Interaction between intracellular tetanization and pairing-induced long-term synaptic plasticity in the rat visual cortex

Long-term changes in synaptic transmission in slices of rat visual cortex w ere induced either by pairing the excitatory postsynaptic potentials with p ostsynaptic depolarization or by intracellular tetanization without synapti c stimulation. Changes in the excitatory postsynaptic potential amplitude i nduced by any of the protocols applied in isolation persisted for longer th an 1 h. Fairing-induced long-term potentiation was input specific. We studi ed the interaction between intracellular tetanization and pairing-induced p lasticity by applying the two protocols one after the other at 10-min inter vals. The pairing procedure applied after intracellular tetanization did no t lead to any further potentiation, but to a depotentiation of the potentia ted inputs. A second pairing protocol applied 10 min later led to further d epotentiation, while previously unaffected inputs became weakly depressed. If intracellular tetanization was applied after the pairing procedure, the synaptic responses did not change immediately, but a slow return of the exc itatory postsynaptic potential amplitude to the control level could be obse rved. Therefore, intracellular tetanization is not capable of inducing furt her potentiation after pairing, and pairing cannot further potentiate the i nputs which have already been potentiated by intracellular tetanization. Th e maintenance of long-term potentiation induced by any of the protocols was impaired by successive application of another procedure. These results suggest a similarity of the mechanisms of synaptic changes in duced by the two protocols and demonstrate that the direction of synaptic g ain change depends on the history of the synapse. (C) 1999 IBRO. Published by Elsevier Science Ltd.