GABAA receptor-mediated activation of L-type calcium channels induces neuronal excitation in surgically resected human hypothalamic hamartomas.
OBJECTIVE
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 GABAA receptors in surgically resected HH tissue.


METHODS
HH tissue slices (350 microm) were studied using cellular electrophysiological, calcium imaging, and immunocytochemical techniques.


RESULTS
Two neuronal cell types were seen: small (10-16 microm) spontaneously firing GABAergic neurons and large (20-28 microm) quiescent neurons. In gramicidin-perforated patch recordings, muscimol (30 microM) 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 microM). Depolarizing neurons also exhibited more positive reversal potentials (Emuscimol) 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 microM), 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 microM) prevented muscimol-induced neuronal excitation.


CONCLUSIONS
GABAA 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.
Kim
Do Young
DY
Division of Pediatric Neurology, Barrow Neurological Institute, St. Joseph's Hospital & Medical Center, Phoenix, AZ 85013, USA.
Fenoglio
Kristina A
KA
Simeone
Timothy A
TA
Coons
Stephen W
SW
Wu
Jie
J
Chang
Yongchang
Y
Kerrigan
John F
JF
Rho
Jong M
JM
D000200:Action Potentials / Q000187:drug effects / Q000502:physiology*; D000293:Adolescent; D000328:Adult; D020746:Calcium Channels, L-Type / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D002675:Child, Preschool; D018118:Chloride Channels / Q000378:metabolism; D004828:Epilepsies, Partial / Q000378:metabolism / Q000503:physiopathology; D005260:Female; D006222:Hamartoma / Q000378:metabolism / Q000503:physiopathology* / Q000601:surgery*; D006801:Humans; D007027:Hypothalamic Diseases / Q000378:metabolism / Q000503:physiopathology* / Q000601:surgery*; D007150:Immunohistochemistry; D007223:Infant; D008297:Male; D008564:Membrane Potentials / Q000187:drug effects / Q000502:physiology; D008959:Models, Neurological; D009118:Muscimol / Q000494:pharmacology; D009474:Neurons / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D009543:Nifedipine / Q000494:pharmacology; D018408:Patch-Clamp Techniques; D011963:Receptors, GABA-A / Q000187:drug effects / Q000378:metabolism / Q000502:physiology*; D028021:Sodium-Potassium-Chloride Symporters / Q000378:metabolism; D064506:Solute Carrier Family 12, Member 2; D027981:Symporters / Q000187:drug effects / Q000378:metabolism; D000096922:K Cl- Cotransporters
D020746:Calcium Channels, L-Type; D018118:Chloride Channels; D009118:Muscimol; D009543:Nifedipine; D011963:Receptors, GABA-A; D028021:Sodium-Potassium-Chloride Symporters; D064506:Solute Carrier Family 12, Member 2; D027981:Symporters; D000096922:K Cl- Cotransporters; C578877:SLC12A2 protein, human