[Effect of elimination of brain stem-septal connections on prolonged posttetanic changes in the hippocampus].

Comparative analysis of long-lasting effects of Schaffer's collaterals tetanization (15 Hz, 15 s) was performed in 61 extracellularly recorded units of the intact hippocampus (field CA1) and in 51 units after complete septo-hippocampal disconnection in chronic alert rabbits. The number of units with long-lasting potentiation (LLP) was significantly greater in the hippocampus deprived of brain stem-septal afferents (63%) as compared to the intact hippocampus (21%); the number of units with posttetanic depression was reduced (21% versus 34%). The mean level of LLP in the deafferentated hippocampus was significantly higher than in the intact hippocampus (mean 220% and 180% of control level; p less than 0,001), and its duration was greater. Conversely, the mean level of depression was lower in the deafferentated hippocampus than in the normal one (140% and 170% of control level; p less than 0,01). This increase of LLP may result from elimination of inhibitory influences of the brain stem-septal afferent input, and/or from sprouting of Schaffer's collaterals after deafferentation with increase in number of functional synapses.