Differential expressions of glycine transporter 1 and three glutamate transporter mRNA in the hippocampus of gerbils with transient forebrain ischemia

The extracellular concentrations of glutamate and its co-agonist for the N- methyl-d-aspartate (NMDA) receptor, glycine, may be under the control of am ino acid transporters in the ischemic brain. However, there is little infor mation on changes in glycine and glutamate transporters in the hippocampal CA1 field of gerbils with transient forebrain ischemia. This study investig ated the spatial and temporal expressions of glycine transporter 1 (GLYT1) and three glutamate transporter (excitatory amino acid carrier 1, EAAC1; gl utamate/aspartate transporter, GLAST; glutamate transporter 1, GLT1) mRNA i n the gerbil hippocampus after 3 minutes of ischemia, The GLYT1 mRNA was tr ansiently upregulated by the second day after ischemia in astrocytelike cel ls in close vicinity to hippocampal CA1 pyramidal neurons, possibly to redu ce glycine concentration in the local extracellular spaces. The EAAC1 mRNA was abundantly expressed in almost all pyramidal neurons and dentate granul e cells in the control gerbil hippocampus, whereas the expression level in CA1 pyramidal neurons started to decrease by the fourth day after ischemia in synchrony with degeneration of the CA1 neurons. The GLAST and GLT1 mRNA were rather intensely expressed in the dentate gyrus and CA3 field of the c ontrol hippocampus, respectively, but they were weakly expressed in the CA1 field before and after ischemia. As GLAST and GLT1 play a major role in th e control of extracellular glutamate concentration, the paucity of these tr ansporters in the CA 1 field may account for the vulnerability of CAI neuro ns to ischemia, provided that the functional GLAST and GLT1 proteins are al so less in the CA1 field than in the CA3 field. This study suggests that th e amino acid transporters play pivotal roles in the process of delayed neur onal death in the hippocampal CA1 field.