LONG-TERM MODIFICATIONS OF THE EFFICACY O F INHIBITORY SYNAPTIC CONNECTIONS IN THE THALAMOCORTICAL CIRCUITRY INDUCED BY INTRACORTICAL MICROSTIMULATION

Long-term posttetanic modifications of the efficacy of inhibitory syna ptic connections were studied in auditory thalamo-cortical assemblies. We demonstrated that intracortical microstimulation (ICMS, high-frequ ency pulses of 5 mcA) which activated a small group of cotrical neuron s produced long-term (at least 30 min) modifications (potentiation - L TPi and depression - LTDi) of the efficacy of inhibitory monosynaptic transmission between numerous elements of thalamo-cortical network. LT Pi was accompanied by an increase in the firing rate of inhibitory neu ron. LTPi was input-specific and did not lead to decrease in the firin g rate of the postsynaptic cell. LTP of the efficacy of excitatory and inhibitory inputs of the same target cell could be induced simultaneo usly. The efficacy of inhibitory synapses formed by the terminals of o ne axon on different cells could be modified variously. These results allowed us to suggest that we dealt with inhibitory synapses located o n dendritic spines and that both pre- and postsynaptic mechanisms coul d underly long-term modifications of inhibitory transmission.