MMP-9 regulation: (A) MMP-9 mRNA was assayed by RT-PCR, and normalized to cyclophilin RNA. MMP-9 mRNA was significantly increased by lesion, and estrogen teatment resulted in a small but signficant decrease in MMP-9 mRNA expression. (B) MMP-9 activity was measured by gelatin zymography at 6 and 24 h post injury, and representative examples from each group are shown here. The location of the lytic area corresponded to the expected size of MMP-9 (96 kD), indicated by the filled-arrow head, as well as that of a positive control (conditoned media from endothelial cells). Line-arrow head indicates pre-stained protein size marker (86 kD). Virtually no MMP-9 activity was apparent in the sham-injected animals. At 24 h after lesion, olfactory bulb lesions increased MMP-9 activity, although this was attenuated in the estrogen-treated (OVX+E), lesioned animals. Estrogen-treated lesioned animals that received anti-p75NTR, however, had MMP-9 activity that was similar to that of the control-pellet (OVX) replaced lesioned animals. Histogram represents means+SEM of the measured lytic area for MMP-9 at the 24 h time point, n = 6 per group. Sham: Sham lesion, Lesion+Vehicle: NMDA injection with pre immune serum, Lesion+Anti p75: NMDA injections with anti p75NTR antibodies. *:p < 0.05.