Increase in levels of MMP-9 during L-LTP requires NMDA receptor activation and protein synthesis. A, Representative pairs of immunoblots of area CA1 homogenates frozen 60 min after control stimulation, after L-LTP tetanic stimulation (LTP), after L-LTP tetanic stimulation in the presence of the NMDA receptor antagonist APV (APV+LTP), or after control stimulation in the presence of APV alone (APV). Membranes were probed for the active form of MMP-9 or tubulin. The increase in levels of active MMP-9 evident 60 min after post-LTP tetanic stimulation (left) is blocked in tetanically stimulated slices incubated with APV (middle). Incubation in APV alone, without L-LTP stimulation, has no effect on MMP-9 levels (right). Blots shown are representative of results from three to six slices from at least three rats. B, Representative immunoblots of area CA1 homogenates frozen 30 min after Sp-cAMPS washout used to induce cLTP. Membranes were probed with the MMP-9 antibody; both pro and active forms of MMP-9 are shown. The increase in levels of both forms of MMP-9 evident in the cLTP slices is blocked by incubating slices in the protein synthesis inhibitor anisomycin (20 μm). The blots shown are representative results from three to six slices from at least three rats. C, Pairs of representative immunoblots of area CA1 homogenates frozen 60 min after receiving control stimulation, tetanic L-LTP-stimulation in the presence of anisomycin, or control stimulation plus anisomycin alone. Membranes were probed with the MMP-9 antibody or an antibody to GAPDH. Both pro and active forms of MMP-9 are shown. The L-LTP-associated increase in levels of MMP-9 induced tetanically is blocked by anisomycin. The blots shown are representative of results from three to six slices from at least three rats. con, Control; act, active form; tub., tubulin; aniso., anisomycin.