Search PubMed⌕ Search

Biomedical subjects

O Mameli

Publications and source records attributed to O Mameli.

At least 55 records · Page 3Linked to original sources
PubMed1982

Cerebellar impairment following acute nontoxic administration of phenytoin in rat.

In awake paralyzed Wistar rats, the following effects of an acute nontoxic dose of phenytoin (PHT) on different parameters of cerebellar electrical activity were evaluated: spontaneous discharge rate of single Purkinje cells (P-cells), field potentials, and responses of P-cells generated by electrical stimulation of a forelimb nerve. Variations of the response of single neurons located in the inferior olive were also studied, in order to assess the effects of PHT on this precerebellar relay station. The drug was administered orally and plasma and cerebellar levels regularly estimated. The results indicate that an acute, nontoxic dose of PHT is associated with an increase of P-cell firing rate. This finding is supported by the analysis of the frequency distribution of interspike intervals, and by the field potentials, P-cell, and olivary responses induced by stimulation of a radial nerve. In addition, it was observed that the increase in P-cell firing was mainly depending upon a higher activity of the climbing fibers. The increase in the response of P-cells and olivary cells was correlated with plasma and cerebellar drug levels. The conclusion was reached that PHT increases the cerebellar cortical activity through two mechanisms: (a) by acting directly on the cerebellar P-cell; and (b) indirectly by acting on the origin of climbing fibers at the inferior olive nucleus.

Animals↗
PubMed1981

[Influence of the spinal cord on the cerebral cortex nystagmogenic area].

We have investigated the effect of section of the spinal cord, at cervical and thoracic levels, on the excitability of the nystagmogenic area in the rabbit. Cervical transection (C2 level) induced a modification of excitability of this area since the threshold for cerebral eye nystagmus was lowered and the frequency of eye jerks was increased. Dorsal spinal transection (T4 level) did not affect the cerebral nystagmogenic area. During electrical stimulation of the dorsal quadrants of the proximal stump of the spinal cord, we found a lowering of excitability of cerebral nystagmogenic area, while ventral quadrants stimulations induced a facilitating effect on the cerebral nystagmogenic area. The evoked potentials and the responses of single units to photic stimulation of contralateral retina confirmed these results. In conclusion, the spinal cord influences the cortical nystagmogenic area by modulating its output.

Animals↗
PubMed1981

[The vestibular nuclei as the integration center of central and peripheral afferent projections].

Responses of individual vestibular units were recorded in cat following electrical stimulation of the cerebral cortex and peripheral nerves. Convergence of central and peripheral inputs were recorded from 28 out of 75 cells (37%), localized in the lateral vestibular nucleus. The most important inputs to vestibular neurons come from the areas of sensorimotor cortex and peripheral nerves concerned with the same limb. However, crossed effects were observed in a limited number of vestibular neurons.

Animals↗
PubMed1980

Distribution of visual input to the vestibular nuclei.

The electrical activity of individual vestibular nuclear neurons was recorded in anesthetized and paralyzed cats and their responses to photic stimulation of the retina were studied. The visual input produced various types of unit responses. The cells of the superior vestibular nucleus showed a predominant excitatory response, the neurons of the medial vestibular nucleus displayed different combinations of excitatory and inhibitory effects, while those of the descending vestibular nucleus responded with excitation followed by inhibition. Photic stimulation of the retina elicited responses of vestibular nuclei with different latencies. The superior and medial vestibular nuclei showed shorter latencies. It is concluded tht the visual input may reach the vestibular complex thus participating in the reflex control of the ocular motoneurons.

Animals↗
PubMed1978

Functional role of the cerebral nystagmogenic area in the cat.

A nystagmogenic area has been identified in the occipital lobe of the cerebral cortex of the cat. The electrical stimulation of this area induces a horizontal eye nystagmus directed toward the opposite side. The chronic lesion of both cerebral nystagmogenic areas provokes dramatic modifications of the eye nystagmus elicited by optokinetic stimulations. In particular, it has been observed that following the ablation of the two nystagmogenic areas the optokinetic eye nystagmus is abolished being replaced by pendular oscillations of the eyes with intercalated eye jerks in the same direction of the normal optokinetic eye nystagmus.

Animals↗
PubMed1977

Vestibular units during decompensation.

Typical modifications of the unitary discharge of vestibular units have been recorded following the transection of the spinal cord of hemilabyrinthectomized and compensated guinea-pigs. These results support the concept that the spinal cord is essential in the compensation of the symptoms resulting from a lesion of one labyrinth.

Animals↗
PubMed1976

Vestibular nuclei of hemilabyrinthectomized guinea pigs during decompensation.

1. The effects of the post-brachial section of the spinal cord on the field potentials recorded from the vestibular nuclei during stimulation of the right vestibular receptors have been studied in left hemilabyrinthectomized and then compensated guinea pigs. 2. Facilitation of the field potentials in the right vestibular nuclear complex and inhibition in the left nuclei have been observed. 3. These results confirm that the spinal cord is involved in the compensation of the release syndrome brought about by the lesion of one labyrinth. 4. The possible mechanisms underlying such a compensation are discussed.

Animals↗
PubMedDate not supplied

Brain electrobiogenesis protection induced by nimodipine and MK-801 during acute hypoxia in hypertensive rats.

The protective effect of nimodipine, a calcium entry blocker, and MK-801, an excitatory amino acid antagonist, on the cortical electrobiogenesis of hypertensive SHR-Charles-River adult rats during a 90-s session of acute hypoxia, was tested either with a single treatment or with a therapeutic association. Pretreatment with nimodipine alone (0.1 mg kg-1, i.v.) was particularly effective in increasing the rat brain resistence to hypoxia when compared to the controls. MK-801 pretreatment alone (3 mg kg-1, subcutaneous), improved significantly the recovery of brain electrical activity from hypoxia, as it not only shortened the recovery time but also abolished the post-hypoxic burst activity. The combined pretreatment with both drugs, using the same doses, displayed a more powerful brain protective effect on the cortical electrobiogenesis than the single drug pretreatment, suggesting the existence of a synergy between nimodipine and MK-801.

Acute Disease↗
PubMedDate not supplied

Effects of phenytoin administration on vestibular function in the rat.

Acute or chronic treatment of epileptic patients with phenytoin is often associated with the appearance of disturbances such as postural impairment and ocular nystagmus, probably due to high toxic plasma levels of the drug. We describe the changes in spontaneous electrical activity of vestibular units in cerebellectomized rats following an acute nontoxic dose of phenytoin, in static conditions and after macular stimulation. Administration of phenytoin induced an inhibition of Deiters cells and a drug level-dependent biphasic effect (excitation followed by inhibition) on medial and superior vestibular cells. The experiments pointed to a direct action of phenytoin on the vestibular nuclear complex, indicating that postural and motor disturbances are not only cerebellar but also vestibular in origin.

Animals↗
PubMedDate not supplied

Postrotatory nystagmus during phenytoin treatment.

This article reports an investigation into the vestibuloocular reflex (VOR) recorded in rats during acute nontoxic treatment with phenytoin (PHT). In animals adapted to the dark, latency and duration of postrotatory nystagmus (VAN), cumulative trend of slow phases (CTSP), slow-phase velocity, temporal trend of the frequency and amplitude of the nystagmic beats, and mean frequency-amplitude ratio were analyzed. Observations were correlated with plasma and brain levels of the drug. Results showed that an acute nontoxic dose of PHT impairs some parameters of the VAN. At low concentrations (8.24 +/- 2.56) (microgram/ml in plasma and 6.02 +/- 3.24 micrograms/g in brain), only CTSP and slow-phase velocity were remarkably modified in each animal. At higher concentrations but still subthreshold for evoking the appearance of evident signs of drug toxicity (17 +/- 6.13 micrograms/ml in plasma and 11.4 +/- 5.28 micrograms/g in brain), all parameters were modified in each animal. In the same animal, VOR impairment was always linearly correlated to the plasma and brain drug levels. A considerable individual biovariability in the drug response appeared, and an individual subtoxic threshold for each animal was evident. Thus, when results of all experiments were averaged, the statistical significance of the differences of the greater part of the VOR parameters disappeared. However, VOR analysis performed before and after drug administration, i.e., with each subject as its own control, proved to be an excellent diagnostic pointer to the approach of the particular subject's toxic threshold before the appearance of spontaneous nystagmus or postural impairments.

Animals↗
PubMedDate not supplied

Neurogenic myocardial arrhythmias in experimental focal epilepsy.

The potential for cardiac arrhythmia was studied in an experimental focal epilepsy induced in hemispherectomized rats by topical application of buffered penicillin G onto the thalamus. The epileptic burst triggered cardiac and hemodynamic responses, as simultaneously monitored by arterial pressure, and hypothalamic and heart activity. During interictal epileptic activity, the single burst triggered a short-latency cardiac arrhythmia, characterized by sinus bradyarrhythmia and junctional rhythm, and lengthening of intervals between sphygmic waves with significant reduction of diastolic pressure. When the epileptic burst stopped, the cardiac activity resumed normal rhythm, and diastolic pressure returned to basal value. During ictal epileptic activity, the sinus and junctional bradyarrhythmic episodes lasted longer, and supraventricular extrasystoles, sinus arrest, and bigeminal ventricular extrasystoles were observed. Both systolic and diastolic pressures decreased from 120/85 to 100/65 mm Hg. The end of the ictal episode always marked resumption of normal cardiac rhythm and systemic pressure. Considering the absence of metabolic complications (blood-gas analytic parameters and acid-base balance being controlled) and the short latency of the cardiac and hemodynamic responses, it is suggested that during paroxysmal hypothalamic activity the observed cardiac arrhythmias and the hemodynamic modifications were neurogenic in origin. A role for cardiovascular alterations in sudden unexplained epileptic death is postulated.

Animals↗
PubMedDate not supplied

Convergence of central and peripheral signals on vestibular cells.

Nerve and cortical input convergence patterns, representing the fore- and hindlimb, were studied in single cells located in the lateral vestibular nucleus of the cat. Deitersian cells responded with excitation to cortical stimulation with a latency ranging from 4 to 14 msec, while responses ranged from 9 to 12 msec to radial nerve stimulation and from 14 to 18 msec to sciatic nerve stimulation. Lateral vestibular nuclear neurons responding to radial nerve stimulation also receive the main cortical input from the sensorimotor cortical area concerned with the forelimb. Neurons responding to sciatic nerve stimulation receive an equal cortical input from both fore- and hindlimb areas of the sensorimotor cortex. In a few cells different combinations of convergence of cortical and peripheral inputs were also observed.

Action Potentials↗
PubMedDate not supplied

Assessment of the metals contamination of the low Sebou sediments (Morocco).

The heavy metals contamination of the lower Sebou sediments was studied to determine the average degree of contamination and to assess the extent of anthropogenic contamination. The spatial and temporal distribution of these metals and the results of the contamination indices showed very serious metallic contamination principally of Cr, Pb and Hg. However accurate analysis of the situation in the river mouth was complicated by the fact that the metals could be moved by the tides and currents.

Chromium↗
PubMedDate not supplied

The impact of lead pollution on the environment of Rabat-Sale' (Morocco).

There are numerous possible vectors of industrial lead poisoning in unprotected work environments and the areas surrounding industrial sites. In the Rabat-Salé region, ceramics is the industry which uses most lead. Galena (PbS) is used in the fabrication of some types of pottery, and other lead-based compounds are used as glaze. A second source of lead pollution is the production of some fuels, in which lead is used as an anti detonator. In order to evaluate the impact of lead contamination on the environment, our investigation is focused on the lead concentration in the atmosphere, soil and vegetation at five stations in the Rabat-Salé region. We found concentrations of lead higher than those published for any other country in the atmosphere and vegetation near the ceramics factories of Rabat-Salé. These concentrations decreased significantly as we moved away from urban areas.

Air Pollutants↗