Electrophysiological properties of human hypothalamic hamartomas

The University of Arizona, Tucson, Arizona, United States
Annals of Neurology (Impact Factor: 11.91). 09/2005; 58(3):371-82. DOI: 10.1002/ana.20580
Source: PubMed

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.

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    • "Some observations suggest such a possibility. It has been demonstrated with patch-clamp electrophysiological recordings that glutamate might evoke whole-cell currents in human hypothalamic hamartoma slices immediately after surgical resection (Wu et al. 2005). Similarly, glutamate and NMDARs agonists in the presence of glycine increased membrane-depolarization currents in neuroblastoma cells (North et al. 1997), and glioblastoma, astrocytoma, and oligodendroglioma cells responded to kainate by depolarization of tumor cells in culture or tissue slices (Labrakakis et al. 1998). "
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    ABSTRACT: Glutamate, a nonessential amino acid, is a major bioenergetic substrate for proliferating normal and neoplastic cells on one hand and an excitatory neurotransmitter that is actively involved in biosynthetic, bioenergetic, metabolic, and oncogenic signaling pathways on the other. It exerts its action through a family of receptors consisting of metabotropic glutamate receptors (mGluRs) and ionotropic glutamate receptors (iGluRs), both of which have been implicated previously in a broad spectrum of acute and chronic neurodegenerative diseases. In this review, we discuss existing data on the role of glutamate as a growth factor for neoplastic cells, the expression of glutamate receptors in various types of benign and malignant neoplasms, and the potential roles that GluRs play in cancer development and progression along with their clinical significance. We conclude that glutamate-related receptors and their signaling pathways may provide novel therapeutic opportunities for a variety of malignant human diseases.
    Journal of Neural Transmission 03/2014; 121(8). DOI:10.1007/s00702-014-1182-6 · 2.87 Impact Factor
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    • "HH tissue has at least two neuronal phenotypes: small (soma diameter usually <16 μm) and large (>16 μm) HH neurons (14–16). Microelectrode patch-clamp recordings have shown that small HH neurons have intrinsic pacemaker-like activity and fire spontaneously even in the absence of synaptic inputs (16, 17). Small HH neurons are abundant (approximately 90% of all HH neurons), express glutamic acid decarboxylase (GAD), and have an interneuron-like phenotype (15, 16). "
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    ABSTRACT: Objective: Human hypothalamic hamartomas (HH) are intrinsically epileptogenic and are associated with treatment-resistant gelastic seizures. The basic cellular mechanisms responsible for seizure onset within HH are unknown. We used intra-operative microwire recordings of single neuron activity to measure the spontaneous firing rate of neurons and the degree of functional connection between neurons within the tumor. Technique: Fourteen patients underwent transventricular endoscopic resection of HH for treatment-resistant epilepsy. Prior to surgical resection, single neuron recordings from bundled microwires (total of nine contacts) were obtained from HH tissue. Spontaneous activity was recorded for two or three 5-min epochs under steady-state general anesthesia. Off-line analysis included cluster analysis of single unit activity and probability analysis of firing relationships between pairs of neurons. Results: Altogether, 222 neurons were identified (mean 6 neurons per recording epoch). Cluster analysis of single neuron firing utilizing a mixture of Gaussians model identified two distinct populations on the basis of firing rate (median firing frequency 0.6 versus 15.0 spikes per second; p < 10−5). Cluster analysis identified three populations determined by levels of burst firing (median burst indices of 0.015, 0.18, and 0.39; p < 10−15). Unbiased analysis of spontaneous single unit behavior showed that 51% of all possible neuron pairs within each recording epoch had a significant level of firing synchrony (p < 10−15). The subgroup of neurons with higher median firing frequencies was more likely to demonstrate synchronous firing (p < 10−7). Conclusion: Hypothalamic hamartoma tissue in vivo contains neurons which fire spontaneously. The activity of single neurons is diverse but distributes into at least two electrophysiological phenoytpes. Functional linkage between single neurons suggests that HH neurons exist within local networks that may contribute to ictogenesis.
    Frontiers in Neurology 12/2013; 4:210. DOI:10.3389/fneur.2013.00210
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    • "HH tissue is composed of small-neuron clusters that are interspersed with large neurons (Coons et al., 2007). Although small caminobutyric acid (GABA)ergic neurons (10–16 lm) spontaneously fire action potentials (Wu et al., 2005; Kim do et al., 2008), the large neurons (20–28 lm and often embedded in a GABA-rich neuropil) are quiescent at resting membrane potential and depolarize in response to GABA A -receptor activation (Kim do et al., 2008; Kim et al., 2009; We et al., 2008). Serial reconstruction studies traced axonal projections from small neurons to symmetric (putative inhibitory) terminal synapses onto the soma of large neurons (Beggs et al., 2008), further supporting our current working hypothesis of HH tissue epileptogenicity (see Fenoglio et al., 2007): Clusters of small, spontaneously firing neurons release GABA onto large neurons and activate GABA A receptors, inducing depolarization and action potential firing of large neurons. "
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    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
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