Figure 4.

Effect of temperature (a and b) and stimulus frequency (c and d) on EPSCs elicited in CA1 pyramidal neurons by Schaffer collateral stimulation. (a) PPS (at 0.5 Hz) of Schaffer collaterals evoked no responses to the first stimulus (open circles) but some to the second one (filled circles; P5 rat) at 24°C. Raising the temperature from 24°C to 32°C resulted in the appearance of responses to the first stimulus and increased the number of successes to the second. Insets represent six individual traces recorded at 24°C and 32°C, respectively (calibration bars: vertical, 10 pA; horizontal, 10 ms). (b) Mean percentage of successes to the first (open column) and to the second (filled column) stimulus at 24°C and 32°C (n = 7). At 32°C, the percentage of successes to both stimuli was significantly higher than at 24°C (P < 0.05, Wilcoxon test). (c) Effects of frequency changes in a representative experiment. Stimulation frequency was changed from 0.1 to 1 Hz (bar) and then to 0.025 Hz. Notice the disappearance of the EPSC during 0.1 Hz stimulation. (Insets) Seven individual traces of EPSCs evoked at 0.1, 1, and 0.025 Hz. Calibration bars: vertical, 15 pA; horizontal, 5 ms. (d) Mean percentage of successes obtained in eight cells by changing the stimulation frequencies as in a. For comparison, the mean percentage of successes obtained at 0.5 Hz (n = 7 cells) and 0.05 Hz stimulation (n = 8) in two additional sets of experiments is shown. The value obtained at 0.025 Hz is significantly different from that at 0.1, 0.5, or 1 Hz (P < 0.05 and P < 0.01, respectively, Wilcoxon test). Note that synapses showed a low efficacy at all frequencies and became silent during 1-Hz test stimulation.