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G Horcholle-Bossavit

Publications and source records attributed to G Horcholle-Bossavit.

At least 37 records · Page 2Linked to original sources
PubMed1988

[Effects of partial unfused contractions of the gastrocnemius medialis muscle on homonymous and synergist motor neurons in cats].

Autogenetic inhibition of homonymous and synergist motoneurones can be elicited by very weak partial twitches of gastrocnemius medialis muscle, but during sustained contractions the amplitude of inhibitory post-synaptic potentials decreases quickly. A similar decrease also occurs during stronger contractions. The mechanism responsible for this decrease is still active in low spinal preparations. Pre-synaptic inhibition of Ib afferent fibres might contribute to this reduction of efficiency in the transmission of Ib afferent inputs to motoneurones.

Animals↗
PubMed1987

Activation of cat motor units by paired stimuli at short intervals.

1. In adult cats, paired stimulations at short intervals were applied in ventral root filaments to single motor axons innervating the peroneus tertius muscle. Paired impulses were recorded from the muscle nerve simultaneously with the electrical and mechanical responses of the muscle portion of the motor unit (muscle unit). The interstimulus interval was gradually reduced in order to determine the minimum compatible with a full activation of the muscle unit by the second impulse. 2. For motor units of all physiological types, this minimum stimulus interval was the shortest interval allowing initiation and conduction of two impulses in the axon, that is, the absolute refractory period for conduction. Its duration ranged between 0.58 and 0.88 ms, displaying no correlation with the axonal conduction velocity. 3. The amount of tension enhancement produced by paired stimulations at the shortest interval varied with the type of the motor unit: it was largest for fast-fatigable units, intermediate for fast-resistant units and smallest for slow units. 4. Paired impulses elicited by paired stimulations at the shortest possible interval arrived near the muscle at a longer interval because the second impulse was conducted at a slower velocity. The minimum interval between arrival of impulses at the muscle depended on conduction velocity and on conduction distance. 5. In motor axons to peroneus tertius, paired impulses leaving the spinal cord at a mean interval of 0.78 ms arrived near the muscle separated by a mean interval of 1.90 ms. Since such an interval always allowed full activation of the muscle unit by the second impulse, this interval is longer than the refractory period of motor units in this muscle.

Action Potentials↗
PubMed1986

Histochemical identification of two fibre types in the retractor bulbi muscle of the cat.

In adult cats, the fibre population of the retractor bulbi muscle (RB) was analysed, using the histochemical reactions of ATPases. The muscle was found to contain type-2 fibres only, of which 70% were 2a and 30% 2b. Such ATPase profiles, corresponding to fast-twitch fibers, are in agreement with the mechanical properties of the muscle. Both types, 2a and 2b, included fibres in which the oxidative enzyme content was high and fibres in which it was low. The glycogen content of all fibers in the RB was uniformly low.

Adenosine Triphosphatases↗
PubMed1986

Red nucleus inputs to retractor bulbi motoneurones in the cat.

Rubral projections to retractor bulbi motoneurones were investigated by intracellular recording in the accessory abducens nucleus in the cat. Their post-synaptic effects were compared with those of trigeminal afferent pathways. Post-synaptic potentials evoked by stimulation of the contralateral red nucleus were predominantly excitatory, with latencies in the monosynaptic range. Post-synaptic potentials evoked by stimulation of the ipsilateral red nucleus, at threshold, were predominantly inhibitory with latencies indicating a di- or trisynaptic pathway. At above threshold intensity, an earlier excitatory post-synaptic potential (e.p.s.p.) preceded the inhibitory post-synaptic potential (i.p.s.p.) in about half the recorded neurones. Convergence of rubral and trigeminal inputs was also observed in other neurones, not identified as retractor bulbi motoneurones, but situated within the accessory abducens nucleus.

Abducens Nerve↗
PubMed1985

Resistance to glycogen depletion of motor units in the cat rectus lateralis muscle.

In nembutal anesthetized adult cats, intracellular stimulation of single abducens motoneurones was used to elicit glycogen depletion of their muscle units. Stimulation by short trains (13 pulses at 40 Hz) delivered once a second, was applied for 20 to 110 min. The activation of the motor unit was monitored by intracellular recording of motoneurone action potentials and by EMG. After the end of stimulation, the muscle was excised and frozen to be cut in serial sections that were processed for demonstration of either glycogen, ATPases or SDH. In two experiments, a motor unit could be histochemically identified because 10-15 fibres showed zones of complete glycogen depletion measuring about 5 mm in length. All the depleted fibres had the same histochemical profile: ATPases reactions gave dark staining with alkaline preincubation and light staining with acid preincubation whereas SDH activity was low. In other experiments, prolonged stimulation produced either no depletion at all or very limited zones of partial depletion in a few muscle fibres.

Action Potentials↗
PubMed1983

Cerebellar output response to afferent stimulation: energy consumption and unit activity in the cat fastigial nucleus.

The cerebellar output function was studied using cerebellopetal proprioceptive stimulation which produces simple and complex excitatory discharges as well as inhibitory activity in the Purkinje cells. The activity of the intracerebellar nuclei (and of the entire brain stem) was measured by the energy consumption as revealed with the [14C )-2-deoxyglucose method. The stimulations consisted of repetitive (1-20 c/s) electrical excitation of the nerve leading to the inferior oblique, to the masseteric and to the gastrocnemius soleus muscle. Compared to a group of non-stimulated controls, heavy bilateral labeling was obtained in the posterior pole of the fastigial nucleus. This was not observed with stimulation of the vibrissal pad which, however, produced a clear increase of [14C]-2-deoxyglucose uptake in the secondary trigeminal complex. Labeling of the posterior part of the fastigial nuclei was suppressed by ablation or pharmacologic inactivation of the overlying cerebellar cortex which suppresses the inhibitory activity of the Purkinje cells into the nuclear cells. Labeling of the posterior fastigial nuclei was also decreased in animals not stimulated but with ablation or pharmacologic inactivation of the overlying cerebellar cortex. The hypothesis proposed is that the marking results are the consequence of an increased activity in the Purkinje cell terminals. The activity of the Purkinje cells was also recorded extracellulary both before and during repetitive stimulation of a muscle nerve. The discharge activity of those in the cerebellar vermis and giving axons to the posterior fastigial nucleus was increased by the stimulation, whereas the activity of those of the hemispheral parts remained unchanged. Units in the fastigial nucleus were also recorded. Their activity was found to be deeply depressed so that only a few units were encountered and no further decrease of their discharge could be detected with the stimulation of a muscle nerve. Nevertheless, using the present data and those previously obtained, the conclusion is advanced that the cerebellar output function is actually decreased during afferent cerebellar stimulation.

Afferent Pathways↗
PubMed1983

Morphological and electrophysiological properties of trigeminal neurones projecting to the accessory abducens nucleus of the cat.

Horseradish peroxidase was injected into the somata or axons of neurones located in the nucleus oralis of the spinal trigeminal complex and projecting to the accessory abducens nucleus. A group of 43 axons with electrophysiologically identified responses to the stimulation of three different areas of the face were studied. The latencies of their orthodromic responses following trigeminal stimulation and their pattern of discharges were compared to those of secondary trigeminal neurones and retractor bulbi motoneurones. Labelled trigeminal axons were found to generate collaterals for the accessory abducens nucleus. Terminal ramifications are present in the rostro-caudal part of the motor nucleus where the dendritic arborization of the motoneurones has been described. Connections to facial and trigeminal motor nuclei were also present, suggesting that secondary trigeminal axons distributed the information to the three motor targets at the brain stem level. It is suggested that the trigemino-retractor bulbi reflex is part of facial reflexes involved in orienting reactions, and protective responses resulting in coordinated movements of the facial musculature.

Abducens Nerve↗
PubMed1983

Ultrastructural and electrophysiological properties of accessory abducens nucleus motoneurones: an intracellular horseradish peroxidase study in the cat.

The physiological and morphological (light and electron microscopy) properties of six retractor bulbi motoneurones were analysed using the technique of intracellular recording and intracellular labelling with horseradish peroxidase. The retractor bulbi motoneurones were identified by antidromic invasion and orthodromic responses following stimulation of trigeminal afferents were studied. Two of these motoneurones were examined ultrastructurally. Terminal boutons forming synapses with labelled soma, labelled proximal and distal dendrites were characterized. Serial sections allowed the axon hillock to be analyzed and the initial segment of a presumed motoneurone to be observed in the section where the injected motoneurone was described. The ultrastructure of unidentified elements observed in the accessory abducens nucleus is stressed.

Abducens Nerve↗
PubMed1983

Convergence of trigeminal afferents on retractor bulbi motoneurones in the anaesthetized cat.

Retractor bulbi motoneurones were identified by intracellular recording of their antidromic invasion following stimulation of the motor axons. Characteristics of excitatory post-synaptic potentials (e.p.s.p.s) evoked by electrical stimulation of long ciliary nerves (corneal afferents), the supraorbital nerve and the ipsilateral or contralateral vibrissae were analysed. Comparison of the orthodromic responses induced by supra-threshold stimulation of the four trigeminal inputs showed that the most powerful excitatory effect was due to corneal afferent stimulation. Excitatory synaptic potentials were followed in some cases by a period of hyperpolarization lasting 15-20 msec. It is suggested that this is an inhibitory potential of post-synaptic origin. Interaction between condition and test e.p.s.p.s evoked by long ciliary nerve and supraorbital nerve stimulation revealed a partial blocking of test e.p.s.p.s over a longer period (more than 30 msec), and it is suggested that inhibitory mechanisms within the trigeminal nucleus may be in part responsible for the absence of facilitation at the level of the motoneurone.

Action Potentials↗
PubMed1983

[Recent findings on the external oculomotor nucleus: the center for horizontal ocular movement].

Various neurobiological methods allowing the analysis of electrophysiological and morphological properties of a cell population within the central nervous system will be illustrated in the study of the abducens nucleus. Intracellular recordings provided the functional identification of the different types of cells within the abducens nucleus. Antidromic excitation, refractoriness, conduction velocity and frequency of discharges indicated the properties of the abducens motoneurones. Various types of afferent stimulations were applied to study the synaptic responses of the neurones. A dye was then electrophoretically injected and the labelled neurone observed with a light microscope. Full reconstruction of dendritic arborization and of axon trajectory was performed. The morphological study has shown the heterogeneity of the population of the motor nucleus, and the ultrastructural features indicated a complex synaptic organisation. The origin of some afferent terminals was determined.

Abducens Nerve↗
PubMed1983

Harmaline-induced rhythm in the lateral reticular nucleus.

Extracellular unit recordings were performed in the lateral reticular nucleus of cats under tremogenic doses of harmaline. The 8-12 Hz rhythmic activity induced by the drug in the reticular neurons was suppressed by a total spinal transection and by an ipsilateral injection of xylocaine but not by a contralateral injection of xylocaine. Under harmaline, autoradiographic labelling with 14C-2-deoxyglucose was increased in the lateral reticular nucleus, indicating an increased mean neuronal activity. This labelling was also suppressed by spinal cord transection. A spinal hemisection resulted in the absence of the differential labelling of the ipsilateral lateral reticular nucleus and in a reduction of the labelling of the contralateral lateral reticular nucleus. These data, which indicate that both the rhythmic activity and increased autoradiographic marking under harmaline are elicited through spinoreticular neurons, are discussed in view of the descending olivo-cerebello-spinal pathways.

Action Potentials↗
PubMed1981

[Regulation of metabolic activity of intracerebellar nuclei].

The metabolic activity of the intracerebellar nuclei was studied in the cat, using the radioautographic method of marking active brain structures with 14C-2-deoxyglucose. Electrical stimulation of afferent fibers in the muscle nerve of an extrinsic eye muscle was used to activate mossy and climbing cerebellar afferents. A heavy bilateral labelling of the posterior parts of the fastigial nuclei was consistently obtained compared to controls. This result could no longer be obtained after ablation or inactivation of the cerebellar cortex overlying this part of the fastigial nuclei.

Afferent Pathways↗
PubMed1981

[Spinal origin of the rhythmic activities induced by harmaline in the lateral reticular nucleus].

Extracellular unit recordings were performed in the lateral reticular nucleus of Cats under tremorogenic doses of harmaline. The 8-12 Hz rhythmic activity induced by the drug in the reticular neurons was suppressed by a total spinal transection. Under harmaline, the lateral reticular nucleus also increased its radioautographic marking with 14C-2-deoxyglucose, indicating an increased average frequency of discharges of the neurons. Such labelling was also suppressed by spinal cord transection. This data indicates that both the rhythmic activity and increased radioautographic marking under harmaline are elicited through spinoreticular neurons.

Alkaloids↗
PubMed1981

Harmaline-induced tremor. II. Unit activity correlation in the interposito-rubral and oculomotor systems of cat.

Units were recorded extracellularly in the cat brainstem under the effect of tremogenic doses of harmaline. They were localized post mortem and the units discharging at the harmaline tremor frequency were mapped. Harmaline-sensitive neurons were found in the bulbo-pontine reticular formation, in particular, in the lateral reticular nucleus and the nucleus reticularis tegmenti pontis. The nucleus interpositus as well as the red nucleus also displayed numerous units discharging at the tremor frequency, indicating that the cerebello-interposito-rubro-spinal system controlling the flexor muscles participate in harmaline tremor. Participation of the oculomotor system in the harmaline-induced tremor was tested at the level of the vestibular neurons relaying the vestibulo-ocular reflex, the motoneurons, the eye muscles and the eye movements. No rhythmic discharge at the tremor frequency nor eye movements could be detected, indicating that harmalie tremor does not affect the oculomotor system.

Alkaloids↗
PubMed1981

The vibrissal pad as a source of sensory information for the oculomotor system of the cat.

Responses from lateral rectus, medial rectus and retractor bulbi nerves were obtained following electrical stimulation of the vibrissal pad of the cat. Discharges in afferent fibres dissected from the infraorbital nerve were recorded during movements of the vibrissae and following electrical stimulation of the vibrissal pad. Both stimuli activated the same population of A alpha fibers. Intracellular records were obtained from lateral rectus motoneurones identified antidromically in the principal abducens nucleus and from retractor bulbi motoneurones similarly identified in the accessory abducens nucleus. EPSPs (3 mV) were recorded in lateral rectus motoneurones following electrical stimulation of the ipsilateral vibrissal pad at a latency of 3.5 ms. Large-amplitude disynaptic EPSPs (15 mV) were recorded in retractor bulbi motoneurones following the same vibrissal stimulation. The synaptic excitation evoked in both lateral rectus and retractor bulbi motoneurones through stimulation of the ipsilateral vibrissal pad induced an early retraction followed by an abduction of the eye ball. The hypothesis is that the vibrissal message might complement other sensory modalities in the generation of patterned eye movements.

Abducens Nerve↗
PubMed1981

Reflex control of the retractor bulbi muscle in the cat.

The effects of vestibular and trigeminal stimulation on reflex responses of each slip of the retractor bulbi muscle were tested by recording the electromyogram. 1. In "encéphale isolé" cat, phasic electrical stimulation of the horizontal canal induced no response in the RB slips. Repetitive vestibular stimulation did not produce nystagmus in the RB muscle while strong muscular discharges were observed in the nystagmus lateral rectus muscle. 2. In anaesthetized cats, three trigeminal inputs elicited strong reflex responses in each slip of the RB muscle. Electrical stimulation of the vibrissae or the infra-orbital nerve evoked a two component reflex response (latencies: 5 ms +/- 0.5 and 14 ms +/- 2). Electrical stimulation of the supraorbital nerve elicited a single component reflex response (latency: 6 ms +/- 0.5). Electrical stimulation of the long ciliary nerves evoked a complex response with four components (latencies: 7.5 ms +/- 0.5, 10 ms +/- 2, 15 ms +/- 2,20 ms +/- 2). 3. Pentobarbital and morphine produced lasting depression of the reflex responses of the RB muscle. The depressive effect of morphine was reversed by naloxone.

Animals↗
PubMed1980

[Harmaline tremor: activity of the interposito-rubral system and of the bulbo-ponto-reticular formation].

The effects of tremogenic doses of harmaline have been studied by extracellular unit recordings and 14C 2-deoxyglucose marking in two groups of cats. Harmaline sensitive neurons were found in the lateral reticular nucleus and the nucleus reticularis tegmenti pontis. The nucleus interpositus as well as the red nucleus were also found to be discharging at the tremor frequency, indicating that the cerebello-interposito-rubral system participates in harmaline tremor. In cats with unilateral sections of the inferior cerebellar peduncle, 14C 2-deoxyglucose marking demonstrated that the increased activity previously observed in those structures was a consequence of harmaline acting on the inferior olive.

Alkaloids↗