Abstract
Excitatory postsynaptic potentials (EPSP) were recorded from 14 neurons in guinea pig hippocampal slices (area CAl) after stimulating the stratum radiatum (Schaffer collaterals) and stratum oriens. An increase occurring in EPSP amplitude in 7 units (9 pathways) recorded 15–45 min after tetanic stimulation of Schaffer collaterals is viewed as long-term potentiation (LTP). Statistical analysis conducted according to two sets of quantal theory (histogram and variance methods) showed an increase in mean quantal content (m) during LTP. An increase in quantal size, found only when using the histogram method, did not correlate with LTP level. This increase is thought to be associated with the considerably greater sensitivity of the histogram method to noise level in comparison with the variance method, the latter being more reliable with signals of high noise level. The increase found in m using both methods matches findings previously obtained for the whole brain; it also points to presynaptic location of mechanisms responsible for raised synaptic efficacy during LTP.
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