Potentiation of Neuromuscular Transmission by an Octopaminergic Neurone in the Locust

1979 ◽  
Vol 79 (1) ◽  
pp. 169-190 ◽  
Author(s):  
MICHAEL O'SHEA ◽  
PETER D. EVANS
Keyword(s):  
Indirect Effects ◽  
Neuromuscular Transmission ◽  
Time Course ◽  
Muscle Tone ◽  
Muscle Tension ◽  
Presynaptic Receptors ◽  
Extensor Muscle ◽  
Muscle Membrane ◽  
Muscle Fibres ◽  
Central Synapses

1. Spikes in the octopaminergic dorsal unpaired median (DUM) neurone which innervates the extensor tibiae muscle of the locust metathoracic leg (DUMETi) produce direct and indirect effects on muscle tension. 2. Direct effects include a slowing of an intrinsic rhythm of contraction and relaxation, a relaxation of muscle tone and a small hyperpolarization of the muscle membrane potential. The latter two effects are weak and variable. All three effects are mimicked by superfusion of octopamine and are mediated by octopamine receptors on the muscle fibres. 3. Indirect effects are found when the DUMETi neurone is stimulated at the same time as the motoneurones innervating the extensor muscle. They include (a) potentiation of tension generated in the extensor muscle by spikes in the slow excitatory motoneurone (SETi), (b) reduction in duration of each twitch contraction generated by SETi due to an increase in the rate at which the muscle relaxes, (c) increase in the amplitude of the synaptic potential generated by SETi. These various effects have a time course of several minutes and far outlast the duration of DUMETi stimulation. They can be mimicked by superfusion of octopamine. 4. The effect of DUMETi on neuromuscular transmission is mediated by receptors with a high affinity for octopamine located both on the muscle and on the terminals of the slow motoneurone. The presence of the presynaptic receptors is revealed by the increase in the frequency of spontaneous miniature end plate potentials recorded in the muscle in the presence of octopamine. 5. DUMETi is a member of a group of similar aminergic neurones and it is suggested that they may share a role in modulating transmission at peripheral neuromuscular synapses, and possibly central synapses.

A note on the structure of immunized endplates

1977 ◽  
Vol 195 (1119) ◽  
pp. 323-326
Keyword(s):  
Electron Microscope ◽  
Acetylcholine Receptors ◽  
Neuromuscular Transmission ◽  
Neuromuscular Junctions ◽  
Muscle Membrane ◽  
Muscle Fibres

Neuromuscular junctions of rabbits immunized against acetylcholine receptors were examined with the electron microscope. Many endplates appeared normal, or showed changes which, by themselves, would not account for the blockage of neuromuscular transmission which develops after immunization. An unexpected organelle was found in the muscle fibres, associated with the endplate nuclei and the cytoplasm between them and the synaptic muscle membrane.

scholarly journals Cholinergic action on the heart of the leech, Hirudo medicinalis

1986 ◽  
Vol 125 (1) ◽  
pp. 205-224 ◽  
Author(s):  
R. L. Calabrese ◽  
A. R. Maranto
Keyword(s):  
Heart Muscle ◽  
Neuromuscular Transmission ◽  
Reversal Potential ◽  
Muscle Cells ◽  
Hirudo Medicinalis ◽  
Muscle Membrane ◽  
Muscle Fibres ◽  
Dependent Manner ◽  
Heart Muscle Cells ◽  
Alpha Bungarotoxin

Experiments were performed to determine the role of acetylcholine (ACh) in neuromuscular transmission in the heart of the leech Hirudo medicinalis. Superfused or iontophoretically applied ACh rapidly depolarized both isolated heart muscle cells and muscle cells in isolated hearts in a dose-dependent manner. the depolarization was associated with a conductance increase of the muscle membrane that had a reversal potential of −9 mV. Eserine potentiated the response to superfused ACh, reducing the threshold from 10(−6) to 10(−8) mol l-1. Acetylcholinesterase was localized histochemically to be in the immediate area of neuromuscular terminals. Superfused nicotinic agonists mimicked the effects of ACh, while superfused nicotinic antagonists reversibly blocked the iontophoretic response of heart muscle fibres to ACh. 5 X 10(−7) mol l-1 curare, 5 X 10(−5) mol l-1 nicotine and 1 X 10(−4) mol l-1 atropine reduced the iontophoretic response to half its original amplitude. Alpha-bungarotoxin did not block the response of heart muscle cells to iontophoretically applied ACh. Curare was used to determine whether the neurones that innervate the heart-HE motor neurones and HA modulatory neurone--use ACh as a neuromuscular transmitter. The fast depolarizing component of the HE cell's neuromuscular transmission was reversibly blocked by 10(−4) mol l-1 curare, while the HA cell's modulatory effects on the heart were apparently unaffected by 10(−4) mol l-1 curare. Our results indicate that heart muscle cells have nicotinic acetylcholine receptors that open in the presence of ACh, thereby increasing membrane conductance. The HE motor neurone is probably cholinergic and engages these receptors in its neuromuscular transmission, while the HA modulatory neurone is probably not cholinergic.

scholarly journals Temperature Effects on Membrane Chloride Conductance and Electrical Excitability of Lizard Skeletal Muscle Fibres

1989 ◽  
Vol 144 (1) ◽  
pp. 551-563 ◽  
Author(s):  
BRETT A. ADAMS
Keyword(s):  
Skeletal Muscle ◽  
Neuromuscular Transmission ◽  
Threshold Current ◽  
Chloride Ions ◽  
Muscle Membrane ◽  
Muscle Fibres ◽  
Electrical Excitability ◽  
Ringer’S Solution ◽  
Single Nerve ◽  
Skeletal Muscle Fibres

1. Intracellular recording techniques were used to study the effects of temperature on resting membrane conductances, electrical excitability and synaptic efficacy in fast-glycolytic (FG) skeletal muscle fibres from the lizard Dipsosaurus dorsalis. 2. The conductance of the resting muscle membrane to chloride ions (gCl) increased from 488μS cm−2 at 15°C (pH7.8) to 730μS cm−2 at 45°C (pH7.4), yielding a temperature coefficient (thermal ratio, R10) of 1.14. Resting potassium conductance (gK) increased from 84μS cm−2 at 15°C to 236μScm−2 at 45 °C (R10=1.41). 3. Fibres bathed in Cl− -free Ringer's solution were hyperexcitable, and produced repetitive action potentials both during and following intracellular current injection. At the preferred body temperature of Dipsosaurus (near 40°C) the fibres also fired repetitively in response to single nerve shock. 4. The electrical excitability of Dipsosaurus fibres decreased with increasing temperature. Threshold current, measured at endplate regions of fibres bathed in normal Ringer's solution, was 146 nA at 15°C and 353 nA at 45°C (R10= 1.34). 5. Despite the temperature-dependent change in threshold current, at both 15 and 45°C all fibres examined had suprathreshold neuromuscular transmission response to single nerve shock. 6. The relative thermal independence of gCl in Dipsosaurus fibres may be an adaptation that contributes to a large safety factor for neuromuscular transmission at the high body temperatures preferred by this lizard species.

Neuromuscular transmission after immunization against acetylcholine receptors

1975 ◽  
Vol 189 (1094) ◽  
pp. 57-68 ◽  
Keyword(s):  
Acetylcholine Receptors ◽  
Neuromuscular Transmission ◽  
Electric Organ ◽  
Frog Muscle ◽  
Muscle Membrane ◽  
Muscle Fibres ◽  
End Plate ◽  
Acetylcholine Sensitivity

Injection of acetylcholine receptors from the electric organ of Torpedo into rabbits or rats, produces antibodies which bind to acetylcholine receptors in the muscle membrane or in solution. Binding of antibody to the receptors results in diminished acetylcholine sensitivity of the muscle fibres, reduced amplitude of miniature end-plate potentials, block of neuromuscular transmission and a decrease in the ability of the receptors to bind a -bungarotoxin. Antibodies raised against acetylcholine receptors from Torpedo cross-react with acetylcholine receptors from rabbit, rat and frog muscle.

Dantrolene Sodium: Effects on Crustacean Muscle

1974 ◽  
Vol 52 (4) ◽  
pp. 887-890 ◽  
Author(s):  
L. L. Odette ◽  
H. L. Atwood
Keyword(s):  
Skeletal Muscle ◽  
Electrical Properties ◽  
Neuromuscular Transmission ◽  
Contractile Response ◽  
Callinectes Sapidus ◽  
Muscle Membrane ◽  
Dantrolene Sodium ◽  
Muscle Contractile ◽  
Indirect Stimulation ◽  
Vertebrate Skeletal Muscle

The effect of dantrolene sodium, a muscle relaxant effective on vertebrate skeletal muscle, has been studied on the stretcher muscle of a crab (Callinectes sapidus). The drug rapidly and reversibly attenuates the muscle contractile response to direct and indirect stimulation. Neuromuscular transmission is unaffected, as are the electrical properties of the muscle membrane. It is concluded that dantrolene sodium uncouples excitation–contraction mechanisms in crustacean tonic muscle.

The resting membrane potential of white muscle from brown trout (Salmo trutta) exposed to copper in soft, acidic water

2000 ◽  
Vol 203 (14) ◽  
pp. 2229-2236 ◽  
Author(s):  
M.W. Beaumont ◽  
E.W. Taylor ◽  
P.J. Butler
Keyword(s):  
Membrane Potential ◽  
Brown Trout ◽  
Salmo Trutta ◽  
White Muscle ◽  
Low Ph ◽  
Ammonium Ion ◽  
Muscle Membrane ◽  
Resting Membrane Potential ◽  
Muscle Fibres ◽  
Brown Trout Salmo Trutta

Previously, the distribution of ammonia between the intracellular and extracellular compartments has been used to predict a significant depolarisation of the resting membrane potential (E(M)) of white muscle from brown trout (Salmo trutta) exposed to a sub-lethal combination of copper and low pH. However, this prediction is based upon two assumptions (i) a relatively high membrane permeability for the ammonium ion with respect to that for ammonia gas and (ii) that this is unaltered by exposure to copper and low pH. Since there is conflicting evidence in the literature of the validity of these assumptions, in the present study E(M) was directly measured in white muscle fibres of trout exposed to copper and low pH (E(M)=−52.2+/−4.9 mV) and compared with that of unexposed, control animals (E(M)=−86.5+/−2.9 mV) (means +/− s.e.m., N=6). In confirming the predicted depolarisation, these data support the hypothesis of electrophysiological impairment as a factor in the reduction in the swimming performance of trout exposed to these pollutants. In addition, the results of this study support the role of a significant permeability of the muscle membrane to NH(4)(+) in determining the distribution of ammonia in fish.

Long-lasting excitability changes of soleus alpha-motoneuron induced by midpontine stimulation in decerebrate, standing cat

1986 ◽  
Vol 55 (3) ◽  
pp. 449-468 ◽  
Author(s):  
T. Sakamoto ◽  
Y. Atsuta ◽  
S. Mori
Keyword(s):  
Muscle Tone ◽  
Motor Units ◽  
Input Resistance ◽  
Extensor Muscle ◽  
Membrane Excitability ◽  
Peak Voltage ◽  
Resistance Change ◽  
Time To Peak ◽  
Dorsal Portion ◽  
Force Reduction

Stimulation of the dorsal portion of the caudal tegmental field (DTF) in the pons resulted in hyperpolarization of extensor alpha-motoneurons (alpha-MNs) that persisted for several minutes after cessation of the stimulation. The resulting inhibition of alpha-MN discharge led to a progressive reduction in the number of active motor units. Renshaw cells, persistently active at high levels of extensor muscle tone, were abruptly silenced by DTF stimulation. Active discharge was renewed at the time of cessation of the stimulation but at a frequency reduced in proportion to the persistently lowered level of extensor muscle tone. Ia primary afferents were tonically active during the high extensor tonus of reflex standing. DTF stimulation was accompanied by a brief, slight increase in Ia discharge frequency followed by a reduction in frequency variably correlated to the magnitude of extensor force reduction. Orthodromically elicited Ia EPSPs in the soleus alpha-MNs were reduced in peak voltage, time to peak, and half width during the hyperpolarization accompanying DTF stimulation. All of these parameters recovered beyond their prestimulus values with the cessation of DTF stimulation in spite of the persisting hyperpolarization. Antidromically initiated invasion of the somatodendritic (SD) segment of the motoneuron membrane was delayed and sometimes blocked during DTF stimulation. At the same time, the peak voltage of the SD action potential was reduced. There was an immediate recovery of these changes on termination of DTF stimulation, although the poststimulus hyperpolarization persisted. Intracellular injection of depolarizing current steps during DTF stimulation revealed a depression of membrane excitability that persisted during the hyperpolarization that followed the termination of the DTF stimulation. Depolarizing and hyperpolarizing steps of intracellular current were used to demonstrate a reduction of cellular input resistance during DTF stimulation. The resistance values rapidly returned to prestimulus levels following the cessation of DTF stimulation. It was demonstrated that the degree of resistance change is greater and that the magnitude of DTF-induced hyperpolarization is smaller for low-resistance cells than for high-resistance cells. Iontophoretically induced increase in intracellular Cl- resulted in a reversal of both Ia IPSPs and the hyperpolarization induced by DTF stimulation. The hyperpolarization enduring after DTF stimulation was not affected by the Cl- injection.

Respiratory and cardiovascular responses to static handgrip exercise in humans

1993 ◽  
Vol 75 (6) ◽  
pp. 2789-2796 ◽  
Author(s):  
G. A. Fontana ◽  
T. Pantaleo ◽  
F. Bongianni ◽  
F. Cresci ◽  
R. Manconi ◽  
...  
Keyword(s):  
Heart Rate ◽  
Time Course ◽  
Minute Ventilation ◽  
Muscle Tension ◽  
Maximum Voluntary Contraction ◽  
Cardiovascular Responses ◽  
Inspiratory Flow ◽  
Electromyographic Activity ◽  
Handgrip Exercise ◽  
Cardiovascular Variables

We studied the time course of respiratory and cardiovascular responses by evaluating changes in the breathing pattern, mean blood pressure (MBP), and heart rate elicited by 3 min of static handgrip at 15, 25, and 30% of the maximum voluntary contraction (MVC) in 15 healthy volunteers. Muscle tension and integrated electromyographic activity remained fairly constant during each trial. During 15% MVC bouts, initially only mean inspiratory flow increased; then, tidal volume and minute ventilation (VI) also rose progressively. No significant changes in MBP and heart rate were observed. During 25 and 30% MVC bouts, not only did mean inspiratory flow, VT, and VI increase but MBP and heart rate increased as well. A slight and delayed rise in respiratory rate was also observed. Unlike 15 and 25% MVC handgrip, 30% MVC handgrip caused a small decrease in end-tidal PCO2. Changes in the pattern of breathing occurred more promptly than those in cardiovascular variables in the majority of subjects. Furthermore, we found a positive correlation between changes in VI and those in cardiovascular variables at the end of 25 and 30% MVC trials. This study indicates that respiratory and cardiovascular responses to static handgrip exercise are controlled independently.

Viscerosomatic interaction induced by myocardial ischemia in conscious dogs

2007 ◽  
Vol 103 (2) ◽  
pp. 511-517 ◽  
Author(s):  
Patricia A. Gwirtz ◽  
Jerry Dickey ◽  
David Vick ◽  
Maurice A. Williams ◽  
Brian Foresman
Keyword(s):  
Myocardial Ischemia ◽  
Contractile Function ◽  
Muscle Tone ◽  
Muscle Tension ◽  
Left Ventricular ◽  
Diagnostic Potential ◽  
Myocardial Contractile ◽  
Muscle Groups ◽  
The Right ◽  
Somatic Response

Studies tested the hypothesis that myocardial ischemia induces increased paraspinal muscular tone localized to the T2–T5 region that can be detected by palpatory means. This is consistent with theories of manual medicine suggesting that disturbances in visceral organ physiology can cause increases in skeletal muscle tone in specific muscle groups. Clinical studies in manual and traditional medicine suggest this phenomenon occurs during episodes of myocardial ischemia and may have diagnostic potential. However, there is little direct evidence of a cardiac-somatic mechanism to explain these findings. Chronically instrumented dogs [12 neurally intact and 3 following selective left ventricular (LV) sympathectomy] were examined before, during, and after myocardial ischemia. Circumflex blood flow (CBF), left ventricular contractile function, electromyographic (EMG) analysis, and blinded manual palpatory assessments (MPA) of tissue over the transverse spinal processes at segments T2–T5 and T11–T12 (control) were performed. Myocardial ischemia was associated with a decrease in myocardial contractile function and an increase in heart rate. MPA revealed increases in muscle tension and texture/firmness during ischemia in the T2–T5 segments on the left, but not on the right or in control segments. EMG demonstrated increased amplitude for the T4–T5 segments. After LV sympathectomy, MPA and EMG evidence of increased muscle tone were absent. In conclusion, myocardial ischemia is associated with significant increased paraspinal muscle tone localized to the left side T4–T5 myotomes in neurally intact dogs. LV sympathectomy eliminates the somatic response, suggesting that sympathetic neural traffic between the heart and somatic musculature may function as the mechanism for the interaction.

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