Extrasynaptic GABAA receptors （GABAARs）-mediated tonic inhibition is reported to involve in the patho- genesis of epilepsy. In this study, we used cyclo- thiazide （CTZ）-induced in vitro brain slice seizure model to explore the effect of selective activation of extrasynaptic GABAARS by 4,5,6,7-tetra- hydroisoxazolo[5,4-c] pyridine-3-ol （THIP） on the CTZ-induced epileptiform activity in hippocampal neurons. Perfusion with CTZ dose-dependently induced multiple epileptiform peaks of evoked population spikes （PSs）in CA1 pyramidal neurons, and treatment with THIP （5 μmol/L） significantly reduced the multiple PS peaks induced by CTZ stimulation. Western blot showed that the 6-subunit of the GABAAR, an extrasynaptic specific GABAAR subunit, was also significantly down-regulated in the cell membrane 2 h after CTZ treatment. Our results suggest that the CTZ-induced epileptiform activity in hippocampal CA1 neurons is suppressed by the activation of extrasynaptic GABAARs, and further support the hypothesis that tonic inhibition mediated by extrasynaptic GABAARs plays a prominent role in seizure generation.
Li WanXu LiuZheng WuWanting RenShuzhen KongRaya Abou DarghamLongzhen ChengYun Wang
Pentylenetetrazole（PTZ）is a widely-used convulsant used in studies of epilepsy;its subcutaneous injection generates an animal model with stable seizures.Here,we compared the ability of PTZ via the intravenous and subcutaneous routes to evoke progressive epileptiform activity in the hippocampal CA1 neurons of anesthetized rats.The involvement of the BDNF-TrkB pathway was then investigated.When PTZ was given intravenously,it induced epileptiform bursting activity at a short latency in a dose-dependent manner.However,when PTZ was given subcutaneously,it induced a slowly-developing pattern of epileptogenesis;first,generating multiple population-spike peaks,then spontaneous interictal discharge-like spike,leading to the final ictal discharge-like,highly synchronized bursting firing in the CA1 pyramidal layer of the hippocampus.K252a,a TrkB receptor antagonist,when given by intracerebroventricular injection,significantly reduced the probability of multiple population spike peaks induced by subcutaneous injection of PTZ,delayed the latency of spontaneous spikes,and reduced the burst frequency.Our results indicate that PTZ induces a progressive change of neuronal epileptiform activity in the hippocampus,and the BDNF-TrkB signaling pathway is mainly involved in the early phases of epileptogenesis,but not the synchronized neuronal burst activity associated with epileptic seizure in the PTZ animal model.These results provide basic insights into the changing pattern of hippocampal neuronal activity during the development of the PTZ seizure model,and establish an in vivo seizure model useful for future electrophysiological studies of epilepsy.
