Abnormal GABA sub(A) receptors from the human epileptic hippocampal subiculum microtransplanted to Xenopus oocytes

We studied the properties of GABA sub(A) receptors microtransplanted from the human temporal lobe epilepsy (TLE)-associated brain regions to Xenopus oocytes. Cell membranes, isolated from surgically resected brain specimens of drug-resistant TLE patients, were injected into frog oocytes, which rapidly incorporated human GABA sub(A) receptors, and any associated proteins, into their surface membrane. The receptors originating from different epileptic brain regions had a similar run-down but an affinity for GABA that was similar to 60% lower for the subiculum receptors than for receptors issuing from the hippocampus proper or the temporal lobe neocortex. Moreover, GABA currents recorded in oocytes injected with membranes from the subiculum had a more depolarized reversal potential compared with the hippocampus proper or neocortex of the same patients. Quantitative RT-PCR analysis was performed of the GABA sub(A) receptor alpha1-to alpha5-, beta 1-to beta 3-, gamma2-to gamma3-, and delta -subunit mRNAs. The levels of expression of the alpha3-, alpha5-, and beta 1-to beta 3-subunit mRNAs are significantly higher, with the exception of gamma2-subunit whose expression is lower, in subiculum compared with neocortex specimens. Our results suggest that an abnormal GABA-receptor subunit transcription in the TLE subiculum leads to the expression of GABA sub(A) receptors with a relatively low affinity. This abnormal behavior of the subiculum GABA sub(A) receptors may contribute to epileptogenesis.