Figure 4.
The PREGS-induced long-term enhancement of postsynaptic AMPA responses in P3-P4 slices is NMDA receptor and Ca2+ dependent. a1, Traces illustrating that the late phase of the 25 μm PREGS-induced increase of AMPA mEPSC frequency cannot be observed when the Ca2+ chelator BAPTA (10 mm) is internally dialyzed via the patch electrode. Calibration: 15 pA, 100 ms. a2, time course of the effect of 25 μm PREGS on a neuron internally dialyzed with BAPTA and a control neuron from the same batch of slices. a3, Summary of the effect of 25 μm PREGS on neurons internally dialyzed with 10 mm BAPTA (**p < 0.01; ***p < 0.001; n = 6). b1, NMDA receptor-mediated EPSCs (Vhold = +40 mm; calibration: 20 pA, 200 ms) are significantly inhibited by intracellular dialysis of MK-801 (5 mm; see Results for more details; ***p < 0.001; n = 11 by t test). To promote entrance of MK-801 to the pore, neurons were depolarized from -70 to -15 mV (5 times for 10 s each). b2, In six of these 11 neurons, after NMDA EPSC inhibition was confirmed, 500 nm tetrodotoxin was applied, and the effect of 25 μm PREGS on mEPSC frequency was assessed [experiment (Exp.) 1]. Under these conditions, application of PREGS did not induce a long-lasting increase in mEPSC frequency. In a separate batch of neurons, tetrodotoxin was present from the start of the experiment, and basal mEPSC frequency was recorded (experiment 2; see Results for more details). Neurons were then depolarized as described above to promote entrance of MK-801 to the pore. mEPSC frequency was recorded again and found to be unchanged by the depolarization procedure (see Results). As shown in the summary graph, 25 μm PREGS did not induce a long-lasting increase in mEPSC frequency under these conditions (n = 4). *p < 0.05; **p < 0.01; ***p < 0.001. c1, Extracellular application of 10 μm ifenprodil (ifen) induces a long-lasting decrease in the amplitude of NMDA EPSCs (recorded at Vhold = -10 mV). Note that these events are blocked by 100 μm dl-AP-5. Calibration: 20 pA, 200 ms. c2, In a separate batch of neurons, mEPSC frequency was recorded in the presence of tetrodotoxin (500 nm). Under these conditions, ifenprodil blocked the late phase of the 25 μm PREGS effect on mEPSC frequency. Ifenprodil alone did not have an effect on mEPSC frequency (see Results). *p < 0.05; **p < 0.01; n = 6. Ctrl, Control. Error bars represent SEM.