[Disordered associative long-term potentiation in the hippocampus after the tetanization of the reinforcing input].

Field potentials (FPs) were recorded from stratum radiatum of CA1 region of mouse hippocampal slices after weak orthodromic stimulation (C2). Associative long-term potentiation (ALTP), induced by simultaneous tetanization of C2 with strong tetanization of another group of fibres (C1) was investigated. Effects of the additional tetanization of C1 delivered 50-300 ms before and 50-300 ms after conjoint tetanization of two inputs were compared. In experiments with intervals 50-200 ms preliminary tetanizations of C1 suppressed ALTP (the FPs amplitude increase was 10.4 +/- 5.2%) in comparison with procedure in which an additional tetanization of C1 follows conjoint tetanization (the FPs increase was 32.4 +/- 5.3%). There was no significant difference between two procedures in experiments with 300 ms intervals. Three mechanisms have been considered to explain the influence of the preliminary strong tetanus on ALTP: inactivation of "fast" calcium channels, afterburst hyperpolarization and synaptic inhibition. It is suggested that mechanisms of this suppression are similar to mechanisms underlying relative inefficacy of the "backward" association procedure in behavioral conditioning.