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We consider the question whether the inferior olive (IO) is required for essential tremor (ET). Much evidence shows that the olivocerebellar system is the main system capable of generating the widespread synchronous oscillatory Purkinje cell (PC) complex spike (CS) activity across the cerebellar cortex that would be capable of generating the type of bursting cerebellar output from the deep cerebellar nuclei (DCN) that could underlie tremor. Normally, synchronous CS activity primarily reflects the effective electrical coupling of IO neurons by gap junctions, and traditionally, ET research has focused on the hypothesis of increased coupling of IO neurons as the cause of hypersynchronous CS activity underlying tremor. However, recent pathology studies of brains from humans with ET and evidence from mutant mice, particularly the hotfoot17 mouse, that largely replicate the pathology of ET, suggest that the abnormal innervation of multiple Purkinje cells (PCs) by climbing fibers (Cfs) is related to tremor. In addition, ET brains show partial PC loss and axon terminal sprouting by surviving PCs. This may provide another mechanism for tremor. It is proposed that in ET, these three mechanisms may promote tremor. They all involve hypersynchronous DCN activity and an intact IO, but the level at which excessive synchronization occurs may be at the IO level (from abnormal afferent activity to this nucleus), the PC level (via aberrant Cfs), or the DCN level (via terminal PC collateral innervation).

Background Available essential tremor (ET) therapies have limitations. Objectives The objective of this study was to evaluate CX-8998, a selective T-type calcium channel modulator, in essential tremor. Methods Patients 18-75 years old with moderate to severe essential tremor were randomized 1:1 to receive CX-8998 (titrated to 10 mg twice daily) or placebo. The primary end point was change from baseline to day 28 in The Essential Tremor Rating Assessment Scale performance subscale scored by independent blinded video raters. Secondary outcomes included in-person blinded investigator rating of The Essential Tremor Rating Assessment Scale performance subscale, The Essential Tremor Rating Assessment Scale activities of daily living subscale, and Kinesia ONE accelerometry. Results The video-rated The Essential Tremor Rating Assessment Scale performance subscale was not different for CX-8998 (n = 39) versus placebo (n = 44; P = 0.696). CX-8998 improved investigator-rated The Essential Tremor Rating Assessment Scale performance subscale (P = 0.017) and The Essential Tremor Rating Assessment Scale activities of daily living (P = 0.049) but not Kinesia ONE (P = 0.421). Adverse events with CX-8998 included dizziness (21%), headache (8%), euphoric mood (6%), and insomnia (6%). Conclusions The primary efficacy end point was not met; however, CX-8998 improved some assessments of essential tremor, supporting further clinical investigation. © 2021 The Authors. Movement Disorders published by Wiley Periodicals LLC on behalf of International Parkinson and Movement Disorder Society. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

We review advances in understanding Purkinje cell (PC) complex spike (CS) physiology that suggest increased CS synchrony underlies syndromic essential tremor (ET). We searched PubMed for papers describing factors that affect CS synchrony or cerebellar circuits potentially related to tremor. Inferior olivary (IO) neurons are electrically coupled, with the degree of coupling controlled by excitatory and GABAergic inputs. Clusters of coupled IO neurons synchronize CSs within parasagittal bands via climbing fibers (Cfs). When motor cortex is stimulated in rats at varying frequencies, whisker movement occurs at ~10 Hz, correlated with synchronous CSs, indicating that the IO/CS oscillatory rhythm gates movement frequency. Intra-IO injection of the GABAA receptor antagonist picrotoxin increases CS synchrony, increases whisker movement amplitude, and induces tremor. Harmaline and 5-HT2a receptor activation also increase IO coupling and CS synchrony and induce tremor. The hotfoot17 mouse displays features found in ET brains, including cerebellar GluRδ2 deficiency and abnormal PC Cf innervation, with IO- and PC-dependent cerebellar oscillations and tremor likely due to enhanced CS synchrony. Heightened coupling within the IO oscillator leads, through its dynamic control of CS synchrony, to increased movement amplitude and, when sufficiently intense, action tremor. Increased CS synchrony secondary to aberrant Cf innervation of multiple PCs likely also underlies hotfoot17 tremor. Deep cerebellar nucleus (DCN) hypersynchrony may occur secondary to increased CS synchrony but might also occur from PC axonal terminal sprouting during partial PC loss. Through these combined mechanisms, increased CS/DCN synchrony may plausibly underlie syndromic ET.

Background Perampanel is a noncompetitive antagonist of alpha-amino-3-hydroxy-5-methylisoxazole propionic acid glutamate receptors suggested to modulate tremor. Objectives To assess the efficacy and tolerability of perampanel for essential tremor. Methods This was a double-blind, placebo-controlled, randomized, cross-over trial involving 26 patients titrated to 8 mg/day or a lower maximally tolerated dose as monotherapy or adjunct to antitremor medication. Tremor was assessed at the beginning and end of each 14-week treatment arm. The primary endpoint was change in the videotaped performance subscale of The Essential Tremor Rating Assessment Scale, scored by a blinded rater. Secondary endpoints included change in The Essential Tremor Rating Assessment Scale Activity of Daily Living and Quality of Life in Essential Tremor and Subject Global Impression of Change subscales. Results Data are available for 15 and 11 participants who completed placebo and perampanel arms, respectively. Perampanel was superior to placebo on the primary endpoint (P = 0.028), Activity of Daily Living (P = 0.009), and Subject Global Impression of Change (P = 0.016), but not Quality of Life (p = 0.48). Video scores were rated >50% improved in 3/11 on perampanel and 0/15 on placebo. Adverse events were more likely on perampanel (especially at >4 mg/day) than on placebo, leading to withdrawal (36% vs. 10%) and dose reduction (41% vs. 15%). Adverse events more common with perampanel included imbalance/falls (50% vs. 10%), dizziness (36% vs. 10%), and irritability (27% vs. 5%). Conclusions These findings suggest that perampanel exerts efficacy for some persons with essential tremor, but this population appears prone to adverse events.

Tremor is the most common movement disorder; however, we are just beginning to understand the brain circuitry that generates tremor. Various neuroimaging, neuropathological, and physiological studies in human tremor disorders have been performed to further our knowledge of tremor. But, the causal relationship between these observations and tremor is usually difficult to establish and detailed mechanisms are not sufficiently studied. To overcome these obstacles, animal models can provide an important means to look into human tremor disorders. In this manuscript, we will discuss the use of different species of animals (mice, rats, fruit flies, pigs, and monkeys) to model human tremor disorders. Several ways to manipulate the brain circuitry and physiology in these animal models (pharmacology, genetics, and lesioning) will also be discussed. Finally, we will discuss how these animal models can help us to gain knowledge of the pathophysiology of human tremor disorders, which could serve as a platform towards developing novel therapies for tremor.

Objective: To report long-term efficacy and safety results of the SANTE trial investigating deep brain stimulation of the anterior nucleus of the thalamus (ANT) for treatment of localization-related epilepsy. Methods: This long-term follow-up is a continuation of a previously reported trial of 5- vs 0-V ANT stimulation. Long-term follow-up began 13 months after device implantation with stimulation parameters adjusted at the investigators9 discretion. Seizure frequency was determined using daily seizure diaries. Results: The median percent seizure reduction from baseline at 1 year was 41%, and 69% at 5 years. The responder rate (≥50% reduction in seizure frequency) at 1 year was 43%, and 68% at 5 years. In the 5 years of follow-up, 16% of subjects were seizure-free for at least 6 months. There were no reported unanticipated adverse device effects or symptomatic intracranial hemorrhages. The Liverpool Seizure Severity Scale and 31-item Quality of Life in Epilepsy measure showed statistically significant improvement over baseline by 1 year and at 5 years ( p Conclusion: Long-term follow-up of ANT deep brain stimulation showed sustained efficacy and safety in a treatment-resistant population. Classification of evidence: This long-term follow-up provides Class IV evidence that for patients with drug-resistant partial epilepsy, anterior thalamic stimulation is associated with a 69% reduction in seizure frequency and a 34% serious device-related adverse event rate at 5 years.

Recent work exploring the use of high-molecular weight alcohols to treat essential tremor (ET) has identified octanoic acid as a potential novel tremor-suppressing agent. We used an established harmaline-based mouse model of ET to compare tremor suppression by 1-octanol and octanoic acid. The dose-related effect on digitized motion power within the tremor bandwidth as a fraction of overall motion power was analyzed. Both 1-octanol and octanoic acid provided significant reductions in harmaline tremor. An 8-carbon alkyl alcohol and carboxylic acid each suppress tremor in a pre-clinical mouse model of ET. Further studies are warranted to determine the safety and efficacy of such agents in humans with ET.

In this review, we hope to stimulate interest in animal models as opportunities to understand tremor mechanisms within the cerebellar system. We begin by considering the harmaline model of essential tremor (ET), which has ET-like anatomy and pharmacology. Harmaline induces the inferior olive (IO) to burst fire rhythmically, recruiting rhythmic activity in Purkinje cells (PCs) and deep cerebellar nuclei (DCN). This model has fostered the IO hypothesis of ET, which postulates that factors that promote excess IO, and hence PC complex spike synchrony, also promote tremor. In contrast, the PC hypothesis postulates that partial PC cell loss underlies tremor of ET. We describe models in which chronic partial PC loss is associated with tremor, such as the Weaver mouse, and others with PC loss that do not show tremor, such as the Purkinje cell degeneration mouse. We postulate that partial PC loss with tremor is associated with terminal axonal sprouting. We then discuss tremor that occurs with large lesions of the cerebellum in primates. This tremor has variable frequency and is an ataxic tremor not related to ET. Another tremor type that is not likely related to ET is tremor in mice with mutations that cause prolonged synaptic GABA action. This tremor is probably due to mistiming within cerebellar circuitry. In the final section, we catalog tremor models involving neurotransmitter and ion channel perturbations. Some appear to be related to the IO hypothesis of ET, while in others tremor may be ataxic or due to mistiming. In summary, we offer a tentative framework for classifying animal action tremor, such that various models may be considered potentially relevant to ET, subscribing to IO or PC hypotheses, or not likely relevant, as with mistiming or ataxic tremor. Considerable further research is needed to elucidate the mechanisms of tremor in animal models.

Recently, a variant of insulin-like growth factor-1, mechano-growth factor (MGF), has been discovered whose 24-amino-acid carboxy end is protective in models of stroke, nerve injury, and amyotrophic lateral sclerosis, suggesting broad-spectrum neuroprotective properties. Moreover, we recently demonstrated in vitro and in vivo that a modified protease-resistant 24-amino-acid MGF derivative (MGF24) protects dopaminergic neurons from oxidative stress-induced apoptosis via induction of the stress response protein heme oxygenase-1. However, the underlying mechanism by which MGF24 up-regulates heme oxygenase-1 expression is unknown. In this study, we demonstrate that MGF24-induced heme oxygenase-1 up-regulation is dependent on activation of protein kinase Cϵ and NF-E2-related factor-2 (Nrf2). MGF24 induces nuclear translocation of Nrf2, and siRNA knockdown of Nrf2 or of heme oxygenase-1 prevents MGF24-induced heme oxygenase-1 up-regulation and neuroprotection of SH-SY5Y cells against 6-hydroxydopamine-induced cell death. Pharmacological inhibition of ERK, p38 MAPK, PI3K/Akt, or PKC signaling revealed that only PKC inhibition by GF109203X prevents MGF24's ability to protect against 6-hydroxydopamine-induced cell death. GF109203X also prevented MGF24-induced Nrf2 nuclear translocation and heme oxygenase-1 up-regulation. siRNA knockdown of protein kinase Cϵ blocks MGF24-induced Nfr2 nuclear translocation, heme oxygenase-1 expression, and neuroprotection. Taken together, these results demonstrate that PKC activity is needed for MGF24's activation of Nrf2, which in turn increases heme oxygenase-1 expression, a critical event in mediating MGF24's neuroprotection against 6-hydroxydopamine-induced apoptosis.

Essential tremor is a common disorder that lacks molecular targets for therapeutic development. T-type calcium channel activation has been postulated to underlie rhythmicity in the olivo-cerebellar system that is implicated in essential tremor. We therefore tested whether compounds that antagonize T-type calcium channel currents suppress tremor in two mouse models that possess an essential tremor-like pharmacological response profile. Tremor was measured using digitized spectral motion power analysis with harmaline-induced tremor and in the GABA(A) receptor α1 subunit-null model. Mice were given ethosuximide, zonisamide, the neuroactive steroid (3β,5α,17β)-17-hydroxyestrane-3-carbonitrile (ECN), the 3,4-dihydroquinazoline derivative KYS05064, the mibefradil derivative NNC 55-0396, or vehicle. In non-sedating doses, each compound reduced harmaline-induced tremor by at least 50% (range of maximal suppression: 53-81%), and in the GABA(A) α1-null model by at least 70% (range 70-93%). Because the T-type calcium channel Cav3.1 is the dominant subtype expressed in the inferior olive, we assessed the tremor response of Cav3.1-deficient mice to harmaline, and found that null and heterozygote mice exhibit as much tremor as wild-type mice. In addition, ECN and NNC 55-0396 suppressed harmaline tremor as well in Cav3.1-null mice as in wild-type mice. The finding that five T-type calcium antagonists suppress tremor in two animal tremor models suggests that T-type calcium channels may be an appropriate target for essential tremor therapy development. It is uncertain whether medications developed to block only the Cav3.1 subtype would exhibit efficacy.

Summary Purpose: We report a multicenter, double-blind, randomized trial of bilateral stimulation of the anterior nuclei of the thalamus for localization-related epilepsy. Methods: Participants were adults with medically refractory partial seizures, including secondarily generalized seizures. Half received stimulation and half no stimulation during a 3-month blinded phase; then all received unblinded stimulation. Results: One hundred ten participants were randomized. Baseline monthly median seizure frequency was 19.5. In the last month of the blinded phase the stimulated group had a 29% greater reduction in seizures compared with the control group, as estimated by a generalized estimating equations (GEE) model (p = 0.002). Unadjusted median declines at the end of the blinded phase were 14.5% in the control group and 40.4% in the stimulated group. Complex partial and “most severe” seizures were significantly reduced by stimulation. By 2 years, there was a 56% median percent reduction in seizure frequency; 54% of patients had a seizure reduction of at least 50%, and 14 patients were seizure-free for at least 6 months. Five deaths occurred and none were from implantation or stimulation. No participant had symptomatic hemorrhage or brain infection. Two participants had acute, transient stimulation-associated seizures. Cognition and mood showed no group differences, but participants in the stimulated group were more likely to report depression or memory problems as adverse events. Discussion: Bilateral stimulation of the anterior nuclei of the thalamus reduces seizures. Benefit persisted for 2 years of study. Complication rates were modest. Deep brain stimulation of the anterior thalamus is useful for some people with medically refractory partial and secondarily generalized seizures.

To assess potential efficacy of mechano growth factor (MGF) for chronic neurodegenerative disorders, we studied whether MGF protects dopamine (DA) neurons subjected to neurotoxic stress. We show that a short 24-amino acid C-terminal peptide of MGF (MGF24) upregulates heme oxygenase-1 (HO-1) expression and protects SH-SY5Y cells against apoptosis and cell loss induced by three DA cell-specific neurotoxins: 6-hydroxydopamine (6-OHDA), 1-methyl-4-phenylpyridinium (MPP(+)), and rotenone. MGF24 maintains the mitochondrial membrane potential and blocks the release of mitochondrial apoptotic-inducing factor into the cytoplasm induced by 6-OHDA, MPP(+), and rotenone. Chemical inhibition of HO-1 with zinc protoporphyrin-IX prevents neuroprotection by MGF24 against the three neurotoxins. MGF24 does not activate Akt signaling nor does Akt inhibition block MGF24 protection of SH-SY5Y cells. In 6-OHDA-lesioned rats, central or peripheral MGF24 administration protects against the development of contralateral forelimb under-utilization, reduces ipsilateral nigral DA cell body loss, and attenuates tyrosine hydroxylase fiber loss in the ipsilateral striatum, independent of IGF-1 receptor activation. Peripheral MGF24 administration upregulates HO-1 expression in striatal and midbrain tissue. This report is the first to demonstrate that a small peptide, MGF24, upregulates HO-1, an important cell defense mediator, and protects DA cells, suggesting new strategies for neuroprotection in Parkinson's disease.

In this evaluator-blinded open-treatment trial, subjects with moderate/severe upper limb essential tremor were titrated to 300 mg/day zonisamide, or adjusted to a lesser dose if symptoms warranted, as monotherapy or as adjunct to stable antitremor medication, followed by a 12-week extension phase. The primary efficacy outcome variables were blinded rater videotaped/drawing tremor score changes at the Treatment and Extension visits compared to Baseline, based on Fahn-Tolosa-Marin and Postural Tremor Scales. Subjects also rated Functional Disabilities. Primary outcomes showed reduced tremor scores at the Treatment (P < 0.00001, n = 25) and Extension (n = 16) visits, at mean doses of 252 and 225 mg/day, respectively. Subject ratings indicated 200 mg/day was superior to 100 mg/day, whereas 300 mg/day produced no additional benefit, but instead was associated with more adverse symptoms, most commonly somnolence, poor energy, imbalance, and altered taste. Future double-blind placebo-controlled trials are warranted.

Essential tremor affects the hands during actions and can be disabling. Although common, no medications for it have emerged from basic research. Animal tremor models offer an approach to identify targets for drug development. In one model, the drug harmaline induces whole-body tremor in a rodent that lasts at least 1.5 h. In another model, the α1 subunit of the γ-aminobutyric acid type A (GABAA) receptor is knocked out, leading to tremor that is best seen when the mouse is picked up by the tail. Each model has limitations and does not perfectly predict drug efficacy for essential tremor. Nonetheless, they offer a useful starting point to test hypotheses on what may suppress tremor. In this chapter, we describe the models and review progress to date. The models suggest that drugs that block neuronal gap junctions or T-type calcium channels, or activate certain GABA receptors, might be useful for tremor.

Summary: Purpose:γ-Aminobutyric acid receptor (GABAAr) subunit β3–deficient mice model Angelman syndrome by displaying impaired learning, abnormal EEG with interictal spikes and slowing, myoclonus, and convulsions. The β3-subunit deficiency causes a failure of intrathalamic reticular nucleus inhibition, leading to abnormally synchronized thalamocortical oscillations. We postulated that this pathophysiology underlies the abnormal cortical EEG and triggers interictal spikes and seizures, but extrathalamic regions also contribute to interictal spikes and seizures, so that the EEG slowing should reveal an absence-like response profile, whereas spikes and seizures have dual responsiveness to absence and partial-seizure drugs. Methods: Recording electrodes were implanted over the parietal cortices of wild-type, heterozygotes, and homozygous null mice. In each experiment, EEG was recorded for 45 min, either drug or vehicle administered, and EEG recorded for another 3 h. Each EEG was scored for slow-wave activity, interictal spikes, and seizures by a reader blinded to treatments. Results: Interictal spiking and percentage of time in EEG slowing in heterozygotes were increased by the proabsence drug baclofen (GABAB-receptor agonist), whereas CGP 35348 (GABAB-receptor antagonist) had the opposite effect. The antiabsence drug ethosuximide markedly suppressed EEG slowing and interictal spiking in heterozygote and null mice. Broad-spectrum clonazepam and valproate were more effective on interictal spiking than on EEG slowing, and fosphenytoin suppressed only interictal spiking. Conclusions: The results suggest that this model of Angelman syndrome, although not expressing typical absence seizures, is characterized by hypersynchronous thalamocortical oscillations that possess absence-like pharmacologic responsiveness and promote EEG slowing, interictal spikes, and convulsive seizures.

The purpose of this pilot single-site study was to assess efficacy and safety of levetiracetam for essential tremor, using a placebo-controlled, double-blind, randomized crossover design with an interim analysis planned after completion of the first 10 to 15 subjects. The study was designed to detect a mean 30% reduction in composite tremor score, comparable to that of primidone or propranolol, which can be demonstrated with 30 or fewer subjects. Each treatment arm included baseline tremor assessments, a 4-week medication titration, 2 weeks of stable dose, and treatment tremor assessments. Levetiracetam was titrated to 3,000 mg/day or to a lower maximal tolerated dose. The median age was 72 years, with 28 years median tremor duration. There was no statistically significant difference in response between placebo and levetiracetam on any tremor rating scale or accelerometry measure. The 95% confidence interval for the true mean difference between placebo and levetiracetam treatments was +18.5 to -22.5%, which excludes the minimum 30% drop required to consider levetiracetam clinically effective to a degree comparable to primidone or propranolol. Whether levetiracetam has lesser-degree antitremor efficacy was not addressed in this pilot study.

Objective: To assess the safety and efficacy of vagus nerve stimulation (VNS) for essential tremor (ET).Methods: This was a pilot open-treatment trial at three centers, with masked videotape tremor assessments. Inclusion required a severity score of 3 or 4 on the Tremor Rating Scale (TRS) in one or both hands. At baseline, tremor was assessed with TRS and Unified Tremor Rating Assessment (UTRA), accelerometry, and a videotape protocol. The VNS device was implanted with leads placed around the left cervical vagus nerve. Stimulation was adjusted over 4 weeks before the repeat tremor assessments. Two raters masked to the study visit scored the videotapes.Results: Nine subjects participated, with a mean age of 65 years and a mean age at onset of tremor of 24. Investigators rated hand tremor as mildly improved (TRS 2.3 ± 0.7 during VNS vs 3.0 ± 0.4 during baseline, p = 0.06). Accelerometry-measured total power improved 50.2 ± 31.8% (p < 0.01). Videotape tremor scores were highly correlated between the masked raters and revealed no changes in tremor scores with treatment. VNS was well tolerated, with the most common adverse events being stimulation related.Conclusions: VNS was judged by investigators to mildly improve upper extremity tremor. This finding was not confirmed in videotape scoring by masked raters. VNS is not likely to have a clinically meaningful effect on ET.

Summary: Purpose: Early animal studies of the therapeutic mechanisms of vagus nerve stimulation (VNS) suggested that seizure suppression requires maximal activation of small, unmyelinated vagal C fibers. However, effective therapeutic stimulation parameters appear to be subthreshold for these fibers in humans, and there are no clinical reports of the autonomic side effects that would be expected if these fibers were maximally activated. We report here that selective destruction of C fibers with capsaicin does not affect VNS-induced seizure suppression in rats. Methods: Rats were pretreated with capsaicin or vehicle in three injections over a 2-day period. A cuff electrode was later implanted on the left cervical vagus nerve. Two days after surgery, VNS was given to half of the capsaicin- and vehicle-treated rats. The remaining rats were connected to the stimulator but did not receive VNS. Thirty seconds after VNS onset, seizures were induced by pentylenetetrazol (PTZ), and seizure severity was measured. Two days later, the reciprocal VNS treatment was given, and PTZ-induced seizure severity was again measured. Results: VNS effectively reduced seizure severity in both capsaicin- and vehicle-treated rats as compared with their non-VNS baselines. Conclusions: These results indicate that activation of vagal C fibers is not necessary for VNS-induced seizure suppression.

We studied whether vagus nerve stimulation could suppress tremor in the harmaline tremor model in the rat. Animals were chronically implanted with helical leads around the left vagus nerve and a disk-shaped electrode positioned subcutaneously in the dorsal neck. Harmaline-induced tremor was recorded on a physiograph while each animal received a sequence of five 20-minute trials. Each trial consisted of five minutes of pre-stimulation baseline, five minutes of vagus nerve stimulation, and ten minutes of post-stimulation. Vagus nerve stimulation significantly suppressed harmaline-induced tremor. The suppressive effect was present within the first minute of stimulation and was reproducible across the five trials of the study. The results of this study suggest that the central generator or expression of tremor in the harmaline animal model can be suppressed by vagus nerve stimulation.

Summary: Purpose: To determine the long-term efficacy of vagus nerve stimulation (VNS) for refractory seizures. VNS is a new treatment for refractory epilepsy. Two short-term double-blind trials have demonstrated its safety and efficacy, and one long-term study in 114 patients has demonstrated a cumulative improvement in efficacy at 1 year. We report the largest prospective long-term study of VNS to date. Methods: Patients with six or more complex partial or generalized tonic-clonic seizures enrolled in the pivotal EOS study were prospectively evaluated for 12 months. The primary outcome variable was the percentage reduction in total seizure frequency at 3 and 12 months after completion of the acute EO5 trial, compared with the preimplantation baseline. Subjects originally randomized to low stimulation (active-control group) were crossed over to therapeutic stimulation settings for the first time. Subjects initially randomized to high settings were maintained on high settings throughout the 12-month study. Results: The median reduction at 12 months after completion of the initial double-blind study was 45%. At 12 months, 35% of 195 subjects had a >50% reduction in seizures, and 20% of 195 had a >75% reduction in seizures. Conclusions: The efficacy of VNS improves during 12 months, and many subjects sustain >75% reductions in seizures.

The present study investigated the seizure-suppressing effects of systemic epinephrine. Rats were injected with epinephrine, and seizures induced with pentylenetetrazol. Seizure severities were significantly reduced 15 min after 1 mg/kg of epinephrine. Severing the subdiaphragmatic vagus nerves abolished this effect, demonstrating that epinephrine-induced seizure suppression is mediated by subdiaphragmatic vagal afferents. The development of novel anti-epileptic drugs that exploit this peripheral pathway may yield new seizure treatments.

Background and Methods Although generalized convulsive status epilepticus is a life-threatening emergency, the best initial drug treatment is uncertain. We conducted a five-year randomized, double-blind, multicenter trial of four intravenous regimens: diazepam (0.15 mg per kilogram of body weight) followed by phenytoin (18 mg per kilogram), lorazepam (0.1 mg per kilogram), phenobarbital (15 mg per kilogram), and phenytoin (18 mg per kilogram). Patients were classified as having either overt generalized status epilepticus (defined as easily visible generalized convulsions) or subtle status epilepticus (indicated by coma and ictal discharges on the electroencephalogram, with or without subtle convulsive movements such as rhythmic muscle twitches or tonic eye deviation). Treatment was considered successful when all motor and electroencephalographic seizure activity ceased within 20 minutes after the beginning of the drug infusion and there was no return of seizure activity during the next 40 minutes. Analyse...

Objective: The purpose of this multicenter, add-on, double-blind, randomized, active-control study was to compare the efficacy and safety of presumably therapeutic (high) vagus nerve stimulation with less (low) stimulation. Background: Chronic intermittent left vagus nerve stimulation has been shown in animal models and in preliminary clinical trials to suppress the occurrence of seizures. Methods: Patients had at least six partial-onset seizures over 30 days involving complex partial or secondarily generalized seizures. Concurrent antiepileptic drugs were unaltered. After a 3-month baseline, patients were surgically implanted with stimulating leads coiled around the left vagus nerve and connected to an infraclavicular subcutaneous programmable pacemaker-like generator. After randomization, device initiation, and a 2-week ramp-up period, patients were assessed for seizure counts and safety over 3 months. The primary efficacy variable was the percentage change in total seizure frequency compared with baseline. Results: Patients receiving high stimulation (94 patients, ages 13 to 54 years) had an average 28% reduction in total seizure frequency compared with a 15% reduction in the low stimulation group (102 patients, ages 15 to 60 year; p = 0.04). The high-stimulation group also had greater improvements on global evaluation scores, as rated by a blinded interviewer and the patient. High stimulation was associated with more voice alteration and dyspnea. No changes in physiologic indicators of gastric, cardiac, or pulmonary functions occurred. Conclusions: Vagus nerve stimulation is an effective and safe adjunctive treatment for patients with refractory partial-onset seizures. It represents the advent of a new, nonpharmacologic treatment for epilepsy.

Summary: Purpose: We studied the efficacy and safety of bilateral subthalamic deep brain stimulation (DBS) for refractory partial-onset epilepsy in two cases. Methods: This was an open treatment pilot study for subjects who had failed numerous medications and had seizure injuries. Seizure counts and adverse events were collected during a 3-4 month baseline, and for 26-32 months after DBS surgery, with AEDs held constant. Results: Case 1, age 45, with bitemporal seizures, had about half the seizure frequency but still fell with injuries. Case 2, age 46, with left frontal encephalomalacia, had a frequency reduction of about one-third, but a more meaningful reduction of seizure severity and injuries. Conclusions: Subthalamic DBS partly reduced partial-onset seizures, but the quality of life was more affected by seizure-related injuries.

We have previously described a model of limbic status epilepticus in which chronic prolonged seizure states of immobile, exploratory, minor convulsive or clonic convulsive behavior are induced by intracerebral electrical stimulation; these states appear to belong to the same behavioral progression as kindled seizures. We postulated that the underlying seizure substrates, as mapped by the 14C-2-deoxyglucose method, should reflect a corresponding anatomic progression of discharge spread. Status epilepticus was induced in rat by pulsed-train current delivered for up to 90 min to one of several subcortical areas. Autoradiographs revealed that most of the observed patterns of seizure-induced metabolic activation comprised a hierarchical sequence, such that progressively more extensive patterns subsumed anatomic territories activated in less extensive patterns, thus allowing inferences as to the progression of discharge spread. In this sequence, the basolateral amygdala ipsilateral to the induction electrode was among the first structures to be activated. In successively larger activation patterns a small unilateral network related to basolateral amygdala was involved; this evolved through a transitional state to a unilateral extensive limbic pattern; which in turn was succeeded by bilateral extensive limbic activation. This hierarchical sequence culminated in a neocortical activation pattern, in which most of the forebrain was involved in intense seizure-induced activation. Seizure behaviors increased in severity in correspondence with the underlying seizure-activated anatomic substrate. In contrast, patterns of seizure activation were observed which did not fit within the early stages of the above sequence, although analysis indicates that the later stages of spread may be shared. The study of these patterns and those reported in the literature indicates that although limbic seizure networks may be anatomically distinct at their origination, further expansion is characterized by overlap; upon assumption of extensive patterns of activation the number of nuclei participating is so vast that the identity of the limbic originator is lost and common convulsive manifestations occur.

Much remains to be learned about mechanisms underlying entry into, and temporal progression of, status epilepticus (SE). This report describes a non-pharmacologic model of generalized convulsive SE in rat. Pulsed trains of suprathreshold electric current, were administered bilaterally to either of four rostral forebrain sites: orbital cortex, medial precentral cortex, deep prepiriform cortex, or rostral caudate-putamen (n = 8 per site). This induction method resulted in 30/32 animals attaining limb-clonic convulsive SE within a mean of 30-35 min for each forebrain site, with no differences between sites. Subsequent SE proceeded without further interventions, permitting observation of the natural course of progression. A stereotyped behavioral/electrographic sequence occurred, characterized by devolution. Behaviorally, animals progressed from predominantly limb clonus to head clonus, then to subtle twitching, and finally to electrical SE before cessation of spikes. The corresponding electrographic progression was from fast and slow spiking to periodic epileptiform discharges (PEDs). In 20 animals surviving to 48 h, pathologic damage affected mainly limbic sites; damage was related to total convulsive time rather than to clonic activity. High-dose phenobarbital but not phenytoin suppressed SE when given during orbital cortex-induced limb-clonic SE. These findings are compatible with human observations and indicate that this model will enable investigations of generalized SE mechanisms and evaluation of new therapeutic agents for refractory SE.

We studied the potential efficacy and tolerance of memantine for essential tremor in an open-treatment trial.Participants with upper-limb tremor were titrated to no more than 40 mg/d memantine, as monotherapy or as adjunct to stable antitremor medication, followed by a 12-week extension phase. Tremor was assessed in study 1 with accelerometry and in study 2 by blinded ratings of videotaped Washington Heights Inwood Genetic Essential Tremor (WHIGET) rating scale items. Subjects also rated their tremor treatment response and tremor-associated impairment on the Functional Disabilities scale.In study 1, average accelerometry-measured tremor at last titration visit (average dose, 30.3 mg/d) did not change from baseline, but 2 of 9 subjects, taking 40 mg/d, had greater than 70% accelerometry tremor reduction. In study 2, 13 of 16 provided evaluable data. Average blinded rater-evaluated WHIGET scores were significantly different from baseline scores among those taking 20 mg/d (-12.7%; P0.05), but not at last titration visit (-8.4%; average dose, 30.4 mg/d), 40 mg/d (-14.1%), or at end-of-extension visit (-18.2%). Raters judged WHIGET scores as greater than 30% improved in 2 subjects. Unblinded subjects rated Functional Disabilities significantly improved at 30 to 40 but not at 10 to 20 mg/d, and tremor treatment response was positive at all doses. Adverse events were more common at higher doses and included dizziness, somnolence, and poor energy.These pilot results with small samples indicate that the average effect of memantine on tremor is mild or not significant. However, in a small subset of patients, memantine may confer meaningful tremor benefit.

NNC 55-0396 [(1S,2S)-2-(2-(N-[(3-benzimidazol-2-yl)propyl]-N-methylamino)ethyl)-6-fluoro-1,2, 3,4-tetrahydro-1-isopropyl-2-naphtyl cyclopropanecarboxylate dihydrochloride], is a mibefradil derivative that retains potent in vitro T-type calcium channel antagonist efficacy. We compared the two compounds for behavioral toxicity, effects on cytochrome P450 activity, and efficacy against tremor in the γ-aminobutyric acid type A (GABAA) receptor subunit α1-null mouse, and the harmaline tremor model of essential tremor in wild-type mice. NNC 55-0396 was better tolerated than mibefradil in the horizontal wire test of sedation/motor function, with 3/6 failing at 300 and 30 mg/kg respectively. To assess for a potential interaction with harmaline, mice were given the drugs, followed by harmaline or vehicle, and tested 30 min later in the inverted wire grid test. Mibefradil exacerbated, whereas NNC 55-0396 ameliorated harmaline-induced test deficits. In mouse liver microsomes, NNC 55-0396 was a less potent inhibitor of harmaline O-demethylation than mibefradil (Ki: 0.95 and 0.29 μM respectively), and also less potent at inhibiting testosterone 6-β-hydroxylation (Ki: 0.71 and 0.12 μM respectively). In the GABAA α1-null model, NNC 55-0396 but not mibefradil, (each at 20 mg/kg), suppressed tremor while NNC 55-0396 at 12.5 mg/kg suppressed harmaline-induced tremor by half by 20–100 min, whereas mibefradil at the same dose did not significantly affect tremor. In contrast to mibefradil, NNC 55-0396 is well tolerated and suppresses tremor, and exerts less cytochrome P450 inhibition. These results suggest potential clinical utility for NNC 55-0396 or similar derivatives as a T-type calcium antagonist.

We report a multicenter, double-blind, randomized trial of bilateral stimulation of the anterior nuclei of the thalamus for localization-related epilepsy.Participants were adults with medically refractory partial seizures, including secondarily generalized seizures. Half received stimulation and half no stimulation during a 3-month blinded phase; then all received unblinded stimulation.One hundred ten participants were randomized. Baseline monthly median seizure frequency was 19.5. In the last month of the blinded phase the stimulated group had a 29% greater reduction in seizures compared with the control group, as estimated by a generalized estimating equations (GEE) model (p = 0.002). Unadjusted median declines at the end of the blinded phase were 14.5% in the control group and 40.4% in the stimulated group. Complex partial and "most severe" seizures were significantly reduced by stimulation. By 2 years, there was a 56% median percent reduction in seizure frequency; 54% of patients had a seizure reduction of at least 50%, and 14 patients were seizure-free for at least 6 months. Five deaths occurred and none were from implantation or stimulation. No participant had symptomatic hemorrhage or brain infection. Two participants had acute, transient stimulation-associated seizures. Cognition and mood showed no group differences, but participants in the stimulated group were more likely to report depression or memory problems as adverse events.Bilateral stimulation of the anterior nuclei of the thalamus reduces seizures. Benefit persisted for 2 years of study. Complication rates were modest. Deep brain stimulation of the anterior thalamus is useful for some people with medically refractory partial and secondarily generalized seizures.

Harmaline induces burst-firing in inferior olive neurons that propagates to cerebellum, brainstem, and spinal cord, causing 8–16 Hz action tremor in animals that responds to many drugs used for essential tremor (propranolol, primidone, benzodiazepines, alcohol, octanol). As a preclinical model, its predictive validity for clinical therapy awaits further evaluation.

Summary: Repeated electrical stimulation was delivered to the amygdala in a paradigm of electrogenic limbic status epilepticus induction in rats. We observed four distinct initial behavioral states associated with prolonged spiking, comprising an ordered hierarchy of severity: immobile, exploratory, minor convulsive, and clonic convulsive. The EEG and behavioral topography of the initial prolonged seizure state behaviorally and electrographically resembled the acute seizures that occurred earlier during induction. Onset of status epilepticus on limbic induction appears to represent not a new type of seizure activity, but instead the extended version of repeated brief limbic-onset seizures as seizure-terminating mechanisms gradually become ineffective. These prolonged seizure states can therefore be used to study the anatomy and mechanisms of brief limbic seizures. We also examined the temporal progression of amygdala-induced prolonged-seizure states. At one end of the severity spectrum, immobile-associated spiking was prone to terminate early, within 90 min, accompanied by normalization of behavior. At the other end of the spectrum, clonic convulsive status epilepticus slowly decreased in behavioral severity together with a change in EEG from fast to slow spiking. Exploratory status epilepticus was characterized by incessant explorationlike behavior that could last hours and was associated with slow periodic spikecomplexes on EEG. The long-term course consisted either of slow devolution, with eventual cessation of spiking, or of spontaneous late ascension to convulsive status. Prolonged-seizure states may thus be considered to fall not only within an anatomiclbehavioral hierarchy of severity, but also within a temporal physiologic progression. RESUME Les auteurs ont administre des stimulations electriques repetitives au niveau amygdalien dans un protocole d'induction d'etat de ma1 epileptique limbique chez le rat. IIs ont observe 4 etats comportementaux initiaux distincts associes avec des decharges prolongees de pointes, avec une hierarchie dans la severite: etat immobile, exploratoire, etat confulsif mineur et etat convulsif clonique. La topographie EEG et comportementale de I'etat critique prolonge initial ressemblait sur le plan comportemental et electrographique aux crises aigues qui etaient survenues plus tot pendant I'induction. L'installation de l'etat de mal epileptique apres induction limbique parait representer non un type d'activite critique mais plutot une version etendue de breves crises a debut limbique repetees, au fur et a mesure que les mecanismes de terminaison des crises deviennent inefficaces. Ces etats de crises prolongees peuvent donc etre utilises pour etudier l'anatomie et les mecanismes de crises limbiques breves. La progression temporelle des etats critiques prolonges induits au niveau de I'amygdale a egalement eteetudiee. Pour les manifestations les moins severes, les pointes associees a l'immobilite avaient tendance a se terminer rapidement, en moins de 90 minutes avec normalisation du comportement. A I'autre extremite du spectre de severite I'etat de ma1 epileptique clonique convulsif a diminue progressivement en severite sur le plan comportemental, parallelement a une modification de I'EEG passant de pointes rapides a des pointes lentes. L'etat de ma1 epileptique exploratoire etait caracterise par un comportement exploratoire incessant qui pouvait durer des heures et qui etait associe avec des complexes de pointes-ondes periodiques lents sur I'EEG. L'evolution a long terme a ete representee soit par une diminution progressive, avec cessation finale de la production des pointes, soit par la transformation spontanee, tardive, en etat de ma1 convulsif. Des etats critiques prolonges peuvent donc etre consideres non seulement comme entrant dans une hierarchie anatomique et comportementale de severite, mais aussi en fonction de leur progression physiologique dans le temps. RESUMEN Se ha aplicado una estimulacion electrica repetida en la amigdala en un modelo de status epilepticus electrogenico inducido en ratas. Los autores han observado cuatro comportamientos iniciales distintos asociados a descargas de puntas prolongadas que comprendian, jeraquicamente, segun la severidad: inmovilidad, actitud exploratoria, convulsiones menores y convulsiones clinicas. El EEG y la topografia del comportamiento del prolongado estado de ataques inicial se parecia, desde el punto de vista del comportamiento y electrograficamente, a los ataques agudos que aparecieron precozmente durante la induccion. El comienzo del status, tras la induccion limbica, no parece representar un nuevo tipo de actividad epileptica. Mas bien consiste en una version ampliada de ataques de comienzo limbico, breves y repetidos, a medida que los mecanismos de control de los ataques se hacen gradualmente ineficaces. Estos estados prolongados de ataques pueden utilizarse en el estudio de la anatomia y de los mecanismos de ataques limbicos breves. La progresion en el tiempo de los estados de ataques prolongados inducidos en la amigdala ha sido tambien examinada. En un extremo del espectro de severidad, las puntas asociadas a la inmovilidad del animal tenian tendencia a terminar precozmente (en unos 90 minutos) y se asociaron a una normalizacion del comportamiento. En el otro extremo del espectro, el status convulsivo clonico declino lentamente en la severidad del comportamiento a la vez que se observo un cambio en el EEG desde puntas rapidas a mas lentas. El status epilepticus exploratorio se caracterizo por un comportamiento incesante de exploracion del ambient que podia durar horas y se asocio a complejos de puntas lentas periodicas en el EEG. El curso, a large plazo, consistio en una resolucion lenta con interrupcion eventual de las puntas o en una ascension lenta y espontanea al estado convulsivo que puede considerarse como un fallo no solo de la jerarquia anatomico-compartamental de severidad sino tambien de la progresion fisiologica en el tiempo. ZUSAMMENFASSUNG Bei einem Paradigma des elektrogenen limbischen Status epilepticus bei Ratten wurden den Amygdala wiederholte elektrische Reize appliziert. Wir beobachteten 4 verschiedene initiale Verhaltenszustande, die mit verlangertan Spike-Ausbruchen einhergingen und eine Hierarchie im Schweregrad darstellten: Einen immobilen Zustand, einen exploratorischen Zustand, einen kleineren konvulsiven und einen klonisch-konvulsiven Zustand. EEG und Verhaltenstopographie des anfanglichen verlangerten Anfallsstatus ahnelten verhaltensmaβig und elektrographisch den akuten Anfallen, die fruh wahrend der Induktion auftraten. Der Beginn des Status epilepticus bei limbischer Induktion scheint keinen neuen Anfallstyp darzustellen, sondern eine ausgedehnte Version von wiederholten kurzen, im limbischen System beginnenden Anfallen, wenn die anfallsbeendigenden Mechanismen schrittweise unwirksam werden. Diese verlangerten Anfallsstaten konnen deshalb dazu dienen, Andtomie und Mechanismen von kurzen limbischen Anfallen zu untersuchen. Der zeitliche Verlauf von Amygdalon-induzierten verlangerten Anfallsstaten wurde ebenfalls untersucht. Am einen Ende des Schwerespektrums neigte das mit Immobilitat einhergehende Auftreten von Spikes zu einer fruhen Beendigung innerhalb von 90 Minuten, begleitet von einer Verhaltensnormalisierung. Am anderen Ende des Spektrums zeigten klonische konvulsive epileptische Staten eine allmahliche Abnahme im Schweregrad der Verhaltensanderung zusammen mit einer Anderung im EEG von schnellen zu langsamen Spikefolgen. Der exploratorische Status epilepticus war durch ein andauendes Exploratorionsverhalten charakterisiert, das uber Stunden anhalten konnte und mit langsamen periodischen Spike-Komplexem im EEG einherging. Der Langzeitverlauf bestand entweder in einem langsamen Ende mit evt. Nachlassen der Spike-Aktivitat oder in einem spontanen spaten Auftreten eines konvulsiven Status. Verlangerte Anfallsstaten konnen somit nicht nur hinsichtlich einer anatomischen bzw. verhaltensmaβigen Hierarchie des Schweregrades betrachtet werden, sondern auch hinsichtlich einer zeitlichen physiologischen Entwicklung.

In this evaluator-blinded open-treatment trial, subjects with moderate/severe upper limb essential tremor were titrated to 300 mg/day zonisamide, or adjusted to a lesser dose if symptoms warranted, as monotherapy or as adjunct to stable antitremor medication, followed by a 12-week extension phase. The primary efficacy outcome variables were blinded rater videotaped/drawing tremor score changes at the Treatment and Extension visits compared to Baseline, based on Fahn-Tolosa-Marin and Postural Tremor Scales. Subjects also rated Functional Disabilities. Primary outcomes showed reduced tremor scores at the Treatment (P0.00001, n = 25) and Extension (n = 16) visits, at mean doses of 252 and 225 mg/day, respectively. Subject ratings indicated 200 mg/day was superior to 100 mg/day, whereas 300 mg/day produced no additional benefit, but instead was associated with more adverse symptoms, most commonly somnolence, poor energy, imbalance, and altered taste. Future double-blind placebo-controlled trials are warranted.

A novel mibefradil derivative, NNC55-0396, designed to be hydrolysis-resistant, was shown to be a selective T-type Ca(2+) channel inhibitor without L-type Ca(2+) channel efficacy. However, its effects on cytochromes P450 (P450s) have not previously been examined. We investigated the inhibitory effects of NNC55-0396 toward seven major recombinant human P450s--CYP3A4, CYP2D6, CYP1A2, CYP2C9, CYP2C8, CYPC19, and CYP2E1--and compared its effects with those of mibefradil and its hydrolyzed metabolite, Ro40-5966. Our results show that CYP3A4 and CYP2D6 are the two P450s most affected by mibefradil, Ro40-5966, and NNC55-0396. Mibefradil (IC(50) = 33 +/- 3 nM, K(i) = 23 +/- 0.5 nM) and Ro40-5966 (IC(50) = 30 +/- 7.8 nM, K(i) = 21 +/- 2.8 nM) have a 9- to 10-fold greater inhibitory activity toward recombinant CYP3A4 benzyloxy-4-trifluoromethylcoumarin-O-debenzylation activity than NNC55-0396 (IC(50) = 300 +/- 30 nM, K(i) = 210 +/- 6 nM). More dramatically, mibefradil (IC(50) = 566 +/- 71 nM, K(i) = 202 +/- 39 nM) shows 19-fold higher inhibition of CYP3A-associated testosterone 6beta-hydroxylase activity in human liver microsomes compared with NNC55-0396 (IC(50) = 11 +/- 1.1 microM, K(i) = 3.9 +/- 0.4 microM). Loss of testosterone 6beta-hydroxylase activity by recombinant CYP3A4 was shown to be time- and concentration-dependent with both compounds. However, NNC55-0396 (K(I) = 3.87 microM, K(inact) = 0.061/min) is a much less potent mechanism-based inhibitor than mibefradil (K(I) = 83 nM, K(inact) = 0.048/min). In contrast, NNC55-0396 (IC(50) = 29 +/- 1.2 nM, K(i) = 2.8 +/- 0.3 nM) and Ro40-5966 (IC(50) = 46 +/- 11 nM, K(i) = 4.5 +/- 0.02 nM) have a 3- to 4-fold greater inhibitory activity toward recombinant CYP2D6 than mibefradil (IC(50) = 129 +/- 21 nM, K(i) = 12.7 +/- 0.9 nM). Our results suggest that NNC55-0396 could be a more favorable T-type Ca(2+) antagonist than its parent compound, mibefradil, which was withdrawn from the market because of strong inhibition of CYP3A4.

Excessive olivo-cerebellar synchrony is implicated in essential tremor. Because synchrony in some networks is mediated by gap junctions, we examined whether the gap junction blockers heptanol, octanol, carbenoxolone, and mefloquine suppress tremor in the mouse harmaline model, and performed an open-treatment clinical study of mefloquine for essential tremor. Digitized motion was used to quantify tremor in mice administered harmaline, 20 mg/kg s.c. In mice the broad-spectrum gap junction blockers heptanol, octanol (350 mg/kg i.p. each), and carbenoxolone (20 mg/kg) suppressed harmaline tremor. Mefloquine (50 mg/kg), which blocks gap junctions containing connexin 36, robustly suppressed harmaline tremor. Glycyrrhizic acid (related to carbenoxolone) and chloroquine (related to mefloquine), which do not block gap junctions, failed to suppress harmaline tremor in mice. Clinically, tremor was assessed with standard rating scales, and subjects asked to take 62.5, 125, and 250 mg mefloquine weekly for 12 weeks at each dose. None of the four human subjects showed a meaningful tremor reduction with mefloquine, likely because clinical levels were below those required for efficacy. In view of recent genetic evidence, the anti-tremor mechanism of these compounds is uncertain but may represent a novel therapeutic target, possibly involving gap junctions other than those containing connexin 36.

No preclinical method to evaluate potential new medications for essential tremor (ET) is available currently. Although harmaline tremor is a well known animal model of ET, it has not found utility as a preclinical drug screen and has not been validated with anti-ET medications. We measured harmaline tremor in rats (10 mg/kg s.c.) and mice (20 mg/kg s.c.) with a load sensor under the cage floor and performed spectral analysis on 20-minute epochs. The motion power over the tremor frequency bandwidth (8-12 Hz in rats; 10-16 Hz in mice) was divided by the motion power over the full motion frequency range (0-15 Hz in rats; 0-34 Hz in mice). The use of these measures greatly reduced data variability, permitting experiments with small sample sizes. Three drugs that suppress ET (propranolol, ethanol, and octanol) all significantly suppressed harmaline-induced tremor. We propose that, with this methodology, harmaline-induced tremor may be useful as a preclinical method to identify potential medications for ET.

The homozygous knockout mouse for the beta3 subunit of the GABAA receptor has been proposed as a model for the neurodevelopmental disorder, Angelman syndrome, based on phenotypic similarities of craniofacial abnormalities, cognitive defects, hyperactivity, motor incoordination, disturbed rest-activity cycles, and epilepsy. Since most children with Angelman syndrome are autosomal heterozygotes of maternal origin, apparently through genomic imprinting, we used gabrb3-deficient heterozygote mice of defined parental origin to investigate whether this phenotype is also maternally imprinted in mouse. Whole brain extracts showed greatly reduced beta3 subunit levels in male mice of maternal origin but not in male mice of paternal origin. Females of both parental origin showed greatly reduced beta3 subunit levels. Heterozygotes did not exhibit hyperactive circling behavior, convulsions, or electrographically recorded seizures. EEGs showed qualitative differences among heterozygotes, with male mice of maternal origin demonstrating more abnormalities including increased theta activity. Ethosuximide inhibited theta bursts, suggesting an alteration in the thalamocortical relay. Carbamazepine induced EEG slowing in males and EEG acceleration in females, with a larger effect in paternal-origin heterozygotes. Evidence thus suggests both parent-of-origin and gender-related components in developmental regulation of beta3 expression, in particular, that the maternally-derived male heterozygote may carry a developmental modification resulting in less beta3 protein, which may reflect partial genomic imprinting of the gabrb3 gene in mice.

Excessive olivo-cerebellar burst-firing occurs during harmaline-induced tremor. This system receives rich sensory inputs, including visceral. We hypothesized that electrical vagus nerve stimulation (VNS) would suppress harmaline tremor, as measured with digitized motion power in the rat. Cervical vagus nerve stimulation suppressed power in the 8-12-Hz tremor range by 40%, whereas sham stimulation was ineffective. This study raises the possibility that activation of various sensory modalities, as well as visceral, may reduce tremor.

As currently utilized, vagus nerve stimulation (VNS) is applied to the cervical trunk of the left vagus nerve to suppress seizures clinically. Demonstration that VNS can also reduce seizure severity when electrodes are placed on the right cervical vagus nerve in rats would provide empirical evidence that the antiepileptic effects of VNS are not an exclusive property of the left vagus nerve. Rats were implanted with a custom cuff electrode on either the left or right cervical vagus nerve. Two days later, continuous VNS was begun in half the rats with left-sided and half with right-sided electrodes. The remaining rats were connected to the stimulator, but did not receive VNS. After 30 s, pentylenetetrazole (PTZ) was administered systemically and seizures were rated by a blinded observer. The PTZ test was repeated two days later, with VNS administered to the previously unstimulated rats, while the others received no stimulation. VNS significantly reduced the severity of PTZ-induced seizures in rats regardless of the side of stimulation as compared to their no-VNS (control condition) seizure severity. No significant differences in efficacy existed based on the side of stimulation. These results indicate that right-sided VNS in rats is just as effective as left-sided VNS, suggesting that fibers necessary for seizure suppression are not unique to the left vagus nerve.

Summary: Purpose: To determine the effect of changes in device settings and duty cycle (on and off times) on the efficacy of vagus nerve stimulation (VNS) for refractory epilepsy. In the long-term XE5 study of VNS for intractable epilepsy, the median reduction in seizure frequency improved significantly after 1 year of follow-up. A central question is whether device changes improve efficacy. We analyzed the effects of device parameter changes on seizure frequency in 154 subjects who completed the study and who had complete data for analysis. Methods: Retrospective analysis of device changes during the XE5 long-term study of VNS. During the XE5 long-term follow-up study, the subject's device settings were modified within a Food and Drug Administration (FDA)-approved range of output current, pulse duration, frequency, on time, and off time. Significant changes in device settings occurred after 3 months. We investigated the relationship between percentage reduction in seizures and changes in device parameters between the 3- and 12-month visits. Within-group comparisons were performed for those who continued on standard on/off cycle of 30 s on and 5 min off, and those with the most common off times of 3, 1.8, and 50% reduction in seizures) also significantly improved from 19 to 35% (McNemar's test, p = 0.046). Conclusions: The data from this retrospective analysis indicate that device changes were not the primary determinant of increased efficacy at 12 months of long-term follow-up. In general, patients who remained on the original settings of 30 s on and 5 min off continued to respond or improve in their response over the 1-year period. However, some patients may benefit from reductions in off time (increases in duty cycle). In a subgroup initially resistant to VNS, a change in off time to ≤1.1 min off did result in significant improvements in efficacy.

Unfortunately, none of these compounds has high selectivity for these channels. Mibefradil has been marketed worldwide for the treatment of hypertension and angina for a short period before it was withdrawn due to its pharmacokinetic and pharma- codynamic interactions with some other drugs such as terfen- adine, astemizole, cisapride, cyclosporine, tricyclic antidepre- ssants. 4 Mibefradil binds to skeletal muscle L-type calcium channels and brain voltage-gated sodium channels with disso- ciation constants of 2.3 and 17 nM, respectively. 5 It also can block potassium and chloride channels. 6 Obviously, this makes it not an ideal tool for in vitro or in vivo studies on T-type channels. Therefore, more potent and selective blockers are required to study the fundamental function of T-type channel and the related pathophysiological diseases such as epilepsy, neuronal pain, hypertension, congestive heart failure, and can- cer. 7-8

A July 1997 assessment of the American Academy of Neurology (AAN) Therapeutics and Technology Subcommittee reviewed vagus nerve stimulation (VNS) for epilepsy, and concluded that it was promising, but not yet established.1 Subsequent to that review, a second multicenter, randomized, controlled clinical trial has shown safety and efficacy of VNS for treatment of intractable partial seizures. Given the importance of this novel therapy for epilepsy, and the new information provided by a second major study, the Therapeutics and Technology Subcommittee requested an update on VNS. Use of VNS in epilepsy has recently been reviewed.2-4 VNS uses intermittent stimulation of the left vagus nerve in the neck to reduce the frequency and intensity of seizures. Mechanism of action of VNS remains uncertain, but stimulation does not induce grossly visible alterations in the human EEG.5 Recent studies suggest that metabolic activation of certain thalamic, brainstem, and limbic structures may be important in mediating the effect of VNS.6,7 Depletion of norepinephrine in the locus coeruleus attenuates the antiseizure affect of VNS.8 After open-label studies,9,10 sponsors of VNS engaged in a multicenter randomized study, named E03,11 details of which were reviewed in the previous assessment.1 Results of this trial were positive, and the technology was considered promising, but the number of patients receiving VNS was insufficient to achieve Food and Drug Administration approval. Therefore, a second randomized, controlled, multicenter clinical trial, called E05, was undertaken.12 The E05 study12 of VNS evaluated 254 patients, ages 13 to 60 years, with intractable partial seizures. To be eligible, subjects had to have at least six complex partial, visible partial motor, or secondarily generalized seizures in the month before entry, and to be free from other complicating neurologic, psychiatric, or medical conditions. …

Angelman syndrome (AS) is a severe neurodevelopmental disorder resulting from a deletion/mutation in maternal chromosome 15q11–13. The genes in 15q11–13 contributing to the full array of the clinical phenotype are not fully identified. This study examines whether a loss or reduction in the GABAAreceptor β3subunit (GABRB3) gene, contained within the AS deletion region, may contribute to the overall severity of AS. Disrupting the gabrb3 gene in mice produces electroencephalographic abnormalities, seizures, and behavior that parallel those seen in AS. The seizures that are observed in these mice showed a pharmacological response profile to antiepileptic medications similar to that observed in AS. Additionally, these mice exhibited learning and memory deficits, poor motor skills on a repetitive task, hyperactivity, and a disturbed rest–activity cycle, features all common to AS. The loss of the single gene, gabrb3, in these mice is sufficient to cause phenotypic traits that have marked similarities to the clinical features of AS, indicating that impaired expression of the GABRB3 gene in humans probably contributes to the overall phenotype of Angelman syndrome. At least one other gene, the E6-associated protein ubiquitin-protein ligase (UBE3A) gene, has been implicated in AS, so the relative contribution of the GABRB3 gene alone or in combination with other genes remains to be established.

Gabapentin (GBP) has shown antiepileptic efficacy and good tolerance in clinical trials. Much remains to be learned about its clinical use. As a participating center in the US Gabapentin Study Group, we report observations that have practical implications for patient management. Twenty-three patients with intractable partial-onset seizures initiated open-label treatment after a blinded placebo-controlled add-on dose efficacy study. In the titration phase, GBP and concurrent antiepileptic drugs (AEDs) were adjusted to achieve optimal efficacy on maximally tolerated GBP doses. Nine patients had no significant improvement in seizure control and discontinued GBP. The remaining 14 patients were observed while treated long-term with stable-dose GBP and concurrent AEDs. Improvement was maintained as long as patients were followed: < or = 4 years. The protocol-allowed upper dose limit, 2,400 mg/day, was well tolerated by 16 of 23 patients, indicating that higher doses may be tolerated. GBP discontinuation did not cause rebound increases in seizure frequency. The most common adverse events (AEs) (in 14 of 23) were similar to those induced by concurrent AEDs and responded to reduction of concurrent AEDs. Many patients reported positive psychostimulatory effects. These observations extend previous findings indicating that GBP is an effective and well-tolerated drug for treatment of partial-onset seizures.

Background: Dezinamide (DZM, ADD 94057) is a potential antiepileptic drug that binds to the voltage-sensitive sodium channel and showed preliminary evidence of efficacy and safety in an open-label study.Methods: Our double-blind, placebo-controlled trial at two sites used an n-of-1 (single-patient) design. All 15 patients had medically intractable partial-onset seizures and were comedicated with phenytoin (PHT) only. Treatment was for six 5-week periods (three active paired with three placebo in random sequence). Assuming nonlinear kinetics, we used an initial pharmacokinetic profile to estimate dosages for reaching target plasma concentrations of DZM.Results: Statistically significant seizure reduction was found by both a randomization test (p = 0.0025) and a signed rank test (p = 0.048). Median seizure frequency decreased 37.9%, and 40% of patients had > 50% seizure reduction, both compared with placebo. Pharmacokinetic predictions were not accurate; mean plasma concentrations fell well below target values. Plasma PHT concentrations increased (mean = 17.1%) during DZM treatment. The most common adverse experiences were fatigue, light-headedness, and abnormal gait; five patients required DZM dosage reductions.Conclusions: DZM showed minimal clinical toxicity and significant efficacy despite lower plasma concentrations than predicted by pharmacokinetics. This trial establishes the suitability of the n-of-1 design to investigational antiepileptic drug trials.