Abstracts

Rationale: Human hypothalamic hamartoma (HH) is a rare developmental malformation usually characterized by gelastic seizures. Almost all HH patients are refractory to antiepileptic drugs (AEDs). Since the epileptogenic mechanisms of gelastic seizures are unknown, there is no available AEDs that can effectively control seizure activity. Previously, we have found that the neurons within HH tissue are distributed in clusters of variable size, and that most (~90%) of HH neurons are small, GABAergic neurons with pacemaker-like firing. We believe that these neuronal clusters represent the functional unit for seizure initiation within HH tissue, and that hypersynchrony of these small, intrinsically-firing GABAergic neurons is a mechanistic component of ictogenesis. Methods: Multiple experimental approaches were used for this study, which include electrophysiological recording from HH slices, immunohistochemical staining of HH sections with specific antibodies for gap-junction protein connexin 36 (Cx36) and Cx43, Western-blot to compare Cx36 expression between HH and control tissues, and electron microscopy (EM) to show the gap-junction structures. Results: Immunostaining and Western-blot experiments show that neuronal type of gap-junction protein connexin 36 (Cx36) is highly expressed in human HH tissues freshly resected from gelastic seizure patients. EM shows a gap-junction-like structure between small HH neuronal pairs. Electrophysiological recordings from HH slices demonstrate that there are spontaneous epileptiform discharges in HH slice in normal artificial cerebrospinal fluid (ACFS) at 33±1 °C. Bath-application of gap-junction blocker (carbenoxolone) significantly eliminates these spontaneous discharges in a concentration-dependent manner. Conclusions: Our results suggest that the gap-junction is likely an important target for epileptogenesis within HH lesion, and pharmacological block of gap-junction is a novel therapeutic strategy for patients with refractory gelastic seizures and perhaps other forms of intractable epilepsy. This work is supported by Arizona Biomedical Research Commission.