Figure 9.

Induction of LTP in the CA3-CA1 increases MMP-3 protein and in situ activity. A–D, The induction of LTP resulted in an increase in the fluorescence intensity and area of MMP-3-positive puncta in the stratum radiatum 2 h after HFS (right) compared with basally stimulated controls (left). The average normalized integrated density of fluorescence in MMP-3-positive puncta (B) (CTR: 100 ± 10%; 2 h after LTP: 138 ± 11%; t test, t₍₁₉₎ = 2.24, p = 0.034) and average area of single MMP-3-positive puncta (C) (CTR: 1.12 ± 0.10 μm²; 2 h after LTP: 1.44 ± 0.083 μm²; t test, t₍₁₉₎ = 2.47, p = 0.023) increased 2 h after LTP induction, but the density of MMP-3-positive puncta was unaltered (D) (CTR: 0.025 ± 0.003 μm⁻²; 2 h after LTP: 0.026 ± 0.002 μm⁻², t test, t₍₁₉₎ = 0.20, p = 0.84). Scale bars, 10 μm. E–H, In situ caseinolytic activity (E, left) and MMP-3 immunostaining (middle) showed substantial colocalization (right), and the extent of colocalization increased 2 h after LTP in the stratum radiatum. The average normalized ISZ fluorescence in the CA1 stratum radiatum (F) (CTR: 100 ± 2%; 2 h after LTP: 115 ± 4%; Mann–Whitney U test, U₍₁₉₎ = 9.0, p = 0.001), average ISZ activity only in MMP-3-positive puncta (G) (CTR: 835 ± 80 AU; 2 h after LTP: 1171 ± 93 AU; t test, t₍₁₉₎ = 2.75, p = 0.016), and ratio of mean ISZ activity in MMP-3-positive puncta to mean ISZ activity in the MMP-3-negative area (H) (CTR: 1.28 ± 0.02; 2 h after LTP: 1.38 ± 0.03; t test, t₍₁₉₎ = 3.18, p = 0.005) were all higher 2 h after LTP. I–K, The induction of LTP increased pro-MMP3 expression and its cleavage to the active form of MMP-3. I, Typical blots of homogenates that were prepared from control slices and slices 15 or 60 min after HFS. J, K, Summary graphs of the semiquantitative analysis of pro-MMP-3 and active MMP-3 protein, respectively, at different time points after HFS (unpaired t test). *p < 0.05. **p < 0.01. ***p ≤ 0.001. n.s., not significant.