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Biomedical subjects

E Tolu

Publications and source records attributed to E Tolu.

At least 19 recordsLinked to original sources
PubMed1999

Trigeminal integration of vestibular and forelimb nerve inputs.

Experiments were carried out on anaesthetized guinea pigs to evaluate whether vestibular and somatosensory informations converge upon the same trigeminal motoneurones and, if so, how they interact in the modulation of their activity. It was found that excitatory responses occurred in these motoneurones when an appropriate electrical stimulation was applied to the common radial nerve. The same was true if the electrical stimulus was applied to the vestibular ampullae. In another set of experiments the stimulation was applied both to the vestibular ampullae and to the common radial nerve at various time-intervals. The amplitude of the motoneuronal responses to common radial nerve stimulation was reduced when preceded by a vestibular stimulation. The same was true when the sequence of stimulations was reversed: in this case there was a decrease in amplitude of the testing response to vestibular stimulation. The degree of these reductions depended upon the time-interval elapsed between the afferent stimulations. The maximal degree of depression was observed at 4-6 ms time-interval for conditioning vestibular stimulation and at 10-12 ms time-interval for conditioning radial nerve stimulation. It appears, therefore, that somatosensory and vestibular signals may modulate the activity of trigeminal motor units innervating masticatory muscles, suggesting that extratrigeminal afferents may control the contraction of these muscles.

Afferent Pathways↗
PubMed1998

Responses of vestibular neurons to arginine vasopressin microinjection.

The aim of the present research was to evaluate the effects induced by arginine vasopressin (VP) microinjection on the electrical activity of single vestibular neurons. Experiments were performed on anaesthetized guinea-pigs in which the spontaneous and the evoked electrical activity of vestibular neurons were recorded before and after intranuclear VP microinjection (0.25.10(-5) pg VP in 0.25 microliter NaCl 0.9% solution). Results showed that VP microinjection affects the spontaneous as well as the evoked vestibular neuron activity. More precisely, 60% of 30 tested neurons were inhibited, 30% were excited and the remaining 10% were unaffected by VP microinjection. The changes in neuronal activity reported above were attributed to a direct action exerted by the polypeptide on vestibular complex neurons. The possible role played by VP in the mechanisms of postural control exerted by the vestibular system was considered as well.

Animals↗
PubMed1997

Effect of atrazine administration on spontaneous and evoked cerebellar activity in the rat.

The effect of atrazine oral administration on cerebellar forelimb projection area was studied in rats in vivo. Rats acutely treated with atrazine (100 mg kg-1, BW) showed a significant decrease in spontaneous Purkinje cell firing rate. Atrazine also decreased the cerebellar potentials evoked by electrical stimulation of the ipsilateral radial nerve, affecting mostly the response to climbing fiber input. These results demonstrate that atrazine exerts a toxic action on central nervous system. The effects on the cerebellar somatosensory cortex could be responsible for motor disorders frequently observed in animals intoxicated with atrazine.

Animals↗
PubMed1996

Trigeminal motoneuron responses to vestibular stimulation in the guinea pig.

Experiments performed in the guinea pig were aimed at evaluating the effect of electric or caloric stimulations of the vestibular afferents on the electrical activity of the jaw-closing and jaw-opening trigeminal motoneurons. Results showed that masseter and digastric motoneurons mainly responded to vestibular ampullar activation with excitatory responses, with latencies being shorter for contralateral than ipsilateral ampullar stimulation. Differences in latencies between the jaw-closing and jaw-opening trigeminal motoneurons were observed: the masseter motoneurons constantly responded about 2 msec earlier than the digastric motoneurons. These results suggest that the vestibular-trigeminal relationship is quite complex and uses multiple systems to connect the vestibular apparatus with the trigeminal motor nuclei. From the functional point of view, the vestibular-trigeminal relationship may play a role in the dynamic control of the jaw muscle tone during head movements.

Animals↗
PubMed1994

Muscle spindle and periodontal trigeminal afferents modulate the hypoglossal motoneuronal activity.

Hypoglossal responses to electrical or natural activation of the afferent fibers of the masseteric nerve and to periodontal mechanoreceptors were recorded in rats. Electrical stimulation of the masseteric nerve, at an intensity adequate to excite prevalently the primary spindle afferents, induced various sequences of excitation-inhibition and inhibition-excitation in 55% of the tested hypoglossal motoneurons. Responses were characterized by excitation, inhibition or excitation-inhibition sequences occurring at short and long latencies. Different pattern of responses were evoked in both the protrusive and the retractive motoneurons of the homolateral hypoglossal nucleus. Moreover, jaw lowering and pressure on the incisor tooth induced antagonistic and synergistic effects on the electrical activity of the same hypoglossal motoneurons. The results show for the first time that afferent signals from both muscle spindles and periodontal receptors modulate the activity of the hypoglossal motoneurons aimed at controlling the tongue position in the mouth during mastication.

Action Potentials↗
PubMed1993

Masseter muscle responses to forelimb nerve stimulation in the guinea pig.

These experiments were aimed at clarifying the spinal-masseteric connections by observing the effect of electrical stimulation of radial nerve afferents on masseter muscle activity. Spontaneous and evoked electrical responses of the masseter motor units were recorded with tungsten microelectrodes and analysed on computer. Results show that electrical stimulation of both radial nerves induces responses in single masseter motor units. The response patterns were characterized most frequently by excitation, but also by a sequence of excitation inhibition. The latency in masseter muscle responses were found to be lower in contralateral recordings: 18.26 +/- 4.04 msec (x +/- SD) compared with a latency of 24.3 +/- 5.25 msec in ipsilateral recordings. These observations confirm the hypothesis that somatosensory impulses eminating from the radial nerve participate in the postural control of the masseter muscle aimed at maintaining correct jaw position during forelimb displacement.

Animals↗
PubMed1993

The vestibular system modulates masseter muscle activity.

The aim of this study was to investigate whether, and in what way, the vestibular input may influence the activity of the masseter muscles. The variations in the spontaneous electrical activity and the evoked responses in the masseter motor units to natural or electrical activation of the vestibular afferents were recorded in anesthetized guinea pigs. The effects of a unilateral lesion of the labyrinth on the firing rate of the masseter motor units were also studied. Results show that: 1) vestibular input elicited an excitatory tonic control on masseter muscle activity; 2) a faster labyrinthine control is driven to the contralateral than the homolateral masseter muscles; 3) vestibular macular input does exert an asymmetrical control on masseteric muscles of both sides, in relation to the head displacement in space. The latencies of responses recorded from the masseter motor units suggest that polysynaptic pathways are involved in connecting the vestibular system to the trigeminal complex. The possible anatomical substrates for this vestibulomasseteric reflex are discussed.

Animals↗
PubMed1993

Responses of hypoglossal motoneurons to mechanical stimulation of the teeth in rats.

Reflex discharges were evoked in the XIIth nerve single fibers and in the genioglossal muscle following mechanical stimulation of the homolateral incisor tooth in rats. The tooth mechanoreceptors affected the firing rate of 70% of the tested motoneurons mainly localized in the ventral region of the hypoglossal nucleus. Different types of response in relation to stimulus direction were recorded. Type A responded with excitation to labio-lingual and with inhibition to linguo-labial stimulus direction. Opposite effects were observed in type B motoneurons. However, these neurons did not respond to mechanical stimuli applied in medio-distal or disto-medial directions. Type C showed excitatory or inhibitory responses to mechanical stimulation in all directions. Type D only responded to one direction of stimulation. The stimulus was often able to excite motoneurons previously silent (type E). Some motoneurons showed complex responses to one stimulus direction. The results demonstrate that stimulation of the periodontal mechanoreceptors can evoke hypoglossal responses probably aimed at controlling tongue position in the mouth during mastication.

Animals↗
PubMed1991

Penicillin-induced paroxysmal activity in brainstem neurons.

The spontaneous electrical activity of single mesencephalic and bulbar neurons was recorded in hemispherectomized rats, following topical application of the GABA-antagonist penicillin-G on the mesencephalon or on the rhombencephalon, to investigate whether these structures could develop a specific penicillin paroxysmal activity independently of the upper structures. Twenty minutes following penicillin-G, the mesencephalic neurons developed paroxysmal activity characterized by a significant increase in the spontaneous electrical activity, the appearance of multiunit activity and, frequently, phasic activity with rhythmical outbursts. The paroxysmal activity at bulbar level appeared later than that observed in the mesencephalon and was characterized by a significant increase of the spontaneous firing rate of the neurons, single short bursts and sometimes rhythmical outbursts. The bulbar outbursts always discharged at lower frequency than those at the mesencephalic level. Following a midcollicular transection the paroxysmal bulbar activity abruptly disappeared. This phenomenon might be explained by a loss of facilitation from superior structures on the bulbar neurons which in roditors show a poor GABA-receptor distribution. In other words, penicillin alone, due to the scarcity of GABA receptors, might not be sufficient to induce paroxysmal activity in bulbar neurons but the simultaneous presence of both the superior facilitation and the drug might enhance neuronal excitability to a critical level. However, the diffusion of the drug upwards to the mesencephalon, with consequent activation of a system allowing the downward propagation of paroxysmal activity, cannot be excluded. In conclusion, while the mesencephalic neurons demonstrate a proper ability to develop penicillin paroxysmal discharge, the bulbar neurons must be sustained by intact connections with upper structures to be able to do so.

Animals↗
PubMed1990

Analysis of central cardioarrhythmogenic triggers in experimental epilepsy.

The cardioarrhythmogenic potential of epileptic foci induced at mesencephalic and rhombencephalic levels was analyzed in hemispherectomized rats. Topical application of penicillin-G onto the mesencephalic quadrigeminal lamina or onto the fourth ventricle induced paroxysmal activity at the mesencephalic or bulbar neurone level. At the mesencephalic levels, the paroxysmal activity was characterized by a significant increase in the spontaneous frequency of the neurones, with the appearance of multiunit activity and rhythmical outbursts. The simultaneous recording of myocardial electrical activity and blood pressure showed that the paroxysmal activity triggered short-latency sinus bradyarrhythmias with wandering of the sinus pacemaker, the appearance of biphasic or negative P waves, some premature ventricular contractions and non-significant reduction of systolic and diastolic pressures. When the paroxysmal activity stopped, the cardiac rhythm and blood pressure returned to basal values. At the bulbar level, the paroxysmal activity appeared with longer latency and usually the rhythmical outbursts were not observed. Following bulbar paroxysmal activity only short-lasting episodes of sinus bradyarrhythmias appeared. Midcollicular transection eliminated paroxysmal activity at the bulbar level, and blood pressure and cardiac rhythm resumed basal values. After transection, an additional application of convulsant drug (penicillin-G or pentylenetetrazole) onto the fourth ventricle did not induce the reappearance of paroxysmal activity and the consequent cardiovascular alterations. The results showed the existence of a cardioarrhythmogenic trigger localized at the mesencephalic level which spreads paroxysmal activity upwards. A hypothesis to explain the appearance of fetal haemodynamic modifications and life-threatening arrhythmias has been proposed.

Animals↗
PubMed1988

Physostigmine and metoclopramide in oesophageal peristaltic spread in man.

Simultaneous recordings of electrical and mechanical activities at different levels of the oesophagus were performed in normal men before and after physostigmine and metoclopramide injections. Various parameters of the basal oesophageal peristalsis were significantly modified following drug treatment. In particular, physostigmine injections induced a shortening of electromechanical coupling time and a reduction of the propagation velocities of the electrical and mechanical oesophageal events. Metoclopramide shortened the electromechanical coupling time but increased the electrical and mechanical propagation velocities along the oesophagus.

Electrodes↗
PubMed1988

Labyrinthine projection to the hypoglossal nucleus.

Evoked potentials and responses of single hypoglossal neurons were recorded in response to electrical stimulation of the labyrinth. In addition, the spontaneous electrical activity of hypoglossal neurons was significantly modified in response to ipsi- and contralateral static tilt of the whole animal and thermic stimulation of the labyrinth. The experiment showed that the labyrinth modulates the electrical activity of hypoglossal neurons with phasic inputs in response to ampullar stimulation and with tonic inputs in response to macular stimulation. The vestibular phasic influence of hypoglossal neurons represents the most adequate functional pattern to obtain a quick, short lasting response of the tongue muscles instantly modifiable with every abrupt head displacement. On the contrary, the vestibular tonic influence of hypoglossal neurons represents the most adequate functional pattern to obtain not only adjustment but also maintenance of the muscular lingual response to static displacement of the head.

Animals↗
PubMed1988

Improvement of vestibular plasticity in the guinea pig with a calcium entry blocker.

The influence of flunarizine on vestibular compensation was investigated in hemilabyrinthectomized guinea pigs. The results showed that the vestibular deficits from hemilabyrinthectomy disappeared more rapidly in the treated animals than in the controls. To elucidate the mechanism by which the drug could affect the compensatory process, further studies on the spontaneous and evoked activity of vestibular nuclei were performed in normal, labyrinthectomized and labyrinthectomized-cerebellectomized animals. These electrophysiological data implied that flunarizine improved the vestibular compensation by inhibiting the receptor and nuclear activities of the intact labyrinth. The drug excited the cerebellar cortex, which modulated the activity of the vestibular nuclei of both sides, restoring the balance disrupted by hemilabyrinthectomy.

Animals↗
PubMed1987

Comparison of the effect of althesin with diazepam and thiopental sodium on cortical and subcortical epileptic activity in the rat.

Althesin antiparoxysmal effect was comparatively studied with diazepam and thiopental sodium on penicillin induced cortical epileptic focus and on mesencephalic reticular unitary activity triggered by cortical spikes. Althesin was shown to abolish both cortical and subcortical epileptic activity, while diazepam was able to suppress the paroxysmal unitary activity evoked from the cortical spikes at the level of the reticular mesencephalic formation, but was ineffective on focal paroxysm. Thiopental sodium exhibited behaviour similar to Althesin, but its action was weak and short lasting at both levels. A comparative study showed that Althesin had, at cortical and subcortical level, a more drastic and longer antiparoxysmal effect than the other two drugs tested. Althesin would seem to exert a potent antiepileptic effect through a double action: i) it suppresses abnormal activity at cortical focus level ii) it depresses the multineural mechanism involved in the seizure spread at subcortical level.

Alfaxalone Alfadolone Mixture↗
PubMed1987

Direct and indirect action of flunarizine on vestibular activity.

Flunarizine administration (5 mg/Kg/os) in normal, labyrinthectomized and labyrinthectomized-cerebellectomized guinea pigs induced a depressant effect on spontaneous and evoked vestibular activities. Maximum effect was observed 90-120 min after drug administration and partial recovery at 180 min. Three different processes were involved: reduction of vestibular receptor excitability; direct inhibition of vestibular cells; inhibition of vestibular cells through strong activation of the cerebello-vestibular circuitry.

Animals↗
PubMed1987

Hypoglossal responses to macular stimulation in the rabbit.

This paper describes preliminary work on the role of the vestibular system in the hypoglossal neurons modulation. Natural stimulation of the otolith organ showed that hypoglossal motoneurons are responsive to gravity stimulation. The spontaneous firing rate of single cells, antidromically identified, was significantly modified during ipsi- or contralateral static tilting of the whole animal. Several response patterns were observed. These results infer that vestibular macular receptors may modulate hypoglossal nucleus activity in response to static head displacement.

Animals↗
PubMed1986

Somatosensory input from the forelimb nerves to the hypoglossal neurons.

Our results showed that hypoglossal neurons localized in the mediocaudal part of the XIIth nucleus modulate their firing in relation to somatosensory information travelling along the forelimb nerves. Large evoked potentials and responses of single hypoglossal units were recorded during electrical stimulation of the common radial nerve of both sides. A spinohypoglossal pathway has not been described before, but our results indicate this possibility. The latencies of the hypoglossal responses to somatosensory stimulation suggest that somatic afferent volleys may stop at the reticular level and contact the XIIth nucleus through a spinoreticulohypoglossal pathway. Previous work showed that visual and vestibular input contact the same mediocaudal region of the hypoglossal nucleus. Thus it is possible that the postural arrangement of the tongue is subject to a complex control depending on the vestibular, visual, and somatosensory system.

Action Potentials↗