Abstracts

Rationale: Human hypothalamic hamartomas (HH) are associated with gelastic seizures and are notoriously refractory to medical therapy. Clinical studies using intracranial electrode recordings indicate that the HH itself is intrinsically epileptogenic. However the mechanisms remain unknown. In the current study, we used a 64-microelectrode array to examine the spontaneous network excitability and synchrony in surgically-resected human HH tissue, as it is well known that at a cellular level, epileptiform activity arises from neuronal hyperexcitability and hypersynchrony.Methods: Surgically resected HH tissue was immediately submerged in bubbled aCSF. Tissue slices (350μm) were placed over a 64-microelectrode array and perfused with oxygenated aCSF (Fig.1). The inherent electrophysiological events that occurred spontaneously throughout the tissue were recorded, i.e. action potentials fired by single cells and field potentials generated by the collective firing of a group of neurons. Changes in network spontaneous activity were examined after application of 4-aminopyridine (4AP, 50μM). Based on our previous findings that the L-type calcium channel antagonist nifedipine blocked spontaneous action potentials and GABAA-induced depolarization of single cells in HH tissue slices, we examined whether nifedipine (100μM) reduced the spontaneous network activity and synchrony in HH tissue slices.Results: Neuronal populations within HH tissue were spontaneously active under baseline conditions, demonstrating both sustained action and field potential firing (Fig.2). Irregular firing and bursts of action potentials occurred throughout the tissue. In addition, field potentials were randomly detectable in most regions of the tissue. Application of 4AP increased network synchrony and excitability 4-fold: specifically, the firing rate of action and field potentials per electrode increased and previously quiescent regions of the tissue fired spontaneous discharges. In addition, these events propagated across the multi-electrode array more frequently in response to 4AP. These events are comparable to the 4AP-induced ictal-like discharges reported in other human epilepsies. Blocking calcium channels with nifedipine reduced the frequency of spontaneous potentials by approximately 20% and significantly diminished the synchronicity of these events.Conclusions: This study is the first to provide direct in vitro evidence of spontaneous network activity in human epileptic tissue. Here, we demonstrate that human HH tissue, known to be intrinsically epileptic, is comprised of neuronal networks that are spontaneously active, i.e. single neurons discharging action potentials and groups of neurons collectively firing field potentials. In addition, the network hyperexcitability and hypersynchrony induced by 4AP is attenuated by the currently available FDA-approved calcium channel antagonist, nifedipine. These findings further support our previous studies suggesting L-type calcium channels as a potential novel target for the treatment of medically refractory epilepsy associated with HH.