BDNF modulates GABAA receptors microtransplanted from the human epileptic brain to Xenopus oocytes.

Cell membranes isolated from brain tissues, obtained surgically from six patients afflicted with drug-resistant temporal lobe epilepsy and from one nonepileptic patient afflicted with a cerebral oligodendroglioma, were injected into frog oocytes. By using this approach, the oocytes acquire human GABAA receptors, and we have shown previously that the "epileptic receptors" (receptors transplanted from epileptic brains) display a marked run-down during repetitive applications of GABA. It was found that exposure to the neurotrophin BDNF increased the amplitude of the "GABA currents" (currents elicited by GABA) generated by the epileptic receptors and decreased their run-down; both events being blocked by K252A, a neurotrophin tyrosine kinase receptor B inhibitor. These effects of BDNF were not mimicked by nerve growth factor. In contrast, the GABAA receptors transplanted from the nonepileptic human hippocampal uncus (obtained during surgical resection as part of the nontumoral tissue from the oligodendroglioma margins) or receptors expressed by injecting rat recombinant alpha1beta2gamma2 GABAA receptor subunit cDNAs generated GABA currents whose time-course and run-down were not altered by BDNF. Loading the oocytes with the Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetate-acetoxymethyl ester (BAPTA-AM), or treating them with Rp-8-Br-cAMP, an inhibitor of the cAMP-dependent PKA, did not alter the GABA currents. However, staurosporine (a broad spectrum PK inhibitor), bisindolylmaleimide I (a PKC inhibitor), and U73122 (a phospholipase C inhibitor) blocked the BDNF-induced effects on the epileptic GABA currents. Our results indicate that BDNF potentiates the epileptic GABAA currents and antagonizes their use-dependent run-down, thus strengthening GABAergic inhibition, probably by means of activation of tyrosine kinase receptor B receptors and of both PLC and PKC.