Figure 2.

MMP-3 and MMP-9 are required for the late phase of LTP in the hippocampal CA3-CA1 projection. A–I, Time course of LTP recorded in the CA1 and induced by 100 Hz tetanic stimulation delivered at time = 0 min under control conditions (open circles) and in the presence of different MMP inhibitors (filled circles). Insets, Representative average fEPSP traces recorded before (gray) and 115–120 min after (black) LTP induction. Calibration: vertical, 0.5 mV; horizontal, 5 ms. A, MMP-9 KO slices had a strong deficit in late LTP that was measured 2 h after induction (CTR: 157 ± 11%; MMP-9 KO: 121 ± 7%; Mann–Whitney U test, U₍₁₈₎ = 17, p = 0.014) and normal early LTP (CTR: 168 ± 9% 15–20 min after induction relative to baseline; MMP-9 KO: 159 ± 10%; Mann–Whitney U test, U₍₁₈₎ = 48, p = 0.28) compared with LTP that was recorded in WT controls. B, Only the late phase of LTP was significantly impaired by the specific MMP-2/MMP-9 inhibitor SB-3CT (10 μm, CTR DMSO: 186 ± 15%; SB-3CT: 137 ± 15%; t test, t₍₁₂₎ = 2.29, p = 0.041). Early LTP was unaffected by SB-3CT (CTR DMSO: 188 ± 15%; SB-3CT: 180 ± 11%; t test, t₍₁₂₎ = 0.51, p = 0.62). C, Administration of a high concentration of the broad-spectrum MMP inhibitor FN439 (180 μm) blocked both early LTP that was measured 20 min after induction (CTR: 171 ± 12%; FN439: 129 ± 8%; t test, t₍₁₇₎ = 2.5, p = 0.02) and late LTP that was measured 2 h after HFS (CTR: 171 ± 12%; FN439: 115 ± 8%; Mann–Whitney U test, U₍₁₇₎ = 2.0, p < 0.001). D, A lower concentration of FN439 (25 μm) blocked only late LTP (CTR: 171 ± 12%; FN439: 124 ± 9%; Mann–Whitney U test, U₍₁₇₎ = 9.0, p = 0.006). E, The broad-spectrum MMP inhibitor NNGH at a concentration that blocks MMP-3 (10 μm) impaired late LTP (CTR DMSO: 153 ± 6%; NNGH: 112 ± 11%; t test, t₍₁₀₎ = 3.44, p = 0.006) but not early LTP (CTR DMSO: 162 ± 11%; NNGH: 147 ± 11%; t test, t₍₁₀₎ = 1.0, p = 0.34). F, The specific MMP-3/MMP-13 inhibitor UK356618 at a concentration of 750 nm reduced the magnitude of late LTP (CTR: 160 ± 10%; UK356618: 120 ± 6%; Mann–Whitney U test, U₍₂₁₎ = 29, p = 0.025) but not early LTP (CTR DMSO: 151 ± 8%; UK356618: 164 ± 8%; t test, t₍₂₁₎ = −0.95, p = 0.36). G, A higher concentration of UK356618 (2 μm) yielded similar results as in F. H, The specific MMP-13 inhibitor WAY170523 did not affect LTP (late LTP, CTR DMSO: 182 ± 13%, n = 8; WAY170523: 174 ± 30%, n = 5; t test, t₍₁₁₎ = 0.27, p = 0.79). I, Hippocampal slices that were exposed to a mix of NNGH (10 μm) and SB-3CT (10 μm) showed impairment of both early LTP (CTR DMSO: 181 ± 10%; NNGH+SB-3CT: 129 ± 7%; t test, t₍₁₀₎ = 3.78, p = 0.01) and late LTP beginning during the first minutes after HFS (CTR DMSO: 198 ± 22%; NNGH+SB-3CT: 128 ± 14%; t test, t₍₁₀₎ = 2.73, p = 0.021). J, K, Summary plots that depict the effects of different MMP inhibitors and MMP-9 deficiency on late (J) and early (K) LTP phases. The blockade of MMP-9 or MMP-3 activity similarly impaired late LTP, suggesting that the activity of both proteases is needed for the maintenance of LTP. *p < 0.05. **p < 0.01. ***p ≤ 0.001. n.s., not significant.