Binomial Analysis of Long-Term Potentiation of Minimal EPSPs in Hippocampal Slices

Abstract

Our studies of hippocampal LTP (Chap. 12) revealed an increase in m without changes in v, the result traditionally considered to be a strong indication of presynaptic location of underlying mechanisms (Sect. 6.1). However, the number of neurones recorded was small and only a relatively short post-tetanic period (up to 12 min) was studied because of difficulties related to recordings from the in vivo preparation. More recent quantal analysis of long-term postactivation phenomena at peripheral junctions (see Sects. 7.10 and 12.7) also showed mainly an increase in m, although an increase in v was noted in some cases. The in vitro slice preparation provides favourable conditions for long-lasting intracellular recordings from neurones of the mammalian brain. Of the several authors who attempted a quantal analysis in hippocampal slices (see Sect. 7.8.5), Yamamoto et al. [1129] were the first to analyze long-lasting changes. They studied a potentiating action of phorbol esters with recording from CA3 pyramidal cells. However, they based their analysis on Poisson statistics which might lead to erroneous conclusions about changes in quantal parameters (Sects. 11.2, 11.5). More recently, when our in vitro studies were partly published [1022, 1023, 1052, 1057, 1058], several groups [100, 500, 662] reported results based on the analysis of the variability of PSCs recorded after tetanic stimulation [100] and during LTP-like enhancement produced by pairing afferent stimulation with intracellular depolarization of CA1 neurones [500, 662]. The results favour a presynaptic location of the mechanisms of LTP maintenance (see also reports on the quantal analysis of LTP in CA3 [715] and DG [91, 431]). However, one research group [342, 343, 697] demonstrated an increase in v without changes in m after LTP induction in CA1 neurones.