Figure 1. Properties of basal synaptic transmission in PSD-93^−/− and PSD-95 mutant mice.

A, left, input/output curves were generated by comparing fibre volley amplitude (mV) to field EPSP slope (in mV ms⁻¹) across four different intensities of presynaptic fibre stimulation that elicited field EPSPs corresponding to 25, 50, 75 and 100% of the maximum field EPSP amplitude. The responses recorded in slices from PSD-93^−/− mice (▲, n = 15 slices from 6 mice) are similar to those seen in slices from wild-type mice (○, n = 15 slices from 9 mice). In contrast, the input/output curve is right-shifted in slices from PSD-95 mutants (•, n = 10 slices from 4 mice). Right, example fEPSPs recorded in slices from wild-type, PSD-93^−/− and PSD-95 mutant mice. Calibration bars are 2 mV and 2 ms. B, fibre volley/fEPSP slope ratios for each of the stimulation intensities shown in A. A repeated-measure ANOVA revealed a significant main effect of genotype and follow up Dunnett t test comparisons showed that ratios from PSD-95 mutants were significantly different (*P < 0.01) from wild-type values at all stimulation strengths. C, paired-pulse facilitation is enhanced in the hippocampal CA1 region of PSD-93^−/− mutant mice. Pairs of presynaptic fibre stimulation pulses were delivered with interpulse intervals of 25, 50, 100, or 200 ms. Significantly greater paired-pulse facilitation is seen at interpulse intervals between 25 and 100 ms in slices from PSD-93^−/− mutant mice (▲, n = 14 slices from 7 mice) and PSD-95 mutant mice (•, n = 13 slices from 4 mice, *P < 0.02, #P < 0.01 compared to wild-type littermates). The open circles show paired-pulse facilitation in slices from all wild-type mice (n = 27 slices from 11 mice).