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Biomedical subjects

J Gybels

Publications and source records attributed to J Gybels.

At least 19 recordsLinked to original sources
PubMed2001

Effect of the serotonin agonist 8-OH-DPAT on the sensorimotor system of the rat.

8-Hydroxy-2-(di-n-propylamino)-tetralin hydrobromide (8-OH-DPAT, 2 mg/kg) is used to induce perseverative behavior in rats in a T-maze as a model for obsessive-compulsive disorder (OCD). Using the open-field test, radiant heat test, and the test with von Frey filaments, we examined whether alterations in sensorimotor functioning could contribute to the perseverative tendencies in this model by measuring differences in left versus right hind paw reactions after 8-OH-DPAT administration (2 mg/kg, sc). Also, the effect of repeated 8-OH-DPAT administration on sensorimotor functioning was tested every third day. 8-OH-DPAT administration induced a significantly decreased sensorimotor performance in the open-field test, an increased threshold for noxious thermal stimulation (increased withdrawal latency, WL, and decreased elevation time, ET) in the radiant heat test, and a decreased nociceptive threshold for mechanical stimulation in the test with von Frey filaments. All changes in sensorimotor functioning were similar for left and right hind paws suggesting that, these changes as measured with the tests in the present study, are not likely to contribute to the perseverative behavior of rats in a T-maze. Further, repeated administration of 8-OH-DPAT had no effect in the radiant heat test and the test with the Frey filaments, but produced a tolerance effect in the open-field test.

8-Hydroxy-2-(di-n-propylamino)tetralin↗
PubMed2001

Thalamic stimulation in neuropathic pain: 27 years later.

An overview is given of CNS mechanisms which are behind the beneficial effects of VPL-VPM thalamic stimulation in the treatment of neuropathic pain. Further research in this field is urgently needed and the recent possibility to combine Deep Brain Stimulation with positron emission tomography (PET) will certainly help to unravel the brain circuitry implicated in stimulation-produced analgesia. Brain stimulation is an artificial way to activate nervous tissue that is reversible and, when correctly applied, has few complications. The clinical results warrant a continued dissemination of brain stimulation as a treatment in well selected cases of neuropathic pain.

Electric Stimulation Therapy↗
PubMed2000

Targeting the basal ganglia for deep brain stimulation in Parkinson's disease.

The revitalization of surgery for Parkinson's disease (PD) has fueled discussion about the best methodology to define the target. Placement of electrodes for deep brain stimulation (DBS) requires the usual stereotactic technique but the argument is mainly centered on whether or not microrecording neuronal activity is necessary. We compared the accuracy of calculating the coordinates X (medio-lateral) and Y (rostro-caudal) considered by the classic stereotactic method, i.e., definition of the AC-PC intercomissural line by MRI and a digitized version of the Schaltenbrand's atlas, with final electrode placement according with microrecording and microstimulation in 21 patients. For both the globus pallidum internum (GPi) (n = 21) and the subthalamic nucleus (STN) (n = 36) there was, respectively, a 43% and 45% mismatching of more than 3 mm between the theoretic coordinates and the final site of electrode location. This applies to both the X and Y planes. Accuracy was not improved in patients (n = 11) in whom the bilateral procedure was undertaken in a single day. We conclude that proper electrode positioning of the STN and GPi requires fine electrophysiologic assessment.

Adult↗
PubMed1999

[The placebo effect: classes of explanation].

The placebo effect is a frequent phenomenon in medicine, but very little is known about its mechanisms. An overview is given of the different classes of explanation of the placebo effect in analgesia and in particular the role of endogenous opioids, classical conditioning and expectations. Then the question is raised which are the properties of placebo for which a theory has to provide answers in order to be coherent. These properties are, between others, the efficacy of placebo in a variety of conditions, in individuals with different personality characteristics, etc. Finally, the difficulty of observing individual placebo is emphasized and problems concerning the diagnostic and therapeutic use of placebo are mentioned.

Conditioning, Classical↗
PubMed1997

[Image-guided surgery].

Initially, stereotactic surgery was developed to treat functional brain diseases only. The localisation of targets was based on stereotactic atlases and radiographs. The introduction of computer based imaging techniques, such as CT and MRI, have offered the possibility to "see" anomalies and to approach them stereotactically. The working principle of such a procedure consists of three steps. It is assumed that brain tissue does not move with respect to the skull. 1. Acquisition of the images and their registration with the patient, usually based on a series of reference points (fiducials) that belong to a stereotactic localizer attached to the base ring of the stereotactic frame, 2. planning and simulation of the surgical intervention, mostly based on two-dimensional (2D) images resliced along arbitrary directions, and 3. intra-operative guidance of the instruments mounted onto the stereotactic frame. This procedure has continuously been updated by new image acquisition techniques, 3D visualization and frameless stereotaxy. 1. PET, MRI and angiography (DSA, MRA) have been used in addition to CT. Moreover, such images of different modalities can automatically be fused without using a stereotactic frame or other artificial fiducials. 2. 3D images for surgery planning have become available, a feature that has proved to be very useful for the cerebral blood vessels. 3. The stereotactic frame can be replaced by a robot arm or an optical guidance system. Registration of the instruments with the patient is then performed by using markers in the cranial bone or on the scalp, or by means of intra-operative images such as radiographs or video images. Recently the use of registered video images has resulted in a number of experiments with "improved reality" and telesurgery. The same working principle has shown to be useful for bone and bone related surgery. As in brain surgery, the prerequisites of rigidity and immobility with respect to a reference are satisfied. Because bone structures are rigid and can easily be outlined in CT images, 3D graphical as well as stereolithographic representations can be produced for the purpose of planning and even for navigation. Unfortunately, for most organs or soft tissue the above conditions of inflexibility and fixed position with respect to a reference are not fulfilled. Real time imaging, partly due to the introduction of the "open" MR scanner, may offer a solution. It can be expected that interventional diagnostic imaging will become increasingly important in the future, also for neurosurgery.

Humans↗
PubMed1996

Production of tumor necrosis factor in spinal cord following traumatic injury in rats.

Production of tumor necrosis factor (TNF) in the spinal cord following traumatic injury has been studied. In these experiments, the level of TNF was examined in the homogenate of the spinal cord, cerebrospinal fluid (CSF) and serum (n = 56). TNF could be detected in the injured spinal cord but not in the normal spinal cord. The TNF level increased in the spinal cord after the injury. At the lesion site, a maximal TNF concentration was observed 1 h after the injury, and the TNF concentration remained at this level until 8 h after the injury. Thereafter, it decreased gradually. However, TNF still could be detected 72 h after the injury. No TNF could be detected in the CSF and serum, collected from rats both with and without spinal cord injury (SCI). This study thus suggests that TNF is produced locally in the spinal cord following traumatic injury, and this TNF production is caused by the injury. The present results also demonstrate that TNF production is an acute and rapid reaction in the spinal cord following traumatic injury.

Animals↗
PubMed1995

The consumption of fentanyl is increased in rats with nociceptive but not with neuropathic pain.

The question whether opioids relieve neuropathic pain remains a controversial issue. Experimental as well as clinical studies report contradictory results. This study investigated the consumption of fentanyl, a short-acting opioid, in rats with neuropathic pain, induced by partial sciatic nerve injury. The experiment consisted of a drug choice procedure in which the animals could choose between a solution containing 0.008 mg/ml of fentanyl and a highly palatable sweet solution. It was reasoned that if opioids have an analgesic effect in neuropathic pain, this will reinforce the intake of fentanyl more so in rats with neuropathic pain than in pain-free controls. This protocol was previously already used by Colpaert et al. (1982) in a rat model of chronic pain of nociceptive origin, namely polyarthritis. No significant differences were found in the relative oral intake of the fentanyl solution in mononeuropathic and pain-free control rats. In contrast, rats with nociceptive pain, adjuvant monoarthritis, drank significantly more of the fentanyl solution than did control rats. These data give experimental support for the clinical findings that opioids have a poor analgesic effect in neuropathic pain.

Analysis of Variance↗
PubMed1995

The use of magnetic resonance angiography in stereotactic neurosurgery.

The authors discuss the advantages and disadvantages of the use of magnetic resonance (MR) angiography images in stereotactic neurosurgery. Current computer programs designed to assist the neurosurgeon in the planning of stereotactic neurosurgical interventions use intraarterial digital subtraction angiography images to visualize the blood vessels. Magnetic resonance angiography is a recent technique with a number of advantages over the digital subtraction method: it is less invasive and less prone to complications; it provides truly three-dimensional data sets that can be viewed from any direction; and it can visualize both stationary and flowing tissues with the same imaging device and localizer frame. Although digital subtraction images are still superior in contrast and vascular detail, state-of-the-art high-resolution MR angiography sequences provide sufficient vascular detail for planning surgery. Contrast-enhanced MR angiography images were acquired using adapted gradient-echo sequences to compensate for flow-induced distortions; postacquisition distortion correction was not necessary. Five methods to integrate and inspect a possible trajectory in the MR angiography data are discussed. Initial clinical experience with eight patients led to the conclusion that MR angiography is a valuable imaging modality that can be integrated reliably into a stereotactic neurosurgery planning procedure.

Adult↗
PubMed1994

[Pain of autonomic nervous system origin].

Reflex sympathetic dystrophy (algodystrophy) is a descriptive term used to designate a clinical phenomenology, which appears after a trauma, often a minor one; it is thought that the sympathetic nervous system plays an important role in its physiopathology. The same applies to sympathetic maintained pain appearing after a lesion of a peripheral nerve (causalgia). There is no agreement as to which are the criteria necessary to make the diagnosis and as to what is the physiopathology of these syndromes. Research in this field is very active today.

Autonomic Nervous System Diseases↗
PubMed1994

On the problem of geometric distortion in magnetic resonance images for stereotactic neurosurgery.

In this paper, we discuss the issue of geometric distortion in magnetic resonance (MR) images used to plan stereotactic neurosurgical interventions. We analyze the process for the case of Fourier transform imaging and demonstrate that spatial misregistrations are fundamentally due to two causes: deviations of the magnetic field from its ideal value and blood flow. This enables us to relate the causes of geometric distortion to the MR imaging system, the patient and the stereotactic localizer frame. Based on the general model, we propose model refinements and discuss methods for the quantification and correction of all causes. The results of our calculations and experiments indicate that, using the proposed corrections, MRI and MR angiography should be considered valuable and reliable acquisition modalities for the planning of stereotactic neurosurgical interventions.

Brain↗
PubMed1994

How does the stereotactic workstation help the neurosurgeon?

At the KUL University of Leuven a workstation for the planning of neurosurgical stereotactic procedures has been developed. Its benefits are illustrated in three exemplary cases. The CT and/or MR images, acquired under stereotactic conditions, are transmitted via a PACS network (picture archiving and communication systems) directly to the stereotactic workstation in the operating theater. Target and entry point can be accurately defined on zoomed images. The trajectory can be checked and modified on all registered data sets and on resliced images along any plane. Maximum intensity projection of magnetic resonance angiography data sets along any arbitrary direction show the relative position of the blood vessels and the trajectory. During the preceding 32 months 29 patients were operated on using the stereotactic workstation. Postoperatively no new neurological deficit was observed in any of these patients. The workstation improves patient safety and increases the accuracy of neurosurgical stereotactic operations, because it helps the neurosurgeon to avoid blood vessels and/or important functional areas.

Adult↗
PubMed1993

What can the neurosurgeon offer in peripheral neuropathic pain?

Neurosurgery has much to offer in the treatment of peripheral neuropathic pain but selection of the best procedure for a given patient remains problematic: planning of the treatment must be based on an analysis of the pathophysiological mechanism in the given case but the identification of this mechanism is often difficult. Available procedures are: 1) Nerve repair, neurolysis and nerve relocation; 2) Interventions on the sympathetic nervous system; 3) Neurostimulation; 4) Intraspinal morphine; 5) Ablative lesions. Neurosurgeons have, or should have, the necessary neuroscience background and microsurgical skills to be important partners of the team caring for patients with peripheral neuropathic pain.

Animals↗
PubMed1993

Therapeutic stereotactic procedures on the thalamus for pain.

Thalamotomy and electrical stimulation of a thalamic target as treatment for persistent pain are discussed. Thalamotomy is only rarely performed these days according to a questionnaire, given to some colleagues, about the type and the number of operations they performed in the years 1984, 1985 and 1986. The need for stimulation in the periventricular or periaqueductal grey for nociceptive pain is decreasing due to the advent of intraspinal and intraventricular administration of opioids. Nowadays medial and lateral ventro-posterior thalamic nuclei are frequently stimulated for treatment of deafferentation pain. Of 36 patients with deafferentation pain, 22 initially had benefit from this stimulation, but long-term success was only achieved in 11 (30%) of them. It was a general trend that the patients with an initial high pain relief score obtained the best long-term results.

Electric Stimulation Therapy↗
PubMed1992

Further evidence for myelinated as well as unmyelinated fibre damage in a rat model of neuropathic pain.

A mononeuropathy, produced by ligation of the sciatic nerve in rats, has recently been proposed as an animal model of experimental pain and pain-related disorders (hyperalgesia and allodynia). We investigated quantitatively the morphological changes in myelinated and unmyelinated fibres of the sciatic nerves 2 weeks after ligation in rats exhibiting allodynia to thermal stimulation. There was a marked reduction in the number of large myelinated fibres distal to the ligature (711 +/- 34 compared with 5315 +/- 230 in normal nerves). We also found a significant loss of small myelinated fibres (2429 +/- 109 compared with 3197 +/- 308 in normal nerves), the remaining fibres of this type showing pathological properties. Finally, ultrastructural evidence of damage to unmyelinated fibres was found. The typical pattern of large clusters of normal unmyelinated axons was no longer present within most regions of the nerve. There was a significant reduction in the size of the unmyelinated fibres (0.41 micron +/- 0.15 compared with 0.71 micron +/- 0.08 in normal nerves), together with a twofold increase in their number per cluster. Hypotheses about the mechanism of thermal allodynia in this pain model therefore must take into account the fact that all fibre classes show pathological changes.

Animals↗