[Long-term changes in the efficiency of inhibitory transmission in the thalamocortical neuronal networks evoked by cortical microstimulation].

Long-term posttetanic modifications of the efficacy of inhibitory synaptic connections were studied in auditory thalamo-cortical assemblies. We demonstrated that intracortical microstimulation (ICMS, high-frequency pulse of 5 mcA) which activated a small group of cortical neurons produced long-term (at least 30 min) modifications (potentiation--LTPi and depression--LTDi of the efficacy of inhibitory monosynaptic transmission between numerous elements of thalamo-cortical network. LTPi was accompanied by an increase in the firing rate of inhibitory neuron. LTPi was input-specific and did not lead to decrease in the firing rate of the postsynaptic cell. LTP of the efficacy of excitatory and inhibitory inputs of the same target cell could be induced simultaneously. The efficacy of inhibitory synapses formed by the terminals of one axon on different cells could be modified variously. These results allowed us to suggest that we dealt with inhibitory synapses located on dendritic spines and that both pre- and postsynaptic mechanisms could underly long-term modifications of inhibitory transmission.