| Abstract: | Field potentials (FP) induced in area C1 by gentle orthodromic stimulation were recorded in murine hippocampal slices and associative long-term potentiation (ALTP) produced by C2 tetanization associated with intensive tetanization of another group of fibers (C1) was investigated. A comparison was made between the effects of additional C1 tetanization produced at 50–300 msec before and after combined tetanization of both afferents. Where these intervals measured 50–200 msec, preliminary tetanization of C1 suppressed ALTP (rise in FP amplitude: 10.4±5.2%) in comparison with the regimen whereby additional C1 tetanization came later (giving a rise of 32.4±5.3%); no significant difference was noted at an interval of 300 msec. The three possible reasons for ALTP suppression are discussed, namely: inactivation of "fast" calcium channels, post-activation hyperpolarization of postsynaptic neurons, and synaptic inhibition. The ALTP suppression mechanism is thought to resemble that underlying the relative inefficacy of "reversible" combinations in the shaping of behavioral conditioned reflexes.Institute for Brain Research, Academy of Medical Sciences of the USSR, Moscow. Institute of Chemical Physics, Academy of Sciences of the USSR, Moscow. Translated from Neirofiziologiya, Vol. 21, No. 5, pp. 636–643, September–October, 1989. |
