Jonathan E. Kurz

A significant increase in both basal and maximal calcineurin activity in the rat pilocarpine model of status epilepticus.

This study focused on the effects of status epilepticus on the activity of calcineurin, a neuronally enriched, calcium‐dependent phosphatase. Calcineurin is an important modulator of many neuronal processes, including learning and memory, induction of apoptosis, receptor function and neuronal excitability. Therefore, a status epilepticus‐induced alteration of the activity of this important phosphatase would have significant physiological implications. Status epilepticus was induced by pilocarpine injection and allowed to continue for 60 min. Brain region homogenates were then assayed for calcineurin activity by dephosphorylation of p‐nitrophenol phosphate. A significant status epilepticus‐dependent increase in both basal and Mn2+‐dependent calcineurin activity was observed in homogenates isolated from the cortex and hippocampus, but not the cerebellum. This increase was resistant to 150 nm okadaic acid, but sensitive to 50 µm okadaic acid. The increase in basal activity was also resistant to 100 µm sodium orthovanadate. Both maximal dephosphorylation rate and substrate affinity were increased following status epilepticus. However, the increase in calcineurin activity was not found to be due to an increase in calcineurin enzyme levels. Finally, increase in calcineurin activity was found to be NMDA‐receptor activation dependent. The data demonstrate that status epilepticus resulted in a significant increase in both basal and maximal calcineurin activity.

A cellular mechanism for dendritic spine loss in the pilocarpine model of status epilepticus

Purpose:  Previous studies have documented a synaptic translocation of calcineurin (CaN) and increased CaN activity following status epilepticus (SE); however, the cellular effect of these changes in CaN in the pathology of SE remains to be elucidated. This study examined a CaN‐dependent modification of the dendritic cytoskeleton. CaN has been shown to induce dephosphorylation of cofilin, an actin depolymerization factor. The ensuing actin depolymerization can lead to a number of physiological changes that are of interest in SE.

Mechanisms of Dendritic Spine Remodeling in a Rat Model of Traumatic Brain Injury

Traumatic brain injury (TBI), a leading cause of death and disability in the United States, causes potentially preventable damage in part through the dysregulation of neural calcium levels. Calcium dysregulation could affect the activity of the calcium-sensitive phosphatase calcineurin (CaN), with serious implications for neural function. The present study used both an in vitro enzymatic assay and Western blot analyses to characterize the effects of lateral fluid percussion injury on CaN activity and CaN-dependent signaling in the rat forebrain. TBI resulted in an acute alteration of CaN phosphatase activity and long-lasting alterations of its downstream effector, cofilin, an actin-depolymerizing protein. These changes occurred bilaterally in the neocortex and hippocampus, appeared to persist for hours after injury, and coincided with synapse degeneration, as suggested by a loss of the excitatory post-synaptic protein PSD-95. Interestingly, the effect of TBI on cofilin in some brain regions was blocked by a single bolus of the CaN inhibitor FK506, given 1 h post-TBI. Overall, these findings suggest a loss of synapse stability in both hemispheres of the laterally-injured brain, and offer evidence for region-specific, CaN-dependent mechanisms.

Treatment of Mitochondrial Disorders

Opinion statementWhile numerous treatments for mitochondrial disorders have been suggested, relatively few have undergone controlled clinical trials. Treatment of these disorders is challenging, as only symptomatic therapy is available. In this review we will focus on newer drugs and treatment trials in mitochondrial diseases, with a special focus on medications to avoid in treating epilepsy and ICU patient with mitochondrial disease, which has not been included in such a review. Readers are also referred to the opinion statement in A Modern Approach to the Treatment of Mitochondrial Disease published in Current Treatment Options in Neurology 2009. Many of the supplements used for treatment were reviewed in the previous abstract, and dosing guidelines were provided. The focus of this review is on items not previously covered in depth, and our discussion includes more recently studied compounds as well as any relevant updates on older compounds . We review a variety of vitamins and xenobiotics, including dichloroacetate (DCA), arginine, coenzyme Q10, idebenone, EPI-743, and exercise training. Treatment of epilepsy, which is a common feature in many mitochondrial phenotypes, warrants special consideration due to the added toxicity of certain medications, and we provide a discussion of these unique treatment challenges. Interesting, however, with only a few exceptions, the treatment strategies for epilepsy in mitochondrial cytopathies are the same as for epilepsy without mitochondrial dysfunction. We also discuss intensive care management, building upon similar reviews, adding new dimensions, and demonstrating the complexity of overall care of these patients.

A persistent change in subcellular distribution of calcineurin following fluid percussion injury in the rat

Calcineurin, a neuronally enriched, calcium-stimulated phosphatase, is an important modulator of many neuronal processes, including several that are physiologically related to the pathology of traumatic brain injury. The effect of moderate, central fluid percussion injury on the subcellular distribution of this important neuronal enzyme was examined. Animals were sacrificed at several time points post-injury and calcineurin distribution in subcellular fractions was assayed by Western blot analysis and immunohistochemistry. A persistent increase in calcineurin concentration was observed in crude synaptoplasmic membrane-containing fractions. In cortical fractions, calcineurin immunoreactivity remained persistently increased for 2 weeks post-injury. In hippocampal homogenates, calcineurin immunoreactivity remained increased for up to 4 weeks. Finally, immunohistochemical analysis of hippocampal slices revealed increased staining in the apical dendrites of CA1 neurons. The increased staining was greatest in magnitude 24 h post-injury; however, staining was still more intense than control 4 weeks post-injury. The data support the conclusion that fluid percussion injury results in redistribution of the enzyme in the rat forebrain. These changes have broad physiological implications, possibly resulting in altered cellular excitability or a greater likelihood of neuronal cell death.

Prolonged seizure activity leads to increased Protein Kinase A activation in the rat pilocarpine model of status epilepticus

Status epilepticus is a life-threatening form of seizure activity that represents a major medical emergency associated with significant morbidity and mortality. Protein Kinase A is an important regulator of synaptic strength that may play an important role in the development of status epilepticus-induced neuronal pathology. This study demonstrated an increase in PKA activity against exogenous and endogenous substrates during later stages of SE. As SE progressed, a significant increase in PKA-mediated phosphorylation of an exogenous peptide substrate was demonstrated in cortical structures. The increased activity was not due to altered expression of either regulatory or catalytic subunits of the enzyme. Through the use of phospho-specific antibodies, this study also investigated the effects of SE on the phosphorylation of the GluR1 subunit of the AMPA subtype of glutamate receptor. After the onset of continuous seizure activity, an increase in phosphorylation of the PKA site on the GluR1 subunit of the AMPA receptor was observed. These data suggest a potential mechanism by which SE may increase neuronal excitability in the cortex, potentially leading to maintenance of seizure activity or long-term neuronal pathology.

Variation in Anticonvulsant Selection and Electroencephalographic Monitoring Following Severe Traumatic Brain Injury in Children-Understanding Resource Availability in Sites Participating in a Comparative Effectiveness Study.

Objectives : Early posttraumatic seizures may contribute to worsened outcomes after traumatic brain injury. Evidence to guide the evaluation and management of early posttraumatic seizures in children is limited. We undertook a survey of current practices of continuous electroencephalographic monitoring, seizure prophylaxis, and the management of early posttraumatic seizures to provide essential information for trial design and the development of posttraumatic seizure management pathways. Design: Surveys were sent to site principal investigators at all 43 sites participating in the Approaches and Decisions in Acute Pediatric TBI trial at the time of the survey. Surveys consisted of 12 questions addressing strategies to 1) implement continuous electroencephalographic monitoring, 2) posttraumatic seizure prophylaxis, 3) treat acute posttraumatic seizures, 4) treat status epilepticus and refractory status epilepticus, and 5) monitor antiseizure drug levels. Setting: Institutions comprised a mixture of free-standing children’s hospitals and university medical centers across the United States and Europe. Subjects: Site principal investigators of the Approaches and Decisions in Acute Pediatric TBI trial. Interventions None. Measurements and Main Results: Continuous electroencephalographic monitoring was available in the PICU in the overwhelming majority of clinical sites (98%); however, the plans to operationalize such monitoring for children varied considerably. A similar majority of sites report that administration of prophylactic antiseizure medications is anticipated in children (93%); yet, a minority reports that a specified protocol for treatment of posttraumatic seizures is in place (43%). Reported medication choices varied substantially between sites, but the majority of sites reported pentobarbital for refractory status epilepticus (81%). The presence of treatment protocols for seizure prophylaxis, early posttraumatic seizures, posttraumatic status epilepticus, and refractory status epilepticus was associated with decreased reported medications (all p < 0.05). Conclusions: This study reports the current management practices for early posttraumatic seizures in select academic centers after pediatric severe traumatic brain injury. The substantial variation in continuous electroencephalographic monitoring implementation, choice of seizure prophylaxis medications, and management of early posttraumatic seizures across institutions was reported, signifying the areas of clinical uncertainty that will help provide focused design of clinical trials. Although sites with treatment protocols reported a decreased number of medications for the scenarios described, completion of the Approaches and Decisions in Acute Pediatric TBI trial will be able to determine if these protocols lead to decreased variability in medication administration in children at the clinical sites.

Early presence of sleep spindles on electroencephalography is associated with good outcome after pediatric cardiac arrest

Objectives: The role of sleep architecture as a biomarker for prognostication after resuscitation from cardiac arrest in children hospitalized in an ICU remains poorly defined. We sought to investigate the association between features of normal sleep architecture in children after cardiac arrest and a favorable neurologic outcome at 6 months. Design: Retrospective review of medical records and continuous electroencephalography monitoring. Setting: Cardiac and PICU of a tertiary children’s hospital. Patients: All patients from 6 months to 18 years old resuscitated from cardiac arrest who underwent continuous electroencephalography monitoring in the first 24 hours after in- or out-of-hospital cardiac arrest from January 2010 to June 2015. Interventions: None. Measurements and Main Results: Thirty-four patients underwent continuous electroencephalography monitoring after cardiac arrest. The median age was 6.1 years (interquartile range, 1.5–12.5 yr), 20 patients were male (59%). Most cases (n = 23, 68%) suffered from in-hospital cardiac arrest. Electroencephalography monitoring was initiated a median of 9.3 hours (5.8–14.9 hr) after return of spontaneous circulation, for a median duration of 14.3 hours (6.0–16.0 hr) within the first 24-hour period after the cardiac arrest. Five patients had normal spindles, five had abnormal spindles, and 24 patients did not have any sleep architecture. The presence of spindles was associated with a favorable neurologic outcome at 6-month postcardiac arrest (p = 0.001). Conclusions: Continuous electroencephalography monitoring can be used in children to assess spindles in the ICU. The presence of spindles on continuous electroencephalography monitoring in the first 24 hours after resuscitation from cardiac arrest is associated with a favorable neurologic outcome. Assessment of sleep architecture on continuous electroencephalography after cardiac arrest could improve outcome prediction.

Allostery between two binding sites in the ion channel subunit TRIP8b confers binding specificity to HCN channels

Tetratricopeptide repeat (TPR) domains are ubiquitous structural motifs that mediate protein–protein interactions. For example, the TPR domains in the peroxisomal import receptor PEX5 enable binding to a range of type 1 peroxisomal targeting signal motifs. A homolog of PEX5, tetratricopeptide repeat–containing Rab8b-interacting protein (TRIP8b), binds to and functions as an auxiliary subunit of hyperpolarization-activated cyclic nucleotide (HCN)–gated channels. Given the similarity between TRIP8b and PEX5, this difference in function raises the question of what mechanism accounts for their binding specificity. In this report, we found that the cyclic nucleotide–binding domain and the C terminus of the HCN channel are critical for conferring specificity to TRIP8b binding. We show that TRIP8b binds the HCN cyclic nucleotide–binding domain through a 37-residue domain and the HCN C terminus through the TPR domains. Using a combination of fluorescence polarization– and co-immunoprecipitation–based assays, we establish that binding at either site increases affinity at the other. Thus, allosteric coupling of the TRIP8b TPR domains both promotes binding to HCN channels and limits binding to type 1 peroxisomal targeting signal substrates. These results raise the possibility that other TPR domains may be similarly influenced by allosteric mechanisms as a general feature of protein–protein interactions.

Loss of HCN2 leads to delayed gastrointestinal motility and reduced energy intake in mice

Hyperpolarization-activated Cyclic Nucleotide-gated (HCN) channels are important regulators of excitability in neural, cardiac, and other pacemaking cells, which are often altered in disease. In mice, loss of HCN2 leads to cardiac dysrhythmias, persistent spike-wave discharges similar to those seen in absence epilepsy, ataxia, tremor, reduced neuropathic and inflammatory pain, antidepressant-like behavior, infertility, and severely restricted growth. While many of these phenotypes have tissue-specific mechanisms, the cause of restricted growth in HCN2 knockout animals remains unknown. Here, we characterize a novel, 3kb insertion mutation of Hcn2 in the Tremor and Reduced Lifespan 2 (TRLS/2J) mouse that leads to complete loss of HCN2 protein, and we show that this mutation causes many phenotypes similar to other mice lacking HCN2 expression. We then demonstrate that while TRLS/2J mice have low blood glucose levels and impaired growth, dysfunction in hormonal secretion from the pancreas, pituitary, and thyroid are unlikely to lead to this phenotype. Instead, we find that homozygous TRLS/2J mice have abnormal gastrointestinal function that is characterized by less food consumption and delayed gastrointestinal transit as compared to wildtype mice. In summary, a novel mutation in HCN2 likely leads to impaired GI motility, causing the severe growth restriction seen in mice with mutations that eliminate HCN2 expression.