Biomedical subjects

L Jami

Publications and source records attributed to L Jami.

At least 37 records · Page 2Linked to original sources

PubMed1988

Motor nuclei of peroneal muscles in the cat spinal cord.

The cat peroneal muscles have been used in numerous investigations dealing with the physiological properties of motor units, muscle spindles, and Golgi tendon organs. This report presents a study of the organization of peroneal motor pools in the cat spinal cord by means of retrograde axonal transport of horseradish peroxidase from individual muscles to the corresponding motoneurons. The motor nuclei of peroneus longus (PL), peroneus brevis (PB), and peroneus tertius (PT) muscles formed thin columns in the lateral part of the ventral horn in spinal segments L6-S1. In the transverse plane, the PT and PL nuclei occupied, respectively, dorsolateral and ventromedial positions, with PB nucleus in an intermediate position overlapping with the other two nuclei. Measurements of cell body diameters allowed identification of alpha and gamma subgroups in peroneal motoneuron populations. The average numbers of motoneurons were about 96 alpha and 60 gamma in PL, 75 alpha and 54 gamma in PB, and 34 alpha and 23 gamma in PT. Comparison with data from electrophysiological studies indicated that whole populations of motoneurons were labeled in each motor nucleus. The proportions of gamma motoneurons were the same, and cell bodies of gamma motoneurons had similar sizes in the three peroneal populations. In contrast, alpha motoneurons were significantly smaller in PB than in the two other pools, in keeping with the fact that PB contains a proportion of slow motor units larger than the two other muscles. In large samples of homonymous motoneurons, the numbers of first-order dendrites correlated linearly with motoneuron sizes.

Animals↗

PubMed1988

Further evidence for synaptic actions of muscle spindle secondaries in the middle lumbar segments of the cat spinal cord.

1. The aim of this study has been to investigate the receptor origin of postsynaptic actions evoked by group II muscle afferents in mid-lumbar segments of the cat spinal cord. The experiments tested the hypothesis that the afferents involved were the secondary endings of muscle spindles. 2. Spindle afferents were activated by contractions of intrafusal muscle fibres which were induced by electrical stimulation of fusimotor axons in the distal parts of transected ventral roots by one to three stimuli at 150-500 stimuli/s. A separate series of experiments has shown that such stimuli are effective in activating a considerable proportion of muscle spindle secondaries when contractions of extrafusal muscle fibres are eliminated by differential fatigue of these fibres, provided that several fusimotor axons are stimulated simultaneously. 3. Extracellular field potentials were recorded in the dorsal horn, at such locations where synaptic actions were evoked by electrical stimulation of group II but not group Ia muscle spindle or group Ib tendon organ afferents of pretibial flexors. Effects of activation of spindle afferents following stimulation of fusimotor axons were then compared with effects evoked by electrical stimulation of group II afferents of anterior tibial or extensor digitorum longus nerves and by small stretches of these muscles. 4. Distinct field potentials were evoked by stimulation of ventral root fibres at all locations at which field potentials were obtained from group II afferents stimulated electrically. The latencies of these field potentials were in both cases shorter in the dorsal horn than in the ventral horn. 5. The appearance of these field potentials was not related to contractions of extrafusal muscle fibres and was also observed when these contractions were practically eliminated. Furthermore, their threshold and similar dependence on a potentiating effect of two to three stimuli, as found for single secondaries, allow them to be attributed to secondary endings of muscle spindles.

Action Potentials↗

PubMed1988

Effects of muscle shortening on the responses of cat tendon organs to unfused contractions.

1. The discharges from individual Golgi tendon organs of peroneus tertius and brevis muscles were recorded in anesthetized cats. Responses to unfused isometric contractions of single motor units and combinations of motor units were compared with responses to contractions eliciting muscle shortening (i.e., shortening contractions). 2. In 75% of the examined instances, the effect of muscle shortening during unfused contractions was a slight decrease in tendon organ activation, in keeping with the reduction of contractile tension recorded at the muscle tendon. In other instances there was either no change in tendon organ response or, in less than 10% of instances, a slight increase For two motor units eliciting similar activation of a given tendon organ under isometric conditions, the effect of shortening contraction was not necessarily the same. 3. The reductions observed in tendon organ discharges upon muscle shortening were less than proportional to the reductions of contractile tension and difficult to correlate with the properties of motor units, as determined under isometric conditions. The present observations suggest three main reasons for this lack of relation. 4. The first reason depended on the properties of motor units, in that the relation between length changes and tension changes was not the same for all units. Two motor units developing similar isometric tensions did not necessarily produce the same degree of muscle shortening. Some units produced relatively significant shortening without much loss of tension. 5. Second, the dynamic sensitivity of tendon organs is known to exert a major influence on their responses to isometric unfused contractions, accounting for 1:1 driving of discharge during tension oscillations and high frequency bursts upon abrupt increase of tension. Although less tension was produced and the rate of tension development was slower in shortening contractions, similar manifestations of the dynamic sensitivity of tendon organs were observed. In such cases, the responses of tendon organs were the same whether or not the muscle shortened during contraction. 6. Third, when several motor units were stimulated in combination, the unloading influences of in-parallel units were facilitated by muscle shortening so that unloading effects, which were hardly visible under isometric conditions became evident during shortening contractions.

Animals↗

PubMed1988

[Functional properties of the Golgi tendon organs].

Golgi tendon organs are encapsulated mechanoreceptors present at the myo-tendinous and myo-aponeurotic junctions of mammalian skeletal muscles. Within the tendon organ capsule, the terminal branches of a large diameter afferent fibre, called Ib fibre, are intertwined with collagen bundles in continuity with tendon or aponeurosis at one end. The other end is connected with a fascicle of 5-25 muscle fibres, contributed by several motor units. The contraction of these fibres, exerting strain on the collagenous bundle and causing deformation of sensory terminals, is the adequate stimulus of the tendon organ. For this stimulus, the tendon organ has a very low threshold, so that a single fibre twitch can elicit a discharge from the receptor. A tendon organ can thus signal the contraction of a single one of the 10-15 motor units which contribute fibres to the fascicle connected with the receptor. The number of tendon organs present in a muscle, taken together with the fact that a given motor unit can activate several tendon organs, strongly suggests that the contraction of every motor unit in this muscle is monitored by at least one tendon organ. The exact nature of the information provided by tendon organs to the central nervous system remains an open question because no simple relation could be established between the discharge frequency of a receptor and the contractile forces of its activating motor units. It is known, however, that, due to their dynamic sensitivity, tendon organs are efficient in signaling rapid variations of contractile force. The dynamic parameters of muscle contraction prevail in the information carried by afferent discharges from tendons organs.

Afferent Pathways↗

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↗

PubMed1985

Lack of summation of dynamic and static components in the responses of cat tendon organs.

Discharges of single tendon organs of cat peroneus tertius muscle were recorded during tetanic contractions of motor units. On combined stimulation of several motor units activating the same tendon organ, the static components of responses sum, although not linearly, whereas the dynamic component of a response superimposed on a pre-existing discharge does not sum at all with this discharge.

Animals↗

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↗

PubMed1985

Activation of cat muscle spindles by static skeletofusimotor axons.

The discharges from primary and secondary spindle endings of the cat peroneus tertius muscle were recorded during stimulation of static skeletofusimotor (static beta) axons at frequencies comparable with the presumed range of motoneuronal firing rates. When stimulated at 20-40/s, static beta-axons exerted typical static actions on the spindles they innervated, including activation of primary endings with reduction of their dynamic sensitivity and activation of secondary endings. For these frequencies, the extrafusal portions of static beta-motor units developed unfused contractions producing oscillations of tension within the muscle. After suppression of extrafusal contractions, the effects of the stimulation of static beta-axons on spindle discharge could persist unaltered, showing that extrafusal events need not interfere with the specific intrafusal actions of static beta-axons. Stimulation of a static beta-axon at 20-40/s often elicited a response of primary endings in which the discharge exactly followed the stimulation frequency, i.e. it was driven 1:1. Purely mechanical excitation of a spindle by unfused extrafusal contractions could also drive its discharge at the stimulation frequency. The persistence of static beta-driving after suppression of extrafusal contraction provided evidence for its intrafusal origin. Driving elicited by static beta-axons could persist during changes in muscle length, but small fluctuations in the delay between each impulse and the preceding stimulus were observed. These fluctuations were clearly related to the changes in muscle length, indicating that although the primary ending discharge remained driven 1:1 at the stimulation frequency, the receptor was not totally insensitive to length changes.

Action Potentials↗

PubMed1985

Responses of tendon organs to unfused contractions of single motor units.

The discharges of individual tendon organs of peroneus longus and tertius muscles were examined in anesthetized cats during stimulation of single motor units at frequencies that elicit unfused contraction (5-50/s). At these frequencies nearly all the fast-contracting motor units activating a tendon organ elicited responses whose discharge rates reproduced the stimulation frequency ("1:1 driving"), whereas slow-contracting motor units elicited responses in which the discharge rate was higher than the stimulation frequency. When a motor unit stimulated at 40/s developed a gradually potentiating tension, the tendon organ discharge could remain locked on stimulation frequency over an appreciable range of the increasing tension as if the receptor responded to the tension oscillations rather than to the mean level of tension. The only visible effect of the gradual increase in mean tension on the tendon organ response was a gradual decrease of the delay between each stimulus and the corresponding impulse. Driving of tendon organ discharge at the stimulation frequency occurred not only when relatively large oscillations were superimposed on a low level of static tension but also when the static component of the tension was quantitatively preponderant. These observations suggest that during unfused contractions the dynamic component of the stimulus (i.e., oscillation of tension) exerts a prevailing influence on the discharge pattern of tendon organs. Computed simulations of tendon organ responses confirmed that a relatively strong dynamic sensitivity could account for the observed behavior of the receptor.

Animals↗

PubMed1984

Some effects of sympathetic stimulation and isoprenaline on fatigued tetanic contractions of skeletal muscle in the cat.

In anaesthetized cats, stimulation of the lumbar sympathetic trunk inconsistently elicited small increases in the contraction of fatigued Peroneus Longus muscles (Orbeli phenomenon). Facilitation of this anti-fatigue effect was regularly observed following close intra-arterial injection of isoprenaline, a beta-adrenergic agonist. Injection of the drug by itself exerted a marked anti-fatigue effect on muscle contraction.

Animals↗

PubMed1984

Glycogen depletion elicited in tenuissimus intrafusal muscle fibres by stimulation of static gamma-axons in the cat.

In this study the experimental conditions used to elicit glycogen depletion in tenuissimus intrafusal muscle fibres were different from those used by Barker, Emonet-Dénand, Harker, Jami & Laporte (1976): the tenuissimus was left in situ; several (4-6) static gamma-axons were stimulated together; the blood flow through the muscle was not reduced during the periods of gamma stimulation except in two experiments; very much longer periods (up to 9 h) of intermittent stimulation by bursts at 50-500/s were used. Bag1 and bag2 fibres were identified by their different ATPase activities in the B region. In two experiments with normal circulation, test responses of several primary endings to short periods of stimulation at 50-100/s were still very strong after stimulation of several static gamma-axons for 5 and 9 h, respectively. Glycogen depletion was observed in a large number of chain and bag2 poles but in only one of nineteen bag1 poles examined. In two other experiments with normal circulation, there was a very pronounced reduction of the test responses after stimulation of several static gamma-axons for 7 and 9 h, respectively. Out of twenty-four bag1 poles examined, nineteen exhibited zones of depletion. In an experiment in which stimulation was conducted as in Barker et al. (1976), i.e. with reduction of muscle blood flow during 1 min periods of stimulation at 50-100/s, the primary endings still gave a strong response after fifteen periods of stimulation in contrast with the marked 'fatigue' that was constantly observed in the former study. No depleted intrafusal fibres were found in the spindles of this muscle. In a last experiment, after an initial pattern of stimulation similar to that described above, the new pattern of stimulation, but with periodical reduction of blood flow, was applied, leading to a 'fatigue' of the test responses in 2 h. In the spindles of this muscle three out of ten bag1 poles were depleted. The variability of glycogen depletion in bag1 fibres appears to be linked to the degree of spindle 'fatigue' which may develop after static gamma stimulation. It seems that in 'fatigued' spindles some factor or factors liberated by the contraction of neighbouring fibres may deplete glycogen in bag1 fibres by a non-neural mechanism. When, in spite of a prolonged stimulation of static gamma-axons, no fatigue of the test responses develops, zones of depletion in bag1 fibres--possibly of neural origin--are very rare, although a large proportion of bag2 and chain fibres are depleted.

Animals↗

PubMed1983

Action of dantrolene sodium on single motor units of cat muscle in vivo.

Dantrolene sodium, a skeletal muscle relaxant, was investigated for its action on single motor units of the peroneus tertius muscle in cats anaesthetized with pentobarbitone sodium. Motor axons were isolated in ventral root filaments and their muscle units were identified as either fast-fatiguable (FF), fast-resistant (FR), fast-intermediate (FI) or slow-resistant (S). Dantrolene sodium (2 mg/kg) was administered intravenously in a solution of 1,2-propanediol. Effects were observed on the twitches, unfused tetanic contractions and maximal tetanic tensions of 78 motor units in 5 experiments. Contractile tension was depressed whereas muscle action potentials appeared unaffected. Maximal tetani were less depressed than unfused tetani and twitches. The reduction of tension was more pronounced for fast (FF, FR and FI) than for slow units. After drug injection, the mean tensions developed at the end of a 3 s period of stimulation at 40/s were: 13.1%, 10.6% and 12.7% of pre-drug control for FF, FR and FI units, respectively, and 67.1% for S units. Upon prolonged stimulation at 40/s fast units depressed by Dantrolene sodium were able to potentiate back to their initial pre-drug tension.

Action Potentials↗

PubMed1983

After-effects of repetitive stimulation at low frequency on fast-contracting motor units of cat muscle.

Twitch and tetanic contractions of single motor units of the cat peroneus tertius muscle were examined after application of a test allowing their identification as either fast fatigable (f.f.) or fast fatigue-resistant (f.r.) or fast intermediate (f.i.) or slow units as established by Burke, Levine, Tsairis & Zajac (1973). The test was found to leave two kinds of after-effects in f.f., f.r. and f.i. units whereas it did not affect slow units. The first after-effect was an early and brief potentiation of twitch tension occurring in all f.r. and f.i. units and in most f.f. units. The second after-effect, termed 'delayed fatigue', was a prolonged depression of tension output, that developed slowly following the early potentiation in all f.f. and f.i. units and more than half of the f.r. units. One hour after the test, unfused tetanic contractions elicited by 20-40/sec stimulation were deeply depressed in motor units that had been left without stimulation since the end of the test. Recovery took place in 3-5 hr. Motor units affected by delayed fatigue could nevertheless be made to develop nearly normal tension by gradual build-up upon prolonged stimulation at 30-40/sec. Maximal tetanic contractions elicited by 200/sec stimulation were much less depressed during delayed fatigue than unfused tetanic contractions. These observations suggest that contractile mechanism were not impaired by delayed fatigue. Since absence of change in muscle action potential indicated that excitation of muscle fibres was not affected either, delayed fatigue might be due to a temporary failure of excitation-contraction coupling.

Action Potentials↗

PubMed1982

Distribution of physiological types of motor units in the cat peroneus tertius muscle.

Motor units of the cat peroneus tertius muscle were systematically analyzed using the criteria established by Burke et al. (1973). On the basis of their speed of contraction and resistance to fatigue, 121 (97%) of 125 motor units examined in ten adult cats could be classified as belonging to one of four types: fast-fatigable (FF), fast-resistant (FR), fast-intermediate (FI), and slow-resistant (S). Peroneus tertius was found to contain 30% FF motor units, 9% FI units, 39% FR units, and 22% S units. Contraction times of fast motor units (FF, FR, and FI) ranged from 15 to 27 ms and those of S units from 26 to 42 ms. The mean tetanic tensions were 37 g for FF units, 29 g for FI units, 7.5 g for FR units, and 1.1 g for S units. Fast motor units displayed considerable post-tetanic potentiation of twitch tension. Under similar conditions of stimulation, FF units appeared able to potentiate more and faster than FR units.

Animals↗

PubMed1982

A quantitative study of skeletofusimotor innervation in the cat peroneus tertius muscle.

1. Physiological tests were used to identify skeletofusimotor or beta axons to the cat peroneus tertius muscle in order to assess the proportion of beta axons in the motor supply to this muscle. 2. Static beta axons (beta S) were identified by: (a) observation of a delay between the complete block of extrafusal contraction and the failure of spindle activation upon prolonged stimulation, (b) increase of spindle excitation with stimulation frequencies above that eliciting maximal extrafusal contraction, (c) observation of 'unfused' frequencygram of spindle primary afferent discharge during stimulation of the axon at frequencies above that eliciting complete fusion of extrafusal contraction and (d) static action exerted on the response of the spindle afferent to ramp stretch. 3. Dynamic beta axons (beta D) were identified by the persistence of spindle activation after selective block of extrafusal neuromuscular junctions and by their dynamic action on spindle primary endings. 4. The actions of 116 motor axons (conduction velocity 56-104 m/sec) on ninety-five spindle afferents (fifty-seven from primary and thirty-eight from secondary endings) were examined in ten experiments. Thirty-six beta axons (31% of the total sample) were identified: twenty-four beta S (conduction velocity 69-104 m/sec) and twelve beta D (conduction velocity 56-91 m/sec). 5. Twenty (35%) primary endings were activated by a beta S and sixteen (28%) by a beta D axon. Nineteen (45%) secondary endings were activated by a beta S and five (13%) by a beta D axon. Convergence of beta D and beta S axons on the same spindle occurred in 10% of instances. beta-innervated spindles were also supplied by gamma axons. 6. Most of the beta S motor units were of the fast-fatigue resistant (FR) type, with a few units of the fast-fatigable (FF) type, and nearly all the beta D motor units were of the slow (S) type.

Action Potentials↗

PubMed1982

Effects of stimulating the lumbar sympathetic trunk on cat hindlimb muscle spindles.

1. The effect of stimulating the lumbar sympathetic trunk has been observed on cat lumbrical and tenuissimus muscle spindles. 2. Spindle afferent discharges were recorded either from single Ia fibers in teased dorsal root filaments or from a large number of spindles by integrating their discharges led from muscles nerves. 3. Blood flow in small arteries supplying the muscle was observed through a microscope during and after the stimulation of the sympathetic trunk. 4. In some spindles repetitive stimulation of the sympathetic trunk elicited, after a few seconds delay, a small increase in firing rate. This can be ascribed to a direct action of sympathetic axons on the spindles because it precedes by about 20-30 sec the reduction of blood flow observed in the muscle arteries. This effect is not accompanied by a change in dynamic sensitivity of the primary ending. 5. This early effect is followed, after 20-30 sec, by a later rise in firing frequency which still progresses after the end of stimulation and eventually terminates in an abrupt fall in firing often leading to interruption of the ending activity. Recovery takes places at a variable time after the blood flow has bee reestablished. These long lasting effects can be ascribed to reduction of blood flow in muscle spindles since they are always associated with changes in blood flow in muscle arteries and since they are mimicked by occlusion of the muscle circulation. 6. In some spindles, the amplitudes of frequencygrams elicited by stimulation of static gamma axons were slightly increased suggesting a weak facilitatory effect on the contraction of some intrafusal muscle fibers.

Adrenergic Fibers↗