AMPK-mediated potentiation of GABAergic signalling drives hypoglycaemia-provoked spike-wave seizures.

Metabolism regulates neuronal activity and modulates the occurrence of epileptic seizures. Here, using two rodent models of absence epilepsy, we show that hypoglycaemia increases the occurrence of spike-wave seizures. We then show that selectively disrupting glycolysis in the thalamus, a structure implicated in absence epilepsy, is sufficient to increase spike-wave seizures. We propose that activation of thalamic AMP-activated protein kinase, a sensor of cellular energetic stress and potentiator of metabotropic GABAB-receptor function, is a significant driver of hypoglycaemia-induced spike-wave seizures. We show that AMP-activated protein kinase augments postsynaptic GABAB-receptor-mediated currents in thalamocortical neurons and strengthens epileptiform network activity evoked in thalamic brain slices. Selective thalamic AMP-activated protein kinase activation also increases spike-wave seizures. Finally, systemic administration of metformin, an AMP-activated protein kinase agonist and common diabetes treatment, profoundly increased spike-wave seizures. These results advance the decades-old observation that glucose metabolism regulates thalamocortical circuit excitability by demonstrating that AMP-activated protein kinase and GABAB-receptor cooperativity is sufficient to provoke spike-wave seizures.

Sleep Fragmentation, Electroencephalographic Slowing, and Circadian Disarray in a Mouse Model for Intensive Care Unit Delirium.

BACKGROUND: We aimed to further validate our previously published animal model for delirium by testing the hypothesis that in aged mice, Anesthesia, Surgery and simulated ICU conditions (ASI) induce sleep fragmentation, electroencephalographic (EEG) slowing, and circadian disarray consistent with intensive care unit (ICU) patients with delirium. METHODS: A total of 41 mice were used. Mice were implanted with EEG electrodes and randomized to ASI or control groups. ASI mice received laparotomy, anesthesia, and simulated ICU conditions. Controls did not receive ASI. Sleep was recorded at the end of ICU conditions, and hippocampal tissue was collected on EEG recording. Arousals, EEG dynamics, and circadian gene expression were compared with t tests. Two-way repeated measures analysis of variance (RM ANOVA) was used to assess sleep according to light. RESULTS: ASI mice experienced frequent arousals (36.6 ± 3.2 vs 26.5 ± 3.4; P = .044; 95% confidence interval [CI], 0.29-19.79; difference in mean ± SEM, 10.04 ± 4.62) and EEG slowing (frontal theta ratio, 0.223 ± 0.010 vs 0.272 ± 0.019; P = .026; 95% CI, -0.091 to -0.007; difference in mean ± SEM, -0.05 ± 0.02) relative to controls. In ASI mice with low theta ratio, EEG slowing was associated with a higher percentage of quiet wakefulness (38.2 ± 3.6 vs 13.4 ± 3.8; P = .0002; 95% CI, -35.87 to -13.84; difference in mean ± SEM, -24.86 ± 5.19). ASI mice slept longer during the dark phases of the circadian cycle (nonrapid eye movement [NREM], dark phase 1 [D1]: 138.9 ± 8.1 minutes vs 79.6 ± 9.6 minutes, P = .0003, 95% CI, -95.87 to -22.69, predicted mean difference ± SE: -59.28 ± 13.89; NREM, dark phase 2 (D2): 159.3 ± 7.3 minutes vs 112.6 ± 15.5 minutes, P = .006, 95% CI, -83.25 to -10.07, mean difference ± SE, -46.66 ± 13.89; rapid eye movement (REM), D1: 20.5 ± 2.1 minutes vs 5.8 ± 0.8 minutes, P = .001, 95% CI, -24.60 to -4.71, mean difference ± SE, -14. 65 ± 3.77; REM, D2: 21.0 ± 2.2 minutes vs 10.3 ± 1.4 minutes, P = .029, 95% CI, -20.64 to -0.76, mean difference ± SE, -10.70 ± 3.77). The expression of essential circadian genes was also lower in ASI mice (basic helix-loop-helix ARNT like [BMAL1] : -1.3 fold change; circadian locomotor output cycles protein kaput [CLOCK] : -1.2). CONCLUSIONS: ASI mice experienced EEG and circadian changes mimicking those of delirious ICU patients. These findings support further exploration of this mouse approach to characterize the neurobiology of delirium.

CaV3.2 calcium channels control NMDA receptor-mediated transmission: a new mechanism for absence epilepsy.

CaV3.2 T-type calcium channels, encoded by CACNA1H, are expressed throughout the brain, yet their general function remains unclear. We discovered that CaV3.2 channels control NMDA-sensitive glutamatergic receptor (NMDA-R)-mediated transmission and subsequent NMDA-R-dependent plasticity of AMPA-R-mediated transmission at rat central synapses. Interestingly, functional CaV3.2 channels primarily incorporate into synapses, replace existing CaV3.2 channels, and can induce local calcium influx to control NMDA transmission strength in an activity-dependent manner. Moreover, human childhood absence epilepsy (CAE)-linked hCaV3.2(C456S) mutant channels have a higher channel open probability, induce more calcium influx, and enhance glutamatergic transmission. Remarkably, cortical expression of hCaV3.2(C456S) channels in rats induces 2- to 4-Hz spike and wave discharges and absence-like epilepsy characteristic of CAE patients, which can be suppressed by AMPA-R and NMDA-R antagonists but not T-type calcium channel antagonists. These results reveal an unexpected role of CaV3.2 channels in regulating NMDA-R-mediated transmission and a novel epileptogenic mechanism for human CAE.

Unexpected role of interferon-γ in regulating neuronal connectivity and social behaviour.

Immune dysfunction is commonly associated with several neurological and mental disorders. Although the mechanisms by which peripheral immunity may influence neuronal function are largely unknown, recent findings implicate meningeal immunity influencing behaviour, such as spatial learning and memory. Here we show that meningeal immunity is also critical for social behaviour; mice deficient in adaptive immunity exhibit social deficits and hyper-connectivity of fronto-cortical brain regions. Associations between rodent transcriptomes from brain and cellular transcriptomes in response to T-cell-derived cytokines suggest a strong interaction between social behaviour and interferon-γ (IFN-γ)-driven responses. Concordantly, we demonstrate that inhibitory neurons respond to IFN-γ and increase GABAergic (γ-aminobutyric-acid) currents in projection neurons, suggesting that IFN-γ is a molecular link between meningeal immunity and neural circuits recruited for social behaviour. Meta-analysis of the transcriptomes of a range of organisms reveals that rodents, fish, and flies elevate IFN-γ/JAK-STAT-dependent gene signatures in a social context, suggesting that the IFN-γ signalling pathway could mediate a co-evolutionary link between social/aggregation behaviour and an efficient anti-pathogen response. This study implicates adaptive immune dysfunction, in particular IFN-γ, in disorders characterized by social dysfunction and suggests a co-evolutionary link between social behaviour and an anti-pathogen immune response driven by IFN-γ signalling.

Mice Harboring a Non-Functional CILK1/ICK Allele Fail to Model the Epileptic Phenotype in Patients Carrying Variant CILK1/ICK.

CILK1 (ciliogenesis associated kinase 1)/ICK (intestinal cell kinase) is a highly conserved protein kinase that regulates primary cilia structure and function. CILK1 mutations cause a wide spectrum of human diseases collectively called ciliopathies. While several CILK1 heterozygous variants have been recently linked to juvenile myoclonic epilepsy (JME), it remains unclear whether these mutations cause seizures. Herein, we investigated whether mice harboring either a heterozygous null Cilk1 (Cilk1+/-) mutation or a heterozygous loss-of-function Cilk1 mutation (Cilk1R272Q/+) have epilepsy. We first evaluated the spontaneous seizure phenotype of Cilk1+/- and Cilk1R272Q/+ mice relative to wildtype littermates. We observed no electrographic differences among the three mouse genotypes during prolonged recordings. We also evaluated electrographic and behavioral responses of mice recovering from isoflurane anesthesia, an approach recently used to measure seizure-like activity. Again, we observed no electrographic or behavioral differences in control versus Cilk1+/- and Cilk1R272Q/+ mice upon isoflurane recovery. These results indicate that mice bearing a non-functional copy of Cilk1 fail to produce electrographic patterns resembling those of JME patients with a variant CILK1 copy. Our findings argue against CILK1 haploinsufficiency being the mechanism that links CILK1 variants to JME.

Tenuous Inhibitory GABAergic Signaling in the Reticular Thalamus.

Maintenance of a low intracellular Cl- concentration ([Cl-]i) is critical for enabling inhibitory neuronal responses to GABAA receptor-mediated signaling. Cl- transporters, including KCC2, and extracellular impermeant anions ([A]o) of the extracellular matrix are both proposed to be important regulators of [Cl-]i Neurons of the reticular thalamic (RT) nucleus express reduced levels of KCC2, indicating that GABAergic signaling may produce excitation in RT neurons. However, by performing perforated patch recordings and calcium imaging experiments in rats (male and female), we find that [Cl-]i remains relatively low in RT neurons. Although we identify a small contribution of [A]o to a low [Cl-]i in RT neurons, our results also demonstrate that reduced levels of KCC2 remain sufficient to maintain low levels of Cl- Reduced KCC2 levels, however, restrict the capacity of RT neurons to rapidly extrude Cl- following periods of elevated GABAergic signaling. In a computational model of a local RT network featuring slow Cl- extrusion kinetics, similar to those we found experimentally, model RT neurons are predisposed to an activity-dependent switch from GABA-mediated inhibition to excitation. By decreasing the activity threshold required to produce excitatory GABAergic signaling, weaker stimuli are able to propagate activity within the model RT nucleus. Our results indicate the importance of even diminished levels of KCC2 in maintaining inhibitory signaling within the RT nucleus and suggest how this important activity choke point may be easily overcome in disorders such as epilepsy.SIGNIFICANCE STATEMENT Precise regulation of intracellular Cl- levels ([Cl-]i) preserves appropriate, often inhibitory, GABAergic signaling within the brain. However, there is disagreement over the relative contribution of various mechanisms that maintain low [Cl-]i We found that the Cl- transporter KCC2 is an important Cl- extruder in the reticular thalamic (RT) nucleus, despite this nucleus having remarkably low KCC2 immunoreactivity relative to other regions of the adult brain. We also identified a smaller contribution of fixed, impermeant anions ([A]o) to lowering [Cl-]i in RT neurons. Inhibitory signaling among RT neurons is important for preventing excessive activation of RT neurons, which can be responsible for generating seizures. Our work suggests that KCC2 critically restricts the spread of activity within the RT nucleus.

The effect of rho kinase inhibition on morphological and electrophysiological maturity in iPSC-derived neurons.

Induced pluripotent stem cell (iPSC)-derived neurons permit the study of neurogenesis and neurological disease in a human setting. However, the electrophysiological properties of iPSC-derived neurons are consistent with those observed in immature cortical neurons, including a high membrane resistance depolarized resting membrane potential and immature firing properties, limiting their use in modeling neuronal activity in adult cells. Based on the proven association between inhibiting rho kinase (ROCK) and increased neurite complexity, we seek to determine if short-term ROCK inhibition during the first 1-2 weeks of differentiation would increase morphological complexity and electrophysiological maturity after several weeks of differentiation. While inhibiting ROCK resulted in increased neurite formation after 24 h, this effect did not persist at 3 and 6 weeks of age. Additionally, there was no effect of ROCK inhibition on electrophysiological properties at 2-3, 6, or 12 weeks of age, despite an increase in evoked and spontaneous firing and a more hyperpolarized resting membrane potential over time. These results indicate that while there is a clear effect of time on electrophysiological maturity, ROCK inhibition did not accelerate maturity.

Disruption of Rapid Eye Movement Sleep Homeostasis in Adolescent Rats after Neonatal Anesthesia.

BACKGROUND: Previous studies suggest that rapid eye movement sleep rebound and disruption of rapid eye movement sleep architecture occur during the first 24 h after general anesthesia with volatile anesthetics in adult rats. However, it is unknown whether rapid eye movement sleep alterations persist beyond the anesthetic recovery phase in neonatal rats. This study tested the hypothesis that rapid eye movement sleep disturbances would be present in adolescent rats treated with anesthesia on postnatal day 7. METHODS: Forty-four neonatal rats were randomly allocated to treatment with anesthesia consisting of midazolam, nitrous oxide, and isoflurane or control conditions for 2 h or 6 h. Electroencephalographic and electromyographic electrodes were implanted and recordings obtained between postnatal days 26 and 34. The primary outcome was time spent in rapid eye movement sleep. Data were analyzed using two-tailed unpaired t tests and two-way repeated measures analysis of variance. RESULTS: Rats treated with midazolam, nitrous oxide, and isoflurane exhibited a significant increase in rapid eye movement sleep three weeks later when compared with control rats, regardless of whether they were treated for 2 h (174.0 ± 7.2 min in anesthetized, 108.6 ± 5.3 in controls, P < 0.0001) or 6 h (151.6 ± 9.9 min in anesthetized, 108.8 ± 7.1 in controls, P = 0.002). CONCLUSIONS: Treatment with midazolam, nitrous oxide, and isoflurane on postnatal day 7 increases rapid eye movement sleep three weeks later in rats.

Hyperexcitability of rat thalamocortical networks after exposure to general anesthesia during brain development.

Prevailing literature supports the idea that common general anesthetics (GAs) cause long-term cognitive changes and neurodegeneration in the developing mammalian brain, especially in the thalamus. However, the possible role of GAs in modifying ion channels that control neuronal excitability has not been taken into consideration. Here we show that rats exposed to GAs at postnatal day 7 display a lasting reduction in inhibitory synaptic transmission, an increase in excitatory synaptic transmission, and concomitant increase in the amplitude of T-type calcium currents (T-currents) in neurons of the nucleus reticularis thalami (nRT). Collectively, this plasticity of ionic currents leads to increased action potential firing in vitro and increased strength of pharmacologically induced spike and wave discharges in vivo. Selective blockade of T-currents reversed neuronal hyperexcitability in vitro and in vivo. We conclude that drugs that regulate thalamic excitability may improve the safety of GAs used during early brain development.

Role of voltage-gated calcium channels in the regulation of aldosterone production from zona glomerulosa cells of the adrenal cortex.

Zona glomerulosa cells (ZG) of the adrenal gland constantly integrate fluctuating ionic, hormonal and paracrine signals to control the synthesis and secretion of aldosterone. These signals modulate Ca2+ levels, which provide the critical second messenger to drive steroid hormone production. Angiotensin II is a hormone known to modulate the activity of voltage-dependent L- and T-type Ca2+ channels that are expressed on the plasma membrane of ZG cells in many species. Because the ZG cell maintains a resting membrane voltage of approximately -85 mV and has been considered electrically silent, low voltage-activated T-type Ca2+ channels are assumed to provide the primary Ca2+ signal that drives aldosterone production. However, this view has recently been challenged by human genetic studies identifying somatic gain-of-function mutations in L-type CaV 1.3 channels in aldosterone-producing adenomas of patients with primary hyperaldosteronism. We provide a review of these assumptions and challenges, and update our understanding of the state of the ZG cell in a layer in which native cellular associations are preserved. This updated view of Ca2+ signalling in ZG cells provides a unifying mechanism that explains how transiently activating CaV 3.2 channels can generate a significant and recurring Ca2+ signal, and how CaV 1.3 channels may contribute to the Ca2+ signal that drives aldosterone production.

Canonical Organization of Layer 1 Neuron-Led Cortical Inhibitory and Disinhibitory Interneuronal Circuits.

Interneurons play a key role in cortical function and dysfunction, yet organization of cortical interneuronal circuitry remains poorly understood. Cortical Layer 1 (L1) contains 2 general GABAergic interneuron groups, namely single bouquet cells (SBCs) and elongated neurogliaform cells (ENGCs). SBCs predominantly make unidirectional inhibitory connections (SBC→) with L2/3 interneurons, whereas ENGCs frequently form reciprocal inhibitory and electric connections (ENGC↔) with L2/3 interneurons. Here, we describe a systematic investigation of the pyramidal neuron targets of L1 neuron-led interneuronal circuits in the rat barrel cortex with simultaneous octuple whole-cell recordings and report a simple organizational scheme of the interneuronal circuits. Both SBCs→ and ENGC ↔ L2/3 interneuronal circuits connect to L2/3 and L5, but not L6, pyramidal neurons. SBC → L2/3 interneuronal circuits primarily inhibit the entire dendritic-somato-axonal axis of a few L2/3 and L5 pyramidal neurons located within the same column. In contrast, ENGC ↔ L2/3 interneuronal circuits generally inhibit the distal apical dendrite of many L2/3 and L5 pyramidal neurons across multiple columns. Finally, L1 interneuron-led circuits target distinct subcellular compartments of L2/3 and L5 pyramidal neurons in a L2/3 interneuron type-dependent manner. These results suggest that L1 neurons form canonical interneuronal circuits to control information processes in both supra- and infragranular cortical layers.

Respiratory alkalosis provokes spike-wave discharges in seizure-prone rats.

Hyperventilation reliably provokes seizures in patients diagnosed with absence epilepsy. Despite this predictable patient response, the mechanisms that enable hyperventilation to powerfully activate absence seizure-generating circuits remain entirely unknown. By utilizing gas exchange manipulations and optogenetics in the WAG/Rij rat, an established rodent model of absence epilepsy, we demonstrate that absence seizures are highly sensitive to arterial carbon dioxide, suggesting that seizure-generating circuits are sensitive to pH. Moreover, hyperventilation consistently activated neurons within the intralaminar nuclei of the thalamus, a structure implicated in seizure generation. We show that intralaminar thalamus also contains pH-sensitive neurons. Collectively, these observations suggest that hyperventilation activates pH-sensitive neurons of the intralaminar nuclei to provoke absence seizures.

Intrinsic Adrenal TWIK-Related Acid-Sensitive TASK Channel Dysfunction Produces Spontaneous Calcium Oscillations Sufficient to Drive AngII (Angiotensin II)-Unresponsive Hyperaldosteronism.

BACKGROUND: Ion channel mutations in calcium regulating genes strongly associate with AngII (angiotensin II)-independent aldosterone production. Here, we used an established mouse model of in vivo aldosterone autonomy, Cyp11b2-driven deletion of TWIK-related acid-sensitive potassium channels (TASK-1 and TASK-3, termed zona glomerulosa [zG]-TASK-loss-of-function), and selective pharmacological TASK channel inhibition to determine whether channel dysfunction in native, electrically excitable zG cell rosette-assemblies: (1) produces spontaneous calcium oscillatory activity and (2) is sufficient to drive substantial aldosterone autonomy. METHODS: We imaged calcium activity in adrenal slices expressing a zG-specific calcium reporter (GCaMP3), an in vitro experimental approach that preserves the native rosette assembly and removes potentially confounding extra-adrenal contributions. In parallel experiments, we measured acute aldosterone production from adrenal slice cultures. RESULTS: Absent from untreated WT slices, we find that either adrenal-specific genetic deletion or acute pharmacological TASK channel inhibition produces spontaneous oscillatory bursting behavior and steroidogenic activity (2.4-fold) that are robust, sustained, and equivalent to activities evoked by 3 nM AngII in WT slices. Moreover, spontaneous activity in zG-TASK-loss-of-function slices and inhibitor-evoked activity in WT slices are unresponsive to AngII regulation over a wide range of concentrations (50 pM to 3 µM). CONCLUSIONS: We provide proof of principle that spontaneous activity of zG cells within classic rosette assemblies evoked solely by a change in an intrinsic, dominant resting-state conductance can be a significant source of AngII-independent aldosterone production from native tissue.

Astrocytes as gatekeepers of GABAB receptor function.

The long-lasting actions of the inhibitory neurotransmitter GABA result from the activation of metabotropic GABA(B) receptors. Enhanced GABA(B)-mediated IPSCs are critical for the generation of generalized thalamocortical seizures. Here, we demonstrate that GABA(B)-mediated IPSCs recorded in the thalamus are primarily defined by GABA diffusion and activation of distal extrasynaptic receptors potentially up to tens of micrometers from synapses. We also show that this diffusion is differentially regulated by two astrocytic GABA transporters, GAT1 and GAT3, which are localized near and far from synapses, respectively. A biologically constrained model of GABA diffusion and uptake shows how the two GATs differentially modulate amplitude and duration of GABA(B) IPSCs. Specifically, the perisynaptic expression of GAT1 enables it to regulate GABA levels near synapses and selectively modulate peak IPSC amplitude, which is primarily dependent on perisynaptic receptor occupancy. GAT3 expression, however, is broader and includes distal extrasynaptic regions. As such, GAT3 acts as a gatekeeper to prevent diffusion of GABA away from synapses toward extrasynaptic regions that contain a potentially enormous pool of GABA(B) receptors. Targeting this gatekeeper function may provide new pharmacotherapeutic opportunities to prevent the excessive GABA(B) receptor activation that appears necessary for thalamic seizure generation.

Nonlinearities between inhibition and T-type calcium channel activity bidirectionally regulate thalamic oscillations.

Absence seizures result from 3 to 5 Hz generalized thalamocortical oscillations that depend on highly regulated inhibitory neurotransmission in the thalamus. Efficient reuptake of the inhibitory neurotransmitter GABA is essential, and reuptake failure worsens human seizures. Here, we show that blocking GABA transporters (GATs) in acute rat brain slices containing key parts of the thalamocortical seizure network modulates epileptiform activity. As expected, we found that blocking either GAT1 or GAT3 prolonged oscillations. However, blocking both GATs unexpectedly suppressed oscillations. Integrating experimental observations into single-neuron and network-level computational models shows how a non-linear dependence of T-type calcium channel gating on GABAB receptor activity regulates network oscillations. Receptor activity that is either too brief or too protracted fails to sufficiently open T-type channels necessary for sustaining oscillations. Only within a narrow range does prolonging GABAB receptor activity promote channel opening and intensify oscillations. These results have implications for therapeutics that modulate inhibition kinetics.

Angiotensin II induces coordinated calcium bursts in aldosterone-producing adrenal rosettes.

Aldosterone-producing zona glomerulosa (zG) cells of the adrenal gland arrange in distinct multi-cellular rosettes that provide a structural framework for adrenal cortex morphogenesis and plasticity. Whether this cyto-architecture also plays functional roles in signaling remains unexplored. To determine if structure informs function, we generated mice with zG-specific expression of GCaMP3 and imaged zG cells within their native rosette structure. Here we demonstrate that within the rosette, angiotensin II evokes periodic Cav3-dependent calcium events that form bursts that are stereotypic in form. Our data reveal a critical role for angiotensin II in regulating burst occurrence, and a multifunctional role for the rosette structure in activity-prolongation and coordination. Combined our data define the calcium burst as the fundamental unit of zG layer activity evoked by angiotensin II and highlight a novel role for the rosette as a facilitator of cell communication.

Presynaptic inhibition selectively weakens peptidergic cotransmission in a small motor system.

The presence and influence of neurons containing multiple neurotransmitters is well established, including the ability of coreleased transmitters to influence the same or different postsynaptic targets. Little is known, however, regarding whether presynaptic regulation of multitransmitter neurons influences all transmission from these neurons. Using the identified neurons and motor networks in the crab stomatogastric ganglion, we document the ability of presynaptic inhibition to selectively inhibit peptidergic cotransmission. Specifically, we determine that the gastropyloric receptor (GPR) proprioceptor neuron uses presynaptic inhibition to selectively regulate peptidergic cotransmission from the axon terminals of MCN1, a projection neuron that drives the biphasic (retraction, protraction) gastric mill (chewing) rhythm. MCN1 drives this rhythm via fast GABAergic excitation of the retraction neuron Int1 and slow peptidergic excitation of the lateral gastric (LG) protraction neuron. We first demonstrate that GPR inhibition of the MCN1 axon terminals is serotonergic and then establish that this serotonergic inhibition weakens MCN1 peptidergic excitation of LG without altering MCN1 GABAergic excitation of Int1. At the circuit level, we show that this selective regulation of MCN1 peptidergic cotransmission is necessary for the normal GPR regulation of the gastric mill rhythm. This is the first demonstration, at the level of individual identified neurons, that a presynaptic input can selectively regulate a subset of coreleased transmitters. This selective regulation changes the balance of cotransmitter actions by the target multitransmitter neuron, thereby enabling this neuron to have state-dependent actions on its target network. This finding reveals additional flexibility afforded by the ability of neurons to corelease multiple neurotransmitters.

Maintenance of thalamic epileptiform activity depends on the astrocytic glutamate-glutamine cycle.

The generation of prolonged neuronal activity depends on the maintenance of synaptic neurotransmitter pools. The astrocytic glutamate-glutamine cycle is a major mechanism for recycling the neurotransmitters GABA and glutamate. Here we tested the effect of disrupting the glutamate-glutamine cycle on two types of neuronal activity patterns in the thalamus: sleep-related spindles and epileptiform oscillations. In recording conditions believed to induce glutamine scarcity, epileptiform oscillations showed a progressive reduction in duration that was partially reversible by the application of exogenous glutamine (300 muM). Blocking uptake of glutamine into neurons with alpha-(methylamino) isobutyric acid (5 mM) caused a similar reduction in oscillation duration, as did blocking neuronal GABA synthesis with 3-mercaptoproprionic acid (10 muM). However, comparable manipulations did not affect sleep spindles. Together, these results support a crucial role for the glutamate-glutamine cycle in providing the neurotransmitters necessary for the generation of epileptiform activity and suggest potential therapeutic approaches that selectively reduce seizure activity but maintain normal neuronal activity.

Cracklin' Fish Brains.

Whole-Brain Neuronal Activity Displays Crackling Noise Dynamics Ponce-Alvarez A, Jouary A, Privat M, Deco G, Sumbre G. Neuron. 2018;100(6):1446-1459.e6. Previous studies suggest that the brain operates at a critical point in which phases of order and disorder coexist, producing emergent patterned dynamics at all scales and optimizing several brain functions. Here, we combined light-sheet microscopy with GCaMP zebrafish larvae to study whole-brain dynamics in vivo at near single-cell resolution. We show that spontaneous activity propagates in the brain's 3-dimensional space, generating scale-invariant neuronal avalanches with time courses and recurrence times that exhibit statistical self-similarity at different magnitude, temporal, and frequency scales. This suggests that the nervous system operates close to a nonequilibrium phase transition, where a large repertoire of spatial, temporal, and interactive modes can be supported. Finally, we show that gap junctions contribute to the maintenance of criticality and that, during interactions with the environment (sensory inputs and self-generated behaviors), the system is transiently displaced to a more ordered regime, conceivably to limit the potential sensory representations and motor outcomes.

Out of thin air: Hyperventilation-triggered seizures.

Voluntary hyperventilation triggers seizures in the vast majority of people with absence epilepsy. The mechanisms that underlie this phenomenon remain unknown. Herein, we review observations - many made long ago - that provide insight into the relationship between breathing and absence seizures.