Contrasting of synaptic signals by simultaneous modification of excitatory and inhibitory inputs.

Conditions facilitating long-term contrasting of interneuronal connections were studied using a mathematical model of posttetanic Ca(2+)-dependent postsynaptic processes in pyramidal neurons of hippocampal field CA3. These studies demonstrated that modified inhibition selectively facilitates. long-term potentiation of the efficiency of one of the interneuronal connections when the presynaptic neuron discharges at a given frequency for a short time, while connections formed from the same postsynaptic cell with other presynaptic neurons undergo long-term depression. The mechanism underlying this contrasting may involve long-term depression of the efficiency of disynaptic inhibitory transmission to the rhythmically stimulated input, even when the efficiency of monosynaptic excitatory transmission at the same input is low and undergoes minimal potentiation. When the "common" inhibitory neuron is simultaneously activated by various presynaptic cells. heterosynaptic potentiation of inhibitory transmission can simultaneously develop at the other inputs of the postsynaptic cell, without change in the efficiency of excitatory transmission, which leads to long-term depression of the efficiency of the connections between other excitatory neurons and the postsynaptic cell.