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Biomedical subjects

G Horcholle-Bossavit

Publications and source records attributed to G Horcholle-Bossavit.

At least 19 recordsLinked to original sources
PubMed1992

Distribution of glycinergic terminals on lumbar motoneurons of the adult cat: an ultrastructural study.

The distribution of glycine-like immunoreactivity on cat lumbar motoneurons was examined in electron microscopy, using pre-embedding immunocytochemistry. In the dorsolateral portion of the ventral horn, numerous labeled axon terminals were presynaptic to somatic and dendritic profiles of alpha-motoneurons. Most of the glycinergic boutons contained pleomorphic vesicles and showed symmetrical contacts. On the somatic and proximal dendritic compartments, glycinergic terminals accounted for, respectively, 24.6 and 26.6% of the total number of terminals. There were very few glycinergic terminals on gamma-motoneurons. Immunoreactive axons, dendrites and cell bodies were also observed near the motoneurons. These results support the view that glycine plays a major role in the inhibition of alpha-motoneurons and suggest that inhibitory mechanisms occur on the soma as well as on dendrites.

Animals↗
PubMed1992

Alpha and gamma motoneurons in the peroneal nuclei of the cat spinal cord: an ultrastructural study.

The aim of the present study was to investigate whether ultrastructural features can be used as a guide to identify alpha- and gamma-motoneurons among the intermediate-size neurons of the peroneal motor nuclei. The peroneus brevis and peroneus tertius muscles of adult cats were injected with horseradish peroxidase, and motoneurons labeled by retrograde axonal transport were examined by electron microscopy. In both nuclei, the distributions of cell-body diameters, measured in the light microscope, were bimodal covering the range of 28-84 microns, with a trough around 50 microns. The sample of 25 motoneurons selected for the ultrastructural study included not only large (presumed alpha) and small (presumed gamma) neurons but also intermediate-size cell bodies with diameters in the 40-60 microns range. For each motoneuron, 2-5 profiles were reconstructed from ultrathin sections taken at 6-8 microns intervals. Synaptic boutons were counted and their lengths of apposition were measured. On the basis of three criteria, namely: (1) bouton types present on the membrane, (2) percentage of membrane length covered by synapses, and (3) the aspect of the nucleolus, all the examined motoneurons, including those with intermediate sizes, fell into one of two categories. Fourteen motoneurons, with cell-body diameters in a range of 55-84 microns, were contacted by all types of boutons (mainly S-type with spherical vesicles, F-type with flattened vesicles, and C-type with subsynaptic cistern); the synaptic covering of the somatic membrane was over 40% and the nucleus contained a vacuolated nucleolus. These were considered alpha-motoneurons. Eleven motoneurons, with only S and F boutons, a synaptic covering under 30%, a compact nucleolus and a cell-body diameter ranging between 28 and 50 microns, were considered gamma-motoneurons. No other combination of the three criteria was observed. These results show that unequivocal distinction of alpha- and gamma-motoneurons is possible in the peroneal nuclei, on the basis of morphological differences independent of cell-body size.

Animals↗
PubMed1992

Depolarization of Ib afferent axons in the cat spinal cord during homonymous muscle contraction.

1. Intra-axonal records from the intraspinal course of Ib and Ia afferent fibres innervating the gastrocnemius medialis muscle were obtained in chloralose or Nembutal-anaesthetized cats during submaximal contractions of the muscle. 2. Afferent fibres in continuity with their muscle of origin were functionally identified by their responses to muscle stretch or contraction. 3. In six out of eight Ib afferents, primary depolarizations (PADs) were recorded during contraction. They were independent of the presence of orthodromic impulses fired by tendon organs. 4. These observations support the assumption that the reduction of Ib autogenetic inhibition in homonymous and synergic motoneurones during GM contractions is due to presynaptic inhibition of transmission in Ib pathways.

Animals↗
PubMed1990

Postnatal development of peroneal motoneurons in the kitten.

In 1- to 72-day-old kittens, motoneurons of the 3 peroneal muscle nuclei were labeled by retrograde axonal transport of horseradish peroxidase from individual muscles. At birth, the locations of peroneal nuclei were similar to those of the adult cat. Counts of motoneurons at different ages indicated that postnatal cell death does not occur in peroneal motor nuclei. Primary dendrites were as numerous in motoneurons of newborn kittens as in adult motoneurons but they were thinner, shorter and poorly ramified. The number of recurrent axon collaterals was higher in the first postnatal week than at later stages. The growth of motoneurons followed similar rates in the 3 peroneal nuclei. Distributions of cell body diameters and volumes were unimodal at birth and became bimodal between 15 and 20 days postnatal. The separation of peroneal motoneurons in two size subgroups, presumably corresponding to alpha and gamma populations, was followed by an increase in growth rate which became faster for alpha than for gamma motoneurons.

Aging↗
PubMed1990

Ensemble discharge from Golgi tendon organs of cat peroneus tertius muscle.

1. The responses of individual tendon organs of the cat peroneus tertius muscle to motor-unit contractions were recorded in anesthetized cats during experiments in which all the Ib-afferent fibers from the muscle had been prepared for recording in dorsal root filaments. This was possible because the cat peroneus tertius only contains a relatively small complement of approximately 10 tendon organs. 2. Motor units of different physiological types were tested for their effects on the whole population of tendon organs in the muscle. Effects of unfused tetanic contractions were tested under both isometric and anisometric conditions. Each motor unit activated at least one tendon organ, and each tendon organ was activated by at least one motor unit. Individual slow-type units were found to act on a single or two receptors, whereas a fast-type unit could activate up to six tendon organs. 3. In one experiment, the effects of 8 motor units on 10 tendon organs were examined. One fast-twitch, fatigue resistant (FR)-type unit acted on six tendon organs, of which four were also activated by another FR unit. The contraction of each unit, on its own, elicited a range of individual responses, from weak to strong. The discharge frequencies of individual responses displayed no clear relation with the strength of contraction, nor did they accurately represent the shape of force profiles. But when all the discharges were pooled, a fairly good correspondence appeared between variations of contractile force and variations of averaged discharge frequencies.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗
PubMed1990

Reduction of Ib autogenetic inhibition in motoneurons during contractions of an ankle extensor muscle in the cat.

1. Triceps surae and plantaris (Pl) motoneurons were recorded intracellularly in chloralose or pentobarbital sodium (Nembutal)-anesthetized cats during unfused tetanic contractions of gastrocnemius medialis muscle (GM) produced by stimulating either a cut branch of the GM nerve or the muscle directly. 2. In alpha-motoneurons, during a series of GM twitches at 10/s, contraction-induced inhibitory potentials, probably the result of input from Golgi tendon organs (autogenetic inhibition), rapidly subsided before the end of the series. In contrast, excitatory potentials, probably the result of the activation of spindle primary endings during relaxation from contraction, persisted. 3. In gastrocnemius lateralis-soleus (GL-S) and Pl motoneurons lacking an excitatory connection with Ia afferents from GM, the sustained contraction of this muscle also elicited a declining inhibition. Rapid reduction of contraction-induced autogenetic inhibition was also observed in homonymous gamma-motoneurons. During unfused tetanic contractions lasting 0.5-4s, inhibitory potentials quickly subsided, but an abrupt increase in contractile force elicited a new series of decreasing inhibitory potentials. 4. The assumption that the inhibition induced by GM unfused tetanic contractions was due to activation of homonymous Ib afferents was supported by observations of the effects of electrical stimulation of the GM nerve. In Pl motoneurons lacking an excitatory connection with Ia afferents from GM, repetitive trains applied to the GM nerve, at a strength just above threshold for group I fibers, elicited rapidly declining inhibitory potentials similar to those produced by GM contraction. It was verified that during such stimulation, the amplitude of the group I afferent volleys did not decrease. 5. Reduction of contraction-induced Ib inhibition during sustained GM contraction was still present after a low spinalization of the preparation. As GM tendon organ discharges were verified to persist throughout prolonged contractions, the observed decline of autogenetic inhibition is likely to depend on a spinal mechanism, possibly involving presynaptic inhibition of Ib afferents and/or mutual inhibition of Ib-inhibitory interneurons.

Animals↗
PubMed1989

Activation of Golgi tendon organs by asynchronous contractions of motor units in cat leg muscles.

Discharges from individual tendon organs of peroneus tertius muscle activated by the isometric contractions of single motor units were recorded in anaesthetized cats. Pairs of motor units acting on the same tendon organ were stimulated asynchronously at frequencies eliciting unfused contractions. Tendon organ responses to such contractions did not display a linear relation between discharge frequency and contractile force recorded at the muscle tendon. In several instances, one of the motor units exerted a predominant influence on the response of the tendon organ, even though this unit did not produce the strongest activation of the receptor when stimulated on its own.

Action Potentials↗
PubMed1989

Unloading of tendon organ discharges by in-series motor units in cat peroneal muscles.

1. The discharges from individual Golgi tendon organs of peroneus tertius and brevis muscles were recorded in anaesthetized cats during the isometric contractions of single motor units. Upon combined contractions of several motor units, two sorts of unloading effects were observed. 2. First, the contraction of a motor unit which, by itself, was without action on a tendon organ could produce a reduction in the response of the receptor to one of its activating motor units. Unloading effects exerted by such in-parallel motor units could effectively interfere with the actions of in-series motor units on the receptor. 3. Second, the contraction of a motor unit activating a tendon organ could reduce the response of this tendon organ to the contraction of another of its activating units. This new type of unloading effect, exerted by in-series motor units, was demonstrated by the fact that the simultaneous contraction of both units elicited less discharge from the receptor than the contraction of a single unit. 4. Unfused contractions of a fast-type motor unit eliciting a response in which the tendon organ discharge was driven 1:1 at the frequency of stimulation of the motor unit, could exert unloading actions on the response of the receptor to another motor unit eliciting a higher discharge frequency. 5. In-series unloading actions were exerted not only by fast-type motor units developing large forces, but also by relatively small slow-type motor units. 6. The high incidence of in-parallel and in-series unloading effects suggests that their consequences may be functionally significant. When large numbers of motor units are being recruited in a muscle, unloading effects might result in a limitation of the Ib afferent discharges from this muscle, preventing an excessive increase of autogenetic inhibition.

Action Potentials↗
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↗
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↗
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↗
PubMed1979

[Oculomotor reflex evoked by vibrassae stimulation in the cat].

The oculomotor effects of vibrissae stimulation have been studied in the "encéphale isolé" non-anaesthetized Cat. Intracellular recording of lateral rectus motoneurones showed an excitatory projection via the ipsilateral infraorbital nerve to these motoneurones. The afferent fibers are type A alpha, recuited with a low threshold (0.2-0.5 mA) and convey information about vibrissae displacement.

Afferent Pathways↗
PubMed1979

[Interaction between the vestibulo-ocular and the oculomotor systems].

Optomotor nystagmic activity has been elicited in the "encéphale isolé" cat during repetitive electric stimulation of selective oculomotor regions of the frontal cortex and superior colliculus. These regions were nystagmogenic only when facilitated by a cortical arousal or a vestibular activation.

Animals↗
PubMed1979

Anatomical and electrophysiological identification of motoneurones supplying the cat retractor bulbi muscle.

Motoneurones innervating the retractor bulbi muscle in the cat have been identified by retrograde labelling with horseradish peroxidase, by intracellular recording and by intracellular staining with horseradish peroxidase. Their somata are found in an accessory abducens nucleus, analogous to that described in some other species, which consists of a narrow column of cells situated in the lateral tegmental reticular field, above the superior olive and medial to the facial nerve. The column of cells extends over approximately 1.5 mm from P 5.5 to P 7. The retractor bulbi motoneurones number from 80 to 120 and have large, elongated somata which give rise to five or six major dendrites. Their axons cross the reticular formation in a dorso-medial direction to pass through the principal abducens nucleus before turning to leave the brain stem in the 6th nerve. Antidromic latencies ranged from 0.4 to 0.7 ms. Some retractor bulbi motoneurones could also be activated antidromically by stimulation of the lateral rectus muscle nerve.

Abducens Nerve↗
PubMed1979

Morphological characteristics of lateral rectus motoneurones shown by intracellular injection of HRP.

The morphology of identified lateral rectus motoneurones is described after staining by intracellular iontophoresis of horseradish peroxidase. Soma vary in shape and size according to the number and orientation of primary dendrites. The basic pattern of arborisation shows short primary dendrites which branch close to the soma, forming a distal ramification extending over 600 to 1,200 micrometer from the soma. Distal dendrites extend into the ipsilateral medial vestibular nucleus, the reticular formation and amongst the fibres of the medial longitudinal fasciculus. This extension is greater than that previously seen in procion yellow and Golgi stained lateral rectus motoneurones. The axon originates from the perikarya or from the base of a primary dendrite. No axon collaterals have been observed.

Abducens Nerve↗
PubMed1978

[Electrotonic transmission in the mammalian central nervous system (author's transl].

The aim of this review is to present the electrophysiological data, obtained in the mammalian central nervous system, which show that depolarisations recorded intracellularly, under certain experimental conditions can be interpreted in terms of electrotonic coupling. The results were obtained from very different structures: primary sensory nuclei, sensori-motor integration centres and motor nuclei. The association of the phenomenon of electrotonic transmission with a known ultrastructural substrate--the "gap junction"--has been defined by the term electrotonic coupling. In the cases where it has not been possible to link depolarisations with the presence of gap junctions, other possible morphological correlates have been envisaged. The functional significance of electrotonic interactions are discussed on the basis of information obtained from different experimental approaches.

Animals↗
PubMed1978

[Electrophysiology of vestibulo-ocular reflexes].

Electrophysiological and morphological properties of premotor neurones in the vestibulo-ocular system have been studied intracellularly in the unanesthetized "encéphale isolé" cat. 1. Secondary neurones of the vestibulo-abducens reflex, identified both by their antidromic and orthodromic responses, showed no nystagmic modulation of their activity. 2. Only 12% of the recorded population in the medial vestibular nucleus showed burst firing patterns correlated with the phases of nystagmus. 3. Two classes of neurones which did not respond to stimulation of the abducens nerve were recorded in the abducens nucleus. The first were inhibited by phasic vestibular stimulation and fired 180 degrees out of phase with the ipsalateral motor nerve discharge. The second type of neurones was excited by vestibular stimulation and fired in synchrony with the motor nerve activity.

Abducens Nerve↗