Cellular activity underlying altered brain metabolism during focal epileptic activity

'Remote inhibition' of motor cortex in Epileptic encephalopathy with spike-wave activation in sleep (EE-SWAS): A TMS based cortical excitability study

OBJECTIVES

The study compared real-time motor cortex excitability using transcranial magnetic stimulation (TMS)-derived parameters between children with epileptic encephalopathy with spike-wave activation in sleep (EE-SWAS) and age-matched neurotypical controls. The EE-SWAS group received steroids as standard of care and were longitudinally followed for three months.

MATERIALS & METHODS

Children aged 5-12 years with immunotherapy-naive EE-SWAS (spike-wave-index≥50 %) and neurotypical controls were enrolled. Cognitive and behavioral assessments were performed using valid psychometric tools. Real-time motor cortex excitability was assessed by measuring resting motor threshold (RMT), short intra-cortical inhibition (SICI) and long intra-cortical inhibition (LICI) in both groups. In EE-SWAS group, a follow up evaluation with TMS at 4- and 12-week intervals, EEG, and neurobehavioral assessments at 12-weeks were performed to assess the effect of steroids on cortical excitability and to determine electroclinical outcome.

RESULTS

Forty-eight children with suspected EE-SWAS and 26 neurotypical controls were screened; 20 were enrolled in each group. Children with EE-SWAS (mean age: 8.05 ± 1.76 years) had cognitive and behavioral problems (20/20), and ongoing seizures (12/20). At baseline, the dominant motor cortex was significantly inhibited in the EE-SWAS group compared to neurotypical children{RMT(%)[86.3 ± 6.96 vs 58.05 ± 4.71(p < 0.0001)]; LICI(%)[55.05 ± 4.39 vs 73.9 ± 3.75(p < 0.0001)]; SICI(%)[39.2 ± 4.36 vs 55.45 ± 4.78(p < 0.0001)]}. Reversal of motor cortex inhibition was sequentially observed in EE-SWAS group at 4- and 12-week follow-ups{(RMT[4, 12 weeks]: 71.45 ± 9.83, 63.45 ± 8.48); (LICI[4, 12 weeks]: 66.00 ± 6.26, 74.50 ± 5.36); (SICI[4, 12 weeks]: 49.35 ± 6.24, 56.05 ± 5.57)}[repeated-measures ANOVA: p < 0.0001].

CONCLUSION

Motor cortex is remotely inhibited in EE-SWAS, which may contribute to neurobehavioral impairment. Steroids can disinhibit/reverse the epilepsy-induced motor cortex inhibition leading to improvement in neurobehavior.

2-Deoxy-D-glucose administration after seizures has disease-modifying effects on kindling progression

2-deoxy-D-glucose (2DG) is a glucose analog and reversible inhibitor of glycolysis with anticonvulsant and antiepileptic effects in multiple seizure models. 2DG at a dose of 250 mg/kg intraperitoneally (IP) delays progression of repeated seizures evoked by kindling in rats when administered 30 min prior to twice daily kindling stimulation. As toxicological studies have demonstrated that repeated daily oral administration of 2DG at doses of 60-375 mg/kg/day in rats induces dose-dependent, reversible cardiac myocyte vacuolation, it was of interest to determine if 2DG also slowed kindling progression when administered at or below doses causing cardiac toxicity and at various time points after evoked seizures. We found that: (1) 2DG slowed kindling progression nearly 2-fold when administered at a dose of 37.5 mg/kg given IP 30 min prior to kindling stimulation, and (2) 2DG 37.5 mg/kg IP also slowed kindling progression when given immediately after, and for as long as 10 min after evoked (kindled) seizures. These observations suggest potential clinical usefulness of post-seizure administration of 2DG to reduce seizure clusters and long-term consequences of repeated seizures at human equivalent doses that are likely to be safe and well tolerated in patients.

Focal cortical hypermetabolism in atypical benign rolandic epilepsy

OBJECTIVE

Atypical benign rolandic epilepsy (BRE) is an underrecognized and poorly understood manifestation of a common epileptic syndrome. Most consider it a focal epileptic encephalopathy in which frequent, interictal, centrotemporal spikes lead to negative motor seizures and interfere with motor and sometimes speech and cognitive abilities. We observed focal cortical hypermetabolism on PET in three children with atypical BRE and investigated the spatial and temporal relationship with their centrotemporal spikes.

METHODS

EEG, MRI and PET were performed clinically in three children with atypical BRE. The frequency and source localization of centrotemporal spikes was determined and compared with the location of maximal metabolic activity on PET.

RESULTS

Cortical hypermetabolism on thresholded PET t-maps and current density reconstructions of centrotemporal spikes overlapped in each child, in the central sulcus region, the distances between the "centers of maxima" being 2 cm or less. Hypermetabolism was not due to recent seizures or frequent centrotemporal spikes at the time of FDG uptake.

SIGNIFICANCE

The findings suggest that localized, increased cortical activity, in the region of the EEG focus, underlies the negative clinical manifestations of atypical BRE. Similar findings are reported in the broader group of epileptic encephalopathies associated with electrical status epilepticus in sleep.

The Impact of Interictal Discharges on Performance

PURPOSE OF REVIEW

Our purpose is to review evidence relating to the concept that interictal epileptiform discharges (IEDs) impair brain performance.

RECENT FINDINGS

Sophisticated measures of motor and cognitive performance have clarified older observations, confirming that in both animals and humans, IEDs affect aspects of performance, IED morphology, frequency, anatomical distribution, and duration matter. However, we now know that it is difficult to draw a line between IEDs and seizures, not only by electrical criteria but even by metabolic and molecular measures. IEDs impair performance acutely and probably chronically. Thus, there are good theoretical reasons for suppressing them, but no consensus has been reached on how much effort this deserves. Many antiepileptic medications effective for control of clinical seizures have little effect on IEDs. Better methods of measuring outcomes may allow selection of individual patients for whom treatment aimed at IEDs is worthwhile.

Evolution of lobar abnormalities of cerebral glucose metabolism in 41 children with drug-resistant epilepsy

OBJECTIVE

We analyzed long-term changes of lobar glucose metabolic abnormalities in relation to clinical seizure variables and development in a large group of children with medically refractory epilepsy.

METHODS

Forty-one children (25 males) with drug-resistant epilepsy had a baseline positron emission tomography (PET) scan at a median age of 4.7 years; the scans were repeated after a median of 4.3 years. Children with progressive neurological disorders or space-occupying lesion-related epilepsy and those who had undergone epilepsy surgery were excluded. The number of affected lobes on 2-deoxy-2(18 F)-fluoro-D-glucose-PET at baseline and follow-up was correlated with epilepsy variables and developmental outcome.

RESULTS

On the initial PET scan, 24 children had unilateral and 13 had bilateral glucose hypometabolism, whereas 4 children had normal scans. On the follow-up scan, 63% of the children showed an interval expansion of the hypometabolic region, and this progression was associated with persistent seizures. In contrast, 27% showed less extensive glucose hypometabolism at follow-up; most of these subjects manifested a major interval decrease in seizure frequency. Delayed development was observed in 21 children (51%) at baseline and 28 (68%) at follow-up. The extent of glucose hypometabolism at baseline correlated with developmental levels at the time of both baseline (r = .31, P = .05) and follow-up scans (r = .27, P = .09).

SIGNIFICANCE

In this PET study of unoperated children with focal epilepsy, the lobar pattern of glucose hypometabolism changed over time in 90% of the cases. The results support the notion of an expansion of metabolic dysfunction in children with persistent frequent seizures and its association with developmental delay, and support that optimized medical treatment to control seizures may contribute to better neurocognitive outcome if no surgery can be offered.

Roles of electro-acupuncture in glucose metabolism as assessed by 18F-FDG/PET imaging and AMPKα phosphorylation in rats with ischemic stroke

Targeted energy metabolism balance contributes to neural survival during ischemic stroke. Herein, we tested the hypothesis that electro‑acupuncture (EA) can enhance cerebral glucose metabolism assessed by 18F‑fluorodeoxyglucose/positron emission tomography (18F‑FDG/PET) imaging to prevent propagation of tissue damage and improve neurological outcome in rats subjected to ischemia and reperfusion injury. Rats underwent middle cerebral artery occlusion (MCAO) and received EA treatment at the LI11 and ST36 acupoints or non‑acupoint treatment once a day for 7 days. After EA treatment, a significant reduction in the infarct volume was determined by T2‑weighted imaging, accompanied by the functional recovery in CatWalk and Rota-rod performance. Moreover, EA promoted higher glucose metabolism in the caudate putamen (CPu), motor cortex (MCTX), somatosensory cortex (SCTX) regions as assessed by animal 18F‑FDG/PET imaging, suggesting that three‑brain regional neural activity was enhanced by EA. In addition, the AMP‑activated protein kinase α (AMPKα) in the CPu, MCTX and SCTX regions was phosphorylated at threonine 172 (Thr172) after ischemic injury; however, phosphorylation of AMPK was further increased by EA. These results indicate that EA could promote AMPKα phosphorylation of the CPu, MCTX and SCTX regions to enhance neural activity and motor functional recovery after ischemic stroke.

Glucose Metabolic Profile by Visual Assessment Combined with Statistical Parametric Mapping Analysis in Pediatric Patients with Epilepsy

PET with ¹⁸F-FDG has been used for presurgical localization of epileptogenic foci; however, in nonsurgical patients, the correlation between cerebral glucose metabolism and clinical severity has not been fully understood. The aim of this study was to evaluate the glucose metabolic profile using ¹⁸F-FDG PET/CT imaging in patients with epilepsy. Methods: One hundred pediatric epilepsy patients who underwent ¹⁸F-FDG PET/CT, MRI, and electroencephalography examinations were included. Fifteen age-matched controls were also included. ¹⁸F-FDG PET images were analyzed by visual assessment combined with statistical parametric mapping (SPM) analysis. The absolute asymmetry index (|AI|) was calculated in patients with regional abnormal glucose metabolism. Results: Visual assessment combined with SPM analysis of ¹⁸F-FDG PET images detected more patients with abnormal glucose metabolism than visual assessment only. The |AI| significantly positively correlated with seizure frequency (P < 0.01) but negatively correlated with the time since last seizure (P < 0.01) in patients with abnormal glucose metabolism. The only significant contributing variable to the |AI| was the time since last seizure, in patients both with hypometabolism (P = 0.001) and with hypermetabolism (P = 0.005). For patients with either hypometabolism (P < 0.01) or hypermetabolism (P = 0.209), higher |AI| values were found in those with drug resistance than with seizure remission. In the post-1-y follow-up PET studies, a significant change of |AI| (%) was found in patients with clinical improvement compared with those with persistence or progression (P < 0.01). Conclusion:¹⁸F-FDG PET imaging with visual assessment combined with SPM analysis could provide cerebral glucose metabolic profiles in nonsurgical epilepsy patients. |AI| might be used for evaluation of clinical severity and progress in these patients. Patients with a prolonged period of seizure freedom may have more subtle (or no) metabolic abnormalities on PET. The clinical value of PET might be enhanced by timing the scan closer to clinical seizures.

Functional Neuroimaging in Stroke Recovery and Neurorehabilitation: Conceptual Issues and Perspectives

Background

In stroke, functional neuroimaging has become a potent diagnostic tool; opened new insights into the pathophysiology of ischaemic damage in the human brain; and made possible the assessment of functional–structural relationships in postlesion recovery.

Summary of review

Here, we give a critical account on the potential and limitation of functional neuroimaging and discuss concepts related to the use of neuroimaging for exploring the neurobiological and neuroanatomical mechanisms of poststroke recovery and neurorehabilitation. We identify and provide evidence for five hypotheses that functional neuroimaging can provide new insights into: adaptation occurs at the level of functional brain systems; the brain–behaviour relationship varies with recovery and over time; functional neuroimaging can improve our ability to predict recovery and select individuals for rehabilitation; mechanisms of recovery reflect different pathophysiological phases; and brain adaptation may be modulated by experience and specific rehabilitation. The significance and application of this new evidence is discussed, and recommendations made for investigations in the field.

Conclusion

Functional neuroimaging is an important tool to explore the mechanisms underlying brain plasticity and, thereby, to guide clinical research in neurorehabilitation.

Migraine and epilepsy: review of the literature

Migraine and epilepsy are disorders that are common, paroxysmal, and chronic. In many ways they are clearly different diseases, yet there are some pathophysiological overlaps, and overlaps in clinical symptomatology, particularly with regard to visual and other sensory disturbances, pain, and alterations of consciousness. Epidemiological studies have revealed that the two diseases are comorbid in a number of individuals. Both are now recognized as originating from electrical disturbances in the brain, although their wider manifestations involve the recruitment of multiple pathogenic mechanisms. An initial excess of neuronal activity in migraine leads to cortical spreading depression and aura, with the subsequent recruitment of the trigeminal nucleus leading to central sensitization and pain. In epilepsy, neuronal overactivity leads to the recruitment of larger populations of neurons firing in a rhythmic manner that constitutes an epileptic seizure. Migraine aura and headaches may act as a trigger for epileptic seizures. Epilepsy is not infrequently accompanied by preictal, ictal, and postictal headaches that often have migrainous features. Genetic links are also apparent between the two disorders, and are particularly evident in the familial hemiplegic migraine syndromes where different mutations can produce either migraine, epilepsy, or both. Also, various medications are found to be effective for both migraine and epilepsy, again pointing to a commonality and overlap between the two disorders.

Changes in functional integration with the non-epileptic temporal lobe of patients with unilateral mesiotemporal epilepsy

Purpose

To investigate epilepsy-induced changes in effective connectivity between the non-epileptic amygdalo-hippocampal complex (AHC) and the rest of the brain in patients with unilateral mesiotemporal lobe epilepsy (MTLE) associated with hippocampal sclerosis (HS).

Methods

Thirty-three patients with unilateral MTLE associated with HS (20 females, mean age: 36 years, 19 left HS) and 33 adult controls matched for age and gender underwent ¹⁸F-Fluorodeoxyglucose positron emission tomography (FDG-PET). Right-HS patients' FDG-PET data were flipped to obtain a left–epileptic–focus–lateralized group of patients. Voxels of interest (VOI) were selected within the cytoarchitectonic probabilistic maps of the non-epileptic AHC (probability level  = 100%, SPM8 Anatomy toolbox v1.7). Patients and controls were compared using VOI metabolic activity as covariate of interest to search for epilepsy-induced changes in the contribution of the non-epileptic AHC to the level of metabolic activity in other brain areas. Age, gender, duration of epilepsy, seizure type and frequency were used as covariates of no-interest for connectivity analyses.

Key findings

Significant decrease in effective connectivity was found between the non-epileptic AHC and ventral prefrontal cortical areas bilaterally, as well as with the temporal pole and the posterior cingulate cortex contralateral to HS. Significant increase in connectivity was found between the non-epileptic AHC and midline structures, such as the anterior cingulate and dorsal medial prefrontal cortices, as well as the temporo-parietal junction bilaterally. Connectivity analyses also revealed a preserved positive connectivity between the non-epileptic and the epileptic AHC in the patients' group.

Significance

This study evidences epilepsy-induced changes in connectivity between the non-epileptic AHC and some limbic and default mode network areas. These changes in connectivity probably account for emotional, cognitive and decision-making impairments frequently observed in MTLE patients. The preserved neurometabolic connectivity between the non-epileptic and the epileptic AHC in MTLE patients is pivotal to explain the epilepsy-induced changes found in this study.

Acquired auditory agnosia in childhood and normal sleep electroencephalography subsequently diagnosed as Landau-Kleffner syndrome: a report of three cases

AIM

  We report three cases of Landau-Kleffner syndrome (LKS) in children (two females, one male) in whom diagnosis was delayed because the sleep electroencephalography (EEG) was initially normal.

METHOD

  Case histories including EEG, positron emission tomography findings, and long-term outcome were reviewed.

RESULTS

  Auditory agnosia occurred between the age of 2 years and 3 years 6 months, after a period of normal language development. Initial awake and sleep EEG, recorded weeks to months after the onset of language regression, during a nap period in two cases and during a full night of sleep in the third case, was normal. Repeat EEG between 2 months and 2 years later showed epileptiform discharges during wakefulness and strongly activated by sleep, with a pattern of continuous spike-waves during slow-wave sleep in two patients. Patients were diagnosed with LKS and treated with various antiepileptic regimens, including corticosteroids. One patient in whom EEG became normal on hydrocortisone is making significant recovery. The other two patients did not exhibit a sustained response to treatment and remained severely impaired.

INTERPRETATION

  Sleep EEG may be normal in the early phase of acquired auditory agnosia. EEG should be repeated frequently in individuals in whom a firm clinical diagnosis is made to facilitate early treatment.

The impact of positron emission tomography imaging on the clinical management of patients with epilepsy

Clinical positron emission tomography (PET) imaging of human epilepsy has a 30-year history, but it is still searching for its exact role among rapidly advancing neuroimaging techniques. The vast majority of epilepsy PET studies used this technique to improve detection of epileptic foci for surgical resection. Here, we review the main trends emerging from three decades of PET research in epilepsy, with a particular emphasis on how PET imaging has impacted on the clinical management of patients with intractable epilepsy. While reviewing the latest studies, we also present an argument for a changing role of PET and molecular imaging in the future, with an increasing focus on epileptogenesis and newly discovered molecular mechanisms of epilepsy. These new applications will be facilitated by technological advances, such as the use of integrated PET/MRI systems and utilization of novel radiotracers, which may also enhance phenotype-genotype correlations and assist rational, individualized treatment strategies.

Epileptic encephalopathy with continuous spike-waves during slow-wave sleep including Landau-Kleffner syndrome

Epileptic encephalopathy with continuous spike-waves during slow-wave sleep (CSWS) is a spectrum of epileptic conditions best defined by the association of cognitive or behavioral impairment acquired during childhood and not related to another factor other than the presence of abundant interictal epileptiform discharges (IED) during sleep, which tend to diffuse over the whole scalp. It is part of the childhood focal epileptic syndromes, some cases being idiopathic and overlapping with benign rolandic epilepsy, and others being symptomatic of a structural brain lesion. Landau-Kleffner syndrome (LKS) is a particular presentation where acquired aphasia is the core symptom. Clinical, neurophysiological, and cerebral glucose metabolism data support the hypothesis that IED play a prominent role in the cognitive deficits by interfering with the neuronal networks at the site of the epileptic foci but also at distant connected areas. Therefore, the treatment should aim to suppress IED. This may be achieved using conventional antiepileptic drugs, but corticosteroids seem to have more pronounced and sustained efficacy. Outcome for epilepsy is usually good, CSWS being an age-dependent EEG pattern, whereas outcome for cognition, language, and behavior is variable. Rehabilitation represents an important part of the treatment and visual forms of language should be encouraged in children with LKS.

Increased brain metabolism after acute administration of the synthetic cannabinoid HU210: a small animal PET imaging study with 18F-FDG

Cannabis use has been shown to alter brain metabolism in both rat models and humans although the observations between both species are conflicting. In the present study, we examined the short term effects of a single-dose injection of the synthetic cannabinoid agonist HU210 on glucose metabolism in the rat brain using small animal (18)F-2-fluoro-deoxyglucose (FDG) Positron Emission Tomography (PET) 15 min (Day 1) and 24h (Day 2) post-injection of the agonist in the same animal. Young adult male Wistar rats received an intra-peritoneal injection of HU210 (100 μg/kg, n=7) or vehicle (n=5) on Day 1. Approximately 1mCi of (18)F-FDG was injected intravenously into each animal at 15 min (Day 1) and 24h (Day 2) post-injection of HU210. A 5-min Computer Tomography (CT) scan followed by a 20-min PET scan was performed 40 min after each (18)F-FDG injection. Standardised Uptake Values (SUVs) were calculated for 10 brain regions of interest (ROIs). Global increased SUVs in the whole brain, hence global brain metabolism, were observed following HU210 treatment on Day 1 compared to the controls (21%, P<0.0001), but not in individual brain regions. On Day 2, however, no statistically significant differences were observed between the treated and control groups. At the 24h time point (Day 2), SUVs in the HU210 treated group returned to control levels (21-30% decrease compared to Day 1), in all ROIs investigated (P<0.0001). In the control group, SUVs did not differ between the two acquisition days in all brain regions. The present results suggest that high-dose HU210 increases brain glucose metabolism in the rat brain shortly after administration, in line with normalised human in vivo studies, an effect that was no longer apparent 24 h later.

Preictal and ictal neurovascular and metabolic coupling surrounding a seizure focus

Epileptic events initiate a large focal increase in metabolism and cerebral blood flow (CBF) to the ictal focus. In contrast, decreases in CBF have been demonstrated surrounding the focus, the etiology of which is unknown (i.e., arising either from active shunting of blood or passive steal). The relationship between these events and neuronal activity and metabolism are also unknown. We investigated neurovascular and neurometabolic coupling in the ictal surround using optical imaging of light scattering and cerebral blood volume, autofluorescence flavoprotein imaging (AFI), direct measurements of the cortical metabolic rate of oxygen and two-photon imaging of blood vessel diameter in a rat model of ictal events elicited with focal injection of 4-aminopyridine. We discovered a novel phenomenon, in which ictal events are preceded by preictal vasoconstriction of blood vessels in the surround, occurring 1-5 s before seizure onset, which may serve to actively shunt oxygenated blood to the imminently hypermetabolic focus or may be due to small local decreases in metabolism in the surround. Early ictal hypometabolism, transient decreases in cell swelling and cerebral blood volume in the surround are consistent with early ictal surround inhibition as a precipitating event in seizure onset as well as shaping the evolving propagating ictal wavefront, although the exact mechanism of these cerebrovascular and metabolic changes is currently unknown. AFI was extremely sensitive to the ictal onset zone and may be a useful mapping technique with clinical applications.

Epilepsy duration impacts on brain glucose metabolism in temporal lobe epilepsy: results of voxel-based mapping

OBJECTIVE

[(18)F]Fluorodeoxyglucose positron emission tomography ([(18)F]FDG-PET) is a valuable method for detecting focal brain dysfunction associated with epilepsy. Evidence suggests that a progressive decrease in [(18)F]FDG uptake occurs in the epileptogenic cortex with an increase in the duration of epilepsy. In this study, our aim was to use statistical parametric mapping (SPM) to test the validity of this relationship in a retrospective study of patients with temporal lobe epilepsy (TLE).

METHODS

[(18)F]FDG-PET scans of 46 adult patients with pharmacoresistant unilateral TLE (25 RTLE and 21 LTLE) were subjected to SPM analysis.

RESULTS

Forty-six patients were diagnosed with nonlesional TLE, 16 of whom had hippocampal sclerosis (HS). The average duration of epilepsy was 17.4 +/- 12.3 years (3-46 years), <5 years in 10 patients and >or=10 years in 30 patients. Visual analysis of [(18)F]FDG-PET scans revealed hypometabolism in the epileptogenic temporal cortex in 31 (67%) patients. After SPM analysis of all [(18)F]FDG-PET images, hypometabolism was unilateral and reported in lateral and mesial structures of the epileptogenic temporal cortex in addition to the ipsilateral fusiform and middle occipital gyrus. Subsequent analysis revealed that temporal lobe hypometabolism was present only in patients with longer epilepsy duration (>or=10 years) in parahippocampal gyrus, uncus, and middle and superior temporal gyrus (P < 0.05 corrected). Epilepsy duration was inversely correlated with decreased glucose uptake in the inferior temporal gyrus, hippocampus, and parahippocampal gyrus of the epileptogenic temporal cortex (P < 0.05). Age at seizure onset did not affect the correlation between epilepsy duration and glucose uptake except in the inferior temporal gyrus (P < 0.05).

CONCLUSION

Voxel-based mapping supports the assertion that glucose hypometabolism of the epileptogenic temporal lobe cortex and other neighboring cortical regions increases with longer epilepsy duration in TLE.

Quantitative brain surface mapping of an electrophysiologic/metabolic mismatch in human neocortical epilepsy

The spatial relationship between an intracranial EEG-defined epileptic focus and cortical hypometabolism on glucose PET has not been precisely described. In order to quantitatively evaluate the hypothesis that ictal seizure onset and/or rapid seizure propagation, detected by subdural EEG monitoring, commonly involves normometabolic cortex adjacent to hypometabolic cortical regions, we applied a novel, landmark-constrained conformal mapping approach in 14 children with refractory neocortical epilepsy. The 3D brain surface was parcellated into finite cortical elements (FCEs), and hypometabolism was defined using lobe- and side-specific asymmetry indices derived from normal adult controls. The severity and location of hypometabolic areas vs. ictal intracranial EEG abnormalities were compared on the 3D brain surface. Hypometabolism was more severe in the seizure onset zone than in cortical areas covered by non-onset electrodes. However, similar proportions of the onset electrodes were located over and adjacent to (within 2 cm) hypometabolic regions (46% vs. 41%, respectively), whereas rapid seizure spread electrodes preferred these "adjacent areas" rather than the hypometabolic area itself (51% vs. 22%). On average, 58% of the hypometabolic regions had no early seizure involvement. These findings strongly support that the seizure onset zone often extends from hypometabolic to adjacent normometabolic cortex, while large portions of hypometabolic cortex are not involved in seizure onset or early propagation. The clinical utility of FDG PET in guiding subdural electrode placement in neocortical epilepsy could be greatly enhanced by extending grid coverage to at least 2 cm beyond hypometabolic cortex, when feasible.

Metabolic evidence for remote inhibition in epilepsies with continuous spike-waves during sleep

Epileptic syndromes with continuous spikes and waves during sleep (CSWS) are characterized by an acute phase with the emergence of psychomotor deficits and CSWS activity and by a recovery phase in which patients' clinical condition improves together with the remission of CSWS activity. The pathophysiological mechanisms of how CSWS activity induces psychomotor regression are still poorly understood. PET studies using [18F]-fluorodeoxyglucose (FDG) were performed in 9 children during acute and recovery phases of CSWS. PET data were analyzed at individual and group levels using statistical parametric mapping via subtractive, exclusive masking and variance analyses. Pathophysiological interaction analyses were conducted to determine the evolution of changes in effective connectivity between hypermetabolic and hypometabolic brain areas. At the individual level, CSWS recovery was characterized by a complete or almost complete regression of both hypermetabolic and hypometabolic abnormalities observed during the acute phase. Similar evolution was observed at the group level. Indeed, altered effective connectivity between focal hypermetabolism (centro-parietal regions and right fusiform gyrus) and widespread hypometabolism (prefrontal and orbitofrontal cortices, temporal lobes, left parietal cortex, precuneus and cerebellum) was found at the acute phase and markedly regressed at recovery. This study shows that the neurophysiological effects of CSWS activity are not restricted to the epileptic foci but spread via the inhibition of remote neurons within connected brain areas. The present study suggests that these reversible remote effects participate to the psychomotor repercussions of CSWS activity.

Hyperbaric oxygen treatment attenuated the decrease in regional glucose metabolism of rats subjected to focal cerebral ischemia: A high resolution positron emission tomography study

Cerebral hypoxia may be the main component of cell damage caused by ischemia. Previous studies demonstrated a neuroprotective effect of early hyperbaric oxygen (HBO) treatment in various animal models of focal cerebral ischemia. Neuropathologic study showed that exposure of HBO may prevent cell death in ischemic cortex. In the present study, we aimed to assess cellular function of ischemic rat brain after HBO treatment by means of a high-resolution positron emission tomography scanner (microPET) used specifically for small animal imaging. The male Sprague-Dawley rats were subjected to permanent middle cerebral artery occlusion (MCAO), with the regional cerebral blood flow monitored in vivo by laser Doppler flowmetry. One hour after ischemia, HBO therapy (3 atm absolute, 1 h) was initiated. Local cerebral glucose utilization in the ischemic area was measured before, 1 h and 3 h after ischemia, with 2-[(18)F]-fluoro-2-deoxy-d-glucose (FDG) as a tracer. Neurological deficits and infarct volumes were assessed at 24 h after ischemia. Our study showed that early HBO therapy significantly reduced infarct volume of brain 24 h after ischemia. Moreover, glucose utilization in the ischemic area underwent a severe decrease during 1-3 h after MCAO, while the early HBO treatment significantly attenuated the decrease in cerebral metabolic rate of glucose in the ischemic core of the cortex compared with controls. We report for the first time the application of microPET to quantify the rates of glucose metabolism in the ischemic core of rats exposed to HBO. Our results suggest that the early exposure of HBO can partially reverse the downward trend for glucose utilization in the ischemic core, which might contribute to the reported beneficial effects of early HBO therapy on permanent cerebral ischemia.

Congenital perisylvian syndrome: MRI and glucose PET correlations

Congenital perisylvian syndromes are late migration/cortical organization disorders associated with distinctive clinical and imaging features. The clinical, magnetic resonance imaging, and 2-deoxy-2-[18F] fluoro-D-glucose (FDG) positron emission tomography scan findings of six children (age range: 3.2-16.7 years; 5 males) with congenital perisylvian syndrome were evaluated. The patients presented with heterogenous neurologic impairments, depending upon the involved hemisphere and the extension of perisylvian malformation. Two manifested bilateral malformation and four manifested unilateral. The characteristic MRI finding consisting of a vertically oriented sylvian fissure continuous with the central and postcentral sulcus was associated with variable extension of bordering polymicrogyric cortex. The positron emission tomography scans of all patients revealed perisylvian metabolic abnormalities corresponding to the magnetic resonance imaging-defined abnormality. Variable extent of abnormal glucose metabolism was also observed in areas with normal magnetic resonance imaging features. All patients with unilateral magnetic resonance imaging abnormality exhibited abnormal glucose metabolism also in the contralateral side. The two patients with bilateral malformation had more extensive positron emission tomography abnormalities than the morphologic anomalies on MRI. Although MRI remains the diagnostic gold standard to detect the lesion, positron emission tomography scan is helpful to evaluate the full functional extension of the cortical anomaly, thereby contributing to the definition of the clinical severity of the syndrome.

Relationship between brain glucose metabolism positron emission tomography (PET) and electroencephalography (EEG) in children with continuous spike-and-wave activity during slow-wave sleep

We studied the relationship between brain glucose metabolism patterns and objectively measured interictal epileptiform abnormalities in six children with intractable epilepsy and continuous spike-and-wave activity during slow-wave sleep. Five of the six patients showed lateralized positron emission tomographic (PET) findings, with the hemisphere showing a relative increase in glucose metabolism concordant with the presumed origin of the generalized interictal spike activity delineated by quantitative electroencephalographic (EEG) analysis. One of these five patients achieved seizure freedom following cortical resection involving the areas of unilateral multifocal hypermetabolism, and another patient has been approved for cortical resection. The results in the present study add further support to the hypothesis that the generalized spike-waves in most cases of continuous spike-and-wave activity during slow-wave sleep are the result of secondary bilateral synchrony. Resective surgery can be effective in selected patients with uncontrolled seizures associated with continuous spike-and-wave activity during slow-wave sleep provided that there is concordance between focal abnormalities on PET and EEG.

Metabolic correlates of lesion-specific plasticity: an in vivo imaging study

High-resolution positron emission tomography (microPET) allows for repeated observations of brain function in the same animal. In a previous study, using [(18)F] fluorodeoxyglucose (FDG) microPET, we demonstrated diminished glucose metabolism and subsequent recovery in the Neostriatum and thalamus ipsilateral to cortical aspiration (ASP) lesions. Thermocoagulation (TCL) of pial vessels has been shown to result in the same degree of cortical injury but induce more compensatory re-organization than ASP. In the present work, FDG microPET was used to compare glucose metabolism following both TCL and ASP lesions in order to determine whether metabolic differences correlate with the previously described anatomical and functional changes in the two lesion models. Animals were scanned 3-day, 10-day and 1-month post-injury. Estimated cortical lesion size did not differ between the two models at 1 month following injury. Both lesions induced ipsilateral neostriatal and thalamic hypometabolism 3-day post-injury, with subsequent metabolic improvement over time. However, complete recovery was not observed by 1 month in either group. ASP lesions resulted in an overall greater metabolic deficit in the subcortical structures and a greater cortical deficit 1 month following injury when compared to the TCL. Contralateral cortical glucose metabolism at 3 days following injury was not different in the two lesions. These data demonstrate that the two lesions differ somewhat in their metabolic response to injury, and that the relative hypometabolism observed following ASP may be a reflection of the diminished capacity of the contralateral cortex to compensate for ASP as compared to TCL.

Gender-specific Differences of Hypometabolism in mTLE: Implication for Cognitive Impairments

PURPOSE

To determine gender differences of hypometabolism and their implications for cognitive impairment in patients with medically refractory mesial temporal lobe epilepsy (mTLE).

METHODS

Regional cerebral glucose metabolism (rCMRGlu) was studied in 42 patients (21 male, 21 female) with either left- or right-sided mTLE (22 left, 20 right) and in 12 gender- and age-matched healthy controls during resting wakefulness and in 12 sex- and age-matched healthy controls. Clinical characteristics were balanced across the patient subgroups. All patients were subjected to neuropsychological assessment: 41 patients had histologic changes of definite or probable hippocampal sclerosis.

RESULTS

Data analysis based on pixel-by-pixel comparisons and on a laterality index of regions of interest (ROIs) showed significant depressions of the mean rCMRGlu extending beyond the mesiotemporal region and temporolateral cortex to extratemporal regions including the frontoorbital and insular cortex in mTLE patients. Extramesiotemporal hypometabolism prevailed in the male patients. Metabolic asymmetry in temporal and frontal regions was related to performance in the Trail-Making Test and WAIS-R subitems.

CONCLUSIONS

Our data showed a gender-specific predominance of extramesiotemporal hypometabolism in male patients with mTLE related to abnormalities of temporal and frontal lobe functions.

Pathophysiology and functional consequences of human partial epilepsy: lessons from positron emission tomography studies

Positron emission tomography (PET) is a powerful clinical and research tool that, in the past two decades, has provided a great amount of novel data on the pathophysiology and functional consequences of human epilepsy. PET studies revealed cortical and subcortical brain dysfunction of a widespread brain circuitry, providing an unprecedented insight in the complex functional abnormalities of the epileptic brain. Correlation of metabolic and neuroreceptor PET abnormalities with electroclinical variables helped identify parts of this circuitry, some of which are directly related to primary epileptogenesis, while others, adjacent to or remote from the primary epileptic focus, may be secondary to longstanding epilepsy. PET studies have also provided detailed data on the functional anatomy of cognitive and behavioral abnormalities associated with epilepsy. PET, along with other neuroimaging modalities, can measure longitudinal changes in brain function attributed to chronic seizures as well as therapeutic interventions. This review demonstrates how development of more specific PET tracers and application of multimodality imaging by combining structural and functional neuroimaging with electrophysiological data can further improve our understanding of human partial epilepsy, and helps more effective application of PET in presurgical evaluation of patients with intractable seizures.

Metabolic and electrophysiological alterations in an animal model of neocortical neuronal migration disorder

Cortical migration disorders are a major cause for intractable epilepsy syndromes. High resolution MRI and PET are increasingly capable to identify cortical dysgenesis. In this study we used the rat freeze lesion model to investigate cortical morphological and functional changes in adult rats after induction of a cortical freeze lesion at postnatal day (p) 0. Autoradiographic measurements of basic cortical [14C]deoxyglucose metabolism showed a significant reduction up to 1 mm lateral to the lesion but no remote changes. Electrophysiological in vitro recordings revealed a significant reduction in the amplitude of stimulus-evoked field potential responses recorded lateral to the lesion as compared to medial recording sites. Our data provide further evidence that spatially restricted developmental alterations of cortical morphology cause functional changes in surrounding and histologically normal areas that need to be considered for a better understanding of the resulting pathophysiology.

Interictal spikes in focal epileptogenesis

Interictal electroencephalography (EEG) potentials in focal epilepsies are sustained by synchronous paroxysmal membrane depolarization generated by assemblies of hyperexcitable neurons. It is currently believed that interictal spiking sets a condition that preludes to the onset of an ictal discharge. Such an assumption is based on little experimental evidence. Human pre-surgical studies and recordings in chronic and acute models of focal epilepsy showed that: (i) interictal spikes (IS) and ictal discharges are generated by different populations of neuron through different cellular and network mechanisms; (ii) the cortical region that generates IS (irritative area) does not coincide with the ictal-onset area; (iii) IS frequency does not increase before a seizure and is enhanced just after an ictal event; (iv) spike suppression is found to herald ictal discharges; and (v) enhancement of interictal spiking suppresses ictal events. Several experimental evidences indicate that the highly synchronous cellular discharge associated with an IS is generated by a multitude of mechanisms involving synaptic and non-synaptic communication between neurons. The synchronized neuronal discharge associated with a single IS induces and is followed by a profound and prolonged refractory period sustained by inhibitory potentials and by activity-dependent changes in the ionic composition of the extracellular space. Post-spike depression may be responsible for pacing interictal spiking periodicity commonly observed in both animal models and human focal epilepsies. It is proposed that the strong after-inhibition produced by IS protects against the occurrence of ictal discharges by maintaining a low level of excitation in a general condition of hyperexcitability determined by the primary epileptogenic dysfunction.

Intact functional inhibition in the surround of experimentally induced focal cortical dysplasias in rats

Early postnatal injections of ibotenate into the rat neopallium induce cortical dysplasias mimicking human polymicrogyria which often goes along with seizure disorders. Under in vitro conditions these experimentally induced dysplasias cause widespread hyperexcitability. The underlying mechanisms are as yet not fully understood. Electrophysiologically there is clear evidence of widespread alterations of the excitatory system. Intracellular recordings also showed some changes of the inhibitory system but have concentrated on recordings from focal areas close to the microgyrus. We investigated the integrity of functional inhibition using a paired-pulse paradigm to map the whole ipsilateral hemisphere. In rat cortical slices double-pulses were applied in layer VI/white matter and field potentials recorded in layer II/III. The ratio of the field potential amplitude did not show significant alterations in the dysplasias or their surround as compared with control and sham-injected animals. This result was obtained with two different locations of the dysplasias, excluding a mere areal specific effect. Our results show that despite prominent hyperexcitability in the surround of ibotenate-induced cortical dysplasias the inhibitory network appears to be functionally intact.

In vivo imaging of neuronal activation and plasticity in the rat brain by high resolution positron emission tomography (microPET)

The study of neural repair and neuroplasticity in rodents would be enhanced by the ability to assess neuronal function in vivo. Positron emission tomography (PET) is used to study brain plasticity in humans, but the limited resolution and sensitivity of conventional scanners have generally precluded the use of PET to study neuroplasticity in rodents. We now demonstrate that microPET, a PET scanner developed for use with small animals, can be used to assess metabolic activity in different regions of the conscious rodent brain using [18F]fluorodeoxyglucose (FDG) as the tracer, and to monitor changes in neuronal activity. Limbic seizures result in dramatically elevated metabolic activity in the hippocampus, whereas vibrissal stimulation results in more modest increases in FDG uptake in the contralateral neocortex. We also show that microPET can be used to study lesion-induced plasticity of the brain. Cerebral hemidecortication resulted in diminished relative glucose metabolism in the neostriatum and thalamus ipsilateral to the lesion, with subsequent, significant recovery of metabolic function. These studies demonstrate that microPET can be used for serial assessment of metabolic function of individual, awake rats with a minimal degree of invasiveness, and therefore, has the potential for use in the study of brain disorders and repair.

Hemodynamic and metabolic aspects of photosensitive epilepsy revealed by functional magnetic resonance imaging and magnetic resonance spectroscopy

PURPOSE

To study in humans the hemodynamic and metabolic consequences of both photic stimulation-triggered and spontaneous generalized epileptiform discharges.

METHODS

Simultaneous EEG, functional magnetic resonance imaging (fMRI) and MR spectroscopy were performed in a 1.5-T scanner in 16 patients with generalized epilepsy, including nine with photosensitive epilepsy, and 12 normal subjects.

RESULTS

With a flash stimulation duration of 2 s, prominent visual cortex activation was seen in all normals and patients. There were no fMRI-registered hemodynamic abnormalities found in relation to the brief photoparoxysmal spike-wave activity evoked in the photosensitive patients. However, irrespective of the presence of a spike-wave response to the photic stimulation, the photosensitive patients showed four unique findings compared with normals: (a) slightly, but significantly, increased lactate levels in the occipital cortex in the resting state, (b) an increased area of visual cortical activation with photic stimulation, (c) simultaneous with the occipital cortex stimulus-induced increased fMRI signal there were noncontiguous areas of signal attenuation most prominent in perirolandic regions, and (d) a marked decrement (undershoot) of fMRI signal intensity immediately after the photic stimulation in the occipital cortex and in the region of the posterior cingulate gyrus.

CONCLUSIONS

These findings suggest abnormal interictal metabolism and increased vascular reactivity in the photosensitive patients.

Effects of tetanus toxin on functional inhibition after injection in separate cortical areas in rat

Tetanus Toxin is widely used as a model of chronic focal epilepsy and is assumed to act by blocking neurotransmitter release with high selectivity for inhibitory synapses. However, the exact mechanisms are not fully understood, since, e.g., GABA release is only temporarily decreased although epileptiform activity persists pointing towards a change in the interplay of excitation and inhibition. Furthermore there have been reports about different effects of tetanus toxin after injection in separate brain areas. Therefore, we investigated the functional inhibition after injecting tetanus toxin either in the motor or sensory cortex of adult rats by using a paired-pulse paradigm as a measure of excitatory and inhibitory drive. Tetanus toxin injection into the motor cortex (n=10) induced a marked, long-lasting reduction in inhibition which was highly significant in most parts of the injected cortical area. Injections into the sensory cortex, however, showed less marked changes in inhibition which were more widespread and significant only in 3 of 14 animals injected. These results give further evidence for a prominent effect of tetanus toxin on functional inhibition and strengthen the idea of a differential effect in separate cortical areas. They may be accounted for by the different cytoarchitecture of cortical areas with variable inhibitory and excitatory intracortical connections.

Bilateral decrease in interictal hippocampal blood flow in unilateral mesiotemporal epilepsy

OBJECT

The goal of this study was to determine whether regional cerebral blood flow (rCBF) changes that were found contralaterally to a verified unilateral epileptic focus were associated with the spatiotemporal organization of epileptic abnormalities.

METHODS

The CBF in both hippocampi was assessed using stable Xe-enhanced computerized tomography in a series of 19 patients with unilateral mesiotemporal epilepsy. Results were compared according to the distribution of interictal spiking and the spatiotemporal organization of the ictal discharges as determined by stereoelectroencephalography. Two groups were defined: in Group 1 (nine patients), the discharge remained unilateral; in Group 2 (10 patients), the discharge spread to contralateral mesiotemporal structures. For Group 1, the rates of ipsi- and contralateral hippocampal blood flow (HBF) were 32.88+/-15.53 and 45.88+/-17.19 ml/100 g/minute, respectively, whereas in Group 2 they were 36.7+/-11.54 and 36.4+/-11.27 ml/100 g/minute (mean+/-standard deviation). A two-way analysis of variance combining type of seizure (Group 1 compared with Group 2) and HBF (ipsi- compared with contralateral absolute values) demonstrated a main effect for HBF (F[1,17] = 5.051; p = 0.0382), a significant interaction between the two factors (F[1,17] = 6.188; p = 0.0235), and no main effect for type of seizure (F[1,17] = 0.258; p = 0.6178).

CONCLUSIONS

In unilateral mesiotemporal epilepsy, asymmetrical interictal hippocampal perfusion was correlated with restricted unilateral ictal discharges, whereas bilateral hippocampal hypoperfusion was correlated with ictal discharges spreading to the contralateral mesiotemporal structures. The lack of correlation between the degree of hypoperfusion and the percentage of neuron cell loss indicated that the decrease in rCBF has both functional and lesional origins.

Enlargement of cortical vibrissa representation in the surround of an ischemic cortical lesion

It has been shown that cortical lesions are associated with an increase of excitability in surrounding brain regions, and with a downregulation of GABA(A) receptors. In the present study we investigated whether this increased excitability affects the cortical map of inputs represented in areas surrounding the lesioned brain area. Focal lesions with a diameter of 2-2.5 mm were induced photochemically in the hindlimb area at the border of the primary somatosensory cortex of the rat. One week after lesioning, the cortical representation of the B3 vibrissa was studied using 14C-deoxyglucose (DG) autoradiography. In all animals mechanical stimulation of the B3 vibrissa produced a column-shaped DG-labeling in the somatosensory cortex, corresponding to the B3-barrel with a maximum of the glucose uptake in layer IV. In control animals without cortical lesions (n=6), stimulation increased the glucose uptake rate by 50.8+/-10.5% in layer IV. In lesioned animals (n=6) maximum DG-uptake in layer IV (54.8+/-8.6%) did not differ significantly from that in controls. However, as compared to control animals, lesioned animals showed also increased glucose uptake within the activated column in layers II/II (51.+/-11.1%, lesioned animals; 31.8+/-11.2%, controls; P<0.05, lesioned vs. control) and V (47.5+/-5.8%, lesioned animals, 28.8+/-10.5%, controls; P<0.05, lesioned vs. control). The diameter of the metabolically activated B3-barrel area of layer IV was expanded from 461.8+/-77.6 microm in control animals to 785.5+/-103.6 microm; P<0.01) in lesioned animals. Lesioned animals also showed expansion of the activated area in layers II/III (890.4+/-134.8 microm, lesioned animals; 430.6+/-95.1 microm, controls; P<0.01) and layer V (1117.5+/-163.6 microm, lesioned animals; 648.7+/-114.1 microm, controls; P<0.01). The depth profile of the activation columns showed a maximum in layer IV in control animals, which was expanded towards layers II/III and layer V in lesioned animals. It is concluded that cortical lesions alter the representational area of neighboring afferent inputs through disinhibition or 'unmasking' of pre-existing silent or ineffectual intracortical synapses. The present observations raise the possibility that the brain supports recovery from lesions by decreasing GABAergic inhibition, thereby facilitating a remapping of the cortical representation in neighboring brain areas.

Cerebral hemodynamic response to generalized spike-wave discharges

PURPOSE

Data in the literature concerning metabolic demand during generalized spike-wave activity (gSW) are conflicting. We investigated instantaneous changes in cerebral blood flow velocities (CBFV) in both middle cerebral arteries (MCAs) by transcranial Doppler sonography (TCD) during gSW paroxysms recorded by scalp EEG.

METHODS

In 13 patients, CBFVs in both MCAs were averaged, time-locked to the occurrence of the gSW; respiratory rate (RR) and end-expiratory pco2 were measured in one patient.

RESULTS

Nine patients showed significant changes in CBFV during gSW. Four had biphasic flow changes with an initial increase (p < 0.05) and a subsequent decrease (p < 0.01). This was partially paralleled by an increase in RR (p < 0.01) and a decrease in pco2 (p < 0.01). In three patients, an increase in CBFV that preceded the onset of gSW by several seconds was observed, followed by a decrease in CBFV. Two patients showed a significant decrease only of CBFV. Only gSWs of a median duration of >0.8 s were associated with significant changes in CBFV.

CONCLUSIONS

We were able to demonstrate that gSWs of several seconds duration lead to cortical perfusion changes. We suggest that the initial increase of CBFV demonstrated in some patients reflects neuronal activation, whereas the subsequent decrease might in part be due to hyperventilation-induced hypocapnia.

Uncoupling of blood flow and metabolism in focal epilepsy

PURPOSE

Interictal measurements of cerebral blood flow are less helpful in localizing epileptic foci than are measurements of brain metabolism. This may be related to an uncoupling of blood flow and metabolism. In this study, brain metabolism and blood flow were compared in an acute experimental model of focal interictal epilepsy.

METHODS

Interictal epileptic foci were induced by an epicortical application of penicillin in rats. After 1 h, stereotyped interictal activity was initiated, lasting until the end of the experiment. Brain metabolism was determined with [14C]deoxyglucose, and cerebral blood flow with [14C]iodoan-tipyrine autoradiography.

RESULTS

In control experiments, metabolism and blood flow were coupled. In animals with focal interictal epileptic activity, the metabolism was strongly increased in the focus and reduced in areas lateral to the focus. In contralateral brain areas, blood flow and metabolism varied in a parallel fashion. Ipsilateral to the focus, however, blood flow and metabolism were altered disproportionately. In the focus, the increase of blood flow was less marked than the increase of metabolism, and the area with increased blood flow was larger than the area with increased metabolism. Lateral to the focus, in the area with a hypometabolism, blood flow was not concomitantly reduced.

CONCLUSIONS

The experiments show that blood flow and metabolism in focal epilepsy may be uncoupled in widespread regions. This is due neither to structural abnormalities nor to the duration or discharge pattern of epileptic activity. The results explain why interictal metabolic investigations have a higher predictive value in presurgical epilepsy evaluation than do interictal measurements of blood flow.

Thalamocortical circuits causing remote hypometabolism during focal interictal epilepsy

The functional circuit causing depression of cerebral glucose metabolism in brain areas remote from an epileptic focus was investigated in experiments on the cortex of the rat. Epileptic activity was induced by direct epicortical application of Na-penicillin onto the motor cortical area Fr1/Fr2. The increased neuronal activity was associated with an increase of metabolism in the focal area and a decrease in somatosensory cortical areas. Metabolism was also massively increased in the thalamus, predominantly in the posterior nucleus. Stereotactic radiofrequency lesioning of this nucleus, 30 days prior to the induction of the epileptic focus, restricted the area with increase of metabolism to the upper cortical laminae, and abolished the cortical hypometabolism in the sensory cortex. It is suggested that the primary functional circuit affected by the acute epileptic focus in the present model consists of the motor cortex, the thalamic nucleus posterior and the somatosensory cortex.

Modification of activity-dependent increases of cerebral blood flow by excitatory synaptic activity and spikes in rat cerebellar cortex

1. Mechanisms of activity-dependent increases in cerebral blood flow (CBF) were examined in rat cerebellar cortex using the laser Doppler flow technique and extracellular recordings of single unit activity and field potentials. 2. Stimulation of the monosynaptic climbing fibre system evoked long-lasting complex spikes in Purkinje cells, and extracellular field potentials with a characteristic profile that indicated contributions from both passive and active membrane mechanisms. The concomitant CBF increases were reproducible at fairly short intervals, and suggest that both synaptic activity and spikes may contribute to increased CBF. 3. Stimulation of the disynaptic parallel fibre system inhibited the spiking activity in Purkinje cells, while the postsynaptic activity increased as indicated by the simultaneously recorded field potential. Nevertheless, CBF always increased. The inhibition of spike firing activity was partly dependent on GABAergic transmission, but may also relate to the intrinsic membrane properties of Purkinje cells. 4. The CBF increases evoked by parallel or climbing fibre stimulation were highly correlated to the sum of neural activities, i.e. the negativity of field potentials multiplied by the stimulus frequency. This suggests a robust link between extracellular current flow and activity-dependent increases in CBF. 5. AMPA receptor blockade attenuated CBF increases and field potential amplitudes, while NMDA receptor antagonism did not. This is consistent with the idea that the CBF responses are of neuronal origin. 6. This study has shown that activity-dependent CBF increases evoked by stimulation of cerebellar parallel fibres are dependent on synaptic excitation, including excitation of inhibitory interneurones, whereas the net activity of Purkinje cells, the principal neurones of the cerebellar cortex, is unimportant for the vascular response. For the climbing fibre system, not only synaptic activity but also the generation of complex spikes from Purkinje cells contribute to the increases in CBF. The strong correlation between CBF and field potential amplitudes suggests that extracellular ion fluxes contribute to the coupling of brain activity to blood flow.

Brain hypometabolism in a model of chronic focal epilepsy in rat neocortex

PURPOSE

Metabolic mapping of the human brain has become a widely used method for identifying and localizing epileptic foci. A reduction of glucose consumption usually is found interictally in the area of the focus. By contrast, animal models of acute epilepsy show a hypermetabolism in the epileptic focus. Here we investigated how metabolism is altered in an animal model of chronic epilepsy caused by focal injection of tetanus toxin into rat neocortex.

METHODS

A total of 27 male Wistar rats were anesthetized and injected into the motor or sensory cortex either with dissolved tetanus toxin or with the solvent only. Animals recovered for 7, 14, or 30 days and then were anesthetized again for quantitative 14C-deoxyglucose autoradiography. Data were analyzed with an imaging program, and regional cerebral glucose metabolism (rCMRGlc) was determined.

RESULTS

Injection of tetanus toxin into the motor cortex caused a focal hypometabolism which was confined to the cytoarchitectonic boundaries of the injected area, whereas sensory cortex injection caused a more widespread hypometabolism in all sensory cortical and connected, areas. None of the animals displayed focal hypermetabolism and we observed no significant time-dependent alteration of brain metabolism.

CONCLUSIONS

Tetanus toxin injection into the cortex of the rat induces chronic epileptic activity accompanied by a focal hypometabolism. The data suggest that the spread of the metabolic alterations depends on the connectivity of the injected cortical area.

The fundamental neural mechanisms of electroencephalography

We are at an interesting time in the evolution of the EEG. Studies are opening the door to understanding the intrinsic neuronal properties and network operations responsible for the generation of EEG oscillations. I will review some of our knowledge regarding the physiology of the normal and abnormal EEG. Both epileptic and non-epileptic activity will be discussed. Less is known about the latter, because of difficulties in developing appropriate models. The major dichotomy for both types of EEG phenomenon will be focal and generalized (or widespread. Certain distinctive abnormal EEG patterns including burst suppression, periodic phenomena and intermittent rhythmic delta will also be addressed.

Cerebral glucose metabolism and centrotemporal spikes

The pathophysiology of regional glucose hypometabolism often associated with refractory, lesion-related, epilepsy is not well understood. In particular, the role of interictal spiking is controversial since animal models of partial epilepsy have shown that interictal spiking increases glucose metabolism. We addressed this question by studying with positron emission tomography (PET) and 18F-fluorodeoxyglucose (FDG) the regional cerebral metabolism in children with focal spiking unrelated to a brain lesion. Patients (11 children with benign childhood epilepsy with centrotemporal spikes (BCECS) and two children without seizures) had on EEG centrotemporal spikes which were either strictly unilateral (ten cases) or strongly predominant on one side (three cases). We looked for an asymmetry in the distribution of cerebral glucose metabolism in our group of patients using statistical parametric mapping (SPM). After spatial normalization, a reversed copy of the 13 scans was obtained, resulting in 26 scans which were assigned to two groups: a group with left-sided centrotemporal spikes and a group with right-sided centrotemporal spikes. Regional glucose metabolism was not statistically different in the two groups. This suggests that metabolic changes associated with interictal spiking cannot be demonstrated by PET with FDG in BCECS, and that this technique could be helpful for the differentiation between idiopathic and symptomatic cases of partial epilepsy in children.

Induction of FOS and JUN proteins during focal epilepsy: congruences with and differences to [14C]deoxyglucose metabolism

fos and jun belong to multigene families coding for transcription factors. These cellular immediate-early genes (IEGs) are thought to be involved in coupling neuronal excitation to changes of target gene expression. Immunocytochemistry with specific antisera was used to assess regional levels of five IEG-encoded proteins (c-FOS, FOS B, c-JUN, JUN B and JUN D) in a rat model of penicillin-induced focal epilepsy. To assess whether brain regions with post-ictal de novo transcription factor synthesis correspond to those areas with increased glucose metabolism, IEG expression patterns were compared with [14C]deoxyglucose autoradiography performed in a subset of animals. The results demonstrated marked induction of c-FOS, FOS B, c-JUN and JUN B but not JUN D in the cortical epileptic focus. Thereby, individual IEG-encoded proteins exhibited differential temporal and spatial expression patterns. Within the epileptic focus, IEG expression correlated with increased glucose metabolism. In contrast, IEG induction was not observed in brain areas distant from the epileptic focus that also demonstrated increased glucose metabolism, such as homotopic contralateral motor cortex and ipsilateral thalamic nuclei. These findings indicate that in focal epilepsy changes of the genetic programme are restricted to neurons of the epileptic focus. In contrast, the increased [14C]deoxyglucose metabolism in contralateral motor cortex and ipsilateral thalamus seems to indicate functional changes.