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J C Baron

Publications and source records attributed to J C Baron.

At least 91 records · Page 5Linked to original sources
PubMed1996

Estimation of neocortical serotonin-2 receptor binding potential by single-dose fluorine-18-setoperone kinetic PET data analysis.

UNLABELLED: Because it satisfies most of the characteristics required to quantify in vivo neocortical serotonin-2 (5HT2) receptors, 18F-setoperone was selected for use in PET estimation of the neocortical 5HT2 binding parameters in baboons according to a single-dose paradigm. METHODS: The neocortical binding potential (i.e., Bmax/KD or the k3/k4 ratio) was assessed by three different methods, with the cerebellum taken as the reference structure in all instances. Method 1 was based on a Logan-Patlak graphical analysis of both cerebellar and neocortical data, which allows estimation of the neocortical k3'/k4 ratio; it required a separate estimation of k5 and k6 from classical nonlinear least-squares (NLSQ) three-compartment modeling of cerebellar data. Method 2 was an original combination of a four-compartment Logan-Patlak procedure for neocortical data and an NLSQ three-compartment procedure for cerebellar data, allowing the neocortical k3/k4 ratio to be obtained directly. In Method 3, an NLSQ three-compartment procedure was applied to cerebellar data and an NLSQ four-compartment procedure to neocortical data, allowing separate determinations of k3 and k4 for the neocortex and, in turn, the k3/k4 ratio. RESULTS: In all three methods, the arterial plasma input function was corrected for the presence of 18F-metabolites, and the vascular fraction was either fitted or fixed. Statistical analysis showed no significant difference among the k3/k4 values obtained from the three methods. Method 3 was the least stable because of an occasional poor NLSQ four-compartment fit on neocortical data. Method 2 provided the least cumbersome estimate of the k3/k4 ratio and was found easy and accurate for generating parametric maps of the 5HT2 binding potential. CONCLUSION: This method might be useful in clinical investigations to provide quantitative assessment of receptor binding potential. In semiquantitative investigations, the neocortical-to-cerebellum pseudoequilibrium ratio may be adequate, as suggested by the significant correlations with measured k3/k4 ratios found here.

Animals↗
PubMed1996

Clinical use of positron emission tomography in cerebrovascular diseases.

In this article the author reviews the state-of-the-art regarding the clinical applications of positron emission tomography (PET) in cerebrovascular diseases. First, the basic methodology and physiology of cerebral blood flow and metabolism as it pertains to cerebrovascular disease are summarized. The reader is then given an account of the main findings from this technique with respect to (1) the assessment of the hemodynamic and metabolic effects of carotid artery disease in the perspective of surgical versus medical management, (2) the changes in brain perfusion and metabolism in acute ischemic stroke as they relate to the issue of patient management, outcome predictability, and screening in therapeutic trials, and (3) mapping of the remote metabolic effects of stroke and their clinical relevance.

Carotid Stenosis↗
PubMed1995

PET imaging of neocortical monoaminergic terminals in Parkinson's disease.

Post-mortem neurochemical studies in Parkinson's disease (PD) have shown that, in addition to the typical nigro-striatal dopamine denervation, there exists a concomitant neocortical monoamine fibre deafferentation (of variable severity) whose role in motor, and especially in associated cognitive and affective impairment, remains elusive. We have extensively examined whether PET imaging with 11C-S-Nomifensine (11C-NMF), a radioligand of the dopamine and norepinephrine presynaptic reuptake sites which has been used so far to investigate the striatum, could provide a method for assessing in vivo the neocortical monoamine terminal loss in PD; previously, this has been a little addressed and controversial issue. To this end, we prospectively selected a highly homogeneous sample of nine non-demented, non-depressed idiopathic PD patients with mild to marked side-to-side asymmetry in motor impairment. In addition to recovering the previously-reported correlations with putaminal 11C-NMF specific uptake asymmetries, the clinical motor asymmetries also significantly correlated in the clinically expected direction to neocortical (especially frontal) 11C-NMF asymmetries, suggesting the monoamine neocortical denervation might play a direct role in motor impairment in PD. These results demonstrate that it is possible to assess in vivo the neocortical monoamine terminal loss, and to elucidate its potential role in the complex cognitive and affective impairment, in both PD and atypical degenerative parkinsonism.

Aged↗
PubMed1995

Topographic EEG activations during timbre and pitch discrimination tasks using musical sounds.

Successive auditory stimulation sequences were presented binaurally to 18 young normal volunteers. Five conditions were investigated: two reference tasks, assumed to involve passive listening to couples of musical sounds, and three discrimination tasks, one dealing with pitch, and two with timbre (either with or without the attack). A symmetrical montage of 16 EEG channels was recorded for each subject across the different conditions. Two quantitative parameters of EEG activity were compared among the different sequences within five distinct frequency bands. As compared to a rest (no stimulation) condition, both passive listening conditions led to changes in primary auditory cortex areas. Both discrimination tasks for pitch and timbre led to right hemisphere EEG changes, organized in two poles: an anterior one and a posterior one. After discussing the electrophysiological aspects of this work, these results are interpreted in terms of a network including the right temporal neocortex and the right frontal lobe to maintain the acoustical information in an auditory working memory necessary to carry out the discrimination task.

Adolescent↗
PubMed1995

Healthy aging, memory subsystems and regional cerebral oxygen consumption.

The present study was designed to search for concomitant age-related changes in memory subsystems, defined according to current structural theories, and resting oxygen consumption in selected brain regions. We have investigated a sample of subjects between 20 and 68 years of age and strictly screened for their good health. We applied in the same subjects a battery of neuropsychological tests selected to investigate several memory subsystems, and high-resolution positron imaging with stereotaxic localization to study a purposely limited number of cerebral structures, selected on a priori hypotheses to match the different memory subsystems. Our results showed significant age-related changes in performance on some tests, consistent with the literature, including an increase in semantic memory and a decrease in both working memory (central executive system) and verbal episodic and explicit memory. There was also an age-related linear decrease in global brain oxygen consumption which regionally reached statistical significance for the neocortical areas and the left thalamus. There was a limited number of significant, age-independent correlations between the raw psychometric test scores and resting regional oxidative metabolism. Consistent with our present understanding of the functional anatomy of memory, the Associate Learning scores (verbal episodic and explicit memory) were positively correlated with left hippocampal and thalamic metabolism. The positive relationships found between right hippocampal metabolism and performance in the Associate Learning and the Brown-Peterson tests were less expected but would be consistent with findings from recent PET activation studies. The results from this investigation are discussed in the light of current knowledge concerning the neuropsychology and the neurobiology of both aging and memory.

Adult↗
PubMed1995

Contralateral cerebellar diaschisis 7 hours after MCA-occlusion in primates.

2,3,5-triphenyltetrazoliumchloride (TTC) as an indicator of mitochondrial function in combination with regional cerebral blood flow measurements was used in six baboons 6.9 +/- 1.2 h after permanent occlusion of the left middle cerebral artery. Staining with TTC was compared with blood flow data obtained during normocapnia using the microsphere method. Five animals showed a focal area of unstained tissue in the left middle cerebral artery territory. Mean blood flow in the unstained area was 28.3 +/- 15.4 ml min-1 100 g-1. Five of 6 animals showed a significant decrease of contralateral cerebellar blood flow in the presence of normal TTC staining. We conclude that at this early stage of infarction contralateral cerebellar diaschisis is caused by functional deactivation.

Animals↗
PubMed1995

A PET study of the functional neuroanatomy of writing impairment in Alzheimer's disease. The role of the left supramarginal and left angular gyri.

A dissociation in the central processes of spelling, with preferentially lexical over phonological impairment, frequently affects patients with early Alzheimer's disease. The aim of this work was to test whether dissociations in the language domain in Alzheimer's disease can be exploited with PET to assess the neural basis of cognition. To this end, we studied the functional neuroanatomy of writing impairment in Alzheimer's disease by means of PET measurements of the local cerebral glucose utilization and neuropsychological tests specially designed to assess the phonological and lexical components of writing. We analysed the performance in written spelling of irregular words and non-words of 11 right-handed patients with mild-to-moderate Alzheimer's disease. For each patient, we calculated a residual phonological score and a residual lexical score, based on a cognitive interpretation of the errors according to the item category. In each of these 11 patients, using PET, we measured the resting-state utilization of glucose in the left supramarginal gyrus and the left angular gyrus, two cortical regions selected a priori because of their presumed role in the central processes for spelling, and identified on CT scans obtained according to stereotaxic references and coregistered with PET. To assess the relationships between the neuropsychological scores and the metabolic data, we used the 'ratio paradigm', the sensitivity of which has been previously documented in cognitive-metabolic correlative PET studies of Alzheimer's disease that were less focused than the present study in both cognitive and anatomical terms. We found a highly significant positive correlation between phonological score:lexical score neuropsychological ratios and corresponding supramarginal gyrus:angular gyrus metabolic ratios. These findings further support the role of these two left-sided temporo-parietal regions in the central processes of writing and show that the neuropsychological dissociations in early Alzheimer's diseases can be exploited to further our understanding of the functional neuroanatomy of cognitive operations. The role of focal, as compared with more diffuse, brain damage in the development of impaired written language of central origin in Alzheimer's disease is also discussed.

Aged↗
PubMed1995

Sequential studies of severely hypometabolic tissue volumes after permanent middle cerebral artery occlusion. A positron emission tomographic investigation in anesthetized baboons.

BACKGROUND AND PURPOSE: In the positron emission tomography literature, markedly hypometabolic brain tissue (oxygen metabolism < 1.3 to 1.7 mL.100 g-1.min-1) has often been equated with irreversible damage in the human brain. By serial positron emission tomography measurements, we investigated the temporal evolution of the volume of severely hypometabolic brain tissue after permanent middle cerebral artery occlusion in anesthetized baboons with, as a perspective, the development of rational therapeutic strategies. METHODS: Seven anesthetized and ventilated baboons underwent sequential positron emission tomography examinations with the 15O steady-state technique before and 1, 4, 7, and 24 hours and 14 to 29 days after occlusion. In each baboon the infarct volume was calculated by quantitative histological procedures after 19 to 41 days of occlusion. RESULTS: The sequential measurement of regional oxygen metabolism demonstrated an extension (for > or = 24 hours) of the volume of severely hypometabolic tissue as defined by both absolute and relative metabolic thresholds, and this profile of evolutivity is observed no matter the threshold used. Mean (+/- SEM) infarction volume of 2.4 +/- 0.6 cm3 was comparable to a tissue volume with oxygen consumption < 40% of contralateral metabolism. The volume of hypometabolic tissue was essentially stable at the 1-, 4-, and 7-hour postocclusion studies, increased markedly at the 24-hour study point, and increased even further in the chronic-stage study (on average, 17 days after occlusion). The tissue that eventually displayed a severely hypometabolic state at the final measurement showed a significant decrease of oxygen metabolism and cerebral blood flow at each time analyzed. In that tissue, the oxygen extraction fraction increased significantly at 1 hour (although not thereafter). CONCLUSIONS: The extension of severely hypometabolic volume after middle cerebral artery occlusion reinforces the concept of a dynamic penumbra and suggests the existence of a relatively large window of therapeutic opportunity in which it may be possible to develop neuroprotective strategies. Our study suggests that maximum infarct volume is determined at some time between 24 hours and 17 days after permanent middle cerebral artery occlusion in anesthetized baboons.

Animals↗
PubMed1995

[Benign neuropathy of the chin].

A 49-year old man without relevant prior neurological disorder but with overweight, dyslipidaemia and mild glucose dysregulation, noticed on awakening a spontaneous, left-sided and painless numb chin, attributed to isolated mental neuropathy, which regressed entirely within a few weeks. The clinical condition was stable at 1-year follow-up. Ancillary investigations (including electromyography) did not disclose any cause to this episode, notably there was no underlying malignancy or systemic disease. A thorough literature review revealed another similar case which too remained unexplained. The hypothesis of a microvascular neuropathy in relation to vascular risk factors is cautiously raised; such a mechanism has been inferred previously in exceptional cases of regressive mental neuropathy in the context of sickle-cell crisis or systemic vasculitis. Thus, at variance with classical notions, the outlook of the numb chin syndrome is occasionally benign.

Chin↗
PubMed1995

[Genetic alterations in localized cancers of the prostate: identification of a common region of deletion on the chromosome 18q].

Prostate cancer is one of the most common malignancies in men. Few authors have attempted to identify consistent genetic alterations at the molecular level in adenocarcinoma of the prostate, but those most frequently reported are loss of heterozygosity (LOH) involving chromosome arms 8p, 10q, 16q, and 18q and inactivation of the TP53 tumor suppressor gene. In order to determine if alterations frequently found in other adenocarcinomas (breast, ovarian, colorectal), including losses of genetic material from chromosome arms 1p, 3p, 7q, 8p, 11p, 17p, 17q, and 18q, are also involved in prostate cancer, we examined 20 localized early-stage prostate tumors. We detected no mutations of the TP53 gene. Allelic losses were found from 7q (33%), 8p (50%), 10q (20%), and 18q (33%). Furthermore, as the first step toward isolating tumor suppressor genes on 18q, we used six polymorphic markers and identified a small common deleted region between the chromosome 18 centromere and the D18S19 locus.

Aged↗
PubMed1995

[Infarction in the area of the right anterior choroidal artery and minor hemisphere syndrome: clinical and metabolic study using positron-emission tomography].

A 72 year-old right handed woman had a right sided anterior choroidal artery infarction. She presented the triad of hemiplegia, hemianaesthesia, and homonymous hemianopsia, as well as complete non-determinant hemisphere syndrome that combined: disorientation for place and time, anosognosia, hemiasomatognosia, left spatial neglect, constructional apraxia and spatial fabulation concerning both the present time and the weeks that preceded the vascular event. Language and verbal memory were normal. Spatial memory could not be studied because of the severity of the neglect. The clinical course was poor: when tested one and a half year post-onset, the hemiplegia, the hemianaesthesia, and the hemianopsia as well as left spatial neglect remained severe. Vestibular caloric stimulation, carried out with left ear cold water irrigation, resulted in brief but clear-cut alleviation of the spatial neglect. An MRI with both axial and coronal slices showed a right-sided infarct affecting the whole posterior limb of the internal capsule including the genu, the posterior part of the globus pallidus, the anterior third of the cerebral peduncle and the amygdala but sparing the thalamus and the corona radiata. This crescent-shaped lesion transected entirely the thalamo-cortical connection fibers which resulted in a "thalamic exclusion". The measurement of brain glucose utilisation with (18F)-Fluoro-2-Deoxy-D-Glucose and positron emission tomography performed in the chronic phase (3 months post-onset) showed an exceptionally severe and widespread hypometabolism of the right hemisphere, relative to the left hemisphere, which correlated with both the unusual, severe and protracted non-dominant hemisphere syndrome. All the brain regions on the right side were hypometabolic relative to the left including the temporal region (mostly medial temporal), the left cerebellar lobe, the frontal lobe (mostly prefrontal region), the occipital region and the thalamus. The hypometabolism of the basal ganglia, the sensorimotor area and the parietal cortex was less severe. This most uncommon clinical-metabolic presentation presumably reflects a global thalamo-cortical disconnection inducing a diffuse dysfunction of the whole hemisphere.

Aged↗