Autogenic recurrent Renshaw inhibition is elevated in human spinal motor neurones during maximal eccentric muscle contraction in vivo

The metathoracic fast extensor tibiae (FETi) motor neurone of locusts is unusual amongst insect motor neurones because it makes output connections within the central nervous system as well as in the periphery. It makes excitatory chemical synaptic connections to most if not all of the antagonist flexor tibiae motor neurones. The gain of the FETi-flexor connection is dependent on the peripheral conditions at the time of the FETi spike. This dependency has two aspects. First, sensory input resulting from the extensor muscle contraction can sum with the central excitatory postsynaptic potential (EPSP) to augment its falling phase if the tibia is restrained in the flexed position (initiating a tension-dependent reflex) or is free to extend (initiating a movement-dependent resistance reflex). This effect is thus due to simple postsynaptic summation of the central EPSP with peripheral sensory input. Second, the static tibial position at the time of the FETi spike can change the amplitude of the central EPSP, in the absence of any extensor muscle contraction. The EPSP can be up to 30 % greater in amplitude if FETi spikes with the tibia held flexed rather than extended. The primary sense organ mediating this effect is the femoral chordotonal organ. Evidence is presented suggesting that the mechanism underlying this change in gain may be specifically localised to the FETi-flexor connection, rather than being due to general position-dependent sensory feedback summing with the EPSP. The change in the amplitude of the central EPSP is probably not caused by general postsynaptic summation with tonic sensory input, since a diminution in the amplitude of the central EPSP caused by tibial extension is often accompanied by overall tonic excitation of the flexor motor neurone. Small but significant changes in the peak amplitude of the FETi spike have a positive correlation with changes in the EPSP amplitude, suggesting a likely presynaptic component to the mechanism of gain control. The change in amplitude of the EPSP can alter its effectiveness in producing flexor motor output and, thus, has functional significance. The change serves to augment the effectiveness of the FETi-flexor connection when the tibia is fully flexed, and thus to increase its adaptive advantage during the co-contraction preceding a jump or kick, and to reduce the effectiveness of the connection when the tibia is partially or fully extended, and thus to reduce its potentially maladaptive consequences during voluntary extension movements such as thrusting.

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MP06-12 GHRELIN-MEDIATED PROMOTION OF PROSTATE GROWTH AND PROSTATE SMOOTH MUSCLE CONTRACTION: EVIDENCE FROM FUNCTIONAL, IN VIVO, AND GENOMIC APPROACHES

The Journal of Urology ◽

10.1097/01.ju.0000555004.21579.98 ◽

2019 ◽

Vol 201 (Supplement 4) ◽

Author(s):

Xiaolong Wang* ◽

Yiming Wang ◽

Christian Gratzke ◽

Bingsheng Li ◽

Qingfeng Yu ◽

...

Keyword(s):

Smooth Muscle ◽

Muscle Contraction ◽

Smooth Muscle Contraction ◽

Prostate Growth

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2J-5 Ultrafast Ultrasonic Imaging of In Vivo Muscle Contraction

2006 IEEE Ultrasonics Symposium ◽

10.1109/ultsym.2006.260 ◽

2006 ◽

Cited By ~ 2

Author(s):

T. Deffieux ◽

J.-L. Gennisson ◽

M. Tanter ◽

M. Fink

Keyword(s):

Muscle Contraction ◽

Ultrasonic Imaging

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INTEGRATION OF POSITIVE AND NEGATIVE FEEDBACK LOOPS IN A CRAYFISH MUSCLE

Journal of Experimental Biology ◽

10.1242/jeb.187.1.305 ◽

1994 ◽

Vol 187 (1) ◽

pp. 305-313

Author(s):

P Skorupski ◽

P Vescovi ◽

B Bush

Keyword(s):

Negative Feedback ◽

Positive Feedback ◽

Motor Neurone ◽

Chordotonal Organ ◽

Negative Feedback Loops ◽

Reflex Pathways ◽

Motor Neurones ◽

Receptor Organ ◽

Group 2

It is now well established that in arthropods movement-related feedback may produce positive, as well as negative, feedback reflexes (Bassler, 1976; DiCaprio and Clarac, 1981; Skorupski and Sillar, 1986; Skorupski et al. 1992; Vedel, 1980; Zill, 1985). Usually the same motor neurones are involved in both negative feedback (resistance) reflex responses and positive feedback reflexes. Reflex reversal involves a shift in the pattern of central inputs to a motor neurone, for example from excitation to inhibition. In the crayfish, central modulation of reflexes has been described in some detail for two basal limb proprioceptors, the thoracocoxal muscle receptor organ (TCMRO) and the thoracocoxal chordotonal organ (TCCO) (Skorupski et al. 1992; Skorupski and Bush, 1992). Leg promotor motor neurones are excited by stretch of the TCMRO (which, in vivo, occurs on leg remotion) in a negative feedback reflex, but when this reflex reverses they are inhibited by the same stimulus. Release of the TCCO (which corresponds to leg promotion) excites some, but not all, promotor motor neurones in a positive feedback reflex. There are at least two ways in which the reflex control of a muscle may be modulated in this system. Firstly, inputs to motor neurones may be routed via alternative reflex pathways to produce different reflex outputs. Secondly, the pattern of inputs to a motor pool may be inhomogeneous, so that activation of different subgroups of the motor pool causes different outputs. Different crayfish promotor motor neurones are involved in different reflexes. On this basis, the motor neurones may be classified into at least two subgroups: those that are excited by the TCCO in a positive feedback reflex (group 1) and those that are not (group 2). Do these motor neurone subgroups have different effects on the promotor muscle, or is the output of the two promotor subgroups summed at the neuromuscular level? To address this question we recorded from the promotor nerve and muscle in a semi-intact preparation of the crayfish, Pacifastacus leniusculus. Adult male and female crayfish, 8-11 cm rostrum to tail, were decapitated and the tail, carapace and viscera removed. The sternal artery was cannulated and perfused with oxygenated crayfish saline, as described previously (Sillar and Skorupski, 1986).

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Myogenic mechanism for peristalsis in the cat esophagus

AJP Gastrointestinal and Liver Physiology ◽

10.1152/ajpgi.1999.277.2.g306 ◽

1999 ◽

Vol 277 (2) ◽

pp. G306-G313 ◽

Cited By ~ 6

Author(s):

Harold G. Preiksaitis ◽

Nicholas E. Diamant

Keyword(s):

Muscle Contraction ◽

Slow Wave ◽

Circular Muscle ◽

Smooth Muscle Contraction ◽

Slow Waves ◽

Mechanical Activity ◽

Control Mechanisms ◽

Slow Wave Oscillations

A myogenic control system (MCS) is a fundamental determinant of peristalsis in the stomach, small bowel, and colon. In the esophagus, attention has focused on neuronal control, the potential for a MCS receiving less attention. The myogenic properties of the cat esophagus were studied in vitro with and without nerves blocked by 1 μM TTX. Muscle contraction was recorded, while electrical activity was monitored by suction electrodes. Spontaneous, nonperistaltic, electrical, and mechanical activity was seen in the longitudinal muscle and persisted after TTX. Spontaneous circular muscle activity was minimal, and peristalsis was not observed without pharmacological activation. Direct electrical stimulation (ES) in the presence of bethanechol or tetraethylammonium chloride (TEA) produced slow-wave oscillations and spike potentials accompanying smooth muscle contraction that progressed along the esophagus. Increased concentrations of either drug in the presence of TTX produced slow waves and spike discharges, accompanied by peristalsis in 5 of 8 TEA- and 2 of 11 bethanechol-stimulated preparations without ES. Depolarization of the muscle by increasing K+ concentration also produced slow waves but no peristalsis. We conclude that the MCS in the esophagus requires specific activation and is manifest by slow-wave oscillations of the membrane potential, which appear to be necessary, but are not sufficient for myogenic peristalsis. In vivo, additional control mechanisms are likely supplied by nerves.

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Combined diffusion and strain tensor MRI reveals a heterogeneous, planar pattern of strain development during isometric muscle contraction

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.00474.2010 ◽

2011 ◽

Vol 300 (5) ◽

pp. R1079-R1090 ◽

Cited By ~ 33

Author(s):

Erin K. Englund ◽

Christopher P. Elder ◽

Qing Xu ◽

Zhaohua Ding ◽

Bruce M. Damon

Keyword(s):

Muscle Contraction ◽

Muscle Fiber ◽

Diffusion Tensor ◽

Strain Tensor ◽

Three Dimensional ◽

Fiber Direction ◽

Strain Pattern ◽

Isometric Muscle Contraction ◽

Diffusion Tensors

The purposes of this study were to create a three-dimensional representation of strain during isometric contraction in vivo and to interpret it with respect to the muscle fiber direction. Diffusion tensor MRI was used to measure the muscle fiber direction of the tibialis anterior (TA) muscle of seven healthy volunteers. Spatial-tagging MRI was used to measure linear strains in six directions during separate 50% maximal isometric contractions of the TA. The strain tensor (E) was computed in the TA's deep and superficial compartments and compared with the respective diffusion tensors. Diagonalization of E revealed a planar strain pattern, with one nonzero negative strain (εN) and one nonzero positive strain (εP); both strains were larger in magnitude ( P < 0.05) in the deep compartment [εN = −40.4 ± 4.3%, εP = 35.1 ± 3.5% (means ± SE)] than in the superficial compartment (εN = −24.3 ± 3.9%, εP = 6.3 ± 4.9%). The principal shortening direction deviated from the fiber direction by 24.0 ± 1.3° and 39.8 ± 6.1° in the deep and superficial compartments, respectively ( P < 0.05, deep vs. superficial). The deviation of the shortening direction from the fiber direction was due primarily to the lower angle of elevation of the shortening direction over the axial plane than that of the fiber direction. It is concluded that three-dimensional analyses of strain interpreted with respect to the fiber architecture are necessary to characterize skeletal muscle contraction in vivo. The deviation of the principal shortening direction from the fiber direction may relate to intramuscle variations in fiber length and pennation angle.

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