Mice selected for low and high blood magnesium levels: a new model for stress studies

Extra- and intracellular magnesium levels have previously been shown to be genetically controlled in humans and in the mouse. To further study this genetic regulation, mice were selected from a heterogeneous population, for low (MGL mice) and high (MGH mice) red blood cell (RBC) magnesium values. These values diverged rapidly in the two strains, to reach a stable difference between the 14th and 18th generations. MGL mice also exhibited significantly lower plasma, kidney, and skull bone magnesium contents and higher urinary magnesium excretion and total brain weights. Moreover, in stressful conditions, MGL mice displayed a more aggressive behavior that the control MGH strain. Altogether, MGL mice showed a more restless behavior, a higher rectal temperature, and much higher brain (+17%) and urine (+200%) noradrenaline levels than the MGH animals. These strains, thus, constitute a new animal model for the study of magnesium metabolism and its relationships with catecholamines, stress sensitivity, and aggressive behavior.

Functional neuroanatomy of human slow wave sleep

The distribution of regional cerebral blood flow (rCBF) was estimated during sleep and wakefulness by using H215O positron emission tomography (PET) and statistical parametric mapping. A group analysis on 11 good sleepers (8 with steady slow wave sleep, SWS) showed a significant negative correlation between the occurrence of SWS and rCBF in dorsal pons and mesencephalon, thalami, basal ganglia, basal forebrain/hypothalamus, orbitofrontal cortex, anterior cingulate cortex, precuneus, and, on the right side, in a region that follows the medial aspect of the temporal lobe. Given the known decrease in global cerebral blood flow levels during SWS, these negative correlations suggest that rCBF is decreased significantly more in these cerebral areas than in the rest of the brain. The marked rCBF decreases in the pons, mesencephalon, thalamic nuclei, and basal forebrain reflect their close implication in the generation of SWS rhythms. The influence of these rhythms on the telencephalon usually are thought to be global and homogeneous. In contrast, our results show that rCBF is decreased more in some cortical areas (especially in orbitofrontal cortex) than in the rest of the cortex. We hypothesize that cellular processes taking place during SWS might be modulated differently in these regions. Given the functions of the ventromedial frontal areas, we surmise that SWS might be particularly critical for the adaptation of behavior to environmental pressures. This hypothesis is supported indirectly by results of sleep deprivation experiments.

Anterior cingulate and motor network metabolic impairment in progressive supranuclear palsy

Progressive supranuclear palsy is the prototype of subcortical dementia. Using positron emission tomography and statistical parametric mapping, we compared the glucose metabolic pattern obtained in this subcortical dementia to that observed in elderly healthy controls and in Alzheimer's disease, the prototype of cortical dementia. Progressive supranuclear palsy was characterized by a relative decrease of metabolism in anterior cingulate, adjacent supplementary motor area, precentral cortex, middle prefrontal cortex, midbrain tegmentum, globus pallidus, and ventrolateral and dorsomedial nuclei of thalamus. The data in progressive supranuclear palsy highlight predominant metabolic impairment in brain structures engaged in response selection, in attention for action, and in motor networks.

Is 11C-flumazenil PET superior to 18FDG PET and 123I-iomazenil SPECT in presurgical evaluation of temporal lobe epilepsy?

OBJECTIVE

To determine the contribution of 18FDG PET, 11C-flumazenil PET, and 123I-iomazenil SPECT to the presurgical evaluation of patients with medically intractable complex partial seizures.

METHODS

Presurgical evaluation was performed in 23 patients, who were considered candidates for temporal lobe resective surgery (14 females and nine males with a median age of 34 (range 13 to 50) years). The presurgical diagnosis was based on seizure semiology as demonstrated with ictal video recording, ictal and interictal scalp EEG recordings, and MRI.

RESULTS

Eighteen patients had convergent findings in clinical semiology, interictal and ictal EEG with scalp and sphenoidal electrodes, and MRI that warranted surgery without depth EEG (DEEG). In five patients with insufficient precision of localisation, DEEG with intracerebral and subdural electrodes was performed. MRI showed abnormalities in 22 out of 23 patients. Of these 22, 18 had mesial temporal sclerosis. This was limited to the mesial temporal lobe in four and more widespread in the temporal lobe in 14 patients. In one patient only enlargement of the temporal horn was found and in three others only white matter lesions were detected. 18FDG PET showed a large area of glucose hypometabolism in the epileptogenic temporal lobe, with an extension outside the temporal lobe in 10 of 23 patients. Only in one of these patients DEEG showed extratemporal abnormalities that were concordant with a significant extratemporal extension of hypometabolism in 18FDG PET. 18FDG PET was compared with the results of scalp EEG: in none of the patients was an anterior temporal ictal onset in scalp EEG related to a maximum hypometabolism in the mesial temporal area. By contrast, the region of abnormality indicated by 11C-flumazenil PET was much more restricted, also when compared with DEEG findings. Extension of abnormality outside the lobe of surgery was seen in only two patients with 11C-flumazenil and was less pronounced compared with the intratemporal abnormality. Both 18FDG PET and 11C-flumazenil PET reliably indicated the epileptogenic temporal lobe. Thus these techniques provide valuable support for the presurgical diagnosis, especially in patients with non-lesional MRI or non-lateralising or localising scalp EEG recordings. In those patients in whom phase 1 presurgical evaluation on the basis of classic methods does not allow a localisation of the epileptogenic area, PET studies may provide valuable information for the strategy of the implantation of intracranial electrodes for DEEG. Previous studies have suggested that 11C-flumazenil binding has a closer spatial relationship with the zone of ictal onset than the area of glucose hypometabolism, but this study suggests rather that the decrease in the 11C-flumazenil binding simply reflects a loss of neurons expressing the benzodiazepine-GABA receptor. 11C-flumazenil PET did not prove to be superior to 18FDG PET.

CONCLUSION

In 21 patients sufficient material was obtained at surgery for a pathological examination. In 17 mesial temporal sclerosis, in one an oligodendroglioma grade B, in another a vascular malformation and in two patients no abnormalities were found. Although all 21 patients with pathological abnormality showed hypometabolic zones with 18FDG PET and a decreased uptake in 11C-flumazenil binding, there was no strong correlation between pathological diagnosis and functional abnormal areas in PET. Grading of medial temporal sclerosis according to the Wyler criteria showed no correlation with the degree of hypometabolism in either 18FDG or 11C-flumazenil PET. The interictal 123I-iomazenil SPECT technique was highly inaccurate in localising the lobe of surgery.

Regional brain activity during working memory tasks

The first aim of our PET study was to replicate previous findings concerning the brain areas activated by a verbal working memory task. The second aim was to specify the neural basis of the central executive, using a task of working memory updating. Our data confirm that the lower left supramarginal gyrus and premotor area are the key regions subserving short-term verbal memory processes. They also suggest that the updating memory task is related to middorsolateral prefrontal activation, most probably responsible for the updating function of the central executive. An unexpected, predominantly right activation occurred in the inferior parietal region during the verbal memory updating task, which we related to a visuospatial strategy used to maintain the information in short-term memory. A third purpose was to explore the brain regions activated by a nonverbal, visual memory task, and our results confirm the importance of the superior occipital gyrus in the visual short-term memory.

Functional neuroanatomy of human rapid-eye-movement sleep and dreaming

Rapid-eye-movement (REM) sleep is associated with intense neuronal activity, ocular saccades, muscular atonia and dreaming. The function of REM sleep remains elusive and its neural correlates have not been characterized precisely in man. Here we use positron emission tomography and statistical parametric mapping to study the brain state associated with REM sleep in humans. We report a group study of seven subjects who maintained steady REM sleep during brain scanning and recalled dreams upon awakening. The results show that regional cerebral blood flow is positively correlated with REM sleep in pontine tegmentum, left thalamus, both amygdaloid complexes, anterior cingulate cortex and right parietal operculum. Negative correlations between regional cerebral blood flow and REM sleep are observed bilaterally, in a vast area of dorsolateral prefrontal cortex, in parietal cortex (supramarginal gyrus) as well as in posterior cingulate cortex and precuneus. Given the role of the amygdaloid complexes in the acquisition of emotionally influenced memories, the pattern of activation in the amygdala and the cortical areas provides a biological basis for the processing of some types of memory during REM sleep.

Anterior cingulate dysfunction in presenile dementia due to progressive supranuclear palsy

We report neuropsychological and neuroimaging investigations performed in a patient suffering from presenile onset degenerative dementia and subsequent mild extrapyramidal and pyramidal signs. Early neuropsychological testing revealed frontal lobe dysfunction. Neuroanatomical pictures were not contributive. After four years of evolution, the clinical pattern was consistent with progressive supranuclear palsy. Statistical parametric mapping analysis of functional imaging revealed a highly significant metabolic impairment in the anterior cingulate gyrus, that might be a key feature of subcortico-frontal dementia in progressive supranuclear palsy.

Frontal lobe dementia presenting as personality disorder

The early differential diagnosis of frontal lobe dementia is particularly difficult because changes of personality or behaviour overwhelm intellectual and cognitive impairments. We report the case of a patient presenting with paranoid personality disorder who refused to collaborate in neuropsychological testing. Initial functional imaging showed frontal hypometabolism that served as an early marker of frontal lobe dysfunction.

Combined study of cerebral glucose metabolism and [11C]methionine accumulation in probable Alzheimer's disease using positron emission tomography

There is a characteristic decrease in glucose metabolism in associative frontal and temporo-parietal cortices of patients suffering from Alzheimer's disease (AD). The decrease in metabolism might result from local neuronal loss or from a decrease of synaptic activity. We measured in vivo [11C]methionine accumulation into proteins with positron emission tomography (PET) to assess cortical tissue loss in AD. Both global regional activity and compartmental analysis were used to express [11C]methionine accumulation into brain tissue. Glucose metabolism was measures with [18F]fluorodeoxyglucose and autoradiographic method. Combined studies were performed in 10 patients with probable AD, compared to age-matched healthy volunteers. There was a significant 45% decrease of temporo-parietal glucose metabolism in patients with AD, and frontal metabolism was lowered in most patients. Temporo-parietal metabolism correlated to dementia severity. [11C]methionine incorporation into temporo-parietal and frontal cortices was not significantly decreased in AD. There was no correlation with clinical symptoms. Data suggest that regional tissue loss, assessed by the decrease of [11C]methionine accumulation, is not sufficient to explain cortical glucose hypometabolism, which reflects, rather, reduced synaptic connectivity.

Regional cerebral glucose metabolism in children with deterioration of one or more cognitive functions and continuous spike-and-wave discharges during sleep

The Landau-Kleffner syndrome (LKS) and the syndrome of continuous spike-and-wave discharges during slow sleep (CSWS) were originally described, and are still considered, separately. The former combines an acquired aphasia with spike-and-wave discharges that are activated by slow wave sleep, behavioural disturbances, and sometimes epileptic seizures. The latter is characterized by continuous spike-and-wave discharges during slow wave sleep, usually combined with global intellectual deterioration and epileptic seizures. These two syndromes share many common features: (i) onset during childhood; (ii) deterioration of cognitive functions that were previously normally acquired; (iii) seizure type; (iv) EEG pattern; (v) pharmacological reactivity; (vi) regression of the neuropsychological symptoms, of the EEG abnormalities and of the seizures before the end of adolescence; (vii) absence of obvious structural lesion detected by CT or MRI scan. Therefore, we postulated that these patients might, in fact, be presenting several facets of a single process associating the deterioration of cognitive functions and continuous spike-and-wave discharges during slow wave sleep. The pathogenesis of this syndrome remains unknown. Seven patients, presenting CSWS associated with neuropsychological deterioration (isolated aphasia, three cases; language disturbances with more widespread cognitive deterioration, three cases; isolated apraxia, one case) were studied using PET with [18F]fluorodeoxyglucose (FDG). We hoped to find metabolic arguments in favour of a unifying hypothesis, and to reveal clues as to pathogenesis. We present the retrospective analysis of 21 studies performed between 1986 and 1993, 12 of which were done during sleep. For three of these patients, follow-up studies were obtained until recovery. The metabolic patterns were very variable from one patient to another and in the same patient over time. Among the six patients studied during the active phase of the affection, our results showed unilateral, focal or regional increase in glucose metabolism of the cortex in five patients. This hypermetabolism was observed during sleep with continuous spike-and-wave discharges, but also persisted during wakefulness. In the last patient, the metabolic pattern was different: decreased regional glucose metabolism was observed during wakefulness, whereas during sleep, the metabolic pattern in the temporal areas varied during the course of the affection. After recovery, the metabolic pattern in four children (including the seventh patient) was either normal or showed focal or regional, uni- or bilateral decrease in cortical glucose metabolism. Despite this apparent disparity, four basic metabolic characteristics formed a common pattern in all patients, in line with our unifying postulate: (i) the metabolism of the cortical mantle was higher than in the subcortical structures, especially in the thalamic nuclei. This metabolic pattern is characteristic of an immature brain. (ii) The metabolic abnormalities involved focal or regional areas of the cortex. This finding is in good agreement with recent neurophysiological data suggesting a focal origin of the spike-and-wave discharges. (iii) The metabolic disturbances predominantly involved associative cortices. The pattern of neuropsychological deterioration is in good agreement with the topography of the disturbances of cortical glucose metabolism. (iv) The thalamic nuclei remained symmetrical despite significant cortical asymmetries, suggesting either that cortico-thalamic neurons do not participate in the generation of spike-and-wave discharges or that they are inhibited by the pathologic mechanisms. We hypothesize that the acquired deterioration of cognitive function with CSWS is caused by an alteration of the maturation of one or several associative cortices, primarily involving local interneurons and cortico-cortical associative neurons.

Is positron emission tomography a useful tool for studying migraine?

Despite the high prevalence of migraine in the population, the pathophysiology of this condition remains poorly understood. Vascular changes have been postulated. With positron emission tomography and various radiotracers, it is possible to have a non-invasive access to a number of parameters of interest in migraine research. These are presented and discussed in this article. PET has great potential for answering some basic questions concerning the physiological or biochemical changes that can occur during and between migraine attacks. Few studies have been published, however, probably because of (i) limitations inherent to the technique and (ii) problems in study design.

PET studies of patients with partial epilepsy: visual interpretation vs. semi-quantification/quantification

One of the advantages of PET is to allow for precise regional measurements of radioactive tracers in slices of brain. Furthermore, complex compartment modelling methods have been designed to transform the regional radioactive concentrations into biological units. The question is often raised whether quantification of PET studies is necessary in clinical practice. In epileptology, the regional biochemical changes associated with temporal lobe epilepsy are easily detected by experienced eyes and quantification is not required for diagnosis purposes. By contrast, inter-patient or inter-population comparisons can only be performed if regional measures have been obtained; if the PET method has been previously validated, simple measurements (regional activity) are sufficient and (kinetic) compartmental modelling is not necessary in routine.

Differential diagnosis of Alzheimer's disease with PET

PET studies have demonstrated bilateral temporo-parietal hypoperfusion and hypometabolism in probable and definite Alzheimer's disease (AD), a pattern that may help differentiate AD from other dementias.

METHODS

To evaluate the diagnostic power of cerebral metabolic distribution patterns for "cortical" degenerative dementias, PET scans obtained from 129 patients referred for differential diagnosis of dementia were analyzed visually.

RESULTS

Sixty-five patients had a final clinical diagnosis of probable AD. Ninety-seven percent (97%) of those had abnormal metabolic scans and 94% showed a suggestive pattern of bilateral or unilateral temporo-parietal hypometabolism (with or without frontal involvement). Hypometabolism was unilateral in 23% of patients. Five subjects with a neuropathologically proven diagnosis of Alzheimer's disease had a suggestive metabolic pattern. One of those was an early case with frontal hypometabolism exceeding temporo-parietal involvement. Two patients with Alzheimer's-type dementia had isolated bilateral frontal hypometabolism.

CONCLUSIONS

This alternative metabolic pattern may correspond to a non-Alzheimer pathology occurring in 10%-20% of patients suffering from clinically probable Alzheimer's disease. Most of the patients with possible but atypical Alzheimer's-type dementia showed isolated bilateral frontal involvement. This metabolic pattern probably corresponds to different diseases, such as Pick's disease, frontal lobe dementia or progressive subcortical gliosis.

Comparability of FDG PET studies in probable Alzheimer's disease

Results of studies with positron emission tomography (PET) of 18F-2-fluoro-2-deoxy-D-glucose (FDG) in patients with probable Alzheimer's disease (AD) were compared among three European centers with different PET scanners (in-plane resolution ranging between 6.75 mm and 9.2 mm). A ratio of glucose metabolism in the most typically affected regions over the least typically affected regions was calculated to quantitatively analyze the characteristic pattern of AD. Diagnostic accuracy of this composite ratio was high (95.8%) and was superior to that of most ratios derived from single regions. Correspondingly, there was a consistent, highly significant difference between patients (mean ratio 0.77 +/- 0.11) and normals (mean 0.99 +/- 0.04) without significant differences among laboratories. Possible small effects of rate constant variation and region size were analyzed by computer simulation. The results demonstrate that a common investigation protocol may yield FDG PET data in different laboratories that are closely comparable in spite of differences between scanners and imaging equipment.

Regional brain glucose metabolism in patients with complex partial seizures investigated by intracranial EEG

We performed interictal 18F-2-fluoro-2-deoxy-D-glucose positron emission tomography (18FDG-PET) studies in 57 patients with complex partial epilepsy (CPE), not controlled by medical treatment and considered for surgical resection of their epileptic focus. A precise localization of the epileptic focus was obtained in 37 of these patients with a combination of subdural and depth electrodes. We visually inspected the metabolic images; we also measured glucose consumption in a number of brain regions and compared the values with those obtained in 17 normal controls. Eighty-two percent of the 57 patients had an area of glucose hypometabolism on the 18FDG-PET images. Six patients had a frontal epileptic focus, 3 of them had a frontal lobe hypometabolism. Twenty-six patients had a unilateral temporal lobe focus and all of them displayed a temporal lobe hypometabolism. The asymmetry was more pronounced in the lateral temporal cortex (-20%) than in the mesial part of the temporal lobe (-9.6%). In each cortical brain region on the side of the epileptic focus (except the sensorimotor cortex), glucose consumption rate was lower than in the contralateral region or than in controls. No differences could be found between patients with a seizure onset restricted to the hippocampus and patients with a seizure onset involving the hippocampus and the adjacent neocortex. Divergent metabolic patterns were obtained in 5 patients with bilateral temporal seizure foci. Combined with other non invasive techniques (EEG, neuroradiology), PET contributes increasingly to the selection of patients with CPE who could benefit from surgical treatment.(ABSTRACT TRUNCATED AT 250 WORDS)

High cardiac zinc levels in spontaneously hypertensive rats

OBJECTIVES

Higher cardiac zinc levels have been observed previously in spontaneously hypertensive rats (SHR) compared with Wistar-Kyoto (WKY) rats. However, this difference was established in adult males only and needed to be confirmed on a larger number of animals of both sexes. We also explored the respective roles of genetic and environmental factors in the genesis of this zinc anomaly as well as the causal relations with hypertension.

DESIGN

Cardiac zinc levels were determined in adult male and female SHR and WKY rats originating from various colonies and submitted to various experimental conditions (anaesthesia, stress). These determinations were also performed in 3-week prehypertensive SHR and in adult Wistar rats submitted or not to deoxycorticosterone acetate-salt-induced hypertension.

METHOD

Zinc levels were measured by flame atomic absorption spectrophotometry.

RESULTS

In adults, cardiac zinc content was significantly higher in SHR than in WKY rats irrespective of sex and experimental conditions. In young prehypertensive rats, the difference between SHR and WKY cardiac zinc levels was also very significant. Experimental hypertension induced in Wistar rats did not entail any significant rise in cardiac zinc levels.

CONCLUSIONS

These findings indicated that the higher cardiac zinc of SHR is not secondary to blood pressure elevation. High erythrocyte zinc, previously described in SHR, together with the present data suggest the occurrence of a primary genetic defect leading to high intracellular zinc in SHR. The possible role of this zinc anomaly in the development of hypertension and/or cardiac hyperplasia is discussed.

Cerebral glucose utilization during stage 2 sleep in man

Using [18F]fluorodeoxyglucose method and positron emission tomography, we performed paired determinations of the cerebral glucose utilization at one week intervals during sleep and wakefulness, in 12 young normal subjects. During 6 of 28 sleep runs, a stable stage 2 SWS was observed that fulfilled the steady-state conditions of the model. The cerebral glucose utilization during stage 2 SWS was lower than during wakefulness, but the variation did not significantly differ from zero (mean variation: -11.5 +/- 25.57%, P = 0.28). The analysis of 89 regions of interest showed that glucose metabolism differed significantly from that observed at wake in 6 brain regions, among them both thalamic nuclei. We conclude that the brain energy metabolism is not homogeneous throughout all the stages of non-REMS but decreases from stage 2 SWS to deep SWS; we suggest that a low thalamic glucose metabolism is a metabolic feature common to both stage 2 and deep SWS, reflecting the inhibitory processes observed in the thalamus during these stages of sleep. Stage 2 SWS might protect the stability of sleep by insulating the subject from the environment and might be a prerequisite to the full development of other phases of sleep, especially deep SWS.