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PubMed1985

Morphological and electrophysiological determination of the projections of jaw-elevator muscle spindle afferents in rats.

The fluorescent compound Lucifer Yellow was injected into the somata of nine identified jaw-elevator muscle spindle afferents, located in the V mesencephalic nucleus. Reconstructions of the central course of their axons were subsequently made from serial, transverse, sections to identify sites of projection. Three sites of termination were identified on the basis of collaterals that ended in varicosities and/or boutons. All afferents projected to the V nucleus oralis and, all but one, also to the V motor nucleus. Two out of nine afferents had terminations in the supra-trigeminal nucleus, though a further four appeared to send collaterals to this area. The relative density of projection, judged by the number of collaterals supplied to each area, decreased in the order: V nucleus oralis, V motor nucleus and supra-trigeminal nucleus. The central course of the afferent axons was such that impulses from the periphery would arrive first at the V motor nucleus, then the V nucleus oralis, the supra-trigeminal nucleus, and finally the afferent somata in the V mesencephalic nucleus. In animals in which the masseter nerve was exposed in-continuity for electrical stimulation, electrophysiological recordings were made in the three areas described above to identify units that received a monosynaptic input from spindles in the masseter muscle. Criteria were formulated on the basis of the pattern of responses on stimulation of the masseter nerve, and the morphology of labelled neurones, for differentiating between afferents, interneurones, and motoneurones. In the V motor nucleus, monosynaptic excitatory post-synaptic potentials (e.p.s.p.s) were obtained in both synergist and masseter motoneurones. These were assumed to arise from a masseter muscle spindle input as the thresholds for exciting such afferents and eliciting e.p.s.p.s were similar. Some interneurones, chiefly in the V nucleus oralis, were activated at thresholds close to that of muscle spindle afferents and could also fire in response to muscle stretch. As their latencies (measured extracellularly) were similar to that of e.p.s.p.s in motoneurones, they were assumed to receive a monosynaptic muscle spindle input. However, most interneurones were activated at longer latencies (up to 7 ms) and some also fired to muscle stretch. Arguments are advanced, based on the long rise time of e.p.s.p.s recorded in some, that the majority of these may also be candidates for monosynaptic activation.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1985

Reversal of the static component of spindle potential by imposed depolarizing current in the frog muscle spindle.

The static component of the spindle potential provoked during stretch of isolated muscle spindles of the frog was reversed during the application of depolarizing currents ranging from 0.2 to 5 nA in normal Ringer solution and also in Na+-free Ringer solution. In the same range of current intensities, spontaneous rhythmic hyperpolarizations due to [Ca2+]i-activated GK, an attenuation of membrane impedance, and an anomalous decrease in amplitude of the afferent spikes were observed. All 4 phenomena were abolished by K+ channel blockers (10 mM CsCl, 1-2 mM 4-aminopyridine (4-AP), or 20 mM tetraethylammonium chloride (TEA], Ca2+ channel blockers (5-10 mM CoCl2, MnCl2, 1-2 mM CdCl2 or 0.5 mM verapamil) or 0.1 mM quinine. The amplitude of the static component of the spindle potential was markedly increased at threshold concentration of the K+ channel blockers (5 mM CsCl, 0.1-0.5 mM 4-AP or 5-10 mM TEA), but the component disappeared at that of the Ca2+ channel blockers. The rhythmic hyperpolarizations are associated with the spindle potential, except for its dynamic component, which often triggers a hyperpolarizing deflection. We suggest that both the static component of the spindle potential and rhythmic hyperpolarizations are due to GK(Ca) in the intracapsular axon, either along the terminal or at the branching nodes, or both; and that the receptor potential contributes to, but is not the same as, the spindle potential.

Animals↗
PubMed1988

Muscle spindles in the paraspinal musculature of patients with adolescent idiopathic scoliosis.

Electromyographic studies have determined that muscle imbalance and asymmetry of stretch receptors in the paraspinal muscle of patients with idiopathic scoliosis may have a large role to play in the development and production of the deformity. This project consisted of a detailed histologic and histochemical analysis of the distribution of muscle spindles in paraspinal musculature of patients suffering from idiopathic scoliosis, using the reduced form of nicotinamide-adenine dinucleotide (NADH), adenosine triphosphatase (ATPase), and Tri-chrome stain techniques. Muscle biopsy samples were taken at operation for spinal instrumentation from each of 13 patients (mean age: 16.2 years; 3 males, 10 females) with all but one female exhibiting right thoracic curves. The samples were collected from two specific sites (superficial and deep) on both sides of the vertebral column at the level of the apex of the primary curve and two vertebral levels above and below the apex. From the results there appear to be few muscle spindles in the scoliotic muscle of this region. All of the patients from whom muscle samples were taken possessed at least one sample with a muscle spindle. However, each patient had very few samples which contained a minimum of one muscle spindle (mean: 20.3%; SD: 12.6). It is clear that further examination is necessary, particularly in the area of comparison with 'normal' standards when these standards become available.

Adolescent↗
PubMed1987

Ultrastructural localization of non-specific cholinesterase activity in rat muscle spindles.

Electron microscopical localization of non-specific cholinesterase activity was studied in the encapsulated part of rat hindlimb muscle spindles. After incubation of the muscle tissue in a medium containing butyrylthiocholine bromide as substrate and BW284c51 as the specific inhibitor of acetylcholinesterase, a distinct electron-dense precipitate corresponding to non-specific cholinesterase activity was found along the whole length of muscle spindles. The richest source of non-specific cholinesterase activity were the motor end-plates present in the polar and juxtaequatorial regions. Much smaller amounts of reaction deposits were found at the secondary sensory terminals in the juxtaequatorial zones. The primary sensory terminals in the equatorial zone contained only low amounts of the reaction product. A fine homogeneous reaction product was localized in the narrow spaces between Schwann cell processes or in gaps between the Schwann cell, and axonal and muscle membranes. A granular precipitate was localized on the basal lamina in the synapse region of motor terminals or covering Schwann cell processes and sensory terminals with adjacent intrafusal muscle fibres. Our results suggest that most of non-specific cholinesterase in muscle spindles is synthesized by the Schwann cells; but a small amount can also be synthesized by fibroblast-like cells forming the inner capsule of muscle spindles. Non-specific cholinesterase thus coexists with acetylcholinesterase at motor end-plates, but is single at sensory terminals. The function of non-specific cholinesterase in sensory receptors is still not clear. It seems most probable that non-specific cholinesterase in muscle spindles may play a role in the maintenance of the external milieu around nerve endings, especially in the sensory region.

Acetylcholinesterase↗
PubMed1991

Development of hindlimb muscle spindles in the marsupial Macropus eugenii (tammar wallaby).

The development of muscle spindles was studied in the hindlimb of pouch young of the marsupial Macropus eugenii (tammar wallaby) from birth to 100 days. Primary myogenesis was evident in hindlimb muscles at birth. Presumptive muscle spindles were identified as early as day 30 postnatally. The intrafusal muscle fibres developed sequentially, to form the full juvenile complement by day 50, followed by development of the periaxial space. The formation of muscle spindles in the marsupial's hindlimb after birth was in contrast to the mainly prenatal development of spindles noted in placental mammals.

Aging↗
PubMed1979

Autogenetic inhibition of motoneurones by impulses in group Ia muscle spindle afferents.

1. Inhibitory post-synaptic potentials evoked by adequate stimulation of group Ia muscle spindle afferents of homonymous and synergistic muscles and by selective electrical stimulation of tendon organ afferents were analysed in motoneurones of triceps surae and plantaris. 2. Selective activation of Ia afferents was verified to occur with brief stretches of triceps surae and plantaris 35 micrometer or less in amplitude with an initial muscle tension of 5 N; stretches of 30--35 micrometer were estimated to activate 80--90% of Ia afferents in these muscles. Under the same conditions the lowest thresholds for group Ib tendon organ afferents were about 40 micrometer. 3. Stretches less than or equal to 30 micrometer evoked i.p.s.p.s in 80% of triceps surae and plantaris motoneurones; lowest thresholds for evoking i.p.s.p.s wef triceps surae and plantaris motoneurones; lowest thresholds for evoking i.p.s.p.s were 10 micrometer or less. However, such low thresholds for stretch-evoked i.p.s.p.s, lower than the thresholds for activation of Ib afferents, were found mainly in spinalized, unanaesthetized (after decerebration) or lightly anaesthetized animals. The latencies of these i.p.s.p.s indicated disynaptic and trisynaptic coupling between Ia afferents and motoneurones. The i.p.s.p.s were evoked (i) from the homonymous and synergistic muscles stretched together, (ii) from the homonymous muscles alone and (iii) from the synergistic muscles alone. 4. Control experiments showed that i.p.s.p.s could be evoked by stretches sub-threshold for discharging motoneurones, thus showing that those i.p.s.p.s were not mediated by Renshaw cells. The stretch-evoked i.p.s.p.s disappeared after sectioning the nerves from the corresponding muscles, further excluding their mediation by afferents other than group Ia afferents from thf stretched muscle. 5. In order to selectively activate tendon organ afferents, thresholds for excitation of Ia afferents by electrical stimuli were increased to a level above the threshold for Ib afferents by prolonged muscle vibration (Coppin, Jack & MacLennan, 1970). I.p.s.p.s evoked by stimuli near threshold for Ib afferents appeared with latencies indicating disynaptic coupling. Later (trisynaptic) components of Ib i.p.s.p.s required somewhat stronger stimuli. 6. Amplitudes of Ia i.p.s.p.s evoked by muscle stretches activating about 80% of muscle spindle afferents were compared with amplitudes of Ib i.p.s.p.s due to less than 50% of tendon organ afferents of the same muscles. The Ia i.p.s.p.s were much smaller (16--35%) than the Ib i.p.s.p.s. The amplitudes of such Ia and Ib i.p.s.p.s constituted about 10 and 25--66%, respectively, of the maximal i.p.s.p.s evoked by electrical stimulation of all group I afferents. 7. We conclude that inhibition of motoneurones may be evoked from Ia muscle spindle afferents from homonymous and synergistic muscles as well as from Ib tendon organ afferents...

Animals↗
PubMed1987

Fusimotor reflexes to antagonistic muscles simultaneously assessed by multi-afferent recordings from muscle spindle afferents.

Several single agonist/antagonist primary muscle spindle afferents were simultaneously recorded in chloralose anaesthetized cats. It was shown that their dynamic and static sensitivity to sinusoidal muscle stretches could be increased or decreased via the fusimotor system by extension and flexion of the contralateral hind limb as well as by stretch of ipsilateral muscles and stimulation of ipsilateral skin nerves. The results seem to support the hypothesis that the primary muscle spindle afferents convey complex multisensory messages to the central nervous system (CNS).

Afferent Pathways↗
PubMed1970

The effects of dimethothiazine on muscle spindle activity in the decerebrate cat.

1. The effects of dimethothiazine have been studied on the response of afferent fibres from primary and secondary endings of muscle spindles in the soleus muscle of the decerebrate cat during stretching of the muscle under controlled conditions.2. Dimethothiazine in doses of 1 to 4 mg/kg intravenously reduced the discharge frequency of primary and secondary endings. Higher doses of dimethothiazine had little further significant effect on the discharge frequency.3. The discharge frequency recorded from de-efferented muscle spindles in soleus of the decerebrate cat were similar to the discharge frequencies obtained in preparations with intact ventral roots which had received a high dose of dimethothiazine.4. Dimethothiazine had little significant effect on the discharge frequency of afferent fibres from muscle spindles in the soleus muscle of decerebrate preparations where the ventral roots were cut.5. These effects of dimethothiazine on muscle spindle activity were not related to any changes in blood pressure of the decerebrate cat.6. Dimethothiazine appears to reduce the effects of both the dynamic and static fusimotor fibres on the spindle.7. The doses of dimethothiazine which effect spindle discharge frequency are similar to those required to reduce decerebrate rigidity.

Action Potentials↗
PubMed1995

Expression of alpha-cardiac myosin heavy chain in normal and denervated rat muscle spindles.

Whether any fibers in rat hindlimb muscles express alpha-cardiac myosin heavy chain (MHC) is uncertain. Expression of alpha-cardiac MHC mRNA and the polypeptide for which it codes were examined in control and denervated rat muscle spindles using in situ hybridization (ISH) and immunocytochemistry (ICC). Both nuclear bag2 and bag1 intrafusal fibers in the extensor digitorum longus (EDL) muscles expressed alpha-cardiac MHC and its precursor mRNA. Furthermore, denervation of the hindlimb down-regulated alpha-cardiac MHC mRNA expression in rat nuclear bag intrafusal fibers, even though they continued to display a strong affinity for anti-alpha-cardiac MHC monoclonal antibody. These data show that (1) intrafusal fibers express the alpha-cardiac MHC gene; (2) innervation regulates alpha-cardiac MHC gene expression at a pre-translational level; and (3) ISH is more sensitive than ICC to changes in alpha-cardiac MHC gene expression in adult rat muscle spindles.

Animals↗
PubMed1998

Sensory ataxia and muscle spindle agenesis in mice lacking the transcription factor Egr3.

Muscle spindles are skeletal muscle sensory organs that provide axial and limb position information (proprioception) to the central nervous system. Spindles consist of encapsulated muscle fibers (intrafusal fibers) that are innervated by specialized motor and sensory axons. Although the molecular mechanisms involved in spindle ontogeny are poorly understood, the innervation of a subset of developing myotubes (type I) by peripheral sensory afferents (group Ia) is a critical event for inducing intrafusal fiber differentiation and subsequent spindle formation. The Egr family of zinc-finger transcription factors, whose members include Egr1 (NGFI-A), Egr2 (Krox-20), Egr3 and Egr4 (NGFI-C), are thought to regulate critical genetic programs involved in cellular growth and differentiation (refs 4-8, and W.G.T. et al., manuscript submitted). Mice deficient in Egr3 were generated by gene targeting and had gait ataxia, increased frequency of perinatal mortality, scoliosis, resting tremors and ptosis. Although extrafusal skeletal muscle fibers appeared normal, Egr3-deficient animals lacked muscle spindles, a finding that is consistent with their profound gait ataxia. Egr3 was highly expressed in developing muscle spindles, but not in Ia afferent neurons or their terminals during developmental periods that coincided with the induction of spindle morphogenesis by sensory afferent axons. These results indicate that type I myotubes are dependent upon Egr3-mediated transcription for proper spindle development.

Animals↗
PubMed1982

Excitatory post-synaptic potentials from single muscle spindle afferents in external intercostal motoneurones of the cat.

1. The discharges of muscle spindle afferents from the external intercostal muscles of anaesthetized, paralysed cats were recorded from dorsal roots in continuity. The dynamic responses, regularities of firing and conduction velocities of the afferents were measured and used to characterize the afferents as primary-like or secondary-like. 2. The synchronization of afferent discharges was investigated by the construction of cross-correlation histograms from the simultaneously recorded discharges of pairs of afferents. The discharges of primary-like afferents with high dynamic responses were found to be synchronized within a few msec. The cardiac pulse was a strong contributary factor in this synchronization. 3. Intracellular recordings were made from external intercostal motoneurones, and spike-triggered averaging was used to reveal unitary e.p.s.p.s evoked by muscle spindle afferents which were from the same spinal cord segment. Dorsal roots other than the rootlet containing the afferent were cut to prevent the synchronization of afferent discharges from affecting the averaged e.p.s.p.s. 4. For primary-like afferents the mean amplitude of the e.p.s.p.s was 171 microV and the mean connectivity (the proportion of motoneurones connected by one afferent) was between 42 and 48%. 5. The amplitudes and shapes of the e.p.s.p.s varied with the respiratory phase, usually being larger in inspiration than in expiration and sometimes also having a longer time course. In particular some e.p.s.p.s showed that components, only represent in inspiration, which were interpreted as indicating polysynaptic connexions gated by the respiratory cycle. 6. The results are discussed in comparison with the connexions of individual muscle spindle afferents from other muscles, with particular reference to the conduction velocities of the afferents.

Action Potentials↗
PubMed1980

[Rate of occurrence and reproducibility of the initial burst of frequency of muscle spindle receptors].

The initial burst (IB) of activity of the passive muscle spindle receptors occurs sometimes during muscle stretching with minor speed starting from the completely relaxed state. Its rare occurrence, unstability and variability reject the suggestion of acceleration-sensitivity in the muscle spindle receptors. The receptors respond sometimes to initial enhancement of rigidity in the extra- and intrafusal muscle fibers. The IB occurs as the result of interaction between both types of fibers during stretching.

Animals↗
PubMed1982

Analysis of bimodal interspike interval histograms of primary muscle spindle endings in active triceps surae muscles of cats.

A feature frequently observed in interspike interval histograms (IH) derived from stationary Ia fibre discharge patterns was a bimodality suggesting a mixed population composed of two sub-populations of possibly different origins. To verify this hypothesis a separation of these subpopulations was attempted by assuming a Gaussian distribution for the longer intervals. The success of such a separation depended on the distinctness of the histogram peaks and the relative sizes of each mode. Both factors in turn depended on the overall muscle length and, hence, on the mean spindle discharge rate. The smaller intervals were then isolated from the spike trains and submitted to further statistical analysis. By averaging overall muscle tension with respect to the smaller intervals, the latter could often be linked to tension trajectories which were of higher amplitude and faster time course than the trajectories obtained by averaging with respect to the rest of the spikes. In some cases, auto-correlation histograms of isolated small intervals as well as serial correlograms computed for all intervals indicated that some muscle spindle afferents responded sensitively to activity of single motor units. This would confirm recent results of Cameron et al. (1980).

Afferent Pathways↗
PubMed1976

[The effect of hypertonic solutions on the electrical activity of isolated frog muscle spindles].

Electrical activity of an isolated frog muscle spindle was investigated in hypertonic solutions obtained by adding 400 mM of sucrose, glucose or glycerine to the Ringer solution. In sucrose and glucose hypermedia the frequency of background impulse activity first increased and then decreased up to zero; receptor potentials and evoked impulse activity simultaneously decreased and disappeared. In the glycerine hypermedia impulse activity after some increase returned to normal and then a second rise of frequency to a constant supernormal level was observed. After returning to the Ringer solution from sucrose or glucose the background and evoked impulse activity progressively returned to normal. But after glycerine hypermedia a significant growth in the background impulse activity and a small change in frequency of evoked impulse activity were observed. The observed changes of electrical activity of the muscle spindle in hypermedia are discussed in terms of deformation of sensory endings and intrafusal muscles fibres leading to depolarization of the receptor membrane.

Animals↗
PubMed1996

Morphology of the musculus articularis genus in dog with description of ectopic muscle spindles.

The gross morphology of the musculus articularis genus and the location of muscle spindles at its point of insertion were studied in 18 adult dogs. The m. articularis genus was usually small and bipartite. From its originate on the cranial surface of the distal femur, it passed distally to terminate at the femoropatellar-joint capsule surface and extend into the synovial membrane. Although the m. articularis genus was usually composed of two parts, only a medial part was present in some dogs and was entirely absent in one specimen. Innervation to the m. articularis genus was provided by a branch of the femoral nerve. Muscle spindles were abundant in the termination of the muscle. spindles were abundant in the termination of the muscle. Frequently, the spindles were not in contact with muscle fibers (dissociated). Muscle spindles were located in close proximity to the surface of the synovial membrane. Morphological adaptations of the m. articularis genus support its potential function as a monitor of joint movement rather than an extensor of the stifle joint.

Animals↗
PubMed1984

Muscle fibre types and muscle spindles in the jaw musculature of the rat.

The fibre composition and occurrence of muscle spindles was studied in the masticatory, the suprahyoid and the infrahyoid muscles of the rat. Muscle fibres were typed as fast-white, fast-intermediate, fast-red and slow-red according to their ATPase and SDH activity. Fibre type appeared to be closely related to fibre diameter. In most of the muscles, all four fibre types were found. Slow-red fibres were absent in the superficial masseter, the transverse mandibular and the omohyoid muscles; fast-white fibres were absent in the mylohyoid muscle. The masticatory muscles were mainly composed of the three fast-fibre types; the jaw-opener muscles (the anterior digastric, the posterior digastric, the posterior digastric, the stylohyoid and the lateral pterygoid muscle) showed more slow-red fibres. In the masticatory and most of the suprahyoid muscles, the slow-red fibres were restricted to an area with high SDH activity. In the infrahyoid muscles, the fibre types were evenly distributed. Many muscle spindles, often clustered, were found in the masticatory muscles, except in the lateral pterygoid. In most of the suprahyoid muscles, these sensory structures were absent. In the infrahyoid muscles, solitary muscle spindles were found.

Adenosine Triphosphatases↗
PubMed1976

[Influence of adequate stimulation on the impulse electrical activity of isolated frog muscle spindles].

Impulse activity of an isolated frog muscle spindle was investigated using mechanical stimulation of various amplitude, rate and form. It is found out that firing frequency during linear-increasing stimulation is determined by the amplitude of the stimulus and alteration of firing frequency by the rate of the stimulation increase. At sinusoidal stimulation the impulsation "repeates" the form of the stimulus, i.e. the muscle spindle is influenced not only by its amplitude or rate, but also by its acceleration. The sensitivity to accelerations may depend on changes in discharge threshold during alteration of the tension rate change.

Action Potentials↗