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Figure 2


Fig. 2. Inhibitors of CaMKs and PKA impair PTP at C1-B2 synapses. (A) Sample electrophysiological recording of PTP induction and decay at C1-B2 synapses in culture. Single action potentials in the C1 neuron are elicited at 0.05 Hz (lower trace) and the corresponding EPSPs evoked in the B2 neuron are simultaneously recorded (upper trace). After five basal stimuli, a tetanus (10 Hz for 2 seconds) is induced in the C1 neuron (arrowhead); 30 seconds later, the basal 0.05 Hz stimulation is resumed. The amplitude of the post-tetanic EPSPs is increased, reaching its peak 30 seconds after tetanus and progressively declining to pre-tetanic levels during the following 3-4 minutes. Bars, horizontal, 20 seconds; vertical, 8 mV upper trace, 60 mV lower trace. (B) Time-course of EPSP amplitude changes in two episodes of PTP evoked at a 30-minute interval in the same synapses. Values are normalized to the average amplitude of the last five pre-tetanic EPSPs. The peak amplitude and decay kinetics of PTP are nearly the same at t=0 ({circ}) and at t=30 min ({blacksquare}) after tetanus. (C) Time-course of EPSP amplitude changes in two episodes of PTP evoked in the same synapses immediately before ({circ}) and 30 minutes after bath application of the CaMKs inhibitor KN-93 (5 µM, {blacksquare}). KN-93 nearly abolished the expression of PTP. (D) Time-course of the EPSP amplitude changes in episodes of PTP evoked in two distinct groups of synapses. In one group, the presynaptic C1 neuron was injected with the MLCK peptide (50-100 µM), an inhibitor of CaMKs ({blacksquare}). In the other group of synapses, the inactive MLCK control peptide was injected as a control ({circ}). In both groups, PTP was evoked 30 minutes after injection of peptides. The MLCK peptide induces a dramatic impairment of PTP, similar to KN-93. (E) Time-course of EPSP amplitude changes in two episodes of PTP evoked in the same synapses immediately before ({circ}) and 30 minutes after bath application of the PKA inhibitor Rp-cAMPS (500 µM, {blacksquare}). (F) Mean peak PTP amplitudes measured at 30 seconds after tetanus in the experimental groups shown in panels B-E. Values are normalized to the mean peak potentiation measured under control conditions in each group. The peak amplitude of PTP is significantly reduced in the presence of KN-93, MLCK peptide and Rp-cAMPS. (G) Mean pre-tetanic EPSP amplitude in the PTP episodes shown in panels B-E. The various inhibitors used did not significantly alter the basal EPSP amplitude with respect to control conditions.





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