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Biomedical subjects

G Cruccu

Publications and source records attributed to G Cruccu.

At least 19 recordsLinked to original sources
PubMed1995

Inhibition of hand muscle motoneurones by peripheral nerve stimulation in the relaxed human subject. Antidromic versus orthodromic input.

In active muscle, a supramaximal conditioning stimulus to peripheral nerve produces a classic silent period in the EMG. The present experiments examined the effect of this type of conditioning stimulus on motoneurone excitability in relaxed muscle. EMG responses evoked by transcranial magnetic stimulation of the brain were recorded from the first dorsal interosseus muscle (FDI) in 10 healthy subjects and 5 patients with sensory neuropathy. These responses (motor evoked potentials) were conditioned by supramaximal peripheral nerve stimuli given 0-150 msec beforehand. In the normal subjects, the classic silent period in the FDI lasted about 100 msec. The same conditioning stimulus only abolished motor evoked potentials when the conditioning-test interval was so short that the antidromic peripheral nerve volley collided with the orthodromic volley set up by magnetic brain stimulation. At longer conditioning-test intervals, although remarkably inhibited (65% mean suppression between 10 and 40 msec), the test motor potential was never completely abolished and gradually recovered by 100 msec. Inhibition of cortically evoked motor potentials did not depend upon activity set up by the conditioning stimulus in peripheral nerve sensory fibres. The patients with complete peripheral sensory neuropathy had the same extent and time-course of inhibition as the normal subjects. We conclude that in relaxed subjects the inhibitory effect of peripheral conditioning results almost exclusively from the motoneuronal inhibitory mechanisms consequent to antidromic invasion.

Adult↗
PubMed1994

Quantitative EEG modifications during the Cold Water Pressor Test: hemispheric and hand differences.

In a study designed to investigate the neurophysiological correlates of the Cold Water Pressor Test, a standardized experimental model of tonic pain, spectral EEGs were examined during the test in 15 young right-handed adults. Each subject performed a "cold water" and a "warm water" session. The subject immersed in cold water (0 degree C) either the right or the left hand alone, in a randomized way. EEG activity was recorded for an initial 3 min baseline and for the first and second minute epochs after immersion. A further EEG recording was obtained after a 30-min rest. Pain intensity was measured with a visual analogue scale. The EEG recordings showed several patterns of cortical activation during the test. Alpha 2 desynchronization was more evident on the contralateral parietal electrodes of the stimulated hand and lasted longer over all the right hemisphere. Delta activity increased bilaterally, predominantly in the frontal leads. Stimulation of the left hand resulted in a higher delta increase during the second minute after immersion.

Adult↗
PubMed1992

Piroxicam-induced analgesia: evidence for a central component which is not opioid mediated.

Piroxicam is a nonsteroidal anti-inflammatory drug with a potent analgesic effect. In order to establish whether the analgesic action of Piroxicam has a central component, we studied the effect of the drug on the nociceptive orbicularis oculi reflexes evoked by electrical stimulation of the cornea and supraorbital nerve in healthy subjects. Piroxicam significantly suppressed the corneal reflex and R3 component of the blink reflex by 28% (p < 0.05) and 50% (p < 0.01), respectively. This effect was not reversed by the i.v. injection of naloxone. Beta-endorphin levels did not change. Piroxicam administration induces distinct inhibitory changes in nociceptive reflexes, which suggests that the analgesic action of the drug has a central component. The ineffectiveness of naloxone, and the lack of beta-endorphin changes, indicate that this central action is independent of the opioid system; other pain regulatory systems are probably involved.

Adult↗
PubMed1992

Side asymmetry of the jaw jerk in human craniomandibular dysfunction.

The jaw jerk elicited by tapping the chin with a reflex hammer was electromyographically recorded in 14 patients with craniomandibular dysfunction, who were selected because of their strictly unilateral symptoms. Mandibular deviation, as measured by means of a kinesiograph, was on the same side as the pain. Neurological and neurophysiological investigations, including the recording of masseter motor potentials evoked by transcranial stimulation, showed normal function of the sensory and motor trigeminal nerve fibres. Latency and amplitude of the jaw jerk recorded in postural position and intercuspal occlusion were, respectively, longer and smaller on the affected side. In some cases the latency difference exceeded 1 ms, the limit usually considered significant for trigeminal neuropathy or brainstem lesions. Jaw-jerk asymmetry is probably due to facilitation on the side contralateral to mandibular deviation. In intercuspal occlusion, contralateral facilitation might be produced by a stronger input from muscle spindles and periodontal mechanoreceptors. In postural position, other factors probably intervene.

Adult↗
PubMed1991

Nociceptive quality of the orbicularis oculi reflexes as evaluated by distinct opiate- and benzodiazepine-induced changes in man.

The corneal reflex and the three components of the blink reflex (R1, R2, and R3) were recorded electromyographically in volunteers. The area of these responses was measured before and after administration of the narcotic-analgesic fentanyl (1.5 mg i.m.) and its antagonist naloxone, and after administration of the benzodiazepine diazepam (10 mg i.v.) and its antagonist flumazenil. Saline was given as a control placebo. The corneal reflex was 71% reduced by fentanyl, 43% by diazepam. R1 was 35% reduced and R2 was 60% reduced by diazepam. R3 was abolished by both drugs. Whereas the fentanyl-induced changes were completely reversed by naloxone, the diazepam-induced changes were only partly reversed by flumazenil. The corneal reflex appears to be a 'nociceptive' reflex under all points of view. Recording of the orbicularis oculi reflexes in man may be valuable in the evaluation of central-acting neurotropic drugs.

Adult↗
PubMed1991

Corticobulbar and corticospinal projections to neck muscle motoneurons in man. A functional study with magnetic and electric transcranial brain stimulation.

The cortical projections to neck muscle motoneurons were studied in normal subjects by electrical and magnetic transcranial brain stimulation. After magnetic stimulation with a large coil, motor evoked potentials were present in about 20% of relaxed and 100% of contracting neck muscles. The latency of these responses was short: about 7 ms in the sternomastoid and splenius and 9 ms in the trapezius muscles. Subtraction of the M-wave latency after stimulation of the accessory nerve at the skull base resulted in a central latency of about 4.5 ms. We suggest that rapid cortical projections connect with neck muscle motoneurons mono or disynaptically. The latency difference between the responses after electrical and magnetic stimulation was smaller in neck than in limb muscles but similar to that seen in masticatory muscles. A small magnetic coil was used to study the pattern of functional lateralization of cortical projections to neck muscle motoneurons; the projections for the sternomastoid and splenius are bilateral but predominantly contralateral, whereas those for the trapezius are exclusively contralateral.

Adult↗
PubMed1991

Histometric study of myelinated fibers in the human trigeminal nerve.

The trigeminal ganglion, roots and the initial portion of the ophthalmic, maxillary and mandibular nerves were dissected in 3 cadavers, to study the number, area and composition of the fascicles, and the density and diameter spectra of myelinated fibers. The total number of fibers (x 1000) was 26 in the ophthalmic, 50 in the maxillary, and 78 in the mandibular division, 7.7 in the motor root and 170 in the sensory root. In all nerves, the histograms of fiber diameter had a bimodal distribution. Cutaneous and muscle nerve fascicles clearly differed in the fiber density and diameter. The ophthalmic and maxillary nerves (cutaneous) had similar fascicles, and their maximum fiber diameter averaged 14.5 microns. Most fascicles of the mandibular nerve (probably cutaneous fascicles) closely resembled those of the ophthalmic and maxillary nerves, but in some fascicles (probably muscle nerves) the fibers were larger, with a maximum diameter of 19.3 microns. The findings in the three peripheral divisions agree with electrophysiological data about sensory and motor conduction in human trigeminal nerves. The observation that the ophthalmic and maxillary nerves have similar fiber spectra indicates that a special fiber composition does not account for the sparing of the ophthalmic division in trigeminal neuralgia. The absence of very large (A alpha) fibers in the sensory root does not support the view that impulses from muscle spindles are conducted along this root.

Humans↗
PubMed1991

Electrical and magnetic transcranial stimulation in patients with corticospinal damage due to stroke or motor neurone disease.

Twenty patients with hemiplegia and 13 patients with motor neurone disease were studied with electrical and magnetic transcranial stimulation. Motor evoked potentials were recorded from the biceps, thenar and tibialis anterior muscles. In both groups of patients magnetic stimulation with a Novametrix stimulator revealed fewer abnormalities than electrical stimulation with a Digitimer D180 stimulator. In patients with hemiplegia, motor evoked potentials after electrical stimulation were absent in 70% of muscles, delayed in 22% and normal in 8%; after magnetic stimulation, they were absent in 53% of muscles, delayed in 28% and normal in 19%. In patients with motor neurone disease, motor evoked potentials after electrical stimulation were absent in 62% of muscles, delayed in 10%, and normal in 29%; after magnetic stimulation, they were absent in 45% of muscles, delayed in 15%, and normal in 40%. The reason why magnetic stimulation reveals fewer abnormalities than electrical stimulation could be that magnetic stimulation repetitively discharges the pyramidal cells and, because of temporal summation mechanisms, produces more powerful excitatory potentials at the lower motoneurone synapse.

Adult↗
PubMed1991

Multiple firing of motoneurones is produced by cortical stimulation but not by direct activation of descending motor tracts.

In the present report we have tested whether stimulation of the motor descending tracts at the brain-stem level could set up repetitive motor unit discharges in a similar manner to that described for motor cortical stimulation. We have seen that a large descending motor volley, evoked by brain-stem stimulation, cannot produce repetitive firing of motor units. Repetitive motoneurone firing is therefore produced by multiple excitatory volleys set up by single cortical shocks.

Brain Stem↗
PubMed1991

Masseter inhibitory reflex in movement disorders. Huntington's chorea, Parkinson's disease, dystonia, and unilateral masticatory spasm.

Evoked by electrical stimulation of the mental nerve, the masseter inhibitory reflex consists of an early and a late silent period (SP1 and SP2), which interrupt the voluntary electromyographic (EMG) activity in the masseter muscle. We recorded the masseter inhibitory reflex and measured its latency, depth of suppression, duration and recovery cycle to paired stimuli, in patients with Huntington's chorea. Parkinson's disease, dystonia, or unilateral masticatory spasm. In patients with Huntington's chorea the reflex data and recovery cycle were normal. In patients with Parkinson's disease or dystonia, although the reflex data were normal, SP2 recovered far more rapidly than it did in control subjects. This is possibly due to hypoactivity of an inhibitory control of the polysynaptic chain of ponto-medullary interneurons that mediate SP2. In patients with unilateral masticatory spasm, both SP1 and SP2 were absent. Suppression is probably absent because this involuntary movement originates at a point along the peripheral course of the nerve.

Adolescent↗
PubMed1991

Quantitative assessment of cerebral blood flow in partial epilepsy using Xe-133 inhalation and SPECT.

The Xe-133 inhalation method was used to study rCBF in 12 patients with partial epilepsy during the interictal phase. SPECT images evidenced a focal CBF defect in 10 out of 12 patients, while quantitative analysis showed CBF abnormalities in all the patients. The focal CBF defect corresponded to the site of EEG abnormalities in nine patients. Additional low-flow areas beyond the EEG focus were found. Five patients presented a significant CBF decrease in the cerebellar hemisphere contralateral to the EEG focus. In five patients with unilateral EEG abnormalities, a CBF reduction was found in the contralateral cerebral hemisphere, mirror to the EEG focus. Finally, a widespread CBF decrease involving one or both cerebral hemispheres was observed in seven patients. Global and rCBF values were not correlated with age, duration of disease, frequency of seizures, secondary generalization, or specific therapy. SPECT may be useful in evaluating EEG epileptic foci, and quantitative SPECT allows the detection of functional effects of the epileptic focus on anatomically connected remote areas, probably due to the decrease of afferent inputs (diaschisis phenomenon).

Administration, Inhalation↗
PubMed1991

Corticospinal potentials after electrical and magnetic stimulation in man.

The present report deals with our study of the descending volley evoked by both electrical and magnetic transcranial stimulation in man. We discuss the differences of these two techniques specifically as regards the latency and amplitude of evoked potentials. In both cases, electrodes were placed either in the epidural space or directly on the spinal cord. Following electrical stimulation, the descending volley consisted of an early wave which appeared at low stimulation intensity and increased in amplitude and decreased in latency when the strength of the stimulus was increased. At high stimulation intensities the early wave was followed by later waves which travel at the same speed as the initial wave. By delivering paired cortical stimuli, the early wave evoked by the test stimuli is present at 1-msec interval and progressively recovered with longer intervals. The recovery cycle of the later waves is also extremely short. Following magnetic stimulation, the descending volley also consisted of an initial wave followed by later waves. The initial wave has a slightly longer latency, a higher threshold and a smaller amplitude than the early wave evoked by electrical stimulation. The results are discussed with reference to the D and I waves recorded from the pyramidal tract in animals.

Adult↗
PubMed1990

Corticobulbar projections to upper and lower facial motoneurons. A study by magnetic transcranial stimulation in man.

To investigate the human corticofacial projections, we recorded the compound motor potentials and single motor unit potentials evoked by magnetic transcranial stimulation, in the frontalis and lower facial muscles of healthy subjects. Potentials secondary to activation of the corticobulbar tract were contralateral in lower and bilateral in upper facial muscles. Even though the latency of responses was longer than would be expected for direct cortico-motoneuronal connections, these cannot be excluded either for lower or upper facial motoneurons.

Adult↗
PubMed1990

Descending volley after electrical and magnetic transcranial stimulation in man.

The descending volley evoked by electrical and magnetic transcranial stimulation was recorded with spinal electrodes in 3 subjects undergoing spinal surgery. The descending volley evoked by electrical stimulation, as previously described, was composed by a short-latency initial wave followed by later waves. In two subjects magnetic stimulation evoked an initial wave of slightly longer latency (0.2-0.3 ms), smaller amplitude and higher threshold than the initial wave evoked by electrical stimulation. In these two subjects, magnetic stimuli probably activated the pyramidal axons directly. In the third subject the initial wave evoked by magnetic stimulation had a latency of 1.4 ms longer and a considerably smaller amplitude than that evoked by electrical stimulation. In this case magnetic stimulation may activate the pyramidal axons indirectly.

Action Potentials↗