Delayed Expression of Both GABA B R1 and GABA B R2 Subunits in Murine Hippocampal Dentate Gyrus After a Single Systemic Injection of Trimethyltin

Trimethyltin (TMT) has been used as a cytotoxin to neurons rather than glial cells in the mammalian hippocampus. The systemic administration of TMT led to declined fluorescence of ZnAF-2 DA staining as a marker of intact mossy fibers and increased fluorescence of Fluoro-Jade B staining as a marker of degenerated neurons during the initial 2 to 5 days after the administration with later ameliorations within 30 days in the hippocampal dentate gyrus (DG) and CA3 region in mice. On immunoblotting analysis, both GABA B R1 and GABA B R2 subunit levels increased during 15 to 30 days after TMT along with significant decreases in glutamatergic GluA1 and GluA2/3 receptor subunit levels during 2 to 7 days in the DG, but not in other hippocampal regions such as CA1 and CA3 regions. Immunohistochemical analysis revealed the constitutive and inducible expression of GABA B R2 subunit in cells immunoreactive to an astrocytic marker as well as neuronal markers in the DG with the absence of neither GABA B R1a nor GABA B R1b subunit from cells positive to an astrocytic marker. These results suggest that both GABA B R1 and GABA B R2 subunits may be up-regulated in cells other than neurons and astroglia in the DG at a late stage of TMT intoxication in mice.