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Rade Durbaba - One of the best experts on this subject based on the ideXlab platform.
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muscle spindle and fusimotor activity in locomotion
Journal of Anatomy, 2015Co-Authors: P H Ellaway, Anthony Newman Taylor, Rade DurbabaAbstract:Mammals may exhibit different forms of locomotion even within a species. A particular form of locomotion (e.g. walk, run, bound) appears to be selected by supraspinal commands, but the precise pattern, i.e. phasing of limbs and muscles, is generated within the spinal cord by so-called central pattern generators. Peripheral sense organs, particularly the muscle spindle, play a crucial role in modulating the central pattern generator output. In turn, the feedback from muscle spindles is itself modulated by static and dynamic fusimotor (Gamma) neurons. The activity of muscle spindle afferents and fusimotor neurons during locomotion in the cat is reviewed here. There is evidence for some alpha–Gamma co-activation during locomotion involving static Gamma Motoneurons. However, both static and dynamic Gamma Motoneurons show patterns of modulation that are distinct from alpha Motoneuron activity. It has been proposed that static Gamma activity may drive muscle spindle secondary endings to signal the intended movement to the central nervous system. Dynamic Gamma Motoneuron drive appears to prime muscle spindle primary endings to signal transitions in phase of the locomotor cycle. These findings come largely from reduced animal preparations (decerebrate) and require confirmation in freely moving intact animals.
Stephan Kröger - One of the best experts on this subject based on the ideXlab platform.
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acetylcholine receptors in the equatorial region of intrafusal muscle fibres modulate mouse muscle spindle sensitivity
The Journal of Physiology, 2019Co-Authors: Laura Gerwin, Katherine A Wilkinson, Corinna Haupt, Stephan KrögerAbstract:KEY POINTS: Acetylcholine receptors are aggregated in the central regions of intrafusal muscle fibres. Single unit muscle spindle afferent responses from isolated mouse extensor digitorum longus muscle were recorded in the absence of fusimotor input to ramp and hold stretches as well as to sinusoidal vibrations in the presence and absence of the acetylcholine receptor blockers d-tubocurarine and α-bungarotoxin. Proprioceptive afferent responses to both types of stretch were enhanced in the presence of either blocker. Blocking acetylcholine uptake and vesicular acetylcholine release by hemicholinium-3 also enhanced stretch-evoked responses. These results represent the first evidence that acetylcholine receptors negatively modulate muscle spindle responses to stretch. The data support the hypothesis that the sensory nerve terminal is able to release vesicles to fine-tune proprioceptive afferent sensitivity. ABSTRACT: Muscle spindles are complex stretch-sensitive mechanoreceptors. They consist of specialized skeletal muscle fibres, called intrafusal fibres, which are innervated in the central (equatorial) region by afferent sensory axons and in both polar regions by efferent γ-Motoneurons. Previously it was shown that acetylcholine receptors (AChR) are concentrated in the equatorial region at the contact site between the sensory neuron and the intrafusal muscle fibre. To address the function of these AChRs, single unit sensory afferents were recorded from an isolated mouse extensor digitorum longus muscle in the absence of γ-Motoneuron activity. Specifically, we investigated the responses of individual sensory neurons to ramp-and-hold stretches and sinusoidal vibrations before and after the addition of the competitive and non-competitive AChR blockers d-tubocurarine and α-bungarotoxin, respectively. The presence of either drug did not affect the resting action potential discharge frequency. However, the action potential frequencies in response to stretch were increased. In particular, frequencies of the dynamic peak and dynamic index to ramp-and-hold stretches were significantly higher in the presence of either drug. Treatment of muscle spindle afferents with the high-affinity choline transporter antagonist hemicholinium-3 similarly increased muscle spindle afferent firing frequencies during stretch. Moreover, the firing rate during sinusoidal vibration stimuli at low amplitudes was higher in the presence of α-bungarotoxin compared to control spindles also indicating an increased sensitivity to stretch. Collectively these data suggest a modulation of the muscle spindle afferent response to stretch by AChRs in the central region of intrafusal fibres possibly fine-tuning muscle spindle sensitivity.
Alexandros G. Rigas - One of the best experts on this subject based on the ideXlab platform.
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A Method of Estimating the Partial Power Spectrum of a Bivariate Point Process and an Application to a Neurophysiological Data Set
Journal of Statistical Theory and Practice, 2020Co-Authors: Georgios E. Michailidis, Ioannis I. Spyroglou, Dimitrios Zaridis, Alexandros G. RigasAbstract:In this paper, we present a method of estimating the partial power spectrum of a bivariate point process. The method is based on the simple and cross-periodograms which are smoothed by applying a simple averaging weighting scheme in order to improve the properties of the estimate. The asymptotic distribution of the estimate is shown to be approximately normal when the amount of smoothing is large. An illustrative example is presented from the field of Neurophysiology when the complex system of the muscle spindle is affected by a static Gamma Motoneuron.
A.g. Rigas - One of the best experts on this subject based on the ideXlab platform.
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PHASE RECOVERY OF A STOCHASTIC POINT PROCESS SYSTEM
2015Co-Authors: A.g. Rigas, V. G. VassiliadisAbstract:Abstract: In this work we present two algorithms for the estimation of the phase of a neuroelectric system of point processes using the third-order spectral density function of the output. The neuroelectric system, which is called muscle spindle, plays an important role in the initiation of the movement and the maintenance of the posture. The system can be modelled with the help of a linear stochastic model. The phase of the transfer function is estimated with the help of the third-order spectral density function of the output. The estimate of the third-order spectral density function is obtained by smoothing the third-order modified periodogram statistic. As illustrative examples we examine the behavior of the muscle spindle under two different conditions: (a) when it is affected by a Gamma Motoneuron and (b) when it is affected by an alpha Motoneuron. It is shown that in the first case there is a delay of the output by about 12 ms whereas in the second case the system is delayed for about 37 ms
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Spectral Analysis Techniques of Stationary Point Processes: Extensions and Applications to Neurophysiological Problems
Computers & Mathematics with Applications, 1996Co-Authors: A.g. Rigas, D.s. TsitsisAbstract:Abstract In this work we examine the behaviour of a complex physiological system (muscle spindle) by using spectral analysis techniques of stationary point processes. In particular, we investigate the effect of a Gamma Motoneuron on the complex system when 1. (a) there is no other stimulus present, and 2. (b) there is an alpha Motoneuron present. It is shown that the presence of an alpha Motoneuron reduces the effect of the Gamma Motoneuron on the muscle spindle.
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Identification of a stohastic System involving Neuroelectric Signals
Proceedings IWISP '96, 1996Co-Authors: A.g. RigasAbstract:Publisher Summary This chapter presents a volterra - type stohastic model to identify a neurophysiological system involving two neuroelectric signals as inputs and one as output. The inputs consist of a series of nerve pulses produced by an alpha and a Gamma Motoneuron applied to the muscle spindle and modifies its response which is transferred to the spinal cord by the axons of sensory neurons. The parameters of the proposed model are estimated by using spectral analysis techniques of stationary point processes. The chapter shows that the effect of the Gamma Motoneuron on the muscle spindle is restricted at low frequencies (0-20Hz), whereas the effect of the alpha Motoneuron occurs at middle and higher frequencies (20-100Hz).
Zhang Y. - One of the best experts on this subject based on the ideXlab platform.
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Differential regulation of AChR clustering in the polar and equatorial region of murine muscle spindles.
Wiley-blackwell, 2015Co-Authors: Zhang Y., Lin S., Karakatsani A., Kröger S.Abstract:Intrafusal fibers of muscle spindles are innervated in the central region by afferent sensory axons and at both polar regions by efferent Γ-Motoneurons. We previously demonstrated that both neuron-muscle contact sites contain cholinergic synapse-like specialisation, including aggregates of the nicotinic acetylcholine receptor (AChR). In this study we tested the hypothesis that agrin and its receptor complex (consisting of LRP4 and the tyrosine kinase MuSK) are involved in the aggregation of AChRs in muscle spindles, similar to their role at the neuromuscular junction. We show that agrin, MuSK and LRP4 are concentrated at the contact site between the intrafusal fibers and the sensory- and Γ-Motoneuron, respectively, and that they are expressed in the cell bodies of proprioceptive neurons in dorsal root ganglia. Moreover, agrin and LRP4, but not MuSK, are expressed in Γ-Motoneuron cell bodies in the ventral horn of the spinal cord. In agrin- and in MuSK-deficient mice, AChR aggregates are absent from the polar regions. In contrast, the subcellular concentration of AChRs in the central region where the sensory neuron contacts the intrafusal muscle fiber is apparently unaffected. Skeletal muscle-specific expression of miniagrin in agrin(-/-) mice in vivo is sufficient to restore the formation of Γ-Motoneuron endplates. These results show that agrin and MuSK are major determinants during the formation of Γ-Motoneuron endplates but appear dispensable for the aggregation of AChRs at the central region. Our results therefore suggest different molecular mechanisms for AChR clustering within two domains of intrafusal fibers
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The development and molecular characterization of muscle spindles from wildtype and mutant mice.
Universitätsbibliothek der Ludwig-Maximilians-Universität, 2014Co-Authors: Zhang Y.Abstract:Muscle spindles are complex stretch-sensitive mechanoreceptors that consist of 4-12 specialized muscle fibers. These intrafusal muscle fibers are innervated in the central (equatorial) region by an afferent sensory axon and in both peripheral (polar) regions by efferent Γ-Motoneurons. Until now little is known about muscle spindle development at the molecular level, especially about the development of cholinergic specializations. My study shows that nicotinic acetylcholine receptors (AChR) are concentrated at the Γ-Motoneuron endplate as well as in the equatorial region. Moreover, enzymes required for the synthesis and removal of acetylcholine, including choline acetyltransferase (ChAT) and acetylcholinesterase (AChE), as well as vesicular acetylcholine transporter (VAChT) and the AChR-associated protein rapsyn are all concentrated at the polar Γ-Motoneuron endplate and (with the exception of AChE) also at the equatorial region. Finally, the presynaptic protein bassoon, involved in synaptic vesicle exocytosis, is also present at the Γ-Motoneuron endplate and at the annulospiral sensory nerve ending. During postnatal development, the AChR subunit composition at the Γ-Motoneuron endplate changes from the Γ-subunit containing fetal AChR to the ε-subunit containing adult AChR. This is similar to the postnatal change at the neuromuscular junction. In the equatorial region the ε-subunit expression starts around postnatal week two; however the Γ-subunit persists in the central region despite the onset of the ε-subunit expression. Therefore, the Γ- and ε-subunits are simultaneously present in the equatorial region. This result was confirmed using a mouse line in which the AChR Γ-subunit was genetically labelled by green fluorescence protein (GFP). In this mouse, the GFP-labelled AChR Γ-subunits are concentrated at the contact site of the intrafusal fiber with the sensory nerve ending. This result indicates different AChR maturation occurs within two areas of the same intrafusal fiber. I also show that agrin and the agrin receptor complex (consisting of LRP4 and MuSK) are present in muscle spindles in the region of the sensory and motor innervation. Moreover, agrin, MuSK, and LRP4 are expressed by proprioceptive neurons in dorsal root ganglia but only agrin and LRP4 were detected in the cell body of Γ-Motoneurons in the spinal cord. In mice with a targeted deletion of agrin, AChR aggregates are absent from the polar region and Γ-Motoneuron endplates do not form. By contrast, AChR aggregates remain detectable in the central part of intrafusal fibers. Moreover, muscle-specific re-expression of mini-agrin is sufficient to restore the formation of synaptic specializations at Γ-Motoneuron endplates. These results show an unusual AChR maturation at the annulospiral endings and confirm that agrin is a major determinant for the formation of Γ-Motoneuron endplates. Agrin on the other hand appears dispensable for the aggregation of AChRs in the central region of intrafusal fibers
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Formation of cholinergic synapse-like specializations at developing murine muscle spindles.
Academic Press Inc Elsevier Science, 2014Co-Authors: Zhang Y., Karakatsani A., Wesolowski M., Kröger S.Abstract:Muscle spindles are complex stretch-sensitive mechanoreceptors. They consist of specialized skeletal muscle fibers, called intrafusal fibers, which are innervated in the central (equatorial) region by afferent sensory axons and in both polar regions by efferent Γ-Motoneurons. We show that AChRs are concentrated at the Γ-Motoneuron endplate as well as in the equatorial region where they colocalize with the sensory nerve ending. In addition to the AChRs, the contact site between sensory nerve ending and intrafusal muscle fiber contains a high concentration of choline acetyltransferase, vesicular acetylcholine transporter and the AChR-associated protein rapsyn. Moreover, bassoon, a component of the presynaptic cytomatrix involved in synaptic vesicle exocytosis, is present in Γ-Motoneuron endplates but also in the sensory nerve terminal. Finally, we demonstrate that during postnatal development of the Γ-Motoneuron endplate, the AChR subunit stoichiometry changes from the Γ-subunit-containing fetal AChRs to the ε-subunit-containing adult AChRs, similar and approximately in parallel to the postnatal subunit maturation at the neuromuscular junction. In contrast, despite the onset of ε-subunit expression during postnatal development the Γ-subunit remains detectable in the equatorial region by subunit-specific antibodies as well as by analysis of muscle spindles from mice with genetically-labeled AChR Γ-subunits. These results demonstrate an unusual maturation of the AChR subunit composition at the annulospiral endings and suggest that in addition to the recently described glutamatergic secretory system, the sensory nerve terminals are also specialized for cholinergic synaptic transmission, synaptic vesicle storage and exocytosis
