Hyperhomocysteinemia-induced loss of short-term memory in mice. Short-term memory of wild type (WT), Cbs+/−, Cbs+/− and matrix metalloproteinase-9 (Mmp9−/−) double knockout (Cbs+/−/Mmp9−/−), and MMP9 gene knockout (Mmp9−/−) mice was assessed by novel object recognition test. Lower discrimination ratio indicates impaired short-term memory. *P<0.05 for all, versus WT; †, versus Cbs+/− n=10 for all groups.