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Biomedical subjects

P Strata

Publications and source records attributed to P Strata.

At least 55 records · Page 3Linked to original sources
PubMed1986

Influence of inferior olive on flexor reflex activity.

In Wistar rats we have studied the effect of inferior olive lesion or activation on the threshold of a flexor reflex elicited by a nociceptive stimulus applied to the hindpaw. When the inferior olive is lesioned by means of 3-acetylpyridine, the threshold value is significantly decreased. A recovery occurs in 3-4 weeks. When the inferior olive is activated by means of harmaline, the threshold value is significantly increased. These experiments suggest the inferior olive activity exerts an inhibitory effect on flexor reflex activity. The recovery of the threshold value depends, probably, on the plastic reorganization of the cerebellar circuits, which occurs after inferior olive lesion.

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PubMed1984

Metabolic activity of intracerebellar nuclei in the rat: effects of inferior olive inactivation.

Metabolic activity of the intracerebellar nuclei during cryoinactivation of the inferior olive was studied in the anaesthetized rat by using the 14C-2-deoxyglucose method. Single unit recording of Purkinje cells was simultaneously monitored in the cerebellar cortex. Local inactivation in the inferior olive resulted in regional suppression of complex spike discharges in the cerebellar cortex. An increased metabolic activity was observed in the cerebellar nuclei contralateral to the cryoinactivation site correlating the somatotopically arranged olivo-cerebello-nuclear circuit. This increase was shown to be due specifically to inactivation of the inferior olive, since it was not obtained in a rat in which the inferior olive was previously destroyed by neurotoxic doses of 3-acetylpyridine. The results are interpreted as being due to an increased presynaptic activity of the terminals of the Purkinje cells which fire simple spikes at high rates after climbing fibre deafferentation.

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PubMed1983

Inferior olive inactivation decreases the excitability of the intracerebellar and lateral vestibular nuclei in the rat.

In rats under sodium pentobarbitone anaesthesia the inferior olive region has been reversibly inactivated by applying a cooling probe to the ventral surface of the medulla. Unitary activity has been recorded from the fastigial, interpositus and Deiters nuclei. Identification of units was based on the presence of a dye spot, left by the recording micropipette. In the Deiters nucleus, an additional criterion of identification was the antidromic activation from spinal cord stimulation. Following cooling of the inferior olive of one side, we have observed suppression of the activity of all the fourteen Deiters neurones and of seventeen out of twenty neurones recorded from the intracerebellar nuclei. In two out of seven Deiters neurones tested the antidromic invasion elicited by spinal cord stimulation was suppressed. In rats, whose inferior olive was previously destroyed, cooling of the inferior olive region was not followed by the powerful depression of spike activity seen in the vestibular and cerebellar nuclei cells in the intact rats. These results indicate that the olivocerebellar system is very important in regulating the level of excitability of the subcerebellar structures and therefore in controlling both postural mechanisms and the processing of information relating to sensorimotor integration.

Animals↗
PubMed1982

The inhibitory effect of the olivocerebellar input on the cerebellar Purkinje cells in the rat.

1. In rats under Nembutal anaesthesia the inferior olive region has been reversibly inactivated by applying a cooling probe to the ventral surface of the medulla. Simple and complex spike activity has been recorded from Purkinje cells of the cerebellar cortex.2. Following cooling of the inferior olive of one side we have observed a remarkable increase of the simple spike activity in all the twenty-two Purkinje cells, showing a disappearance of the complex spike activity.3. In some rats two Purkinje cells were recorded simultaneously from each side of the cerebellar cortex. Following cooling of the left inferior olive the effect on the Purkinje cell was observed only or predominantly on the contralateral cerebellar cortex.4. In a group of animals the inferior olive has been destroyed by 3-acetylpyridine 4-221 days before the recording session. Cooling of the inferior olive region was not accompanied by any significant and consistent increase in the spike activity of presumed Purkinje cells of the contralateral cerebellar cortex.5. These results indicate that the remarkable increase of the simple spike frequency following cooling of the inferior olive region is due specifically to the suppression of the activity of the olivocerebellar neurones.6. Only a small amount of the simple spike frequency increase is attributable to the removal of the post-climbing fibre pause.7. In some lesioned rats recording was made from Purkinje cells, which showed complex spikes due to the few surviving inferior olive cells. In these Purkinje cells cooling of the inferior olive region was accompanied by a disappearance of the complex spike and by a small increase of the simple spike frequency of discharge. Such an increase is mainly attributable to the removal of the post-climbing fibre pause.8. These results suggest that a given Purkinje cell is not only under the inhibitory influence of its own climbing fibre, but also of other olivocerebellar neurones, probably through climbing fibre collaterals to the cerebellar cortical interneurones.9. It is suggested that one role of the olivocerebellar system is to exert a powerful tonic inhibitory action on the Purkinje cells and consequently to exert a significant control on the excitability of the subcerebellar centres.

Action Potentials↗
PubMed1982

Functional aspects of the inferior olive.

A review is presented of a series of recent experiments aimed at studying the effects of irreversible lesion and of reversible inactivation of the inferior olive. Following a permanent lesion of the inferior olive, no alteration has been found: i) in the morphology of the synapse between Purkinje and Deiters neurones, and ii) in the inhibitory properties of the three types of cells of the cerebellar cortex innervated by the olivocerebellar pathway: the Purkinje, the Golgi and the basket cells. Following reversible inactivation of the inferior olive of one side by cooling, a remarkable increase of the simple spike activity has been found in all the Purkinje cells showing a disappearance of the climbing fibre activity. This effect is likely mediated, at a large extent, by climbing fibre collaterals through corticocerebellar interneurones. The same reversible inactivation of the inferior olive induces a drastic reduction of the activity in the cells of intracerebellar and vestibular nuclei. These experiments don't provide support for a trophic function of the inferior olive on its target neurones. They suggest that this nucleus exerts a very powerful tonic inhibitory action on Purkinje cells and consequently a control on the excitability of intracerebellar and subcerebellar centres. Such a control is likely important for the processing of informations through the cerebellum and therefore for the control of motor activities.

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PubMed1981

Are the climbing fibres essential for the Purkinje cell inhibitory action?

Following an almost total chemical lesion of the inferior olive, the inhibitory control of the cerebellar Purkinje cells upon their target neurones, mainly in Deiters nucleus, remains practically unchanged. This result is at variance with some recent findings having important implications in the cerebellar theories of motor learning.

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PubMed1980

On the origin of the climbing fibres of the cerebellar cortex.

Unitary climbing fibre activity has been systematically recorded in the rabbit cerebellar cortex at the level of the Purkinje cell layer every 100 micron along the longitudinal axis of the folium. In one group of animals, spontaneous activity was identified in 197 out of 204 (96.6%) explored layers, and was uninterruptedly present up to 2,400 micron along the folia. In a second group of animals, stimulating electrode were placed in the inferior olive and it was found that spontaneous or evoked climbing fibre activity was absent in only 19 out of 422 explored layers: 377 (89.3%) showed a spontaneous and 396 (93.8%) a short latency evoked activity. If some limitations of the method are considered, it can be concluded that all Purkinje cells receive climbing fibre innervation from cells of the inferior olive. The present experiments support the conclusion that the inferior olive is the unique source of climbing fibres.

Action Potentials↗
PubMed1980

The role of the crossed and uncrossed retinal fibres in mediating the horizontal optokinetic nystagmus in the cat.

While the horizontal optokinetic nystagmus (OKN) was studied in cats in which the optic chiasma was completely split thus leaving only uncrossed retinofugal fibers intact it was found that both temporonasal and nasotemporal surround motion generated symmetrical OKN. Similar findings were obtained when one optic tract was sectioned and the eye ipsilateral (uncrossed fibers only) or contralateral (crossed fibers only) to the lesion was covered. It is concluded that in the cat the crossed and uncrossed retinofugal fibers are equipotent in mediating symmetrical OKN.

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PubMed1974

The projection of the posterior knee joint nerve to the cerebellar cortex.

1. In decerebrate cats, electrical stimulation of the posterior knee joint nerve evokes in the depth of the cerebellar cortex field potentials which have been identified as due to both mossy and climbing fibre inputs.2. The potentials evoked through the mossy fibres have a latency of 15-17 msec and are more widespread. Those evoked through the climbing fibres have a latency of 26-33 msec and are more restricted.3. Stimulation of the larger fibres originating from the Golgi receptors gives only a very restricted projection. When the fibres originating from the Ruffini receptors are also activated, the effect on the cerebellar cortex is more widespread.4. The results have been confirmed by recording unitary activity.

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