Cytotoxic brain edema triggered by neuronal swelling is the chief cause of mortality following brain trauma and cerebral infarct. Using fluorescence lifetime imaging to analyze contributions of ...intracellular ionic changes in brain slices, we find that intense Na(+) entry triggers a secondary increase in intracellular Cl(-) that is required for neuronal swelling and death. Pharmacological and siRNA-mediated knockdown screening identified the ion exchanger SLC26A11 unexpectedly acting as a voltage-gated Cl(-) channel that is activated upon neuronal depolarization to membrane potentials lower than -20 mV. Blockade of SLC26A11 activity attenuates both neuronal swelling and cell death. Therefore cytotoxic neuronal edema occurs when sufficient Na(+) influx and depolarization is followed by Cl(-) entry via SLC26A11. The resultant NaCl accumulation causes subsequent neuronal swelling leading to neuronal death. These findings shed light on unique elements of volume control in excitable cells and lay the ground for the development of specific treatments for brain edema.
Low voltage-activated (LVA) T-type calcium channels are well regarded as a key mechanism underlying the generation of neuronal burst-firing. Their low threshold for activation combined with a rapid ...and transient calcium conductance generates low-threshold calcium potentials (LTCPs), upon the crest of which high frequency action potentials fire for a brief period. Experiments using simultaneous electroencephalography (EEG) and intracellular recordings demonstrate that neuronal burst-firing is a likely causative component in the generation of normal sleep patterns as well as some pathophysiological conditions, such as epileptic seizures. However, less is known as to how these neuronal bursts impact brain behavior, in particular network synchronization. In this review we summarize recent findings concerning the role of T-type calcium channels in burst-firing and discuss how they likely contribute to the generation of network synchrony. We further outline the function of burst-firing and network synchrony in terms of epileptic seizures. This article is part of a Special Issue entitled: Calcium channels.
► T-type calcium channels underlie the generation of neuronal burst-firing. ► Burst-firing is likely causative in the generation of epileptic seizures. ► Burst-firing contributes to the generation of network synchrony. ► We outline the function of network synchrony in terms of epileptic seizures.
Initially developed to generate new treatments for epilepsy, gabapentin, and pregabalin ("gabapentinoids") were engineered to mimic the action of GABA and to modulate GABA metabolism. Rather than ...their intended pharmacological action on GABA neurotransmission, instead, they exhibit a high affinity for the α2δ-1 and α2δ-2 subunits of voltage-activated calcium channels, wherein binding of gabapentinoids inhibits cellular calcium influx and attenuates neurotransmission. Despite a lack of activity on GABA levels, gabapentin and pregabalin are effective at suppressing seizures and subsequently approved as a new class of antiepileptic therapy for partial-onset epilepsy. Through the same hypothesized molecular mechanism and by controlling neuronal hyperexcitability, gabapentinoids demonstrate clear efficacy in pain management, which has arguably been their most extensively prescribed application to date. In this review, we focus on pregabalin as a second-generation gabapentinoid widely employed in the treatment of a variety of pain conditions. We also discuss the wider functional roles of α2δ subunits and the contributions that pregabalin might play in affecting physiological and pathophysiological processes.
Low voltage-activated (LVA) T-type calcium channels play critical roles in the excitability of many cell types and are a focus of research aimed both at understanding the physiological basis of ...calcium channel-dependent signaling and the underlying pathophysiology associated with hyperexcitability disorders such as epilepsy. These channels play a critical role towards neuronal firing in both conducting calcium ions during action potentials and also in switching neurons between distinct modes of firing. In this review the properties of the Ca
V
3.1, Ca
V
3.2 and Ca
V
3.3 T-type channel isoforms is discussed in relation to their individual contributions to action potentials during burst and tonic firing states as well their roles in switching between firing states.
Childhood Absence Epilepsy (CAE) accounts for approximately 10% of all pediatric epilepsies. Current treatments for CAE are ineffective in approximately 1/3 of patients and can be associated with ...severe side effects such as hepatotoxicity. Certain cannabinoids, such as cannabidiol (CBD), have shown promise in the treatment of pediatric epilepsies. However, CBD remains limited or prohibited in many jurisdictions, and has not been shown to have efficacy in CAE. Modulation of the type 1 cannabinoid receptor (CB1R) may provide more desirable pharmacological treatments. Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model many aspects of CAE, including cortical spike and wave discharges (SWDs). We have recently demonstrated that Δ9-tetrahydrocannabinol (THC) increases SWDs in GAERS whereas CBD decreases these events. Here, we characterized aspects of the endocannabinoid system in brain areas relevant to seizures in GAERS and tested whether positive allosteric modulators (PAMs) of CB1R reduced SWDs. Both female and male GAERS had reduced (>50%) expression of CB1R and elevated levels of the endocannabinoid 2-AG in cortex compared to non-epileptic controls (NEC). We then administered the CB1R PAMs GAT211 and GAT229 to GAERS implanted with cortical electrodes. Systemic administration of GAT211 to male GAERS reduced SWDs by 40%. Systemic GAT229 administration reduced SWDs in female and male GAERS. Intracerebral infusion of GAT229 into the cortex of male GAERS reduced SWDs by >60% in a CB1R-dependent manner that was blocked by SR141716A. Together, these experiments identify altered endocannabinoid tone in GAERS and suggest that CB1R PAMs should be explored for treatment of absence seizures.
•GAERS had sex-specific ECS differences compared to non-epileptic controls.•Injection of CB1R-PAMs GAT211 or GAT229 reduced spike and wave discharges in GAERS.•Cortical infusion of GAT229 reduced spike and wave discharges in GAERS.•The CB1R antagonist SR141716A blocked the effects of GAT229.•These data suggest CB1R-PAMs may have anticonvulsive properties in GAERS.
Abstract Childhood absence epilepsy (CAE) is often comorbid with behavioral and cognitive symptoms, including impaired visual memory. Genetic Absence Epilepsy Rats from Strasbourg (GAERS) is an ...animal model closely resembling CAE; however, cognition in GAERS is poorly understood. Crossmodal object recognition (CMOR) is a recently developed memory task that examines not only purely visual and tactile memory, but also requires rodents to integrate sensory information about objects gained from tactile exploration to enable visual recognition. Both the visual and crossmodal variations of the CMOR task rely on the perirhinal cortex, an area with dense expression of T-type calcium channels. GAERS express a gain-in-function missense mutation in the Cav3.2 T-type calcium channel gene. Therefore, we tested whether the T-type calcium channel blocker Z944 dose dependently (1, 3, 10 mg/kg; i.p.) altered CMOR memory in GAERS compared to the non-epileptic control (NEC) strain. GAERS demonstrated recognition memory deficits in the visual and crossmodal variations of the CMOR task that were reversed by the highest dose of Z944. Electroencephalogram recordings determined that deficits in CMOR memory in GAERS were not the result of seizures during task performance. In contrast, NEC showed a decrease in CMOR memory following Z944 treatment. These findings suggest that T-type calcium channels mediate CMOR in both the GAERS and NEC strains. Future research into the therapeutic potential of T-type calcium channel regulation may be particularly fruitful for the treatment of CAE and other disorders characterized by visual memory deficits.
See Noebels (doi:10.1093/brain/awy356) for a scientific commentary on this article.
The mechanisms underlying 'sudden unexpected death in epilepsy' (SUDEP) are unclear. Using behavioural, ...neurophysiological and neuroimaging data, Loonen et al. reveal characteristics specific to fatal seizures in homozygous Cacna1a S218L mice and show that brainstem spreading depolarization may play a critical role in SUDEP.
Abstract
Sudden unexpected death in epilepsy (SUDEP) is a fatal complication of epilepsy in which brainstem spreading depolarization may play a pivotal role, as suggested by animal studies. However, patiotemporal details of spreading depolarization occurring in relation to fatal seizures have not been investigated. In addition, little is known about behavioural and neurophysiological features that may discriminate spontaneous fatal from non-fatal seizures. Transgenic mice carrying the missense mutation S218L in the α1A subunit of Cav2.1 (P/Q-type) Ca2+ channels exhibit enhanced excitatory neurotransmission and increased susceptibility to spreading depolarization. Homozygous Cacna1aS218L mice show spontaneous non-fatal and fatal seizures, occurring throughout life, resulting in reduced life expectancy. To identify characteristics of fatal and non-fatal spontaneous seizures, we compared behavioural and electrophysiological seizure dynamics in freely-behaving homozygous Cacna1aS218L mice. To gain insight on the role of brainstem spreading depolarization in SUDEP, we studied the spatiotemporal distribution of spreading depolarization in the context of seizure-related death. Spontaneous and electrically-induced seizures were investigated by video monitoring and electrophysiological recordings in freely-behaving Cacna1aS218L and wild-type mice. Homozygous Cacna1aS218L mice showed multiple spontaneous tonic-clonic seizures and died from SUDEP in adulthood. Death was preceded by a tonic-clonic seizure terminating with hindlimb clonus, with suppression of cortical neuronal activity during and after the seizure. Induced seizures in freely-behaving homozygous Cacna1aS218L mice were followed by multiple spreading depolarizations and death. In wild-type or heterozygous Cacna1aS218L mice, induced seizures and spreading depolarization were never followed by death. To identify temporal and regional features of seizure-induced spreading depolarization related to fatal outcome, diffusion-weighted MRI was performed in anaesthetized homozygous Cacna1aS218L and wild-type mice. In homozygous Cacna1aS218L mice, appearance of seizure-related spreading depolarization in the brainstem correlated with respiratory arrest that was followed by cardiac arrest and death. Recordings in freely-behaving homozygous Cacna1aS218L mice confirmed brainstem spreading depolarization during spontaneous fatal seizures. These data underscore the value of the homozygous Cacna1aS218L mouse model for identifying discriminative features of fatal compared to non-fatal seizures, and support a key role for cortical neuronal suppression and brainstem spreading depolarization in SUDEP pathophysiology.
There is significant interest in the use of cannabinoids for the treatment of many epilepsies including absence epilepsy (AE). Genetic Absence Epilepsy Rats from Strasbourg (GAERS) model many aspects ...of AE including the presence of spike‐and‐wave discharges (SWDs) on electroencephalogram (EEG) and behavioral comorbidities, such as elevated anxiety. However, the effects of cannabis plant‐based phytocannabinoids have not been tested in GAERS. Therefore, we investigated how SWDs in GAERS are altered by the two most common phytocannabinoids, Δ9‐tetrahydrocannabinol (THC) and cannabidiol (CBD), and exposure to smoke from two different chemovars of cannabis. Animals were implanted with bipolar electrodes in the somatosensory cortex and EEGs were recorded for 2 hr. Injected THC (1–10 mg/kg, i.p.) dose‐dependently increased SWDs to over 200% of baseline. In contrast, CBD (30–100 mg/kg, i.p.) produced a ~50% reduction in SWDs. Exposure to smoke from a commercially available chemovar of high‐THC cannabis (Mohawk, Aphria Inc.) increased SWDs whereas a low‐THC/high‐CBD chemovar of cannabis (Treasure Island, Aphria Inc.) did not significantly affect SWDs in GAERS. Pre‐treatment with a CB1R antagonist (SR141716A) did not prevent the high‐THC cannabis smoke from increasing SWDs, suggesting that the THC‐mediated increase may not be CB1R‐dependent. Plasma concentrations of THC and CBD were similar to previously reported values following injection and smoke exposure. Compared to injected CBD, it appears Treasure Island did not increase plasma levels sufficiently to observe an anti‐epileptic effect. Together these experiments provide initial evidence that acute phytocannabinoid administration exerts the biphasic modulation of SWDs and may differentially impact patients with AE.
Genetic Absence Epilepsy Rats from Strasbourg (GAERS) spontaneously produce spike‐and‐slow wave discharges (SWDs). In the first experiments assessing cannabinoids in GAERS, injected tetrahydrocannabinol (Δ9‐THC) dose‐dependently increased SWDs, whereas injected cannabidiol (CBD) reduced these events. Furthermore, smoke exposure from high‐Δ9‐THC cannabis increased SWDs, but high‐CBD cannabis had no effect. These experiments show dissociable effects using two different exposure paradigms.
Palmitoylation is a reversible post-translational lipid modification that facilitates vesicular transport and subcellular localization of modified proteins. This process is catalyzed by ZDHHC enzymes ...that are implicated in several neurological and neurodevelopmental disorders. Loss-of-function mutations in ZDHHC9 have been identified in patients with X-linked intellectual disability (XLID) and associated with increased epilepsy risk. Loss of Zdhhc9 function in hippocampal cultures leads to shorter dendritic arbors and fewer inhibitory synapses, altering the ratio of excitatory-to-inhibitory inputs formed onto Zdhhc9-deficient cells. While Zdhhc9 promotes dendrite outgrowth through the palmitoylation of the GTPase Ras, it promotes inhibitory synapse formation through the palmitoylation of another GTPase, TC10. Zdhhc9 knockout mice exhibit seizure-like activity together with increased frequency and amplitude of both spontaneous and miniature excitatory and inhibitory postsynaptic currents. These findings present a plausible mechanism for how the loss of ZDHHC9 function may contribute to XLID and epilepsy.
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•Palmitoylation of Ras by Zdhhc9 regulates dendritic growth•Palmitoylation of TC10 by Zdhhc9 regulates inhibitory synapse formation•Loss of Zdhhc9 impairs excitatory/inhibitory synapse balance•Zdhhc9 knockout mice exhibit increased seizure activity and network excitability
Shimell et al. demonstrate that the palmitoylating enzyme Zdhhc9 controls dendritic growth and maintains excitatory/inhibitory synapse balance through distinct substrates. Loss of Zdhhc9 increases network excitability and seizure activity in accordance with Zdhhc9’s association with X-linked intellectual disability and epilepsy.
Genetic Absence Epilepsy Rats from Strasbourg (GAERS) are a rodent model of childhood absence epilepsy (CAE) that display a gain‐of‐function mutation in the gene encoding the Cav3.2 T‐type calcium ...channel. GAERS demonstrate heightened learning and delayed extinction of fear conditioning. Our objective in the present study was to examine the effects of the pan‐T‐type calcium channel blocker Z944 on the acquisition, consolidation and extinction of conditioned fear in GAERS and the non‐epileptic control (NEC) strain. Z944 (10 mg/kg; ip) was administered 15 min prior to either acquisition, extinction day 1 (24 hr later), acquisition and extinction day 1, or during the consolidation (post‐acquisition) of tone‐cued fear conditioning. Extinction was examined 24 and 48 hr after conditioning. In drug naïve GAERS, increased freezing during the acquisition and extinction phases of fear conditioning was found. Short‐term effects of Z944 on performance were observed as Z944 increased freezing during testing on the day it was administered. Z944 administered prior to the acquisition phase had a long‐term effect on extinction. Specifically, both GAERS and NECs showed a decrease in freezing during extinction relative to drug naïve GAERS and NEC rats respectively. Regardless of strain or treatment, female rats showed reduced extinction of fear relative to male rats. These results demonstrate that T‐type calcium channels contribute to the neural systems that mediate the learning and memory of conditioned fear. Overall, these findings suggest that T‐type calcium channel blockers show promise in the treatment of learning impairments observed in disorders such as CAE.
Treatment with the T‐type calcium channel blocker Z944 prior to the acquisition of fear conditioning decreased freezing in Genetic Absence Epilepsy Rats from Strasbourg during the extinction phases to levels comparable to non‐epileptic controls (NECs). NECs treated with Z944 also showed reduced freezing during extinction; however, the results suggest that NECs have impaired recall of conditioned fear as little freezing behaviour was observed during extinction trials.
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