Differential activation of an identified motor neuron and neuromodulation provide Aplysia's retractor muscle an additional function

To survive, animals must use the same peripheral structures to perform a variety of tasks. How does a nervous system employ one muscle to perform multiple functions? We addressed this question through work on the I3 jaw muscle of the marine mollusk Aplysia californica's feeding system. This muscle mediates retraction of Aplysia's food grasper in multiple feeding responses and is innervated by a pool of identified neurons that activate different muscle regions. One I3 motor neuron, B38, is active in the protraction phase, rather than the retraction phase, suggesting the muscle has an additional function. We used intracellular, extracellular, and muscle force recordings in several in vitro preparations as well as recordings of nerve and muscle activity from intact, behaving animals to characterize B38's activation of the muscle and its activity in different behavior types. We show that B38 specifically activates the anterior region of I3 and is specifically recruited during one behavior, swallowing. The function of this protraction-phase jaw muscle contraction is to hold food; thus the I3 muscle has an additional function beyond mediating retraction. We additionally show that B38's typical activity during in vivo swallowing is insufficient to generate force in an unmodulated muscle and that intrinsic and extrinsic modulation shift the force-frequency relationship to allow contraction. Using methods that traverse levels from individual neuron to muscle to intact animal, we show how regional muscle activation, differential motor neuron recruitment, and neuromodulation are key components in Aplysia's generation of multifunctionality.

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Abstract 15596: Maturation of Hipsc-cm Electrophysiological and Contractile Function for Enhanced Sensitivity of Cardiac Safety Assays

Circulation ◽

10.1161/circ.142.suppl_3.15596 ◽

2020 ◽

Vol 142 (Suppl_3) ◽

Author(s):

Heather B Hayes ◽

Anthony M Nicolini ◽

Colin Arrowood ◽

Daniel Millard

Keyword(s):

Contractile Function ◽

Induced Pluripotent Stem Cell ◽

Force Frequency ◽

Cardiac Safety ◽

Electrophysiological Response ◽

Mechanical Conditioning ◽

Enhanced Sensitivity ◽

Frequency Relationship ◽

Positive Force

Human induced pluripotent stem cell-derived cardiomyocytes (hiPSC-CMs) have significantly advanced in vitro cardiac safety and disese modeling, yet remain an immature representation of human myocytes. Electrical or mechanical conditioning of hiPSC-CMs facilitates functional maturation, as measured by a positive force-frequency relationship, but current in vitro protocols require 2-4 weeks of conditioning. Using array-based contractility and local electrical stimulation, we detected functionally mature phenotypes and compound responses in hiPSC-CMs after only 48 hours of chronic pacing. To mature cardiomyocytes, hiPSC-CMs were cultured on 24- and 96-well MEA plates with a dedicated stimulation electrodes. Later, hiPSC-CMs were electrically or optically paced at 2Hz for 48 hours. Multimodal measures quantified contractile and electrophysiological responses to varied pacing rates and compound addition. After 48 hours of pacing, hiPSC-CMs displayed shortened repolarization timing compared to before chronic pacing (baseline: 423 +/- 21 ms; matured: 316 +/- 15 ms), without significant beat period changes (baseline: 1255 +/- 40 ms; matured: 1314 +/- 84 ms). Contractile beat amplitude was measured using array-based impedance during spontaneous beating and at increasing pacing rates (1, 1.2, 1.5, 2, and 2.5 Hz). Before chronic pacing, beat amplitude decreased with increasing pacing rate; after chronic pacing, the same wells displayed increased beat amplitudes with increasing pacing rate. The matured wells also showed enhanced sensitivity to positive inotropes, such as isoproterenol, digoxin, omecamtiv mecarbil, and dobutamine. Local extracellular action potentials (LEAP) further revealed altered electrophysiological response to ranolazine, a multichannel blocker. Unpaced control wells exhibited dose-dependent APD90 prolongation in response to ranolazine, whereas matured wells showed no APD90 change. Similar results were seen with 48 hour of optogenetic pacing at 2 Hz. Overall, hiPSC-CMs chronically paced for only 48 hours exhibited more mature functional phenotypes, including a positive force-frequnecy relationship, enhanced ionotrope sensitivity, and altered compound response.

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Bixafen, a succinate dehydrogenase inhibitor fungicide, causes microcephaly and motor neuron axon defects during development

10.1101/2020.08.15.252254 ◽

2020 ◽

Author(s):

Alexandre Brenet ◽

Rahma Hassan-Abdi ◽

Nadia Soussi-Yanicostas

Keyword(s):

Motor Neuron ◽

Succinate Dehydrogenase ◽

Toxicity Testing ◽

Mitochondrial Respiratory Chain ◽

Modern Agriculture ◽

Transgenic Lines ◽

Vertebrate Model ◽

The Central Nervous System

AbstractSuccinate dehydrogenase inhibitors (SDHIs), the most widely used fungicides in agriculture today, act by blocking succinate dehydrogenase (SDH), an essential and evolutionarily conserved component of mitochondrial respiratory chain. Recent results showed that several SDHIs used as fungicides not only inhibit the SDH activity of target fungi but also block this activity in human cells in in vitro models, revealing a lack of specificity and thus a possible health risk for exposed organisms, including humans. Despite the frequent detection of SDHIs in the environment and on harvested products and their increasing use in modern agriculture, their potential toxic effects in vivo, especially on neurodevelopment, are still under-evaluated. Here we assessed the neurotoxicity of bixafen, one of the latest-generation SDHIs, which had never been tested during neurodevelopment. For this purpose, we used a well-known vertebrate model for toxicity testing, namely zebrafish transparent embryos, and live imaging using transgenic lines labelling the brain and spinal cord. Here we show that bixafen causes microcephaly and defects on motor neuron axon outgrowth and their branching during development. Our findings show that the central nervous system is highly sensitive to bixafen, thus demonstrating in vivo that bixafen is neurotoxic in vertebrates and causes neurodevelopmental defects. This work adds to our knowledge of the toxic effect of SDHIs on neurodevelopment and may help us take appropriate precautions to ensure protection against the neurotoxicity of these substances.

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Felodipine protects human atrial muscle from hypoxia–reoxygenation dysfunction: a force–frequency relationship study in an in vitro model of stunning

International Journal of Cardiology ◽

10.1016/s0167-5273(97)00189-7 ◽

1997 ◽

Vol 62 (2) ◽

pp. 107-132 ◽

Cited By ~ 6

Author(s):

Katsunori Iwashiro ◽

Anna Criniti ◽

Riccardo Sinatra ◽

Amos Adeyemo Dawodu ◽

Giulia d'Amati ◽

...

Keyword(s):

In Vitro Model ◽

Force Frequency ◽

Atrial Muscle ◽

Relationship Study ◽

Vitro Model ◽

Frequency Relationship ◽

Hypoxia Reoxygenation

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Increased susceptibility to fatigue of slow- and fast-twitch muscles from mice lacking the MG29 gene

Physiological Genomics ◽

10.1152/physiolgenomics.2000.4.1.43 ◽

2000 ◽

Vol 4 (1) ◽

pp. 43-49 ◽

Cited By ~ 30

Author(s):

RAMAKRISHNAN Y. NAGARAJ ◽

CHRISTOPHER M. NOSEK ◽

MARCO A. P. BROTTO ◽

MIYUKI NISHI ◽

HIROSHI TAKESHIMA ◽

...

Keyword(s):

Major Protein ◽

Force Frequency ◽

Wild Type ◽

Membrane Structures ◽

Intracellular Ca ◽

Slow Twitch Muscle ◽

Fast Twitch Muscle ◽

Frequency Relationship ◽

Fast Twitch

Mitsugumin 29 (MG29), a major protein component of the triad junction in skeletal muscle, has been identified to play roles in the formation of precise junctional membrane structures important for efficient signal conversion in excitation-contraction (E-C) coupling. We carried out several experiments to not only study the role of MG29 in normal muscle contraction but also to determine its role in muscle fatigue. We compared the in vitro contractile properties of three muscles types, extensor digitorum longus (EDL) (fast-twitch muscle), soleus (SOL) (slow-twitch muscle), and diaphragm (DPH) (mixed-fiber muscle), isolated from mice lacking the MG29 gene and wild-type mice prior to and after fatigue. Our results indicate that the mutant EDL and SOL muscles, but not DPH, are more susceptible to fatigue than the wild-type muscles. The mutant muscles not only fatigued to a greater extent but also recovered significantly less than the wild-type muscles. Following fatigue, the mutant EDL and SOL muscles produced lower twitch forces than the wild-type muscles; in addition, fatiguing produced a downward shift in the force-frequency relationship in the mutant mice compared with the wild-type controls. Our results indicate that fatiguing affects the E-C components of the mutant EDL and SOL muscles, and the effect of fatigue in these mutant muscles could be primarily due to an alteration in the intracellular Ca homeostasis.

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Force potentiation in respiratory muscles: comparison of diaphragm and sternohyoid

AJP Regulatory Integrative and Comparative Physiology ◽

10.1152/ajpregu.1993.264.6.r1095 ◽

1993 ◽

Vol 264 (6) ◽

pp. R1095-R1100 ◽

Cited By ~ 4

Author(s):

E. Van Lunteren ◽

H. Vafaie

Keyword(s):

Respiratory Muscle ◽

Respiratory Muscles ◽

Upper Airway ◽

Rapid Onset ◽

Force Frequency ◽

Twitch Force ◽

Twitch Potentiation ◽

Early Portion ◽

Frequency Relationship

Coordinated contraction of thoracic and pharyngeal upper airway respiratory muscles optimizes ventilation, whereas pharyngeal muscle dysfunction may lead to obstructive apneas during sleep. We hypothesized that the force potentiation exhibited by the pharyngeal respiratory muscle, the sternohyoid, in keeping with its faster contractile kinetics, would be greater than that of the thoracic respiratory muscle, the diaphragm. Rat muscles were studied in vitro at 37 degrees C with three force-potentiating protocols: posttetanic twitch potentiation, staircase phenomenon (twitch potentiation), and a classic fatigue paradigm. The sternohyoid had a faster isometric contraction time, a more rightward located force-frequency relationship, and both a more rapid onset and a greater degree of fatigue than the diaphragm. During the early portion of the fatigue protocols, the increase in force was significantly greater for the sternohyoid muscle than the diaphragm (e.g., 33 vs. 3% increase at 20 Hz, P < 0.005). During repetitive twitches at 2, 3, and 5 Hz (staircase test), sternohyoid muscle force increased more than diaphragm force at the higher stimulus frequencies (e.g., by 38 vs. 23% at 5 Hz, P < 0.01). After brief tetanic stimuli, sternohyoid twitch force increased more than diaphragm twitch force (e.g., 73 vs. 14% increase after 125 Hz tetanus, P < 0.005). These data indicate that force potentiation is exhibited by both diaphragm and sternohyoid respiratory muscles, but to different extents, when activated repetitively.(ABSTRACT TRUNCATED AT 250 WORDS)

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Temperature dependence of oxygen diffusion and consumption in mammalian striated muscle

AJP Heart and Circulatory Physiology ◽

10.1152/ajpheart.1993.264.6.h1825 ◽

1993 ◽

Vol 264 (6) ◽

pp. H1825-H1830 ◽

Cited By ~ 21

Author(s):

T. B. Bentley ◽

H. Meng ◽

R. N. Pittman

Keyword(s):

Diffusion Coefficient ◽

Steady State ◽

Oxygen Diffusion ◽

Striated Muscle ◽

Effect Of Temperature ◽

Retractor Muscle ◽

Oxygen Solubility ◽

Order Of Magnitude

This study investigated the effect of temperature on the oxygen diffusion coefficient (DO2) of hamster retractor muscle from 11 to 37 degrees C. DO2 was measured using a non-steady-state technique, whereas muscle O2 consumption (VO2) was estimated after steady state was reached. DO2 was 0.84 +/- 0.04 x 10(-5) cm2/s at 11 degrees C and rose exponentially to 2.41 +/- 0.19 x 10(-5) cm2/s at 37 degrees C, producing a temperature coefficient for DO2 of 4.60%/degrees C for this temperature range. To measure DO2 directly at 37 degrees C, it was necessary to inhibit tissue VO2 with Amytal. The DO2 measurements made at 37 degrees C were significantly higher than previously reported values, which had been based on extrapolations from lower temperatures (6). Further analysis suggests a possible transition in the diffusion pathway between 23 and 30 degrees C, resulting in a DO2 higher than that previously expected. This larger DO2, together with a recently published value of oxygen solubility (alpha) (21), results in an in vitro Krogh's diffusion coefficient (KO2) that is 2.4 times larger than that previously reported (24) and therefore significantly reduces an order of magnitude discrepancy between in vitro and estimated in vivo KO2 values (24). Muscle VO2 was 0.35 ml O2.min-1.100 g-1 at 11 degrees C and increased with temperature, resulting in an activation energy of the rate-limiting reaction from the Arrhenius equation of -10.5 kcal/mol between 11 and 30 degrees C.

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Upper Motor Neuron Disorders Hereditary Spastic Paraplegia and Primary Lateral Sclerosis

10.1093/med/9780199937837.003.0032 ◽

2017 ◽

Cited By ~ 1

Author(s):

Sabrina Paganoni ◽

Nazem Atassi

Keyword(s):

Motor Neuron ◽

Hereditary Spastic Paraplegia ◽

Disease Modeling ◽

Primary Lateral Sclerosis ◽

Spastic Paraplegia ◽

Underlying Pathophysiology ◽

Primary Lateral ◽

Lateral Sclerosis

Upper motor neuron (UMN) syndromes are a group of rare, degenerative neurological disorders that are classified as either hereditary spastic paraplegia (HSP) or primary lateral sclerosis (PLS). Our understanding of their underlying pathophysiology is unfortunately very limited and has been a significant barrier to the development of disease-modifying treatments. Recent advances in genetics and in vitro and in vivo disease modeling have provided new insights into disease mechanisms and hold the promise to lead to the future development of mechanism-based therapies.

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In vivo loads on airway smooth muscle: the role of noncontractile airway structures

Canadian Journal of Physiology and Pharmacology ◽

10.1139/y92-077 ◽

1992 ◽

Vol 70 (4) ◽

pp. 602-606 ◽

Cited By ~ 5

Author(s):

Philip Robinson ◽

Mitsushi Okazawa ◽

Tony Bai ◽

Peter Paré

Keyword(s):

Smooth Muscle ◽

Airway Smooth Muscle ◽

Muscle Activation ◽

Muscle Length ◽

Tracheal Cartilage ◽

Elastic Load ◽

Muscle Shortening ◽

Trachealis Muscle

The degree of airway smooth muscle contraction and shortening that occurs in vivo is modified by many factors, including those that influence the degree of muscle activation, the resting muscle length, and the loads against which the muscle contracts. Canine trachealis muscle will shorten up to 70% of starting length from optimal length in vitro but will only shorten by around 30% in vivo. This limitation of shortening may be a result of the muscle shortening against an elastic load such as could be applied by tracheal cartilage. Limitation of airway smooth muscle shortening in smaller airways may be the result of contraction against an elastic load, such as could be applied by lung parenchymal recoil. Measurement of the elastic loads applied by the tracheal cartilage to the trachealis muscle and by lung parenchymal recoil to smooth muscle of smaller airways were performed in canine preparations. In both experiments the calculated elastic loads applied by the cartilage and the parenchymal recoil explained in part the limitation of maximal active shortening and airway narrowing observed. We conclude that the elastic loads provided by surrounding structures are important in determining the degree of airway smooth muscle shortening and the resultant airway narrowing.Key words: elastic loads, tracheal cartilage, airway smooth muscle shortening.

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