Decrease of effectivity of "competing" synaptic input requires protein synthesis.
We describe that tetanus-induced long-term increase of the response amplitude in one input to an identified neuron is accompanied by a decrease of synaptic responses in another, non-tetanized input. Induction of the decrease of responses in non-tetanized inputs was prevented by bath application of protein synthesis blockers (anisomycin or cycloheximide). The decrease of responses also did not occur in experiments when tetanization was substituted by short-term serotonin applications or extracellular stimulation of serotonergic cells known to potentiate investigated synaptic inputs. The results suggest that the heterosynaptically evoked decrease of synaptic response amplitude may be due to involvement of postsynaptic protein synthesis-dependent mechanisms.