Electrophysiological properties of human hypothalamic hamartomas
ABSTRACT The hypothalamic hamartoma (HH) is a rare developmental malformation often characterized by gelastic seizures, which are usually refractory to medical therapy. The mechanisms of epileptogenesis operative in this subcortical lesion are unknown. In this study, we used standard patch-clamp electrophysiological techniques combined with histochemical approaches to study individual cells from human HH tissue immediately after surgical resection. More than 90% of dissociated HH cells were small (6-9 microm soma) and exhibited immunoreactivity to the neuronal marker NeuN, and to glutamic acid decarboxylase, but not to glial fibrillary acidic protein. Under current-clamp, whole-cell recordings in single dissociated cells or in intact HH slices demonstrated typical neuronal responses to depolarizing and hyperpolarizing current injection. In some cases, HH cells exhibited a "sag-like" membrane potential change during membrane hyperpolarization. Interestingly, most HH cells exhibited robust, spontaneous "pacemaker-like" action potential firing. Under voltage-clamp, dissociated HH cells exhibited functional tetrodotoxin (TTX)-sensitive Na(+) and tetraethylammonium-sensitive K(+) currents. Both GABA and glutamate evoked whole-cell currents, with GABA exhibiting a peak current amplitude 10-fold greater than glutamate. These findings suggest that human HH tissues, associated with gelastic seizures, contained predominantly small GABAergic inhibitory neurons that exhibited intrinsic "pacemaker-like" behavior.
- SourceAvailable from: Timothy A Simeone[Show abstract] [Hide abstract]
ABSTRACT: Human hypothalamic hamartomas (HHs) are associated with gelastic seizures, intrinsically epileptogenic, and notoriously refractory to medical therapy. We previously reported that the L-type calcium channel antagonist nifedipine blocks spontaneous firing and γ-aminobutyric acid (GABA)(A)-induced depolarization of single cells in HH tissue slices. In this study, we examined whether blocking L-type calcium channels attenuates emergent activity of HH neuronal networks. A high-density multielectrode array was used to record extracellular signals from surgically resected HH tissue slices. High-frequency oscillations (HFOs, ripples and fast ripples), field potentials, and multiunit activity (MUA) were studied (1) under normal and provoked [4-aminopyridine (4-AP)] conditions; and (2) following nifedipine treatment. Spontaneous activity occurred during normal artificial cerebrospinal fluid (aCSF) conditions. Nifedipine reduced the total number and duration of HFOs, abolished the association of HFOs with field potentials, and increased the inter-HFO burst intervals. Notably, the number of active regions was decreased by 45 ± 9% (mean ± SEM) after nifedipine treatment. When considering electrodes that detected activity, nifedipine increased MUA in 58% of electrodes and reduced the number of field potentials in 67% of electrodes. Provocation with 4-AP increased the number of events and, as the number of electrodes that detected activity increased 248 ± 62%, promoted tissue-wide propagation of activity. During provocation with 4-AP, nifedipine effectively reduced HFOs, the association of HFOs with field potentials, field potentials, MUA, and the number of active regions, and limited propagation. This is the first study to report (1) the presence of HFOs in human subcortical epileptic brain tissue in vitro; (2) the modulation of "pathologic" high-frequency oscillations (i.e., fast ripples) in human epileptic tissue by L-type calcium channel blockers; and (3) the modulation of network physiology and synchrony of emergent activity in human epileptic tissue following blockade of L-type calcium channels. Attenuation of activity in HH tissue during normal and provoked conditions supports a potential therapeutic usefulness of L-type calcium channel blockers in epileptic patients with HH.Epilepsia 03/2011; 52(3):531-40. DOI:10.1111/j.1528-1167.2010.02942.x · 4.58 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: To topographically localize the ictogenic zone within hypothalamic hamartomas (HHs) and the symptomatogenic zone for gelastic seizure (GS), we analyzed data from both interictal and ictal single photon emission computed tomography (SPECT). Ictal SPECT was performed immediately after GS onset in 21 patients with HH (aged 2-36 years, mean 13.8 years) who underwent stereotactic radiofrequency thermocoagulation (SRT). SPECT data were statistically analyzed by means of subtraction ictal SPECT coregistered to magnetic resonance imaging (MRI) (SISCOM) and statistical parametric mapping (SPM). Topographic localization of ictal hyperperfusion areas was evaluated. SISCOM obtained in 27 studies demonstrated ictal hyperperfusion in the HH interface zone in 16 studies of 13 patients (hot HH group). In these patients, HHs were significantly larger than those without hyperperfusion of HH in 11 studies of 8 patients (21.4 ± 10.3 vs. 12.3 ± 7.3 mm in diameter, p < 0.05, t-test). In all patients and in the hot HH group, SPM group analysis of individual differences between interictal and ictal data revealed significantly (p < 0.001) hyperperfused areas in the ipsilateral hypothalamus, mediodorsal (MD) nucleus of the thalamus and putamen, bilateral pontine tegmentum, and contralateral inferior semilunar lobule of the cerebellum. There was no hyperperfusion in the mammillothalamocingulate pathway. The present study confirmed that ictogenesis occurs in the HH interface zone, which should accordingly be the target for SRT. We suggest that a thalamopontocerebellar circuit plays an important role for stereotypical and automatic symptomatogenesis of GS and that the hypothalamus and MD nucleus of the thalamus are potentially involved in epileptic encephalopathy.Epilepsia 09/2010; 51(11):2270-9. DOI:10.1111/j.1528-1167.2010.02739.x · 4.58 Impact Factor
- [Show abstract] [Hide abstract]
ABSTRACT: The cellular mechanisms underlying intrinsic epileptogenesis in human hypothalamic hamartoma (HH) are unknown. We previously reported that HH tissue is composed predominantly of GABAergic neurons, but how GABAergic-neuron-rich HH tissue is intrinsically epileptogenic is unclear. Here, we tested the hypotheses that some HH neurons exhibit immature features and that GABA excites these neurons via activation of GABA(A) receptors (GABA(A)Rs). Gramicidin-perforated and cell-attached patch-clamp recordings were performed using freshly-dissociated HH neurons to evaluate GABA(A)R-mediated currents, Cl(-) equilibrium potentials, and intracellular Cl(-) concentrations. Single-cell RT-PCR and immunocytochemical techniques were used to examine cation-Cl(-) co-transporter (NKCC1 and KCC2) gene and KCC2 protein expression and molecular markers of maturation. From a total of 93 acutely-dissociated HH neurons from 34 patients, 76% were small (soma: 6-9 microm) and 24% were large (soma: >20 microm) in size. Under gramicidin-perforated patch recording conditions, GABA(A)R activation depolarized/excited large but hyperpolarized/inhibited small HH neurons in most cases. Compared to small HH neurons, large HH neurons exhibited more positive Cl(-) equilibrium potentials, higher intracellular Cl(-) concentrations, lower KCC2 expression, and an immature phenotype, consistent with GABA(A)R-mediated excitation. Taken collectively, we provide novel evidence for and mechanistic insights into HH epileptogenicity: GABA(A)R-mediated excitation.Experimental Neurology 07/2008; 213(2):397-404. DOI:10.1016/j.expneurol.2008.07.004 · 4.62 Impact Factor