Dynamic responses of vestibular cells during spinal decompensation.
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Afferent Pathways↗
Biomedical subjects
E Tolu
Publications and source records attributed to E Tolu.
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↗
Cerebellar contribution in compensating the vestibular function.
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Afferent Pathways↗
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↗
Responses of vestibular units to visual input.
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Animals↗
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↗
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↗
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↗
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↗
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↗
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↗
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↗
Inner ear pressure changes modify ADH secretion in freely moving guinea pig.
The present study was designed to elucidate the relationship between endolymphatic pressure and plasma ADH levels in conscious guinea pigs. Plasma ADH (pADH) was measured in basal conditions and after having applied positive or negative pressure of 20 cmH2O to the inner ear. The experimental protocol was designed to avoid any interference on ADH release caused by anesthesia and surgical stress. There was no change in blood pressure, heart rate, plasma Na (pNa) and osmolality (pOsm) after inner ear pressure (IEP) modifications. However, pADH was inversely related with IEP: pADH averaged 31.4 +/- 7.0 pg/ml (mean +/- S.D.) in basal conditions, rising to 48.8 +/- 19.3 when IEP was lowered and falling to 16.6 +/- 10.3 when IEP was raised. These results confirm that structures in the inner ear help control of ADH release.
Animals↗
Hypoglossal responses elicited by periodontal afferent activation in the rat.
Mechanical stimulation of the ipsilateral incisor tooth in the rat evoked reflex discharges in the hypoglossal nerve branch innervating the intrinsic and extrinsic tongue muscles. Stimulation elicited biphasic potentials in the whole XIIth nerve and influenced the unitary firing rate in 54 out of 80 fibers tested. The fiber responses were characterized by excitation or inhibition in frequency discharge or sequences of excitation-inhibition or inhibition-excitation. The results observed suggest that the periodontal-hypoglossal reflexes play a role in the control of tongue position during mastication.
Afferent Pathways↗
Vestibular and somatosensory afferents modulate masseter muscle activity.
The aim of the research was to investigate whether somatosensory impulses starting from the forelimbs could modulate masseter muscle activity in anesthetized guinea pigs. The effect of interactions between radial nerve and vestibular stimulations on the masseter motor unit responses was also studied. Results show that electrical stimulation of both radial nerves induces responses in the masseter motor units most frequently characterized by excitation at latency ranging from 14 to 29 ms. The radial nerve responses were strongly reduced by conditioning electrical stimulation of the vestibular ampullar receptors. Similarly, the vestibular responses were reduced by conditioning radial nerve stimulation. The natural activation of the vestibular macular receptors can either decrease or increase the masseter motor unit responses evoked by electrical stimulation of the radial nerve. These complex inhibitory-excitatory interactions between the two sensory inputs could control the masseter postural tone in relation to the head and limb positions in space.
Animals↗
[Sutures without sutures in digestive surgery. Experimental study of the rat intestine].
The aim of the experimental study was to evaluate the possibility of performing an end-to-end anastomosis by using fibrin adhesive as the only means of suture. To this end, 24 Wistar rats were used, of which 16 underwent ilear resection and 8 underwent colotomy, and they were divided respectively into two groups. On the rats of the first group the anastomosis was performed by using only fibrin adhesive; on the rats of the second group operated the anastomosis was performed by using fibrin adhesive in association with non adsorbable suture material, while on those operated of colectomy the anastomosis was performed by fibrin adhesive and adsorbable suture material. The anatomo-phatological studies on the anastomosis have shown a similar healing process in the cases treated only with fibrin adhesive and by using absorbable material and has demonstrated the trange material from the suture, which are a possible causes of complication.
Anastomosis, Surgical↗