Figure 6.
Depression of KAR–EPSPs can also be induced by a large train of action potentials and is important for summation properties of mossy fiber EPSPs. A, Applying a train of five spikes without pairing with synaptic stimulation does not change the amplitude of KAR–EPSPs. B, In contrast to what we observed with a train of five spikes, a train of 30 spikes induces a clear reduction in KAR–EPSP amplitude. C, Summary of the effects of trains of 5, 10, or 30 spikes on KAR–EPSPs. The decrease of KAR–EPSPs induced by the train of 30 spikes also occurred in the presence of 50 μm d-AP5. D, Representative traces of Mf–EPSPs obtained without blocking AMPA receptors in control conditions (ctr; black) and after applying a train of 30 spikes (cond; gray). In conditions in which KAR–EPSPs are depressed by ∼30%, the train of EPSPs displayed significantly less summation (measured as a) compared with the control train of EPSPs. E, The train of 30 spikes did not significantly change the amplitude of the first stimulus, suggesting that this protocol did not have any presynaptic effects, nor did it affect AMPA receptors. F, Summary plot of the effect of a train of 30 spikes in the summation (measured in A as indicated in D) of EPSPs obtained after stimulating mossy fiber with a train of five stimuli. *p < 0.05.