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GABA A receptor‐mediated activation of L‐type calcium channels induces neuronal excitation in surgically resected human hypothalamic hamartomas
Author(s) -
Kim Do Young,
Fenoglio Kristina A.,
Simeone Timothy A.,
Coons Stephen W.,
Wu Jie,
Chang Yongchang,
Kerrigan John F.,
Rho Jong M.
Publication year - 2008
Publication title -
epilepsia
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 2.687
H-Index - 191
eISSN - 1528-1167
pISSN - 0013-9580
DOI - 10.1111/j.1528-1167.2007.01455.x
Subject(s) - muscimol , gabaergic , chemistry , calcium imaging , bicuculline , gabaa receptor , depolarization , calcium in biology , endocrinology , medicine , t type calcium channel , nifedipine , voltage dependent calcium channel , neuroscience , calcium , receptor , biology
SummaryPurpose: The human hypothalamic hamartoma (HH) is a rare, intrinsically epileptogenic lesion associated with gelastic seizures, but the underlying mechanisms remain unclear. Here, we examined the role of GABA A receptors in surgically resected HH tissue.Methods: HH tissue slices (350 μm) were studied using cellular electrophysiological, calcium imaging, and immunocytochemical techniques.Results: Two neuronal cell types were seen: small (10–16 μm) spontaneously firing GABAergic neurons and large (20–28 μm) quiescent neurons. In gramicidin‐perforated patch recordings, muscimol (30 μM) induced membrane depolarization in 70% of large (but not small) neurons and a concomitant rise in intracellular calcium. These responses were blocked by bicuculline methiodide (50 μM). Depolarizing neurons also exhibited more positive reversal potentials (E muscimol ) and significantly higher intracellular chloride concentrations compared to those that hyperpolarized. The cation chloride co‐transporters NKCC1 and KCC2 were coexpressed in the majority of large neurons, but fluorometric measurements revealed that 84% of large HH neurons expressed solely or relatively more NKCC1. Bumetanide (20 μM), a NKCC1 antagonist, partially suppressed muscimol‐induced excitation in large neurons. Concordant with robust expression of CaV1.2 and CaV1.3 subunits in HH neurons, the L‐type calcium channel blocker nifedipine (100 μM) prevented muscimol‐induced neuronal excitation.Conclusions: GABA A receptor‐mediated excitation, due in part to differential expression of NKCC1 and KCC2 and subsequent activation of L‐type calcium channels, may contribute to seizure genesis in HH tissue. Given the ready availability of L‐type calcium channel blockers, our results have clinical ramifications for the treatment of seizures associated with HH lesions.