MMP2 and infectious otitis media: Compared to AOM-treated WT mice, M1R-deficient mice had reduced expression of Mmp-2 (2.95 ± 0.29 vs. 1.72 ± 0.26 fold respectively, p < 0.01; Fig. 3A), Timp-1 (11.98 ± 3.67 vs. 3.92 ± 1.07 fold respectively, p < 0.05), and Timp-2 (2.08 ± 0.18 vs. 1.23 ± 0.13 fold respectively, p < 0.001; Fig. 3B).