The dissection of R genes and locus Pc5.1 in Phytophthora capsici infection provides a novel view of disease resistance in peppers.

BACKGROUND: Phytophthora capsici root rot (PRR) is a disastrous disease in peppers (Capsicum spp.) caused by soilborne oomycete with typical symptoms of necrosis and constriction at the basal stem and consequent plant wilting. Most studies on the QTL mapping of P. capsici resistance suggested a consensus broad-spectrum QTL on chromosome 5 named Pc.5.1 regardless of P. capsici isolates and resistant resources. In addition, all these reports proposed NBS-ARC domain genes as candidate genes controlling resistance. RESULTS: We screened out 10 PRR-resistant resources from 160 Capsicum germplasm and inspected the response of locus Pc.5.1 and NBS-ARC genes during P. capsici infection by comparing the root transcriptomes of resistant pepper 305R and susceptible pepper 372S. To dissect the structure of Pc.5.1, we anchored genetic markers onto pepper genomic sequence and made an extended Pc5.1 (Ext-Pc5.1) located at 8.35 Mb-38.13 Mb on chromosome 5 which covered all Pc5.1 reported in publications. A total of 571 NBS-ARC genes were mined from the genome of pepper CM334 and 34 genes were significantly affected by P. capsici infection in either 305R or 372S. Only 5 inducible NBS-ARC genes had LRR domains and none of them was positioned at Ext-Pc5.1. Ext-Pc5.1 did show strong response to P. capsici infection and there were a total of 44 differentially expressed genes (DEGs), but no candidate genes proposed by previous publications was included. Snakin-1 (SN1), a well-known antimicrobial peptide gene located at Pc5.1, was significantly decreased in 372S but not in 305R. Moreover, there was an impressive upregulation of sugar pathway genes in 305R, which was confirmed by metabolite analysis of roots. The biological processes of histone methylation, histone phosphorylation, DNA methylation, and nucleosome assembly were strongly activated in 305R but not in 372S, indicating an epigenetic-related defense mechanism. CONCLUSIONS: Those NBS-ARC genes that were suggested to contribute to Pc5.1 in previous publications did not show any significant response in P. capsici infection and there were no significant differences of these genes in transcription levels between 305R and 372S. Other pathogen defense-related genes like SN1 might account for Pc5.1. Our study also proposed the important role of sugar and epigenetic regulation in the defense against P. capsici.

Defective interhemispheric inhibition in drug-treated focal epilepsies.

BACKGROUND: Focal epilepsies (FEs) arise from a lateralized network, while in generalized epilepsies (GEs) there is a bilateral involvement from the outset. Intuitively, the corpus callosum is the anatomical substrate for interhemispheric spread. OBJECTIVE: We used transcranial magnetic stimulation (TMS) to explore whether there are any physiological differences in the corpus callosum of drug-treated patients with FE and those with genetic GE (GGE), compared to healthy subjects (HS). METHODS: TMS was used to measure the interhemispheric inhibition (IHI) from right-to-left primary motor cortex (M1) and viceversa in 16 patients with FE, 17 patients with GGE and 17 HS. A conditioning stimulus (CS) was given to one M1 10 and 50 ms before a test stimulus delivered to the contralateral M1. Motor evoked potentials (MEPs) were analysed both as a function of the side of stimulation and of the epileptic focus (left-right). RESULTS: In HS, IHI was reproducible with suppression of MEPs at ISIs of 10 and 50 ms. Similar effects occurred in GGE patients. FE patients behaved differently, since IHI was significantly reduced bilaterally. When FE patients were stratified according to the side of their epileptic focus, the long-ISI IHI (=50 ms) appeared to be defective only when the CS was applied over the "focal" hemisphere. CONCLUSIONS: FE patients had a defective inhibitory response of contralateral M1 to inputs travelling from the "focal" hemisphere that was residual to the drug action. Whilst IHI changes would not be crucial for the GGE pathophysiology, they may represent one key factor for the contralateral spread of focal discharges, and seizure generalization.

TMS and drugs revisited 2014.

The combination of pharmacology and transcranial magnetic stimulation to study the effects of drugs on TMS-evoked EMG responses (pharmaco-TMS-EMG) has considerably improved our understanding of the effects of TMS on the human brain. Ten years have elapsed since an influential review on this topic has been published in this journal (Ziemann, 2004). Since then, several major developments have taken place: TMS has been combined with EEG to measure TMS evoked responses directly from brain activity rather than by motor evoked potentials in a muscle, and pharmacological characterization of the TMS-evoked EEG potentials, although still in its infancy, has started (pharmaco-TMS-EEG). Furthermore, the knowledge from pharmaco-TMS-EMG that has been primarily obtained in healthy subjects is now applied to clinical settings, for instance, to monitor or even predict clinical drug responses in neurological or psychiatric patients. Finally, pharmaco-TMS-EMG has been applied to understand the effects of CNS active drugs on non-invasive brain stimulation induced long-term potentiation-like and long-term depression-like plasticity. This is a new field that may help to develop rationales of pharmacological treatment for enhancement of recovery and re-learning after CNS lesions. This up-dated review will highlight important knowledge and recent advances in the contribution of pharmaco-TMS-EMG and pharmaco-TMS-EEG to our understanding of normal and dysfunctional excitability, connectivity and plasticity of the human brain.

Does the region of epileptogenicity influence the pattern of change in cortical excitability?

OBJECTIVE: To investigate whether cortical excitability measures on transcranial magnetic stimulation (TMS) differed between groups of patients with different focal epilepsy syndromes. METHODS: 85 Patients with focal epilepsy syndromes divided into temporal and extra-temporal lobe epilepsy were studied. The cohorts were further divided into drug naïve-new onset, refractory and seizure free groups. Motor threshold (MT) and paired pulse TMS at short (2, 5, 10, 15 ms) and long (100-300 ms) interstimulus intervals (ISIs) were measured. Results were compared to those of 20 controls. RESULTS: Cortical excitability was higher at 2 & 5 ms and 250, 300 ms ISIs (p<0.01) in focal epilepsy syndromes compared to controls however significant inter-hemispheric differences in MT and the same ISIs were only seen in the drug naïve state early at onset and were much more prominent in temporal lobe epilepsy. CONCLUSION: Disturbances in cortical excitability are more confined to the affected hemisphere in temporal lobe epilepsy but only early at onset in the drug naïve state. SIGNIFICANCE: Group TMS studies show that cortical excitability measures are different in temporal lobe epilepsy and can be distinguished from other focal epilepsies early at onset in the drug naïve state. Further studies are needed to determine whether these results can be applied clinically as the utility of TMS in distinguishing between epilepsy syndromes at an individual level remains to be determined.

On the midway to epilepsy: is cortical excitability normal in patients with isolated seizures?

Paired pulse transcranial magnetic stimulation was used to investigate differences in cortical excitability between patients with isolated (unrecurrent, unprovoked) seizures and those with epilepsy. Compared to controls, cortical excitability was higher in the isolated seizure group at 250-300 ms. Compared to epilepsy, cortical excitability was lower in patients with isolated seizures also at 250 and 300 ms. Lowered seizure threshold caused by disturbances within inhibitory circuits is present in patients who experience a seizure even if no further seizures occur.

TMS, cortical excitability and epilepsy: the clinical impact.

Paired-pulse transcranial magnetic stimulation (ppTMS) is a well-established method for non-invasive measurement of cortical excitability, alterations of which are the core background of epilepsy. For the past 20 years this technique has been extensively used to assess patients with epilepsy. We present here a critical overview of these studies, with emphasis on their translation to the clinical practice.

Exercise-induced seizures and lateral asymmetry in patients with temporal lobe epilepsy.

OBJECTIVE: The objective of this case report is to better characterize the clinical features and potential pathophysiological mechanisms of exercise-induced seizures. METHODS: We report a case series of ten patients from a tertiary epilepsy center, where a clear history was obtained of physical exercise as a reproducible trigger for seizures. RESULTS: The precipitating type of exercise was quite specific for each patient, and various forms of exercise are described including running, swimming, playing netball, dancing, cycling, weight lifting, and martial arts. The level of physical exertion also correlated with the likelihood of seizure occurrence. All ten patients had temporal lobe abnormalities, with nine of the ten patients having isolated temporal lobe epilepsies, as supported by seizure semiology, EEG recordings, and both structural and functional imaging. Nine of the ten patients had seizures that were lateralized to the left (dominant) hemisphere. Five patients underwent surgical resection, with no successful long-term postoperative outcomes. CONCLUSIONS: Exercise may be an underrecognized form of reflex epilepsy, which tended to be refractory to both medical and surgical interventions in our patients. Almost all patients in our cohort had seizures localizing to the left temporal lobe. We discuss potential mechanisms by which exercise may precipitate seizures, and its relevance regarding our understanding of temporal lobe epilepsy and lateralization of seizures. Recognition of, as well as advice regarding avoidance of, known triggers forms an important part of management of these patients.

The cortical excitability profile of temporal lobe epilepsy.

PURPOSE: Transcranial magnetic stimulation (TMS) was used to characterize measurable changes of cortical excitability in patients who were undergoing medical and surgical management of temporal lobe epilepsy (TLE) to investigate whether these alterations depended on timing of achieving seizure control throughout the course of illness and method of management. METHODS: Eighty-five patients with TLE divided into (1) drug naive-new onset, (2) early medically refractor, and (3) late medically refractory, (4) early seizure-free on antiepileptic drugs, and (5) late seizure-free on antiepileptic drugs, (6) postoperative refractory, and (7) postoperative seizure-free groups were studied. Motor threshold (MT) and paired-pulse TMS at short (2, 5, 10, and 15 msec) and long (100-300 msec) interstimulus intervals (ISIs) were measured. Results were compared to those of 20 controls. KEY FINDINGS: A significant interhemispheric difference was observed early at onset prior to starting medication, with higher cortical excitability in the hemisphere ipsilateral to the seizure focus, whereas the unaffected hemisphere was normal. After that, cortical excitability was higher in both hemispheres in the refractory groups (medical and postoperative) compared to the seizure-free and drug-naive groups (p < 0.05). This effect was most prominent at the long ISIs. SIGNIFICANCE: Changes in cortical excitability seen in patients with TLE are influenced by the course of the disease. The alterations that occur due to epilepsy are closely related to course of illness and degree/timing of seizure control. Successful management leads to resolution of this cortical hyperexcitability in a similar fashion regardless of method: medication (intact generator, but modulated by drugs) or surgery (generator removed).

Networks underlying paroxysmal fast activity and slow spike and wave in Lennox-Gastaut syndrome.

OBJECTIVE: To use EEG-fMRI to determine which structures are critically involved in the generation of paroxysmal fast activity (PFA) and slow spike and wave (SSW) (1.5-2.5 Hz), the characteristic interictal discharges of Lennox-Gastaut syndrome (LGS). METHODS: We studied 13 well-characterized patients with LGS using structural imaging and EEG-fMRI at 3 tesla. Ten patients had cortical structural abnormalities. PFA and SSW were considered as separate events in the fMRI analysis. RESULTS: Simultaneous with fMRI, PFA was recorded in 6 patients and SSW in 9 (in 2, both were recorded). PFA events showed almost uniform increases in blood oxygen level-dependent (BOLD) signal in "association" cortical areas, as well as brainstem, basal ganglia, and thalamus. SSW showed a different pattern of BOLD signal change with many areas of decreased BOLD signal, mostly in primary cortical areas. Two patients with prior callosotomy had lateralized as well as generalized PFA. The lateralized PFA was associated with a hemispheric version of the PFA pattern we report here. CONCLUSION: PFA is associated with activity in a diffuse network that includes association cortices as well as an unusual pattern of simultaneous activation of subcortical structures (brainstem, thalamus, and basal ganglia). By comparison, the SSW pattern is quite different, with cortical and subcortical activations and deactivations. Regardless of etiology, it appears that 2 key, but distinct, patterns of diffuse brain network involvement contribute to the defining electrophysiologic features of LGS.

Subcortical epilepsy?

In the past, the cortex has for the most part been considered to be the site of seizure origin in the different forms of epilepsy. Findings from histopathologic, electrophysiologic, and brain imaging studies now provide ample evidence demonstrating that like normal cerebral function, epileptic seizures involve widespread network interactions between cortical and subcortical structures. These studies show that different forms of generalized and focal epileptiform discharges and seizures engage various subcortical structures in varying ways. This interaction has been the subject of many reviews and is not the focus of the current work. The aim of this review is to examine the evidence suggesting the possibility for some of the subcortical structures to initiate seizures independently and the clinical implications of this.

Are patterns of cortical hyperexcitability altered in catamenial epilepsy?

OBJECTIVE: We used transcranial magnetic stimulation to determine menstrual cycle-related changes in cortical excitability in women with and without catamenial epilepsy and investigated whether these changes differed between ovulatory and anovulatory cohorts. METHODS: Healthy nonepilepsy women and women with generalized and focal epilepsy were investigated during ovulatory (n=11, 46, and 43, respectively) and anovulatory (n=9, 42, and 41) cycles. Patients were divided based on seizure pattern into catamenial (C1=perimenstrual, C2=periovulatory, C3=luteal seizure exacerbation), noncatamenial, and seizure free. Cortical excitability was assessed using motor threshold (MT) and paired pulse stimulation at short (2-15 milliseconds) and long (100-300 milliseconds) interstimulus intervals twice, at the (1) late follicular and (2) mid luteal phases of the menstrual cycle. RESULTS: In controls, cortical excitability was greatest in the follicular study, where intracortical facilitation was increased (p<0.05). The opposite was seen in women with epilepsy, where intracortical facilitation was greatest and intracortical inhibition was least in the luteal studies (p<0.05). There were no differences between the ovulatory and anovulatory groups in any of the cohorts. No changes were observed in MT. INTERPRETATION: Nonhormonal factors are involved in the cyclicity of cortical excitability across the menstrual cycle. Normal menstrual cycle variations in cortical excitability are altered in a similar pattern in ovulatory and anovulatory women with epilepsy regardless of seizure patterns. The underlying neural changes associated with epilepsy may alter responses to sex hormones. This may be an important underlying mechanism for catamenial seizure clustering.

Cortical excitability changes correlate with fluctuations in glucose levels in patients with epilepsy.

OBJECTIVE: We used transcranial magnetic stimulation (TMS) to investigate motor cortical excitability changes in relation to blood glucose levels. METHODS: Twenty-two drug-naïve patients with epilepsy [11 generalized and 11 focal] and 10 controls were studied twice on the same day; first after 12h of fasting and then 2h postprandial. Motor threshold and paired-pulse TMS at a number of short and long interstimulus intervals were measured. Serum glucose levels were measured each time. RESULTS: Decreased long intracortical inhibition was seen in patients and controls during fasting compared to postprandial studies. This effect was much more prominent in patients with generalized epilepsy (with effect sizes of up to 0.8) in whom there was also evidence of increased intracortical facilitation (effect size: 0.3). CONCLUSION: Cortical excitability varies with fluctuations in blood glucose levels. This variation is more prominent in patients with epilepsy. Decreased glucose levels may be an important physiological seizure trigger.

Patterns of cortical hyperexcitability in adolescent/adult-onset generalized epilepsies.

PURPOSE: To investigate whether using transcranial magnetic stimulation (TMS) to derive if measures of cortical excitability changes can distinguish between various adolescent/adult-onset generalized epilepsy syndromes at different phases of the disorder. METHODS: One hundred thirty-seven patients with adolescent/adult-onset generalized epilepsy divided into juvenile myoclonic epilepsy, juvenile absence epilepsy, and generalized epilepsy with tonic-clonic seizures only were studied. The cohorts were further divided into drug naive-new onset, refractory, and seizure-free groups. Motor threshold (MT) and paired pulse TMS at short (2, 5, 10, 15 msec) and long (100-300 msec) interstimulus intervals (ISIs) were measured. Results were compared to those of 20 controls. KEY FINDINGS: In the drug-naive cohorts MT was reduced (p < 0.05) and cortical excitability increased at 2 and 5 msec and 150, 250, and 300 msec ISIs (p < 0.01) in juvenile myoclonic epilepsy compared to other generalized epilepsy groups and controls. Cortical excitability increased to a lesser degree in other generalized epilepsy syndromes compared to controls, but those two syndromes were not distinguishable from one another. The changes in paired pulse TMS were more prominent in the groups with refractory seizures and very small in the groups who were seizure free. SIGNIFICANCE: There are syndrome specific changes in cortical excitability associated with generalized epilepsy. These changes are also dependent on seizure control with medication. Juvenile myoclonic epilepsy has a higher cortical excitability profile compared to other adolescent/adult-onset generalized epilepsy syndromes and can be clearly distinguished from them during all phases.

Capturing the epileptic trait: cortical excitability measures in patients and their unaffected siblings.

We used transcranial magnetic stimulation to investigate whether the cortical excitability changes observed amongst the different generalized and focal epilepsy syndromes are reflected in their asymptomatic siblings and if these changes depended on the clinical phenotype. We studied 157 patients with epilepsy (95 generalized and 62 focal) and their asymptomatic siblings (138 and 82, respectively). Motor threshold and paired pulse transcranial magnetic stimulation at short (2, 5, 10 and 15 ms) and long (100-300 ms) interstimulus intervals were measured. Results were compared to those of 12 control subjects and 20 of their siblings. There were no differences in cortical excitability between healthy control subjects and their siblings. Compared with control subjects, cortical excitability was higher in siblings of patients whether generalized (P < 0.05; short and long interstimulus intervals) or focal (P < 0.05; long interstimulus intervals). Compared with epilepsy, motor threshold was lower (P < 0.05) in patients with juvenile myoclonic epilepsy compared with their siblings only early at onset in the drug naïve state. In all groups (generalized and focal) cortical excitability was lower in siblings only at the long interstimulus intervals (250 and 300; P < 0.05). Cortical excitability is higher in asymptomatic siblings of patients with generalized and focal epilepsy in a similar manner. The disturbance seems to involve intracortical inhibitory circuits even in the siblings of patients with a structural abnormality (acquired epilepsy). This implies there are certain genetic factors that predispose to both generalized and focal epilepsies and a complex genetic/environmental interaction then determines the clinical phenotype.

Cortical excitability and refractory epilepsy: a three-year longitudinal transcranial magnetic stimulation study.

Transcranial magnetic stimulation was used to study the effect of recurrent seizures on cortical excitability over time in epilepsy. 77 patients with firm diagnoses of idiopathic generalized epilepsy (IGE) or focal epilepsy were repeatedly evaluated over three years. At onset, all groups had increased cortical excitability. At the end of follow-up the refractory group was associated with a broad increase in cortical excitability. Conversely, cortical excitability decreased in all seizure free groups after introduction of an effective medication.

Intracranial EEG-fMRI analysis of focal epileptiform discharges in humans.

PURPOSE: Combining intracranial electroencephalography (iEEG) with functional magnetic resonance imaging (fMRI) is of interest in epilepsy studies as it would allow the detection of much smaller interictal epileptiform discharges than can be recorded using scalp EEG-fMRI. This may help elucidate the spatiotemporal mechanisms underlying the generation of interictal discharges. To our knowledge, iEEG-fMRI has never been performed at 3 Tesla (3T) in humans. We report our findings relating to spike-associated blood oxygen level-dependent (BOLD) signal changes in two subjects. METHODS: iEEG-fMRI at 3T was performed in two subjects. Twelve channels of iEEG were recorded from subdural strips implanted on the left posterior temporal and middle frontal lobes in a 20-year-old female with bilateral periventricular gray matter heterotopia. Twenty channels of iEEG were recorded bilaterally from two subdural strips laid anterior-posterior along mesial temporal surfaces in a 29-year-old woman with bilateral temporal seizures and mild left amygdalar enlargement on MRI. Functional MRI (fMRI) statistical maps were generated and thresholded at p = 0.01. KEY FINDINGS: No adverse events were noted. A total of 105 interictal discharges were recorded in the posterior middle temporal gyrus of Subject 1. In Subject 2, 478 discharges were recorded from both mesial temporal surfaces (n = 194 left, 284 right). The right and left discharges were modeled separately, as they were independent. Subject 1 showed spike-associated BOLD signal increases in the left superior temporal region, left middle frontal gyrus, and right parietal lobe. BOLD decreases were seen in the right frontal and parietal lobes. In Subject 2, BOLD signal increases were seen in both mesial temporal lobes, which when left and right spikes were modeled independently, were greater on the side of the discharge. In addition, striking BOLD signal decreases were observed in the thalamus and posterior cingulate gyrus. SIGNIFICANCE: iEEG-fMRI can be performed at 3T with low risk. Notably, runs of only 5 or 10 min of EEG-fMRI were performed as part of our implementation protocol, yet a significant number of epileptiform discharges were recorded, allowing meaningful analyses. With these studies, we have shown that deactivation can be seen in individual subjects with focal epileptiform discharges. These preliminary observations suggest a novel mechanism through which focal interictal discharges may have widespread cortical and subcortical influences.

Cortical excitability decreases in Lennox-Gastaut syndrome.

PURPOSE: We used transcranial magnetic stimulation (TMS) to investigate cortical excitability changes in Lennox-Gastaut syndrome (LGS), anticipating we would find a marked increase in excitability compared to other patients with refractory epilepsies. METHODS: Eighteen patients with LGS were studied. Motor threshold (MT), short intracortical inhibition (paired pulse TMS at 2 and 5 msec interstimulus intervals [ISIs]), intracortical facilitation (10 and 15 msec ISIs), and long intracortical inhibition (100-300 msec ISIs) were measured. Results were compared to those of 20 patients with chronic refractory idiopathic generalized epilepsy (IGE), 20 patients with chronic refractory focal epilepsy, and 20 healthy nonepilepsy controls. KEY FINDINGS: A significant decrease in cortical excitability was observed in LGS compared to the other two groups with refractory epilepsy as evidenced by increased MT and intracortical inhibition at both short (2, 5 msec ISIs), and long (100-300 msec ISIs) as well as decreased intracortical facilitation (10, 15 msec ISIs), (p < 0.01; effect sizes ranging from 0.3 to 1.8). Cortical excitability was also lower in LGS compared to nonepilepsy controls (increased MT and decreased intracortical facilitation; p < 0.05; effect sizes ranging from 0.5 to 0.9). SIGNIFICANCE: Interictal cortical excitability is decreased in LGS; a feature that distinguishes it from other refractory epilepsy syndromes. This decrease may be an important mechanism for the neurobehavioral comorbidities associated with LGS.

Cortical excitability in migraine and epilepsy: a common feature?

OBJECTIVE: There is evidence for comorbidity of migraine and epilepsy. We used transcranial magnetic stimulation (TMS) to assess cortical excitability in migraine compared with control subjects and patients with epilepsy. METHODS: Twenty-six patients drug-naive patients with newly diagnosed migraine were studied. These were compared with 19 healthy control subjects and 50 patients with new onset epilepsy. Motor threshold (MT) and responses to paired pulse stimulation at short (2, 5, 10, and 15 milliseconds) and long (50-400 milliseconds) interstimulus intervals (ISIs) were measured. RESULTS: Compared with control subjects, cortical excitability was higher in migraine only at 250 milliseconds (P < 0.05; effect size 0.7), while in epilepsy, it was higher at 2, 5, 250, and 300 milliseconds. Compared with epilepsy, cortical excitability was lower in migraine only at 250 milliseconds (P < 0.05; effect size 0.6 compared with focal epilepsy and 1.1 compared with idiopathic generalized epilepsy [IGE]). CONCLUSIONS: Cortical excitability increases in migraine suggesting the involvement of intracortical inhibitory circuits. This may be a common feature underlying some of the similarities observed in migraine and epilepsy.