Biomedical subjects

X Blaizot

Publications and source records attributed to X Blaizot.

10 recordsLinked to original sources

PubMed2005

[Metabolic imaging for supratentorial oligodendrogliomas].

Metabolic imaging with positron emission tomography (PET) provides, in neuro-oncology, information complementary to that provided by anatomic imaging obtained with CT-scanner or MRI. Only a few publications have yet reported its use in oligodendroglial tumors. These findings and partial results obtained in ongoing work, suggest some preliminary conclusions: 11C-MET (L-methyl-methionine) is a more appropriate tracer than 18F-FDG (fluoro-deoxy-glucose), in terms of both specificity and sensitivity, for the assessment of patients with this category of tumor. PET/MET allows differentiation between grade II and grade III oligodendrogliomas; better targeting for stereotactic biopsy; more accurate assessment of the post-operative residual tumor; identification of progression from low-grade to anaplastic grade during the disease course; differentiation between recurrence and a post-radiation processes. PET/MET allows, to some extent, prediction of response to radiotherapy; and, probably, to chemotherapy.

Adult↗

PubMed2005

[Detection of the sentinal node in squamous-cell carcinoma of the oral cavity and oropharynx. Preliminary study].

INTRODUCTION: The sentinel lymph node is defined as the first relay of the lymphatic drainage of the tumor. Isotopic detection of the sentinel lymph node and absence of its metastatic invasion should theoretically be predictive of total drainage of the tumor. The goal of this study was to evaluate sentinel lymph node detectability by lymphoscintigraphy in N0 and/or N1 squamous-cell carcinoma of oral cavity and oropharynx and to determine its negative predictive value. MATERIAL AND METHOD: Lymphoscintigraphy was used for sentinel lymph node detection. The procedure required peritumoral injection of technicium-labeled colloids to enable anatomical and cutaneous location of the sentinel lymph node. A one-way Tyco-Mallinckrodt probe was used for intraoperative detection of the sentinel lymph node. This prospective study included 21 patients with N0 or N1 squamous-cell carcinoma of the oral cavity and the oropharynx. The surgical attitude based on T and N was not modified in this prospective study without direct individual benefit for the patient. Neck dissection was achieved without difficulty. RESULTS: The sentinel lymph node was identified in 20 out of 21 subjects. The sentinel lymph node was not identified in one patient with recurrence T2N0M0 squamous-cell carcinoma of the oropharynx radiated 3 years earlier. The percentage of false-negatives was 12.5% (1 false-negative out of 8 positive patients), giving a sensibility of the detection method of 87.5% (IC (95%)=[47.35-99.68]). This false-negative patient had a T3N0M0 squamous-cell carcinoma of the oropharynx with a sentinel lymph node removed in territory III. Neck dissection revealed 1 N + R- in the sub-mandibular territory associated with 27 N-R-. The probability of not finding a metastatic node at neck dissection when the sentinel lymph node is not metastatic (negative predictive value) was 92.3% (12/13) (IC (95)=[63.97-99.81]). The specificity of the method was 100%, as was the positive predictive value, because no sentinel node was diagnosed positive wrongly on frozen sections among patients without true histological node metastasis. DISCUSSION: For routine care of patients with squamous-cell carcinoma of the oral cavity and the oropharynx detection of the sentinel lymph node is proposed primarily for patients with T1T2N0 staging. Larger tumors can modify the architecture and flow within the lymphatic ducts, and consequently even the concept of a sentinel lymph node. Systematic neck dissection is required or T3T4, even when N0. Our series of T1T2N0 tumors is too small to enable statistically significant conclusions. A low level of false-negative in a larger series would be necessary to propose this technique instead of convention neck dissection for T1T2 tumors of the oral cavity and oropharynx.

Carcinoma, Squamous Cell↗

PubMed2005

Reciprocal connections between olfactory structures and the cortex of the rostral superior temporal sulcus in the Macaca fascicularis monkey.

Convergence of sensory modalities in the nonhuman primate cerebral cortex is still poorly understood. We present an anatomical tracing study in which polysensory association cortex located at the fundus and upper bank of the rostral superior temporal sulcus presents reciprocal connections with primary olfactory structures. At the same time, projections from this polysensory area reach multiple primary olfactory centres. Retrograde (Fast Blue) and anterograde (biotinylated dextran-amine and 3H-amino acids) tracers were injected into primary olfactory structures and rostral superior temporal sulcus. Retrograde tracers restricted to the anterior olfactory nucleus resulted in labelled neurons in the rostral portion of the upper bank and fundus of superior temporal sulcus. Injections of biotinylated dextran-amine at the fundus and upper bank of the superior temporal sulcus confirmed this projection by labelling axons in the dorsal and lateral portions of the anterior olfactory nucleus, as well as piriform, periamygdaloid and entorhinal cortices. Retrograde tracer injections at the rostral superior temporal sulcus resulted in neuronal labelling in the anterior olfactory nucleus, piriform, periamygdaloid and entorhinal cortices, thus providing confirmation of the reciprocity between primary olfactory structures and the cortex at the rostral superior temporal sulcus. The reciprocal connections between the rostral part of superior temporal sulcus and primary olfactory structures represent a convergence for olfactory and other sensory modalities at the cortex of the rostral temporal lobe.

Amino Acids↗

PubMed2003

Postnatal development of calcium-binding proteins immunoreactivity (parvalbumin, calbindin, calretinin) in the human entorhinal cortex.

The entorhinal cortex is an essential component in the organization of the human hippocampal formation related to cortical activity. It transfers, neocortical information (ultimately distributed to the dentate gyrus and hippocampus) and receives most of the hippocampal output directed to neocortex. At birth, the human entorhinal cortex presents similar layer organization as in adults, although layer II (cell islands) and upper layer III have a protracted maturation. The presence of interneurons expressing calcium-binding proteins (parvalbumin, calbindin-D28K (calbindin) and calretinin) is well documented in the adult human entorhinal cortex. In many of them the calcium binding is co-localized with GABA. Parvalbumin-immunoreactive cells and fibers were virtually absent at birth, their presence increasing gradually in deep layer III, mostly in the lateral and caudal portions of the entorhinal cortex from the 5th month onwards. Calbindin immunoreactive cells and fibers were present at birth, mainly in layers II and upper III; mostly at rostral and lateral portions of the entorhinal cortex, increasing in number and extending to deep layers from the 5th month onwards. Calretinin immunoreactivity was present at birth, homogeneously distributed over layers I, II and upper V, throughout the entorhinal cortex. A substantial increase in the number of calretinin neurons in layer V was observed at the 5th month. The postnatal development of parvalbumin, calbindin and calretinin may have an important role in the functional maturation of the entorhinal cortex through the control of hippocampal, cortical and subcortical information.

Calbindin 1↗

PubMed2002

Excitotoxic lesions of the rhinal cortex in the baboon differentially affect visual recognition memory, habit memory and spatial executive functions.

To specify the functional role of the rhinal cortex, baboons with bilateral excitotoxic lesions of the rhinal cortex (RH group) were tested on a series of computerized memory and learning tasks. Preoperatively, they were trained to and then tested on a delayed nonmatching-to-sample (DNMS) task with trial-unique stimuli. Postoperatively, this visual recognition memory task was given twice. As compared to a sham-operated group, the RH group showed good retention of rule learning and were unimpaired on the Delay memory subtest. Performance on the List Length memory subtest was, however, severely impaired at both postoperative evaluations, with a significant negative correlation between cognitive performance and neuronal loss in rhinal areas. Visual habit memory and spatial working memory were assessed postoperatively only, using a concurrent discrimination learning task and both a delayed-response task (with a two- and four-location choice) and a delayed alternation task, respectively. The RH group was unimpaired on the first two tasks and was even faster than the controls in learning the delayed-response task with four locations. Finally, most RH baboons failed to learn the delayed alternation task within the limits of testing. These results indicate that neuronal loss in the rhinal cortex is sufficient to impair visual recognition memory, and extend the implication of this area to spatial executive functions. Furthermore, the observation of impaired recognition memory and executive processes with preserved procedural memory and retrograde memory suggests that damage to the rhinal cortex probably participates in the cognitive deficits typical of the early stages of Alzheimer's disease.

Animals↗

PubMed2000

Mapping the visual recognition memory network with PET in the behaving baboon.

By means of a novel 18F-fluoro-deoxyglucose PET method designed for cognitive activation imaging in the baboon, the large-scale neural network involved in visual recognition memory in the nonhuman primate was mapped for the first time. In this method, the tracer is injected in the awake, unanesthetized, and unrestrained baboon performing the memory task, and brain imaging is performed later under light anesthesia. Brain maps obtained during a computerized trialunique delayed matching-to-sample task (lists of meaningless geometrical patterns and delay > 9 seconds) were statistically compared pixel-by-pixel to maps obtained during a specially designed visuomotor control task. When displayed onto the baboon's own anatomic magnetic resonance images, foci of significant activation were distributed along the ventral occipitotemporal pathway, the inferomedial temporal lobe (especially the perirhinal cortex and posterior hippocampal region), and the orbitofrontal cortex, consistent with lesion, single-unit, and autoradiographic studies in monkeys, as well as with activation studies in healthy humans. Additional activated regions included the nucleus basalis of Meynert, the globus pallidus and the putamen. The results also document an unexpected left-sided advantage, suggesting hemispheric functional specialization for recognition of figural material in nonhuman primates.

Animals↗

PubMed1999

Combined use of T1-weighted MRI and MRA for stereotaxic lesioning of the nonhuman primate brain: application to the rhinal cortex.

Stereotaxic brain lesioning is widely used to develop experimental models of human brain disease in the nonhuman primate. To avoid intraoperative vascular complications such as intracranial hemorrhage, we developed a methodology that is easy to implement. This method combines T1-weighted magnetic resonance imaging (MRI) and magnetic resonance angiography (MRA). This technique is applied to produce bilateral neurotoxic lesions of the rhinal cortex, a structure located medially in the temporal lobe, in eight baboons (including five sham-operated animals with needle descents but no ibotenic acid injection). Two other baboons were lesioned before the MRA technology was available. The MRA sequence (two-dimensional time-of-flight, axial acquisition) was used to localize the blood vessels in the needle trajectories, i.e., the highly vascularized sylvian fissure and temporal gyri. The vessel coordinates were transposed onto the coronal MRI-TI images, onto which the injection sites were determined and the planned needle tracks drawn. In the eight baboons that had MRA, 26.8% of these needle tracks had to be slightly displaced because of the presence of blood vessels. The stereotaxic coordinates of the final target sites were then calculated with respect to six skull landmarks that also served as a reference during surgery. No intracranial hemorrhage occurred in any of the eight baboons in which MRA was performed, in contrast to one of the two baboons not studied with MRA. The histological analysis showed a good extent of the rhinal lesions in all lesioned animals, with minimal damage to areas other than those that were targeted. Thus, combined use of MRI-TI and MRA proved to be reliable in reducing vascular complications, affording new advances for stereotaxic surgery in nonhuman primates.

Animals↗

PubMed1999

Neocortical and hippocampal glucose hypometabolism following neurotoxic lesions of the entorhinal and perirhinal cortices in the non-human primate as shown by PET. Implications for Alzheimer's disease.

Temporoparietal glucose hypometabolism, neuronal loss in the basal forebrain cholinergic structures and preferential accumulation of neurofibrillary tangles in the rhinal cortex (i.e. in the entorhinal and perirhinal cortices) are three early characteristics of Alzheimer's disease. Based on studies of the effects of neurotoxic lesions in baboons, we previously concluded that damage to the cholinergic structures plays, at best, a marginal role in the association neocortex hypometabolism of Alzheimer's disease. In the present study, we have assessed the remote metabolic effects of bilateral neurotoxic lesions of both entorhinal and perirhinal cortices. Using coronal PET coregistered with MRI, the cerebral metabolic rate for glucose (CMR(glc)) was measured before surgery and sequentially for 2-3 months afterward (around days 30, 45 and 80). Compared with sham-operated baboons, the lesioned animals showed a significant and long-lasting CMR(glc) decline in a small set of brain regions, especially in the inferior parietal, posterior temporal, posterior cingulate and associative occipital cortices, as well as in the posterior hippocampal region, all of which also exhibit glucose hypometabolism in Alzheimer's disease. Remarkably, the degree of CMR(glc) decline in four of these regions significantly correlated with the severity of histologically determined damage in the rhinal cortex, strongly supporting the specificity of the observed metabolic effects. There were also differences between the metabolic pattern observed in the lesioned animals and that classically reported in Alzheimer's disease; for instance, the hypometabolism we found in the stratum has not been reported in early Alzheimer's disease, although this structure can be affected in late stages of the disease and has direct anatomical connections with the rhinal cortex. Nevertheless, this study shows for the first time that the temporoparietal and hippocampal hypometabolism found in Alzheimer's disease may partly result from neuroanatomical disconnection with the rhinal cortex. This, in turn, further strengthens the hypothesis that neuronal damage and dysfunction in the rhinal cortices play a major role in the expression of Alzheimer's disease.

Alzheimer Disease↗

PubMed1998

[11C]S21007, a putative partial agonist for 5-HT3 receptors PET studies. Rat and primate in vivo biological evaluation.

We recently labeled with carbon-11, a high affinity, selective, 5-HT3 receptor (5-HT3R) ligand, S21007, for potential positron emission tomography (PET) applications. To evaluate the in vivo binding properties of [11C]S21007, its brain regional distribution, tissue and plasma pharmacokinetics and plasma metabolisation were characterized. To circumvent the problem of highly discrete brain localization of the 5-HT3R (area postrema, hippocampus), we designed an original approach combining high-resolution imaging techniques (ex vivo phosphor plate autoradiography and MRI-guided coronal PET in the rat and baboon, respectively). After i.v. injection of trace amounts of [11C]S21007 to rats, phosphorimager autoradiography failed to reveal in vivo specific binding to, nor selectivity for 5-HT3R-rich areas. PET studies in the baboon showed consistent results, i.e., there was no selective accumulation of [11C]S21007 in the area postrema or hippocampus, and neither displacement nor presaturation with cold S21007 resulted in significant changes in tissue distribution or kinetics of [11C]S21007.

Animals↗

PubMedDate not supplied

Comparative aspects of the olfactory portion of the entorhinal cortex and its projection to the hippocampus in rodents, nonhuman primates, and the human brain.

The entorhinal cortex is a component of the hippocampal formation characterized by its projection to the dentate gyrus. Cortical input is relayed to the hippocampus through the entorhinal cortex. The entorhinal cortex can be recognized best in mammals, and it reaches its maximal importance in both human and nonhuman primates. In primates, but not in rodents, the olfactory projection from the olfactory bulb is the only direct sensory projection reaching the entorhinal cortex, where it defines a rostromedial subfield (olfactory subfield of the entorhinal cortex, EO). In this communication, we consider some comparative aspects of this projection in rodents, nonhuman primates, and human brains, in relation to the forward projection to the hippocampus. We base our analysis on the following three considerations: (1) Topology: Topologically, the entorhinal cortex lies medial to the rhinal fissure, well developed in all mammals except in humans. EO maintains the same topological relationship to the rhinal fissure in the three mammalian orders. (2) Cytoarchitecture: The rostromedial portion shows poorer lamination compared with caudomedial portions of the entorhinal cortex in the three mammalian orders examined. (3) Connectivity: In rodents, the olfactory projection covers the whole extent of the entorhinal cortex, whereas it decreases substantially in macaques, where it roughly covers 15% of the entorhinal cortex. The human EO as defined by topological and cytoarchitectonic criteria may be even less than in macaques. Interestingly, good evidence exists that all of these mammalian orders maintain the same topographical scheme of projection to the rostral end of the hippocampus.

Animals↗