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Biomedical subjects

M E Meyer

Publications and source records attributed to M E Meyer.

At least 19 recordsLinked to original sources
PubMed2006

Value of phase contrast magnetic resonance imaging for investigation of cerebral hydrodynamics.

OBJECTIVE: Phase Contrast Magnetic Resonance Imaging (PCMRI) is a noninvasive technique that can be used to quantify variations of flow during the cardiac cycle. PCMRI allows investigations of blood flow dynamics in the main arteries and veins of the brain but also the dynamics of cerebrospinal fluid. These cerebral flow investigations provide a description of the regulation mechanisms of intracranial pressure during the cardiac cycle. The objective of this paper is to describe the contribution of this technique in diseases related to disorders of cerebral hydrodynamics in the light of 5 clinical cases. METHOD: Flow measurements were performed using PCMRI sequences on a 1.5 Tesla MR imager in 4 patients with symptomatic ventricular dilation and 1 patient with a syringomyelic cavity. RESULTS: Flow quantification in these 5 patients, representative of the diseases mainly concerned by cerebral hydrodynamics, is useful to guide the indication for ventricular shunting in patients with hydrocephalus, to demonstrate obstruction of the cerebral aqueduct, to demonstrate recirculation of ventricular CSF after ventriculostomy and to characterize the dynamic features of CSF inside a spinal cavity. CONCLUSION: PCMRI, now available to neurosurgeons, is complementary to morphological MR and provides quantitative information on cerebral hydrodynamics. This information is mainly used to confirm alteration of CSF flow in the cerebral and spinal compartments. PCMRI is also a functional tool to better understand the pathophysiology of hydrocephalus and syringomyelia.

Adult↗
PubMed2005

Ventricular dilation as an instability of intracranial dynamics.

We address the question of the ventricles' dilation as a possible instability of the intracranial dynamics. The ventricular system is shown to be governed by a dynamical equation derived from first principles. This general nonlinear scheme is linearized around a well-defined steady state which is mapped onto a pressure-volume model with an algebraic effective compliance depending on the ventricles' geometry, the ependyma's elasticity, and the cerebrospinal fluid (CSF) surface tension. Instabilities of different natures are then evidenced. A first type of structural instability results from the compelling effects of the CSF surface tension and the elastic properties of the ependyma. A second type of dynamical instability occurs for low enough values of the aqueduct's conductance. This last case is then shown to be accompanied by a spontaneous ventricle's dilation. A strong correlation with some active hydrocephalus is evidenced and discussed. The transfer function of the ventricles, compared to a low-pass filter, are calculated in both the stable and unstable regimes and appear to be very different.

Animals↗
PubMed2004

Neural correlates of implicit object identification.

The present study sought to assess neural correlates of implicit identification of objects by means of fMRI, using tasks that require matching of the physical properties of objects. Behavioural data suggests that there is automatic access to object identity when observers attend to a physical property of the form of an object (e.g. the object's orientation) and no evidence for semantic processing when subjects attend to colour. We evaluated whether, in addition to neural areas associated with decisions to specific perceptual properties, areas associated with access to semantic information were activated when tasks demanded processing of the global configuration of pictures. We used two perceptual matching tasks based on the global orientation or on the colour of line drawings. Our results confirmed behavioural data. Activations in the inferior occipital cortex, fusiform and inferior temporal gyri in both tasks (orientation and colour) account for perceptual and structural processing involved in each task. In contrast, activations in the posterior and medial parts of the fusiform gyrus, shown to be involved in explicit semantic judgements, were more pronounced in the orientation-matching task, suggesting that semantic information from the pictures is processed in an implicit way even when not required by the task. Thus, this study suggests that cortical regions usually involved in explicit semantic processing are also activated when implicit processing of objects occurs.

Adult↗
PubMed2000

Transmembrane and cytoplasmic domains of syndecan mediate a multi-step endocytic pathway involving detergent-insoluble membrane rafts.

Syndecan heparan sulphate proteoglycans directly mediate a novel endocytic pathway. Using Chinese hamster ovary cells expressing the human syndecan 1 core protein or a chimaeric receptor, FcR-Synd, consisting of the ectodomain of the IgG Fc receptor Ia linked to the transmembrane and cytoplasmic domains of syndecan 1, we previously reported that efficient internalization is triggered by ligand clustering, requires intact actin microfilaments and tyrosine kinases, proceeds with a t(1/2) of approx. 1 h and is distinct from coated-pit pathways. We have now examined the involvement of cholesterol-rich, detergent-insoluble membrane rafts. On clustering, (125)I-labelled IgG bound to FcR-Synd rapidly became insoluble in cold Triton X-100, well before endocytosis. Insolubility of clustered FcR-Synd ligand did not require the syndecan ectodomain, linkage of the cytoplasmic tail to the cytoskeleton, or energy-dependent cellular metabolism. Pretreatment of cells with cyclodextrin to deplete cholesterol from rafts abolished insolubility of the clustered ligand and inhibited endocytosis in a dose-responsive fashion. Similar results were obtained with (125)I-labelled lipoprotein lipase bound to authentic cell-surface syndecan. In contrast, the 39 kDa receptor-associated protein (RAP), a coated-pit ligand, was more than 80% soluble in cold Triton even after internalization; cellular cholesterol depletion failed to substantially affect the internalization of (125)I-RAP. Overall, our results indicate a multi-step endocytic process consisting of ligand binding, clustering, energy-independent lateral movement into detergent-insoluble membrane rafts and finally recruitment of actin and tyrosine kinases to bring the ligands into the cell.

Animals↗
PubMed2000

Automatic object identification: an fMRI study.

Boucart and Humphreys reported an automatic access to object identity when observers attend to a physical property of the form of an object (e.g. the orientation) but not to its colour. We sought evidence for automatic identification in a brain imaging study using fMRI. In an orientation decision task participants decided whether a picture was vertical or horizontal. In the colour decision task participants decided if a picture was blue or green. Activation of areas 18-19 was found for both color and orientation. Activation of the temporal area 37 occurred more frequently in the orientation than in the colour decision task. This result suggests that automatic identification activates the same brain area as overt processing of semantic information.

Adult↗
PubMed1999

The pitfalls of planar three-phase bone scintigraphy in nontraumatic hip avascular osteonecrosis.

PURPOSE: This study documented the previously reported lower sensitivity of routine planar three-phase bone scintigraphy (BS) performed using a high-resolution parallel-hole collimator compared with MRI to diagnose nontraumatic avascular necrosis of the hip (AVN). METHODS: Six observers reviewed 143 bone scintigrams obtained in patients with nontraumatic hip pain (n = 120) or a control group (n = 23). All patients had a standard radiograph and MRI within 2 months of the BS. Of 280 hips, 148 (53%) were painful on the day of the examination. The osteonecrosis group (AVN) consisted of 93 instances of AVN in 58 patients. Although it departs from the clinical situation, this method evaluated the intrinsic performance of the imaging method. The data were analyzed using a receiver operating characteristic method. RESULTS: For the six observers, the A(z) values were 0.65, 0.67, 0.66, 0.67, 0.73, and 0.79, respectively, and 0.66, 0.71, 0.75, 0.81, 0.81, 0.82, and 0.84 after removing hip diseases other than AVN through data manipulation. Bone marrow edema, as seen on MRI, was the most frequently reported misleading sign in false-positive diagnoses, especially in the early or late phases of the disease. False-negative diagnoses misclassified the scans as "asymptomatic hips" in 28 of 30 cases. Twenty-two of 30 scans appeared normal, but these AVN lesions were small (<25%) and were discovered by chance on MRIs that displayed bilateral involvement associated with radiographic evidence (stage 0 or 1). Thirteen of 20 patients were followed for 3 or more years, and only one worsened. CONCLUSIONS: BS is not indicated to diagnose possible contralateral AVN if the hip is asymptomatic. This study emphasizes the results from the literature; if indicated, a radionuclide hip investigation requires the use of a pin-hole collimator, a SPECT study with scatter correction and iterative reconstruction algorithms, or both.

Adult↗
PubMed1996

Mesolimbic 7-OH-DPAT affects locomotor activities in rats.

This study tested the hypotheses that the dopamine D3 receptor is both an autoreceptor and a postsynaptic receptor and has an affinity for dopamine at the nanomolar level. The effect of bilateral microinjections of a dopamine D3-like agonist, 7-OH-DPAT, into the nucleus accumbens and into the ventral tegmental area (VTA) was tested with rats in activity monitors. Horizontal movement, rearing, and stereotypy times in seconds were automatically measured during 12 consecutive 10-min time blocks. Intraaccumbens 7-OH-DPAT (0.0001-10.0 micrograms/side) resulted in a highly significant dose by time block interactions. The dose of 0.0001 microgram/side resulted in the potentiation of horizontal movement time during the time blocks 10-40 min; whereas, 0.001-1.0 microgram/side potentiated locomotion during the early blocks following the 10-min interval. However, 10.0 micrograms/side resulted in a biphasic effect, attenuation followed by potentiation. 7-OH-DPAT (0.0001-1.0 microgram/ side) potentiated rearing time in the early time blocks and (0.001-10.0 micrograms/side) attenuated stereotypy time during the first 20 min time blocks. On the other hand, intra-VTA 7-OH-DPAT (10.0 micrograms/side) attenuated horizontal movement time during the first 20-min time blocks and (0.01 and 0.0001 microgram/side) potentiated movement time at the 20-min time block. Intraventral tegmental area 7-OH-DPAT had no effects on rearing and stereotypy times. These data support the hypothesis that the D3 receptor has an affinity for dopamine at the nanomolar level and question the hypothesis that the D3 receptors are both autoreceptors and postsynaptic receptors.

Animals↗
PubMed1995

NMR relaxation rates and blood oxygenation level.

A linear relationship between the proton relaxation rates and the fraction of deoxyhemoglobin of circulating whole blood (fHb) has been established in vitro at 4.7 T. These results have been interpreted on the basis of the additivity of relaxation rates. The slope of the lines of transverse relaxation rates (R2) versus fHb was found to increase with interpulse delay in Carr-Purcell Meiboom-Gill (CPMG) experiments. The Luz-Meiboom relation applied to this interpulse delay dependence of R2 suggests a two-site chemical exchange rather than a diffusion mechanism. The 1-ms water proton exchange time derived from these observations has been interpreted in terms of exchange between exchangeable protons close to the paramagnetic center of hemoglobin and protons of bulk water.

Animals↗
PubMed1995

DALDA (H-Tyr-D-Arg-Phe-Lys-NH2), a potent mu-opioid peptide agonist, affects various patterns of locomotor activities.

The central effects of mu-opioid receptor agonist DALDA (ICV 0.00, 0.1, or 1.0 micrograms) were investigated in rats for 120 min on activity monitors. The durations in seconds of horizontal movement time, rearing time, and stereotypy time were measured during 12 consecutive 10-min time blocks. DALDA (ICV, 0.1 and 1.0 micrograms) resulted in biphasic effects, inhibition followed by activation for horizontal movement, rearing, and stereotypy times.

Amino Acid Sequence↗
PubMed1994

Biphasic effects of intraaccumbens mu-opioid peptide agonist DAMGO on locomotor activities.

The effects of bilateral microinjections of mu-opioid receptor agonist DAMGO (0.00, 0.01, 0.1, or 1.0 microgram/side) were tested in rats for 120 min in activity monitors. The horizontal movement, rearing, and stereotypy times in seconds were measured during 12 consecutive 10-min time blocks. DAMGO (0.01, 0.1, and 1.0 microgram) resulted in biphasic effects, inhibition followed by activation for each of the three measures. These data replicate the behavioral effects of ICV DAMGO except that the duration of the behavioral effects were longer with Acb injections.

Amino Acid Sequence↗
PubMed1994

Ontogeny of biphasic locomotor effects of quinpirole.

The effects of the dopamine D2/D3 receptor agonist quinpirole (LY171555) on locomotor activity were tested on rats of 10, 15, 20, 30, and 60 days of age. In two separate experiments, doses of 0 (vehicle), 0.02, 0.2, or 2.0 mg/kg quinpirole were injected SC into rats at each age, and their effects measured either for 2 h at 15-min intervals, or 30 min at 5-min intervals. At 10, 15, and 20 days of age, quinpirole significantly increased distance travelled in a dose-dependent manner. At 30 and 60 days of age, quinpirole significantly decreased distance travelled early in the session and increased it later. These results suggest that a dopamine autoreceptor begins to function between 20 and 30 days of age. Concomitant with the appearance of quinpirole-induced locomotor suppression early in the session, the amount of quinpirole-induced activation late in the session declined.

Aging↗
PubMed1993

Differential effects of SCH 23390 on immobility behaviors in developing rats.

The effects of a single injection of a dopamine D1 antagonist, SCH 23390, at doses of 0, 0.05, 0.1, and 0.2 mg/kg on three different kinds of immobility behavior were tested in rats of 10, 15, 20, and 30 days of age. Each animal was tested for the dorsal immobility response (DIR), vertical cling catalepsy, and bar catalepsy. A different pattern of results was found for each of the three immobility behaviors. SCH 23390 significantly increased the DIR at each age except 15 days; there was a progressive increase in effect from 10 to 20 to 30 days of age. At the lowest dose, drug-induced bar catalepsy peaked at 15 days of age and declined at 20 and 30 days of age. The effect of SCH 23390 on vertical cling catalepsy increased with age, plateauing at 20 days. Thus, the developmental pattern of immobility responses to this dopamine D1 antagonist differs with each behavior measured.

Age Factors↗
PubMed1993

Locomotor activity following intra-accumbens microinjections of dopamine D1 agonist SK&F 38393 in rats.

The present study examined the effects of the dopamine D1 receptor subtypes agonist SK&F 38393 on locomotor activities after bilateral microinjection (0.00, 0.01, 0.1, 1.0, 10.0 micrograms) into the nucleus accumbens (Acb). The dose of 0.1 microgram elicited the highest response rate across measures of locomotion, rearing and stereotypy behavior. On the other hand, the largest dose of 10.0 micrograms was associated with significant increase in center time behaviors. The data were supportive of the hypothesis that dose-related locomotor activities elicited by microinjections of SK&F 38393 into the Acb are independently mediated by D1 receptors.

2,3,4,5-Tetrahydro-7,8-dihydroxy-1-phenyl-1H-3-ben↗
PubMed1993

Somatosensory pressure affects immobility and grasping reactions in bilateral labyrinthectomized rats.

The effects of dorsal clip pressure and proprioceptive plate pressure to soles of the feet on tonic immobility; dorsal clip pressure on contact righting, horizontal bar, and vertical cling; forepaw and slope board grasp reactions were investigated in bilateral labyrinthectomized (BL) rats. Both dorsal and proprioceptive pressures potentiated the duration of tonic immobility in BL animals whereas only the dorsal pressure affected the controls. Dorsal pressure potentiated the duration of the horizontal bar, vertical cling, and slope board grasps in both the control and BL group. However, the behavioral patterns were different. The BL animals had weak grasp reactions and with the dorsal clip, emitted "head-back fall" during the vertical cling and slope board grasp conditions. The results were discussed in terms of the tactile and vestibular interactions and control on the postural mechanisms.

Animals↗
PubMed1993

Biphasic effects of dopamine agonist N-0434 on locomotor behaviors in rats.

The effects of a dopamine agonist, (+/-)-2-(N-penylethyl-N-propyl)amino-5- hydroxytetralin (N-0434) (SC doses of 0.00, 0.01, 0.1, and 1.0 mg/kg) were tested in rats for 120 min in an activity monitor. The durations in seconds of horizontal locomotor time, rearing time, stereotypy time, and margin time (thigmotaxis) were measured during 12 10-min time blocks. N-0434 (0.1 and 1.0 mg/kg) resulted in biphasic effects (initial inhibition followed by potentiation) of linear locomotor time and an attenuation of thigmotaxis. The 0.1- and 1.0-mg/kg doses initially suppressed rearing time but had mixed potentiation effects. The 0.01- to 1.0-mg/kg doses suppressed stereotypy time. The differential behavioral profiles were discussed in reference to the functions of dopamine receptors.

Animals↗
PubMed1993

Behavioral effects of long-term administration of an anabolic steroid in intact and castrated male Wistar rats.

Once a week, intact and castrated male Wistar rats were intramuscularly injected with a 0.2 ml suspension of either 0, 10, or 50 mg nandrolone decanoate in cottonseed oil, for 8 consecutive weeks. After the sixth injection, locomotor activity was measured in an open-field and the acquisition of lever press behavior was assessed in an autoshaping procedure. Subsequently, all subjects were exposed to four sessions of continuous reinforcement prior to one session in which the effects of steroid administration on extinction were assessed. Locomotor activity decreased for all groups of rats with continued exposure to the open-field, differences between groups were not observed. Rats treated with the highest dose of nandrolone decanoate spent more time in the margin of the open-field. There were no significant differences between groups on any of the learning measures. Long-term, high-dose steroid administration in conjunction with mild food deprivation inhibited growth in intact and castrated rats, while low dose administration affected body weight in intact rats only. Steroid administration resulted in heavier and enlarged kidneys and lighter testes as well. These results suggest that the administration of anabolic steroids not only produces observable physiological changes, but that it may also affect spontaneous behavior. The failure to find differences in learning indices may have been a function of the particular paradigms used in the present experiment.

Anabolic Agents↗