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Biomedical subjects

E Tolu

Publications and source records attributed to E Tolu.

At least 37 records · Page 2Linked to original sources
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↗
PubMed1986

Vestibular ampullar modulation of hypoglossal neurons.

This paper describes preliminary observations on vestibular ampullar involvement in the control mechanism of the hypoglossal nucleus activity. Thermic stimulation of the labyrinth, performed by irrigating the external auditory meatus with cold water (20 degrees C), significantly modified the spontaneous electrical activity of hypoglossal neurons localized in the medio-caudal part of the nucleus. Tonic spontaneous discharge of the units following labyrinthine stimulation was modified into a phasic activity and bursts with multi-unit recruitment appeared. This modified activity was observed during 5-6 minutes after the onset of ear irrigation. Similar response patterns, but with shorter duration, were recorded following contralateral stimulation of the labyrinth. These results show that hypoglossal neurons are triggered by the vestibular system following dynamic conditions in response to every spatial head displacement.

Animals↗
PubMed1986

Involvement of the inferior olivary neurons in vestibular compensation.

Vestibular decompensation induced by spinal cord transection in left labyrinthectomized guinea pigs provoked asymmetrical excitability of the inferior olivary nuclei. In the right nucleus, spinal deafferentation induced a significantly increased response to electrical stimulation of the contralateral radial nerve and decreased response to ipsilateral radial nerve stimulation. In the left nucleus, opposite results were obtained. Increased responses were recorded in the I.O. neurons during electrical stimulation of the radial nerve ipsilateral to a previous hemilabyrinthectomy, and reduced responses during the electrical stimulation of the radial nerve of the opposite side. Since the inferior olive impinges on the vestibular nuclei both directly and indirectly through the cerebellar loop, it is possible that the inferior olive is involved in the spinal compensation of the vestibular deficits resulting from the hemilabyrinthectomy.

Animals↗
PubMed1985

Visual input to the hypoglossal nucleus.

Photic stimulation of the retina elicits in the mediocaudal part of the XIIth nucleus the appearance of pronounced field potentials and responses of single hypoglossal units. The latency of the evoked potentials, characterized by a complex sequence of positive-negative waves, was 32.75 +/- 2.5 ms for the initial component p1, 42.25 +/- 3.30 ms for n1, 49.75 +/- 3.09 ms for p2, and 67 +/- 3.94 ms for n2. The hypoglossal neurons, antidromically identified by electrical stimulation of the XIIth nerve, responded with several combinations of excitation-inhibition at various latencies. Nineteen percent of the units responded to both retinae and 10% only to one retina, mainly to the contralateral one. As the mediocaudal part of the hypoglossal nucleus receives vestibular information, it can be concluded that the hypoglossal units adjust their firing in relation to head position and also by using visual information.

Animals↗
PubMed1984

Pharmacological improvement of vestibular plasticity. Effects of a Ca2+-antagonist agent.

Repeated oral flunarizine administration (5 mg/Kg) in hemilabyrinthectomized guinea pigs induced increased and accelerated vestibular compensation. The disappearance of nystagmus and reduction of head deviation occurred more rapidly than in the control. These effects were irreversible and not dose-dependent. The possible mechanism of the drug action is discussed.

Animals↗
PubMed1984

Correlations between cerebellar activity and chronic nontoxic administration of phenytoin in rats.

The effect of long-term nontoxic treatment with phenytoin on the cerebellar Purkinje cell activity as determined by simultaneous monitoring of plasma and cerebellar levels of the drug has been studied in rats for the first time. The electrophysiological observations allowed the analysis of the spontaneous firing rate of the Purkinje cells and of the cerebellar field potentials generated by electrical stimulation of the ipsilateral radial nerve. The responses of single Purkinje cells to radial nerve stimulation were studied by constructing poststimulus time histograms and cumulative frequency distributions. The chronic treatment with phenytoin, which did not induce motor impairment or cerebellar symptoms, modified the firing rate of the Purkinje cells and the two modalities of Purkinje cell activation. In fact, phenytoin decreased significantly the spontaneous activity of the Purkinje cells and modified the strength of the mossy and climbing afferents.

Animals↗
PubMed1984

Further observations on the action of phenytoin on the cerebellum in rats: involvement of the lateral reticular nucleus.

The action of phenytoin (PHT) on both the spontaneous and evoked activity of lateral reticular nucleus (LRN) neurons in rats was studied. An inhibition appeared at 90 min after drug administration, with a maximum peak at 135 min, followed by an excitation at 220 min. This biphasic action depended on plasma-tissue concentrations: At low concentrations, PHT exerted an inhibitory effect that became excitation at relatively high doses (7.5 micrograms/ml and 10.36 micrograms/g in plasma and brain, respectively). It was concluded that PHT modified cerebellar cortical activity not only by exerting a direct control on the Purkinje cells and an indirect modulation through the climbing fibers, but also through the mossy afferents originating from the LRN.

Animals↗
PubMed1983

Omental transposition or transplantation to the brain and superficial temporal artery--middle cerebral artery anastomosis in preventing experimental cerebral ischaemia.

Transposition of lengthened omentum to the brain surface, transplantation of an omental graft, or superficial temporal artery--middle cerebral artery anastomosis were performed in dogs prior to transcranial occlusion of the ipsilateral middle cerebral artery at its origin, including the bifurcation of the internal carotid artery. Both omentum and by-pass were able to reduce the changes in cerebral blood flow, somatosensory evoked responses, cerebral water and electrolyte content, consequent to the ischaemic insult. In the experimental conditions adopted in this study, the effect of omental transposition in maintaining high levels of flow throughout the entire occluded hemisphere was more marked compared to that resulting from the other methods, while the onset of ischaemic cerebral oedema was affected approximately at the same degree by all procedures. The results point to the role of the transposed omentum in providing an effective collateral circulation to the ischaemic brain.

Animals↗
PubMed1983

Protective effects of Ca++-antagonist agents on the cerebral electrical activity during anoxia in the rat.

Transient anoxia obtained in curarized rats by momentary stopping of the artificial respiration (80 sec duration) induced a failure of the cerebral electrical activity. This effect was characterized by cessation of the spontaneous unitary discharge of cortical neurons and reduction of amplitude of somatosensory evoked potentials. Pretreatment with flunarizine (10 mg/kg/os) or suloctidil (50 mg/kg/os) induced a distinct improvement of the resistance to anoxia and of the recovery of the cerebral electrical activity.

Animals↗
PubMed1982

Relationship between cerebral nystagmogenic area and spinal cord.

The effect of section of the spinal cord upon the cerebral nystagmogenic area was investigated in rabbits. Cervical transection was found to result in an increase of excitability of such area, which is demonstrated by lowering of the threshold for cerebral eye nystagmus, whereas dorsal spinal transection does not affect the cerebral nystagmogenic area. Moreover, it was found that stimulation of the proximal stump of the spinal cord, at level of the dorsal quadrants, depresses the excitability of the cerebral nystagmogenic area, while ventral quadrants stimulation has a facilitating effect on the CNA. Modification of the excitability of the cerebral nystagmogenic area was also studied recording NPPs (Non-Primary Potentials) and unitary responses to photic stimulation prior to and after cervical transection as well as following dorsal and ventral quadrants stimulation. The Authors suggest that since the nystagmogenic area is located in the perivisual fields it receives visual and sensitive afferent impulses from the upper part of the body and it, in turn, projects onto the oculomotor nuclei, so that it could be considered as an integrator center for extrinsic musculature of the eye.

Animals↗
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↗