials in surviving...

Excitatory postsynaptic potentials (EPSPs) from 14 neurons have been recorded in hippocampal slices (area CA1) of guinea pigs after stimulation of stratum radiatum (Schaffer collaterals) and stratum oriens. An increase of EPSP amplitudes observed in 7 neurons (9 pathways) recorded 15-45 min after titanic stimulation of Schaffer collaterals is considered as a long-term potentiation (LTP). A statistical analysis in the frame of two methods of the quantal hypothesis (histogram and variance methods) has shown an increase in the mean quantal content (m) during LTP. An increase in the quantal size found only by the histogram method is considered to be less reliable because comparatively strong dependence of the histogram method on the noise level. An increase in m revealed by two methods corresponds to the previous in vivo studies and favours a presynaptic location of mechanisms responsible for the growth of the synaptic efficacy during LTP.