Enhanced seizures and hippocampal neurodegeneration following kainic acid-induced seizures in metallothionein-I plus II-deficient mice

Metallothioneins (MTs) are major zinc binding proteins in the CNS that coul d be involved in the control of zinc metabolism as well as in protection ag ainst oxidative stress. Mice lacking MT-I and MT-II (MT-I + II deficient) b ecause of targeted gene inactivation were injected with kainic acid (KA), a potent convulsive agent, to examine the neurobiological importance of thes e MT isoforms. At 35 mg/kg KA, MT-I + II deficient male mice showed a highe r number of convulsions and a longer convulsion time than control mice. Thr ee days later, KA-injected mice showed gliosis and neuronal injury in the h ippocampus. MT-I + II deficiency decreased both astrogliosis and microglios is and potentiated neuronal injury and apoptosis as shown by terminal deoxy nucleotidyl transferase-mediated in situ end labelling (TUNEL), detection o f single stranded DNA (ssDNA) and by increased interleukin-1 beta-convertin g enzyme (ICE) and caspase-3 levels. Histochemically reactive zinc in the h ippocampus was increased by KA to a greater extent in MT-I + II-deficient c ompared with control mice. KA-induced seizures also caused increased oxidat ive stress, as suggested by the malondialdehyde (MDA) and protein tyrosine nitration (NITT) levels and by the expression of MT-I + II, nuclear factor- kappa B (NF-kappa B), and Cu/Zn-superoxide dismutase (Cu/Zn-SOD). MT-I + II deficiency potentiated the oxidative stress caused by KA. Both KA and MT-I + II deficiency significantly affected the expression of MT-III, granulocy te-macrophage colony stimulating factor (GM-CSF) and its receptor (GM-CSFr) . The present results indicate MT-I + II as important for neuron survival d uring KA-induced seizures, and suggest that both impaired zinc regulation a nd compromised antioxidant activity contribute to the observed neuropatholo gy of the MT-I + II-deficient mice.