Biomedical subjects

D Le Bars

Publications and source records attributed to D Le Bars.

At least 91 records · Page 5Linked to original sources

PubMed1993

Diffuse noxious inhibitory controls in humans: a neurophysiological investigation of a patient with a form of Brown-Séquard syndrome.

In normal subjects, the application of heterotopic painful stimuli induces simultaneous and parallel decrease in the sensation of pain and of the spinal nociceptive flexion (RIII) reflex evoked by electrical stimulation of the sural nerve. This inhibition of the RIII reflex is absent in tetraplegic patient with clinically complete spinal cord transections and can be triggered only from the analgesic hand in patients with Wallenberg's syndrome. These findings suggest that the inhibitory phenomena observed in normal subjects are likely to be examples of diffuse noxious inhibitory controls (DNICs), being sustained by a loop involving supraspinal structures, the ascending part of which is localized in the spinoreticular tract. We now report an exceptional case of a patient with Brown-Séquard syndrome due to a 4-year-old spinal cord lesion (left side, T-6 level) produced by a knife-wound in the back. Nociceptive flexion (RIII) reflexes elicited by stimulation of cutaneous afferents in the ulnar and sural nerves were studied in the upper and lower limbs by recording from the biceps brachialis and biceps femoris muscles, respectively. For each limb, the RIII reflex threshold was determined. The reflex was then elicited regularly by stimuli of 1.2 times threshold before, during, and after periods of nociceptive electrical conditioning stimulation (15 mA; 4 Hz; 1 min) applied successively to the other three limbs.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗

PubMed1993

Relief of akinesia by apomorphine and cerebral metabolic changes in Parkinson's disease.

The cerebral metabolic rate of glucose was measured in 14 Parkinson's disease patients with severe on-off fluctuations. Two positron emission tomography (PET) scans with [18F]fluorodeoxyglucose were performed, one after a challenge of subcutaneous apomorphine at a dose able to relieve akinesia within 15 min and the other with the vehicle. Apomorphine reduced glucose utilization by 4-6% in the lenticular nuclei and the occipital cortex and by 6-9% in the thalamic nuclei, but this effect was not statistically significant. Thus, central stimulation of dopamine receptors by apomorphine in advanced Parkinson's disease is not associated with cerebral metabolic changes as assessed by PET. Despite a dramatic improvement of the motor state, the global neuronal activity in the striatum and its downstream projections remains stable, suggesting an equilibrium between excitatory and inhibitory dopaminergic activities.

Aged↗

PubMed1993

Computer-assisted reconstruction of axonal arborizations anterogradely labelled with the Phaseolus vulgaris leucoagglutinin technique.

This paper describes a computer-assisted method which allows the tracing of axonal arborizations, and the reconstruction in a either grey-scale or a binary image representation, of all labelled neuronal processes located within different focal planes of a single tissue section. The system includes a Nikon microscope connected to a CCD video camera, and a Macintosh microcomputer. Each step of the method is described in order to show that the capturing of images, retouching and pasting are easily and rapidly performed using commercially available hardware and software.

Animals↗

PubMed1993

Studies of brain structures involved in diffuse noxious inhibitory controls in the rat: the rostral ventromedial medulla.

1. Previous electrophysiological, pharmacological and anatomical evidence had suggested a possible participation of rostral ventromedial medulla (RVM) in the supraspinal part of the loop underlying diffuse noxious inhibitory controls (DNICs). In order to test this hypothesis, two experimental series were performed during which DNICs were compared in control sham-operated rats and rats with lesions of the RVM and of an adjacent candidate for such a role, the nucleus gigantocellularis reticularis (Gi). 2. In the first experimental series, lesions were induced, in anaesthetized animals, by injections of quinolinic acid (0.3-0.8 microliter of a 360 nmol/microliter solution) into the RVM or Gi. In the control animals (n = 10), the vehicle alone (artificial cerebrospinal fluid) was injected. Histological lesion reconstructions were performed after each electrophysiological experiment. Three groups of animals were considered: in the first group (n = 5), the lesion was centered on the RVM, including the two caudal thirds of nucleus raphe magnus (NRM) and adjacent reticular areas; in the second group (n = 5), the lesions extended more rostrally and involved the rostral pole of NRM; in the third group (n = 5), the lesion extended more laterally and dorsally and included nucleus reticularis gigantocellularis pars alpha (GiA), nucleus reticularis paragigantocellularis lateralis (LPGi) and the Gi. In each case, all the neuronal cell bodies within the lesioned area were destroyed. 3. In the second experimental series, electrolytic lesions of the total rostrocaudal extent of the NRM (n = 5) were induced, in anesthetized animals, by passing cathodal current (5 mA, 8 s). In the control animals (n = 5), the electrode was lowered but current was not applied. 4. One week after lesioning, the animals were anaesthetized, paralysed, artificially ventilated and recordings were made from convergent neurones in trigeminal nucleus caudalis. These neurones gave responses due to activation of A and C fibres when percutaneous electrical stimuli were applied to their receptive fields. DNICs were triggered by immersion of each paw in a 50 degrees C water-bath. Both the general properties of the convergent neurones and the inhibitions of the C fibre-evoked responses produced by these heterotopic noxious stimuli were compared in the different groups of animals. 5. The sizes of receptive field, spontaneous activities, thresholds for C fibre-evoked responses and responses to C fibre activation were not different in the control and lesioned animals. The percentage inhibitions of the C fibre-evoked responses both during and in the 44s following the conditioning periods were also very similar in the different groups of animals.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗

PubMed1992

Effects of systemic morphine on diffuse noxious inhibitory controls: role of the periaqueductal grey.

The effects of systemic morphine (1 mg/kg i.v.) on diffuse noxious inhibitory controls (DNIC) were studied in both sham-operated animals and those with quinolinic acid-induced lesions of the periaqueductal grey (PAG). DNIC acting on convergent neurones in the dorsal horn of the spinal cord were similar in the sham-operated and lesioned animals. However, following morphine injection, DNIC were blocked in the sham-operated but not in the PAG-lesioned animals. It is concluded that, although the PAG is not directly involved in the supraspinal loop subserving DNIC, it can modulate these controls. In addition, as naloxone reversed the effects of morphine in the control group but reduced DNIC in the PAG-lesioned animals, it is suggested that more than one opioidergic system is involved in DNIC.

Animals↗

PubMed1992

Effects of lesions of locus coeruleus/subcoeruleus on diffuse noxious inhibitory controls in the rat.

Diffuse noxious inhibitory controls (DNIC) acting on trigeminal convergent neurons were compared in sham-operated animals and rats with quinolinic acid induced lesions of the locus coeruleus/subcoeruleus (LC/SC). No significant differences were observed between control animals and those with ipsilateral, contralateral or bilateral lesions of the LC/SC, in respect of: (1) the general properties of the recorded units; and (2) the magnitude of the depressions of C-fiber-evoked responses of convergent neurons produced by immersing each paw in a 50 degrees C water bath (i.e. DNIC). It is concluded that the LC/SC is not involved, at least directly, in the supraspinal part of the loop which subserves DNIC in the rat.

Animals↗

PubMed1992

Functional neuroimaging strategy in temporal lobe epilepsy: a comparative study of 18FDG-PET and 99mTc-HMPAO-SPECT.

We performed 99mTc-hexamethylpropyleneamineoxime-single-photon emission computed tomography (SPECT) and 18F-fluorodeoxyglucose-positron emission tomography (PET) in 20 epileptic patients with well-lateralized temporal electroencephalographic focus, normal computed tomographic scan, and brain magnetic resonance imaging (MRI) either normal (n = 10) or showing nonspecific changes in the epileptogenic temporal lobe (n = 10). In patients with a normal MRI, PET exhibited focal hypometabolism in 80%, whereas SPECT showed corresponding hypoperfusion in only 20%. In patients with an abnormal MRI, PET and SPECT yielded 100% and 90% sensitivity, respectively. The metabolic and regional cerebral blood flow disturbances were topographically concordant with electroencephalographic and MRI findings in all these patients. Only patients with a large and pronounced hypometabolism on PET images exhibited hypoperfusion on SPECT. Spatial resolution appeared to be the critical factor responsible for the higher sensitivity of PET. However, this superiority of PET did not prove clinically useful in patients whose SPECT was abnormal, particularly when brain MRI showed nonspecific changes in the epileptogenic temporal lobe.

Adolescent↗

PubMed1992

In vivo release of calcitonin gene-related peptide-like material from the cervicotrigeminal area in the rat. Effects of electrical and noxious stimulations of the muzzle.

The continuous perfusion with an artificial cerebrospinal fluid of the cervicotrigeminal area of the spinal cord in halothane-anaesthetized rats allowed the collection of calcitonin gene-related peptide-like material with the same immunological and chromatographic characteristics as authentic rat alpha-calcitonin gene-related peptide. The spinal release of calcitonin gene-related peptide-like material could be significantly increased by the local application of 60 mM K+ (approximately +100%), high-intensity percutaneous electrical stimulation (approximately +200%) and noxious heat (by immersion in water at 52 degrees C; approximately +150%) applied to the muzzle. By contrast, noxious mechanical (pinches) and chemical (subcutaneous formalin injection) stimulations and deep cooling (by immersion in water at 0 degrees C) of the muzzle did not alter the spinal release of calcitonin gene-related peptide-like material. In addition, low-intensity electrical stimulation, recruiting only the A alpha/beta primary afferent fibres, significantly reduced (approximately -30%) the release of calcitonin gene-related peptide-like material from the cervicotrigeminal area. These data suggest that among the various types of natural noxious stimuli, noxious heat may selectively excite calcitonin gene-related peptide-containing A delta and C primary afferent fibres projecting within the dorsal horn of the spinal cord, and that activation of A alpha/beta fibres reduces spontaneous calcitonin gene-related peptide-like material release possibly through an inhibitory presynaptic control of calcitonin gene-related peptide-containing A delta/C fibres.

Animals↗

PubMed1992

Convergence of visceral and somatic inputs onto subnucleus reticularis dorsalis neurones in the rat medulla.

1. In anaesthetized rats, recordings were made within the medullary subnucleus reticularis dorsalis (SRD) from neurones that exhibited convergence of nociceptive inputs from the entire surface of the body. Neurones with total nociceptive convergence responded to supramaximal percutaneous electrical stimuli (2 ms duration) with early and late peaks due to the activation of A delta and C fibres, respectively, no matter which part of the body was stimulated. Neurones with partial nociceptive convergence responded to identical stimuli with an A delta peak of activation regardless of which part of the body was stimulated and with a C peak of activation from some, mainly contralateral, parts of the body. The characteristics of the responses of these neurones to graded colo-rectal distension (< or = 100 mmHg) were analysed. 2. The majority of neurones with total nociceptive convergence (n = 13 out of 16) responded to colo-rectal distension by increasing their firing rates. Although these neurones were virtually unresponsive to the lowest pressure employed (12.5 mmHg), they increased their discharges monotonically for distensions in the 26-100 mmHg range and these responses were sometimes followed by after-discharges. One of these neurones, which exhibited a high level of spontaneous activity, was inhibited during colo-rectal distension. None of the neurones with partial nociceptive convergence recorded (n = 10) ever changed its firing rate during increases of intracolonic pressure up to 100 mmHg. 3. It is concluded that neurones with total nociceptive convergence give monotonic stimulus-response relationships for colo-rectal distensions. Thus, neurones with total nociceptive convergence can encode the strength of visceral stimuli, probably within the noxious range, just as they have previously been shown to do for thermal and mechanical cutaneous stimuli. Together with previous electrophysiological and neuroanatomical findings, this study provides further evidence for the convergence of noxious inputs onto single SRD neurones. 4. It is suggested that neurones with total nociceptive convergence could be a link in spino-bulbospinal loops involved in autonomic reactions to strong visceral stimulation. In addition, SRD neurones could be an important supraspinal relay in the mechanisms of visceral pain.

Action Potentials↗

PubMed1991

Spinal afferent projections to subnucleus reticularis dorsalis in the rat.

Small amounts of the retrograde tracer WGA-apoHRP-Au complex were injected in the caudal medulla to study the spinal afferents to the subnucleus reticularis dorsalis (SRD). Labelled neurones were found at all levels of the spinal cord: the highest numbers were in the ipsilateral cervical spinal cord (mainly laminae I, V, VI, VII, VIII and X), the lowest were at the thoracic and lumbar levels bilaterally, while an intermediate density was found bilaterally at the sacral level. When injection sites were located in the underlying subnucleus reticularis ventralis (SRV), labelling was bilateral and mainly in the deep layers of the cervical spinal cord. Together with our previous electrophysiological and anatomical data, this study suggests that the SRD provides a link in spino-reticulo-spinal loops implicated in the processing of pain.

Afferent Pathways↗

PubMed1991

Acupuncture-like stimulation induces a heterosegmental release of Met-enkephalin-like material in the rat spinal cord.

In order to investigate the effects induced by acupuncture on the activity of enkephalinergic neurons in the spinal cord, either the lumbar or the cervico-trigeminal area was perfused with artificial cerebrospinal fluid (CSF) (0.1 ml/min) in halothane-anaesthetized rats, and Met-enkephalin-like material (MELM) was measured in 0.5 ml fractions of the perfusates. The effects of manual acupuncture performed by a traditional Chinese acupuncturist at the 'Zusanli' point on the right hind limb were compared to the effects induced by acupuncture applied at a non-acupoint next to 'Zusanli.' The manipulation of needles either at the 'Zusanli' point or at the non-acupoint had no effect on the release of MELM from the lumbar area but significantly increased the release from the cervico-trigeminal zone. It is concluded that manual acupuncture triggers a heterosegmental activation of enkephalinergic neurones within the spinal cord and that this effect is non-specific in terms of the location of the stimulated point.

Acupuncture Therapy↗

PubMed1991

Acupuncture-evoked responses of subnucleus reticularis dorsalis neurons in the rat medulla.

Recordings were made from neurons in subnucleus reticularis dorsalis of the rat. Two populations of neurons could be distinguished: those with total nociceptive convergence which were driven by activating A delta- and C-fibers from any part of the body and those with partial nociceptive convergence which were driven by activating A delta-fibers from any part of the body or C-fibers from some, mainly contralateral, regions. The effects on subnucleus reticularis dorsalis neurons of manual acupuncture, performed by a traditional Chinese acupuncturist at the "Renzhong", "Sousanli", "Changqiang", and "Zusanli" acupoints and at a non-acupoint next to "Zusanli", were studied. Acupuncture stimulation for 30 s at the acupoints or the non-acupoint strongly excited all the total nociceptive convergence neurons tested; these neurons responded with a discharge of rapid onset which was often followed by after-discharges lasting for approximately 30-60 s. The majority but not all of the partial nociceptive convergence neurons responded to 30 s of acupuncture stimulation at the acupoints or the non-acupoint. This was especially the case when the stimulus was applied to contralateral or midline parts of the body. The potency of acupuncture as a means of activating subnucleus reticularis dorsalis neurons varied significantly with the area of the body being stimulated such that: contralateral greater than midline greater than ipsilateral areas. The levels of induced activity were of similar magnitude to those evoked by noxious mechanical stimuli applied under identical experimental conditions. No differences were found between the capacities to activate subnucleus reticularis dorsalis neurons of the "Zusanli" point and the adjacent non-acupoint, no matter whether these were stimulated ipsi- or contralaterally; this suggests a lack of topographical specificity in the activation of these neurons. Since subnucleus reticularis dorsalis neurons are activated exclusively or preferentially by noxious inputs, it is concluded that the signals elicited by manual acupuncture travel through pathways responsible for the transmission of nociceptive information. Since acupuncture, a manoeuvre which is known to elicit widespread extrasegmental antinociceptive effects, activates subnucleus reticularis dorsalis neurons which, anatomically, send dense projections to the dorsal horn at all levels of the spinal cord, we would suggest that this structure may be involved not only in signalling pain but also in modulating pain by means of spino-reticulo-spinal feed-back mechanisms.

Action Potentials↗

PubMed1991

PET and plasma pharmacokinetic studies after bolus intravenous administration of [11C]melatonin in humans.

A human PET study was performed with carbon-11 labelled melatonin in a healthy volunteer. Plasma pharmacokinetics of melatonin and 6-sulfatoxymelatonin were simultaneously determined using radioimmunoassay. Analysis of tracer kinetics showed maximum activity in the brain 8.5 min following injection, which was different from the curve observed for the plasma radioactivity (maximum at 3.5 min). The results confirmed that melatonin readily crosses the blood-brain barrier and that 6-sulfatoxymelatonin is the main plasma metabolite. The distribution of tracer as a function of time in this study failed to reveal any specific binding.

Adult↗

PubMed1991

Metabolic patterns associated with non-specific magnetic resonance imaging abnormalities in temporal lobe epilepsy.

We investigated the cerebral metabolic patterns associated with non-specific hyperintense T2-weighted image on Magnetic Resonance Imaging (MRI) in Temporal Lobe Epilepsy (TLE). Nineteen patients suffering from TLE with a normal CT scan underwent Positron Emission Tomography (PET) using 18F-fluorodeoxyglucose; 8 had hyperintense T2-weighted image on MRI in the epileptogenic temporal lobe and 11 had a normal MRI. Interictally, PET exhibited focal hypometabolism in all the patients with hyperintense T2-weighted image and in 8 of the 11 whose MRI was normal. The hypometabolic area was significantly more extensive in patients with hyperintense T2-weighted image in whom it always encompasses the site of the MRI abnormality. Moreover, these patients had higher metabolic asymmetry index in the temporal and parietal lobes than patients with a normal MRI. One patient with mesial temporal hyperintense T2-weighted image underwent an ictal PET, which showed that the focal hypermetabolism fitted remarkably with the site and size of the abnormal MR signal. Thus, non-specific hyperintense T2-weighted images are associated with particular interictal and ictal metabolic patterns which might suggest that these MRI abnormalities reflect an epileptogenic lesion.

Adolescent↗

PubMed1991

Rabbit whey acidic protein concentration in milk, serum, mammary gland extract, and culture medium.

Rabbit whey acidic protein has been purified from whey using an AcA54 column. The purified whey acidic protein had an amino acid composition in agreement with the previously defined cDNA sequence. An antibody against whey acidic protein was raised in guinea pig. This antibody did not crossreact with mouse or cow milk or with rabbit alpha s1-casein and beta-casein. Whey acidic protein concentration was measured in rabbit milk using the antibody with a radioimmunoassay. The concentration of whey acidic protein in rabbit milk was 15 mg/ml, whereas the concentrations of alpha s1-casein and beta-casein were 16 and 45 mg/ml, respectively. The concentration of the three proteins was also evaluated in culture medium of rabbit primary mammary cells. The three proteins were induced by prolactin alone. Glucocorticoids amplified the prolactin effect on whey acidic protein more intensively than on caseins. The three proteins were present in mammary extract from virgin rabbit. The concentration of these proteins was lower at d 8 and 14 of pregnancy, and it was very high at d 25 of pregnancy. Whey acidic protein was undetectable in blood of virgin, weaned, and midpregnant females and of males. Whey acidic protein was present in blood of lactating rabbits, but alpha s1-casein and beta-casein were not detectably present in rabbit blood at the examined physiological states.

Amino Acids↗

PubMed1991

Depressive effects of mu and delta opioid receptor agonists on activities of dorsal horn neurones are enhanced by dibencozide.

The effects on C fiber evoked activity in lumbar dorsal horn convergent neurones of i.v. morphine alone, of Tyr-D-Thr-Gly-Phe-Leu-Thr (DTLET) alone or of either of these drugs in association with 5-deoxyadenosylcobalamine (dibencozide) were investigated in anesthetized rats. Both morphine and DTLET depressed the neuronal responses in a dose-related fashion, with the former requiring lower doses. Although dibencozide alone was devoid of any effect, it significantly enhanced the depressive effects of all doses of morphine tested and of the lower two doses of DTLET. It is concluded that dibencozide enhances the spinal depression of nociceptive information elicited by mu and delta opioid agonists. This drug could provide a useful tool for the study of interactions between opioids and opioids receptors. It is also suggested that dibencozide could be useful in clinical practice for reducing the dosage of opioids.

Amino Acid Sequence↗

PubMed1991

[Visuo-constructional disorders and alexia-agraphia associated with posterior cortical atrophy].

A 57 year-old woman developed a slowly progressive environmental agnosia and dressing apraxia without disturbances of language, memory, orientation and social activities. Two years later, alexia, agraphia, visual agnosia, constructional apraxia, simultagnosia and imitation apraxia of nonsymbolic gestures were also noted. Ophthalmic examination demonstrated a left inferior quadranopsia. Oral comprehension was normal. There was no loss of insight, and behavioral response was appropriately concerned. Computed tomography and magnetic resonance imaging revealed bilateral cortical atrophy in parieto-occipital areas, most pronounced on the right side, with enlargement of the ventricles. Positron emission tomography demonstrated low flow and metabolism values in the right parietal, temporal and occipital regions. This case is very similar to those of posterior cortical atrophy recently reported by Benson et al. (1988). It suggests a selectively degenerative dysfunction of posterior association cortex, sparing oral language and verbal memory.

Agnosia↗

PubMed1991

[Different clinical types of degenerative aphasia].

The authors report 3 cases of slowly progressive aphasia with different language disturbances: anomia, pure word deafness and Broca's aphasia. All patients were independent in daily life activities. Insight, judgement and overall behaviour were intact. There was no major disturbance of other cognitive functions, but psychometric tests showed mild deficits suggesting widespread involvement. CT scans and magnetic resonance imaging showed focal dilatation of the left sylvian fissure. A positron emission tomographic study showed left perisylvian hypometabolism. A review of the literature yielded an increasing number of cases of this degenerative syndrome affecting dominant hemisphere language areas. Our cases confirm the clinical heterogeneity of degenerative aphasia. Postmortem neuropathological examinations are rare and many causes are found: Pick's disease, Alzheimer's disease or aspecific gliosis.

Aged↗