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Biomedical subjects

M Manfredi

Publications and source records attributed to M Manfredi.

At least 163 records · Page 9Linked to original sources
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

Two sisters with generalized dystonia associated with homocystinuria.

Two sisters with progressive dystonic syndromes and homocystinuria are presented. The biochemical defect was not accompanied by the typical clinical features of homocystinuria. Magnetic resonance imaging (MRI) revealed bilateral lesions of the basal ganglia. Homocystinuria should be considered among the causes of symptomatic or secondary dystonias associated with basal ganglia lesions.

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

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↗
PubMed1990

Botulinum A toxin injection in patients with blepharospasm, torticollis and hemifacial spasm.

Botulinum A toxin was injected into the affected muscles in 20 patients with blepharospasm, 8 with torticollis and 12 with hemifacial spasm. In all cases blepharospasm and hemifacial spasm was abolished or markedly reduced. The only side effect was transient ptosis and diplopia. Patients with torticollis had a mild to moderate improvement of the dystonic posture and pain; dysphagia was the most troublesome side effect. Botulinum A toxin is an effective therapy in patients with focal dystonia and spasms.

Blepharospasm↗
PubMed1990

Effects of brainstem lesions on the masseter inhibitory reflex. Functional mechanisms of reflex pathways.

The masseter inhibitory reflex (MIR) was investigated in 16 patients with localized brainstem lesions involving the trigeminal system. The MIR consists of two phases of EMG silence (S1 and S2) evoked by stimulation of the mental nerve during maximal clenching of the teeth. The extent of the lesions was assessed by neurological examination, nuclear magnetic resonance imaging (MRI), and recording of trigeminal reflexes with known paths (jaw jerk and blink reflex). The MIR appeared to be abnormal in lesions involving the pontine tegmentum, from the pontomedullary junction to midpons, and some lesions selectively affected one component of the MIR, proving that S1 and S2 are relayed by independent circuits. The results indicate that afferent fibres for S1, which reach the pons via the trigeminal sensory root, enter the ipsilateral trigeminal spinal tract and terminate at the level of the midpons; impulses are then relayed by interneurons to the ipsilateral and contralateral trigeminal motor nuclei. The afferent fibres for S2 follow a similar path, but descend to the pontomedullary junction; at this level impulses are conducted along bilateral interneuronal paths, which probably ascend through the lateral reticular formation, before connecting with the trigeminal motor nucleus on either side. Analysis of MIR recordings can be of particular value because brainstem inhibitory reflexes cannot be tested by clinical examination.

Adult↗