Research reportAltered expression of GABAA receptors (α4, γ2 subunit), potassium chloride cotransporter 2 and astrogliosis in tremor rat hippocampus

Impaired GABAergic inhibitory neurotransmission plays an essential role in the pathogenesis of epilepsy. GABAA receptor (GABAAR), potassium chloride cotransporter 2 (KCC2) and astrocytes are of particular importance to GABAergic transmission and thus involved in the development of increased seizure susceptibility.The tremor rat (TRM: tm/tm), a genetic mutant discovered in a Kyoto-Wistar colony, can manifest both absence-like seizures and tonic convulsions without any external stimuli. So far, there are no reports that can elucidate the effects of GABAAR (α4, γ2 subunit), KCC2 and astrocytes on TRMs. The present study was undertaken to detect the expressions of GABAAR α4, GABAAR γ2 and KCC2 in TRMs hippocampus at mRNA and protein levels. In this work, mRNA and protein expressions of GABAAR α4 were significantly elevated while GABAAR γ2 and KCC2 were both evidently decreased in TRMs hippocampus by real-time RT-PCR and western blot, respectively. Furthermore, a dramatic elevation of KCC2 protein level was found after cerebroventricular injection with K252a to TRMs than that in the DMSO-treated TRMs. Besides, our present study also demonstrated that GFAP (a major component of astrocyte) immunoreactivity was much more intense in TRMs hippocampal CA1, CA3 and DG regions than that in control group with immnohistochemistry and confocal microscopic analyses. The protein expression of GFAP was also markedly elevated in TRMs hippocampus, suggesting that astrogliosis appeared in the TRM model. These data demonstrate that altered expressions of GABAAR (α4, γ2) and KCC2 and astrogliosis observed in TRMs hippocampus may provide us good therapeutic targets for the treatment of genetic epilepsy.

► An obvious elevation of GABAAR α4 and a decrease of GABAAR γ2 were noted in TRMs. ► There was a dramatic reduction in KCC2 gene and protein expressions in TRMs. ► Blockade of BDNF/TrkB pathway markedly increased KCC2 protein level in TRMs. ► Astrogliosis appeared in TRMs hippocampus.