Abstracts

Rationale: Human hypothalamic hamartoma (HH), a rare nonmalignant tumor, is often accompanied with gelastic seizures. The mechanisms of the epilepogenesis within the HH are largely unknown. Gamma aminobutyric acid (GABA) is an important inhibitory neurotransmitter in adult brain, and impairment of GABAergic signals is the major reason to induce epilepsy. GABAA receptors mediated phasic and tonic inhibitions, which plays a key role in maintaining balance between brain excitation and inhibition. It has been reported that functional GABAA receptor rundown was found in human temporal lobe epilepsy tissues and likely contributes to epileptogenesis. In the present study, we ask whether functional GABAA receptor rundown also occurs in the HH tissues of patients with gelastic seizures. Methods: 1) Patch-clamp perforated (amphoterisin B) whole-cell recordings in freshly dissociated neurons from human HH tissue after surgical resection. 2) Microtransplantation of HH and control human hypothalamic tissue (membrane fregment) into Exnopus oocytes, respectively and comparison of functional GABAA receptors between HH and control tissues. Results: In perforated patch-clamp recordings, repetitively exposure of GABA (0.1 mM, 2s exposure at 40s interval) cause time-dependent rundown of whole-cell currents in small HH neurons, but large HH neurons showed much less GABA-induced rundown using the same protocol. Supplementary with 5 mM ATP (Mg2+ salt) intracellularly significantly prevented functional GABAA receptor rundown in small HH neurons. To confirm these patch-clamp findings, the microtransplantation of the membrane protein from either HH or normal human hypothalamic tissue (control) into Xenopus oocytes was employed. After the rundown protocols (7 consecutive 1 mM GABA with 10s duration and 40s intervals for oocytes) were applied, an apparent rundown was observed on the oocytes microtransplanted with the HH membrane protein compared to that with normal control. Intracellular injection of 5 mM ATP or pretreated with 2 nM okadaic acid for 10 min significantly prevented functional GABAA receptor rundown. Conclusions: We conclude that time-dependent rundown of GABAA receptor reduces GABAergic inhibition, which may involve into seizure genesis in HH patients. Blockage of phosphatases could stabilize the HH GABAA receptors and strengthen GABAergic function, and this mechanism will open a novel therapeutic strategy for controlling and/or treating gelastic seizures.