Rats were pretreated with lactulose or vehicle for 2 days before treatment with Meth or saline. Active and pro-MMP-9 were measured via gelatinase zymography in cortical homogenates 2 h after Meth or saline treatments. A) Meth significantly increased the ratio of active to pro-MMP-9 (*, p < 0.05, compared to Vehicle Saline), which was blocked by lactulose (#, p < 0.005, compared to Vehicle Meth). (n = 8 per group). B) Representative zymography images for active and pro-MMP-9 in cortical tissue.