GABA_A, not GABA_B, receptor shows subunit- and spatial-specific alterations in the hippocampus of seizure prone gerbils

In the present study, we investigated site-specific expressions of GABA_A and GABA_B receptor subunits in the seizure-sensitive (SS) and seizure-resistant (SR) gerbil hippocampus to elucidate the function of the γ-aminobutyric acid (GABA) receptor in seizure activity in this animal. There were no differences of the immunoreactivities of GABA_B receptor and some GABA_A receptor subunits (α3, α4, pan β and δ) in the hippocampus between SR and SS gerbils. The α1 subunit expression was mainly detected in interneurons of stratum radiatum and hilar region of dentate gyrus in the SR gerbil. However, in SS gerbil, interneurons were nearly devoid of α1 subunit immunoreactivity and mainly detected in the molecular layer of dentate gyrus. In SR gerbil, α2 subunit immunoreactivity was detected in Ammon's horn, particularly in the CA2 region. In SS gerbil, granule cell layer of the dentate gyrus in SS gerbil showed strong α2 subunit immunoreactivity. The distribution of α5 and γ2 subunit immunoreactivity in the hippocampus was similarly detected in SR and SS gerbil. However, α5 immunodensity of SR gerbil was slightly lower than that of SS gerbil in CA1 region and was slightly strong than that of SS gerbil in subiculum. These differences in distribution of GABA_A receptor, not GABA_B receptor, in the SR and SS gerbil hippocampus may indicate that abnormal hyperactive neuronal discharges are occurred in SS gerbil, which presumably result in spontaneous and repetitive seizure activity in this animal.